Fast penetration of Ga in Al : liquid metal embrittlement near the threshold of grain boundary wetting

Abstract

Abstract The thermodynamic conditions for spontaneous grain boundary wetting and stress driven liquid metal embrittlement are related to each other and the kinetic mechanism responsible for fast GB penetration under small stress is described. The dissolution – condensation mechanism of liquid metal embrittlement and linear fracture mechanics for calculation of a crack profile are applied to the classical system “Al – liquid Ga”. The results tend to support the idea that the recently observed fast linear penetration of Ga along 150° tilt GB of Al should be considered as propagation of a liquid metal embrittlement crack under a small residual stress rather than as spontaneous grain boundary wetting. With the residual tensile stress σ ≈ 0.5 MPa acting normal to the GB plane, all major findings reported for this model system are explained in a semiquantitative way assuming that the GB spreading coefficient is extremely small by its absolute value, i. e. that the system is near the threshold of spontaneo...