Published online by Cambridge University Press: 01 January 1992
Low cycle fatigue (LCF) behavior of polycrystalline NiAl was investigated near the monotonic brittle-to-ductile transition temperature (BDTT) at plastic strain ranges of 0.5 and 1.0%. Between 600 and 700 K, NiAl exhibited rapid hardening for the first few cycles followed by a stress plateau and a subsequent return to hardening. Slip traces were observed on the gage surfaces of most LCF specimens using scanning electron microscopy (SEM). The fatigue properties in this intermediate temperature range (600 to 700 K) were found to be a logical transition between previously reported ambient and elevated temperature properties. Transmission electron microscopy (TEM) confirmed that the dislocations had typical <100> Burgers vectors. A cellular dislocation structure began developing before saturation was achieved. This structure transformed at longer lives to elongated cells and eventually to veins of dislocation tangles. The resulting dislocation morphology did not change from 600 to 700 K, but the dislocation density decreased noticeably.