A study of dynamic embrittlement in bicrystals of Cu-7%Sn

In a kinetic model [1] for the phenomenon of dynamic embrittlement, the cracking rate is predicted to be proportional to the diffusivity of the embrittling species along the grain boundary. To test this model, bicrystals of Cu-Sn with Σ5 symmetrical tilt boundaries in which tin is the embrittling element are being used. The diffusivities parallel and perpendicular to the tilt axis are expected to be different, therefore, the crack growth rates in these two directions should vary in the same ratio as the diffusivities. Measurements of the crack-growth rate along the [100] direction in the Cu-Sn alloy bicrystal at 265 °C showed that the cracking occurred by decohesion along the grain boundary with almost no observable plasticity at a maximum crack growth rate of approximately 10−6 m s−1. A model for steady-state crack growth has recently been developed and is discussed here.