Plastic deformation behavior and strengthening mechanism of SLM 316L reinforced by micro-TiC particles

Abstract

In this work, the integrated study on the microstructure evolution, plastic deformation behavior, and strengthening mechanism of Selective Laser Melting (SLM) 316L austenitic stainless steel (ASS) reinforced with micro-TiC particles was investigated. The results indicated that there were lots of small angle grain boundaries in SLM 316L ASS, and the high dislocation density and component segregation of the cellular dislocation structure resulted in a good combination of high strength and good elongation in performance. The tensile strength, yield strength, and elongation of SLM 316L ASS were 682 MPa, 571 MPa, and 49.9%, respectively. The addition of TiC reinforced particles induced microstructure evolution, including grain refinement, reduction of epitaxial columnar dendrites, reduction of low angle grain boundary (LAGB) ratio and increase of Σ3 (60°/<111>) twin boundaries. Through the effects of grain refinement strengthening, Orowan strengthening, and dislocation strengthening, SLM 316L-2TiC showed a higher tensile strength of 1021 MPa and higher yield strength of 809 MPa, while maintaining an elongation of 30.8% due to the suppression of plasticity by twinning induced plasticity (TWIP) effect. Although nano-reinforced particles were commonly used to improve mechanical properties, in our work, we chose to add micrometer-sized TiC particles, and the strength of the SLM 316L-2TiC metallic matrix composites (MMCs) exceeded the previous reports of adding nanoparticles. The reason was that the small contact angle between TiC and 316L provides good wettability between the particles and the melt, and the selection of laser processing parameters ensures good bonding between TiC particles and the substrate.