Effect of laser polishing parameters on residual stress, surface roughness, and microhardness of Ti6Al4V

The present study explores the impact of laser polishing (LP) process parameters of Ti6Al4V on the induced residual stress and surface properties. LP is a thermal process that involves melting a thin surface layer. The flows within the molten layer reduce the surface undulations caused due to initial surface roughness, resulting in a smoother surface. The material undergoes heating and cooling cycles in LP, resulting in residual stresses. This paper details the trade-offs between the residual stresses and the surface properties for various process parameters. The induced residual stresses show dependency on the cooling rate during the process, predicted using a validated finite element-based numerical model. For the set of process parameters, it was observed that the induced residual stress has no significant variation with a change in laser power. However, it increases with an increase in scan speed. A reduction of around 71% in surface roughness is observed at 100 W and 0.1 m/s, with a minimum induced residual stress of ~?372 MPa. However, the surface hardness is maintained for all sets of process parameters. A comparative study is also conducted for the induced residual stress between pure Ti and Ti6Al4V. It is noted that for all process parameters, the induced residual stress is higher for Ti6Al4V. However, pure Ti also follows the trend of variation of laser power and scan speed on the induced residual stress.