Microstructure changes and mechanical properties of U-2Nb alloy induced by shot peening treatment

Abstract

The microstructure changes and mechanical properties of dual-phase U-2 Nb alloy subjected to shot peening treatment (SPT) were investigated. SPT induced severe plastic deformation in the U-2 Nb alloy surface, and a gradient nanostructure was formed on the surface with the grain size ranging from nanocrystallization structure to coarse grains from the surface to the matrix. The results showed that both the α phase with an orthorhombic crystal structure and the γ phase with a body-centered cubic structure in the surface layer of the U-2 Nb alloy were refined to nanocrystals with an average nanocrystallization structure size of 63 nm. Due to the concentration of stress at the α/γ interface and grain size effect, the refinement of the α phase matrix occurred before γ phase. Furthermore, dislocation slipping caused by deformation, rather than deformation twinning, played a key role in the grain refinement of U-2 Nb alloy. Microhardness and tensile tests showed that both surface microhardness and tensile strength were improved after SPT.