A STUDY OF DYNAMIC EMBRITTLEMENT IN BICRYSTALS OF CU-7-PERCENT-SN

In a kinetic model [1] for the phenomenon of dynamic embrittlement, th e 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 Sigma 5 symmetrical tilt boundaries in which tin is the embrittling element are being used. The diffusivities paral lel and perpendicular to the tilt axis are expected to be different, t herefore, the crack growth rates in these two directions should Vary i n the same ratio as the diffusivities. Measurements of the crack-growt h rate along the [100] direction in the Cu-Sn alloy bicrystal at 265 d egrees C showed that the cracking occurred by decohesion along the gra in boundary with almost no observable plasticity at a maximum crack gr owth rate of approximately 10(-6) m s(-1). A model for steady-state cr ack growth has recently been developed and is discussed here. (C) 1997 Elsevier Science S.A.