Production and characterization of the Cu5Cr35Fe35V20Mo5 high entropy alloy as a coupling interlayer for plasma facing components

This work presents the development of a high entropy alloy (HEA) that can act as a thermomechanical coupling layer in high heat flux components of next generation fusion reactor cooling systems, such as DEMO, which are based on W monoblocks coupled to CuCrZr components. A novel non-equiatomic HEA, Cu 5 Cr 35 Fe 35 V 20 Mo 5 was produced by arc melting, and its microstructure, mechanical and thermal properties were analyzed in the as-cast and aged states. Consistent with model predictions, the as-cast alloy exhibits a BCC single phase, and the presence of sparsely V-enriched submicron precipitates that are retained up to 700 °C. Heat treatment at 750 °C results in the formation of the sigma phase, which causes hardening of the alloy and promotes the formation of Cu precipitates. The alloy aged at 700 °C exhibits exceptional compressive ductility, even at room temperature, with serration behavior in the initial stages. Mechanical twinning was observed after nanoindentation and compression tests at room temperature. However, samples deformed at 500 °C did not show mechanical twinning, presenting a deformed microstructure in which slip deformation is present. The 700 °C aged material presents a good combination of thermal conductivity (15.5 W/K·m at RT), thermal expansion coefficient (11.2 × 10 −6 K −1 ) and mechanical properties to act as a thermal barrier interlayer between the W and the CuCrZr. Through the application of an analytical model, it has been demonstrated that the residual stresses generated in the W-HEA-CuCrZr system, in which the HEA has been used as a coupling interlayer, resulting from the maximum temperature variations allowed for the CuCrZr-based heat extraction system, Δ T ≈ − 350 °C, are below the yield stress of the materials, thereby ensuring the integrity of the components and improving the mechanical performance of the heat sink components of the divertor.