ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR. MICH. NINTH QUARTERLY PROGRESS REPORT TO MATERIALS LABORATORY, WRIGHT AIR DEVELOPMENT CENTER DEPARTMENT OF THE AIR FORCE ON INTERMEDIATE TEMPERATURE CREEP AND RUPTURE BEHAVIOR OF TITANIUM AND TITANIUM ALLOYS By J. V. Gluck J. W. Freeman Contract No. AF 33(616)-244 Supplemental Agreement No. S9 (55-1113) Task No. 73510 Project 2076 covering the period from June 1, 1955 to August 31, 1955

SU MMAR Y This report, the ninth to be issued under Contract AF33(616)-244, covers research carried out on the elevated temperature properties of titanium alloys during the period from June 1, 1955 to August 31, 1955. During this period almost all of:the test stock for study under the present program was received. This program is principally concerned with effects of contaminents on properties and the relative stability of various structures. Vacuum annealing was carried out on a number of materials in order to produce material of low hydrogen content. In addition, hydrogenation tests were carried out on Ti 75A and Ti-10%oMo alloys to produce desired higher hydrogen contents. The study of the effects of cold working on the 1000~F properties of a Ti-6%Al-1/2%Si alloy was brought almost to completion. The study of the effect on room temperature tensile properties of exposure of Ti 150A to creep test conditions was started. The initial tests covered material of low hydrogen content and the effects of stressed exposure at 600~F and 1000~F.

INTRODUCTION This report is the ninth progress report to be issued under Contract No. AF 33(616)-244 and covers research carried on during the period from June 1, 1955 to August 31, 1955. The work herein described is a continuation of research into the properties of titanium and its alloys at temperatures up to 1000~F. Under one phase of this contract a number of titanium alloys, representing typical and different transformation behavior, were surveyed in order to develop information regarding the.effects of structure and treatment on elevated temperature properties. Another phase of the investigation covered a study of the deformation properties for selected treatments of several alloys for time periods up to 1000 hours. Other research included a study of the effect of hot working conditions, and brief studies of the effects of hydrogen content and the effects of exposure to creep test conditions. The present extension of the contract has been broken into three main divisions as outlined below. General Effects of Structure (Continuation of previous work as warranted) a. Effect of cold working on alpha alloys bo Effects of commercial stabilization treatments Effect of Contaminents a. Relative effects of sponge hardness b. Effect of hydrogen on long-time creep properties c. Mechanism of room temperature embrittlement after exposure to creep test conditions

2 Effect of Structural Instability? i, i i..,., a. Effect of instability on properties of transitional structures The alloys to be studied under each phase of the program are indicated by (x) in the following tabulation: Test Program Ti-6%Al Ti-30%Mo Ti-8%Mo Ti10%Mo Ti-150A Sponge Hardness (previous data) x x - Hydrogen on Creep x x x x Room Temperature Embrittlement - x x Stability - - x - A detailed discussion of each phase of the work was included in the Eighth Progress Report (1). TEST MATERIALS The analysis of all materials to be investigated under this contract is given in Table 1. All test materials were received by the end of the period covered by this report. However, forging cracks in the as-received material rendered about half the Ti-6%Al stock (Heat 4c) useless for machining to creep test specimens. Consequently, an additional heat of this material is being made by the ArmourResearch Foundation. The analyses given in Table I were made by the producer with the exception of the hydrogen analyses. Where available, the analysis of the sponge used to produce each heat is given.

3 RESULTS AND DISCUSSION Operation of Vacuum Annealing Furnace A number of runs were made with the vacuum furnace during the period covered by this report. Details of the design and construction of the apparatus were discussed in the Eighth Progress Report (1). A redetermination was made of the temperature distribution within the furnace and it was discovered that the nominal annealing temperature reported as 1200~F was actually 1350~F. Since this temperature did not. result in contamination of the test stock (measured as weight gain) it was decided that standard vacuum annealing conditions for removal of hydrogen would continue to be 24 hours at 1350~F. Throughout this period pumping was carried on to a pressure below the limit of sensitivity of the thermocouple gage. A standard run size of 8 or 9 pieces was adopted. The pieces were one-half inch diameter rounds, three inches long. A blank slug of the same diameter and approximately one inch long was included with each run to furnish the samples for hydrogen analysis. At the conclusion of the run the blank slug was machined to a one-fourth inch square bar and then cut into cubes. Two random cubes were analyzed for each annealing run. The results of annealing runs on four alloys are tabulated in Table 2. The final hydrogen content showed generally good agreement both between duplicate runs on the same materials and between the materials themselves. In addition, the agreement between the two random samples from each run was excellent. The initial hydrogen content of the various alloys ranged as high as 310 parts per million (by weight) and the vacuum annealing treatment produced final hydrogen contents averaging 48 parts per million with a deviation of plus or minus 15 parts per million. During this period the furnace was also operated as a hydrogenation apparatus. A test run was made on a batch of Ti 75A.

4 With the in-formation furnished from the test hydrogenation of Ti 75A, a run was planned to achieve a final hydrogen content of 250 parts per million in a batch of Ti-10% Mo alloy. The batch of 9 pieces was first vacuum annealed for 24 hours at 1350'F. Following this, the furnace temperature was raised to 1500~F and a calculated amount of hydrogen was added to the reaction chamber (which was isolated from the pumping system, of course). A hydrogen content of 50 parts per million was assumed as a starting point for hydrogenation and the additional hydrogen requirement was calculated from this value. After absorption for 1 hour at 1500~F, the furnace was allowed to cool to 1250~F and held for one hour in order that structural equilibrium might be approached. Finally, the run was furnace cooled to room temperature. Throughout the period readings were made of the pressure within the reaction chamber, From these data it was determined that further absorption had ceased at the conn clusion of the holding period at 15000F. The expected final hydrogen content of the metal was calculated from the difference between the weight of hydrogen added and that measured as the final pressure at the end of the run. For the run in question, it was expected that the final hydrogen level would be 265 parts per million. Analysis gave a value of 260 parts per million as the average of two determinations (see Table II), Since the performance of this run several others have been made, Hydrogen analyses are not yet available, however, it appears that the rate of absorption is dependent to some extent on the material being treated. Materials of predominantly beta phase have shown much more rapid hydrogen absorption than did Ti 150A, a mixed alpha-beta structure. In order to reach what was considered a satisfactory final pressure during a run on a batch of Ti 150A, it was necessary to increase the absorption time to as much as 4 hours. On the other hand, a batch of Tih30% Mo (stabilized beta structure) achieved almost complete absorption in less than one-half hour. These observations should be recognized as being

5 purely qualitative since no effort has been made to determine accurately the kinetics of the absorption process. Mechanism of Embrittlement After Elevated Temperature Exposure As one phase of the general program on the effects of contaminents on the properties of titanium alloys a study is being made of the effect of elevated temperature test conditions on the room temperature tensile properties of both Ti-150A and a Ti-8% Mn alloy. A brief, previous study had shown that Ti 150A containing an appreciable amount of hydrogen showed room temperature embrittlement after creep test exposure while a Ti-8%o Mn alloy having a low amount of hydrogen did not show this effect. In the present program both materials in the annealed condition are to be exposed to stress, time, and temperature. Three levels of hydrogen, approximately 50 ppm, 250 ppm, and 500 ppm, are to be considered. Exposure is to be made. at stresses of approximately 40 and 80% of the 1000-hour rupture strength at the temperature under consideration. The initial tests are to be for 100 hours and the subsequent exposure times are adjusted in order that the time for embrittlement might be established. Following this, metallographic and X-ray studies are planned in order that the mechanism by which such embrittlement occurs can be defined. The data obtained to date cover studies of Ti 150A having a hydrogen content of 64 parts per million. The temperatures considered are 600~ and 1000~F. The results are summarized in Table III and a plot of the exposure time versus tensile strength and elongation is presented in Figure 1. The data are not complete, however, it appears that embrittlement does not occur at 600~F, at least, at this hydrogen level. Exposure at 64,000 psi does result in some increase in tensile strength, however, a comparison with the 32, 000 psi data suggests that this is due to strain hardening, particularly since the total deformation for the

6 64, 000 psi tests was many times greater than for the tests at the lower stress. However, the tests at 10000F indicate that there was a significant drop in ductility accompanied by a slight decrease in tensile strength after exposure. This appeared to be the case for both stresses investigated, 2,800 psi and 5,600 psi. In addition, the mode of fracture changed from that encountered with samples exposed at 600~F. The 1000~F samples failed with no necking at the point of fracture. The elongation and reduction of area appeared to be uniform throughout the gage section of the specimen. The as-treated and 600~F samples failed with localized necking at the point of fracture and with a cup and cone type of fracture. No explanation can be offered for this behavior at the present time. Additional tests are contemplated for longer exposure times at both these temperatures. In addition, one or more additional temperatures will be studied. Tests of specimens of higher hydrogen content are to be initiated shortly. Effect of Cold Working on Ti-6%Al-1/2%Si During the course of survey studies on both Ti 75A and a stabilized alpha alloy, Ti-6%Al, it was determined that an optimum amount of cold working existed above which instability was introduced to the material. This effect was further investigated during the studies of total deformation properties carried on under the second phase of the over-all program (2). In these studies it was shown that at 1000~F the effect of 12% cold work on Ti-6%Al was to increase the creep rate and lower the total deformation strengths from those of the as-forged material. The general validity of the results obtained on the alpha alloys was checked by extending the survey studies to a modification of the Ti-6%Al alloy. The modified alloy contained 1/2% Si in addition to 6% Al. In these studies it was indicated that approximately 20% cold working would produce a similar instability at 1000~F (2). It was decided to extend the survey studies to provide data out

7 to 1000 hours on this effect. In this way, it was hoped that the validity of the results on the Ti-6% Al could be confirmed. The data obtained in this study are summarized in Table IV. It should be noted that the original survey studies were carried out on material cold worked 19 percent. A second batch of stock that was cold rolled using the same roll settings achieved 21. 6% reduction. The slight amount of additional reduction did not appear to affect the properties. A plot of the rupture data and the time to reach indicated total deformations for both the as forged and the cold worked material is presented in Figure 2. As this plot shows,the immediate effect of cold working was to increase the tensile and rupture strength of the material. However, the strengthening was dissipated in about 100 hours and the as-forged material had a higher rupture strength throughout the remainder of the testing period. The total deformation data show that the cold worked condition had consistently poorer properties than the as-forged condition. In Figure 2, it is shown that the time to reach a given deformation was less at all stresses for the cold worked material than it was for the as-forged material. Figure 3, a plot of stress versus minimum creep rate, shows that the creep strength of the as-forged condition was consistently higher at 1000~F than for the cold worked material. Survey work indicated that the instability of the cold-worked material was manifested by recrystallization occurring during the course of the test. Additional metallographic studie.s are to be made on the completed test specimens from the present investigation. The present work has confirmed the observation that the instability introduced to an alpha alloy by cold working can result in a loss of properties. Although the loss of rupture strength was not excessive, the time to reach a given total deformation at 10000F was greatly reduced.

8 Other Work in Progress In addition to the work described in detail in other sections of this report, work is in progress on several phases of the program covering the effects of contaminents, At the present time, the data are not sufficiently complete to warrant detailed discussion. These studies include a survey of the Ti-30% Mo alloy to determine the relative effects of sponge hardness and a study of the effects of hydrogen contents on the creep properties of the Ti10%Mo alloy. To date, tensile tests have been completed on these materials and the survey rupture and creep tests have been initiated.

9 REFERENCES (1) Gluck, J. V. and Freeman, J. V. "Intermediate Temperature Creep and Rupture Behavior of Titanium and Titanium Alloys", Eighth Progress Report, Contract No. AF 33(616)-244, May-31, 1955, pages 1-5. (2) Gluck, J. V. and Freeman, J. V., Second Summary Report, Contract No. AF 33(616)-244 (to be published in 1955).

10 TABLE I Producer's Chemical Analysis of Test Materials Alloying Constituents -Wt (%) U. of M. Suppliers Sponge Maor Minor Alloy Alloy No. Heat No. Hardness Fe Cr C G- N:- H2 Ti 150A 2c M739 1.47 2.76.08.026.0310* Mo Ti-30%Mo 6 140 2958 - -.0300* 9042 107 30.50.59.020 na Al Si Ti-6%Al-1/2%Si 8 7011 124 -6.5.48 -.017.017 Mn Ti-8%Mn 3a 9056,58 148 -8.62.109.051 na 3b 9035-39 107 8.85.063.015 na Al Ti-6%Al 4c 9033 107 6. 13.044.045.0084 Mo Ti-10%Mo 5a 9038 107 1047.051.034.0033 * hydrogen analysis by WADC, remainder at University of Michigan na hydrogen analysis not yet available Analysis of Sponge - Wt. (%) Brinell Hardness Si C N Fe Ti 107 <0.02.045.010.012 bal. 148.02.054.045.240 bal.

11 TABLE II Hydrogen Analysis of Vacuum Annealed Alloys Hydrogen Content U. M. Run No. (parts per million by wt) Material Alloy No. No. Spec. De. 1 Detn. Z Avg Ti-30%Mo 6 3 9 45 43 44 Ti-150A 2c 4 9 63 64 64 5 9 57 57 57 Ti-10%Mo 5a 6 8 43 44 44 7 9 44 42 43 Ti-6%A1 4c 10 9 34 34 34 11 9 53 49 51 Hydrogen Analysis of Hydrogenated Alloy Aim: 250 ppm Ti-10.%oMo 5a 12 9 286 234 260

TABLE III Effect of Elevated Temperature Stressed Exposure on Room Temperature Tensile Properties of Vacuum Annealed Ti-150A Stress-Exposure Conditions Room Temperature Tensile Properties -''.. Def. at End 0.2% Off et Reduction (a) Temp. Stress Time Loading Def. of Test Tensile Strength Yield Strength Elongation of Area Modulus (~F) (psi) (hrs) (%) (%) (psi) (psi) (% in 1 in) (%) (psi x 106) As Vacuum Annealed* 136,600 (136,600) 27.0 55.4 18.1 600 32,000 100.32 -133,700 -- 30.0 52.9 32,000 500.33.34 135,500 -- 26.0 51.5 32,000 In progress to 1000 hours 64,000 99.4 - - 140,000 -- 25.2 50.8 64,000 500 3,03 3.71 150,800 - 21.0 43.5 64,000 In progress to 1000 hours 1000 2,800 100.04.26 136,500 (127,000) 9.0 7.9 5,600 50.10.41 133,200 114,000 11.0 11.0 13.0 5,600 99.5.06.38 132,800 120,500 10.0 10.0 13.4 * Hydrogen content: 64 parts per million (wt.) (a) Modulus determined from slope of stress-strain curve. - N

TABLE IV Creep-Rupture Data for Ti-6%Al-1/2%Si Alloy Test Rupture Reduction Loading Time to Reach Indicated Minimum Temp. Stress Time Elongation of Area Def. Deformation (hours) Creep Rate Condition (~F) (psi) (hours) (% in 1 in) (%) (%) 0. 5% 1.0% 5 (in/in/hr) As Forged 1000 74,800 Tensile Test 11.7 - 50,000 41.1 14.3 31.4.47 0.2 4 - 1.4x103 45,000 97.8 22.0 22.2.39 2 5 40 8.3x10-4 36,000 473.9 15.0 26.9.34 4 15 330 1.2x 104 32,000 526.4 15.0 22.0.37 10 45 365 1.0x10- 4 30,000 >986.1 ( 5.0)* ( 7.9)*.27 15 105 (1000)est 2.8x 0-5 24,000 >1581.4 ( 2.0-)* ( 0.8)*.22 180 - 20,000 >1083.8 (0)* (0)*.19 1030 - - 1.3x10-6 Cold Worked 19% 1000 92,400 Tensile Test 11.7 34.9 - - - 52,000 48.4 29.1 49.5.55 14 - 3.3x104 44,000 126.0 35.6 53.5.48 0.5 5 46 7.7x10-4 21.6% 1000 44,000 145.6 33.0 32.2.47 - - 32,000 393.4 30.0 46.4.33 4 16 180 2.1x10-4 25,000 1472.0 22.0 42.7.27 8 35 800 4.0x10'5 20,000 >1034.7 ( 1.0)* ( 0.8)*.20 30 450 - 7.6x10'6 13,000 >1104.3 (0)* (0)*.12 690 - 1.8x 10-6 > Test stopped without rupture at this time ( )* Permanent deformation after cooling, if measurable Tensile Test Data for Ti-6%Al-1/2%Si Alloy 0.2% Offset Reduction Test Temp. Ult. Tensile Strength Yield Strength Elongation of Area Modulus Condition (~F) (psi) (psi) (% in 1 in) (%) (psi x 106) As Forged 75 140,200 133,500 19.4 32.1 13.5 600 97,000 86,200 15.7 21.8 13.5 1000 74,800 60,700 11.7 22.4 9.8 Cold Worked 19% 75 178,800 162,700 8.2 24.2 12.7 600 115,500 104,000 7.6 27.2 12.1 1000 92,400 82,300 11.7 34.9 10.4

50 U 40 30 ~ 0~ __ ___0_ _ —_6 00-0 600F - 32,000 psi Tr 20, O 600~F 64,000 psi |I \\000'F - 5600 psi w 10 ^1000F - 2800 psi 160 -, 150- _O0 6000F 64,000 psi x 140 - 0_ - 1000F - 2800 psi L 600*F 32,000 psi IZ0 130-100011F - 5600 psi I 120 4-, 110 H I I 10 O-a D-o U i Jb U 400 s-0 600 700 800 900 1000 1100 Exposure Time-hours Figure 1.- Effect of Creep Test Exposure on Room Temperature Tensile Properties of Vacuum Annealed Ti 150A. (Hydrogen Content: 64 parts per million)

Total Condition Rupture Deformation As Forged - - - - 60 _19% cold work A 21.6% cold work -— * —---- -- 0.5% 1,.% 0A% 50 D.. \D 5. 0. 40 -'O 0 2~ "C "'"- \" -^\' k 5U).^ 1 0 >.%, I^ 0^^ —^^^ --- ^^ 5.0% 20- 0` 0 1.0% ^ 0.5% 10 0.1 I 1.0 10.0 100.0 1000.0 Time -hours Figure 2. - Stress versus Rupture Time and Time to Reach Indicated Total Deformation at 1000OF for Ti.6%Ali/2%Si Alloy.

60 50{> -"0 3. 1 40 - 9? ^ FIg. D 10 f |T' 6%A1-'.1/2%SI~ —-- - As Forged 10 -v — 19% Cold Work Figure 3. - Stress versus Minirrmum Creep Rate at 1000~F for Ti-6%Al-l /2%Si Alloy. ------- 21 6% Cold Work 0 1 t I I I5I I I I 1 10 1('- 5 — 4 10-3 - - 10-2 Mihimum Creep Rate-in/in/hr