Impact of High-Energy Mechanical Activation on Sintering Kinetics and Mechanical Properties of UFG Heavy Tungsten Alloys: SPS Versus Sintering in Hydrogen
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.
KeywordsHeavy tungsten alloys Mechanical activation Spark plasma sintering Diffusion Grain boundaries Strength
This study has been funded by the Ministry of Education and Science of Russia (Grant No. 11.5944.2017/6.7).
The authors recognize N.Yu. Tabachkova of the National University of Science and Technology “MISiS” (Moscow) for help in analyzing XRD data.
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