Engineering Research Institute University of Michigan Ann Arbor SECOND 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. S-1(53-247) Expenditure Order Nos. R605-225 SR 3c R605-227 SR 3a R615- 11 SR 3c Project 2076 covering the period 16 October 1952 to 15 January 1953

SUMMARY This report covers the period from October 16, 1952 to January 15, 1953. The objective of the investigation is to relate types of microstructure obtained by variation in heat treatment and cold work to the creep resistance of typical titanium alloys in the range from 600~ to 10000 F. The work will be guided to develop general fundamental metallurgical principles. Five typical alloys will be studied. These include commercially pure titanium (Ti 75), a commercial martensite forming alloy (Ti 150A), an alpha alloy (6% Al), a meta-stable beta alloy (10% Mo), and a stable beta alloy (30% Mo). The last three are being obtained in the form of small experimental heats. Variables of investigation include alloy type, heat treatment, and cold work. Microstructural examination and x-ray diffraction analysis will be the major tools utilized to attain the objective of the investigation. Work to date has been confined principally to material procurement and preparation of equipment. Four of the five materials have been received, the exception being the meta-stable beta alloy. Tensile testing is almost complete on the commercially pure titanium and rupture testing is now underway. Heat treatment and tensile testing are being carried out on the other alloys.

2 INTRODUCTION It is well known that for materials subjected to creep testing the effects of prior treatment have more influence on creep behavior than wide ranges of chemical composition. Prior treatment variables include hot and cold working, temperatures and cooling rates of solution treatments, temperatures and times of aging treatments, and, in those materials subject to phase changes, the type of microstructure produced. In general, melting practice has been shown to be of prime importance. Thus, observed creep properties are functions not only of final treatments, but even of the particular lot of stock being tested. Relations between creep behavior and treatments are often very complicated. A treatment producing maximum creep resistance at a low testing temperature may produce just the opposite result at a higher temperature. Treatments best for short time periods of service may not be best for prolonged times. Relationships may change depending on the deformation criterion over the time interval under consideration. Thus, in an investigation whose scope is as wide as the present one, it is difficult to select any one alloy and/or condition for singular. emphasis. Instead, it is desirable to survey in as systematic a fashion as possible a wide range of properties. Fortunately, a considerable amount of information is now available covering the general metallurgy of titanium and a number of its alloy systems. At low alloy contents and low temperatures an alpha phase (hexagonal close packed) exists which transforms at higher temperature to a beta phase (body centered cubic). At intermediate temperatures a mixture of these phases exists. Dependent upon cooling rate and alloy content, different transformation products are obtained from the beta phase. In addition, subsequent reheat or primary isothermal transformation are significant.

3 Purely on the basis of the metallographically observed response to such treatments, it is possible to characterize titanium alloys as "type" alloys. Selection of the systems for study under this contract has been made on this basis. Commercially pure titanium forms the basis for the work. Even this may be considered an alloy since the small amounts of impurities present have an effect on its properties. The other materials chosen for study have the following characteristics: an alloy in which the alpha is stablilized; an alloy undergoing the so-called martensitic transformation (i, e. formation of an acicular transformation product) on fast cooling from the beta region; a meta-stable beta alloy, one in which beta retention would be possible, yet which would permit structural variations from both isothermal and aging treatments; and a stable beta alloy, one permitting complete beta retention on slow cooling. Complete details of composition and testing variables for each alloy are given in following sections of this report. The purpose of mentioning them here is to emphasize the philosophy of the testing program. TEST MATERIALS Five materials, four of which have been received, were ordered for the investigation after consultation between representatives of the Wright Air Development Center and the University of Michigan. The test materials were selected as mentioned previously in order to be represenative of the "type" transformation reactions possible with titanium alloy systems. Two are available from commercial sources. The remaining three are being obtained in the form of small (approximately ten pounds each) experimental ingots and will be melted for the University by special arrangements with the Armour Research Foundation of Chicago, Illinois,

4 Material in the form of bar stock was chosen for study in order to minimize both procurement difficulties and contamination problems during treating and testing. The available details of the test materials are given in Table I. PROCEDURE In general, the experimental program is planned to study the effects on creep behavior of the metallurgical variables appropriate to the alloy under consideration. Testing will be guided by experience from other research work in progress at lower temperatures. In the present program it is anticipated that tests can be confined to 600~ and 1000F for the experimental alloys and 600~, 800~, and 1000~F for the commercial materials; however, if necessary for fundamental explanations or to develop more complete data some intermediate temperature may also be employed. The effects of the variables are being surveyed by the following approximate testing procedure at each temperature: (a) A short time tensile test; (b) Tests designed to cause fracture in 30-40 hours and 100 hours. It must be realized that it will be unusual to actually obtain these times. Every effort will be made to cover the time period with two tests. (c) Creep tests at a stress level which will result in a creep rate of between 10-5 and 10 6inches per inch per hour and for a length of time sufficient for the approximation of a second stage creep rate. These tests should be adequate to indicate relative creep strength properties. If more complete engineering data appears desirable for any

5 particular condition and/or alloy, rupture tests will be extended to approximately 1000 hours and enough additional creep tests made to establish the total deformation characteristics. In addition, mechanical properties will also be determined at room temperature. The room temperature tensile tests will show the general mechanical properties and serve to indicate whether or not treatments usedc are giving normal results. Tensile tests at elevated temperatures are mainly required to arrive at a reasonable stress for rupture testing. The limited number of testing units and the limited number of specimens of experimental materials require very little error be made in the selection of stresses. In addition to creep, rupture, and tensile testing, the following general techniques will be employed to delineate the observed influences of metallurgical variables: (a) Microstructural examination both before and after creep and rupture testing; (b) Hardness changes due both to initial treatment and to the effect of testing; (c) Changes in x-ray diffraction characteristics induced by treatments, particularly diffraction line broadness where applicable as a measure of internal strain and lattice parameter changes as a measure of precipitation effects. The purpose of these measurements is particularly to establish the effects of grain size, cold work, and precipitation phenomena on creep characteristics. Where the 3 —-a transformation changes not only the relative amounts of the phases but also their distribution, a correlation of the two effects will be attempted. Also included in such correlation will be the effects of initial structure and changes during testing.

6 Details of Planned Treatments I. Commercially Pure Titanium (Ti 75) Tested at 600~, 800~, 1000~F 1. As produced (exact details not yet available, 2. Annealed at 1500~F,. 3. Annealed at 1700~F. 4. Annealed at 1500~F + 10% cold work. 5. Annealed at 1500~F + 30% cold work. 6. Annealed at 1700~F + 10% cold work. 7. Annealed at 1700~F + 30% cold work. 8. Partially stress relieved specimens after cold working are to be tested for both reductions. Selection of the exact conditions will be delayed pending results of the above tests. II. Martensite-forming Alloy (Ti 150) Tested at 600~, 800~, 1000~F 1. As produced (exact details not yet available). 2. Annealed at 1500~F. 3. Air Cooled from 1500~F. 4. Water Quenched from 1500~F. 5. Annealed from 1350~F. 6. Air Cooled from 1350~F. 7. Water Quenched from 1350~F. 8. * from 1500~F + 1350~F Anneal. 9. * from 1500~F + 900~F Anneal. 10. * from 1350~F + 900~F Anneal. 11. Solution treat at 1800~F + full isothermal transformation at 1300~F. 12. Solution treat at 1800~F + full isothermal transformation at 1000~F. * Cooling rate to be determined by work in items (3) through (7).

7 Items 1 -7 represent variations in the properties of a + P. Items 8-10 vary a + P properties through a different procedure. Items 11 and 12 are representative isothermal transformation structures. Sufficient stock is available for checking about three more conditions in addition to those listed on the preceding page. III. Experimental Alpha Alloy (6% Al) Tested at 600~and 1000~F 1. Cold worked about 17% and annealed to fine grained structure. 2. Cold worked about 17% and annealed to coarse grained structure. 3. Water quenched from 2025~F (middle of 3 range). 4. Cold worked 10%. 5. Cold worked 17%. 6. Cold work as in (4) and (5) plus reheating to a terrperature below which recrystallization occurs. In addition, mechanical properties will be determined on the material as-forged. IV. Experimental Meta Stable P Alloy (10o Mo) Tested at 600~ and 1000~F 1. Water quench from p range to retain p. 2. Quenched from p range and aged to transform 3 at a lower temperature. 3. Quenched from P range to full isothermal transformation at 1100~ and 1300~F. 4. Quenched from two temperatures in the a + p range in order to obtain the maximum difference in a + P properties. The above planned procedure may be modified pending receipt of the material,

8 V. Experimental Stable P Alloy (30% Mo) Tested at 600~ and 1000~F 1. Testing original retained 3 structure. 2. Quenching and aging 3 structure for transformation. 3. Quenched plus cold work. 4. Long time isothermal holding after cooling from all P region. Little response to heat treatment is to be expected from this material. As results are obtained it is anticipated that changes and modifications of the above schedules may become necessary; therefore, it should not be accepted as a hard and fast statement of work. RESULTS The following results are presented without comment at the present time: Commercially Pure Titanium (Ti 75) All specimens have been treated for conditions (1) through (7). The following tensile and rupture data have been obtained to date: (see following page)

9 Tensile Test Results - Ti 75 Test Tensile.2% Offset Reduction Treatment Temp. Strength Yield Strength Elongation of Area (~F) (psi) (psi) (% in 1 in.) (%) As Received 75 90,700 67,500 30.2 50.4 Ann. 1500~F 75 87,900 68,400 30.4 48.6 Ann. 1700~F 75 87,600 65,600 34.0 44.6 Ann. 1500~F + 10.9% Cold Worked 75 115,000 102,000 12.7 43.5 Ann. 1700~F + 10.9% Cold Worked 75 109,000 99,400 10. 7 32 5 Ann. 1500~F + 31.3%0 Cold Worked 75 129,000 116,000 12.3 39.8 Ann, 1700~F + 31.3%0 Cold Worked 75 127,000 114,000 11.5 34. 1 As Received 600 37,600 19,100 34.9 68.6 As Received 800 32,700 19,500 22.6 69.5 Ann. 1500~F 800 28,300 14,700 34.3 70.4 Ann. 1700~F 800 28,500 14,800 36.6 69.2 Ann. 1500~F + 10. 9% Cold Worked 800 41,300 36,600 17.3 67.3 Ann, 1700~F + 10.9% Cold Worked 800 42,400 37,000 15.6 61.5 Ann. 1500~F + 31.3% Cold Worked 800 50,800 44, 100 21.4 66. 7 Ann. 1700~F + 31.3% Cold Worked 800 48,900 39,800 18.6 66.2 As Received 1000 22,000 12,700 72.0 83.4 Ann. 1500~F 1000 17,790 10,550 114.0 92.0 Ann. 1700~F 1000 19,750 11,200 93.4 87.0 Ann. 1500~F + 10.9% Cold Worked 1000 23,800 14,700 103.0 85.4 Ann. 1700~F + 10. 9% Cold Worked 1000 20,900 14,000 144.5 94.6 Ann. 1500~F + 31.3% Cold Worked 1000 26,800 17,000 70.5 87.4 Ann. 1700~F + 31.3% Cold Worked 1000 23,700 15,000 91.4 91.8 Rupture Test Results - Ti 75 Time for Treatment Test Temp. Stress Rupture Elongation _____ (F) (psi) (hours) (% in 1 in. ) As Received 1000 9,500 4.9 109.2 As Received 1000 5,000 54.4 119.4

10 Martensite Forming Alloy (Ti 150) (Specimens of the as-received condition have been prepared for tensile testing. Specimens of the heat treated conditions are being prepared. Stable Alpha Alloy (6% Al) Experimental work has led to the following observations: 1. The maximum cold work the as-forged structure will take without cracking is about 17 percent. 2. It has not yet been determined if 17 percent cold work will give the desired recrystallization structures (i. e. fine and coarse grained). 3. The as-forged stock showed no appreciable microstructural change on reheating between 1300~ and 1700~F except grain growth. Depending on the time period this was encountered between 1500~ and 1700~F. The following tensile data have been obtained: Tensile Test Results - Alpha Alloy Test Tensile. 2% Offset Reduction Treatment Temp. Strength Yield Strength Elongation of Area (~F) (psi) (psi) (% in 1 in.) (%) 2025~F 1 hr. + Water Quench 75 142,400 122,000 18.2 38.6 2025~F 1 hr. + Air Cool 75 141,200 121,000 7.1 14.7 2025~F 1 hr. + Water Quench 600 97,900 78,500 17.6 34. 1 2025~F 1 hr. + Water Quench 1000 80,300 64,800 14.9 33.8 The other test materials have not yet been received or have been received too recently for experimental work in the period of time covered by this report.

11 Structural Studies In additioT., electro-polishing techniqgues have been developed for several of the materials; however, metallographic data is not yet extensive enough to warrant report at this time.

TABLE I TEST MATERIALS Designation and Supplier Chemical Composition (percent) 02_________________ O N2 C Fe Ti Form and Date of Receipt 1. Ti. 75 (Commercial Pure Ti) Nominal trace.02 -.10 bal. 50 ft. 1/2" round bar stock (Titanium Metals Corp.) Actual -.061.025.19 bal. October 15, 1952 2. Ti 150 (Martensite forming Z NZ C Fe Cr Ti Alloy) Nominal.25.02.02 1.3 2. 7 bal. 50 ft. 1/2" round bar stock (Titanium Metals Corp.) Actual -.124.046 1.52 2.68 bal. December 10, 1952 3. Experimental Alpha Alloy Nominal 6% Al -bal. Ti. 20 ft. 1/2"11 rounds and squares (Armour Res. Foundation) Actual 6.21% Al - bal. Ti. October 15, 1952 4. Experimental Stable BetaAlloy) Nominal 30% Mo. - bal. Ti. 20 ft. 1/2"1 rounds (Armour Res. Foundation) Actual Not yet available January 15, 1953 5. Experimental Meta-Stable Beta Alloy Nominal 10% Mo - bal. Ti. Not yet received. (Armour Res. Foundation)