Mitigation of metal whisker growth from MAX phases by A-site alloying strategy

Abstract

The A-site alloying strategy has been recognized as an effective approach to tailor the properties of MAX phases. Herein, the whiskering behaviors on Ti2(Sn1−x, Gax)C (x = 0–1), a group of solid solutions between Ti2SnC and Ti2GaC, were investigated to explore the possibility of mitigating metal whisker growth from MAX phase by A-site alloying strategy. The whisker cultivation experiments suggested that the Ga alloying at A-site of Ti2SnC can significantly reduce the density of Sn whiskers observed on sample surface, which got completely eliminated when the ratio of Sn/Ga was lower than 0.25. Afterwards, the first principles calculation on the solution and diffusion behaviors was performed to elucidate the mitigation mechanism behind. The results implied that the Sn atoms feeding whisker can only diffuse through the Sn part of the A-element layer in Ti2(Sn1−x, Gax)C. In addition, the Sn vacancy formation energy as well as the migration barrier was found to be elevated with the presence of Ga substitution. Consequently, the diffusion paths of Sn atoms, which played a significant role in realizing the matter transfer during the whiskering process, got narrowed (reducing accessible paths) and rugged (rising motion barrier) by the A-site Ga alloying atoms in Ti2(Sn1−x, Gax)C.