Fabrication Of Composite TiC Cermets By In-Situ Reaction Of Metal Oxide SPS

Due to the advantages of high melting, high hardness,and good chemical stability and electrical conductivity, TiC cermets are one of the preferred materials of cemented carbide, wear parts, cutting tools, electrodes and so on. In the preparation of TiC-based cermets, Ni or Co powders are generally selected as a binder. However, as two rare and strategic metals, the market prices of Ni and Co are quite expensively. Therefore,it is very necessary to replace Ni and Co partly or completely with a cheap metal with better bonding properties. It is commonly known that Fe, Ni and Co belong to the same? A group elements in the periodic table and these elements have the similar characteristics. Moreover , the Fe resource reserves in the earth' s crust are more abundant and the Fe powders have cheaper price compared with Ni and Co. Therefore,Fe is an ideal alternative binder phase of TiC cennets Unfortunately, unlike Ni and Co,the surface wettability between liquid Fe and solid TiC is poorer. In addition, the fabrication of TiC cermets by the conventional powder metallurgical method from TiC and Fe has the disadvantages of long process cycle, large energy consumption and high carbide cost. Meanwhile, due to Fe being easily oxidized, it is difficult to control the compositions of TiC cermets and the interface pollution between ceramic substrate and metal binder phase. As a result of the above mentioned factors existence, it is adverse to improving mechanical properties of TiC cermets. Therefore, it is very important to explore a new way to fabricate higher performance TiC cermets with at low cost and short process.In this experiment, the cheap metal metal oxide powder, such as TiO2, Fe2O3 and MoO3 were used as the main raw material and nano-carbon black powder (99.7% in purity) was used as the carbon source. And the composite TiC cermet was fabricate by spark plasma assisted in-situ carbothermal reduction through three different methods.The first is spark plasma sintering method: TiC based cermets prepared directly by in-situ carbothermal reduction method. It is showed that the hardness and the relative density of samples reached the maximum , which were 77.8HRA and 87.3% respectively at 1350? by studying the phase and mechanical properties of samples. Due to the limitations of itself, the reaction cannot be completely, leading to poor performance of TiC cermet.Next, the second sintering assisted spark plasma sintering: the composite cermet powders rapidly synthesized by spark plasma assisted in-situ carbothermal reaction at 14500C for 15min, with the average heating rate of 60 0C/min, after ball milled 20h. Then the composite TiC cermets with the average grain size of about 1 ?m were rapidly fabricated by spark plasma sintering (SPS) using the ultrafine composite TiC cermet powders synthesized by spark plasma assisted in-situ carbothermal reaction from metal oxides as starting powders. The phase and microstructure of starting powders and composite TiC cermets were analyzed and observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The measurement of the hardness and bending strength of composite TiC cermets were conducted on Rockwell hardness tester and universal material testing machine respectively. The results from phase study indicate that in the preparation of the cermets powders and the composite TiC cermet , the TiC phase was formed in the sequence of TiC and (Ti , Mo)C. The performances also increased with the rise of temperature. Finally, the fine grained composite TiC cermet with the best mechanical performance was obtained at 1300? with 40MPa. At this time,the Rockwell hardness, flexural strength, fracture toughness and relative density were 91.6 HRA, 1484.6 MPa, 8.2 MPa. m1/2 and 97.3% respectively.Finally, the two step sintering method was used to prepare TiC based cermet by using SPS. In this process, the raw materials were heating and cooling down, and then heating and pressurizing directly. According to the results of phase and mechanical properties test, the hardness and relative density of the samples reached the maximum,which were 80.1HRA and 84.17%, respectively at 1600? of the first step.