Effect of pulsed laser irradiation on the coincidence site lattice grain boundary of 316L stainless steel

The work aims to improve the intergranular corrosion resistance by increasing the proportion of coincidence site lattice (CSL) grain boundaries and reducing the proportion of random grain boundaries in 316L stainless steel. The surface of SUΣ316L austenitic stainless steel was irradiated by femtosecond and nanosecond laser with Nd:YAG laser at suitable temperature. The grain boundary character distributions of irradiated samples were analyzed by electron backscatter diffraction (EBSD) to study the effect of different laser irradiation conditions on the grain boundary. In addition, the crystal defects and Σ3 grain boundaries in the pulsed laser irradiation sample were observed under a transmission electron microscope (TEM). Compared with non-irradiated specimens, the proportion of the Σ3 grain boundary of specimens under femtosecond laser irradiation at 723 K increased by 2.88% and random grain boundary decreased by 4.24%; Compared with non-irradiated specimens, the proportion of the Σ3 grain boundary of specimens under nanosecond laser irradiation at 723 K increased by 10.78% and random grain boundary decreased by 9.97%; The proportion of the Σ3 grain boundary of specimens under nanosecond laser irradiation at 773 K increased by 12.52% and random grain boundary decreased by 10.68%. TEM images showed that there were a large number of stacking fault tetrahedrons in the pulsed laser irradiated sample at 773 K, but few such defects were found in the step of twin nucleation. The change of CSL grain boundary ratio is mainly related to grain boundary migration and twin formation, in which the energy generated by the pulse laser irradiation provides favorable conditions for the grain boundary migration in the skin layer of specimens, and the crystal defects caused by pulsed laser irradiation might promote the nucleation and growth of twins during grain boundary migration. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.