A Simple Evaluation of Grain Boundary Diffusion in Liquid Metal Embrittlement

Most works on liquid metal embrittlement up to 1960 are compiled by Rostoker et al. (1) They stated that grain boundary diffusion is not an origin of embrittlement, since its rate, in general, is too small. However, Waterhouse et al. (2), performing the experiment on 70/30 brass wetted with mercury, suggested that dissolution of zinc from grain-boundaries into mercury accelerates the degree of embrittlement. From a work on the Cu-2% Be alloy in the presence of a liquid 2% sodium amalgam, Rinnovatore et al. (3) found that the contact time of the liquid metal with the solid is a factor affecting the degree of embrittlement. Then, the extent of grain boundary diffusion of a liquid metal has to be determined. If the embrittling liquid is in the solid state at room temperature, the diffusion depth is easily determined by ordinary metallographic techniques, as done by Bishop et al. (4) Since mercury which is often used as the embrittling liquid is -still in the liquid state at room temperature, the ordinary techniques cannot be adopted. The purpose of this paper is to determine the degrees of grain boundary diffusion of mercury into 70/30 brass and of 3%Zn amalgam into aluminium by a simple tensile test and to assess the role of diffusion in embrittlement.