Deformation behavior of single crystal silicon induced by laser shock peening

Abstract

Laser shock peening can significantly improve the fatigue life of metals by introducing plastic deformation and compressive residual stresses near the surface. It has been widely applied on metals for surface strengthening. The plastic deformation behavior of brittle materials such as single crystal silicon under LSP is rarely studied. In the present research, the surface integrity and residual compressive stress of P-type single crystal silicon in <100> orientation shocked by LSP at imposed high temperature were measured to investigate the plastic deformation mechanism at high temperature and high compressive stress. The surface morphology of shocked silicon, observed using optical microscopy, showed that the cracks on the shocked silicon surface became less and the fragments were smaller while the temperature or the laser power density increased, which indicates that the plasticity of single crystal silicon is improved at high stress and temperature. However, the excessive laser power density would lead to local damage of the shocked silicon. The residual stress, measured using Raman scattering method, showed that the compressive residual stresses with magnitude of a few hundreds of MPa were introduced in the surface layer of silicon after LSP at imposed high temperature, and it increased with respect to the temperature and the laser power density. The experimental result indicates the material has experienced the plastic deformation and provides a potential processing method to improve the mechanical behavior of brittle material like single crystal silicon.