Microstructure and mechanical properties of a Monel K-500 alloy fabricated by directed energy deposition

Directed energy deposition (DED) is a mainstream metal additive manufacturing technique that can fabricate near-net-shape components and repair damaged parts with a high build rate. Monel K-500 is a Ni-based alloy widely used for marine and offshore applications because of its excellent corrosion resistance and good com-bination of strength and ductility. In this study, laser-assisted DED (L-DED) was used to print Monel K-500 parts from powder. The key process parameters, including the laser power and scanning speed, were optimized to obtain single beads with desirable geometry and blocks with nearly full density (>= 99%). The block samples printed by L-DED exhibit-20% higher ultimate tensile strength and-60% higher elongation to failure than their conventional cast counterparts. From the microstructure examination, it is found that the parts printed with a low laser power have fine grains and an alternating equiaxed/columnar-grain sandwich structure with high tensile strength. In contrast, those printed with a high laser power have coarse columnar grains with a strong < 001 > texture but low tensile strength. The mechanism accounting for the grain structure evolution was studied by computational fluid dynamics and cellular automata simulations. The anisotropy in mechanical properties is mainly attributed to the difference in grain boundary strengthening effects. Moreover, the increase in hardness and tensile strength of the heat-treated samples is attributed to the precipitation hardening effect. This work exemplifies how the process parameters can be tuned to control the grain texture to achieve superior mechanical properties for parts of Monel K-500 and other metals printed by L-DED.

Automated summary

Directed energy deposition (DED) is a mainstream metal additive manufacturing technique that can fabricate near-net-shape components and repair damaged parts with a high build rate. This study utilized laser-assisted DED (L-DED) to print Monel K-500 parts from powder, optimizing key process parameters to achieve desired geometry and nearly full density. The resulting samples exhibited higher ultimate tensile strength and elongation to failure compared to their cast counterparts. The difference in grain structure, attributed to the process parameters, accounted for the anisotropy in mechanical properties. This work demonstrates the control of grain texture to achieve superior mechanical properties in metal parts printed by L-DED.