Impact of High-Energy Mechanical Activation on Sintering Kinetics and Mechanical Properties of UFG Heavy Tungsten Alloys: SPS Versus Sintering in Hydrogen

Abstract

This paper is a study of sintering mechanisms, structure, and mechanical properties of ultrafine-grained (UFG) W-Ni-Fe tungsten heavy alloys. Powder particle sizes were controlled by mechanical activation (MA) of original coarse-grained components and by addition of ultrafine particles. W-Ni-Fe alloys were obtained by sintering in hydrogen and spark plasma sintering (SPS) in a vacuum. The dependence of UFG alloy density on sintering temperatures has been found to be non-monotonic with a maximum corresponding to the optimal sintering temperature. It has been demonstrated that the sintering activation energy of UFG alloys is significantly lower than that of coarse-grained alloys. It has also been demonstrated that the optimal sintering temperature of UFG tungsten alloys is lower than that of coarse-grained alloys by 400 °C. The reason for a lower optimal sintering temperature lies in a decreased activation energy of grain-boundary diffusion and formation of a non-equilibrium solid solution of Ni and Fe in the surface layer of α-W particles during high-energy MA. High-energy MA and SPS were used to obtain samples of ultra-strong tungsten alloys with high mechanical properties: macro-elastic limit – up to 2250 MPa, yield stress – up to 2500 MPa.