Additive manufacturing of a Ni-20 wt%Cr binary alloy by laser powder bed fusion: Impact of the microstructure on the mechanical properties

Abstract

In the present work, microstructure and mechanical properties of a binary Ni-20 wt%Cr alloy manufactured by laser powder bed fusion process were investigated. It was shown that this alloy can be manufactured with a relative density above 99% in a specific range of volume energy density Ev (50–250 J/mm3). The solidification was characterized by the growth of dendritic cell-substructures. The primary dendrite arm spacing increased with the volume energy density, related to the cooling rate decrease. A precipitation of Cr-rich particles was depicted in the inter-dendritic spacing, consequence of the high cooling rate experienced by the melting pool, assisted by the internal stress coming from the high dislocation density present around the dendritic cells. Increasing Ev from 60 J/mm3 to 120 J/mm3 decreased the yield stress and the ultimate stress. Correspondingly, the ductility was enhanced but the fracture surfaces became progressively elliptical, reflecting a plastic anisotropy in specimens built with higher energies. The softening of the mechanical properties of the samples built with the highest Ev was explained by the evolution of texture and size effects related to grain size and primary dendrite arm spacing. However, electrical resistivity measurements also revealed an increase of the short-range order which involved a mechanical hardening and so counteracts in part this softening. Ni-20 wt%Cr alloys built by laser powder bed fusion exhibit mechanical properties lying in the same range as the alloys currently available on the market. This opens the way to obtaining complex structural parts using this alloy, with high-performance mechanical and electrical properties.