IN-SITU STRESS-STRAIN RESPONSE OF SMALL METAL PARTICLES EMBEDDED IN A CERAMIC-MATRIX

The in situ stress-strain response of metal particles embedded in a ceramic matrix was obtained by combining the measurement and the modeling of the crack opening displacement field of a crack in a brittle material bridged by metal particles. The experiments were done on a composite made from platinum particles with a volume fraction of 10% in a magnesium aluminate spinel matrix. The size of the platinum particles was varied from 1 to 12 mum to study the influence of scale on the deformation behavior. Large strain to failure (85%) and ultimate tensile strength of 550 MPa were obtained for the 1 mum particles. But the larger particles failed at a strain of less than 25%; the ultimate tensile strength was also lower. This difference in ductility is explained in terms of debonding at the metal ceramic interface. It is argued that the debonding depends on the length of the dislocation pile up at the interface, and, therefore, on the particle size. The results and the metallographic observations are consistent with a model presented here; in this model the failure condition is given by a combination of the intrinsic yield stress of platinum, and the hydrostatic constraining stress in the metal particle.