Engineering Research Institute University of Michigan Ann Arbor SIXTH 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) -44 Supplemental Agreement No. S4 (54-288) Expenditure Order No. R615-11 SR 3 c Project 2076 covering the period January 15, 1954 to April 14, 1954

SU MMAR Y This report covers the period from January 15, 1954, to April 14, 1954, and is the sixth progress report to be issued under Contrat AF 33(616)-244. The 10% Cr Alloy was received. Metallographic investigation has been started on the 10% Mo alloy and proposed test conditions are discussed. Total deformation studies have been started on the as-forged conditions of the 6% Al and 30% Mo alloys at 600~ and 1000~F. Tensile and rupture test data at 800~F are discussed for hot worked conditions of Ti 150A. Results of tensile tests at room temperature for Ti 75A, Ti 150A, 6% Al, and 30% Mo alloys after creep testing at 600~ to 1000~F are presented. INTRODUCTION This report is the sixth progress report to be issued under Contract No. AF 33(616)-244 and covers the period from January 15, 1954, to April 14, 1954. The investigation has been concerned with properties of titanium and its alloys in the temperature range from 600~ to 1000 F. Under the present phase of the contract, the investigation has three major divisions. First, the properties of a number of typical titanium alloys are to be surveyed, utilizing tensile and relatively short time creep-rupture tests. The purpose of this survey is to establish if the type of alloy or this survey is to establish if the type of alloy or the alloying element itself is the controlling factor for high-temperature properties. Secondly, selected treatments of materials previously surveyed in the above manner are to be

2 tested out to 1000 hours in order to establish more completely the effects of the alloy type on the rupture properties and the stress for one-percent total deformation. The third phase of the investigation concerns itself with a study of the effect of hot working conditions on the rupture properties of two of the alloys at 800~F. In addition, investigation continues on several aspects of the physical metallurgy of these alloys as brought out in the first year's work. In particular, attention is being directed to the influence of exposure to stress in the temperature range from 600~ to 1000~F during creep testing on the room temperature mechanical properties. TEST MATERIALS Rupture and total deformation data are being obtained for the following materials: 1. Commercially Aire Ti (Ti 75A) - new heat previously received (Heat M-626). 2. Ti 150A - new heat previously received (Heat M-739). 3. 6% Al - new 20-pound heat previously received. 4. 30% Mo - old original heat being used. The status of the materials for the survey of the relative influence of type of structure and alloying is as follows: 1. 10% Mo - Meta Stable Beta Alloy - previously received. 2. 10% Cr - Meta Stable Beta Alloy - received from Armour Research Foundation during report period. Reported analysis: 9. 95% Cr - 0. 059% C - 0. 022% N. 3. Ti 155AX - Alpha Beta Alloy - on order. 4. 6% Al - 0. 5% Si - Alpha Alloy - on order.

3 5. 50% V - All Beta Alloy - on order. The status of material for the hot-rolling program is as follows: 1. Ti 150A - new heat of material previously received (Heat L897). 2. 6% Al - on order. RESULTS AND DISCUSSION Effect of Creep Test Conditions on Room Temperature Tensile Properties of Titanium Alloys A group of specimens previously creep tested were subjected to tensile tests at room temperature (75~F), in order to determine what effects the creep test conditions had on their properties. The data are summarized in Table I and show two types of effects. The Ti 75A and the 6% Al alpha alloy were similar in behavior. Conditions of cold working showed lower tensile strength and higher ductility after long time creep tests at 600~ and 1000~F. This can be attributed to relaxation of internal stress originally induced by cold working. Conditions of annealing alone or of cold working followed by recrystallization showed an increase in tensile strength accompanied by some decrease in ductility. This might be attributed to strain hardening. In all cases, a quantitatively greater effect was obtained on the specimens tested at higher temperatures. The Ti 150A and 30% Mo alloys, on the other hand, showed extreme embrittling effects on exposure to temperatures from 6000 to 10000F. For instance, all specimens of Ti 150A except one showed brittle failure in the threaded sections at gage section stresses well below the original tensile strength. The exception was a sample annealed at 1350~F and tested at 600~F

4 for 1173 hours at 83, 000 psi. In this instance, the tensile strength was 206, 500 psi, versus an original strength of 156, 200 psi. However, the elongation and reduction of area values dropped from 27. 7 percent and 43. 5 percent respectively to zero. A similar effect was noted for the tests on the 30% Mo beta alloy. One specimen, tested at 600~F, did fail in the gage section. The tendency to fracture in the threads for the latter two alloys suggests that they became extremely notch brittle. Presumably, these specimens would also show poor impact properties. The brittleness of the Ti 150A and 30% Mo beta alloys can be correlated with the appearance of a dark etching precipitate in the beta matrix. This has been described metallographically in preceding reports (1), (2). The reaction is that of the breakdown of non-equilibrium beta to alpha and compounds. Most likely, the brittle transition product, omega, also enters into the reaction. For properties measured at high temperatures, the net result of these reactions was to remove the differences between conditions of heat treatment. This result also correlates with the more birttle room temperature properties of the specimens creep tested at the higher temperatures. In the case of all beta 30% Mo alloy, the embrittlement was perhaps unexpected. There is a possibility that hydrogen could be an unrecognized contributing factor to the embrittlement, The implication of these results is that Ti 150A, for instance, would be severely embrittled if materials having the indicated prior heat treatments were exposed at 6000 to 10000F for periods of 1000 hours ( and probably less). For a brief survey of the embrittling conditions for Ti 150A, the following approximate procedure has been adopted. A specimen will be treated and loaded for a creep test at one of the conditions showing embrittlement.

5 The test is to be stopped after 100 hours and unloaded. The specimen is then to be tensile tested at room temperature. Depending upon the results of the tensile test, the test time will be increased or decreased for another sample. In this manner, it is expected that a rough measure of the time for embrittlement can be established. In addition, it is planned to expose several specimens to time and temperature, both in air and in vacuum, but not under stress. The combined procedures should show the relative effect of stress and temperature on the ductility. Effect of Hot Working Conditions on Ti 150A The effect of hot working conditions on the tensile and creep-rupture properties at 800~F is under study for Ti 150A. Four hot-rolling temperatures either in or above the alpha plus beta phase region were used and three different one-pass reductions were accomplished at each temperature. The hot-rolling temperatures were 1200~, 1350~, 1500~, and 1650~F. The actual reductions obtained are summarized in Table II, in conjunction with tensile test data. The maximum one-pass reduction that was obtained was 37. 8 percent at 1650~F. Tensile tests at 800~F are nearly complete for all conditions of hot working. The data, as mentioned above, are tabulated in Table II. In addition, the tensile strength is plotted in Figure 1 as a function of the percent reduction and temperature. The points used for zero reduction were taken from previous data for heat treatments which approximated the air cool incurred in the course of the hot working. These data were also for material from different heats than that used for the hot-working study. The rupture data available from the tests run to date are summarized in Table III. An estimate of the 1Q00-hour rupture strength at 800~F is

6 included in this table for each condition. The values of 100-hour rupture strength are also plotted on Figure 1. Creep data are not yet available for enough tests to permit any comparison to be made. Over the range of reductions studied, strengths increased with percent reduction. The indicated possibility of a minimum in strength at small amounts indicated by Figure 1 is doubtful, the points for no reduction being estimated from data for different heats air cooled from the temperatures used in hot working. Only a limited amount of the stock used for the hotworking study is available. Spot check tests, however, will be made to clarify the possibility of reduced strength from small reductions. Increasing the temperature of working in the a + P range increased strength. The increases were somewhat less and more inconsistent than had previously been obtained for simply heating to the same temperatures and air cooling. Effects due to heating temperature alone seemed to correlate with the increased amounts of retained 3 with increasing temperature of heating. Hot working apparently modified this to some extent. Heating to 1650~F in the all 3 region for hot working resulted in lower strength than working at lower temperatures in the a + P range. Thus, other factors than the amount of retained p were operating. Ductility values for the hot-worked samples were high, although somewhat lower than had previously been obtained at 800 F for samples heated to the same temperatures and air cooled. Perhaps the explanation of the behavior of the samples can better be explained when check tests are made on the specific heat for simply reheating to the temperatures of hot working. Metallographic examination may also help. These tests were undertaken because experience has indicated that usable properties at room temperature can only be obtained after heating to

7 the all p region by hot working Ti 150A down into the a + 3 region. Thus, in practice, structures will generally be limited to those obtained by such procedures. The results to date seem to indicate that if a reasonably good structure is present in stock, reheating to the a + P region and working further will not result in any marked change in properties at 800~F over those obtained by simply reheating to the same temperature and air cooling. The limited data for material heated to 1600~F suggests somewhat larger effects are possible. Further work seems justified where working is started well in the all p range and carried down into the a + p region. Influence of Total Deformation and Time on Properties Creep and rupture testing are being extended to ascertain how the deformation characteristics vary with time and degree of deformation for the metallurgical variables of titanium alloys being considered. Typical conditions of each type of alloy are to be subjected to sufficient creep and rupture tests to establish rupture time curves and curves for stress versus onepercent total deformationto 1000 hours. Original testing was limited to a few survey tests, most of which were relatively short in duration. Representatives of the Materials Laboratory and the University of Michigan have agreed on the following conditions for the tests: 1. Ti 75A at 600 ~F (a) 1500~F anneal. (b) 1500~F anneal + 31% cold work. (c) Slow and fast cool specimens after heating to 1700~, 1800~ and 2000~F to determine if basket weave or acicular structures can be produced for testing.

8 2. Ti 150A at 600~, 800~, and 1000~F. The material from the new heat is to be subjected to the survey type tests before undertaking long time tests. The conditions being surveyed are: 1500~F anneal, 15000F air cool, and 1800~F + isothermal transformation at 1300~F. 3. 6% Al at 600~ and 1000~F. (a) As forged. (b) As forged + 10% cold work. (c) Water quench after 1 hour at 2025 F. 4. 30% Mo alloy at 600~ and 1000~F. (a) As forged. 5. Decision to include other alloys has been deferred, pending results of survey type work. Long time creep and rupture tests are now in progress on the asforged conditions for the 6% Al and 30% Mo alloys. Samples are being heat treated for the other conditions. The tests on Ti 75A will be started during the next period. Extension of the Survey Tests to Other Alloys with Similar Structures The purpose of the check survey portion of this investigation is to determine if the type of structure or the alloying element governs the creeprupture properties of titanium alloys. To this end, materials are being procured having similar structures and transformation characteristics, but utilizing different alloying elements to- obtain the structures than used under the first portion of the contract.

9 Only the 10% Cr and 10% Mo alloys have been received. No work has been done on the 10% Cr material. Some metallographic work has been done on the 10% Mo alloy. It is planned to survey the 10% Mo alloy in the following conditions: 1. Quenched from the beta region. 2. Beta quenched and aged. 3. Beta solution treatment and isothermal transformation at (a) 1200~F for 60 minutes, (b) 950~F for 15 minutes. 4. Mixed alpha-beta structures (equi-axed alpha) representing (a) Equilibrium amount of alpha (maximum), (b) 75 - 85 percent beta. Figures 2 through 5 summarize the type of structure obtained with the 10% Mo alloy. Figure 2 shows the material in the as-forged condition. The finish forging temperature was 1850~F. Somewhat variable sized beta grains are present and appear to contain a fine precipitate. Heating this material to 1800~F and water quenching after 30 minutes resulted in the structure shown in Figure 3. The average beta grain size appears to be considerably larger, and evidences of the precipitate seem to have disappeared. Heating for 30 minutes at 1450~F (the upper portion of the alpha-beta region as determined from the phase diagram) and water quenching resulted in the structure shown in Figure 4. The general appearance of the beta phase is "cleaner" than in the case of the as-forged condition, and precipitation appears to be restricted to grain boundaries and crystaloographic planes. The last photomicrograph, Figure 5, shows a sample held at 1350~F for 24 hours and then water quenched. A fine veined-type of phase occupies much of the area within the original beta grains. In addition, the beta grain

10 boundaries contain a rod-like phase. This structure probably represents a close approach to the equilibrium alpha-beta proportions for this material at 1350~F. One additional sample was heat treated for 30 minutes at 1100~F and water quenched. Although polished in the same manner as all other metallographic samples, it was not possible to etch this sample (or a duplicate, for that matter) successfully. An adherent blue-black coating formed on the surface within 3 seconds, no matter what the etchant employed. There have been reports in the literature of a similar staining effect in other alloys. REFERENCES 1. Fourth Progress Report, Contract AF 33(616)-244, July 14, 1953, page 11 ff. 2. Ibid., page 21 ff.

TABLE I Results of Room Temperature Tensile Tests on Completed Creep Specimens of Ti 75A, Ti 150A, 6% Al, and 30% Mo Alloys Creep Test Conditions When Tensile 0.2o Yield Elongation Reduction Treatment Temp Stress Time Tensile Strength Strength of Area (F) (psi) (hrs) Tested (psi) (psi) (% in 1 in.) (%) Ti 75A (Commercially Pure Ti) As Received 600 35,000 911 Before 90,700 67,500 30.2 50.4 After 96,800 89,200 21.7 47.0 1700~F Anneal 800 6,000 1178 Before 87,600 65,600 34.0 44.6 After 89,300 71,000 27.5 45.8 1500~F Anneal 1000 2,500 1126 Before 87,900 68,400 30.4 48.6 After 86,000 65,000 16.3 46.6 1700~F Anneal + 10% Cold Work 600 1-0,000 1026 Before 109,000 99,400 10.7 32.5 After 100,900 89,300 22.2 42.9 1500~F Anneal + 10% Cold Work 800 12,000 1052 Before 115,000 102,000 12.7 43.5 After 94,900 83,000 21.8 44.6 1700~F Anneal + 31. 3% Cold Work 800 15,000 1188 Before 127,000 114,000 11.5 34.1 After 96,700 79,300 24.0 47.8 Ti 150A (Commercial a + 3 Alloy) 1350~F Anneal 600 83,000 1173 Before 156,200 154,100 25.7 43.5 After 206,500 206,000 0 0 1500~F Anneal 800 29,000 1535 Before 153,800 147,600 26.7 35.2 After Broke in threads at 100,500 psi 1500~F Anneal 1000 5,000 860 Before 153,800 147,600 26.7 35.2 After Broke in threads at 104,400 psi 1350~F Water Quench 600 116,000 1052 Before 173,100 159,900 18.2 39.2 After Broke in threads at 126,200 psi 1500FF Air Cool 800 35,000 1190 Before 177,200 162,500 16.7 32.0 After Broke in threads at 73,500 psi 1500~F Air Cool 1000 5,000 978 Before 177,200 162,500 16.7 32.0 After Broke in threads at 140,800 psi 1500~F Water Quench 800 -i1,000 811 Before 222,000 220,000 3.9 3.5 After Broke in threads at 58,600 psi 1500~F Water Quench 1000 5,000 1035 Before 222,000 220,000 3.9 3.5 After Broke in threads at 71,900 psi 6% Al Alloy (Experimental Stable a Alloy) As Forged 600 87,000 3001 Before 146,000 135,000 18.8 34.1 After 162,000 159,000 17.1 36.7 17% Cold Work 600 102,000 955 Before 177,200 163,800 10.7 28.0 After 170,000 168,000 8.8 27.4 17% Cold Work 1000 15,000 1337 Before 177,200 163,800 10.7 28.0 After 159,000 152,000 10.0 39.8 17% Cold Work + 1500~F Anneal 600 84,000 3167 Before 137,000 129,800 15.5 20.7 After 153,800 151,300 14.9 31.4 17% Cold Work + 1500'F Anneal 1000 17,000 3000 Before 137,000 129,800 15.5 20.7 After 140,400 135,700 9.6 11.2 17% Cold Work + 1700~F Anneal 600 79,500 1556 Before 135,000 129,000 13.0 34.6 After 147,600 144,000 17.0 37.3 30% Mo Alloy (Experimental Stable 3 Alloy) As Forged 1000 20,000 912 Before 144,700 142,500 14.0 27.4 After Broke in threads at 101,800 psi 1325"F Water Quench 600 102,500 983 Before 145,800 142,200 12.6 28.0 After 162,500 162,500 5.6 0

TABLE II Tensile Data at 800 F for Hot Rolled Ti 150A Hot Rolling Per Cent Ultimate Yield Strength Elongation Reduction Temperature Hot Strength (psi) of Area (~F) Reduction (psi) (0.2% Offset) (% in 1 in.) (%) 1200 14.9 79,700 (a) 33.3 74.7 18. 1 (a) (a) (a) (a) 30. 7 86, 300 (a) 30.9 74.5 1350 14.4 84,400 55,000 35.4 76.2 17.7 87,600 (a) 28.2 64.0 29.3 93,800 62,900 34.0 75.2 1500 15.8 83,200 51,600 35.3 81.1 20.4 87,700 55,000 43.6 82.1 34. 8 93,700 60,000 30. 8 79.2 1650 19. 1 75,100 48,600 34.0 76.2 25. 6 77,400 53,400 34.0 76.9 37.8 81,500 52,700 33.0 75.3 (a) Not yet available.

TABLE III Rupture Test Data at 800~F for Hot Rolled Ti 150A Hot Rolling Percent Stress Time Elongation Reduction 100-Hr RupTemperature Hot of Area ture Strength (OF) Reduction (psi) (hrs) (% in 1 in.) (%) (psi, est.) 1200 14.9 43, 000 155. 6 (a) (a) 40,000 296.8 42.0 79. 5 44,500 1350 14.4 45,500 74. 7 45.6 82. 3 44,500 175.5 (a) (a) 45,000 17.7 48,000 98.5 (a) (a) 48,000 29.3 53,500 73.6 35.4 76.2 51,000 177. 8 31.0 76.4 53,000 1500 15.8 48,000 188.8 (a) (a) 45,000 239. 0 34.6 80.8 48,500 20.4 49,500 143.6 (a) (a) 47,500 175.9 40. 0 82. 1 50,000 34.8 55,000 147.7 (a) (a) 51,000 383. 5 45. 2 78. 9 56,500 1650 19.1 41,000 535.5 37.4 78.2 46,000 25.6 47,000 199.7 38.8 76.9 42,000 519.0 (a) (a) 49,000 37. 8 51,000 153.6 39.6 80.2 46,000 460. 2 35. 9 78. 6 52,000 (a) Not yet available.

Effect of Heat Treatment on Microstructures of 10% Mo Alloy -\.:,*,.\. 4., " *.-:. ^.^. -.^".'..' 4. Figure 4 X250 Figure 3 X250 As Forged. 30 Minutes at 1450F 24Hours at 1350F, ~Water Quenched Water Quenched.Etchant: 1 HF, 1 Glycerine 30 Minutes at 1450F, 24,Hours at 1350!F, Etchant: 1 HF, 1 Glycerine