Effect of heat treatment on microstructure and mechanical properties of tungsten heavy alloy with a non-equiatomic Ni5.5Fe2.5CoCr high-entropy binder

Abstract

Tungsten heavy alloys (WHAs) hold extensive and promising application prospects in the defense industry as well as the aerospace filed because of their high melting point, high strength, and low thermal expansion coefficient. However, the grain size of WHAs prepared by conventional liquid phase sintering is coarse, which limits the further improvement of their mechanical properties. Designing high-entropy alloys (HEAs) as the binder phase provides a novel way to inhibit tungsten grain coarsening and improve the properties of WHAs due to the hysteresis diffusion effect of HEAs. In our previous research, a fine-grain and ultrahigh-strength WHA with non-equiatomic Ni_5.5Fe_2.5CoCr HEA as the binder phase was designed and successfully fabricated through the spark plasma sintering (SPS)method. In this study, vacuum heat treatment was adopted to further enhance the strength - toughness matching performance of the material. A systematic investigation was carried out on the impacts of the heat treatment process on the microstructure and mechanical properties of the 90W-Ni_5.5Fe_2.5CoCr alloy. The results show that the single - heat - treatment process exerts little influence on the microstructure and properties of 90 W-Ni_5.5Fe_2.5CoCr alloy. In contrast, the two - step heat - treatment process can remarkably optimize the distribution of the precipitated phases within the alloy. This optimization effectively enhances the plasticity of the alloy. Specifically, the fracture elongation can be increased from approximately 10 % to around 16 %. Moreover, it has been discovered that dislocations are predominantly distributed at the interface between the binder phase and the W phase. This distribution pattern is conducive to promoting the plastic - deformation capacity of the alloy.