Abstract: We developed a novel low-activation, ultrafine-grained W-Cr-V multicomponent alloy (MCA) with excellent thermal stability and desirable high-temperature strength. The as-sintered W₇₀Cr₁₅V₁₅ (at.%) alloy was mainly composed of a body-centered cubic (BCC) solid solution matrix with an average grain size of ∼0.45 μm, minor hexagonal close-packed (HCP) phase, and ultrafine oxides at grain boundary (GB) regions. The average grain size of the MCA was < 2 μm after heating at 1500 °C for 1 h, showing a high thermal stability of the microstructure. Accordingly, the estimated grain growth exponent n (∼7) and the corresponding activation energy (∼433 kJ mol^-1) of the MCA indicate that diffusion during the grain growth in the present W-Cr-V alloy is dominated by the GB diffusion. Such high thermal stability can be mainly attributed to the significant pinning effects from the in-situ formed oxides at GBs. Besides, the nonequilibrium segregation of Cr and V at GBs also contributes to the thermal stability of the alloy at temperatures of 1200 °C and below. Furthermore, the average high-temperature compressive strength of the alloy was over 1376 MPa at 1100 °C, mainly due to the prominent solid solution and GB strengthening which were still effective at the high temperature. The results indicate that the present low-activation W-Cr-V alloy system with exceptional thermal stability and high-temperature mechanical properties could be a promising candidate for structural materials in future fusion reactors.

Key words: Ultrafine-grain, Low-activation, Refractory multicomponent alloy, Thermal stability, Ultrahigh-temperature strength, In-situ second phases