Fracture behavior of ∑9 [1 1 0] asymmetric tilt boundaries in Cu doped with Bi

Considerable intergranular embrittlement of Cu takes place due to segregation of Bi on grain boundaries. However, the concentration of Bi for the grain boundary segregation varies depending on the character of the grain boundary. In order to examine the relationship between the embrittlement and the character of the grain boundary, the dependence of the behavior of fracture on the inclination angle was experimentally observed at temperatures of T = 298 and 77 K for the ∑9 [1 1 0] asymmetric tilt boundary in Cu doped with Bi. For the high-energy boundary, the brittle fracture occurs in an intergranular manner at both temperatures. On the other hand, for the low-energy boundary, the ductile fracture takes place in a transgranular manner at T = 298 K but in a transgranular or intergranular manner at T = 77 K. The concentration of Bi for the grain boundary segregation may be large in the high-energy boundary but small in the low-energy boundary. According to estimation, the thermodynamic interaction between Cu and Bi in the grain boundary is repulsive. Furthermore, the repulsive interaction is more notable for the high-energy boundary than for the low-energy boundary. Consequently, the fracture occurs brittlely for the high-energy boundary with a large Bi concentration but ductilely for the low-energy boundary with a small Bi concentration.