The invention discloses a high strength and high entropy alloy NbMoTaWV and a preparation method thereof. Mechanical alloying and spark plasma sintering are used in this process. Compared with the traditional vacuum arc furnace melting casting method, the operation of the invention method is more convenient, the temperature required for forming is greatly reduced, the sintering time is short, and the block material with uniform composition and nearly full density can be obtained by sintering once, and the dendrite segregation of the alloy is eliminated, so that the grain is significantly refined, and the density of the alloy is 11.6 ~ 11.9g/cm3. The optimum compressive mechanical properties at room temperature are 2770MPa σ0.2, 3661MPa σ BC, 12.5% ε P at fracture. The compressive strength and plasticity of the alloy at room temperature are significantly improved, showing excellent comprehensive mechanical properties.
The selection of high entropy alloy element system mainly focuses on post-transition metals, such as Cr, Mn, Fe, Co, N1, Cu, etc. In 2011, Senkov 0.N. et al. first prepared a new high entropy alloy with niobium, molybdenum, tantalum, tungsten and vanadium high melting point metals as the main elements by casting method. Its microstructure is single-phase BCC structure, and the compressive yield strength at room temperature is 1246MPa and the maximum compressive strength is 1270MPa. The plastic strain at fracture is 1.7%, and the alloy can still maintain high strength at 600 ~ 1600°C, so it is very likely to become a new generation of superalloy, tools, molds and wear-resistant materials, widely used.
At present, high entropy alloys are mainly prepared by vacuum arc furnace casting. However, there are a series of difficulties in the preparation of NbMoTaWV alloy with high melting point and high entropy: due to the high melting point of the alloy (about 2673°C), the traditional casting method must overcome the problem of high heating temperature. In order to make the composition uniform, need to go through several remelting; Meanwhile, the NbMoTaWV alloy can be easily grown into coarse dendrites with an average grain size of about 80μπι. Dendrite segregation and other non-uniformity phenomena will inevitably occur in the solidification process of molten liquid, which will have a great influence on the performance of the final product.
