Deformation behaviour, microstructural evolution and mechanical property of the shaped parts fabricated by laser shock forming with different laser energy

Abstract

Laser shock forming (LSF) is a promising technique for fabricating thin-walled microparts with complex geometries in microelectromechanical systems (MEMS). This work investigated the formation of cup-shaped parts via LSF under varying laser energies (4, 5, and 6 J). Finite element analysis was employed to systematically model the material deformation behaviors during LSF. Subsequently, microstructure evolution and mechanical properties of both undeformed and LSFed samples were analyzed using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and nanoindentation test. The topography of formed cup-shaped parts indicates that the highest forming accuracy was achieved at 5 J laser energy. Microstructural characterization of both central and bottom corner regions of cup-shaped part revealed distinct trends with increasing laser energy. In the central regions, the average grain size first decreased and then increased at higher energy levels, while the proportion of low-angle grain boundaries (LAGBs) and geometrically necessary dislocation (GND) density increased then declined. In contrast, the bottom corner regions displayed progressive grain refinement along with a steady increase in LAGBs and GND density. Texture analysis indicated minimal changes in the central region, while the bottom corner subjected to 6 J exhibited a transition from the primary cubic texture {001} <100> to Goss texture {011} <100>. A substantial number of dislocation structures, including dislocation lines, tangles, walls, and cell blocks, were predominantly distributed across both the central and bottom corners of the LSFed cup-shaped parts. The part formed at 5 J demonstrated optimal mechanical performance, attributed to strain-hardening effect for copper, coupled with dislocation accumulation and twin formation. Notably, the microhardness values at the bottom corners generally exceeded those at the central locations.