Rapid penetration of bismuth from solid Bi2Te3 along grain boundaries in Cu and Cu-based alloys

As well known, bismuth rapidly penetrates into copper grain boundaries at about 550 °C and embrittles copper. In the experiments, the authors have used solid Bi2Te3 for the embrittlement of pure copper and copper-based solid solutions containing iron and silver. The investigated alloys were heated in the closed volume together with Bi2Te3 for a short time (5–90 min) at 570 °C in the hydrogen atmosphere. Bi2Te3 did not contact with copper samples during annealing. After that, the samples were bent and grain boundary cracks were formed (with the depth about 10–500 μm). Experiment showed that silver accelerates the embrittlement in the contrast to iron. The cracks in the silver–copper alloys were deeper than in the iron–copper ones. It was assumed that the depth of cracks is equal to the penetration depth. The reasons for this phenomenon were discussed in terms of the impurities effect on the grain boundary segregation.