Reactions Of Interfacial Zone Between Non-stoichiometric TiN_1-x And Covalent Compounds For PcBN Applications

TiN represented transition metal carbides and nitrides are attractive materials for engineering applications because of the exceptional physical and chemical properties. The experiment were carried out by preparing highly N-deficient nanocrystalline non-stoichiometric TiN_1-x(0.3<_1-x<0.5) powders through mechanical alloying（MA）. Interfacial reaction between TiN_1-x and AlN, solid solution between TiN_1-x and transition metal carbides（VC, NbC, Mo2 C, and TaC）, and reaction induced microstructure and mechanical property changes of TiN_1-x composites were investigated. TiN_1-x based multiple strong covalent bonding metal carbides/nitrides composites were prepared for Polycrystalline cubic Boron Nitride（PcBN） cutting tool materials in high speed and high temperature dry machining applications.Densification of TiN_1-x powders were conducted by spark plasma sintering（SPS） and high pressure high temperature（HPHT） sintering. The N vacancy reduced strong covalent nature of TiN_1-x, combined with release of surface energy and lattice strain, interaction between composition inhomogeneity, and MA induced defects in crystals enhanced the sintering activity of TiN_1-x.The highly N-deficient structure induced interfacial reaction between TiN0.3 and AlN, reaction formed complex interfacial structure. The interfacial reaction zone consisted of a continuous stoichiometric TiN layer and a multi-phase region close to TiN0.3 which with re-formed AlN grains distributed in TiN_1-x matrix. The re-formed AlN grains presented coherent interface with TiN_1-x at grain boundary according to core-shell structure. The decomposed AlN released N and Al free atoms at high temperatures by the effect of N vacancies. N atoms diffused into TiN0.3 and substituted at N vacancies gave rise to the formation of TiN and TiN_1-x region, Al atoms diffused across the TiN region to produce AlN. The interfacial reaction was controlled by N vacancy content and temperature, reaction will proceed at high N vacancy content and the system will stay equilibrium at low N vacancy content. The interfacial reaction led to a significant microstructural evolution and mechanical property increase. Second phase particles strengthening, core-shell structure strengthening, coherent interface strengthening mechanisms, and the complex interfacial structure enhanced mechanical properties of TiN0.3/AlN composites.TiN0.3 and AlN type elemental diffusion between TiN0.3 and strong covalent bonding transition metal carbides can proceed by the effects of highly N-deficient structure and temperature. Solid solution between TiN0.3 and VC, NbC, Mo2 C, and TaC powder mixture can react on different levels after sintering to form uniform fcc structured（Ti,V）（C,N）,（Ti,Mo）（C,N）,（Ti,Ta）（C,N）, and（Ti,Nb）（C,N）, respectively. Mechanical properties of multielement transition metal carbonitrides exceeded any single components. The effect of multiscale atoms lead to lattice distortion and complex strain field in crystal lattice, the complex crystal plane and strain field react with crack tip strain, disperse strain concertation, hindered crack propagation, and enhance mechanical properties.TiN_1-x and various strong covalent bonding metal carbides and nitrides were used for the binder phase of PcBN, dense PcBN compacts without low melting temperature phase or low hardness phase were obtained after sintering. PcBN provides high hardness, high strength, excellent thermostability and wear resistant. PcBN cutting tool materials in high speed and high temperature dry machining applications were manufactured. PcBN cutting tool remains good performance on high speed, high precision, and high efficiency machining quenched steel.