Flow behavior and microstructure evolution during dynamic deformation of 316 L stainless steel fabricated by wire and arc additive manufacturing

Abstract

Additively Manufactured structural components would often serve the impact environment while sufficient efforts have not been paid on their dynamic response. In this study, cold metal transfer wire and arc additive manufacturing (CMT-WAAM) process was used to fabricate 316 L stainless steel and initial well-aligned coarse austenitic columnar crystals with 〈100〉 texture along deposition direction were developed. Samples of as-built 316 L were subjected to dynamic compressions with various strain rates and strains by split hopkinson pressure bar (SHPB). The as-built 316 L dynamically exhibits ~50% higher yield strength and twice elastic modulus than quasi-static condition. Twinning acts as main deformation mode whereas strain induced martensitic transformation has not been found. Microstructure evolution upon progressive strains at similar high strain rates reveals continuously increase in the population of deformation twins associated with a gradual decrease in average twin thickness from 120 nm to 20 nm. Average twin thickness as the key physical parameter from evolving microstructures and flow behavior are well fitted using empirical equation. A careful texture analysis suggests a remarkable transition from initial 〈100〉 ||CD (compression direction) to the component 〈110〉 ||CD. Our findings provide the mechanistic insights into understanding the dynamic behavior of additively manufactured stainless steel.