- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR PROGRESS REPORT NO. 5 THE INFLUENCE OF SURFACE TREATMENT ON THE FATIGUE PROPERTIES OF TITANIUM AND TITANIUM ALLOYS By L. THOMASSEN M, J. SINNOTT A. W. DEMMLER, JR. Project 2034 WRIGHT AIR DEVELOPMENT CENTER, U. S. AIR FORCE CONTRACT NO. AF 33(616)-26 SUPPLEMENT S-2(53-582) E. 0. NO. R615-11-SR-3c, PROJECT NO. 53-670A-61 August, 1953

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN SUMMARY The effects of various types of notches on the fatigue strength of annealed Ti75A and RC 130B, and a heat treated form of RC-130B have been determined. The loss in fatigue strength of the annealed Ti-75A notched specimens, as compared to the unnotched, hand finished specimens varies from 0% to 62. 5%0 depending on the type of notch and the fatigue life level. The loss in fatigue strength of the annealed RC-130B notched specimens, as compared to the unnotched, hand finished specimens, varies from 13. 5% to 59. 0%, depending on the type of notch and the fatigue life level. The loss in fatigue strength of the heat-treated RC-130B, water quenched from 1550~F, tempered 2 hours at 700~F, varies from 20. 4% to 56. 5% depending on the type of notch and the fatigue life level, as compared to the annealed, unnotched specimens. ii

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN INTRODUCTION Previous progress reports and the Summary Report of this Project have presented the results of fatigue testing annealed Ti-75A and RC-130B. Various types of surface treatments were given these alloys to determine their effect on the fatigue properties. The purpose of the present investigation is to determine the effects of different notch types and methods of notch preparation on the fatigue properties of these same alloys. In addition, an all alpha, an all beta, and a heat treated form of RC-130B were to be included in this notch fatigue program. EXPERIMENTAL PROCEDURE Sufficient stock of Ti-75A and RC-130B from previous studies of various surface treatments on the unnotched fatigue properties of these alloys was available to enable the preparation of groups of specimens for notch fatigue studies. The analyses and mechanical properties of the alloys being reported are given in Table I. The work on Ti-75A consisted in testing three types of machined notches: a V-notch, a square-notch, and a radius-notch. As in the work on the unnotched specimens, extreme care was taken in preparing the specimens in order to assure uniformity within any one group. Figure 1 gives sketches of each of the types used. The theoretical notch sensitivity, K, as determined from the literature, is- 3. 2 for the V-notch, 2. 4 for the square-notch, and 1,4 for the radius notch (1)(2). Because of the multiplicity of the notch types, methods of notch preparation, and alloys to be investigated, the replicate testing used in previous work to obtain statistical information was curtailed. In place of the six specimens tested at each stress level, only three, in most cases, were tested in these notch studies. i 1

I ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN The data on Ti-75A notched fatigue specimens are given in Table II and the conventional S-N plots are given in Figure 2. The unnotched data are shown for comparative purposes. The data on the annealed, notched, RC-130B specimens are given in Table III and the S-N plots are given in Figure 3. The RC-130B was also tested in a heat treated form. The treatment given the alloy -was a water quench from 1550~ F followed by a twohour tempering at 700~F. This treatment produces a 50% alpha-50% beta structure. The annealed RC-130B had a structure of approximately 75% alpha~25% beta phase. This quench and temper treatment was chosen in order to determine the effect of changing the proportions of alpha and beta. Other studies have shown that such a treatment produces properties that are superior to the annealed properties and the fatigue behavior might also be expected to show improvement (3). The data on the fatigue properties of the RC-130B that had been heat treated are given in Table IV and the resulting S-N plots are shown in Figure 4. The radius-notch specimens of this material showed a tendency to fracture in the threaded ends of the test specimens rather than in the notch region so tests on this type of notch with this material were abandoned. ANALYSIS Using the mean values of the unnotched fatigue results of previous work, it is possible to compute the actual notch sensitivity or what is usually termed the fatigue strength reduction factor. As a reference standard the surface termed Annealed-Hand Finished was used since this type of surface had been used on various heats of the same nominal analysis in the previous testing program. Table V lists the mean stress for a stated fatigue life of the standard surfaces as taken from previously reported data, and for the fatigue life as determined for the notched specimens from Figures 2, 3, -j L 2

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN and 4. Fatigue data on the unnotched, heat treated RC-130B are not available because of the lack of sufficient test material. Figure 5 is a plot of the fatigue strength reduction factors for each type of notch as a function of the fatigue life, for Ti-75A. Figure 6 is a similar plot for the annealed RC-130B, while Figure 7 is a plot for the heat treated RC-130B as compared to the unnotched, annealed, specimens. CONCLUSIONS The notch sensitivity of the titanium alloys tested is generally about the same as that reported for steels (4). The actual sensitivity, as measured by the fatigue strength reduction factors, is somewhat less than the theoretically predicted values. The radius type of notch does not appear to be effective in reducing the fatigue strength of the Ti-75A to any appreciable extent as compared to the effects of the V-Notch and Square-Notch. Heat-treating the RC-130B to a 50% alpha-50% beta structure improved the yield and tensile properties but appeared to affect only slightly the notched fatigue properties. 3

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - BIBLIOGRAPHY 1. Hengebauer, G. H.: "Stress Concentration Factors and Their Effect on Design", Product Engineering, Feb. 1943, pp. 82=87. 2. Peterson, R. E. and Wahl, A. M.: "Two and Three Dimensional Cases of Stress Concentration and Comparison With Fatigue Tests:, Trans. A.S. M.E., Vol. 58, 1936, pp. A-15-22. 3. Phillips, C. W. and Tobin, J. C.: "The Phase Transformations and Heat-Treatability of Titanium Base Alloys", Final Report U. S. Army Ordnance Corps, Contract DA-20-018-ORD-11456, June, 1953. 4. Finch, W. G.: "A Study of Fatigue of Steels in the Finite Region of the S-N Curve", Proceedings ASTM, Vol. 52, 1952, pp. 759778. 4

TABLE I Analyses and Mechanical Properties Material Ti- 75A Heat Number M-270 Carbon 0. 04-0. 07 Nitrogen Iron 0. 10 0.20 Tungsten 0. 01 Hydrogen 0. 02-0. 05 Mangane se Aluminum (Oxygen-0.20) m z z rn rn 70 z m rm tA rn C= i m RC- 130B B-3413 0. 1 0.08 3. 9 3.9 Material Un Ti-75A M-270 Treatment Annealed 1450~F Proportional Limit, psi 47, 900 Tensile Strength, psi 84, 300 Percent Elong. (2") 27. 3 Percent Red. Area 42. 0 RC- 130B B-3413 RC- 130B B -3413 Annealed 1450~F W Q. 1550~F T. 700 F 119, 000 158, 000 160, 000 186, 000 18. 0 2. 8 47. 0 1.0* * Fractured in gage marks r" z m?o t> z J

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE II Fatigue Data, Notched Rotating Beam Annealed Ti-75A, Heat M-270 1000 Cycles of Stress V Notch 27,500 psi 51 87 60 25,000 psi 184 642 297 Square Notch 27, 500 psi 117 111 93 22, 500 psi 1129 1902 1154 Radius Notch 55,000 psi 31 34 38 50,000 psi 56 118 59 22, 500 psi 759 536 352 20,000 psi 12000* 609 1097 18, 000 psi 10939* 10663* 11122* 20,000 psi 1510 2812 1976 17, 500 psi 14872* 14119* 10165* 15,000 psi 22682* 21617* 14687* 47,500 psi 725 130 186 46, 250 psi 654 5124 45,000 psi 10506* 10780* 7541 40,000 psi 10173* *Did not fail. 6

-- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - TABLE III Fatigue Data, Notched Rotating Beam Annealed RC-130B, Heat B-3413 1000 Cycles of Stress I V-Notch 55, 000 psi 19 38 35 50,000 psi 58 65 39 Square Notch 65,000 psi 93 64 86 Radius Notch 80, 000 psi 89 78 32 60,000 psi 446 192 3998 75,000 psi 3517 72 33 45,000 psi 57 139 83 42,500 psi 80 10000* 57 57, 500 psi 1145 831 70,000 psi 144 2254 2786 1 55,000 psi 7699 10130* 10671* 65,000 psi 10500* 269 11000* 40,000 psi 5084 10126* 10260* 45, 000 psi 10445* 10000* 10545* 60,000 psi 12895* 11500* *Did not fail. 7

-- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN - TABLE IV Fatigue Data, Notched Rotating Beam Heat Treated RC-130B, Heat B 3413 1000 Cycles of Stress V-Notch 50, 000 psi 84 83 64 Square Notch 70, 000 psi 36 42 27 47, 500 psi 150 113 93 60, 000 psi 110 108 10575* 45, 000 psi 1922 1766 1562 57,500 psi 107 932 42, 500 psi 16178* 569 15679* 55,000 psi 10149* 10144* 10635* 40, 000 psi 326 10953* 11454* 50, 000 psi 17000* 17227* 12070* * Did not fail. 8

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE V Stress-Fatigue Life Data Cycles 4 5 6 7 10 10 10 10 Material and Treatment Stress, 1000 psi Ti-75A Annealed Unnotched 63.0 52.0 48.0 46.5 Ti-75A Machined V-Notch 38.0 27.0 19.5 17.5 Ti-75A Machined Square Notch 42.0 28.5 22.0 18.0 Ti-75A Machined Radius Notch 63.0 50.0 46.5 45.0 RC- 130B Annealed Unnotched 110 95.0 92.5 90.0 RC- 130B Machined V-Notch 72.0 43.0 38.0 37.5 RC-130B Machined Square Notch 77.5 64.0 56.0 53.0 RC-130B Machined Radius Notch 95.0 76.0 62.5 60. 0 Heat Treated RC-130B Machined V-Notch 64.0 48.0 41.5 39.0 Heat Treated RC-130B Machined Square Notch 87.5 60.0 53.5 51.5 -1 9

'TAPERI/ FT. A60 *\'RELIEVE 0.001" 1- __. S000 TAPER/ FT 0.480_=iT 0.300" - _DRILL -T i 4 RELIEVE 0.001" l e- -34 A -- TAPERj/ FT. O.O RRI ELIEVE 0.00'B:~-_'3 ^ TAP -20 -- Ir B L ELIEVE 0.001 Figure 1. Sketches of Types of Notched Specimens.

U) 0. 0 0 U) Uf) w cr FU) 60 50 4030 20 10 - 10 11% a 10 10' CYCLES Figure 2. Stress-Cycles of Stress Plots. Un-notched and Notched Specimens. Annealed Ti-75A.

100 90 w a. 80 — r 0 0 \ o IRADIUS 0 70 Uc 40 50 -— C — YCE 40 —104 105 CYCLES 0 10~ 10 Figure 3. Stress-Cycles of Stress Plots. Un-notched and Notched Specimens. Annealed RC-130B.

() a. 0 0 0 C( tC) LL Cr -- (l) 100 90 80 70 60 50 40 I 10 10 I CYCLES Figure 4. Stress-Cycles of Stress Plots. Annealed, Un-notched and Heat-Treated, Notched RC-130B.

VEf SQUARE 2.0' -' -- 1.5. RADIUS 105 i0o CYCLES Figure 5. Fatigue Strength Reduction Factors versus Fatigue Life. Annealed Ti-75A. 105 106 CYCLES Figure 6. Fatigue Strength Reduction Factors versus Fatigue Life. Annealed RC-130B. q I% 3.0 - I 2.5 VEE 2,0 ~,,,,,~/ SQUARE c a1A -..._......... ----- -,._ -.I5 I 10 TO* 105 106 CYCLES Figure 7. Fatigue Strength Reduction Factors versus Fatigue Life. Heat-Treated RC-130B.