Microstructure And Mechanical Properties Of TiC-Ni Cermets Prepared With Mechanically Activated Sintering

Cermets exhibit attractive properties such as high strength, high hardness and high resistance to oxidation at elevated temperature. TiC-Ni cermets having been extensively applicated in manufacturing cutting tools and die parts especially represent comparable properties to WC-Co cemented carbides, such as high resistance to erosion, abrasive and thermal stability. The powder metallurgy technique is used widely to manufacture TiC-Ni cermets, yet the sintering temperature is always too high, nearly reaching 1400℃, which leads to low toughness for the material. Thus it is necessary to find an easy and low cost processing way under low sintering temperature to obtain materials with better properties.As nanocrystalline can reduce sintering temperature, high-energy milling was performed as a substitute for traditional Powder Metallurgy process to activate and gain TiC-Ni cermets nanometer powders, and then liquid phase sintering was carried out.By means of X-ray Diffractometry (XRD) and Transmission Electron Microscopy (TEM), the activation and refinement of the nanocrystalline was analysized. Scanning Electron Microscopy(SEM), Optical Microscopy(OM) and Differential Thermal Analysis(DTA) were carried out to analysize microstructure and mechanical properties of TiC-Ni cermets sintered under low temperature (1290 ℃)and high temperature (1340℃,1350℃)with activated nanocrystalline powder mixtures. It was confirmed by x-ray analysis that during dry-milling process grain size of the mixtures refined continuously to 20nm or so, and significant solid solution was induced. While during wet-milling process grain size of mixtures also refined continuously to 20nm or so without appearing obvious solid solution.The results of activated sintering of TiC-Ni, TiC-NiCr, and TiC-NiCrTiAl reveal that during initial period of milling the compressibility of powder mixtures improved quickly. Then the increase of surface energy, which serving as sinteringdriving energy, leads to decreases of sintering activation energy and the sintering temperature. As a result the liquid content increased continuously against milling time during sintering process. The microstructure of the sintered compacts consists of finely dispersed TiC particles, which contribute to better mechanical properties, such as flexural strength and hardness. Sintered compacts composition distribute disorderly when liquid content exceeds certain suitable value ,and severe solid consolidation happened with large amount of liquid phase spilled from the compacts body. The compressibility of powder mixtures turn bad as long as the milling time extended too much. The densification of the sintered compacts reduced to low level suddenly, because of low green density. The activated sintering of TiC-NiCrTiAl shows that segregation of Ni3Al phase from the binder during the cooling after sintering helps toughen the material.