Effects of in situ phase reaction of η M12C and M6C on microstructure and mechanical properties of tungsten heavy alloy via spark plasma sintering

Abstract

Spark plasma sintering (SPS) which densifies metallic or ceramic powders in few minutes can reduce sintering temperature, increase relative density, and inhibit grain growth in the consolidated materials. The phase reaction during the short SPS process is often ignored. In this work, a very important tungsten heavy alloy (WHA), 90 W − 7Ni − 3Fe (wt%) alloy, is taken as a typical example to demonstrate how in situ formation of η M12C or M6C influences the microstructural evolution and mechanical strength of the alloys SPSed at 1000–1200 °C through experimental characteristics combined with first−principles calculation. The results show that the in situ phase reaction from η M12C to M6C carbides plays a key role in the mechanical properties of WHAs, or oven more important than the relative density and grain size. The phase reaction from η M12C to M6C not only alters the phase composition of WHAs, but also lead to distinct interface relationship among matrix W, binder γ − (Ni, Fe) and η carbide phases. A maximum bending strength of 1268 ± 73 MPa was achieved after the phase reaction at 1200 °C, despite the lower relative density (95.8 ± 0.7%), smaller Young's modulus (209 ± 11 GPa) and bigger grain size (2.6 ± 1.0 μm).