Effect of Heat Treatment on the Microstructure and Mechanical Properties of W-7Ni-3Fe Tungsten Heavy Alloy Manufactured by Metal Injection Molding Process

Abstract

This study investigated the microstructure and room temperature mechanical properties of W-7Ni-3Fe (wt%) tungsten heavy alloy (as-fabricated) which was manufactured by metal injection molding (MIM). To identify the effect of heat treatment on the W-7Ni-3Fe alloy, its properties were compared after heattreatment (1,100 °C for 1 hour) in vacuum atmosphere. The initial microstructural observations confirmed that both the as-fabricated and heat-treated specimens were composed of W phase and γ(Ni, Fe) phase. Vickers hardness measurements were 363.7 Hv for the as-fabricated specimen and 387.2 Hv for the heat-treated specimen. Room temperature tensile strength was tested, and the yield strength of the as-fabricated and heattreated specimens were 698.3 and 714.0 MPa, and the ultimate tensile strengths were 760.8 and 960.0 MPa, respectively. The elongation of the two materials was 2.4% (as-fabricated) and 20.3% (heat-treated). It was found that additional heat treatment after MIM significantly improved the alloy’s mechanical properties. In addition, fracture surface observation results confirmed that the main crack propagated along the interface between the spherical W phase and γ(Ni, Fe) phase in the as-fabricated specimen, and traversed the W phase in the heat-treated specimen. Based on the above findings, this study also discusses the fracture mechanisms of tungsten heavy alloy manufactured with MIM. Key words: W-7Ni-3Fe, metal injection molding, tungsten heavy alloy, microstructure, tensile properties