【作者】 朱流；

【导师】 郦剑；

【作者基本信息】 浙江大学 ， 材料加工工程， 2006， 博士

【摘要】 陶瓷材料具有高熔点、高强度、耐磨损和耐腐蚀等优良特性,但同时存在脆性大、难加工、可靠性与重现性差等弱点,给其工程应用带来许多困难。目前,各国研究者从陶瓷材料的材料设计、原始粉体制备技术和成型、烧结工艺等方面进行了大量研究,在强韧化研究方面获得了很大进展。 本文采用低温超声波化学镀的方法,在微米和亚微米级的Al₂O₃、TiC和WC陶瓷粉体上均匀包覆延性金属Co层,成功制备出以下三类金属.陶瓷复合粉体:（1）金属Co质量百分含量分别为3%、5%和8%的Al₂O₃-Co二元复合粉体（2）Al₂O₃-TiC-Co（Al₂O₃-Co+TiC-Co）三元复合粉体（3）金属Co含量分别为3%和10%的WC-Co二元复合粉体。分别对Al₂O₃-TiC-Co三元复合粉体和WC-Co二元复合粉体用热压烧结方法制各高性能Al₂O₃-TiC-Co复合陶瓷（ATC）和WC-Co硬质合金（NYG）。采用CO₂激光熔覆WC-Co二元复合粉体制备性能优良的钢基耐磨涂层。 以Al₂O₃粉体低温超声波化学镀钴为例,对金属-陶瓷复合粉体的制备工艺,影响因素和机理进行了探讨,获得了低温超声波化学镀法制备金属-陶瓷复合粉体的优化工艺。 在Al₂O₃-TiC-Co复合粉体的烧结过程中,烧结温度、烧结气氛以及分级保温时间对ATC复合陶瓷力学性能的影响较明显。研究发现在1550℃,真空条件下烧结时ATC复合陶瓷的性能最好。以化学镀方法引入的金属Co相,在烧结过程中,阻止了陶瓷相发生接触化学反应生成玻璃相和气相,抑制晶粒长大,细化ATC复合陶瓷晶粒,达到超细晶粒增韧目的。烧结成型后,陶瓷相与金属Co相在烧结体中形成三维网状结构,互相交织镶嵌。在ATC复合陶瓷承受载荷时,陶瓷相发挥高强度与高刚度特性,使样品达到高强度与高硬度水平;金属Co相以塑性变形,裂纹偏转与桥接等形式,吸收部分能量,增大断裂功,提高样品的断裂韧性,达到了金属相增韧目的。在ATC复合陶瓷中,气孔、夹杂物和异常长大晶粒是其主要显微结构缺陷,是裂纹发生和扩展源,其失效形式以沿晶断裂和延性金属Co相的塑性变形为主,伴有部分陶瓷颗粒的拔出。 以淬火45钢、粘结SiC陶瓷、人造金刚石为对磨材料,对ATC复合陶瓷的干滑动磨损和润滑滑动磨损性能进行研究。在与淬火45钢和粘结SiC陶瓷对磨时,ATC复合陶瓷表现出良好的耐磨性能;与人造金刚石对磨时,ATC复合陶瓷磨损面发生明显的微切削和塑性变形,延性金属Co相的塑性变形吸收部分能量,提高了ATC复合陶瓷的整体耐磨性能。随对磨材料的不同,ATC复合陶瓷的磨损性能和机理发生变化。在较大载更多还原

【Abstract】 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.更多还原