Irradiation Damage Mechanism of Multicomponent Transition Metal Carbides 

The development of advanced Generation-IV nuclear reactors has put stringent requirements on structural materials, which need to endure high temperatures and high irradiation doses. New materials, including alloys and ceramics that can fulfill these requirements, are urgently needed. Inspired by the concept of entropy stabilization in recently developed high-entropy alloys (HEAs), entropy-stabilized multicomponent transition metal carbides (MTMCs) have received increasing attention due to their unique physical properties, such as low thermal conductivity, high nano hardness, good oxidation resistance, and outstanding irradiation resistance. In these MTMCs with rock-salt structures, multiple principal transition metal elements randomly occupy the cation lattice positions, resulting in extreme chemical disorder and associated local lattice distortions. Similar to HEAs, it is expected that the chemical disorder has profound influences on the irradiation response of MTMCs. However, the role of disorder and the irradiation damage mechanism of MTMCs are still elusive so far, though good irradiation resistance in some MTMCs has been reported in recent experiments. Particularly, how a mixture of the disordered cation sublattice and the ordered C sublattice may contribute to the good irradiation performance of MTMCs remains a mystery. In this proposed research, we aim to reveal the irradiation damage mechanism of MTMCs by means of computational simulations. Particular emphasis is put on the role of compositional complexity. By systematically studying the (Nb0.25Ta0.25Ti0.25Zr0.25)C system and its derived subsystems, including binary, ternary, and quaternary MTMCs, we will address three crucial scientific issues regarding the irradiation performance of MTMCs. First, we will evaluate the influence of element number and elemental species on the stability of MTMCs. With the stable phases, we will explore the effects of compositional complexity on the structural properties, lattice distortion, thermal conductivity, and bonding characteristics in different MTMCs. Second, we will reveal the defect energy landscape and defect evolution mechanisms in different MTMCs, uncovering the governing factors of defect behavior. Based on these results, finally, we will propose possible ways to tailor the composition and concentration of MTMCs so as to further improve their irradiation resistance. For all these tasks, we will exploit the effects of off-stoichiometry and reveal its impact on the properties of MTMCs. The successful implementation of this proposal will lead to a comprehensive understanding of the irradiation response of novel MTMCs, which will significantly promote the design and development of irradiation-resistant carbides. Ultimately, the outcome will provide essential guidelines for further R&D of advanced ceramics for future nuclear systems.