Effect of strain rate on the high-temperature low-cycle fatigue properties of a nimonic PE-16 superalloy

The effects of strain rate on the low-cycle fatigue behavior of a Nimonic PE-16 superalloy have been evaluated in the 523-923 K temperature range. Total-strain-controlled fatigue tests were performed at a strain amplitude of +/-0.6 pct on samples possessing two different prior microstructures: one in the solution-annealed condition (free of gamma-prime and carbides) and the other in a double-aged condition with gamma-prime of 18-nm diameter and M23C6 carbides. The cyclic stress response behavior of the alloy was found to depend on the prior microstructure, testing temperature, and strain rate. A softening regime was found to be associated with shearing of ordered gamma-prime that were either formed during testing or present in the prior microstructure. Various manifestations of dynamic strain aging (DSA) included negative strain rate-stress response, serrations on the stress-strain hysteresis loops, and increased work-hardening rate. Fatigue life increased with an increase in strain rate from 3 x 10 to the -5 to 3 x 10 to the -3/s, but decreased with further increases in strain rate. At 723 and 823 K and low strain rates, DSA influenced the deformation and fracture behavior of the alloy. (AIAA)