Effect of laser shock peening without coating on fretting corrosion of copper contacts

Abstract

The effects of laser shock peening without coating (LSPwC) on the degradation of copper electrical contact was investigated. A Nd:YAG laser with laser energy densities of 5.3 and 10.6 GW/cm2 was used for the LSPwC process. Surface hardness was enhanced from 55 HV to 110 and 120 HV for the laser shock-peened copper at 5.3 GW/cm2 and 10.6 GW/cm2, respectively. Moreover, near the copper surface, LSPwC introduced the max. compressive residual stress of 387.5 and 385.5 MPa for laser energy densities of 5.3 and 10.6 GW/cm2, respectively. Electron backscatter diffraction and transmission electron microscopy revealed that LSPwC introduced dislocation rearrangement, deformation twins, and grain refinement. The laser shock-peened copper exhibited superior wear resistance compared with the base metal. During the fretting test, the wear loss of the base metal was 1.61 × 10-3 mm3, and this decreased to 0.99 × 10-3 and 0.94 × 10-3 mm3 for the laser shock-peened copper at 5.3 and 10.6 GW/cm2, respectively. Thus, the laser shock-peened copper maintained a low electrical contact resistance during the fretting test, resulting in electrical contact failure delay from 2790 cycles for the base metal to 5011 and 5210 cycles for laser shock-peened copper at 5.3 and 10.6 GW/cm2, respectively.