On the mechanism of liquid copper penetration into iron grain boundaries

Abstract

The penetration of liquid copper into iron grain boundaries has been experimentally analysed. During the penetration, Cu diffuses into the iron grains. In this case, a Kirkendall effect is created, leading to vacancies which diffuse to the grain boundaries where they condense. A grain boundary crack is formed, which will be filled with liquid Cu. The driving force for penetration of the Cu-liquid into the grain boundary is the condensation of vacancies and the surface/interface free energy change. A theoretical model describing the penetration rate is derived and a good agreement between theory and experiments was achieved. The model is general and can be used to explain liquid metal embrittlement.