ENGINEERING RESEARCH INSTITUTE THE UNIVERSITY OF MICHIGAN ANN ARBOR Progress Report No. 3 ELECTRON METALLOGRAPHIC INVESTIGATIONS OF THE MINOR PHASES OF HEAT-RESISTANT ALLOYS Period 15 July to 15 October 1956 W. C. Bigelow J. A. Amy M. W. Devers ED L. Jensen Project 2447 METALLURGY RESEARCH BRANCH AERONAUTICAL RESEARCH LABORATORY (WCRRL) WRIGHT AIR DEVELOPMENT CENTER WRIGHT-PATIERSON AIR FORCE BASE, OHIO CONTRACT NO. AF 33 (616)-3250 PROJECT NO. 6- (8-7351), TASK NO. A 70646 December 1956

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The University of Michigan ~ Engineering Research Institute ACKNOWLEDGMENTS The authors wish to express their appreciation to Professor J. W. Freeman, Dr. CO L. Corey, and Messrso R. Fo Decker and J. P. Rowe, who have supplied all alloy specimens studied here, and who have provided metallurgical data on the specimens which have been of inestimable value in selection of the specimens to be included and in interpretation of resuits in terms of metallurgical properties, ii

The University of Michigan ~ Engineering Research Institute TABLE OF CONTENTS Page LIST OF. ILLUSTRATIONS iv SUMMARY v OBJECTIVE vi INTRODUCTION 1 EXPERIMENTAL METHODS STUDIES OF THE MINOR PHASES OF S816 ALLOY 2 IDENTIFICATION OF THE y' PHASE OF THE NICKEL-BASE ALLOYS 5 MICROSTRUCTURE AND HARDNESS OF UDIMET ALLOY 7 INVESTIGATION OF THE o PHASE IN Ti ALLOYS 10 REFERENCES iii

The University of Michigan Engineering Research Institute LIST OF ILLUSTRATIONS Table Page| I'Interplanar Spacings from a Selected-Area Diffraction Pattern of Grain-Boundary Material from a Specimen of S816 Alloy Aged 10 Hours.at 16000F 4 II Electron Diffraction Data from 7' Phase of M-252 Alloy Aged 100 Hours at 1400~F 7 III Polishing Solutions for Titanium Alloys 12 Figure Page 1 Results obtained by the extraction replica technique; S816 alloy specimen aged 10 hours at 1600~Fo 3 2 Application of extraction replica techniques to M-21 alloy aged 100 hours at 1400~F 6o 3 Electron micrographs from specimens of Udimet alloy aged at 14000F (X30,000). 8 4 Hardness values for Udimet alloy specimens, ice-brine quenched from solution treatment at 1975~F, and subsequently aged 1, 10, and 100 hours at 16000F. 9 ~ 5' Microstructure of Udimet alloy specimen aged 100 hours at 1600~F (X30,000). 10 6 Electron micrographs from the titanium-base alloys (X30,000)o, 13 ivI

The University of Michigan * Engineering Research Institute SUMMARY The progress of the experimental work on Contract No. AF 35(616)-35250 during the last half of the contract year is dea ~scribed. This work includes: (1) further examination of the carbide reactions in S816 alloy, (2) extension of microstructural examination of commercial wrought nickel-base alloys, and (3) initiati-on of studies of the mcphase in Ti_8Cr and Ti-l3Mo alloysy

The University of Michigan ~ Engineering Research Institute OBJECTIVE Various recent metallurgical investigations indicate that the minor phases which precipitate in the heat-resistant alloys during exposure to stress ses and high temperatures have a pronounced effect on the metallurgical properties of the alloys'To understand and control better the properties of these alloys, it is therefore desirable to have more detailed information on their minor phases. This project has been undertaken in order to employ the highly sensitive techniques of electron diffraction and electron microscopy in identiSfying the minor phases and in studying their distribution within the alloys, with the overall objective of obtaining such information. The work of this project falls into two general phases. The first is concerned with the development of various experimental procedures necessary for adapting the techniques of electron diffraction and electron microscopy to the study of the complex heat-resistant alloys. This involves principally the development of polishing, etching, and rinsing procedures for use in preparing surfaces of the various alloys for examination by the electron methods. The general problems associated with this phase of the work have been discussed. in WADC Technical Report 54-589, which was prepared under a previous contract. The second phase of the work is concerned with applying these special experimental procedures to studies of typical alloys used in the manufacture of components of jet aircraft engines and similar high-temperature appclose cooperation is maintained with Professor J. W. Freeman and his group in the Department of Chemical and Metallurgical Engineering who are doing metallurgical research in these alloys, and particular attention is given to attempting to correlate variations in the high-temperature properties of the alloys with the variations observed in their minor phases. vi

The University of Michigan ~ Engineering Research Institute INTRODUCT I ON A manuscript entitled "Submicroscopic Precipitates in Commercial Nickel-Base Alloys," which was prepared for publication in a technical journal, was submitted in lieu of a Progress Report for the second quarter of the contract year. This report therefore deals principally with the experimental worh carried out during the last quarter of the contract year, but also includes work done during the second quarter which was not incorporated in the manuscript, Described here are: further studies of the carbides in S816 alloy aged at 1600~F; identifications of the y' phase in Inconel X, Udimet,'Waspalloy, and M-252 alloy by electron diffraction from extraction replicas; continuation of the investigations of the relation of microstructure and hardness in the Udimet alloy; and the development of polishing and etching techniques for electron metallographic studies of Ti-8Cr and Ti-13Mo alloys. The first thriee -of these topics are continuations of work described in Progress Reports Nos. 1 and 2 for this contract, while the third topic represents new work undertaken since the last report. Work on the Guy alloy has been tema porarily discontinued, inasmuch as members of the Department of Chemical and Metallurgical Engineering are now carrying out studies of this material. The following sections of the report describe the results obtained to date in each of these investigations. EXPERIMENTAL METHODS The general procedures for studying the minor phases of alloy systems by electron diffraction and electron microscopy have been described by Heidenreich and his associates,l'2 and some of the special procedures which have been developed for applying these methods to the heat-resistant alloys have been described in a previous Air Force Technical Report.3 Briefly, minor phases are identified byelectron diffraction patterns obtained by directing the electron-beam across surfaces of the alloy specimens which are so etched by special techniques that the minor phases protrude slightly from the matrix metal. Because of the low penetrating power of the electron beam, these patterns arise almost entirely from the protruding min~or-phase particles. These patterns arie analogous to patterns obtained from fine crystalline powders by x-ray diffraction methods and are interpreted similarly~ The size, shape, and:.... f...... ~~1

The University of Michigan ~ Engineering Research Institute distribution of the minor phases are determined by electron microscopic studies which are usually made on the same surfaces used for the diffraction studies. These electron microscopic studies are made through the use of palladium shadowed collodion replicas. The preparation of these replicas and the interpretation of the resulting micrographs have been described prep viously.3 STUDIES OF THE MINOR PHASES OF S816 ALLOY Previous progress reports 5 have described studies of the minor phases of S816 alloy specimens aged at 1200~, 1400o, and 1600~Fo Electron microscopic examinations have shown that these specimens characteristically -contain three types of precipitate particles: very large, slightly angular particles which are randomly distributed through the alloy and are present even in -solution-treated specimens prior to aging- smaller particles which form in the grain boundaries during aging; and fine particles which generally form within the grains after the grain-boundary precipitation is well advanced From the results of electron diffraction and electron microscopic studies on specimens aged at 12000 and 1400oF, it was concluded that the large angular particles were Cb(C,N) and that the other precipitates were a complex carbide of the M23C6 type. Recent results from the specimens aged at 1600~F have raised some questions concerning this latter point, for although. the M3C6 phase has been detected in specimens aged 1 and 10 hours, it has not been doe tected in specimens aged 200 and 1000 hours which show all types of precipit tates o In order to resolve these questions, it was decided to attempt to employ the extraction replica method of Fisher.6 In this method the surface is initially etched to bring the precipitate particles into relief, an appropriate replica film is applied and the surface is etched a second time with the replica in place. This frees the particles from the surface but leaves rany of them embedded in the replica film with the same orientation and relax tive location as in the alloy. When the replica is transferred to the elece tron microscope the particles can be viewed directly, and electron diffraction patterns can be obtained from selected known groups of them by the selectedartea electron diffraction technique' To date examinations have been made of the alloy specimexns aged 1, 10, 200, and 1000 hours at 1600~F. The initial preparation of these specimens was accomplished by electrolytic polishing in a solution of 10 parts perchloric acid (70%) and 90 parts glacial acetic acid, followed by electrolytic etching,in -a solution of 12 parts phosphoric acid (85%), 41 parts nitric acid (70%), and 47 parts sulfuric acid (96%)o Carbon replica films deposited on the etched s.urfaces by evaporation in a vacuumc were used because of their re= ~sistance to chemical attack, and the second etching treatment was carried out 2

The University of Michigan ~ Engineering Research Institute electrolytically using one of the following reagents: ao 1 part nitric acid (70%) and 3 parts hydrofluoric acid (48%) b. 48% hydrofluoric acid. Reagent a was chosen for this purpose because previous results5 indicated that it dissolves the Cb(C,N) phase without dissolving the M23C6 phase, The use of this reagent should therefore permit the M23C6 particles to be picked up on the replicas, but not the Cb(C,N) particles It -was hoped that reagent b would not attack either of these phases and would thus permit particles of both to be picked up on the replicas~ Where reagent a was used in the preparation of the specimens aged i and 10 hours, the precipitate particles from the grain boundaries were picked up by the replica, but not;the large blocky particles, A typical elect tron micrograph of these grain boundary particles is reproduced in Fig. lao The electron diffraction patterns obtained from these particles by the see lected-area diffraction technique consisted of a large number of diffraction spots as shown in Fig, lb. The interplanar spacings corresponding to these spots are listed in Table Io Due to the character of these patterns and difficulties in obtaining accurate calibration of the instrument, measurements of the highest accuracy were not possibleo nonetheless the agreement with the reported values for the M23C6 carbide is quite satisfactory. Similar results' were obtained when reagent b was used in preparing the specimens except that some of the large angular particles were also picked up on the replicas. Generally, no satisfactory diffraction patterns were obtained from these particles, probably because they were too large to transmit the electron beama a. Electron micrograph (X1500)o bo Electron diffraction patterno FLg. 1o Results obtained by the extraction replica technique3 S816 alloy specimen aged 10 hours at 1600~Fo

The University of Michigan * Engineering Research Institute TABLE I INTERPLANAR SPACINGS FROM A SELECTED-AREA DIFFRACTION PATTERN OF GRAIN-BOUNDARY MATERIAL FROM A SPECIMEN OF S816 ALLOY AGED 10 HOURS AT 1600~F Observed Data Standard Data for M23C6 3.67 A 3576 A 2 96 3.21 2.64 2.66 2.42 2.38 2.16 2.17 2.04 2.04 1o87 1o88 1.82 1. 79 1o76 1.77 1.71 1.68 1,62 1o58 1.60 1052 1o53 1a47 1.49 1o44 1042 1o37 1.38 Using these same techniques and procedures, it has been. possible to date to isolate only the large Cb(C,N) particles from the specimens aged 200( and 1000 hours. This may be interpreted to indicate that the grainsboundary and intragranular precipitates in these specimens differ from the corresponding precipitates in the specimens aged 1 and 10 hours, The nature of this differ= ence cannot be deduced from the data presently available, but may involve either composition or crystallographic structure, On the other hand, the inability to extract these precipitates from the 1600~F specimens may be dependent on particle size, In the case of the grain.boundary precipitate, the particles may have grown too big by the additional aging to be freed by the etching treatments used, while a sufficient attack may have been produced on the very small intragranular particles to dissolve them or prevent them from remaining attached to the replicas. Further work is in progress to resolve these questions. This will involve attempts to develop etches which will permit the precipitates to be removed from the specimens aged 200 and 1000 hours at 1600~F for the extraction replica studies, as well as application of standard electron diffraction, elect tron microscopic, and x-ray diffraction- methods. There is particular interest in these results, for Rowe and Freean have recently suggested that decreases in the rupture properties of the alloy accompanying overheating to 1800~F re= suit from replacemnent of other precipitated phases by Cb(C,N)o Some indica= If

The University of Michigan ~ Engineering Research Institute tion of this transformation may be obtained from the present studies on the specimens aged at 16000~F It is also proposed to make studies of the minor phases of the overheated specimens as part of the future work on this alloy. IDENTIFICATION OF THE y7' PHASE OF THE NICKEL-BASE ALLOYS In the work to date, the identification of the intragranular pricipitate in commercial nickel-base alloys as the intermetallic 7y' phase has been based largely on its etching characteristics9 and on x-ray diffraction results obtained from the Inconel-X alloy).More direct identification of these particles has long been desirable, particularly in connection with the studies of the newer alloys such as Udimet, M-252, and Waspalloy. To accomplish this, the extraction replica techniques described above have been employed so that the particles could be isolated from the matrix and studied directly by electron diffraction and electron microscopy. The procedures used were generally the same as those described above for the S816 alloy, except that the second etching treatment was carried out -electrolytically in a 15% phosphoric acid solution This method has been applied to date to specimens of UTdimet, Waspal' loy, and M-252 alloys aged 100 hours at 14000F, and to specimens of Inconel-X alloy aged 1000 hours at 1400~F and 10 hours at 1600~Fo The results have cons6 fir med the identification of the intragranular particles of all these specimens as the y'phase and have also provided evidence that this phase has an ordered Ftrtucture based on a face-centered cubic lattice in all these alloysd As an illustration of these results, a conventional electron micrograph from the M-252 alloy specimen aged 100-hours at 1400~F is reproduced in Figo 2, together with an electron micrograph and an electron diffraction pattern from the intragranular particles isolated from this specimen by the ex., traction replica procedure. The similarity in the shape and distribution of the particles in the two micrographs is quite convincing, and the fact that the particles appear slightly smaller in the extraction replica is undoubtedly due to particle dissolution during the extraction etching process~ The electron diffraction pattern consists primarily of a few single-crystal diffraction spots-corresponding to the usual face-centered cubic reflections having all even or'all odd Miller indices. In addition, careful examination of the original photographic plates revealed several much weaker spots at positions correl Sponding to the remaining cubic reflections and indicating an ordered structure. The Miller indices and interplanar spacings calculated for all thes.e reflections are listed in Table II. As shown, there is very good agreement with values calculated from data on the size of the unit cell of the 7' phase reported by Nordheim and Grantl0 Since the extracted particles have the same orientation in the 5

The University of Michigan ~ Engineering Research Institute a. Regular electron micrograph b. Micrograph from extraction rep(X30,o000o). lica (X30,000). c. Selected-area diffraction pattern from particles in Fig. 2b. Fig. 2. Application of extraction replica techniques to M-252 alloy aged 100 hours at 1400~F.

The University of Michigan * Engineering Research Institute TABLE II ELECTRON DIFFRACTION DATA FROM 7' PHASE OF M-252 ALLOY AGED 100 HOURS AT 1400~F dhkLValues from Calculated Pattern Miller Indices Extraction Replicas for Ordered Nis(Ti,Al) 3-.56 A 100 3.56 Avw 2.52 110 2.52 Vw 2o06 111 2.06, s 1.78 200 1.78 s 1.59 210 1.59 vw 1o.45 211 1.45 vw 1..26 220 1.26 s 11-o9 300/221 1,19 vw 310 1l15 vw 1.07 311 1.07 s 1.03 222 1.03 s ao= 3.56 A ao 5 3.56A replica as in the metal surface, some indication of the degree of preferred orientation of the particles in the alloys can be obtained from comparison of the: character- of the electron diffraction patt-erns obtained from the replicas. A high degree of preferred orientation will result in patterns consisting of a few strong spots, while a random orientation will result in patterns of fmore lor ess spotty rings. The results obtained to date indicate a high degree of preferred orientation in the Inconel-X, Udimet, and M-252 specimens, but very litt;le in the Waspalloy specimeno This is a rather interesting observation and will receive further investigation to see if there is any relationship between the orientation of the y' particles and the compositions and properties of the alloys. MICROSTRUCTURE AND HARDNESS OF UDIMET ALLOY.In the previous report, studies of the hardness of Udimet alloy specimens aged at 14000F were described which indicated that maximuma hardness was reached with about 100 hours of aging at this temperature, and a decrease from a Vickers hardness value of 419 to a value of 404 occurred with further aging to l000 hours, Differences between macro- and microhardness values were also noted which were indicative of a softening of the grain boundaries of the alloy with long periods of aging. Electron micrographs showing the microstruc- ~~~~~~~~7

The University of Michigan ~ Engineering Research Institute tures of the spec imens aged for periods up to 100 hours were presented, but micrographs of the: specimen aged 1000 hours were not available for correlation with the ovemaging effects. The electron microscopic studies of this latter.sp ecimen have now been completed and a representative micrograph is reproduced in Fig. 5 together with a.micrograph from the specimen aged 100 hours. Comparison of these two micrographs shows that increasing the period of aging from 100 to 1000 hours produces a considerable increase in the size and separation of the y" particle; and a marked decrease in the number of these particles per unit volume. There is also a noticeable increase in the size of the carbide particles in the grain boundaries, accompanied by the formation -of a layer of y7' phase surrounding these particles. a. Aged 100 hours: b: Aged 1000 hours. 14000oF (x30, o00 ) the specimen aged 1000 hours as for the specimen aged 100 hourso This i. nd~i the grains~ The decrease observed in the macrohardness of the alloy therefore appears tot be associated with the microstructural changes which occurred at the grain boundaries~ This' is of particular interest, for in independent studies Freeman and Decker have observed layers of the 7~ phase at the grain boundaries of rupture-tested specimens of the alloy, and have obtained some evidence that th formation f these layers is most proouned in specimeres having the loest rupture strengths. ST;~~~9;115~rs~:~~p ~ # 41 dgE~:~b-"_r ~ ~B~P~:~:,:J:,-X; J

The University of Michigan ~ Engineering Research Institute Similar studies have been started on a series of Udirmet alloy specimens aged at 1600~F. Macrohardness measurements have been completed on these specimens and show maximum hardness to be reached with between 1 and 10 hours of'aging and a considerable decrease which accompanies further aging to 100 hours. The observed values are plotted in Fig. 4o Only preliminary microhardness measurements have been completed to date, and these have been rather unsatisfactory. In general, they have been much lower than the macrohardness values and varied over a wide range for each specimen, Considerable additional work to refine these measurements is therefore necessary. 400 0 380 360 a 340 I 320 300. IBQ I 10 [00 AGING TREATMENT Fig. 4. Hardness values for Udimet alloy specimens, icebrine quenched from solution treatment at 1975~F, and subsequently aged 1, 10, and 100 hours at 16000Fo Electron microscopic studies of the microstructures of these specik mens are also in progress. Figure 5 shows the microstructure of the specimen aged 100 hours at 1600~F. The 7' particles in this specimen are very much larger than those produced by 1000 hours of aging at 14000F, and the development of the layers of the y' phase at the grain boundaries is also much more extensive. These studies are being continued to obtain an overall picture of the effect of aging at various temperatures on the microstructure and hardness of the alloy. 9

The University of Michigan ~ Engineering Research Institute Fig. 5. Microstructure of Udimet alloy specimen aged 100 hours at 1600~F (X30,000). INVESTIGATION OF THE j. PHASE IN Ti ALLOYS Ixmprovement of metallurgical properties by precipitation of a second phase in an alloy is not confined to the nickel-base alloys discussed above. Among the other important alloys exhibiting this phenomenon are certain of those based on titanium, in which hardening is produced by the precipitation of the low-temperature o-titanium (hexagonal) within the matrix of the high temnperature e form (body-centered cubic). In some alloys this precipitation process involves the formation of a mnetastable transition structure which is referred to as the M phase. The exact crystallographic structure of this phase is somewhat doubtful and has been reported to be orthorhombic with ao = 6.2, bo = 6.5, co = 13.5 A,1l or to be face-centered cubic with ao = 9.8 A.12 The orientation of the w particles relative to the 3 matrix is also uncertain. At the request of the Metallurgy Research Branch of the Aerornautical Research Laboratory, WADC, attempts have been made to emnploy electron microscot and diffraction techniques to obtain information that might clarify these points. -. For these studies, specimens of Ti-8Cr and Ti-13Mo alloys were obtai~ned by WADC from Dr. W. Rostoker and associates at the Armour Research Foundation. These specimens were reportedly solution-treated at 9000C, waterquenched, and aged to produce maximum content of the c phase with minimum O contente;(8 hours at 400~C for the Ti-8Cr alloy and 4~2 hours at 400~C for the Ti-13Mo,alloy ) As is generally the case whenever studies of a new type of alloy are 10

The University of Michigan * Engineering Research Institute undertaken, considerable difficulty has been encountered in developing procedures which will produce the high quality of polishing and etching required for electron diffraction and microscopy. Both electrolytic and mechanical polishing methods have been tried, and more than 20 different electrolytes for the electrolytic polishing have been investigated. These have included the electrolytes recommended by Tajimal3 and Osadchukl4 for titanium and its alloys, and various modifications of these. An equal number of etching reagents, both immersion and electrolytic, have also been tried. Again these have included the various reagents recommended for etching titanium alloys for optical microscopy, and various modifications thereof. Due to the high resistance of the Ti-8Cr and Ti-13Mo alloys to electrochemical attack, electrolytic polishing results were generally not very satisfactory, and when mechanical polishing was employed, extreme difficulty was encountered in removing the polishing powders to obtain surfaces clean enough for electron diffraction. The most satisfactory overall results were obtained by mechanically polishing with 3/0 emery, then with Linde "A" alumina on a wax lap,.and following this with a light electrolytic polish in one of the reagents, listed in Table III to remove mechanically worked metal and the polishing alumina from the surfaces. Most of the etching reagents tried produced pitting and staining of the surfaces; however, it was possible to obtain satisfactorily etched surfaces, particularly of the Ti-8Cr alloy specimen, by electrolytic etching using low current (0,1 to 0.2 amp) in polishing solution 1 of Table III. Two of the best electron micrographs which have been obtained from the alloys are reproduced in Fig. 6. From these it appears that both alloys contain a very fine dispersion of precipitate particles, and there is some suggestion that these are in the form of rods or platelets. Their "diameter" or tthickness,' as the case may be, appears to be of the order of 400 A. It is felt that these particles are the C phase, for their size and distribution.as indicated by the electron micrographs are consistent with the conclusions of Rostokerll based on x-ray diffraction and metallurgical evidence, and with the hardening accompanying aging. The electron diffraction results to date have been less satisfactory in that it has not been possible to obtain patterns which can be definitely identified as arising from the w phase. The principal difficulty apparently rinvolves surface contamination in the polishing and etching operations. Because of the extremely small size of the o particles, the merest traces of contaminants deposited on the surfaces would be sufficient to screen them from the,electron beam. In some cases, patterns consisting of an array of single crystal spots corresponding to the cubic P phase have been obtained. This iss. encouraging since it indicates that sufficiently clean surfaces have been prepared. Slight modifications of the etching techniques may lead to patterns of the X phase. In continuing this work it is proposed to attempt the refining of -11

The University of Michigan ~ Engineering Research Institute polishing and etching procedures developed so far to improve the reproducibility of the electron microscopic results and to permit -electron diffraction patterns to be obtained of the a phase. The possibility of employing extraction replica techniques is also being considered. TABLE III POLISHING SOLUTIONS FOR TITANIUM ALLOYS (1) 77 ml acetic acid (glacial) 15 ml chromic acid (43%) 8 ml hydrofluoric acid (48%) Must be fresh for best results. Temperature about 10~ C current 3-5 amp. (Best for Ti-13Mo alloy) (2) 100 ml solution (1) 6 ml perchloric acid (70%) Use as above. (3)B — 37 ml nitric acid (tech., conco) 37 ml lactic acid (85%) 18.5 ml hydrochloric acid (37%) 7.5 ml hydrofluoric acid (48%) Temperature 60-80~, inmersion. (Best for Ti-8Cr alloy) 12

The University of Michigan Engineering Research Institute a Ti-8Cr alloy b T i.M..o....aloy -::~'~~~~~~~~~~~~~'~"::~:: —' ":'il"':`~::::::j::':'~:...:.... "-!i;~: —-:-::..~-~i~~~:'~:-".:A:~:::............ I~::'.... rd. ~:~!... X ixrl::~::~:~!'~~~ii' ~"::-~~; b. Ti-13Mo alloy. Fig~ 6o Electron micrographs from the titanium~base alloys (X50,O00). 16~~~~~1

The University of Michigan ~ Engineering Research Institute REFERENCES 1. R. D.;Heidenreich, L. Sturkey, and H. L. Woods, -"Investigation of Secondary Phases in Alloys by Electron Diffraction and Electron Microscopy," Jo Applied Sci 17,127 (1946). 2, R. Do Heidenreich, "Electron Diffraction and Electron Microscopy of Metals," Modern Research Techniques in Physical Metallurgy, American Society for Metals, 1953, po 51. 5 L. 0. Brockway and W. C. Bigelow, "The Investigation of the Minor Phases of Heat-Resistant Alloys by Electron Diffraction and Electron Microscopy:, WADC Technical Report 54-589, Wright Air Development Center, May, 1955. 4. Wo C.Bigelow, J, Ao Amy, and L. 00 Brockway, "Electron Metallographic Investigations of the Minor Phases of Heat-Resistant Alloys," Progress Report No. I, Proj'ect 2447, Engineering Research Institute, University of Michigan, Ann Arbor, April, 1956, 5. Wo C. Bigelow, J. A, Amy, M. W. Devers, and L. 06 Brockway, "Electron Metallographic Investigations of the Minor Phases of Heat-Resistant Alloys, Progress Report No. 2, Project 2447, Engineering Research Institute, University of Michigan, Ann Arbor, June, 1956. 6. R. M. Fisher, "Electron Microstructure of Steels by Extraction Replica Technique, Symposium on Techniques for Electron Metallography, ASTM Special Technical Publication No. 155, 1953, p. 49. 7: Do -E. Bradley, "A High-Resolution EvaporatediCarbon Replica Technique for the Electron Microscope," J. Inst. Metals, 83, 35 (1954-55). 8. J. P. Rowe and J. W. Freeman, "Effect of Overheating on the Creep-Rupture Properties of S-816 Alloy at 1500~"" Report No. 50, Project 1478-10, Engineering Research Institute, University of Michigan, Ann Arbor, March, 1956. 9,.W. CO Bigelow, J. Ao Amy, and L. 0. Brockway, "A Selective Etching Pro-' cedure for:Identifying the -yt Phase of Nickel-Base Alloys by Electron Microscopy.:" Manuscript submitted to WADC in lieu of Progress Report No. 12 under Contract No. AF-533(616)-23. 14

The University of Michigan ~ Engineering Research Institute REFERENCES (Concl.) 10. Ro. Nordheim and No J. Grant, "Aging Characteristics of Nickel-Chromium Alloys Hardened with Titanium and Aluminum " J. Metals, 6, 221 (1954)o 11o S. A. Spochner, R. Fo Domagala, A. W. Goldenstein, and Wo Rostoker, "Structural Changes in Commnercial Titanium and Titanium Base Alloys on Heat Treatment," WADC Technical Report 55-352 (preliminary copy) 12. Po D. Frost,'Background for Practical Heat Treatatment of Various Titanium Alloy Types," J. Metals, 8, 35 (1956). 135 S. Tajima and T. Mori, "Electropolishing Titanium," Products Finishing, 19, 26 (1954); Electrochem. Soco Japan, 22, 289 (1954). 14. R. Osadchuk, W. P. Koster, and J. F. Kahles, "Recommended Techniques for Polishing Titanium for Metallographic Examination," Metal Proress, Oct 1953, p. 129; "Metallographic Structures in Comercial Titanium," ibid., Nov. 1953, p. 93. 15

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