Diffusion-Controlled Liquid Bismuth Induced Intergranular Embrittlement of Copper

Abstract

The consequences of the contact between liquid bismuth and a copper bicrystal are investigated at 500°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°C.

Evidence for a Diffusion-Based Mechanism of Liquid Metal Intergranular Penetration: Case Study of a Ni-Bi Model System

“…The level of saturation was previously estimated from AES quantitative measurements to be within the range 2-3 nm [12] and consequently the existence of nanometre-thick films was postulated in the present system. The formation of such films can be explained on the basis of the Fowler-Guggenheim segregation isotherm together with local equilibrium between grain boundary concentration and very limited bulk Bi solubility, using the formalism proposed in the case of Cu-Bi system [13]. The commonly admitted view of grain boundary penetration is that this is a phenomenon which occurs in some specific systems within the range of temperatures where grain boundary energy is higher than twice the solid metal / liquid metal interfacial energy [14].…”