Elevated temperature deformation and fracture mechanisms in high-strain-rate-superplastic Si3N4p/Al-Cu-Mg composite

Tensile tests have been carried out at 713-843 K on a high-strain-rate-superplastic Si3N4p/Al-Cu-Mg (2124) composite. Analysis of the activation energy suggests that the deformation mechanisms of the material in the absence of liquid phase are the same as those for metals. The deformation characteristics are, however, drastically changed by the presence of a liquid phase. In the absence of liquid, cracks develop perpendicular to the tensile axis by plastic tearing because of the stress concentrations at the interfaces. However, no cracks are formed in the presence of a small volume of liquid, indicating that the stress concentrations are relaxed by the liquid phase. On the other hand, cracks are again formed in the presence of too much liquid. Thus, the presence of a liquid phase drastically changes not only the deformation characteristics, but also the fracture mechanisms during high strain rate superplasticity.