Influence of microstructural change caused by cyclic strain on the low cycle fatigue strength of sintered molybdenum

Abstract

Low cycle fatigue tests of sintered molybdenum with a 70% reduction by hot rolling were performed in a vacuum at room temperature, 573, 773, 1073 and 1223 K in order to examine the influence of microstructural change on the low cycle fatigue strength. The molybdenum exhibited cyclic softening at the temperatures between 573 and 1073 K, though it did not indicate the softening at 1223 K because of static recrystallization. The cyclic softening occurred progressively in some parts of the specimen due to the dynamic microstructural change caused by cyclic strain. Dynamic recrystallization occurred at 1073 K apparently during low cycle fatigue tests, and this recrystallized grain grew with increasing cycles. The plastic deformation was consequently concentrated in the softening region of the specimen. Therefore, the low cycle fatigue lives of molybdenum tested at temperatures below 1073 K were shorter than those at 1223 K, while the specimens were recrystallized and deformed uniformly at 1223 K.