Materials Chemistry

Biography

Biography: Yuexia Wang

Abstract

Layered MAX phase ternary compound, where M is an early transition metal, A is a group A element, and X is either C or N, promised great applications in many applied fields because it combines ceramic and metallic properties. As an exemplar of MAX phase family, Ti3SiC2 exhibits a high melting temperature, high electrical and thermal conductivities, and an excellent resistance to oxidation and thermal shock. Particularly, it possesses unusual mechanical properties, such as easy machinability, a high Young’s modulus, which is thus considered as a candidate in advanced nuclear reactors. In this work, we investigated the effect of hydrogen and helium on the cleavage fracture of Ti3SiC2 in order to evaluate the reliability of Ti3SiC2 for use in nuclear industry. We have performed first-principles mechanical calculations within the density functional theory (DFT). It was found that Ti3SiC2 has the cleavage characteristics and the habit cleavage starts from Si-Ti interlayer because of relative weak Si-Ti bonding. Hydrogen and helium always accumulate along the Si layer. Helium decreases largely the critical stress of cleavage fracture of Ti3SiC2. In contrast, hydrogen does not efficiently affect the cleavage fracturing in Ti3SiC2. The difference between helium and hydrogen behaviors in Ti3SiC2 primarily originates from the difference of electronic hybridization with lattice atoms of Ti3SiC2 for helium and hydrogen. For helium, the neighboring Si atoms will be ejected by helium atoms, and the Si-Ti bonding will be broken, thus resulting in the cleavage fracturing. However for hydrogen, it is primarily hybridized with the s states of neighboring Si atoms, which does not severely disturb the p-d hybridization between Si and Ti atoms. Thus, the cleavage fracturing from Si-Ti interlayer is hardly aggravated in the presence of hydrogen. Fortunately, Ti3SiC2 has self-repair ability at the high temperature. It will desorb helium atoms at high helium pressure through Si layers. This behavior will alleviate the cleavage fracturing induced by helium. In summary, Ti3SiC2 may be a potential application material in light water or other fission reactors in the future.