Laser shock peening induced surface nanocrystallization and martensite transformation in austenitic stainless steel

Surface nanocrystallization and deformation-induced martensite in AISI 304 stainless steel subjected to multiple laser shock peening (LSP) impacts were investigated by means of EBSD and TEM observations. A layer of isometric nanocrystalline with a size of 50-300 nm has been formed on the surface after three LSP impacts. And a grain refinement mechanism induced by ultra-high strain rate plastic (>10(7) s(-1)) deformation during multiple LSP impacts in AISI 304 stainless steel (AISI 304ss) is proposed based on the microstructural observations. Both multidirectional mechanical twins and multidirectional martensites bands led to grain subdivision at the top surface during multiple LSP impacts. (C) 2015 Published by Elsevier B.V.