Enhanced density and fine W particles of W-7Ni-3Fe alloys prepared by binder jetting additive manufacturing with a two-step sintering strategy

Abstract

Binder jetting (BJ) additive manufacturing has emerged as a potential technique for the fabrication of complex tungsten heavy alloy (WHA) parts due to high efficiency and low cost. However, due to the low green density, high sintering temperature or long holding time is required to achieve densification of the BJ WHA samples. This could also lead to excessive growth of W particles, which compromises their mechanical properties. To address these issues, a two-step sintering strategy was proposed in this study to enhance sintering densification and refine W particles. The densification, microstructure evolution, and tensile properties of BJ W-7Ni-3Fe alloys manufactured by two-step sintering (TSS) were investigated and compared with those fabricated by one-step sintering (OSS). Notably, at a sintering temperature of 1520 °C, the TSS samples exhibited a 5.0 % enhancement in density and a 15.9 % reduction in W particle sizes in comparison to the OSS samples. Meanwhile, the mechanical performance of the TSS samples was significantly improved, with increases of 62.8 % in hardness, 7.6 % in yield strength, 14.2 % in ultimate tensile strength, and 32.7 % in elongation, respectively. Furthermore, the relationship between mechanical performance, porosity, and microstructural parameters was analyzed in detail. Linear relationship between microstructural parameters and tensile properties was well fitted with porosity below 10 %. The as-reported TSS strategy offers great potential in obtaining BJ tungsten-based alloys and other refractory metals with high density and fine grains.