Effect of microstructural evolution during melt pool formation on nano-mechanical properties in LPBF based SS316L parts

Abstract

Laser Powder Bed Fusion (LPBF) based SS316L parts have a wide range of industrial applications, mainly due to their high strength and good structural integrity. However, there is a lack of nano-mechanical studies related to microstructural evolution. The SS316L cubes were examined for grain orientation and phase transformation with the help of OM and FESEM with EDX analysis. Cellular and columnar grains were substantiated by FESEM with EDX. Further, the δ ferrite and γ austenite phases occurrence was evident in XRD analysis. The orientation of grains was further examined through EBSD analysis. The microstructural transformation was substantiated by mapping based on modulus. Cellular grains showed a maximum hardness of 6 Gpa, whereas the transverse columnar grains displayed a minimum elastic modulus of 105.8 GPa. Nano-wear and scratch analysis predicted the functions caused by the occurrence of cellular dendritic microstructure, and the topographic wear and scratch tracks confirmed the soft nature of transverse columnar grains by forming more pile-up of materials. Strain Rate Sensitivity (SRS) of the SS316L specimens was analysed based on three different strain rates (4.1 ×10−5 s−1, 2.08 ×10−4 s−1 and 3.3 ×10−4 s−1). It was concluded that the LPBFed SS316L parts possessed a negative strain rate. In contrast, the simultaneous attainment of maximum Ultimate Tensile Strength (UTS) and ductility was possible in the quasi-static strain rate.