Abstract
High-energy shot peening (HESP) was conducted on commercial pure Zr to generate a surface gradient nanostructured layer and compressive residual stress (CRS). The microstructure, residual stress, and fracture morphology were investigated by electron back scattering diffraction (EBSD), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD), respectively. Tensile fatigue tests were conducted and the fatigue property was presented through S-N curve. By the XRD measurement, the residual stress relaxation and the microstructure evolution on the HESPed surface were studied under different stress amplitudes. The results indicated that the fatigue limit of the HESPed sample was 23% higher than that of the as-received. The relaxation of residual stress was observed during fatigue loading; the initial relaxation rate was fast and the later was slow, accompanied by a similar degree of nanocrystalline coarsening and dislocation density reduction. A linear relationship between the surface residual stress and the number of cycles for the HESPed sample was quantitatively described. The higher the applied stress amplitude was, the faster the residual stress relaxation (RSR) was. The stress amplitude had an important influence on the relaxation rate, the degree of nanocrystals coarsening, and dislocation density. Local plastic deformation caused grain coarsening and dislocation density reduction.
Highlights
Owing to its combination of remarkable corrosion resistance, machinability, good mechanical property, and very low neutron absorption cross-section, zirconium (Zr) and its alloys are commonly used as fuel cladding and structural materials in nuclear reactors [1,2,3,4]
With the development of nanoscience and nanotechnology, surface nanocrystallization of metallic materials can be achieved by surface mechanical treatments such as High-energy shot peening (HESP) and surface mechanical grinding treatment [11]
The results revealed that stress relaxation started at a high rate at the initial stages of loading and gradually increased at higher number of cycles [19]
Summary
Owing to its combination of remarkable corrosion resistance, machinability, good mechanical property, and very low neutron absorption cross-section, zirconium (Zr) and its alloys are commonly used as fuel cladding and structural materials in nuclear reactors [1,2,3,4]. Different from laser surface treatment [8], electron beam surface modification [9], and micro-arc oxidation [10], the purpose of surface mechanical treatment technologies such as shot peening, hammering, and cold rolling is to introduce CRS and change the microstructure in the surface layer, and in turn, improve the fatigue life of components. Xie et al studied the RSR of the peened TC4 surface under cyclic loading, finding that RSR was mainly influenced by the original magnitude, the applied stress, and the cycling numbers [17]. Kim et al studied the RSR of shot-peened medium-carbon steel under a low-cycle and high-cycle fatigue regime and found stress relaxation rate depended on the applied strain [18]. There are no studies on the evolution of residual stresses induced by surface nanocrystallization treatment under tensile fatigue loading. The evolution of residual stress, dislocation density, and grains size in the surface layer during the fatigue loading was characterized
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
