Evaluation of microstructure, mechanical properties, and corrosion resistance for Ti-doped inconel 625 alloy produced by laser directed energy deposition

Abstract

Additive manufacturing (AM) technology has opened up new opportunities to efficiently synthesize alloys and produce near-net shape components. In this study, Ti-doped Inconel 625 materials were produced to promote in-situ alloying between pre-alloyed Inconel 625 and elemental Ti powders by laser directed energy deposition, a predominant metal AM technique. The microstructure, mechanical properties, and corrosion resistance were evaluated before and after Ti addition and heat treatment (solutionization followed by aging). It was found that Ti addition alone did not cause significant change in microstructure. However, heat treatment caused migration of segregation species from interdendritic regions to intermetallic precipitates which occupy grain boundaries, and it modestly increased the average grain size for Ti-doped samples. Crystallographic analysis revealed a very strong cubic texture of Ti-doped Inconel 625 which only slightly decreased after heat treatment. Without heat treatment, the addition of Ti was not found to be beneficial to tensile properties of Inconel 625, due to the formation of thin Ti oxide films. However, the combination of Ti addition and heat treatment led to modest increase in hardness and tensile strength compared to the as-built Ti-free case, which is believed to result from the effects of Ti solid solution hardening, precipitation hardening, and dissolution of oxide films. Also, the combined effects can explain the pronounced increase of ductility for Ti-doped Inconel 625 after heat treatment, where the beneficial effect from oxide film dissolution could be dominant. In addition, under the as-built condition, corrosion resistance was found to be slightly higher for Ti-doped materials, but after heat treatment it dropped for Ti-doped materials while almost did not change for Ti-free case.