Research On TiC-based Cermets Prepared By Mechanochemical Method

The powders prepared by mechanochemical method have the character of homogenous chemical composition, small particle size and narrow size distributions. Mechanochemical method also was an efficient, low-cost and simple technology, so it has a big advantage in preparing ultrafine powder materials. In this work, mechanochemical method was applied in the field of preparing TiC-based cermets. In view of the high exothermic reaction between Ti and C, TiC-based solid solution powders, ceramic-metal composite powders, TiC-TiB2composite powders, TiC-Ni3Al ceramic-intermetallic composite powders were synthesized by self-sustained reaction which were induced by high-energy ball milling (mechanical induced self-sustained reaction, MSR), and microstructure as well as mechanical properties of the TiC-based cermets prepared from these synthesized powders were also investigated.(Ti,Mo)C,(Ti,W)C and (Ti,Ta)C solid solution powders were obtained by MSR when Ti, Mo, W, Ta and graphite powders were used as the raw materials, then the synthesized powders were mixed with Ni respectively to prepare cermets. The results showed that the ball milling induced the reaction between Ti and C, then Mo, W and Ta dissolved in the new formed TiC by means of huge reaction heat and generated the (Ti,Mo)C,(Ti,W)C and (Ti,Ta)C solid solution. The solid solution particles selectively dissolved in the binder and then precipitated, which formed a core/rim structure in the microstructure of solid solution cermets. However, this kind of core/rim structure has a little different composition between the core and the rim, which gave rise to a high fracture toughness of solid solution cermets.(Ti,M)C-Ni (M=W, Mo and Ta) ceramic-metal composite powders were obtained by MSR when Ti, Mo, W, Ta, Ni and graphite powders were used as the raw materials. The ball milling induced the reaction between Ti and C and released huge heat which melted the metal particle. On the cooling stage, minority of the melts, which has a fast cooling rate, formed some blocks with the size range from1to15mm, but majority of the melts were impacted by the ball and formed ultrafine powder. Majority of the grains in the microstructure of the cermets prepared by the synthesized composite powders were coreless. Only a small number of grains had core/rim structure, and the interface between the core and the rim was coherent boundary. The ceramic phase and the binder phase had a high bonding strength, and there was a transition layer with a microcrystal structure between them. This kind of transition layer was an ideal connection mode between the ceramic phase and the binder phase in the cermets. So the cermets prepared by MSR show a superior toughness due to the above interface character, especially, the (Ti,W)C-Ni cermets had a fracture toughness as high as13.27MPa-m1. The toughened mechanisms of these cermets were crack deflection and crack bridging.TiC-TiB2composite powders and TiC-TiB2-Ni composite powders with different TiC/TiB2mass ratio were prepared by MSR when Ti, B, Ni and graphite powders were used as the raw materials. The results showed that high-energy ball milling can not induce the reaction between Ti and B, and the self-sustained reaction of the whole system was induced by the firstly formed TiC. The TiC-TiB2cermets can not reach full density when sintering under the vacuum. With the increase of T1B2, the porosity of the cermets increased. The tendency of the hardness was complicated. When the mass ratio TiB2/TiC was3/7, the cermets had the highest hardness,16.32GPa. TRS and KIC of the TiC-T1B2cermets declined with the increase of TiB2, because TRS and KIC were sensitive to the porosity. The pores in the sintering body were mainly present in the ceramic grains, which led to the obvious transgranular fracture in the TiC-TiB2cermets.TiC-NisAl composite powders with different M3AI content were prepared by MSR when Ti, Ni, Al and graphite powders were used as the raw materials. The results showed that the mixture with the composition of atomic ratio Ni/Al=3/1can not be induced by high-energy ball milling. The reaction of Ti-C was firstly induced, and then caused self-sustained reaction of the whole system. The formation of spherical TiC particles had two conditions:(1) reached or approached the stoichiometric ratio of TiC;(2) system had a high enough temperature to complete the roughen transition of TiC particles. With the increase of Ni3Al, hardness and porosity of the TiC-Ni3Al cermets decreased, but TRS and KIC improved markedly, and the microstructure also refined obviously.Ti(C,N) solid solution powder with the particle size of10-20nm were prepared by mechanochemical method through ball milling of Ti and melamine. The chemical composition was Ti(C0.32N0.68)0.93. The synthesis mechanism of Ti(C,N) was gradual diffusion reaction which was one of mechanochemical reaction mechanism. Melamine not only had a role of reactant but also had a role of process control agent (PCA). So melamine restrained the mechanochemical reaction, meanwhile, it also refined the powder, which played a very important effect in the synthesis of Ti(C,N) nanoparticles.