Effects of temperature and shot peening on S-N behavior of a PM Ni-base superalloy UDIMET 720

Fatigue S-N (stress vs life) curve. behavior for a powder metallurgy (PM) Ni-base superalloy UDIMET 720 in both polished and shot-peened surface conditions was investigated at room temperature and 600 degreesC in air. Tests were carried out under four-point bending at a load ratio of 0.1 and a frequency of 10 Hz At 600 degreesC, an offset S-N curve was found for both polished and shot-peened surface conditions; This offset S-N curve is deduced to be controlled by the location of crack nucleation sites. Observations and deductions of crack nucleation Sites, crack nucleation life, crack closure, environmental attack, and cyclic softening and hardening have been used to explain the experimental results.