(CrVW)(1-x)(TaTi)x, (x = 10 and 20 at.%), high entropy alloys as thermal barriers for nuclear fusion reactors

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Due to the extreme operating temperatures in nuclear fusion reactors, current divertor monoblock materials, tungsten (plasma-facing material) and CuCrZr (heat sink), exhibit a substantial mismatch in mechanical and thermal properties. Therefore, a thermal barrier interlayer is required to guarantee continuous operation. In this work, (CrVW)(1-x)(TaTi)x alloys (x = 10 and 20 at.%) were studied for application as interlayers. Atomistic modelling using Monte Carlo simulations combined with a first-principles-based Cluster Expansion Hamiltonian has been performed as a function of temperature to predict the order-disorder transitions in the investigated high entropy alloys. Moreover, the experimental alloys were prepared by mechanical alloying followed by spark plasma sintering. Both alloy compositions display strong negative average chemical short-range ordering below 1500 K for the W-Ta and W-Ti chemical pairs, with an estimated transition temperature around 1300 K. Atomic structures obtained from Monte Carlo simulations for (CrWV)80(TaTi)20indicate that the ordering observed in this composition is stronger than that for (CrWV)90(TaTi)10. Moreover, both systems exhibit a bcc structure, and heat-treated samples exhibit phase growth and a microstructure with four phases. The thermal diffusivity increases with temperature, reaching lower values than those of pure W and CuCrZr.