Mechanical Properties of Laser Shock-Peened Regions of SS316LN and SS304 Studied by Nanoindentation

Abstract

Nanoindentation has been used to evaluate various mechanical properties of affected regions of laser shock-peened (LSP) stainless steels, SS316LN and SS304 plates. Depending on the applied laser parameters (laser energy, pulse width), the hardness was varied in the range 3.5–6.2 GPa in comparison with the untreated sample hardness of 2.93 GPa for SS316LN. Similarly in SS304, the hardness has been improved to 5.73 GPa in comparison with the untreated specimen hardness of 2.57 GPa. The improvement in the hardness for the laser-treated stainless steel targets is attributed to various factors viz., increment in internal frictional stress, dislocation–dislocation interaction and solute–dislocation interactions. Effect of laser energy is not appeared in the hardness values but a difference in hardness values with the pulse width has been observed. The deformation characteristics such as strain rate sensitivity and activation volume were evaluated from the indentation creep data. Notable change in the strain rate sensitivity is not observed for the laser-treated samples in comparison with the untreated samples and the range of values measured between 0.01 and 0.02. The activation volumes for both the treated and untreated samples were in the range, 100–200 b3. There was a slight decrease in activation volume in the laser-treated samples. Several rate-controlling deformation mechanisms appear to be operative in these treated samples, in addition to the dislocation-based mechanisms.