Micromechanical Response of Additively Manufactured 316L Stainless Steel Processed by High-Pressure Torsion

Abstract

For the first time, the plastic deformation behavior of additively manufactured material processed by severe plastic deformation (SPD) is investigated. Herein, high-pressure torsion (HPT) is applied on 316L stainless steel (316L SS) fabricated by laser powder bed fusion (LPBF) to produce ultrafine-grained (UFG) and nanograined (NG) microstructures. Microscopy analysis reveals a final average grain size of ≈42 nm which is achieved upon torsional strain saturation after ten revolutions. In addition, microhardness mapping indicates significant hardness increase with the increasing number of HPT revolutions and saturates at ≈600 HV after ten revolutions. The evolution in plastic deformation mechanism is assessed by calculating the strain rate sensitivity (SRS), m, and activation volume, (Formula presented.) based on nanoindentation measurements at both constant and multiple strain rates. The estimated m values remain relatively consistent throughout all processing conditions, suggesting that superior strength can be achieved by HPT processing while maintaining reasonably high plasticity levels. Based on the calculated (Formula presented.) values correlated with microstructure evolution, it is reasonable to infer that the submicron- and nanoscale microstructural features play an important role in plastic deformation before HPT processing, whereas plastic deformation for all HPT processing conditions is significantly influenced by grain boundary (GB)-driven plasticity.