Abstract: In a fusion reactor, plasma-facing tungsten (W) materials inevitably suffer severe thermal shock, and the performance of W materials under repetitive high heat loads is one of the key concerns for long-term stable operation of the reactor. In this work, the microstructural evolution and thermal fatigue resistance of two representative W-0.5 wt.% ZrC (WZC) and W-1.0 wt.% Y₂O₃ (WYO) composites were investigated under cyclic heat loads. Due to the intrinsic properties of ZrC and Y₂O₃ particles such as coefficients of thermal expansion, particle size and distributions in W grains, the WZC composite exhibited a better thermal shock resistance than WYO. After thermal loads with the absorbed power density (APD) ≥22 MW/m², WYO showed obvious grain growth, Y₂O₃ particles shedding and degradation of mechanical properties. While, in the case of WZC, these damage behaviors only occurred when APD≥25 MW/m². Furthermore, an interesting crack mechanism in W composites was revealed due to interface debonding and progressive shedding of second-phase particles from the W matrix. The microstructures and tensile properties of the thermally loaded WZC and WYO specimens were also investigated and the correlations between the microstructure evolution and performance degradation are demonstrated. The results are useful for evaluating the thermal fatigue resistance of oxide/carbide dispersion strengthened W composites and their application in future fusion reactors.

Key words: Tungsten, Thermal loads, Microstructure, Particle shedding, Mechanical properties