Characterization and analysis on micro-hardness and microstructure evolution of brass subjected to laser shock peening

Abstract

This paper is concerned with the effect of laser shock peening on micro-hardness and microstructure of brass. In order to study the plastic deformation behaviors of brass, laser shock peening with 1, 2, and 3 impacts at pulse energy of 6.5 J were performed in this experiment respectively. The micro-hardness distribution in the near-surface layer is performed by hardness tester, and the microstructure in the surface layer is determined by X-ray diffraction and transmission electron microscopy. The results indicate that higher surface micro-hardness of brass after laser shock peening impacts is induced comparing with untreated brass. Additionally, increasing the impact times of laser shock peening, the surface micro-hardness improves correspondingly. Combined with transmission electron microscopy analysis, the determinate factors for variation of surface micro-hardness owes to the twins spacing and grain refinement induced by laser shock peening. The formation and interaction of surface mechanical twins are accompanied by improving in surface strain and strain rate. The equiaxed grains with an average size of 70–100 nm are generated in the top surface layer after 3 laser shock peening impacts. Furthermore, the grain refinement mechanism in the top surface layer subjected to laser shock peening is summarized as follows: (i) parallel mechanical twins are generated due to the effect of strain deformations induced by laser shock peening; (ii) mechanical twins are subdivided into secondary twins with the formation of dense dislocation tangles at the mechanical twins boundaries; (iii) twins interaction in different directions refine the grain into nano-scale equiaxed grains.