Comprehensive Assessment of Low Cycle Fatigue Behavior of Nickel-Base Superalloy Superni 263 in the Range 298–1023 K

Abstract

The effects of temperature on low cycle fatigue (LCF) behavior of Superni 263 superalloy in the solution annealed plus aged state were examined between 298 and 1023 K. The initial microstructure consisted of intragranular spherical γʹ (22 nm), intergranular M23C6 carbides and a few un-dissolved primary MC particles. Strain-controlled LCF tests were performed at a strain rate of 10−3 s−1. Correlations between the initial microstructure, macroscopic cyclic deformation, fatigue life, crack initiation and propagation modes, evolving deformation substructure and phase changes have been attempted. Cyclic stress response displayed a marked variation in its temperature dependence. In general, the alloy exhibited initial hardening followed by very slight softening up to 473 K, continuous hardening to a maximum stress in between 573 and 873 K, and initial hardening succeeded by rapid softening at and above 923 K. Dynamic Strain Ageing (DSA) was noticed during 573–923 K. In the DSA domain, the alloy exhibited pronounced cyclic hardening at 673 K, displayed planar slip, stacking faults, high dislocation density and shearing of γʹ. The macroscopic features revealed serrated flow in the plastic deformation portions of stress–strain hysteresis loops and inverse temperature dependence of maximum stress and inelastic strain generated at half-life. Fresh precipitation of γʹ occurred at 973 K and 1023 K during LCF testing while prior existing γʹ coarsened marginally above 923 K. The operating deformation mechanisms of γʹ were identified and correlated with microscopic and macroscopic aspects. LCF life displayed a maximum at ~ 473 K and the reduction in life above 473 K was attributed to the deleterious effects of DSA and oxidation.