Study on Low-Temperature Sintering Behavior of 90W-7Ni-3Fe Alloys: The Influence of Sn Addition

In this work, we investigate low-temperature sintering behavior of the 90W-7Ni-3Fe alloy by introducing Sn. The 90W-7Ni-3Fe alloy with different Sn contents (0, 0.5, 1.0 and 1.5 wt.%) was fabricated via vacuum sintering at 1300 °C for 90 min. When 1 wt.% Sn was added, the liquidus temperature of the 90W-7Ni-3Fe alloy decreased from 1477 to 1265 °C, resulting in rapid densification (relative density increased from 77.77 to 98.59%) and an homogeneous liquid-phase sintered microstructure. Electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) observations revealed that, apart from W and the γ-(Ni, Fe) phase, a new Ni3Sn2 phase appeared in the matrix phase. Furthermore, we discuss in detail the formation of the Ni3Sn2 phase based on element selection theory, which can be associated with the larger atomic radius of Sn and with the negative enthalpy of mixing Sn and Ni. Excessive Sn content (1.5 wt.%) led to the increase in Ni3Sn2 phase, and this deteriorated the relative density and tensile strength of the alloy. The 90W-7Ni-3Fe alloy with the addition of 1 wt.% Sn exhibited a maximum tensile strength value (710 MPa), which was much higher than that of the 90W-7Ni-3Fe alloy that was obtained at 1300 °C. Our findings shed light on further research directions and developed a 90W-6.3Ni-2.1Fe-1Sn alloy for low-temperature sintering.