Fatigue crack propagation behavior of titanium alloys 6242S and 5621 S at elevated temperature

The influence of test environment on the fatigue crack propagation performance of titanium alloys Ti-6A1-2Sn-4Zr-2Mo-O. 1Si (6242S) and Ti-5A1-6Sn-2Zr-0.8Mo-0.25Si (5621 S) was investigated at 450 °C. The results show that the crack propagation resistance of 6242S and 5621S was reduced in air compared to that in vacuum at a loading frequency of 0.17 Hz. A similar environmental behavior was observed when a one-minute hold period was included in the fatigue cycle. Both alloys exhibited excellent creep-fatigue resistance at 450 °C as little effect of hold time was observed. Overall, the fatigue crack propagation resistance of 6242S was found to be slightly superior to that of 5621S. These results are discussed in terms of the effects of thermal-mechanical history and microstructure on the fatigue crack propagation characteristics of titanium alloys. This paper is based on a presentation made in the symposium “Crack Propagation under Creep and Creep-Fatigue" presented at the TMS/AIME fall meeting in Orlando, FL, in October 1986, under the auspices of the ASM Flow and Fracture Committee.