Abstract
In order to study the effects of vacuum environment and strain wave form on high temperature low-cycle fatigue properties of Hastelloy XR, a set of strain controlled fatigue tests were conducted with sawtooth type and strain hold type strain wave forms at 950°C in air and vacuum environments. The following conclusions were obtained;
(1) The effect of environment on life under symmetrical wave forms is as follows. The lives in vacuum are longer than those in air. The environmental dependence of fatigue life can be explained based on the properties of high temperature oxide scale and oxidation behaviors.
(2) The fatigue lives under sawtooth type wave forms decreased as follows; Fast-Fast>Fast-Slow≥Slow-Slow>Slow-Fast, and the life under strain hold with the same period decreased as follows; hold in compression>hold in both sides>hold in tension. The fatigue lives under symmetrical strain wave forms were affected more by the environment than that under asymmetrical waves.
(3) Intergranular failures dominated in both of the tested environments. The difference in environmental effect between two loading wave forms can be explained based on the damage model for unidirectionally accumurated strain due to grain boundary sliding.
