【作者】 熊少游；

【导师】 熊惟皓；

【作者基本信息】 华中科技大学 ， 材料学， 2007， 硕士

【摘要】 硬质合金是一种重要的刀具材料和模具材料,对工业的发展和社会的进步有着举足轻重的作用。近年来人们发现当WC-Co硬质合金的晶粒尺寸达到纳米或超细级别时,将具有更高的硬度、断裂韧性、耐磨性和疲劳强度,这样就能够满足更大的工业和社会发展需要。基于此,本课题采用机械合金化方法制备了纳米WC-8Co复合粉末,并研究了其成型特点、烧结工艺以及纳米晶的添加量对YG8硬质合金性能影响情况。本文首先采用高能球磨工艺制备纳米晶颗粒,研究了不同球磨时间对硬质合金原料粒度的影响,通过粒度检测和扫描分析发现,随着球磨时间的增加,粉料的颗粒越来越细,球磨48h和60h后平均粒径分别达到0.37μm和0.29μm。对球磨36h的粉料进行X射线衍射分析,发现球磨过程中粉料中出现了贫碳相以及出现了α-Co向ε-Co的同素异构转变。随后研究了添加两种不同的成型剂对试样成型性能的影响,通过热重(TGA)和差热(DSC)等分析发现SBS(苯乙烯·乙二烯·苯乙烯)成型剂对硬质合金有最佳的成型效果。并通过进一步实验证实了SBS成型剂的优良成型性能。实验还研究了真空烧结工艺对合金的力学性能和组织结构的影响,对烧结后的WC-Co硬质合金的密度、硬度等性能进行了测试分析,确定了最佳的烧结工艺参数:烧结温度为1380℃,烧结时间为60分钟,试样性能最佳。最后本文研究了WC纳米晶的添加量对YG8硬质合金性能的影响,通过对合金的组织结构和力学性能分析发现添加量为12%时试样的性能最佳,晶粒最小达到500nm,硬度达到93HRA。更多还原

【Abstract】 WC-Co hardmetals is a kind of important cutting tool material and die material, which has the pivotal function to the industry development and society’s progress. Recently,researchers have found that ultra-fine or nanostructured WC-Co hardmetals was of superior hardness,superior toughness,superior wearing strength and fatigue strength. In this work,the experiment have been done to study the preparation of nanocrystalline WC-Co powder through high energy ball milling method,the molding of the powder and the binders’influence on it,the vacuum sintering process of the WC-8Co flan and the nanocrystalline WC’s influence on YG8 hardmetals were also studied.The preparation of ultra-fine WC-Co raw powder through high energy ball milling was studied at first. This research showed that the powder got smaller and smaller as the milling time went by. By means of the particle size test equipment and scanning electron microscope (SEM),the results showed that the average size of the particle had reached 0.37μm and 0.29μm when the raw powders were milled for 48 hours and 60 hours. The carbon-lack cemented carbide phase andε-Co phase were both found in the produced powders using X-ray diffraction (XRD). It can be concluded that some of the carbon had been lost from WC-base and someα-Co had changed intoε-Co during the high energy ball milling process.At the same time two different binders were studied to invest their influence on the moulding of the composite powders. By means of thermal gravity analysis(TGA) and differential scanning calorimeter (DSC),we found that SBS was the best binder for the moulding of hardmetals. The further experiment also proved this conclusion.The dependence of microstructure and mechanical property on the technical parameters of vacuum sintering was also investigated in this paper; the density,hardness and microstructure of the sintered nanostructured WC-Co hardmetals was measured and analyzed to have determined the optimal vacuum sintering parameters. It can be concluded that the sintering temperature at 1380℃,the sintering time lasting for 60 minutes was the optimal parameters of vacuum sintering.At last the nanocrystalline WC’s influence on the properties of YG8 hardmetals was studied. The parameters of microstructure and mechanical property reveled that the best amount of the nano-sized WC addition was 12wt%. When addition was at that level,the sintering sample’s grain size would reach 500nm,with the hardness 93HRA.更多还原