Processing, microstructure and mechanical properties of 25 vol% YAG-Al2O3 nanocomposites

A co-precipitation method was investigated to manufacture 25 vol% YAG-Al2O3 nanocomposites with excellent strength characteristics at room temperature. The as-prepared powders were sintered by hot-pressing in N-2 to nearly full density with heating rate of 10 degrees C min(-1) to 1400 degrees C for 1h and at 30MPa pressure. The microstructure was characterised using X-ray diffraction (XRD), scanning election microscopy (SEM), energy-dispersive spectroscopy (EDS) and transmission electron microscope (TEM). Microstructural results of hot-pressed composites reveal that the intergranular YAG grains of micrometer size (approximate to 800nm) were dispersed at the grain boundaries of a dense Al2O3 matrix, and most fine grain YAG grains of nanometric size (approximate to 100nm) were entrapped within the Al2O3 grains in the composite. The room temperature fracture strength and fracture toughness of the hot-pressed composites were 611MPa and 4.53MPa.m(-1/2), respectively. These strength and fracture toughness values are higher than those reported in other studies for YAG-Al2O3 system. It is proposed that the improvement of mechanical property of hot-pressed nanocomposites is due to the reduction of the grain size of the matrix and the improved strength of the grain boundaries in 25 vol% YAG-Al2O3 nanocomposite. (C) 2000 Acta Metallurgica Inc.