Creep-fatigue deformation micromechanisms of a directionally solidified nickel-base superalloy at 850 degrees C

Abstract

In the present exploration, it was attempted to understand the creep‐fatigue (CF) deformation micromechanisms of alloy CM 247 DS LC by conducting low‐cycle fatigue (LCF) and CF tests employing strain amplitude ranging from 0.6% to 1.0% at T = 850°C in the air and performing extensive electron microscopic examinations. The cyclic life of the alloy lessens for all CF tests conducted at 1 and 5 minute dwell time in comparison to LCF tests. Transmission electron microscopy (TEM) examinations confirmed that during CF tests substructure consists of dislocation loop, mixed dislocations, and γ' rafting, a typical creep deformation signature of nickel‐base superalloys, it also consists of features observed during fatigue deformation such as anti‐phase boundary (APB)‐coupled dislocations inside γ' precipitates and local tangles of dislocations. This confirms that the deformation of CF‐tested specimens is ascribed to the synergistic effect of both creep and fatigue. This fact was further verified by scanning electron microscopic (SEM) examinations.