The microstructure evolution, damage behavior and failure analysis of fine-grained W-Y2O3 composites under high transient thermal shock

Abstract

Extreme thermal environment, especially transient high thermal load, is one of the great challenges for plasma facing tungsten materials. In this work, the fine-grained W-Y2O3 composites fabricated by nano in-situ composite method were exposed to transient heat loading using electron beams. The microstructure evolution, damage behavior and failure analysis were investigated by experimentally combing with finite element modelling (FEM). Besides, the correlation among thermal shock resistance, microstructure and mechanical properties of the W-Y2O3 composites were initially analyzed. Results show the W-Y2O3 composites obtains superfine microstructure and coherent interface. The surface morphology evolves from smooth to roughness, cracks and melting as the power density increases. Simultaneously, four crack patterns of surface micro-cracks, crack networks, longitudinal cracks and internal transverse cracks were observed. The W-0.3 wt%Y2O3 composites exhibit superior resistance to crack formation attributed to excellent interfacial performance and diffuse Y2O3 hindrance. No obvious damage was found on the surfaces when the power density reached 600 MW/m2. With the increasing Y2O3 contents, the thermal resistance of W-Y2O3 composites significantly decreases. Finite element modelling (FEM) analysis shows that the surface damage is the most serious compared to the interior after thermal shock. The damage, especially cracks, are preferentially formed on the surface, and then migrate and expand to the interior. The damage and its evolution are attributed to the palstic thermal strain on the surface caused by thermal stress. Moreover, the higher the mechanical properties of W-Y2O3 composites, especially the high temperature yield stress and elongation, the better high thermal load resistance. These results should be of relevance for the optimum design of W plasma facing materials in future nuclear fusion reactors.