(CrVW)(1-x)(TaTi)x, (x = 10 and 20 at.%), high entropy alloys as thermal barriers for nuclear fusion reactors
Due to the extreme operating temperatures in nuclear fusion reactors, current materials exhibit a substantial mismatch in mechanical and thermal properties between the tungsten plasma-facing material and the CuCrZr heat sink cooling system. Therefore, a thermal barrier interlayer is required to guarantee continuous operation. In this work, (CrVW)(1-x)(TaTi)x alloys, where (x = 10 and 20 at.%), were studied to be applied 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 for 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)20 indicate that the ordering observed here is stronger than that for (CrWV)90(TaTi)10. Moreover, both systems display a bcc type structure, and heat treated samples exhibit phase growth and a microstructure with three phases. The thermal diffusivity values increase as the temperature rises, reaching low values compared to pure W and CuCrZr.