| 摘要 | TiC/NiCrAlTi金属陶瓷是在石油、化工、冶金等领域中有高温磨损、冲击及腐蚀的工况环境需求下发展起来的一种新型耐磨耐蚀金属陶瓷复合材料。本研究以制备高性能Ti(C,N)/NiCrMoAlTi金属陶瓷及实现其与钢的连接从而达到实际应用目的为研究目标，在制备高性能金属陶瓷方面，从增强粘结相与硬质相之间润湿性和细化硬质相颗粒两方面着手，分别研究了原始TiC粉末粒度、Mo含量及TiN含量对TiC/NiCrAlTi金属陶瓷微观结构和力学性能的影响；在金属陶瓷与钢的连接方面，从连接方法和连接工艺展开研究，最终成功制备出了具有较高力学性能的Ti(C,N)/NiCrMoAlTi金属陶瓷，并分别通过真空钎焊、真空烧结扩散焊两种连接方法实现了金属陶瓷与钢的牢固连接。
研究了Al、Ti元素在液相烧结制备的TiC/NiCrAlTi金属陶瓷中的存在形态及增强机理。结果表明，Al、Ti元素在烧结过程中与粘结相中的Ni形成球形 相Ni3(Al,Ti)， 相的尺寸平均为80nm，均匀分布在金属陶瓷粘结相中， 相与粘结相基体存在着共格关系。位错切割机制和Orowan绕过机制共同作用使得粘结相获得较好的强化效果。
研究了原始TiC颗粒尺寸、Mo含量及TiN含量对金属陶瓷微观结构和力学性能的影响。细小尺度的原始TiC颗粒有利于获得较高力学性能的金属陶瓷；Mo元素的添加在烧结过程中与TiC颗粒形成(Ti,Mo)C固溶体包覆在TiC颗粒周围形成“芯-壳”结构，“芯-壳”结构的形成减缓了金属陶瓷烧结过程中硬质相颗粒的Oswald熟化长大过程，因此制备的TiC/NiCrMoAlTi金属陶瓷具有良好的微观结构和优异的力学性能；以TiN替代部分TiC制备的金属陶瓷由于烧结过程中生成了热力学更稳定的Ti(C,N)固溶体，进一步减缓了硬质相颗粒的Oswald熟化长大过程，从而使制备的Ti(C,N)/NiCrMoAlTi金属陶瓷具有更好的微观结构和力学性能。
分别以CuMnNi钎料和CuMnCo钎料实现了高性能金属陶瓷和不锈钢的真空钎焊连接，采用CuMnNi钎料比采用CuMnCo钎料获得了更高的接头剪切强度，良好的界面扩散互溶是获得牢固钎焊接头的主要原因。
采用真空烧结扩散焊可更经济、批量地实现金属陶瓷和钢的连接，接头强度也高于真空钎焊接头。本文研究了真空烧结扩散焊的连接机理，并指出 相的长大是真空烧结扩散焊后金属陶瓷硬度下降的主要原因。 |
| 其他摘要 | TiC/NiCrAlTi cermets are newly developed wear and corrosion resistant composite materials, which can be used under high temperature wear, corrosion and shock conditions. This kind of cermets has great potential applications in petroleum, metallurgy and chemical industry. The aim of this research was to prepare high property Ti(C,N)/NiCrMoAlTi cermets and to find effective ways to make the cermets and steels be strongly joined together. In cermets preparation, from the point that whether it could enforce the wettability between hard phase and binder phase and could fine hard particles, both of which were necessary to manufacture high property cermets, size effects of raw TiC particles, the amount of Mo and TiN additions on microstructures and mechanical properties of Ti(C,N)/NiCrMoAlTi cermets were investigated respectively. As a result, Ti(C,N)/NiCrMoAlTi cermets with high properties had been obtained. In the study of joining between cermets and steels, deferent joining techniques and processing were investigated. Strong joining between cermets and steels had been successfully developed by vacuum brazing and vacuum sintering diffusion bonding.
The morphology and strengthening mechanism of Al, Ti elements in TiC/NiCrAlTi cermets, fabricated by liquid-phase-sintering, were studied. The results indicated that Al and Ti elements acted with Ni to form spherical -Ni3(Al,Ti). The -Ni3(Al,Ti) phase, whose average size was 80nm, were uniformly distributed in cermets binder and grown coherently with cermets binder. Therefore, cermets binder could be strengthened by Orowan strengthening mechanism and dislocation cutting.
Sizes effects of raw TiC particles, the amount of Mo and TiN additions on microstructures and mechanical properties of cermets were investigated, respectively. It was found that finer raw TiC particles were beneficial to obtain high property cermets. In the prepared TiC/NiCrMoAlTi cermets, most of hard particles had a Core-rim structure which consisted of undissolved TiC cores, surrounded by a rim phase of (Ti,Mo)C solid solutions. These solid solutions were formed in the sintering process by precipitating of Mo and dissolved TiC in the liquid NiCr alloy. Because the formation of the Core-rim structure hindered Oswald ripening of hard particles during the sintering process, TiC/NiCrMoAlTi cermets had fine microstructures and high mechanical properties. Ti(C,N)/NiCrMoAlTi cermets were fabricated by using TiN hard particles to replace part of TiC hard particles in TiC/NiCrMoAlTi cermets. Ti(C,N)/NiCrMoAlTi cermets had a finer microstructure and higher mechanical properties, because the formed Ti(C,N) solid solutions with good chemical stability hindered Oswald ripening during sintering .
Strong joints between TiC-based cermets and a stainless steel were obtained with CuMnNi and CuMnCo fillers by vacuum brazing. The Result revealed that better joints could be obtained by CuMnNi filler than by CuMnCo filler. Excellent mutual solution was the main reason for achieving the strong brazed joints.
Vacuum sintering diffusion bonding was another method of joining between cermets and steels, which was economical and easy to achieve batch production. The strength of the joints obtained by this method was higher than that by vacuum brazing. In this work, the mechanism of vacuum sintering diffusion bonding was investigated. It was found that the coarsening of the -Ni3(Al,Ti) phase was the reason for the hardness decrease of cermets after vacuum sintering diffusion bonding. |
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