Bi-Continuous W-Rich Refractory High Entropy Alloy-Cu Composite: Toward Material Innovation of Nuclear Reactor Coolant System.

Abstract

Refractory high-entropy alloys (RHEAs) are considered promising candidate materials for next-generation nuclear reactors due to their superior mechanical strength, irradiation resistance, and thermal stability at high temperatures. However, the significant positive heat of mixing between refractory alloying elements and Cu, commonly used in cooling systems, poses challenges in forming composite structures. This study addresses the issue using a liquid metal dealloying (LMD) process. A precursor alloy (WTaVTi) with a directional dendrite-interdendrite structure is fabricated and reacted with molten Cu at 1200 °C for 96 h. This approach produced a RHEA-Cu composite with a stable interface between RHEA (W_31.5Ta_30.9V_21.4Ti_14.3) and Cu, featuring a spontaneously formed W-rich interlayer that enhances interfacial bonding. The composite showed excellent irradiation resistance, with 30% less swelling under α-ion irradiation than pure W. It also exhibited low thermal conductivity at room temperature, but reached ≈120 W m^-1·K^-1 at ≈650 °C, surpassing pure W. This temperature-dependent rise in κ, with a positive gradient of +0.075 W m^-1·K^{- 2}, is attributed to decreasing diffuse mismatch at elevated temperatures. The large-scale reaction and stable microstructure achieved through LMD process highlight its industrial potential. This work offers a strategy for developing high-performance materials by combining RHEA's radiation resistance with Cu's thermal conductivity for extreme environments.