High-Cycle Fatigue Behavior of the Ultrafine-Grained Commercially Pure Zirconium by ECAP plus RS Process

Ultrafine-grained commercially pure Zr (UFG Zr) was fabricated by equal channel angular pressing (ECAP) coupled with subsequent rotary swaging (RS). The tensile properties and fatigue behavior of the commercially pure Zr with ultrafine-grained microstructure were investigated, and the results were compared with those of the commercially pure Zr with coarse-grained counterpart. Fracture surfaces were examined to study the fatigue fracture failure mechanism using SEM. The result shows that the ultimate tensile strength of UFG Zr is obviously higher than that of the coarse-grained Zr (CG Zr) at room temperature, while the CG Zr exhibits a higher fracture elongation. The fatigue life of UFG Zr is significant higher than that of CG Zr. The relationship between the applied stress (sigma(a)) and cycles to failure (N-f) is determined as: sigma(a)=750N(f)(-0.06). The conditional fatigue limit of UFG Zr is about 285 MPa, which is improved by 70% compared with that of CG Zr. The fractography analysis reveals that fatigue cracks mainly initiate from the surface of the UFG Zr specimen. The spacing of the fatigue striations of UFG Zr is smaller than that of CG Zr, which indicates that the crack propagation rate of UFG Zr is lower than that of CG Zr.