Rotation bending high cycle fatigue behaviors of TC21 alloy with bimodal microstructure

Abstract

The TC21 alloy has been extensively utilized in the aerospace structural components, making it crucial to investigate the fatigue damage mechanism of this alloy. In this study, a comprehensive investigation was conducted into the high-cycle fatigue damage mechanism of TC21 alloy under rotation bending, considering variations in primary equiaxed α (αp) phase contents and size in bimodal microstructure (BM). Results demonstrate that the TC21 alloy exhibits optimal strength-ductility and fatigue life at approximately 25 percent of the αp phase content. The content and dimension of the αp phase play a significant role in regulating the onset of fatigue fractures. Dislocation pile-up around the αp phase promotes the formation of microvoids and microcracks. Notably, when the content of the αp phase falls below 15%, there is an increased influence from secondary α phase (αs) on crack initiation. Moreover, excessive amounts of αp coupled with decreased size lead to a reduction in fatigue life. The aforementioned factors contribute to an intensified concentration of stress, facilitate a more uniform path for crack extension, and expedite the rate of fatigue crack propagation.