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

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 degrees 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 gamma' 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 gamma' 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.