THE U N I V ERSIT Y OF MICHIGAN COLLEGE OF ENGINEERING Department of Materials and Metallurgical Engineering Progress Report TIME-DEPENDENT EDGE-NOTCH SENSITIVITY OF INCONEL 718 SHEET IN THE TEMPERATURE RANGE OF 900~ - 1400~F David J. Wilson ORA Project 04368 supported by: NATIONAL AERONAUTICS AND SPACE ADMINISTRATION GRANT NO. NGL-23-005-005 WASHINGTON, D. C. 20025 administered through: OFFICE OF RESEARCH ADMINISTRATION ANN ARBOR October 1971

TABLE OF CONTENTS Page LIST OF TABLES.....................iv LIST OF FIGURES..................... v SUMMARY......................... ix INTRODUCTION............. 1 EXPERIMENTAL DETAILS............2 Heat Treatment.................... 2 Testing Procedures.................. 3 Structural Examination................. INFLUENCE OF HEAT TREATMENT ON THE MECHANICAL CHARACTERISTICS..................... 5 FRACTURE CHARACTERISTICS............... 8 STRESS RELAXATION................... 9 MICROSTRUCTURAL FEATURES CONTRIBUTING TO TIME-DEPENDENT NOTCH SENSITIVITY...........11 Original Microstructures.............. 11 Microstructures of Tested Specimens...... 13 Correlation of the Time-Dependent Notch Sensitivity with the Dislocation Structure.... 16 Additional Features......... 18 SUMMARY OF RESULT S........... 20 REFERENCES.......... 22 iii

LIST OF TABLES Table Page 1. Tensile Properties of 0, 030-Inch Inconel 718 Sheet at 1000~F and 1200~F.......................... 23 Smooth and Notched (Kt>20) Specimen Tensile and Creep-Rupture Properties at 900~F to 1400~F for 0. 030-Inch Thick Inconel 718 Sheet................................. 24-32 2. Heat Treated 10 Hours at 1950~F Plus 48 Hours at 1350~F. 24 3. Heat Treated 1 Hour at 1950~F Plus 48 Hours at 1350~F.. 25 4. Heat Treated 1 Hour at 19500F Plus 2 Hours at 1550~F.. 26 5. Heat Treated 1 Hour at 1950~F Plus 24 Hours at 1550~F... 27 6. Heat Treated 10 Hours at 1800~F Plus 48 Hours at 1350~F.. 28 7. Heat Treated 10 Hours at 1700~F Plus 3 Hours at 13250F. 29 8. Heat Treated 10 Hours at 1700~F Plus 48 Hours at 1350~F. 30 9. Heat Treated 1 Hour at 1700~F Plus 3 Hours at 1325FE.. 31 10. Heat Treated 1 Hour at 1700~F Plus 2 Hours at 1550~F.. 32 11. X-Ray Diffraction Data of Extracted Residues of Inconel 718 in the Heat Treated Conditions............... 33 iv

LIST OF FIGURES Figure Page 1 Types of Test Specimens.............. 34 Stress Versus Rupture Time Data at Temperatures from 800~ to 1400~F Obtained from Smooth and Notched Specimens of Inconel 718 Sheet; and Time-Temperature Dependence of the Rupture Strengths of Smooth and Notched Specimens of Inconel 718 Sheet..-......... 35-58 2, 3 4,5 6, 7 8,9 10, 11 12, 13 14, 15 16, 17 18, 19 20, 21 22, 23 24, 25 Cold Worked and 20 Percent and Aged. 35-36 Heat Heat Heat Heat Heat Heat Heat Heat Heat Heat Treated 1 Hour at 1950~F and Aged...... 37-38 Treated Treated Treated Treated Treated Treated Treated Treated Treated 1 Hour at 10 Hours 1 Hour at 1 Hour at 1 Hour at 10 Hours 10 Hours 10 Hours 1 Hour at 1750~F and Aged..... at 1950~F Plus 48 Hours at 1350~F. 1950~F Plus 48 Hours at 1350~F. 1950~F Plus 2 Hours at 1550~F... 1950~F Plus 24 Hours at 1550~F.. at 1800~F Plus 48 Hours at 1350~F ~ at 1700~F Plus 3 Hours at 1325~F.. at 1700~F Plus 48 Hours at 1350~F. 1700~F Plus 3 Hours at 1325~F. 39 -40 41-42 43-44 45 -46 47 -48 49 -50 51-52 53-54 55-56 Heat Treated 1 Hour at 1700~F Plus 2 Hours at 1550~F.. 57-58 27, 28, 26 Time-Temperature Dependence of the Rupture Strengths at 900~ to 1400~F for Notched Specimens of Inconel 718 in Various Heat Treated Conditions.... 59 29 Time-Temperature Dependence of the Rupture Strengths at 900~ to 1400~F for Smooth Specimens of Inconel 718 in Various Heat Treated Conditions......... 60 30 Optical Photomicrographs of Notched Specimens of Inconel 718 Polished to Remove the Oxidized Surface Layers... 63 -62 V

Figure Page Iso-Creep Strain Curves of Life Fraction Versus Stress at Temperatures from 1000~F to 1400~F for Inconel 718 Sheet..... 64-72 31 Heat Treated 10 Hours at 1950~F Plus 48 Hours at 1350~F~ 64 32 Heat Treated 1 Hour at 1950~F Plus 48 Hours at 1350~F. 65 33 Heat Treated 1 Hour at 1950~F Plus 2 Hours at 1550~F.. 66 34 Heat Treated 1 Hour at 1950~F Plus 24 Hours at 1550~F ~ 67 35 Heat Treated 10 Hours at 1800~F Plus 48 Hours at 1350~F. 68 36 Heat Treated 10 Hours at 1700~F Plus 3 Hours at 1325~F ~ 69 37 Heat Treated 10 Hours at 1700~F Plus 48 Hours at 1350~F. 70 38 Heat Treated 1 Hour at 1700~F Plus 3 Hours at 1325~F. 71 39 Heat Treated 1 Hour at 1700~F Plus 2 Hours at 1550~F. 72 40 Optical Photomicrographs of Inconel 718 in Various Heat Treated Conditions........ 73-75 41 Replica Electron Micrographs of Inconel 718 Sheet in the As-Heat Treated Conditions...... 76-77 42 Transmissions Electron Micrographs of Inconel 718 in Two Heat Treated Conditions Showing y'/y" Size Distributions.,........ 78 43 Thin-Foil Diffraction Pattern 1100J Mattrix Zone... 79 44 Thin-Foil Electron Micrograph of Inconel 718, Heat Treated 1 Hour at 1950~F Plus 48 Hours at 1350~F and Creep-Rupture Tested at 120ksi at 1100~F.. 80 45 Optical and Transmission Electron Micrographs of Inconel 718 Heat Treated 1 Hour at 1950~F Plus 48 Hours at 1350~F and Creep Rupture Tested at 30ksi at 1400F.. 81 46 Thin-Foil Electron Micrographs of Inconel 718 Heat Treated 1 Hour at 1950~F Plus 48 Hours at 1350~F and Creep Rupture Tested at 30ksi at 1400~F.... 82 47 Transmission Electron Micrographs of Inconel 718 Heat Treated 1 Hour at 1950~F Plus 2 Hours at 1550~F and Tested at 100ksi at 1100~F........... 83 vi

Figure Page 48 Thin-Foil Electron Micrographs of Inconel 718 Heat Treated 1 Hour at 1950~F Plus 24 Hours at 1550~F and Tested at 115ksi at 1000~F........84 49 Transmission Electron Micrograph of Inconel 718 Heat Treated 1 Hour at 1700~F Plus 3 Hours at 1325~F and Creep Rupture Tested-(a) at 1000~F at 130ksi and (b) at 1200~F at 65ksi........ 85 50 Thin-Foil Electron Micrograph of Inconel 718 Heat Treated 10 Hours at 1700~F Plus 48 Hours at 1350~F and Creep Rupture Tested at 1000~F at 120ksi 86 51 Effect of Aging Expsoures at 1325~F, 1400~F and 1500~F on the Diamond Pyramid Hardness of Several Heat Treatments of 0. 030-Inch Thick Inconel 718 Sheet... 87-88 vii

SUMMARY A study is being made of the severe time-dependent edge-notch sensitivity known to occur at 1000~ and 1200~F for superalloy sheet materials. An investigation utilizing Waspaloy, to a great extent established the scope and cause of the problem (ref. 1). Presently, reported are results of experiments primarily directed at determining whether the concepts developed also apply to Inconel 718. Heat treatment variations of 0. 030 inch thick Inconel 718 sheet were used to provide a range of mechanical characteristics and microstructural features. Tensile and creep-rupture tests were conducted at temperatures from 900~ to 1400~F. The microstructural features were evaluated for the as-heat treated material and for lested specimens. Most important, the results showed that the time-dependent notch sensitivity of Inconel 718 could be correlated to the same mechanical characteristics and similar microstructural features as evident for Waspaloy. This would suggest even wider applicability of the results. Necessary conditions for time-dependent notch sensitivity were (i) the notch specimen loads had to be below the approximate 0. 2 percent smooth specimen offset yield strength; and (ii) test data from smooth specimens had to indicate that small amounts of creep used up large fractions of rupture life. Time-dependent notch sensitivity was observed at test temperatures from 900~ to 1200~F. Decreasing the solution temperature or increasing the time and/or temperature of the aging treatment decreased the susceptibility to time-dependent notch sensitivity. Variations in heat treatment and test conditions influenced the dislocation motion mechanism. Ni3Cb(bct) particles (and gamma prime) smaller than a "critical size" were sheared by dislocations. This gave rise to localized deformation and time-dependent notch sensitive behavior. Larger particles were by-passed by dislocation and the deformation was homogeneous. Under these conditions no time-dependent notch sensitivity was observed. ix

INTRODUCTION The results presented were derived from a current study being made of the severe time-dependent edge-notch sensitivity that has been observed for nickel-base superalloy sheet materials at temperatures from 900~F to 1300~F. The research was carried out at the University of Michigan, Ann Arbor, Michigan, under sponsorship of the National Aeronautics and Space Administration. Extensive research (ref. 1) established the scope and the cause of the problem for Waspaloy. In addition, heat treatments were defined which eliminated the time-dependent notch sensitivity. Continuing research is directed at broadening the applicability of the concepts developed for Waspaloy. To achieve this, the study is being extended to include other alloys. The experiments reported deal with results obtained for Inconel 718. The composition of this nickel-base superalloy differs considerably from that of Waspaloy. Of major significance, columbium is present in Inconel 718 but not in Waspaloy. This element has a marked influence on phase relationships and hence on the microstructures and mechanical behavior. As part of an evaluation of potential usefulness of various superalloys in sheet form for construction of the Supersonic Transport, Inconel 718 in three heat treated conditions was shown to exhibit time-dependent notch sensitivity at 1000~ and 1200~F (ref. 2). (Representative results from this investigation are included as Figures 2 through 7.) The research presently reported was designed to extend the scope of these initial results. Heat treatments were selected to provide a wide range of microstructural features. These were also expected to produce considerable variation in mechanical characterisitics. Tensile and creep-rupture tests were carried out in the temperature range were severe time-dependent notch sensitivity can occur (900~ - 1200~F). Testing was also carried out at 1400~F in order to provide a contrasting case where the notch sensitivity has not be observed. The microstructural features, particularly the dislocation mechanism in the tested specimens, were evaluated. 1

EXPERIMENTAL DETAILS Materials The commercially produced Inconel 718 used in the investigation had the following reported composition (weight percent): Ni 53,97 C 0,05 Mn 0.12 Fe S 16.50 0.007 Si 0.22 Cr 18.98 Al 0.52 Ti 1.04 Co 0.05 Mo 3.15 Cb 5.25 B 0. 002 The material was received as 0. 030-inch thick cold reduced sheet. Specimen blanks were cut in the longitudinal direction prior to heat treatment. Heat Treatment The heat treatments were designed to produce a wide range of microstructural features. The selection was based primarily on isothermal transformation diagrams reported for the alloy (ref. 3). The heat treatments were as follows: Solution Treatment 1. 10 hours at 1950~F 2. 1 hour at 1950~F 3. 1 hour at 1950~F 4. 1 hour at 1950~F 5. 10 hours at 1800~F 6, 10 hours at 1700~F 7. 10 hours at 1700~F 8. 1 hour at 1700~F 9. 1 hour at 1700~F Aging Treatment +- 48 hours at 1350~F + 48 hours at 1350~F + 2 hours at 1550~F + 24 hours at 1500~F + 48 hours at 1350~F + 3 hours at 1325~F + 48 hours at 1350~F + 3 hours at 1325~F + 2 hours at 1550~F The blanks were solution treated individually in an argon atmosphere and subsequently air cooled. To prevent warping, the blanks were aged while clamped in a fixture in batches of 10 or 12. It should be noted that although the higher temperature exposures are referred throughout this paper as "solution treatments", the use of this designation does not necessarily signify complete solution of all constituent phases. 2

Testing Procedures The testing procedures used have been described in depth elsewhere (ref. 1). After heat treatment blanks were machined into smooth and sharp-edge (Kt>20) notched specimens (fig. 1). The tensile tests were conducted using a hydraulic tensile machine. Smooth specimens were tested at a cross head speed of approximately 0. 01 inches per inch per minute up to about 2 percent deformation. The strain rate was then increased to about 0. 05 inches per inch per minute until failure. Notched specimens were loaded at a rate of 1000 psi per second. The creep-rupture tests were conducted in beam loaded machines. The rupture times were recorded automatically. For both tensile and creep-rupture tests, recommended practices (ASTM-E21, E139) were followed in control of test temperatures and distributions. The extensions were measured by an optical extension system which has a sensitivity of five millionths of an inch. Structural Examination Conventional methods were employed for microstructural examination. Samples for optical microscopy and replica electron microscopy were etched electrolytically in "G" etch, an etchant developed by Bigelow et al (ref. 4). Samples approximately 0. 5 inches wide by 0. 7 inches long for transmission electron microscopy of the tested specimens were cut from the gauge lengths, ground on wet silicon carbide papers and electropolished. This was carried out at an applied voltage of 20 volts in conjunction with a chilled mixture of 83 percent Methanol, 7. 5 percent Sulphuric Acid, 3 percent Nitric Acid, 4.5 percent Lactic Acid and 2 percent Hydrofluric Acid. The thin films were studied and photomicrographed in a JEM electron microscope operated at 100KV. X-ray diffraction analysis of extracted residues was used to identify the phases present in the as-heat treated materials. The residues were obtained by preferentially dissolving the matrix electroytically using a solution of 10 percent Phosphoric Acid in Water. A platinum cathod was used at 3-4 volts potential. The residues were washed with alcohol, 3

dried and formed into thin wires using a Duco Cement binder. X-ray exposures were conducted in a 144. 6mm diameter Debye camera using nickel-filtered copper radiation (40KV, 16mA) for a period of four hours. The line positions were measured and the "d" values calculated. The results were then analyzed by comparison with standard patterns available from the literature and from the files of the Joint Committee on Powder Diffraction Studies. 4

INFLUENCE OF HEAT TREATMENT ON THE MECHANICAL CHARACTERISTICS The results of tensile and creep rupture tests are presented in Tables I through X. The rupture data are included as stress-rupture time curves and as parameter curves in Figures 8 through 25. The Larson-Miller parameter with C of 20 was used simply because it was an effective method of presenting the data. The heat treatment variations resulted in a wide range of mechanical characterisitics. In particular, the severity of the time-dependent notch sensitivity varied considerably with changes in both the solution and aging treatments. The results for the material heat treated 10 hours at 1950~F plus 48 hours at 1350~F (table II), provide an example of severe time-dependent notch sensitivity. At the shorter times at the lower test temperatures, the notched specimen rupture curves were somewhat below those for smooth specimens (figs. 8, 9). The notched to smooth rupture strength ratios (N/S) were the same order as determined by tensile tests (table II). At varying time periods, the notched specimen rupture curves exhibited drastic increases in steepness so that the N/S ratio decreased with time to values considerably below those obtained in tensile tests, i. e. the material exhibited time-dependent notch sensitivity. At intermediate temperatures, upward breaks in the rupture curve were evident. This resulted in an increase in the N/S ratio or a decrease in notch sensitivity. The rupture strength ratio increased with increasing test temperature and longer rupture times, until, at the highest temperature a value of about 1. 0 was obtained. In contrast to the above behavior, the results for the material heat treated 10 hours at 1700~F plus 48 hours at 1350~F are typical of the heat treated conditions that were not susceptible to time-dependent notch sensitivity (table VIII, figs. 20, 20). The N/S rupture strength ratios were generally higher than those obtained in tensile tests. The types of characterisitics described above were evident for the other heat treated materials (figs. 10 through 19 and 22 through 25). The severity of the time-dependent notch sensitivity for the heat treated con 5

ditions studied, including those previously reported (ref. 2), are tabulated below. Ratings of 2 and 1 correspond to severe and limited time-dependent notch sensitivity respectively. Test conditions for which no time-dependent notch sensitivity was evident were rated 0. Solution Treatment 10 hours at 1950~F 1 hour at 1950~F 10 hours at 1800~F 10 hours at 1700~F 1 hour at 1700~F Aging Treatment(s) + 48 hours at 1550~F + 48 hours at 1350~F + 2 hours at 1550~F + 24 hours at 1550~F + 48 hours at 1350~F + 3 hours at 1325~F + 48 hours at 1350~F + 3 hours at 1325~F + 2 hours at 1550~F Test Temperature ~F 900 1000 1100 1200 2 2 2 2 2 2 2 2 2 2 2 1 0 0? 2 2 1? 2 1 0 0 0 0 0 0 2 2? 0 0 0 0 1400 0 0 0 0 0 0 0 0 0 Cold Worked 20% + 1 hour at 1950~F + 1 hour at 1750~F + " Multiple" - 1 1325~F/8 "Multiple" - 2 1350~F/8 "Multiple" 1 "* "Multiple" 2 "Multiple" 1 2 hours, F. C. to 1150~F in hours, F. C. to 1200~F in 2 2 2 1 10 hours, A. 12 hours, A. 2 2 9 C. C. The principle features evident are as follows: (1) Decreasing the solution temperature decreased the susceptibility to time-dependent notch sensitivity. (2) Increasing the severity of the aging treatment (increasing time and/or temperature) reduced the susceptibility to time-dependent notch sensitivity. (3) The materials with the commonly used "multiple" aging treatments exhibited time-dependent notch sensitivity. For all heat treated conditions, the rupture strengths decreased rapidly with increasing time and/or temperature for parameter values above about 37 (figs. 9, 11, 13, 15, 17, 19, 21, 23 and 25). Extensive use is made of Inconel 718 for high temperature applications for which the parameter values are relatively low. Under these conditions, the smooth specimen rupture strengths are high, however, severe time-dependent notch sensitivity can also occur. At low parameter values, the notched rupture strengths were below those for smooth specimens. The rupture strengths for notched specimens 6

varied considerably with heat treatment. Particularily important was whether or not the material exhibited time -dependent notch sensitivity. Those which did not had similar notch rupture strengths while those which were notch sensitive had considerably lower strengths (fig. 26).. It should also be noted that the commonly used "multiple" aging treatments, evaluated previously (fig. 2 through 7), resulted in lower notched rupture strengths than obtained for a number of the heat treatments used in the present investigation. This occurred even though the heat treatments used were not specifically designed to maximize the notched rupture strengths. The heat treatments studied did not result in a very wide range of smooth specimen tensile and creep-rupture strengths (tables I through X). Differences in rupture strength from variations in solution and aging treatments can best be seen from comparison of the parameter curves, such are presented as Figures 27, 28 and 29. Rupture ductility has often been used to indicate the susceptibility of a material to notch sensitivity. Results reported for Waspaloy (ref. 1) indicated that no such relationship occurred which was generally applicable. The same conclusion was drawn from analysis of the elongation and reduction of area values at rupture for Inconel 718 (tables II through X). For both alloys, the results indicated that factors which contribute to ductility rather than the ductility per se, control the time-dependent notch sensitivity. This was evident from analysis of the deformation-time characteristics (reported in a later section for Inconel 718). 7

FRACTURE CHARACTERISTICS The fracture characteristics of Inconel 718 were similar to those established for Waspaloy (ref. 1). Consequently, this aspect is not reported in depth. Both smooth and notched rupture tested specimens failed by initiation and relatively slow growth of intergranular cracks (fig. 30) followed by transgranular fracture. The intergranular part of the fracture was perpendicular to the loading axis and was dark in color from oxidation. The remainder of the fracture was not appreciably discolored by oxidation and was a typical shear failure slanted through the thickness. This latter fracture occurred when the increase in stress on the load bearing area, due to growth of the intergranular crack, exceeded that necessary to cause rapid shear. In consequence, the lengths of the intergranular cracks (expressed as a percentage of specimen width in tables II through X) increased with decreasing test stress and thus with increasing test time. The creep deformation that occurred in the smooth specimens was relatively uniform throughout the gauge section. In contrast, the deformation in the notched specimens was localized. Initially dimples (areas of severe deformation) formed at the base of the notches. Subsequently, intergranular cracks initiated in these regions (fig. 30). The dimples remained at the head of the cracks as they progressed across the specimens. Intergranular cracks were found in notched but not smooth specimen tests discontinued before rupture. This is in agreement with the crack growth rate studies reported for Waspaloy (ref. 1). These showed that visible cracks formed in notched specimens after about 60 percent of the rupture life. The life fraction was smaller than required for crack initiation in smooth specimens (greater than 95%). The results also showed that the occurrence of time dependent notch sensitivity is due to more rapid initiation of intergranular cracks in notched than in smooth specimens. This was shown to be related to the relaxation by creep of stress concentrations introduced by the presence of the edge-notches. 8

STRESS RELAXATION Relaxation of stress concentrations can occur by "yielding" on loading (time-dependent deformation) and by subsequent creep (timedependent deformation). For notched specimen tests loaded above the approximate 0. 2 percent offset yield strengths (established by smooth specimens tests) no time-dependent notch sensitivity was observed (figs. 8 through 25). This occurred since "yielding" on loading reduced the stresses across the specimens at the base of the notches to approximately the nominal stresses. For Waspaloy time-dependent notch sensitivity occurred in notched specimens loaded below their yield strength when tests of smooth specimens showed that small amounts of creep consumed large fractions of creep-rupture life (ref. 1). In other words, when the creep deformation necessary to relax stress concentrations caused excessive damage resulting in premature initiation of intergranular cracks. The smooth specimen deformation characterisitics of Inconel 718 were examined to determine whether a similar correlation existed. Iso-creep-strain curves were constructed for each temperature on plots of life fraction versus test stress (figs. 31 through 39). These curves were derived for 0. 1 and 0. 2 percent creep deformation (the order of deformation necessary to ensure relaxation of elastic stresses from the approximate yield stress to the nominal stresses. ) The inclusion of curves for 0. 5, 1, and 2 percent creep strain aided establishment of the nature of the curves for lower strain. Again, a correlation was evident between the time-dependent notch sensitive behavior and the characterisitics of the iso-creep strain curves. For the material solution treated 10 hours at 1950~F plus 48 hours at 1350~F, the life fractions for small amounts of creep strain at 1000~F increased drastically as the test stress decreased (fig. 31). For notched tests loaded to normal stresses below about 110, 000 psi, the relaxation of the stresses (from the approximate yield stress to the nominal) would utilize considerable if not all of the creep rupture life of the material at the base of the notch. Thus, as observed experimentally (figs. 8, 9), 9

time-dependent notch sensitivity behavior would be expected. At 1200~F (and presumably 1100~F) as the test stress decreased, the life fractions for 0. 1 and 0. 2 percent strain increased to relatively high levels and then subsequently decreased. These results are consistent with the observed increase followed by a decrease in time-dependent notch sensitivity. At 1400~F the life fractions were at relatively low levels and no time-dependent notch sensitivity occurred. The results for the materials heat treated 10 hours at 1700~F plus 48 hours at 1350~F (fig. 37) are in contrast to those presented above. The life fractions for small amounts of creep strain remained at low levels for all test conditions. In accordance with this, no time-dependent notch sensitivity was observed (figs. 20, 21). Analysis of the data for the other heat treated materials showed similar correlations between the nature of the iso-creep strain curves (figs. 32 through 39) and the time-dependent notch sensitive behavior (figs. 10 through 25). 10

MICROSTRUCTURAL FEATURES CONTRIBUTING TO TIME-DEPENDENT NOTCH SENSITIVITY Many nickel-base superalloys (including Waspaloy) age harden by precipitation of an LI2 - ordered fcc phase, Ni3(Al, Ti), called gamma prime. Inconel 718 differs in that age hardening occurs primarily due to precipitation of Ni3Cb(ref. 5). This phase, designated y", has a DOZ - ordered bct structure. The y" phase is metastable so that it is replaced on thermal exposure by the P phase. This phase is also Ni Cb, but it has a Cu Ti - ordered orthorhombic structure. In the study of Waspaloy (ref. 1), a correlation was established between the dislocation motion mechanism operative and the timedependent notch sensitivity. Dislocations sheared y' particles smaller than a critical size. Particles larger than the critical were by-passed by dislocations. The former mechanism promoted the deformation-characteristics that gave rise to the timedependent notch sensitivity. The microstructural features of Inconel 718 were studied to determine whether a similar correlation occurred. Initially optical metallography, replica and transmission electron microscopy and X-ray diffraction studies were carried out for the as-heat treated materials. Subsequently, smooth specimens which had been creep-rupture tested were examined by transmission election microscopy. The specimens studied were selected from heat treatments exhibiting a range of timedependent notch sensitive behavior. Original Microstructures Typical optical and electron micrographs are presented in Figures 40, 41 and 42. These together with the results of the X-ray diffraction studies (Table XI), were used to characterize the microstructural features in the as-heat treated materials. 11

Increasing the time of solution treatment at 1950~F from 1 to 10 hours resulted in a considerable increase in grain size. This reflects the absence of large amounts of precipitate particles which would act to restrain growth. Ti(C,N) is the only precipitate expected to be present at 1950~F. Presumably, these are the large particles evident in the optical micrographs for the material aged 48 hours at 1350~F after solution treatment at 1950~F (figs. 40 a, b). X-Ray diffraction of extracted residues indicated the presence of Cb,Ti(C,N), y' and/or* y" in these materials (Table XI). These latter phases were not readily resolvable in the electron microscope using replica techniques (fig. 4 a, b). In thin films, (fig. 42a), the carbide particles observed were primarily present as 'plate-like" grain boundary precipitates while the y' and/or y" 0 were intragranular precipitates about 300 A in diameter. The presence of y" was demonstrated by an electron diffraction technique (ref. 6). The method uses a [100j diffraction pattern (fig. 43). Superlattice reflections of the form 1-1/2-0 are allowed for the bct y" phase but not for the fcc y'. Thus, the occuarcenice of this reflecti.oa de-nons:trated t:lht ile he hea. treated material contained y'. The presence of y' was inferred from subsequently reported metallographic observations for materials aged at higher temperatures. (In cases such as this where the y' and the y" could not be distinguished visibly, the precipitate will be referred to as /y". ) For the materials solution treated at 1950~F and aged 2 and 24 hours at 1550~F, the presence of y' and y" gave the optical micrographs a mottled appearance (fig. 40 c, d). The particles were large enough to be resolvable using replica techniques (fig. 41 * The y' and y" phases are difficult to distinguish using X-ray diffraction. The "d" values are similar. Differences do occur in the superlattice reflections but these are not readily resolvable (ref. 5). 12

c,d). The y' was present as spherical particles with a relatively low volume fraction. The average size of the particles was about 450 A and 1100 A for the 2 and 24 hour treatments respectively. The majority of the precipitate particles were plates of y" (precipitates coherently with the c-axis normal to the plane of the plates and along any of the three <110> fcc directions - ref. 5). The approximate average thickness and length of the plates were respectively 200 A and 1000 A for the 2 hour treatment and 500 A and 4000 A for the 24 hour treatment. X-ray diffraction indicated the presence of small amounts of ( phase for the materials aged at 1550~F after solution treatment at 1950~F. (Table XI). In micrographs, this phase was evident as needles, predominately alongside grain boundaries (figs. 40 d, 41 d). The areas adjacent to grain boundaries and p precipitate particles were depleted of y" (fig. 41 d). The majority of the precipitate present in the optical micrographs of the material heat treated 10 hours at 1800~F plus 48 hours at 1350~F (fig. 40 f) was P phase. This phase formedduring the 1800~F solution treatment (fig. 40 e). X-ray diffraction showed that the aged material also contained Cb, Ti(C, N), y' and/or y". All of the materials solution treated at 1700~F and aged contained Cb, Ti(C,N), y'/y" and the 3 phase (Table XI). Ni Cb 3 needles precipitated during the 1700~F treatments (fig. 40 g, j). A much larger amount of P phase was present after the 10 hour exposure than the 1 hour treatment. Aging 3 hours at 1325~F or 48 hours at 1350~F after solution treatment at 1700~F resulted in y' /y" too small to be resolved using replica techniques (figs. 41 f, g). In thin films (figs. 42 b), resolution was also difficult because the y'/y" particles were only about 60 A and 200 A in diameter for the 1325~F and 1350~F treatments, respectively. These particle sizes are smaller than those produced by similar aging treatments after solution treatment at 1950~F. This also occurred for the 2 hour at 1550~F aging treatment (fig. 41 c, h). 13

Microstructures of Tested Specimens Examination of tested specimens by transmission electron microscopy was carried out primarily to determine the dislocation structures present. The observations were made for selected heat treatments and test conditions. The dislocation arrangements were expected to be representative of all of the heat treatments used in the study. (1) Material heat treated 1 hour at 1950~F plus 48 hours at 1350~F: For the specimen tested at 1100~F (at 120 ksi ruptured in 1.4 hours) the most obvious feature was the {111} planar slip banding (fig. 44). This reflects shearing of the y'//y" coherent precipitates by dislocations (refs. 5, 7). Similar dislocation structures would be expected to occur in other specimens tested at temperatures low enough so that little or no growth or y'/y" occurs. It was evident from microstructures of the specimen tested at 1400~F (at 30 ksi ruptured in 384 hours) that structural changes had occurred during the test exposure. Ni3Cb needles precipitated 3 0 (fig. 45, 46) and the y' particles increased in size to about 750 A. The y" also grew so that it was clearly resolvable as plates approxi0 0 mately 500 A thick and 4000 A long. Contrast effects associated with coherency (ref. 8) were observed for both y' and y" precipitate particles (fig. 45 b, c). Because of the presence of large precipitates the deformation was homogeneous (fig. 46). Dislocations were observed entangled with the y" particles and in some cases forming loops around the y'. It must be assumed that in the early part of the test when the particles were small, the dislocations sheared the particles, i. e. the microstructure would have been similar to Figure 44. The above observations are analogous to those reported for Waspaloy (ref. 1). In this case, dislocations sheared y' particles smaller than a critical size. When the particles were larger than the critical, they were by-passed by dislocations. These mechanisms 14

resulted in localized and homogeneous deformation respectively. (2) Material heat treated 1 hour at 1950~F plus 2 hours at 1550~F: The deformation that occurred for the specimen tested at 1100~F (at 100 ksi ruptured in 385 hours) was localized in slip bands (fig. 47 a). Presumably, dislocations sheared the y' o 0 particles (about 450 A in diameter) and also the y" (200 A thick o and 1000 A long). The previously described results would indicate that growth of the precipitates during higher temperature tests would cause the deformation to become homogeneous. One additional feature was evident from the study of the specimen tested at 1100~F. In a number of micrographs, a fine 0o precipitate (about 70 A in diameter) was detected (fig. 47 b). Presumably, this is y'/y" that formed subsequent to the 1550~F aging treatment and developed during the test exposure. (3) Material heat treated 1 hour at 1950~F plus 24 hours at 1550~F: The y'/y" in the aged material was larger than "critical" size. Even in a low temperature test specimen (at 1000~F and 115 ksi, ruptured in 1857 hours) the dislocations were homogeneously distributed (fig. 48). 0 A fine dispersion of y'/y" (about 100 A in diameter) was observed in the specimen tested at 11000F (at 100 ksi ruptured in 3528 hours). This feature was similar to that described for the material aged 2 hours at 1550~F. (4) Material heat treated 1 hour at 1700~F plus 3 hours at 1325~F: The deformation in the specimen tested at 1000~F ( at 130 ksi ruptured in 5613 hours) was localized (fig. 49 a). In the majority of cases, the dislocations in pile ups were dissociated to form stacking fault ribbons. This type of deformation was not expected, because in the presence of y" it requires coplanar motion of multiple dislocations. Four whole dislocations must move along the same plane to restore order for all three orientations of y" (ref. 7). (It should be noted that the presence of y" was confirmed by electron diffraction. ) 15

Growth of y'/y" occurred during exposure of the specimen tested at 1200~F (at 65 ksi ruptured in 937 hours). As a result, the dislocations were homogeneously distributed (fig. 49 b). The microstructures indicated that the dislocations bowed between the y'/y" particles (about 250 A in diameter) leaving pinched off dislocation loops, i.e. the dislocations by-passed the particles. This would indicate a much smaller "critical" size than for the materials aged after solution treatment at 1950~F. This probably occurred due to differences in the volume fraction of precipitate. Reducing the volume fraction of the y'/y" precipitate should lower the "critical" size (ref. 9). Although not determined as part of the investigation, less y" was probably present for materials aged after solution treatment at 17000F than for those treated at higher temperatures, i.e. 1950~F. This could be expected because precipitation of Ni3Cb needles during the 1700~F treatment must reduce the amount of Cb in solid solution available to form y" during aging. Further research is necessary to clarify these effects. (5) Material heat treated 10 hours at 1700~F plus 3 hours at 1325~F: Limited study of a specimen tested at 1000~F (at 130 ksi ruptured in 391 hours) did not reveal any inconsistencies from the results described above for the material solution-treated 1 hour at 1700~F and aged at 1325~F. (6) Material heat treated 10 hours at 1700~F plus 48 hours at 1350~F: For the specimen tested at 1000~F (at 120 ksi ruptured in 1382 hours) the deformation was homogeneous (fig. 50). This result demonstrated that the y'/y" produced by the aging treatment (about 0 200 A in diameter) was larger than the "critical" size. Correlation of the Time-Dependent Notch Sensitivity with the Dislocation Structure The results indicate that a correlation exists between the predominant dislocation mechanism and the time-dependent notch sensitivity. The relationship was the same as evident for Waspaloy (ref. 1). Shearing the precipitate particles by dislocations resulted 16

in greater susceptibility to time-dependent notch sensitivity than when they were by-passed. For the materials heat treated 1 hour at 1950~F plus 48 hours at 1350~F, 1 hour at 1950~F plus 2 hours at 1550~F, 1 hour at 1700~F plus 3 hours at 1325~F and 10 hours at 1700~F plus 3 hours at 1325~F, time-dependent notch sensitivity was observed at the lower test temperatures. During these tests, the y'/y" particles were sheared by dislocations and the deformation was localized. During the higher temperature tests, growth of the y" and y' precipitates occurred. This resulted in a change of dislocation motion to "by-passing" so that a homogeneous distribution of dislocations resulted. This correlates with the elimination of time-dependent notch sensitivity by increasing the test temperature. For the materials heat treated 1 hour at 1950~F plus 24 hours at 1550~F and 10 hours at 1700~F plus 48 hours at 1350~F, the dislocations were homogeneously distributed and no timedependent notch sensitivity was observed. There was no evidence to indicate that the other heat treated materials, for which tested specimens were not studied, would not follow the above correlation. It is of interest to compare the behavior of materials with a given aging treatment, e. g. 48 hours at 1350~F. The timedependent notch sensitivity was severe for the material solution treated at 1950~F. Decreasing the solution temperature to 1800~F decreased the notch sensitivity, until for the 1700~F treatment, none was observed. This is consistent with the metallographic observation that the "critical" size decreased with decreasing solution temperature. As suggested previously, this probably occurred because lowering the solution temperature reduced the volume fraction of y'/y". This would also explain why heat treatment 1 hour at 1700~F plus 3 hours at 1325~F resulted in more severe time-dependent notch sensitivity (or occurred at high test temperatures) than for the material heat treated 10 hours at 1700~F plus 3 hours at 1325~F. 17

Additional Features Failure of both smooth and notched creep-rupture specimens occurred by relatively slow intergranular crack initiation and growth followed by transgranular fracture Consequently, factors which affect the intergranular crack initiation influence the rupture times and hence the time-dependent notch sensitive behavior. Intergranular crack initiation must be dependent on (a) the nature of intergranular deformation and (b) the metallurgical characterisitics of the grain boundaries. The influence of variations in the grain boundary characteristics on the time-dependent notch sensitivity were not evident from the results. Nor was a relationship evident from the study of Waspaloy (ref. 1). In both cases, a correlation was evident between the dislocation mechanism and the time-dependent notch sensitive behavior. This would suggest that the influence of the y" and/or y' precipitates on the notch sensitivity overshadows effects from variations in grain boundary characteristics. Increasing the particle size of y' and/or y" increases the critical resolved shear stress (CRSS) for dislocations motion until the particle dimensions exceed a critical size, after which, further increase in size decreases the CRSS. Below the critical size, the dislocations shear the particles while larger particles are by-passed. Hardness tests were conducted for a range of heat treated materials, including those used in the test program, to determine whether these values could be used to monitor the -y'/y" size relative to the critical. The results (fig. 51) showed the following: (1) For the heat treatments for which the hardness indicated that the y'/y" size was clearly above or below the critical size (i.e. maximum hardness), the time-dependent notch sensitive behavior was in accordance with the hardness results. Heat treatment 1 hour at 1950~F plus 24 hours at 1550~F resulted in y'/yr" larger than the critical size (fig. 51 a) and no time-dependent notch sensitivity occurred. The materials 18

heat treated 1 or 10 hours at 1700~F plus 3 hours at 1350~F exhibited time-dependent notch sensitivity and the hardness tests indicated that the y'/y" were smaller than the critical size (fig. 51 b, e). (2) For many heat treated materials, the hardness tests indicated that the y'/y" sizes were near the critical. In these cases, it would not be possible to guarantee correct prediction of the time-dependent notch sensitive behavior from the hardness tests. Certainly, for none of the heat treatments evaluated was there a case for which the hardness test results clearly indicated the incorrect notch sensitive behavior. (3) The times at which the maximum in hardness occurred at each temperature decreased as the solution temperature decreased. This corresponds to the observed decrease in "critical size". (4) The hardness tests also indicate that solution treated material aged 8 hours at 1325~F, F. C. to 1150~F in 10 hours A. C. could be expected to be susceptible to timedependent notch sensitivity. This is in agreement with previously published test results (ref. 2). Thus, the results indicate that hardness testing is a useful method for determining the likelihood of whether heat treatments will be susceptible to time-dependent notch sensitive behavior. 19

SUMMARY OF RESULTS A study was made of the time-dependent edge-notch sensitivity of 0. 030-inch Inconel 718 sheet. Consideration of the results led to the following: (1) Time-dependent notch sensitivity was observed at temperatures from 900~ to 1200~F. No reasons were evident why similar behavior could not be expected at prolonged times at lower temperatures. Notched to smooth rupture strength ratios fell to as low as 0, 37. At 1400~F ratios of about 1. 0 were obtained, i. e. no notch sensitivity was observed. (2) Both smooth and notched creep-rupture specimens failed by relatively slow intergranular crack initiation and growth followed by transgranular fracture. Time-dependent notch sensitivity was due to premature initiation of intergranular cracks. This was caused by localized creep deformation resulting from relaxation of the high stresses introduced by the presence of the edge-notches. Necessary conditions for time-dependent notch sensitivity were (i) the notched specimen loads had to be below the approximate 0. 2 percent smooth specimen offset yield strength; and (ii) test data from smooth specimens had to indicate that small amounts of creep used up large fractions of creep rupture life. These observations are identical to those reported for Waspaloy (ref. 1). (3) The severity of the time-dependent notch sensitivity was dependent of the heat treatment. Decreasing the solution temperature or increasing time and/or temperature of the aging treatment decreased the susceptibility to the time-dependent notch sensitivity. No time-dependent notch sensitivity was observed for materials heat treated 10 hours at 1700~F plus 48 hours at 1350~F and 1 hour at 1700~F plus 2 hours at 1500~F. It should be noted that the commonly used aging treatments: 1350~F/8 hours, F. C. to 1200~F in 12 hours, A. C. (after solution treatment at 1950~F) and 1325~F/8 hours, F.C. to 1150~F in 10 20

hours, A. C. (after solution treatment at 1750~F) resulted in notch sensitive behavior. (4) The dislocation motion mechanism varied with heat treatment and test conditions. Dislocations sheared the bct Ni3Cb particles (and gamma prime) smaller than a "critical size". Larger particles were by-passed by dislocations. These gave rise to localized and homogeneous deformation respectively. Localized deformation increased the susceptibility to notch sensitivity. In consequence, a correlation existed between the occurrence of time-dependent notch sensitivity and the nature of the dislocation motion mechanism operative. Results indicated that room temperature hardness tests can be used to indicate particle size relative to the "critical". Similar relations were evident from the study of Waspaloy (ref. 1). This material differed in that it age hardens solely due to gamma prime, Ni3(Ti, Al). For Inconel 718, although gamma prime is present, the principle strengthening phase is bct Ni3Cb, 21

REFERENCES 1. Wilson, D. J. and Freeman, J. W.: "Sensitivity of the CreepRupture Properties of Waspaloy Sheet to Sharp-Edged Notches in the Temperature Range of 1000 to 1400~F". Prepared under Grant No. NGL-23-005-005 (NASA CR-1849) for NASA by the University of Michigan, Ann Arbor, June 1971. 2. Cullen, T. M. and Freeman, J. W.: "The Mechanical Properties of Inconel 718 Sheet Alloy at 800~F, 1000~F and 1200~F". Prepared under Grant No. NsG-124-61 (NASA CR-268) for NASA by the University of Michigan, Ann Arbor, July, 1965. 3. Eiselstein, H. L.: "Metallurgy of a Columbium-Hardened Nickel-Chromium-Iron Alloy". ASTM-STP No. 369, p. 62, 1965. 4. Bigelow, W. C., Amy, J.A., and Brockway, L. O.: "Electron Microscope Identification of the Gamma Prime Phase of NickelBase Alloys". Proc. ASTM, Vol. 56, p. 945, 1956. 5. Paulonis, D. F., Oblak, J. M., and Duvall, D. S.: "Precipitation in Nickel-Base Alloy 718". Trans. ASM, Vol. 62, p. 611, 1969. 6. Kirman, I. and Warrington, D. H.: "Identification of the Strengthening Phase in Fe-Ni-Cr-Nb Alloys". JISI, Vol. 205, p. 1264, 1967. 7. Kirman I. and Warrington, D. H.: "The Precipitation of Ni3Nb Phases in a Ni-Fe-Cr-Nb Alloy", Metall. Trans., Vol. 1, p. 2667, 1970. 8. Kotval, P. S.: "The Microstructure of Superalloys". Metallography, Vol. 1, p. 251, 1969. 9. Decker, R. F.: "Strengthening Mechanisms in Nickel-Base Superalloys". Presented at the Steel Strengthening Mechanisms Symposium, Zurich, Switzerland, May, 1969. 22

TABLE 1 TENSILE PROPERTIES OF 0. 030 INCH THICK INCONEL 718 SHEET AT 1000~ AND 1200~F Smooth Specimen Properties Heat Treatment 10 hrs. at 1950~F + 48 hrs. at 1350~F 1 hr. at 1950~F + 48 hrs. at 1350~F 1 hr. at 1950~F + 2 hrs. at 1550~F 1 hr. at 1950~F + 24 hrs. at 1550~F 10 hrs. at 1800~F + 48 hrs. at 1350~F 10 hrs. at 1700~F + 3 hrs. at 1325~F 10 hrs. at 1700~F + 48 hrs. at 1350~F 1 hr. at 1700~F + 3 hrs. at 1325~F 1 hr. at 1700~F + 2 hrs. at 1550~F Test Temp (~F) 1000 1200 1000 1200 1000 1200 1000 1200 1000 1200 1000 1000 1200 1000 1200 1000 1200 Tensile Strength (ksi) 145. 4 142.4 160.1 157.5 134 9 133.4 134.2 132.6 162. 0 147.6 157.5 166.0 143. 7 165. 2 160. 2 149.0 135.4 0. 2% Offset Yield Strength (ksi) 118.5 116.5 129. 5 130. 5 90.5 99.5 83. 5 122.0 120.5 116. 0 116.5 115.5 135.0 136.0 101.5 103.0 Y. S. T. S. 0.82 0.82 0.81 0.83 0.67 0.75 0.63 0.75 0.82 0.75 0.71 0.80 0.82 0.85 0.68 0.76 Elong. (%) 15.4 8. 1 22. 5 8. 4 27.0 11.3 32. 8 14. 6 19. 6 16.7 15.5 15.9 16.8 12.9 8. 3 19.8 14. 2 R. A. (%) 23 14 30 14 34 18 30 17 23 15 24 Notched Tensile Strength (ksi) 149.0 135.3 152.4 147.5 113.6 116.0 102. 1 108. 0 135.9 140.8 N/S Tensile Strength Ratio 1.02 0.95 0.95 0.94 0.84 0.87 0. 76 0.81 0.84 0.95 0.75 0.96 0.94 0.88 0.82 0.89 23 125. 1 26 138.1 27 154.9 22 140. 3 27 121.9 20 121.2

TABLE 2 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900~F TO 1400~F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 10 HOURS AT 1950~F PLUS 48 HOURS AT 1350~F SMOOTH SPECIMENS Test Rupture Larson-Miller Min. Creep Intergranular Temp. Stress Time Parameter Elong. R. A. Rate Crack Length (~F) (ksi) ( hrs.) (C20) x 10-3 %) (%) (% / hr.) (%) 1000 145.4 Tensile 15.4 23 0 130 21.5 31.15 7.4 13 8 115 333.7 32.88 3.4 9 0. 00033 11 105 3332. 2ph 34.34 -ve. 1100 100 431.3 35.31 1.5 4 0.0004-1 18 85 9691.4 37.42 1.0 3 -ve. 26 1200 142.4 Tensile 8. 1 14 0 90 216. 1 37.07 1. 1 8 0.00067 26 80 282. 4ph 37.27 0. 00055 70 924.8 38. 12 1. 1 5 0. 00014 34 60 3564.0 39.10 1.3 4 0.000038 44 1400 30 292.1 41.79 1.9 3 0.00091 60 NOTCHED SPECIMENS Test Rupture Larson-Miller Intergranular Temp. Stress Time Parameter Crack Length N/S Strength (~F) (ksi) ( hrs. ) (C=20) x 10-3 (%) Ratio 900 120 360.0 30.68 16 90 1075. 1 31. 32 27 1000 149.0 Tensile 0 1.02 120 18.7 31.06 6 0.92 90 100.7 32.12 26 0.74 60 682.7 33.34 54 0.53 50 2342.4 34.12 38 0.47 1100 80 31.6 33.54 35 0.71 60 212.8 34.83 0.58 50 2121.8 36.39 39 0. 55 1200 135.3 Tensile 1 0.95 60 3.1 34.02 32 0.46 50 1.5 33.49 52 0.37 40 5774.6 39.44 73 0.72 1400 30 451.8 42.14 79 1.13 ph = failed at pin hole

TABLE 3 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900~F TO 1400F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 1 HOUR AT 1950~F PLUS 48 HOURS AT 1350~F SMOOTH SPECIMENS Test Rupture Larson-Miller Min. Creep Intergranular Temp. Stress Time Parameter Elong. R. A. Rate Crack Length (~F) (ksi) ( hrs.) (C=20) x 10 (%) (%) (%/ hr. ) (%) 1000 160. 1 Tensile 22.5 30 0 140 385.0 32.97 2.7 11 0.00043 10 130 2506. 1 34. 16 1.6 7 0.000022 14 1100 120 1.4 31.43 4.2 10 8 110 1930. 1 36.33 1.3 7 0.00015 22 100 6833.6 37. 18 1.6 6 0. 000013 23 1200 157.5 Tensile 8.4 14 0 90 707.6 37.93 1.3 8 0.00028 24 80 228.9ph 37.12 0.00025 70 2469.5 38.83 0.8 2 0.000073 40 60 6261.4 39.50 0.8 2 -ve. 40 60 8168.8 39.69 2 0.000026 48 1400 30 384.0 42. 01 2. 1 5 0. 00077 24 NOTCHED SPECIMENS Te st Rupture Larson-Miller Intergranular Temp. Stress Time Parameter Crack Length N/S Strength (~F) (ksi) ( hrs. ) (C=20) x 10-3 (%) Ratio 900 130 34.6 29.29 6 90 1745.1 32.21 41 1000 152.4 Tensile 0 0.95 90 86.2 32.03 29 0.60 70 221.2 32.62 41 0.49 60 9262 Discontinued >0.49 1100 80 10.8 32.81 30 0.55 60 184.1 34.73 44 0.47 50 ~.J s b. 1200 147.5 Tensile 1 0.94 50 46.3 35.96 45 0.41 45 330.2 37.38 70 0.45 1400 30 419.8 42.08 75 1.02 ph = failed at pin hole,,> Oio

TABLE 4 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900~F TO 1400~F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 1 HOUR AT 1950~F PLUS 2 HOURS AT 10-F 00 SMOOTH SPECIMENS Test Rupture Larson-Miller Min. Creep Intergranular Temp. Stress Time Parameter Elong. R. A. Rate Crack Length (~F) (ksi) ( hrs.) (C=20) x 10-3 (%) (%) (% / hr.) (%) 1000 134.4 Tensile 27.0 34 0 130 63.5 31.83 18.7 19 6 120 154.1 32.39 11.9 14 0.00020 11 115 4402.3 34.52 7.3 13 0.000005 17 1100 110 138& 2 34.54 7.8 13 0.00030 20 100 385.2ph 35.2 <0. 00047 185 J, 6{Yn progress 1200 133.4 TeTisTfe 11.3 18 1 100 72.6 36.29 3.2 9 0. 0025 26 80 938.6 38.13 1.8 6 0.00021 39 70 2094.6 38.71 1.6 5 0.00011 44 1400 60 16.9 39.48 3.5 8 43 30 508.0 42.23 2.9 5 0. 00091 98 ph = failed at pin hole NOTCHED SPECIMENS Test Rupture Larson-Miller Intergranular Temp. Stress Time Parameter Crack Length N/S Strength (~F) (ksi) ( hrs. ) (C=20) x 10-3 (%) Ratio 900 80 30 1000 113.6 Tensile 0 t. 84 90 173.8 32.47 29 0.72 75 752.9 33.40 34 0.62 65 1138.9 33.66 49 0.55 1100 80 20.0 33.23 26 0.67 60 704.8 35.64 59 0. 61 1200 116.0 Tensile 80 4.1 60 225.0 50 5003.7 1400 50 2.8 40 148.3 30 408.5 30 493.8 34.22 37. 10 39. 34 38. 03 41.24 42.06 42. 21 3 29 44 51 44 59 71 73 0.87 0.66 0.65 0.79 0. 58 1.05 0.95 1. 00

TABLE 5 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE AND PROPERTIES AT 900~F TO 1400F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 1 HOUR AT 1950~F PLUS 24 HOURS AT 1550'F Test Temp. Stress (~F) (ksi) 1000 134.2 125 115 1100 110 100 1200 132.6 100 80 70 1400 30 Rupture Time (hrs.) Tensile 40.9 1856. 7 90. 5 3528. 1 Tensile 11.6 926.5 2480.9 558.1 SMOOTH SPECIMENS Larson-Miller Parameter Elong. (C=20) x 10-3 (%) 32.8 31.55 24.9 33.97 10.2 34.25 9.9 36.73 4.7 14.6 34.97 6.9 38.12 3.2 38.84 2.0 42.31 8.7 R.A. (%) 30 23 12 12 6 17 13 6 5 12 Min. Creep Intergranular Rate Crack Length (%/ hr.) (%) 0 0.090 3 0. 00014 10 Test Temp. ("F) 1000 0.0034 0. 000005 0. 17 0.00037 0.000080 0.0011 15 20 NOTCHED SPECIMENS Rupture Larson-Miller Intergranular Stress Time Parameter Crack Length (ksi) (hrs.) (C=20) x 10-3 (%) 102.1 Tensile 0 90 253.5 32.71 14 80 A -A_- SS 0 ks 60 11000 Discontinued 85 40. 6 33. 71 23 75 788.5 35.72 43 60 491e2 ye 108.0 Tensile 4 60 18.9 35.32 26 60 40.3 -35.86 30 50 5588.8 39.42 48 30 373.8 41.98 53 1 19 23 32 92 1100 1200 1400 N/S Strength Ratio 0.76 0.76,fn= > It. >0. 55 0. 70 0. 74 0.81 0.61 0.63 0.81 0.88

TABLE 6 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 9000 TO 1000~F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 10 HOURS AT 1800~F PLUS 48 HOURS AT 1350~F Test Temp (~F) Rupture Stress Time (ksi) (hrs.) SMOOTH SPECIMENS Lar son-Miller Parameter Elong. R.A. (C=20) x 10-3 (%) (%) Min. Creep Rate (% hr.) 1000 162.0 Tensile 130 219.7 115 13437.5 1100 115 336.9 100 1266.5 90 5793.2 32.62 35.23 35. 14 36.04 37. 07 35. 74 37.54 38.43 19.6 23 7.0 10 0.0175 3.1 6 0.000046 4.5 10 0.0052 3.0 8 0. 00035 3.0 10 0. 00010 Inte rgranular Crack Length (%) 0 9 13 12 19 26 Test Temp Stress (~F) (ksi) 900 90 1000 135.9 90 75 65 Rupture Time (hrs.) 980.3 31.27 17 NOTCHED SPECIMENS Larson-Miller Intergranular Parameter Crack Length N/S Strength (C=20) x 10- (%) Ratio Tensile 131.4 238.4 305.8 32. 29 32.67 32.83 1200 147.6 100 80 70 Tensile 34.0 410.4 1420.9 16.7 15 7.2 12 6.2 11 6.0 13 0. 095 0. 027 0.00070 1 5 26 42 1100 90 8.2 32.63 75 105.2 34.35 60 128 6 7 Discontinued 0 20 26 30 19 31 0 32 39 58 0.84 0.68 0.58 0.51 0.67 0.64 >0.68 0.95 0.85 0.68 0.87 1400 30 231.8 41.60 17.4 42 0.0056 52 1200 140.8 Tensile 90 14.0 75 5.1 60 1406.5 35. 10 34. 37 38.42 1400 30 215.4 41.54 70 0.99

TABLE 7 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900~F TO 1400~F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 10 HOURS AT 1700~F PLUS 3 HOURS at 1325~F Test Temp Stress (~F) (ksi) 1000 157.5 145 130 1100 120 90 1200 85 60 50 1400 20 Rupture Time (hrs.) Tensile 26. 5 391. 1 95. 0 2138.2 79.4 1061.8 3766.9 506.9 SMOOTH SPECI Lar son -Mille r Parameter (C=20) x 10-3 [MENS 31.28 32.98 34.38 36. 39 36. 35 38. 22 39. 14 42. 23 Elong. (%) 15. 5 21.6 9.0 8.4 7.8 6. 0 12.6 15.8 32. 3 Min. Creep R.A. Rate (%) (% hr.) 24 22 11 0.0048 13 0.022 13 0. 00024 18 0.012 16 0. 0016 16 0.00038 50 0. 0068 Intergranular Crack Length (%) 0 1 5 8 11 65 NOTCHED SPECIMENS Test Rupture Larson-Miller Intergranular Temp Stress Time Parameter Crack Length N/S Strength (~F) (ksi) (hrs.) (C=20) x 10-3 (%) Ratio 900 90 2639.1 31.85 12 1000 90 598.6 33.25 26 0.72 75 7680 Discontinued >0.95 1100 90 77.4 34.15 25 0.75 80 951.2 35.85 0.83 1200 85 45.2 35.95 31 0.91 60 1024.2 38.20 55 1.00 1400 30 103.9 40.95 70 1.00

TABLE 8 SMOOTH AND NOTCHED (Kt>201 SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900~F TO 1400~F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 10 HOURS AT 1700~F PLUS 48 HOURS AT 1350~F SMOOTH SPECIMENS Test Rupture Larson-Miller Min. Creep Intergranular Temp Stress Time Parameter Elong. R.A. Rate Crack Length (~F) (ksi) (hrs.) (C=20) x 10- (%) (%) (% hr.) (%) NOTCHED SPECIMENS Test Rupture Larson-Miller Intergranular Temp Stress Time Parameter Crack Length N/S Strength (~F) (ksi) (hrs.) (C=20) x 10-3 (%) Ratio 900 90 13140 Discontinued 1000 166.0 130 120 115 Tensile 125.7 1382.8 1163.2. 32.26 33.78 33.68 15.9 23 11.7 14 5.6 8 6.1 10 0.050 0.0022 0.0023 0 2 5 6 1000 125. 1 Tensile 90 299.2 32.81 75 7656 Discontinued 1100 100 192.2 34.76 85 1574.0 36. 19 11.7 14 0.036 2.7 6 0. 00073 10 22 1100 90 167.8 34.67 80 847.9 35.77 1200 143.7 Tensile 85 42.5 60 530.7 50 3378.9 35.90 37.72 39.06 16.8 26 9.2 20 12.0 18 12.4 21 0.087 0.0045 0.00072 0 15 30 47 1200 138.1 Tensile 80 53.2 60 468.2 50 2422. 0 0 20 28 33 1 40 52 65 54 57 67 0. 75 0.72 >0. 70 0.89 0.90 0.96 0.98 0.94 0.97 1.00 1.00 1. 02 36.06 37.63 38.82 1400 30 96.9 40.89 18.0 43 0.040 20 439.0 42.11 32.7 45 0.013 32 1400 35 57. Oph 40.47 30 103.0 40.94 20 483.0 42.19 ph = failed at pin hole

TABLE 9 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900tF TO 14005F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 1 HOUR AT 1700~F PLUS 3 HOURS AT 1325~F Test Temp (~F) Rupture Stress Time (ksi) (hrs.) SMOOTH SPECIMENS Larson-Miller Parameter Elong. R. A. (C=20) x 10-3 (%) (%) Min. Creep Rate (% hr.) Intergranular Crack Length (%) 0 2 13 Test Temp Stress (~F) (ksi) Rupture Time (hrs.) NOTCHED SPECIMENS Larson-Miller Intergranular Parameter Crack Length N/S Strength (C=20) x 10-3 (%) Ratio 1000 165.2 Tensile 145 168.9 130 5613.4 12.9 27 32.45 12.1 14 34.67 3.5 12 900 90 2547.2 0. 0048 0.000086 1100 125 115 100 1200 160.2 100 85 85 65 65 184.8 406.6 2727.0 Tensile 53. 0 291. 1 117. 1 937.4 1501.2 34. 74 35.27 36.56 36. 06 37. 29 36.63 38. 13 38. 47 41.21 1.65 11 0.001 1.60 6 0.00072 3.4 11 0.00017 12 13 26 1000 154.9 130 90 75 65 Tensile 17.5 152. 6 239.4 1561.3 8.3 1.75 5.0 3.0 22 9 23 15 7 9 0.0096 0.0061 0.00096 0 24 18 23 36 32 1100 90 30.7 80 131.4 31.83 31.01 32. 39 32.67 33.86 33.52 34.50 33.89 36.59 38.20 40.97 0 7 23 39 51 28 26 1 35 37 52 61 0.94 0.86 0.62 0. 53 0.49 0.60 0.59 0.88 0.63 0.83 0.99 0.94 30 1200 140.3 85 75 65 Tensile 2.6 109.8 1031.9 1400 30 144.0 10.8 27 0.013 60 1400 30 105.9

TABLE 10 SMOOTH AND NOTCHED (Kt>20) SPECIMEN TENSILE AND CREEP-RUPTURE PROPERTIES AT 900~F TO 1400 F FOR 0. 030-INCH THICK INCONEL 718 SHEET HEAT TREATED 1 HOUR AT 1700~F PLUS 2 HOURS AT 1550~F SMOOTH SPECIMENS NOTCHED SPECIMENS Test Temp. ('F) 1000 1100 1200 1400 Stress (ksi) 149.0 145 130 120 115 110 100 85 135.4 100 85 65 30 20 Rupture Time (hrs.) Tensile 2. 0 18. 1 785.0 4385. 2 486.3 703.6 4078.6 Tensile 21.9 154.3 1011.8 160.1 535.2 Larson-Mille r Parameter (C=20) x 10-3 29. 64 31.04 33. 43 34.52 35. 39 35.64 36.83 35.42 36.83 38. 19 41. 30 42. 28 Elong. (%) 19.8 24. 3 19.4 9.3 2. 6 5.8 1.5 2. 2 14.2 9.3 4. 0 6.2 21.4 25.4 R. A. (%) 27 32 25 12 6 9 7 4 20 15 9 7 34 35 Min. Creep Rate (% / hr.) 1.7 0. 0016 0.000082 0.0018 0.00056 0.00010 0. 0085 0. 0013 0. 030 0. 0053 Intergranular Crack Length (%) 0 7 7 9 19 23 1 12 20 20 Test Rupture Larsor Temp. Stress Time Paraz (~F) (ksi) (hrs. ) (C=20) 1000 121.9 Tensile 90 3205.7 34 75 5133 Discontinued 1100 90 748.4 35 1200 121.2 Tensile 65 223. 3 37 50 1677 38 1400 30 92.5 40 1-Miller meter ) x 10-3. 32 Intergranular Crack Length (%) 0 23 28 N/S Strength Ratio 0.82 0. 78 >0. 66 0.92 0.89 0.80 0.82 0.85.68.10.57.86 0 42 59 61 33

TABLE 11 X-RAY DIFFRACTION DATA OF EXTRACTED RESIDUES OF INCONEL 718 IN THE HEAT TREATED CONDITIONS Solution Treatment 10 hrs. at 1950~F 1 hr. at 1 hr. at 1950~F 1950~F 1 hr. at 1950~F 10 hrs. at 10 hrs. at 10 hrs. at 1 hr. at 1 hr. at 1800~F 1700~F 1700~F 1700~F 1700~F Aging 48 hrs. at Treatment 1350~F d(A) I 3.25 vw 2. 552w 48 hrs. at 1350~F d(A) I 3. 26 vvw 2. 57vw Z hrs. at 1550~F d(A) I 3.25 vw 2. 564w 24 hrs. at 1550~F d(A) I 3. 25 w 2.561w 48 hrs. at 1350~F d(A) I 3.25 vw 2. 643vvw Z. 555w 2.385vvw 2. 257vw 2. 219w 2. 104rs 2. 083vs 2. 033yw 1.992m 1.965s 2. 266vvw 2. 214w 2. 116to* 2. 078vs 1. 850vw 1. 809s 1.568w 1.337w 1. 29 2w 1. 278m 1. 1lOvw 2.226vw 2. 223w 2. 123to* 2. ll1vs 2.087vs 2.080vw 1.994w 1.969w 1.854vw 1.813m 1.818w 1.575vvw 1. 569vw 2. 217w 2. 108vs 2. 080m 2. 040vvw 1.99 2vw 1.948w 1 R4A, 3 hrs. at 1325~F d(A) I 3. 26 vvw 2. 646w 2. 394vvw 2. 272w 2. 231m 2. 117s 2.08 vw 2. 033vvw 2. 000m 1.977s 1.573vvw 1.548vvw 1. 536m 1. 302w 1. 281w 1. 195w 1. 191w 1. 108w w w s 48 hrs. at 1350~F d(A) I 3.26 vvw 2. 659vvw 2. 567vvw 2. 272vw 2. 232m 2. 222vw 2. 116s 2. 081s 2. 000s 1.973s 1. 807m 1.573vvw 1. 549vw 1.534w 1. 337vvw 1. 302w 1.280w 1. 193w 1. 109w 3 hrs. at 1325~F d(A) I 2. 552w 2. 388vvw 2. 330w 2. 232m 2. 118m 2. 080w 2. 043w 2. 003m 1.975s 1.807vvw 1.574w 1.536w 1. 344vvw 1. 303vvw 1. 281vvw 1. 199w 1. 193vvw 1. lllw 2 hrs. at 1550~F d(A) I 3.25 w 2. 644w 2. 553w 2. 264vvw 2. 221w 2. 108vs 2. 079s 2. 038vw 1.996m 1.968s 1. 855w 1. 809m 1. 566vw 1.546vvw 1.535w 1. 338w 1. 300w 1. 280w 1. 192w 1. 108w Indicated Phases Y"? MC L?? MC, L? Y'/Y" L? P, L? Y'/Y" MC? MC 3, Y'/y" MC,? L?? P,? 1. 339vw 1. 296vw 1. 280w 1. 110w w s 0 1. 535vw 1. 338vw 1. 298vw 1. 280vw 1. 193vw 1. 107vw 1.808s 1.805s 1.567w 1.567vw 1.545vvw 1.530w 1. 337w 1.338w 1.294m 1.300w 1.280m 1.278m 1.195w 1.188vvw 1.i89w 1. 110m 1.106w Phases MC Y'/Y" p w s 0 w s w w vs w w s m w m s w w s w s m *Values at extreems of wide reflection Intensities I:s = Strong, m= Medium, w= Weak, v=Very Phases: MC = Cb, Ti(C, N), y' = Ni3(Al, Ti), y" = Ni3Cb(bct), p = Ni3Cb(orthorhombic) L = "Laves", F 2(Ti,Cb).

Smooth (unnotched) Specimen (Kt =1. 0) Pin Hole T Notch Radius <0. 0007 / 0 Rad. 0. 38 0. 88^ 1.3 1.00 1.00 1.13 6.~0 Sharp Edge Notched Specimen (Kt>20) Figure 1. Types of test specimens (all dimensions in inches).

SM0 -_O OH1000 -800~F — SMOOTH100 ' 80 -- - - ot _ _ 0. ~ ~o40 — 20 NOTCHED O 100 -- '; 80 60, 40 --------- 1200 I,20 10 100 1000 10,000 RUPTURE TIME, Hours Figure 2. Stress versus rupture time data at temperatures from 800~F to 1200~F obtained from smooth and notched specimens of Inconel 718 sheet cold worked 20 percent and aged (ref. 2). Time-dependent notch sensitivity was evident at 1000~F and 1200'F.

200 - TEST TEMPERATURE, ~F 800 V 1000 0 sann n 100,IV U *. 80 - * SMOOTH 608 NOTCH ED s s 60 UJ u, 40 20 I I I 29 31 33 35 37 39 P=T(20 +Logt) x 10'3 Figure 3. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 cold worked and 20 percent and aged.

I II 100 ~; 80 C. ~ 60 v- 40 100 20 100 80 ~ 60 V.:. --- --------------------------— __________" 800 OF SMOOTH -- 000 NOTCHED 800F V I t | | I 111111 1 1 1 111111 1 I 1t11111 I 1 1 1 1ll111 40 u, U, (lif 20 I 10 100 RUPTURE TIME, Hours 1000 14000 Figure 4. Stress versus rupture time data at temperatures from 800~F to 1200~F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 1 hour at 1950~F and aged (ref. 2). Time-dependent notch sensitivity occurred for tests at 1000~ and 1200'F.

200 TEST TEMPERATURE, F 800 V 1000 0 1200 a ITH 100 80 60 u, ag I-. %n NOTCHED * 40 I I I I I I I 1 I 1 I 29 31 33 35 P= T (20 + Logt) x 10-3 Figure 5. Time-temperature dependence of the rupture strengths of smooth and notched specimens at 1950~F and aged. 37 39 of Inconel 718 sheet heat treated 1 hour

SMOOTH 200 8000F 1-0 690 - 40 NOTCHED 200 ^^0-^. ^^^^o800~F o 100 _ __ 11 1000 I' 60 ' 40 0 100 1000 10,000 -~~~u - r~~~~~~~RUPTURE TIME, Hours Figure 6. Stress versus rupture time data at temperatures from 800~F to 1200F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 1 hour at 1750'F and aged (ref. 2). Time-dependent notch sensitivity was evident at test temperatures from 9 to 11001F. Little or no notch sensitivity was evident at 1200'F.

-" ope 200 T E1 1 TEMPERATURE, F 1100 D 1200 0 100 *S Te NOTCHED 40 29 P=T(20+ Logt) X10o rature dependence of the rupture strengths of smooth and notched specimens at 1750~F andaged. Fiue.Tiedeprauedeedec o herptr trnth f mot ndnthe peien f n~n178 hethatteae31hu at 175O~~F and aged.

r SMOOTH 10000 F 100 --- —------- _.~.,1100 80 — 200 60 40 l ---- — 0- OTC --- — ' — ----- --— E —^. —0 _ 0.2% Off set Yield 100 Strength at 1,000 F ~~~~~~~~~~~~~~~~~~~~~~~~~~~1200 60 40 - uJ C - ^""^^1400 20 0 NOTC HD1 0 100 1000 10,000 RUPTURE TIME, Hours Figure 8. Stress versus rupture time data at temperatures from 900~F to 1400F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 10 hours at 1950~F plus 48 hours at 1350~F. Time-dependent notch sensitivity was evident at temperatures from 900~F to 1200'F but not at 1400'F.

TEST TEMPERATURE ~F 900 0 1000 0 100 1100 D 1200 0 80 MO 1400 * 60 - NOTCHED u 40 20 30 32 34 36 38 40 42 P = T(20+ Logt)x 103 Figure o. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 10 hours at 1950~F plus 48 hours at 1350~F.

SMOOTH 1000 F. 100 80 60 us 40 00=~ ~ ~ ~ ~~~~~j 00 20 NOTCHED — 900F - 0.2%/ Offset Yield.,too|~~~~~~~~~~~~~~~~~~~~~ 100I _- ^^^~Strength at 1,000 o F ~ -100 --. 80 0 u~' '~!200 60 S 40 K - 00100 20 I I.I tI I I II I il 1 1 l.!.. I I I1,,, l 10 100 1000 10,000 RUPTURE TIME, Hours Figure 10. Stress versus rupture time data at temperatures from 900'F to 1400'F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 1 hour at 1950~F plus 48 hours at 1350'F. Time-dependent notch sensitivity occurred at temperatures from 900~F to 1200~F but not at 1400~F.

TEST TEMPERATURE, ~F 900 0 1000 0 100 1100 D -,l~~~oo ^^~^-t~~ A m~ o1200 o 80. - 1400 L-~~~ ^^^^^^^ ^fi M~~~~~~~~SMOOTH ' 60 i 40 20 30 32 34 36 38 40 42 P = T(20 + Logt)x 10- 3 Figure 11. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1950~F plus 48 hours at 1350~F.

SMOOTH 100 o._ a. 80 8 60 u 40 u.%A 2-0-40 1400 20 100 ' 80 ~ 60 I, 40 i,20 us 20 NOTCHED 10000~F = — 00~U200........ —. O ' 0.2% Offset Yield Strength at 1,000~F 400 I, I I I,, I I I I I,, I I I I I,, I I I I I,,,,1 III - I 1 10 100 1000 10,000 RUPTURE TIME, Hours Figure 12. Stress versus rupture time data at temperatures from 900F to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 1 hour at 1950~ F plus 2 hours at 1550~F. Time-dependent notch sensitivity was evident at temperatures from 900~F to 1200~F but not at 1400 ~F

TEST TEMPERATURE, ~F 900 0 1000 0 11lan rw 100 D1W I LI 100 - ^^^^^ D~ -'^'> —^-~~~~~~1200 0 80 — 400 -3=~~~~~~~~~ *^'^^ ^^^ ^-^SMOOTH ' 60 NOTCHED a. e 40 VW 20 30 32 34 36 38 40 42 P = T(20 + Logt)x 10-3 Figure 13. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1950~F plus 2 hours at 1550~F.

SMOOTH 0 ---- -1000~F o. 100 -- --------—,, ---1100 100o t = ~~~~~~~~~~~~~~~~~~~~~~_1200 o 60 40 VI 40. 1 - 1m400 20 NOTCHED C loo 100oo -Z. 110100000 0.2%Offset 80 - ~Yield Str, g}~~~~~~~~~~ 80ro~~~~~~~~~ t D D - - ield~~at 10000F 60 1200 D_ 0> VI un ac 40 - 0 20 1 11 10 100 1000 10000 RUPTURE TIME, Hours Figure 14. Stress versus rupture time data at temperatures from 1000~F to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 1 hour at 1950~F plus 24 hours at 1550~F. The tests showed no time-dependent notch sensitivity.

TEST TEMPERATURE, F 900 0 1000 0 100 D 1 lou D loo-~ "^^^ — * n^ ~1200 0 80 ^- E 1400 A NOTCHED b-:SMOOTH 5 60 40 u, 20 30 32 34 36 38 40 42 P = T (20 + Logt)x 10-3 Figure 15. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1950~F plus 24 hours at 1550~F.

SMOOTH O 80 -60 v~ - U 40 I1400 20 NOTCHED |-r- -- -NOTCHED ==900~F - 0.2 % Offset Yield,QQ100 _ "^^^ ^^sStrength at 1,000~F r. 80 - 1200 -- ~ 60" w 40 u1 -^ 1400 20 o I I Ii I1I I I 111i I 1 1111111 10 100 1000 10,000 RUPTURE TIME, Hours Figure 16. Stress versus rupture time data at temperatures from 900oF to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat-treated 10 hours at 1800~F plus 48 hours at 1350~F. Time-dependent notch sensitivity occurred at 900~F to 1100~F but not at 1400~F.

TEST TEMPERATURE, OF 900 0 1000 0,. u 0 100 J1UU OD 1200 D - \ \^ NOTCHED - ^^^<1 --- —^_^_ ^^^N SMOOTH 60,, 40 20 - 30 32 34 36 38 40 42 P = T(20 + Logt)x 10-3 Figure 17. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 10 hours at 1800~F plus 48 hours at 1350~F.

SMOOTH 100 80 60 #. id 3 -IUJ *_ --- —140 40 I 20 - 100 80 60 40 20 N.....D --- - -— J=^ -- ---- -- - 900O~F -- 0.20% Offset Yield __NOTCHED 1101000 Strength at 1,000~ F i I. i tI l i I l i l I I 1.. 1 1 1 1 I I I I I I I I I 10 100 RUPTURE TIME, Hours 1000 10,000 Figure 18. Stress versus rupture time data at temperatures from 900~F to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat treated 10 hours at 1700~F plus 3 hours at 1325~F. Time-dependent notch sensitivity was observed at 900~F and 1000'F, but not at 1200~F to 1400~F.

TEST TEMPERATURE, F 100 \ 900 0.,. NO b OTCHE 1000 O ~~~~80 -t~~~ _"^~~~~ ^ -— ^^~ b1100 D ~ ~ — " \ss ^ 1200 0 o 0. 1400 A ~ 60 m 40 - I,.20 l l! I I i I I i I I 30 32 34 36 38 40 42 P= T(20 + Logl)x 10-3 Figure 19. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 10 hours at 17003F plus 3 hours at 1325~F.

SMOOTH ---- 10 100 -80 ~.60 40 -, 0 -20- 0 0.2 /o Offset Yield 1o0 NOTCHED 900 F Strength at 10000F 600 -- 80 - a. fl0 ^^^4 20 VI20L I l I I l,1!l.. i 1.. l I I i i!il..... l..I I.. 111 10 100 1000 10,000 RUPTURE TIME, Hours Figure 20 Stress versus rupture time data at temperatures from 900~F to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat treated 10 hours at 1700~F plus 48 hours at 1350~F. The tests showed no time-dependent notch sensitivity.

TEST TEMPERATURE, F 900 0 100 MOOH NO 1000 0 vi 80> ^ -^^- 0 1100 D.i 80 s 1200 0 6 -1400 A - 60 - VI ti 40 20 II I I I I I i I I I I I I 30 32 34 36 38 40 42 P= T(20+ Logt)x 103 Figure 21 Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 10 hours at 1700~F plus 48 hours at 1350~F.

SMOOTH - 1000 ~ F 1100 -0, 800 =.-I 6 60 4^ 40 u, ~4- - ^^!!400 20 NOTCHED -_ --- -- 0.2 % Offset Yield '- S t Strength at 1,0000F too t ~~~~~C~~ ---~~~ 1100 000 80 -- 900F '~ ~900OF ~ 60,, 40 u, I -201400 2 0 L --, I I I __ I I I ~ ~ I I I __ I I I I I I I I I | I l I l I i 100 00 100,000 RUPTURE TIME, Hours Figure 22. Stress versus rupture time data at temperatures from 900~F to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1700~F plus 3 hours at 1325~F. Time-dependent notch sensitivity was observed at 900~F to 1100~F but not at 1400~F.

TEST TEMPERATURE, F 900 0 | % M \\ 0SMOOTH 1000 0 100 11 00 D 1100 0 NOTCHED 1200 a 80 \ xv^ = — ^ —^ =1400 A 60 VI ~ 40 20 20 i IIlI I I I I I II I 30 32 34 36 38 40 42 P=T(20 + Logt) x 10 3 Figure 23. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1700~F plus 3 hours at 1325~F.

---— 0- 1000 F 100 SMOOTH ---- 0 - 80 10 a. 60 40 MU 3. 1400 20 1 00 -- NOTCHEDF o 0.2% Offset 100 N/OTCHEDED0 _F0 Yield Strength 80 0 o0- at 1,000 OF 0,- — ^ 200 60 u 40 3,'U' L ^^ ^1400 20 L,,,, 11111 1 I I iiIIi, I I I 1,, 1I I I, IIIl 10 100 1000 10,000 RUPTURE TIME, Hours Figure 24. Stress versus rupture time data at temperatures from 1000~F to 1400~F obtained from smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1700~F plus 2 hours at 1550~F. Time-dependent notch sensitivity did not occur.

TEST TEMPERATURE, OF 900 0 1000 0 100 _ 1100 D 1200 C 80 1400 A -' ^^^^^^s^ SMOOTH CL 60 X 40 NOTCHED IA 20! I I I i I I i I I I I I 30 32 34 36 38 40 42 p = T(20 + Logt) x10-3 Figure 25. Time-temperature dependence of the rupture strengths of smooth and notched specimens of Inconel 718 sheet heat treated 1 hour at 1700~F plus 2 hoursat 1550~F.

HEAT TREATMENT 0 10 hrs 1950~ + 48hrs 0 10 hrs 1800~ + " A 10 hrs 1700~ + " 1350~ F,11 1, O O 100 80 0 00 0 0 o Ar 0.. en I.on 60 -- D 0 0 EL ^ 0 0 0 0 40 - 0 0 0 20 - 1 I I I I I I I I I I I 30 32 34 36 P = T(20 + Log t ) x 10'3 38 40 42 Figure 26. Time-temperature dependence of the rupture strengths at 900~ to 1400~F for notched specimens of Inconel 718 in various heat treated conditions.

HEAT TREATMENT O 10 hrs 1950~F + 48 hrs 1350~F 10 hrs 1800~F + - A A 10 hrs 1700~F + - " 100 ' _ in 80 - *. 60 - A IL 40 U, 20 30 32 34 36 38 40 42 P T (20 + Log t) x 10-3 Figure 27. Time-temperature dependence of the rupture strengths at 900o to 1400~F for smooth specimens of Inconel 718 in various heat treated conditions.

HEAT TREATMENT 0 lhr 1950~+ 48 hrs 1350 ~F O " + 2 hrs 1550 ~F A " + 24 hrs 1550~ F 100 - 80 60 40 u, I-I 20 30 32 34 36 38 40 42 P= T (20 + Log t) x 10-3 Figure 28. Time-temperature dependence of the rupture strengths at 900~ to i400~F for smooth specimens of Inconel 718 in various heat trg.t^ CQnditiQns*

HEAT TREATMENT 0 l0hrs 1700~ + 3hrs 1325 ~F 0 lhr 1700~ + 3hrs 1325~F A 1 hr 1700~ + 2hrs 1550~ F 100 80 - ~; 60 U. Vu 40 UI IdI20 I l l l I I I I l i I I 30 32 34 36 38 40 42 P= T(20 + Log t) x 10'3 Figure 29. Time-temperature dependence of the rupture strengths at 900~ to 1400~F for smooth specimens of Inconel 718 in various heat treated conditions.

(a) 75x (b) 75x Figure 30. Optical photomicrographs of notched specilzmens of Inconel 718 polished to remnove the oxidized surface layers. Microcracks in (a) are an early stage of crack initiation (heat treated 10 hours at 1800~Fi plus 48 hours at 13503~F, tested at I100 IT at 6 0 ksi, dis continued after 12,867 hours). The "'through the thickness" crack in (b) is a late stage of crack growth (heat treated'10 hours at 1700 F plus 48 hours at 13500Ftested ct 1000*F1 at 75ksi, discontinued after 76i56 hours),

1200 ~F 60 /o -' 40 20 40 / / U. / 400 1.0 80 0. o 0 1 130 110 90 70 50 30 STRESS, 1,000 psi Figure 3i1. Iso-creep strain curves of life fraction versus stress at temperatures from 1000~ to 1400~F for Inconel 718 heat treated 10 hours at 1950'F plus 48 hours at 1350~F. Time-dependent notch sensitivity occurred under test conditions where large amounts of rupture life were utilized for small creep strains at test temperatures 1000~, 1100~ and 1200~F. 13 109 0 03

100 1200 OF 80 c 60 0 IU. 40 L U.,hA 0.2 0 0.1 / ~ ~~~ __ D 2U 100 80. 60 0. 2 0 I-. U 40 ULl U.. 20 - 20 1100 OF 1400 OF ^^^^^~~05 ^ ^^^aa~0..1 130 110 90 70 50 STRESS, 1,000 psi 30 Figure 32. Iso-creep strain curves of life fraction versus stress at temperatures from 1000~ to 1400~F for Inconel 718 heat treated 1 hour at 1950~F plus 48 hours at 1350~F. Time-dependent notch sensitivity occurred under test conditions where large amounts of rupture life were utilized for small creep strains at test temperatures 1000~; 1100~, and 1200~F.

6 ~ 60 z 0 i- 40 4, 20,. 1100~F 1400~F s80 s. u. 40 - I 60 0.2 / 20 / 20 -i/ X,/ I/ o./ 130 110 90 70 50 30 STRESS, 1,000 ps i Figure 33. Iso-creep strain curves of life fraction versus stress at temperatures from 1000' to 1400~F for Inconel 718 heat treated 1 hour at 1950~F plus 2 hours at 1550~F. Time-dependent notch sensitivity occurred under test conditions were large amounts of rupture life were utilized for small creep strains at test temperatures 1000" and 1100~F (and to a lesser extent at 1200~F).

100 c 0 o u Z 0.2 0.1 100 1400~F 80 e 60 60 iu z a, ~ 40 Wu 20 u. 0.2 130 110 90 70 50 30 STRESS, 1,000 psi Figure 34. Iso-creep strain curves of life fractions versus stress at temperatures from 1000' to 1400'F for Inconel 718 heat treated 1 hour at 1950~F plus 24 hours at 1550~F. For the test conditions evaluated (except possibly those at 1200'F), the life fractions utilized for small amounts of creep were relatively low and no time-dependent notch sensitivity was observed.

100 1200~F 80 2.0 60 1.0 o 1100~F ro 1400~F 80 _ / Z / -0.5 -10 — soL 130 11 0 90 70 50 30 800 b. 60-0 p 0.1 ST1ESS0 1.000 psi u 40 -- 20 -0.1 - 0.1 3 Iol 71 h t 10 os STRESS, 1,000 psi Figure 35. Iso-creep strain curves of life fraction versus stress at temperatures from 1000' to 1400'F for Inconel 718 heat treated 10 hours at 1800'F plus 48 hours at 1350'F. Time-dependent notch sensitivity occurred at 1000' and 1100'F under test conditions where the life fractions utilized for small amounts of creep were high.

100 80 1000 ~F 1200 OF I I I o, C 0 0 0 u. uu 40 I o2.0 11.o 1 0.5 / I0 / /' _e0' --— d — OlI - - 2.0 1.0 0.5 20. 20.2 a. 0.1 100 80 1100 ~F 1400 ~F c Elw z 0 EJ o I-a 60 40 2.0 _-L1.0.2 20 0.5 0.1 140 120 100 80 STRESS, 1,000 psi 60 40 20 Figure 36. Iso-creep strain curves of life fraction versus stress at temperatures from 1000~ to 1400~F for Inconel 718 heat treated 10 hours at 1700~F plus 3 hours at 1325~F. Time-dependent notch sensitivity occurred at 1000~F for test conditions where large amounts of rupture life were utilized for small creep strains.

_ 1000 ~F 1200 ~F ~ u i 0 IU a: u. uJ ILL 80 60 40 20 0 - 2.0 - 0 10 _ — /' 0 0- _0 -0 _ O~~~~~~ 2.0 1^^^-01.0 0.5 _ 2 '5 0 -A A - mmbp~Z IL ~ 1100G'F 1400 ~F E. z 4 L id 60 40 20 A S A A.0 0.5 0.2 - I I I 10'1 -. ~3 1 I I I 130 110 90 70 50 30 STRESS, 1,000 psi Figure 3., Iso-creep strain curves of life fraction versus stress at temperatures from 1000~ to 1400'F for Inconel 718 heat treated 10 hours at 1700'F plus 48 hours at 1350~F. Little rupture life was utilized for small amounts of creep under all test conditions and no time-dependent notch.sensitivity was observed.

2.0 1200 OF C 80 - Z - / 40 0. U.1 _ ' 20 0 00 0.1| 1 00 F 130 110 1400 F 80 STRESS, 1,000 psi 10. 60 -U '404 20 0.2, D D.,,, 0.1 0.11. A I I i I I I I I I 150 130 110 90 70 50 30 STRESS, 1,000:psi Figure 38. Iso-creep strain curves of life fraction versus stress at temperatures from 1000~ to 1400~F for Inconel 718 heat treated 1 hour at 1700'F plus 3 hours at 1325~F. Time-dependent notch sensitivity was observed at 1000~F for test conditions where the life fractions utilized for small amounts of creep were high.

100 1000~ F 1200 F 80.0 S 60 idt~~~~~~~~~~~~~~~~~~.~~.0 20. 40 - / / 2.0 ~~~~~~~~40 ~~ 0 100. 0. 2 68~~~~~~~~~~~~~~0~~~~. 200 I,0.1 130 110 90 70 50 30 STRESS, 1,000 psi Figure 39. Iso-creep strain curves of life fraction versus stress at temperatures from 1000' to 14000F for Inconel 718 heat treated 1 hour at at 1700*F plus 2 hours at 1550~F. No time-dependent notch sensitivity was observed for all test conditions. The life fractions utilized for small amounts of creep were relatively low for all test conditions.

(a) 250OX 10 hrs. at 1950~F + 48 hrs at 1350~F (b) 250X 1 hr. at 1950~F + 48 hrs. at 1350~F (c) 250X (d) 250X 1 hr. at 1950~F + 2 hrs. at 1550~F 1 hr. at 1950~F + 24 hrs. at 1550~F Figure 40. Optical photomicrographs of Inconel 718 in various heat treated conditions.

(e) 250X (f) 25 0X 10 hrs. at 1800~F 10 hrs. at 1800~F + 48 hrs. at 1350~F (g) 250X (h) 250X 10 hrs. at 1700~F 10 hrs.at 1700~F + 3 hrs.at 1325~F Figure 40. (Continued)

X, \o,n.E o./ N 0 0 0 r - tc - N ciN'.-.4 LI' 0 No * 4 e 43# cli rr '-I (d.:f v00 + 0: C.( on o N: 9 00 -<..4 ii c i N ^ I 0 I CO, ' ' N h 0 Ln I-4 4-~ o CQ O 0 r_ - -1 x O N 0 LO e 4-) CO c?4 0 C 4-)?-I 0 rU 0 u 0 () *ri o a - * i {

(a) 6000X (b) 6000X 10 hrs. at 1950~F + 48 hrs. at 1350~F 1 hr. at 1950~F + 48 hrs. at 1350~F (c) 6000X 1 hr. at 1950~F + 2 hrs. at 1550 ~F (d) 1 hr. at 1950~F + 24 hrs. at 6000x 1550~F Figure 41. Replica electron micrographs of Inconel 718 sheet in the as-heat treated conditions.

(e) 6000X 10 hrs. at 1800~F + 48 hrs. at 1350~F (f) 6000X 10 hrs. at 1700~F + 48 hrs. at 1350~F (g) 6000X 1 hr. at 1700~F + 3 hrs. at 1325~F (h) 6000X 1 hr. at 1325~F + 2 hrs. at 1550~F Figure 41. (Continued)

(a) 85, UUUx 1 hr. at 1950~F plus 48 hrs. at 1350~F 1 hr. at 1700~F + 3 hrs. at 1325~F Figure 42. Transmission electron micrographs of Inconel 718 in two heat treated conditions showing y'/y" size distributions.

- * - n -m 000 ' 020 I 0 1 240 220 _ I I. I * Figure 43. Thin foil diffraction pattern. [100 mattrix zone. The superlattice spots arise from y" with three orientations.

Figure 44. 50,00 0x Thin-foil electron micrograph of Inconel 718, heat treated 1 hour at 1950~F plus 48 hours at 1350~F and creep-rupture tested at 120ksi at 1100~F (ruptured in 1.4 hours at 4. 2% elongation). Bands are evident that resulted from localized deformation.

(a) 250x (b) 65,000x (c) 40, 000x Figure 45. Optical and transmission electron micrographs of Inconel 718 heat treated 1 hour at 1950~F plus 48 hours at 1350~F and creep rupture tested at 30ksi at 14000F (ruptured in 384 hours at 2. 1% elongation). During the test exposure Ni3Cb precipitated and the y' and y" increased in size considerably. Contrast effects associated with coherent y' and y" are evident in (b) and (c).

-- " 11-, I I.. (a) 45, 00Ox ::: (b) 40, 0OOx Figure 46. Thin-foil electron micrographs of Inconel 718 heat treated 1 hour at 1950~F plus 48 hours at 13500F and creep-rupture tested at 30ksi at 14000F. The deformation is homogeneous. Dislocation can be observed entangled with the y" percipitate and bowing between y' particles leaving "pinched off" dislocation loops.

(a) 60, 0OOx Figure 47. (b) 75, 000x Transmission electron micrographs of Inconel 718 heat treated 1 hour at 1950~F plus 2 hours at 1550~F and tested at 100 ksi at 1100~F (ruptured in 385 hours). The deformation in (a) is localized. In (b) a fine dispersion of y'/y" is evident which presumably developed during the test exposure.

(a) 60,0 OOOx (b) 30,000x Figure 48. Thin-foil electron micrographs of Inconel 718 heat treated 1 hour at 1950~F plus 24 hours at 1550~F and tested at 115 ksi at 1000~F (rupture in 1857 hours at 10. 2% elongation). The deformation is homogeneous.

(b) 100,000x Figure 49. Transmission electron micrograph of Inconel 718 heat treated 1 hour at 1700~F plus 3 hours at 1325~F and creep rupture tested-(a) at 1000~F at 130ksi (ruptured in 5613 hours at 3. 5% elongation, (b) at 1200~F at 65ksi (ruptured in 937 hours at 3. 0% elongation). In the lower temperature test dislocations, extended to form stacking fault ribbons, sheared the y'/y" precipitates. During the higher temperature test exposure y'/y" growth occured. In consequence, the deformation was homogeneous and the dis - locations by-passed the precipitate particles.

70, OOOx Figure 50. Thin foil electron micrograph of Inconel 718 heat treated 10 hours at 1700~F plus 48 hours at 1350~F and creep-rupture tested at 1000~F at 120ksi (ruptured in 1382 hours at 5. 6% elongation). The deformation is homogeneous. The dislocations can be observed bowing between precipitate particles leaving "pinched off" dislocation loops.

(a) SOLUTION TREATED hr at 1950~ F 400 - In Z 4A z a cf 4 4 a. a z 0.4 a 350 _ 300 H 250 (b)SOLUTION TREATED lhr at 1700 ~F 400 _ tn %n ui z u4 Z z a Ia z 0 4 a 350 _-.1400 A 300 _ 1550 I II I I I,11I I I I I I I II 250 I I I 1 10 100 AGING TIME, HOURS Figure 51 Effect of aging exposures at 1325c, 1400~, and 1500~F on the Diamond Pyramid Hardness of several heat treatments of 0. 030-inch thick Inconel 718 sheet.

(c) SOLUTION TREATED 10hrs at 1950 OF 400 UV z a a x 350 a io 0 a 2 0 4 a -q 250 400 IV v, 4n 1 350 a i 4 a. 300 a 2 0 a l 250 400 1400 (d) SOLUTION TREATED 10hrs at 1800 OF ell", ~ ~ ~ ~ ~ ~ ~ 5 (e) SOLUTION TREATED 10hrs at 1700~F ul LU z 0 4 > 300 a z 0 a 250 H - 1550 I I I 11111 I I I.mL I I I I 1 Figure 51. (continued) 10 AGING TIME, HOURS 100

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