Fine-grained 93W-4.9Ni-2.1Fe alloy with ultrahigh yield strength prepared via low temperature sintering of W nanocomposite powder

Abstract

In this study, to obtain tungsten heavy alloy (WHA, 93W-4.9Ni-2.1Fe) with fine grain, high density and enhanced strength, W–Ni–Fe nanocomposite powder with high sintering driving force and small composite scale was designed and prepared. The effects of sintering temperature on the microstructure and properties of WHAs were systematically investigated. At a relatively low temperature of 1300 °C, WHAs with both high relative density of 98.0±0.31% and fine grain size of 2.07 μm were obtained, which was much smaller than that of traditional WHAs (30–60 μm). This special microstructure made it simultaneously achieve excellent compressive yield strength (1555 MPa), high strain-to-failure (over 40%) and hardness (480 HV0.5). This ultrahigh yield strength was about 2 times as the conventional WHAs with lager grain size. With the further increase of temperature to 1450 °C, the grain size of W grew significantly from 2.07 to 6.57 μm and the yield strength decreased remarkedly to 947 MPa. It was found that the W phase had good interfacial bonding with the γ-(Ni, Fe) matrix phase and the enhanced mechanical properties were mainly contributed by the small grain size and high ratio of phase boundary, which can significantly improve the storage capacity of dislocation.