Mechanical properties and microstructures of Al2O3–5 vol.% YAG composites

Al2O3–5 vol.% YAG powder mixtures were prepared by three different methods: (i) Calcination of co-precipitated Al- and Y-hydroxides; (ii) precipitation of Al(OH)3 in a slurry containing nano-sized YAG particles, followed by calcination; (iii) ball milling of Al2O3 and YAG particles. Almost fully dense Al2O3–5 vol.% YAG compacts were obtained by hot-pressing these powders at a temperature equal to or exceeding 1550°C. Mechanical tests performed at room temperature showed that the bending strength of the Al2O3–5 vol.% YAG composite prepared from powder (i) was 604 MPa, and the fracture toughness 5.0 MPa m1/2, whereas compacts of the other two powders had lower bending strength and fracture toughness values. Microstructure investigations revealed a homogeneous distribution of YAG in the Al2O3 matrix in the compacts prepared from the powders (i) and (ii), although some nano-sized pores were found within the Al2O3 matrix prepared from powder (i).