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