Formation of nano-grains dominated by twin-twin intersection for a RASP-processed 316L stainless steel

Abstract

In this work, the formation mechanism of surface nano-grains was explored for a 316L stainless steel processed by a rotationally accelerated shot peening (RASP). The microstructural evolution below the processed surface was observed to reveal the refining behavior during the continuous impact deformation. The results showed that deformation ultrafine-twins were easily generated by one high-speed impact with the strain rate of ∼102–103 s−1. As it was impacted by the second ball, ultrafine-twin-twin intersections were appeared in the coupled domain, which was attributed to the accumulated strain induced by twice impacts, activating the bidirectional twinning. Twin–twin intersection can effectively divide the coarse-grains into smaller structures. When the impact number further increased, the average thickness of deformation twins decreased, and resulted in segmentation of original structures. Eventually, nano-grains were formed by nano-twin-twin intersections in the topmost surface. The average grain size of nano-grains is ∼30 nm. The current work clearly exhibited the surface microstructural evolution and revealed that twin-twin intersection was the dominated nanocrystallization mechanism for RASP-processed 316L stainless steel.

Keywords

• 316L stainless Steel
• Surface nanocrystallization
• Twin-twin intersection
• Rotationally accelerated shot peening