Synthesis and application of cubic Ti(C,O,N) phases

The present paper deals with the preparation of cubic Ti(C,O,N) hard materials by the carbothermal reduction process and the application of these materials in Al2O3/Ti(C,O,N) composites for cutting operations. The carbothermal reduction of TiO2 is characterized by low volatility of oxide intermediates. Consequently, the mass transfer is realized by the CO/CO2 mass transport mechanism, and the oxide particles are the precursors of the hard phase particles. The whole reaction can be divided into three reaction steps with TinO2n-1 and oxycarbides as solid state intermediates. The use of sol-gel precursors leads to an acceleration of the first reaction step, but is not advantageous for the preparation of the pure carbide. The influence of the presence of nitrogen in the gas phase on the composition and grain size of the hard phase particles prepared from a TiO2+2.7C mixture is discussed. Application of Al2O3/Ti(C,O) composites is especially advantageous in machining of hardened steel at intermediate cutting speed.