Spontaneous growth of Sn whisker on the hot-dipping Al[sbnd]Sn alloy coating on Fe-Cr-B cast steel

Abstract

Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.