Diffusion-controlled liquid bismuth induced intergranular embrittlement of copper

The consequences of the contact between liquid bismuth and a copper bicrystal are investigated at 500 degrees C. Atoms of bismuth are shown to penetrate and embritlle the copper grain boundary. Grain boundary concentration profiles of bismuth are obtained on fracture surfaces by both Auger electron spectroscopy and He4+ Rutherford backscattering spectroscopy. The maximum bismuth intergranular concentration is calculated from experimental data to be about 1.7 monolayers (near the liquid bismuth/solid copper interface). The overall profiles are significantly different from typical erfc profiles and an interpretation is proposed, based on the coupling effect between grain boundary diffusion and non-linear segregation. These results allow us to conclude on the absence of grain boundary wetting for the Cu/Bi system at 500 degrees C.