Microstructure and High Temperature Mechanical Properties of IN718 Fabricated by Metal Injection Molding

Metal Injection Molding (MIM) is an advanced manufacturing technique that integrates the methodologies of plastic injection molding and powdered metallurgy. The MIM process is used in aerospace, medical devices, and automotive industries to produce high-precision complex three-dimensional components. In this study, IN718 alloy was fabricated using the MIM process, and its microstructure, and high-temperature mechanical properties were analyzed and compared with Selective Laser Melted (SLM) IN718 alloy specimens in as-built and heat-treated conditions. Tensile testing revealed that the yield strength of MIM IN718 was similar to that of SLM IN718 in the as-built condition. However, in the heat-treated condition, the yield strength of MIM IN718 was significantly lower than that of the SLM specimens. Additionally, the ductility of MIM IN718 was found to be considerably inferior to that of SLM IN718 in both conditions. This reduction in yield strength and ductility in MIM IN718 was primarily attributed to the formation of Al2O3 due to oxygen contamination. The Al2O3 acted as heterogeneous nucleation sites for brittle Nb-rich carbides, which served as crack initiation points. Furthermore, the presence of these Al2O3 particles and Nb-rich carbides suppressed the formation of the γ′/γ′′ strengthening phases by consuming the necessary forming elements, thereby reducing the overall strength of the material.