Mechanism of Embrittlement and Brittle Fracture in Liquid Metal Environments

Polycrystals and single crystals of normally ductile metals fail in a catastrophic brittle manner when exposed to certain surface active liquid metal environments. The fracture mode changes from ductile to intergranular or transgranular mode or both. In some instances, propagation of cracks in liquid metal environments occur at speeds of order 100 cmsec. Such effects are generally recognized as the phenomena of Liquid Metal Embrittlement. Liquid metal embrittlement is presently considered to result from liquid metal adsorption-induced reduction in cohesion of atomic bonds at regions of high stress concentrations in a solid, such as at the tip of cracks or at the sites of crack nucleation. The prerequisites for embrittlement are the same as those for brittle fracture and liquid metal embrittlement is considered a special case of brittle fracture rather than a diffusion or a corrosion type of phenomena. This paper presents come theoretical considerations 1 concerning the reduced-cohesion mechanism of embrittlement and 2 embrittlement to be a special case of brittle fracture. Experimental results utilizing ideal embrittlement systems in support of the mechanism and also in support of various brittle fracture criteria are presented and discussed.