Synergetic effect of H and He impurities in Ti3AlC2: first principles calculations
Abstract
First principles calculations have been performed to investigate the synergetic effect of H and He impurities with vacancies in Ti3AlC2. The configurations and energetics of Hn–He–VAl complexes (n ≤ 4) and He–He/He–H/H–H interactions have been studied. It is found that the impurity H atom prefers to occupy the tetrahedral interstitial site (Itetr-3), but the He atom prefers to occupy the octahedral interstitial site (Ioct-4) in perfect Ti3AlC2. Within a pre-existing Al vacancy, the most favorable site for a He atom is close to tetr-site, meanwhile the H atom preferentially deviates from the vacancy center with the separation 1.3 Å along the 〈001〉 direction. He–H and He–He show a weakly attractive interaction, but weak repulsion occurs in the H–H interaction, which is different from the case of Ti3SiC2. The He–VAl complex plays an important role in the trapping of H atoms. The He–VAl cluster can trap up to three H atoms in the absence of H2 molecules, which leads to the formation of a H–He hybridized bubble. Thus, the He atom can subsequently suppress further aggregation of H atoms and block hydrogen embrittlement and volume swelling.