含晶粒长大抑制剂的WC-Co硬质合金直接法制备

发布时间：2018-03-03 20:03

  本文选题：硬质合金　切入点：WC-Co　出处：《华南理工大学》2011年硕士论文　论文类型：学位论文

【摘要】：WC-Co硬质合金由于具有极高硬度和在高温下保持硬度的优良力学性能而被广泛应用于各种工业领域,随着科技的发展,如何进一步提高其强韧性成为人们面临的一大挑战。为了提高硬质合金的性能,研究者们在合金中添加晶粒长大抑制剂细化WC晶粒,制备纳米结构硬质合金。本论文首先介绍了硬质合金的发展历程及主要制备方法、晶粒长大抑制剂的种类及机理。随后,在以经介质阻挡放电等离子体(DBDP)辅助高能球磨的添加晶粒长大抑制剂的W-C-Co复合粉体为原料,采取直接法制备硬质合金。首先,分析添加晶粒长大抑制剂的W-C-Co复合粉体在球磨过程中的微观形貌变化;在此基础上研究了不同烧结工艺对WC-Co硬质合金性能的影响,并重点研究了晶粒长大抑制剂的添加量及不同形态对硬质合金力学性能的影响;最后对晶粒长大抑制剂的作用机理进行了初步探索。 研究发现,DBDP辅助高能球磨对添加了晶粒长大抑制剂的W-C-Co混合粉体的作用效果不仅仅是细化单质粉体,还使石墨包覆于W颗粒表面,粉体颗粒呈片层状叠加。DBDP辅助高能球磨对W粉的细化效率呈现出先快后慢的规律,在经过3小时球磨后,其晶粒尺寸大约为23nm。 采用不同工艺的直接法烧结制备含晶粒长大抑制剂的WC-Co硬质合金,发现采用压力烧结工艺较真空烧结制备出的硬质合金其液相Co流动充分,不仅较好的填充了由于气体逸出而造成的孔洞,还均匀分布于硬质相WC之间,起到很好的粘结作用。在1340℃下加载4MPa压力制备的WC-10Co-0.6VC硬质合金,致密度达到99%,洛氏硬度达到HRA91.8,横向断裂强度TRS达到3348MPa。通过改变VC的量,可进一步改善组织,提高其力学性能。随着VC添加量的增加,合金中WC由长条状变为薄片状,晶粒细化趋势明显;合金的硬度呈现出不断提高的规律,而横向断裂强度则先升高后降低。经综合比较后认为,采用相同的工艺制备的添加0.9VC制得的WC-Co硬质合金具有最佳的力学性能,其硬度达到HRA92.4,横向断裂强度TRS约为3600MPa。 为简化工艺,提高经济性,在W-C-Co混合粉体中直接添加V_2O_5,在烧结过程中W、V_2O_5同时发生碳化反应,原位生成抑制剂。结果表明,生成的VC对WC的抑制效果更好,比直接添加VC更能抑制WC晶粒在纵向上的生长。 在透射电镜下观察到WC晶粒呈薄片状(厚度小于100nm),并且在WC/WC界面上发现有VC的聚集。结合SEM图片,可以认为VC主要是抑制WC晶粒在0001方向的生长。VC的加入细化了WC晶粒,WC晶粒细化,晶界增多,能有效阻碍裂纹的扩散,有利于提高硬质合金的横向断裂强度;但是当VC在Co中饱和后,多余的VC会以脆性相的形式在晶界上析出,导致其横向断裂强度降低。
[Abstract]:WC-Co cemented carbide has been widely used in various industrial fields because of its excellent mechanical properties of extremely high hardness and keeping hardness at high temperature, with the development of science and technology. In order to improve the properties of cemented carbides, researchers added grain growth inhibitors to the alloys to refine WC grains. In this paper, the development of cemented carbides, the main preparation methods, the types and mechanisms of grain growth inhibitors are introduced. Cemented carbides were prepared by direct method from W-C-Co composite powder assisted by dielectric barrier discharge plasma (DBDP) assisted high energy ball milling with grain growth inhibitor. The microstructure changes of W-C-Co composite powders with grain growth inhibitor during ball milling were analyzed, and the effects of different sintering processes on the properties of WC-Co cemented carbides were studied. The effects of the amount of grain growth inhibitor and the different morphology on the mechanical properties of cemented carbide were studied. Finally, the mechanism of grain growth inhibitor was preliminarily explored. It is found that the effect of DBDP assisted high energy ball milling on W-C-Co mixed powder with grain growth inhibitor is not only to refine the powder, but also to make graphite coated on the surface of W particle. After 3 hours ball milling, the grain size of W powder is about 23 nm. WC-Co cemented carbides with grain growth inhibitor were sintered by direct sintering with different processes. It was found that the liquid phase Co flow of cemented carbides prepared by pressure-sintering process was more adequate than that prepared by vacuum sintering. The WC-10Co-0.6VC cemented carbide prepared at 1340 鈩，

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