Study On Preparation And Mechanism Of Metal-Ceramics Composite Powders And Their Applications

Ceramics materials have high melting point, high strength, excellent wear resistance and anti-corrosive properties, etc.. But at the same time they have intrinsical brittleness, processing difficultly, the low reliability and repeat properties, that limit their applications. Recently many researches have been performed on the materials design, the primitive powder preparation technology and sintering processing of the ceramics inorder to reduce the brittleness and enhance the strength and fracture toughness of the ceramics materials.In this paper by the low temperature electroless plating with ultrasonic wave vibration reinforcement, the cobalt film was coated on the surface of the micron and sub-micron ceramic particles like Al₂O₃, TiC and WC, respectively. Three kinds of metal-ceramics composite powder were prepared: (1) Al₂O₃-CO composite powder, the mass percentage of the cobalt is 3%, 5%and 8% respectively. (2) Al₂O₃-TiC-Co (Al₂O₃-Co+TiC-Co) composite powder, the mass percentage of the cobalt is 3%, 5%and 8% respectively. (3) WC-Co composite powder, the mass percentage of the cobalt is 3% and 10% respectively. The Al₂O₃-TiC-Co and WC-3%Co composite powder were sintered into the bulk ceramics sample(ATC) and the cemented carbide sample (NYG) by hot-pressed technique respectively. The WC-10%Co composite powder was cladded on the steel matrix to get the wear resistance coating layer by CO₂ laser cladding technology.The low temperature electroless plating with ultrasonic wave vibration reinforcement used to get Al₂O₃-Co composite powder was researched as the example. The preparation processing factors and mechanism were discussed. The optimization processing parameters had been gotten to prepare metal-ceramics composite powders by the low temperature electroless plating with ultrasonic wave vibration reinforcement.During the sintering process of the Al₂O₃-TiC-Co composite powder, the sintering temperature, sintering atmosphere and holding time during heating process were obvious effect factors to the properties of the ATC composite ceramic. The ATC composite ceramic, sintered by the hot-pressed technique at 1550℃ with 30 MPa pressure protected by vacuum, showed the best mechanical properties. Cobalt phase, coated on the ceramics particles by electroless plating method, stopped the reaction between ceramics phase to produce glass phase and gas phase, and limited the growth of the ceramic crystal grain. Therefore, the crystal grain of the ATC composite ceramic shows fine and uniform microstructure. Thestrengthen and toughen aim by ultra-fine grain has been achieved in the sintered sample, the cobalt phase and ceramics phases form three-dimension net structure, and interlace and insert each other. When the ATC composite ceramic receives load, the ceramics phases show high strength and rigidity to make the sample hold high strength and hardness. And the cobalt phase produces plastic deformation to absorb a part of energy by crack deflection and bridge connection, which increases the fracture work. Therefore, the sample shows higher fracture toughness, and the strengthen and toughen aim by metal phase has been achieved. The failure mode is intercrystalline cracking and plastic deformation of cobalt phase with a few ceramic particles drawing out.The quenched 45 steel, binding SiC ceramic and artificial diamond were designed as the friction counterpart to investigate the dry sliding wear resistance and lubricated sliding wear resistance of the ATC composite ceramic. When the friction counterpart are quenched 45 steel and binding SiC ceramic respectively, the ATC composite ceramic shows the excellent wear resistance. When the friction counterpart is the artificial diamond, the micro-cutting and plastic deformation produce in the worn surface of the ATC composite ceramic, and the cobalt phase absorbs a part of energy by plastic deformation to improve the wear resistance. The wear resistance and mechanism of the ATC composite ceramic are different from the friction counterpart materials. When the load is large, the water lubricant accelerates the wear loss, but the oil lubricant can improve the wear resistance performance of the ATC composite ceramic.The WC-3%Co composite powder was sintered into NYG cemented carbide at 148CTC protected by argon. The mean free path of the cobalt phase is decreased for its evenly distribution. The cobalt matrix forms a strong bond with the WC grains because of the suitable solubility of WC in cobalt phase and prevents WC particles pullout during wear. The WC phase also form a skeleton structure that makes it difficult to remove cobalt by plasic extrusion. Therefore, the wear resistance of NYG cemented carbide is improved obviously.The coating layer on the surface of the steel substrate was prepared by CO2 laser cladding technology with the WC-10%Co metal-ceramics composite powder. The quality of the coating layer is effected largely by the processing parameters of laser cladding. The optimal processing parameters are: laser power of 2.0 2.4KW, scanning speed of 4.1 m/min and spot size of 3 mm. The coating layer shows fine micro-structure, decarburisation and soft spot, and binds with the steel substrate firmly. The coating layer shows the excellent wear resistance compared with the quenched steel. There are two reasons for it: (a) The coating layer has highhardness and fine micro-structure of cemented carbide, (b) The cobalt phase absorbs a part of energy by plastic deformation to alleviate the fatigue wear during the sliding wear processing.