Residual stress distribution in a laser peened Ti-2.5Cu alloy

• Laser peening without coating done on Ti-2.5Cu at 6.97 GW cm− 2.
• Work-hardening and twinning (> 70% overlap) scaled with overlap rates.
• Thermal softening observed till a depth of 50 μm.
• Above 80% overlap, softening occurred till a depth of 1000 μm.
• Adiabatic heating and thermal softening contribute to overall softening.

The goal of the present study is to investigate residual stress distributions and the accompanying deformation mechanisms during the process of laser peening without coating (LPwC), carried out on a Ti-2.5Cu alloy at a fixed power density of 6.97 GW cm− 2 with overlap rates from 50 to 90% (in steps of 10%). Thermal softening near surface (confined to a depth of 50 μm) from laser beam-material interaction was observed. Work-hardening increased with increase in overlap percentage till 80%. The maximum residual stress was found to be − 889 MPa for an optimal 70% overlap. Twinning was found to increase with the increase in overlap rates, indicating the hardening of the sample. The combined effect of adiabatic heating and thermal effects at the surface due to laser beam-material interaction (propagating inside the material), results in the softening of the material. The softening was found to be only in the onset stage, without flow localization. Softening predominates hardening beyond the overlap rates of 80% and the implications for this towards multiple peening are discussed.