Influence of the metal particle size on toughness of Al2O3/Mo composite

Abstract Two kinds of Al 2 O 3 /Mo (20 vol.%) have been prepared, containing fine and coarse metal particles, respectively. The load–displacement curves, of these two composites, were measured during stable crack propagation and the corresponding R -curves were calculated from standard fracture mechanics equations. Using an in situ microprobe fluorescence technique it was also possible to measure the evolution of microscopic bridging stresses that develop during crack propagation and relate them to the size of the metal particles embedded in the matrix. Experimental results highlight that the interface of small Mo particles (less than 5 μm) is easily fractured thus reducing the maximum toughness achieved. Coarse Mo particles enhanced the bridging effect, and as a consequence, a higher toughness value was achieved. The toughening effect in these composites can be reasonably explained by considering both the fracture mode and the fracture strength of the bridging sites, as measured by in situ fluorescence spectroscopy.