Al2O3 and ZrO2 composites with high TiC contents fabricated by tailoring oxide powders.

Tailored powders give sintering activities of composites with 35 vol-percent TiC that equal those of reactive sintering (transient liquid phase by TiH2 addition) and of MgO/Y2O3 doping, but powder tailoring results in a higher strength. Surprisingly, a tailored Al2O3 powder processed together with commercial TiC (d50 = 1.2 mym, d90 = 10 mym) gives a higher strength than the use of an extremely fine grained carbide with d50 = 0.2 mym and d90 = 0.75 mym: a bending strength of 800 MPa is afforded without doping additions and without hot-pressing. The reason is a strong impact of oxide dispersion on the milling response of TiC: the smaller the oxide grain sizes the finer is the resulting carbide after homogenization milling. With nanoscale ZrO2(3mol-percent Y2O3) and commercial TiC, the carbide grain size in the sintered microstructure is less than 0.5 mym giving a bending strength of about 1100 MPa at a hardness of 16.5 GPa. High resolution TEM shows that all grain boundaries are free of amorphous phases.