The Liquid Bismuth Penetration from Solid Bi2Te3: Grain Boundary Embrittlement and Effect of Impurities

Abstract

The liquid bismuth penetration from solid bismuth telluride (Bi2Te3) into grain boundaries of copper and copper-based solid solutions was studied. The experiments were performed at 570 oC in hydrogen atmosphere. The copper specimens were annealed from 10 to 90 minutes. Solid Bi2Te3 didn’t contact with copper specimens during experiments, so copper was covered by the decay products of Bi2Te3 through the gas phase. Liquid Bi penetration leads to grain boundary embrittlement of copper. We assumed that the depth of penetration is equal to the length of cracks which are formed after sample bending. It was shown that there is only bismuth at the grain boundaries while on the surface tellurium also exists. Bismuth concentration in the grain boundaries measured by Auger spectroscopy was about 10-20 at. % and the width of penetration channel was less then 10 nm. Bismuth covered the grain boundaries uniformly. Time dependence of the penetration depth was approximately parabolic. In the present work the effect of impurities (silver, iron) on grain boundary liquid bismuth penetration was studied also. It was shown that silver accelerates the penetration in contrast to iron. The probable reasons were discussed.