Sintering of Al2O3-NbC composites using TiO2 and MnO additives:: preliminary results

Cemented carbides have been replaced by ceramic composites in the manufacture of cutting tools characterized by high cutting speeds and hot hardness. Liquid-phase sintering of Al2O3-NbC composites using TiO2 and MnO was studied in an attempt to produce dense composites at relatively lower temperatures than those characteristic of pressure-assisted processes. The sintering behavior of the composite was assessed from a dilatometric study carried out under vacuum up to 1800 degreesC. The formation of crystalline phases was evaluated from X-ray diffraction analyses. Mercury porosimetry and Vicker's microhardness tests were also carried out. Liquid phase sintering took place with the formation of a non-volatile liquid over 1300 degreesC. TiO2 and MnO were effective in densifying Al2O3 to > 95% TD at sintering temperatures as low as 1550 degreesC. Upon cooling, both crystalline and vitreous phases were formed but they did not affect the hardness of the composite (similar to18 GPa). (C) 2002 Elsevier Science B.V. All rights reserved.