Evolution of residual stress, free volume, and hardness in the laser shock peened Ti-based metallic glass

Laser shock peening (LSP) with different cycles was performed on the Ti-based bulk metallic glasses (BMGs). The sub-surface residual stress of the LSPed specimens was measured by high-energy X-ray diffraction (HEXRD) and the near-surface residual stress was measured by scanning electron microscope/focused ion beam (SEM/FIB) instrument. The sub-surface residual stress in the LSP impact direction (about − 170 MPa) is much lower than that perpendicular to the impact direction (about − 350 MPa), exhibiting anisotropy. The depth of the compressive stress zone increases from 400 μm to 500 μm with increasing LSP cycles. The highest near-surface residual stress is about − 750 MPa. LSP caused the free volume to increase and the maximum increase appeared after the first LSP process. Compared with the hardness (567 ± 7 HV) of the as-cast BMG, the hardness (590 ± 9 HV) on the shocked surface shows a hardening effect due to the hardening mechanism of compressive residual stress; and the hardness (420 ± 9 HV) on the longitudinal section shows a softening effect due to the softening mechanism of free volume.