【作者】 雷燕；

【导师】 熊惟皓；

【作者基本信息】 华中科技大学 ， 材料学， 2005， 博士

【摘要】 本论文采用热分析(TG)、X 射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、场发射扫描电镜(FESEM)、X 射线能谱(EDS)、O/N 测定仪等实验手段系统地研究了纳米复合Ti(C,N)基金属陶瓷材料的成分、制备工艺、组织结构与性能等之间的关系。论文首先综述了Ti(C,N)基金属陶瓷的发展概况和研究进展,总结了Ti(C,N)基金属陶瓷的晶粒细化、成分及添加剂对Ti(C,N)基金属陶瓷组织和性能的影响,并对相关材料-硬质合金的晶粒细化研究现状进行了简述; 总结了纳米粉末的压制成型技术、压制特性及相关压制理论、纳米烧结技术和纳米烧结特性。在此基础上指出了本文研究的目的和意义。首先研究了化学成分、粉末粒度及压制工艺参数对Ti(C,N)基金属陶瓷混合粉末可压制性的影响,建立了组分压制特性与金属陶瓷混合粉末压制特性之间的计算公式,且计算值与实验结果相吻合,并且,还从理论上分析了金属-陶瓷混合粉末压制过程的微观力学作用机制。研究了以聚乙烯醇为基,分别添加甘油、聚乙二醇与石蜡的多组元有机物成形剂对纳米复合Ti(C,N)基金属陶瓷混合粉末可压制性、素坯强度、烧结试样机械性能和孔隙率的影响。试验结果表明:在四种有机物成形剂中,聚乙烯醇+石蜡的有机物组成热分解特性对于脱脂过程的进行最为有利,且添加了该成形剂的金属陶瓷孔隙率较低,综合机械性能最好。对纳米复合Ti(C,N)基金属陶瓷热压烧结工艺、及材料在热压烧结过程中的致密化过程、相变特点和组织特征进行了系统的研究。研究结果表明:金属陶瓷致密性主要受热压压力影响,物相之间的相变反应程度主要受烧结温度影响; 1400oC 下保温20min 所获得的金属陶瓷综合机械性能最好。纳米复合Ti(C,N)基金属陶瓷热压烧结过程中VC 添加剂对晶粒长大的抑制作用规律为:纳米硬质相颗粒在从纳米尺寸长大到接近1μm 的过程中,VC 未起到抑制晶粒长大的作用,随着烧结过程的继续进行,VC 对晶粒的细化作用明显,但是当晶粒更多还原

【Abstract】 In this dissertation, the relationship among composition, manufacturing process, microstructure and properties of nano-composite Ti(C,N)-based cermets has been systematically investigated by thermal analysis (TG), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis, and Nitrogen/Oxygen determinator. In the first part of the dissertation, the influence of composition, additive, grain refinement on the microstructures and properties of Ti(C,N)-based cermets has been critically overviewed, which includes the research development on grain refinement of WC-Co cemented carbides; Briquettability of nano-powder, pressing techniques, the relevant pressing theories, and nano-sintering characteristics and nano-sintering techniques have been summarized. Based on above work, the purpose and significance of the dissertation have been pointed out. The influence of chemical composition, particle size and pressing process parameters on briquettability of Ti(C,N) mixed powders has been studied. The calculation relation representing briquettability of component powder and Ti(C,N) mixed powders was established, and the calculated values was consistent with experiment results. Micro-mechanics mechanism on pressing process of metal-ceramic mixed powders was analysed theoretically. Four organic plasticizers of (PVA), PVA+glycerine, PVA+paraffin, PVA+polyethylene glycol (PEG) was designed and used in the die pressing process of Ti(C,N) mixed powders. The influence of the four organic plasticizers on powder briquettability, green strength, mechanical properties and porosity of sintered cermets has been investigated. The conclusions were obtained as follows: compared with other plasticizers, the thermal decomposition characteristic of plasticizer PVA+paraffin was much more in favor of dewaxing process of Ti(C,N)-based cermets, and sintered cermets behaved lower porosity and the best mechanical properties. The preparation of nano-composite Ti(C,N)-based cermets by hot-press sintering (HP) was attempted and the densification process, phase transformation and microstructure characteristics conferred by HP were systemically investigated. It was found that cermet density was decided by hot pressure and phase transformation of cermet was mainly determined by sintering temperature.Cermet sintered at 1400oC for 20min behaved the best mechanical properties. The influence of VC addition on grain growth inhibition of nano-composite Ti(C,N)-based cermets during HP sintering process has been studied. In the earlier stage of sintering, VC didn’t inhibit hard phase grain growth. When grain size was over 1μm, as sintering process continued, VC restrained grain growth obviously. However, the area proportion of abnormally growth grain in cermets increased due to VC addition after grain growed up obviously and grain size was over 5μm. The relation of porosity and grain size of nano-composite Ti(C,N)-base cermets during sintering process has been studies. The experiment results showed that pore, especially for open pores, could inhibit grain growth effectively. The change of oxygen content of nano-composite Ti(C,N)-based cermets during sintering process has been studied. Some conclusions were drawn as follows: when nano-composite Ti(C,N)-based cermets sintered at 1200oC for 30min, 2.68wt% oxygen was wiped off; after holding in 720min at 1200oC, there were still 0.21wt% oxygen keeping in nano-composite Ti(C,N)-based cermets. The preparation of nano-composite Ti(C,N)-based cermets by two-stage vacuum sintering has been attempted. It was found that grain growth of nano-composite Ti(C,N)-based cermets could be inhibited effectively by using two-stage sintering and that 400nm grain size of cermets fabricated by the technique could be obtained, and TRS got 1913MPa, and the hardness reached the level of HRA89. The influence of nano-hard phase powder addition on nano-composite Ti(C,N)-basedcermets has been investigated. As the amount of nano TiC、TiN addition increased, linear shrinkage ratio of cermets increased, and mechanical properties also increased. Sintered cermets containing ball milled nano-hard phase powder addition showed better mechanical properties of that TRS was 2016MPa and hardness was HRA89.2. The addition of nano-WC powder inhibited grain growth of nano-composite Ti(C,N)-based cermets during sintering process.更多还原