Melting behavior of VNbMoTa particle and its influence on microstructure and mechanical properties of laser additively manufactured nickel matrix composites

The currently used reinforcing particles in the additively manufactured nickel matrix composites (NMCs) are limited to non-deformable particles, largely restricting the advancement of novel composite materials. High entropy alloy is a kind of reinforcing particles possessing tremendous potential, however, its application in NMCs has not been realized hitherto. In this work, the ductile VNbMoTa is chosen as the reinforcing particle, and the feasibilities of its employment in two printing processes (laser directed energy deposition, LDED and laser powder bed fusion, LPBF) of Inconel 625 are investigated in detail. The numerical simulation is used to compute the melt pool morphology and the melting time of the VNbMoTa particle. The results demonstrate that the VNbMoTa particles are completely melted in the LDED process, while preserved in the LPBF process, which is ascribed to the longer time for melting offered in the former melt pool. Additionally, the unmelted VNbMoTa particles are conducive to refining grains and inducing equiaxed grain formation, while the fully melted VNbMoTa particles have little effect on grain structure. The main reason lies in the fact that the unmelted VNbMoTa particles can enhance the heterogenous nucleation to induce more new grains formation and hinder the movement of the grain boundary to suppress the grain coarsening. The LPBF-processed NMCs demonstrate excellent strength-ductility synergy with the yield strength of 1083.7 ± 19.3 MPa and the elongation of 12.1 ± 2.2 %. The hetero-deformation induced strengthening effect caused by the ductile VNbMoTa particles attributes to the outstanding yield strength of the LPBF-processed NMCs.