Submicrometer Al2O3/Ti(C,O,N) composites for tool applications

Co-milling of commercial TiC with increasingly fine-grained alumina powders resulted in grain sizes of 0.9 mu m in the sintered microstructure with a hardness HV10 = 22.4 GPa if an alumina powder < 0.2 mu m was used. The grindability of cubic phases on the basis of TiC was greatly improved by the incorporation of oxygen into the lattice, and microstructures with grain sizes close to 0.5 mu m were obtained. Oxycarbonitride increased the strength to 925 MPa. A maximum hardness HV10 = 22.8 GPa was observed for a composition with substoichiometric TiC0.73O0.14. Most fine-grained composite powders were prepared by carbothermal reduction of Al2TiO5, but the pressed samples could not be sintered below 1750 deg C, and the grain sizes in these microstructures were never smaller than 1 mu m.