FATIGUE AND CRACK-GROWTH BEHAVIOR OF V-CR-TI ALLOYS

The results of in-vacuum low cycle fatigue tests are presented for uni rradiated V-5Cr-5Ti tested at 25, 250, and 400 degrees C. A pronounced environmental degradation of the fatigue properties is observed in th is alloy at 25 degrees C. Fatigue life was reduced by as much as 84% w hen testing was completed in a rough vacuum. Cyclic stress range data and SEM observations suggest that this reduction is due to a combinati on of increases in rates of crack initiation and subsequent growth. In high vacuum, the fatigue results also show a trend of increasing cycl ic life with increasing temperature between 25 and 400 degrees C. At 2 50 degrees C, life averages 1.7 times that at 25 degrees C, and at 400 degrees C, life averages 3.2 times that at 25 degrees C. A comparison of low cycle fatigue results for V-5Cr-5Ti was made to 20% cold-worke d 316 stainless steel and several vanadium-base alloys. The results su ggest that V-5Cr-5Ti has better resistance to fatigue than 316-SS in t he temperature range of 25 to 400 degrees C. At 400 degrees C, the dat a also show that V-5Cr-5Ti out performs Vanstar alloys 7 and 8 over th e entire range of strains investigated. Furthermore, the fatigue prope rties of the V-5Cr-5Ti alloy compare favorably to V-15Cr-5Ti (at 25 de grees C) and Vanstar 9 (at 400 degrees C) at strains greater than 1%. At lower strains, the lower fatigue resistance of V-5Cr-5Ti is attribu ted to the higher strengths of the V-15Cr-5Ti and Vanstar 9 alloys.