【作者】 雷纯鹏；

【导师】 唐建成；

【作者基本信息】 南昌大学 ， 材料物理与化学， 2013， 博士

【摘要】 目前,研发WC-Co硬质合金新型的粉末制备方法和烧结技术以开发高性能的超细/纳米或具有特殊微结构的硬质合金材料受到了广泛的重视,但关于粉末形貌结构对材料性能的影响还缺乏深入的研究。为此,本论文研究了W/WC粉末的形貌结构及其对WC-Co硬质合金组织和性能的影响。本论文通过对比分析不同氧化钨原料对W、WC粉末的形貌结构,尤其是晶粒聚集、均匀性的影响,开发出工业化的高效、可控的制备均匀纳米WC粉末的低成本工艺路线,制备出综合性能优良的WC-Co超细晶粒硬质合金；通过研究“高温还原-高温碳化”生产的中颗粒WC粉的形貌结构对其合金性能的影响,制备出具有显微组织均匀、WC硬质相尺寸适中、综合性能优良的低钴WC-Co硬质合金；通过研究不同氧化钨原料制备的不同形貌结构的W粉末对其扁平化程度及其WC-Co合金WC晶粒板晶化的影响,制备出板晶硬质合金。本论文得到了以下创新性研究成果。采用黄钨(YTO)为原料,制备了不同价态的氧化钨及纳米W粉末,同时将所获取的纳米W粉置于惰性气体中于不同温度分别保温不同时间,研究了氧化钨的相变过程中形貌结构的变化,探讨了纳米W粉制备过程中的颗粒长大机制。研究结果表明：还原过程产物均保持了部分YTO颗粒的方块状轮廓特征,呈现出不同程度的形貌结构遗传特性；受不同价态氧化钨的挥发性及其形貌结构的影响,所制备W粉末的粒度随氧化钨价态的降低而变细；过高的还原温度和过长的还原时间,将导致纳米W粉颗粒因烧结合并增粗而长大。以多种氧化钨为原料制备出了纳米W和WC粉末,研究了不同氧化钨原料对W、WC粉末的形貌结构,尤其是晶粒聚集、均匀性的影响。结果表明：纳米W粉基本上保持了其氧化钨前驱体粉末的形貌结构特征,WC粉末也呈现了不同程度的形貌结构遗传特性；受氧化钨的形貌结构的影响,W粉、WC粉末的均匀性和晶粒聚集的状况不同：以APT制备的黄钨(YTO、SYTO)为原料所获纳米W粉、WC粉末,晶粒聚集现象严重,且存在较多的粗大晶粒；紫钨(VTO)、细黄钨(MYTO)和细紫钨(AVTO)制备的W粉和WC粉末也均有不同程度的夹粗和晶粒聚集,而AMT制备的细黄钨(AYTO)为原料制备的纳米W粉、WC粉末夹粗少,均匀性好,晶粒聚集少,明显较优。粉末形貌及相成分单一,生产稳定性好,颗粒细小、均匀,具有疏松、多孔形貌结构的原料,更有利于制备优质纳米W粉和WC粉末。研究了不同形貌结构的纳米W粉末对WC粉末及WC-Co合金烧结性能的影响,并探讨了新型湿式球磨配碳和两步碳化工艺对纳米WC粉末均匀性及其烧结性能的影响,探索了低成本工业化制备均匀纳米WC粉末和显微组织均匀、综合性能优良的WC-Co超细晶粒硬质合金的新途径。实验结果表明：不同形貌结构纳米W粉制备的纳米WC粉末中的晶粒聚集和异常粗大颗粒的产生,主要与碳化过程中彼此接触的纳米W颗粒,尤其是团聚颗粒因烧结合并增粗而长大有关；颗粒细小,具有疏松、多孔形貌结构的氧化钨(细黄钨和紫钨)更容易制备出结构较疏松,分散性、均匀性较好的纳米W粉,继而制备出粒度均匀、晶格缺陷少的纳米WC粉末,用其所制备的WC-Co超细晶粒硬质合金性能也更佳；新型湿式球磨配碳和两步碳化工艺,均可以改善W和C粉末弥散分布的均匀性,能够有效抑制碳化时纳米W颗粒烧结合并增粗的现象,利于制备出粒度均匀、化学稳定性好的纳米WC粉末,用其所制备的显微组织均匀、综合性能优良的WC-7wt%Co超细晶粒硬质合金,洛氏硬度高达93.8,抗弯强度高达4450MPa。通过“高温还原-高温碳化”生产制备出高温中颗粒WC粉,并研究了其形貌结构对合金性能的影响,探索制备了具有显微组织均匀、WC硬质相尺寸适中、综合性能优良的低钴WC-Co硬质合金的新途径。结果表明：高温还原-碳化工艺可以制备出晶粒发育完整、晶格缺陷少、碳化完全、尺寸均匀的中颗粒WC粉末,其所制备的WC-6wt%Co合金组织结构均匀、WC硬质相晶形完整,平均晶粒度2.0μm-2.5μm,综合性能好,明显优于YG6合金,硬度和抗弯强度分别为90.0HRA和3000MPa。研究了不同形貌结构的氧化钨原料所制备W粉末形貌对其扁平化形貌结构及其对板晶硬质合金显微组织结构及性能的影响。结果表明：不同于蓝钨制备的高温中颗粒W粉颗粒呈类球状多面体形貌,采用黄钨为原料制备的W粉末颗粒呈多面体等轴状,更易于通过球磨获取扁平化程度高的W粉末,制备出板状晶明显的特殊显微组织结构的硬质合金。更多还原

【Abstract】 Researches on various preparation methods of cemented carbide powders and sintering technologies for high performance WC-Co cemented carbides with ultrafine grain or special microstructures have been received extensive attention. However, the impacts of powder morphologies on properties of WC-Co cemented carbides need to be explored in depth. Therefore, in this paper, the effects of W/WC powders morphologies on microstructures and properties of WC-Co alloy were researched.In this paper, the morphologies of W/WC powders prepared by different tungsten oxide materials were contrastive analysed, an efficient, controllable and lowcost industrialized process route for nano-WC powders was developed, and the ultrafine grain cemented carbides with excellent comprehensive performances were prepared subsequently. The effects of morphologies of medium-size WC powders, which prepared via high temperature reduction-carbonization process, on properties of cemented carbide were studied, and then high performance WC-6Co (%, mass fraction) alloys with medium-size WC grain and uniform microstructures were prepared. By study the effects of W powders with different morphologies on the flattening morphologies of W powders and the plate-like WC grains, the plate-like grain cemented carbide were prepared. The major contents and important results were given as follows.Different valence tungsten oxide powders and W nano-powders were prepared by yellow tungsten (YTO). W nano-powders were sintered under nitrogen gas with different temperature and duration. The morphology changes of different products in phase-transition were observed and analyzed. The growth mechanism of nano-powders was discussed. The results showed that the reduction products maintained a square shape features were similar to the morphologies of WO3powder particles, which showing morphology genetic characteristics from oxide precursors. Affected by volatile and morphologies of different valence tungsten oxide, the particle sizes of W powders were finer with reducing the valence state of tungsten oxides. The W nano-powders would agglomerate and grow up due to the sintering binding of particles if reduction duration was too long or reduction temperature was too high.W and WC nano-powders were prepared from different tungsten oxide powders. Effects of different raw materials on the morphologies, grain aggregation and uniformity of W and WC powders were researched. It showed that the W nano-powders basically maintained the morphology characteristics of tungsten oxide precursor powders, and WC powder also showed the morphology genetic characteristics. The state of aggregation and uniformity of W and WC powders was different due to the morphologies of different tungsten oxide powders. The W and WC powders prepared through yellow tungsten oxide powders (YTO, SYTO) using APT as raw materials, showed serious grain aggregation and more coarse grains. The W and WC powders prepared by violet tungsten oxide (VTO), fine yellow tungsten (MYTO) or fine violet tungsten oxide (AVTO) also showed both grain aggregation and coarse particles to some extent. But the W and WC nanopowders prepared from fine yellow tungsten (AYTO) using AMT as raw materials showed excellent performance with less coarse grain, less aggregation and better uniformity. All the above conclusions suggested that fine tungsten oxide raw powders with single phase composition, uniform particles size, loose and porous morphology structures were advantage to the preparation of high quality W and WC nano-powders.Effects of W nano-powders with different morphologies on properties of its corresponding WC powders and sintering properties of WC-Co alloy were researched. Impacts of new wet ball mixing method and two step carbonization processes on the uniformity and sintering properties of WC nanopowders were discussed. A novel and lowcost industrialized approach for preparing WC-Co ultrafine grain cemented carbide with excellent comprehensive properties was developed. The experimental results showed that the abnormal coarse WC grains were mainly due to the sintering binding of agglomeration W particles during carbonization process. Homogenous W and WC nanopowders with loose and porous morphology structures can be prepared from fine tungsten oxide powders with similar morphologies structure, and then prepared high performance ultrafine grain WC-Co cemented carbides. Both the wet ball milling method and two step carbonization process could improve the dispersivity of W powders and carbon black; restrain the aggregation and sintering combine phenomenon of nano-powders during carbonization process, which were beneficial to prepare high quality WC nano-powders with homogenous size and good chemical stability. The ultrafine WC-7Co(%, mass fraction) sintered composites prepared by wet ball milling method and two step carbonization method had homogenously microstructures and the excellent properties, the hardness and bending strength were achieved93.8HRA and4450MPa, respectively.High temperature medium-size WC powders were prepared through high temperature reduction-carburization process. Effects of morphologies on properties of alloys were researched. The new preparation method for low cobalt medium-size grain WC-Co hard alloys with homogeneous microstructure and excellent comprehensive performance was developed. It showed that the WC powders prepared by high temperature carburization process were carbonized completely, with uniform and integrated grains, high purity and low lattice defects. The WC-6Co (%, mass fraction) alloys had homogenously microstructure, integrated crystalline, and the grain size of WC crystalline was2μm to2.5μm. The properties of these alloys were better than that of YG6alloys, the hardness and bending strength were90.0HRA and3000MPa, respectively.Effects of the morphologies of tungsten powders prepared by different raw materials on the flattening morphologies of W powders and the microstructures and properties of plate-like grain cemented carbides were researched. It showed that the morphologies of W powders prepared by blue tungsten oxides (BTO) were spherical polyhedron. However, the W powders prepared by yellow tungsten oxides (YTO) were polyhedral equiaxial, which were easier access to prepare plate-like tungsten powders by ball milling, and prepare plate-like WC-Co cemented carbides.更多还原