Quantifying microstructural contribution to yield stress and strain hardening of Ni20Cr alloy manufactured by laser powder bed fusion with different volumetric energy densities

Abstract

Laser powder bed fusion (LPBF) process is an additive manufacturing technique that focuses on intricate metal fabrication using laser processing of metallic powder. Various processing parameters like laser power, scanning speed, and hatch spacing giving out unique applied volumetric energies are involved in such fabrication. Those varied energies bring about microstructural changes leading to modifications in mechanical response such as yield stress and strain hardening behaviour. In this work, we investigated the influence of volumetric energy density on the aforementioned mechanical properties of a Ni-20 wt%Cr alloy manufactured via LPBF. First, an analytical model was employed to study the contribution of each microstructural feature on yield stress of LPBF samples. Dendritic cellular structures (and their sizes) are found to be the most important feature to govern this parameter. The Kocks-Mecking model was further extended to associate the different strain hardening mechanisms with dislocation production and interaction mechanisms via different channels like dendritic cellular structures, grains and forest dislocations. The production of dislocation via dendritic cellular structures is also the most significant mechanism for unique hardening behaviour in LPBF alloys. A modified equation of dislocation production mechanisms is finally proposed to simplify the application of this model for modelling the mechanical behaviour in tension of LPBF Ni20Cr.