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

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 alpha phase with an orthorhombic crystal structure and the gamma 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 alpha/gamma interface and grain size effect, the refinement of the alpha phase matrix occurred before gamma 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. (c) 2021 Elsevier B.V. All rights reserved.