Fatigue and crack growth behavior of V-Cr-Ti alloys

The results of in-vacuum low cycle fatigue tests are presented for unirradiated V-5Cr-5Ti tested at 25, 250, and 400 C. A pronounced environmental degradation of the fatigue properties is observed in this alloy at 25 C. Fatigue life was reduced by as much as 84% when testing was completed in a rough vacuum. Cyclic stress range data and SEM observations suggest that this reduction is due to a combination of increases in rates of crack initiation and subsequent growth. In high vacuum, the fatigue results also show a trend of increasing cyclic life with increasing temperature between 25 and 400 C. At 250 C, life averages 1.7 times that at 25 C, and at 400 C, life averages 3.2 times that at 25 C. A comparison of low cycle fatigue results for V-5Cr-5Ti was made to 20% cold-worked 316 stainless steel and several vanadium-base alloys. The results suggest that V-5Cr-5Ti has better resistance to fatigue than 316-SS in the temperature range of 25 to 400 C. At 400 C, the data also show that V-5Cr-5Ti out performs Vanstar alloys 7 and 8 over the entire range of strains investigated. Furthermore, the fatigue properties of the V-5Cr-5Ti alloy compare favorably to V-15Cr-5Ti (at 25 C) and Vanstar 9 (at 400 C) at strains greater than 1%. At lower strains, the lower fatigue resistance of V-5Cr-5Ti is attributed to the higher strengths of the V-15Cr-5Ti and Vanstar 9 alloys. (orig.)