Microstructural evolution of the surface layer of 316L stainless steel induced by mechanical attrition

Nanostructured surface layer was synthesized on 316L stainless steel by means of the surface mechanical attrition treatment (SMAT), the microstructural evolution was examined by using XRD and TEM. A grain refinement mechanism was proposed as follows: the dislocations in the austenite grains annihilate and recombine to form dislocation cells; the increment of strain and strain rate induces mechanical twinning, and lamellar microstructures form; the microstructures translate gradually from lamellar to equiaxed by means of the development of the dislocations in the twins, accompanying by the reduction of grain size and the increment of misorientations; finally, nano-scale grains with equiaxed shape and random crystallographic orientations form. Besides, the effects of staking fault energy on the deformation and grain refinement behaviors were discussed.