Study On High-Performance Ultra-fine Ti(C,N)-based Cermets For Tool Materials

Ti(C,N)-based cermets have been widely used as the tool materials because of its higher red hardness, better resistance to oxidation, and better resistance to creep at high temperature. The key alloying element used in Ti(C,N)-based cermets tool materials is titanium that has about 70 times storage in the earth than tungsten, hence Ti(C,N)-based cermets show great advantage in cost and resources more than that of the traditional WC-based cemented carbide and become one of the new and main tool materials which have being developed in the globe.Based on a review of the ultra-fine WC-based cemented carbide being used in cutting tool materials, and development and progress of Ti(C,N)-based cermets tool materials, a high-performance ultra-fine Ti(C,N)-based cemented carbide has been studied systematically in this dissertation using all kinds of apparatus such as X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), electron probe (EPMA), hot isostatic press machine (HIP), low-pressure sintering machine (SH), etc.At first, the reason why oxygen content is high in raw material has been deeply analyzed in order to surmount the crux that high-performance cermets containing ultra-fine particles Ti(C,N) is hard to obtain due to the high content of oxygen in raw materials, then a high-performance raw Ti(C,N) powder which average size of particle TiC0.7N0.3 is less than 0.2μm and oxygen content is lower than 0.3wt% has been prepared adopting the conventional TiC0.7No.3 powder which average size is 0.13μm by means of a treatment in vacuum furnace or in hydrogen-deoxidization furnace.On the basis of common production process of cermet, the effect of addition such as Mo2C, WC, TaC on the properties of the ultra-fine cermet has been further investigated.Considering that the ultra-fine particle features high specific surface, high activity, and being easy to pileup, the technology of wet ball milling for the ultra-fine powder has been optimized and a certain dispersant is adopted to improve the stickiness of the slurry so that the ultra-fine grains can be covered by a layer of active material, thus leading to excellent milling behavior. The results investigated indicate that the ultra-fine cermet would have much more ability to occur solid diffusion reaction than common cermet at the lower temperature of 900癈. It is one of the reasons that makes the core-rim structure of ultra-fine become rather complicated. It seems that the reaction became milder at 900~1230癈, but the degree of reaction should be higher than the common cermet according to the changes of the lattice parameter. However, the reaction would become intense again at the temperature above 1230癈, and it could be deduced that the reaction between liquid phases occurs in advance while the denitrogenization reaction appears. Compared with the result obtained in the ultra-fine powder without binder-phase, it is shown that the binder-phase definitely has very important role in the evolvement of phases, and the phase evolvement provides a basis for optimization of technology. Based on the evolvement rule for the phases in the ultra-fine cermet, the conventional sintering technology for the common cermet has been optimized. As the liquid phase appears in advance, the sintering time has to be kept longer to remove the harmful adhesive and volatile, which have lower melt point. Certain N2 gas has to be supplemented in the sintering process to avoid appearance of the denitrogenization reaction. As it is difficult for the liquid phase to flow in the ultra-fine cermet, pressure sintering is used to eliminate the porosity to upgrade the properties of ultra-fine cermet.The fracture of the ultra-fine cermet has been analyzed systematically. The results show that rupture usually occurs can be attributed to the porosities or some very small Ni-lakes. Using Mr. Hisashi Suzuki's strength theory, the essential strength of ultra-fine cermet is calculated to be 5000 MPa much higher than theIVtesting data, the rea...