Preparation Of Core-shell TiC-Ni Composite Powder And Its Sintering Characteristics

TiC-Ni cermet possesses high hardness,wear resistance,high temperature resistance,and corrosion resistance properties,which make it suitable for the fabrication of cutting tools and wear-resistant components.Nowadays,the traditional powder metallurgy method of cermet preparation has the problem of uneven distribution of the binding phase Ni,which is due to the large difference in density between TiC and metal Ni and poor wettability between the two phase,which leads to aggregation between TiC ceramic particles and uneven microstructure distribution of the overall cermet composite.Therefore,TiC-Ni composite powder has been proposed,and the mixing uniformity of the coated powder with the core-shell structure is high.However,the current technology of preparing the coated powder can not take into account the problems of high Ni content,high efficiency and low cost.In response to this problem,a new idea of controllable preparation of Ni-coated TiC composite powder based on the improved technology of impregnation reduction and electroless plating is proposed.The main innovative findings achieved are as follows:（1）It is proposed and verified that the nano-metal Ni particles deposited on the surface of TiC by impregnation reduction have the autocatalytic property,and can autocatalyze the electroless plating Ni reaction to deposit Ni particles on the surface of TiC.By adjusting the concentration of impregnated Ni precursors and the reduction temperature in the furnace during the reduction process,the TiC-Ni composite powder with a Ni content of 0.05～0.20 wt.%can be prepared.The optimal conditions for thedeposition of Ni catalysts by impregnation reduction were as follows:impregnated Ni precursor concentration was 0.10 wt.%,reduction temperature was 650°C,and particle size was 20 nm.The optimal reaction conditions for electroless plating were determined to be as follows:temperature of 80°C,p H value of 9,complexing agent concentration of 50.0 g/L,and reducing agent concentration of 70.0 g/L.Under the optimum conditions,the electroless Ni plating rate is the highest,up to=3.53 mg·g^-1·min^-1.（2）The improvement of the uniformity of coated powder on the microstructure of cermet was verified,and a new sintering system for newly prepared powder was established.In the solid phase sintering stage,the composite powder reduces the direct contact between TiC grains due to the presence of Ni shells,thereby inhibiting the growth of TiC grains.At the same time,the Ni layer also makes the Ni binder phase more evenly distributed in the sintered sample,and the Ni binder phase and TiC are more likely to diffuse,and more liquid phases are produced in the liquid phase sintering stage,which promotes particle rearrangement and dissolution-re-precipitation.Therefore,the composite powder has lower porosity,higher relative density and transverse rupture strength after sintering.The optimized vacuum sintering process is1380°C and holding time of 1.0 h.Under these conditions,the core-shell structure Ni-coated TiC composite powder formed a dense and uniform structure after sintering.And the Ni binder phase was evenly distributed around the TiC grains.The cermet has a relative density of 98.23%,a HV hardness of 2254 MPa and a transverse breaking strength of 1145 MPa.