Investigation of defects and nanoparticles with martensitic phase transformation in surface nanostructured 316L stainless steel by slow-positron beam

In this article, we investigated the defects introduced by surface mechanical attrition treatment by Doppler-broadening spectroscopy of positron annihilation radiation in surface-nanostructured 316L stainless steel. Through the measurement of different thinning layers in the samples treated for 15 min, the slope of line shape parameter S versus wing parameter W curves showed three different values with depth responding to the change of defect configuration. An unusual change of S and W parameters near the surface was mainly from the effect of quantum-dot-like state caused by the formation of nanoparticles. Based on the change of S ˜ W with depth, the martensite phase transformation induced by strain could be estimated to occur within a depth of 35 µm.