Trace Ce addition for inhibiting Bi segregation induced embrittlement in ultrahigh-purity copper

Bismuth (Bi), as an impurity element in copper and copper-based alloys, usually leads to the catastrophic intergranular fracture even with a ppm concentration. However, the intrinsic mechanisms of the embrittlement remain largely unclear and the control of such a brittleness has been rarely reported. Here, we investigate the influence of trace amounts of Bi on the ductility of ultrahigh-purity copper (99.99999%) at temperatures between room temperature (RT) and 900 °C. On this basis, the ductility improvement of CuBi alloy by adding different concentration of Ce is also systematically studied. Compared to the ultrahigh-purity copper, the Bi-containing alloy exhibits a remarkable decrease in ductility, with the severe reduction occurs at 450–900 °C. This is caused by the grain boundary (GB) segregation of Bi layers, which reduces the GB cohesion because of the weak BiBi bonds. However, after trace Ce are added, the ductility of CuBi alloy in the temperature range of 450–900 °C is significantly increased. The obvious enhancement is due to the reaction behavior of Ce and Bi to form the precipitated phases, as well as the preferential segregation of Ce to GBs and phase boundaries, which change the existing form of Bi in copper. Our findings provide a comprehensive understanding on the microstructural origin of Bi-induced GB embrittlement and an effective way for inhibiting such an embrittlement. •The ductility of ultrahigh-purity copper, CuBi and Cu-Bi-Ce alloys in the temperature range of RT–900 °C are systematically investigated.•The configuration of Bi atoms at GBs and the embrittlement of CuBi alloy between 450 and 900 °C are investigated.•The mechanism of ductility improvement due to the inhibition of trace Ce on Bi segregation is revealed.