APT原料粒度分布对碳化钨粉和超细晶硬质合金性能影响

仲钨酸铵(简称APT),多年来普遍采用冶金化学方法进行大规模批量化生产,APT的国家标准也主要涉及其化学性能指标,对于物理性能指标的要求很少,并且不能完全反应APT的内在品质,从而导致了绝大部分APT都符合化学指标要求的国家标准,但是作为原料使用生产氧化钨、钨粉、碳化钨粉以及制备合金,产品性能存在明显差异。特别是在生产超细纳米钨粉、超细纳米碳化钨粉以及超细纳米硬质合金过程中,这种对于原料APT的要求,尤其是物理性能的要求,则格外需要引起重视。本文专门研究了APT的粒度分布对于超细碳化钨以及超细硬质合金性能影响,致力于提醒APT原料生产者们更加关注APT粒度分布等物理性能指标的提升和改善。     

超细碳化钨粉末的制备研究现状及进展

碳化钨是一种重要的硬质合金材料,也是一种性能优良的催化材料,本文对近年来超细碳化钨粉的制备方法分为气相法,液相法和固相法三大类,并围绕碳化钨的颗粒细化,从钨源和碳源的选择,工艺流程等方面进行了归纳,     

专利信息

超细金红石相二氧化钛粒子的合成方法；凹凸棒负载纳米氧化铈的制备方法；一种高比表面积铈铝基复合氧化物及其制备方法；一种无定形硅铝及其制备方法；一种基因传输载体磷酸钙纳米颗粒的制备方法；利用废超细硬质合金机体快速粉碎分离提取碳化钨和碳酸钴的方法。     

用气流粉碎分级法对超细WC粉末研磨

超细硬质合金具有高硬度、高耐磨性的优异性能,保证超细硬质合金的晶粒度小而且均匀的一个关键因素就是以粒度细小、分布均匀的超细WC粉末为原料.在超细WC粉末的制备过程中,对从氧化物还原、碳化后得到的WC粉末的后续处理非常重要,目前普遍采用的是球磨粉碎,但是经过机械方法粉碎后的超细粉末,很难使物料达到所需粒度要求,产品往往处于一个较大的粒度分布范围.文中讨论了一种新型的粉碎技术--气流粉碎分级技术,它兼有气流粉碎和气流分级,使得到的粉末在气流粉碎下细化、在气流分级下减小其粒度分布.气流粉碎分级技术是当今世界原材料加工技术的重要方面,将其应用于超细硬质合金的制备中有很重要的实际意义.     

碳化钨硬质合金制备技术研究进展

碳化钨硬质合金具有极高的硬度和优良的耐磨性,被广泛应用于钻头、工具、模具、针头、刀具等需要耐磨损和特种加工的行业.本文详细论述了硬质合金的研究进展;重点总结了碳化钨粉体制备和硬质合金烧结技术;最后列举了碳化钨硬质合金的应用领域和发展前景.     

成果鉴定

大连理工大学化工学院完成的“球形和纤维状高纯超细氧化铝粉体制备技术”日前通过成果鉴定。　　成都中纳新材料有限公司研制的“纳米结构碳化钨—钴复合粉末制备技术”通过鉴定成果鉴定     

高强韧性特粗晶采掘工具用硬质合金的研究

分析了国内外特粗晶硬质合金的研究成果,通过对"碳化钨粉末生长控制技术"和"特粗晶硬质合金的制品技术"进行研究,成功地研制出了适用于采掘工具用特粗晶硬质合金。     

喷雾干燥-固定床法制备碳化钨粉末

采用喷雾干燥-固定床法制备碳化钨粉末,研究了喷雾干燥和碳化反应温度对制备偏钨酸铵前驱体以及碳化钨的影响,前驱体粉末呈现均匀的球状形态,平均粒径为10~20μm,喷雾温度对影响粒径大小和分布影响小;400℃的进口温度下进行喷雾干燥,喷雾粉末仍然保持偏钨酸铵原来的基本组成不发生分解。以H2/CO为还原碳化介质,在900℃的温度下还原碳化前驱体,制备得到碳化钨粉末,粒径为0.5~2.0μm,比表面积为6.5 m2/g;比较传统的制备碳化钨的实验方法,降低了制备碳化钨的反应温度;颗粒比表面积大,可作为催化剂应用于加氢反应、烷烃裂解、催化重整以及燃料电池等领域。     

电化学法分解硬质合金废料制备氧化钴

利用电化学方法，从硬质合金废料制备氧化钴和碳化钨粉。电解过程在盐酸溶液中进行，以不锈钢作阴极，硬质合金废料作阳极。电解液经净化处理，用草酸沉淀得草酸钴，再经煅烧得到氧化钴。     

抑制剂对纳米WC-10Co复合粉末烧结性能的影响

以液相复合-连续还原碳化方法制备的纳米WC-10Co(以质量计)复合粉末为原料,选择VC和Cr3C2作为超细WC-10Co硬质合金晶粒生长抑制剂,研究晶粒生长抑制剂加入量对超细WC-10Co硬质合金组织、晶粒和性能的影响。实验结果表明：超细WC-10Co硬质合金中WC晶粒度随着晶粒生长抑制剂加入量的增加而减小,纳米WC-10Co复合粉中加入0．4％VC和0．4％Cr3C2(以质量计)晶粒生长抑制剂,经1380℃真空烧结60min,1320℃低压处理30min后,可以得到平均晶粒度380nm、断裂强度3．55 GPa和Rockwell A硬度92．6综合性能较好的超细WC-10Co硬质合金。过多添加晶粒生长抑制剂反而降低了超细WC-10Co硬质合金的性能。     

The effect of tungsten buffer layer on the stability of diamond with tungsten carbide–cobalt nanocomposite powder during spark plasma sintering

WC–Co nanocomposite powder produced by spray pyrolysis–continuous reduction and carbonization technology, diamond coated with tungsten (W) by vacuum vapor deposition and uncoated diamond were used in this study. This work adopted the spark plasma sintering (SPS) process to prepare diamond-enhanced ultrafine WC–Co cemented carbide composite material. The effects of W buffer on the stability of diamond with WC–Co nanocomposite powder during SPS were investigated. Results showed that the uncoated diamond was mechanically embedded in WC–Co cemented carbide matrix, while the diamond coated with tungsten was combined chemically with WC–Co cemented carbide matrix. Moreover, there was a transitional layer between the diamond and the matrix which could improve the thermal stability of the diamond, prevent carbon atom of the diamond from dissolving in Co phase and increase the bonding strength of the interface between the diamond and the matrix.     

Tool life and wear of WC–TiC–Co ultrafine cemented carbide during dry cutting of AISI H13 steel

WC–5TiC–10Co ultrafine cemented carbides were prepared and used for the cutting tool for AISI H13 hardened steel. The effect of cutting parameters on the tool life and tool wear mechanism was investigated, and conventional cemented carbide with the same composition and medium grain size were prepared for comparison. The results showed that WC–5TiC–10Co ultrafine cemented carbides possess higher hardness and transverse rupture strength, and showed better cutting performance than conventional insert with the same cutting condition. Tool life was analyzed by an extended Taylor's tool life equation, indicating that cutting speed played a profound effect on the tool life and wear behavior of both cutting inserts. SEM and EDS analysis revealed that there were major adhesive wear and minor abrasive wear on the rake of WC–5TiC–10Co ultrafine inserts, and increase of cutting speed resulted in a transition from abrasion predominant wear mechanism to adhesive wear on the flank face. As for the conventional inserts, there were combination of more serious abrasive and adhesive wear on the rake and flank. The favorable cutting performance of ultrafine WC–5TiC–10Co inserts was attributed to the higher hardness and less thermal softening during machining.     

陶瓷-硬质合金复合刀片材料的力学性能与界面结构

采用热压烧结工艺制备了刀具用陶瓷－硬质合金复合片．复合片上层为具有一定厚度的Ａｌ２Ｏ３／ＴｉＢ２陶瓷材料,下层为ＷＣ／Ｃｏ硬质合金．结果表明：复合片综合了陶瓷材料的高硬度和硬质合金的高强度,其性能介于陶瓷材料和硬质合金之间．Ｘ射线衍射、电子探针和扫描电子显微镜分析表明：烧结过程中硬质合金和陶瓷材料中的元素在界面相互扩散,并有新相形成,增加了界面结合强度,其界面为化合物型和扩散型的混合．     

High-Temperature Reaction Between Cemented Tungsten Carbide and Copper

Interdiffusion in the system cemented tungsten carbide-molten copper has been studied in the range ≤1120°C with special emphasis on the effects of WC grain size and Co content. Techniques used for analyzing the diffusion layers obtained are EPMA, optical microscopy, and microhardness measurement. A Cu-bonded WC layer develops with simultaneous diffusion of Co from the cemented carbide into the bulk copper. The Cu-bonded WC layer grows until a Co-rich layer forms at the Cu/WC-Co interface; further heating pushes the Cu-bonded WC layer deep into the bulk cemented carbide without any significant change in layer thickness. When the WC grain size is reduced and the cobalt content increased, the penetration of copper into cemented carbides increases. A tentative mechanism of interdiffusion has been proposed based on the experimental results.     

Preparation of nano-sized tungsten carbide via fluidized bed

Ultrafine or nano-sized of tungsten carbide(WC) is the key material to prepare ultrafine grained cemented carbides. In this paper, nano-sized WC powders were directly prepared by using industrial nano-needle violet tungsten oxide(WO_(2.72)) as the raw material, a fluidized bed as the reactor, and CO as the carbonization gas. The relationship between particle sizes and reaction temperatures, residence times, atmospheres has been investigated systematically. In addition, the physical–chemical indexes(such as residual oxygen, total carbon and free carbon) of the products were measured. The results indicated that the particle size of WC increased with the increase of temperature from 800 to 950 °C. As the residence time increased, the particle size decreased gradually,and then increased due to slight sintering. The introduction of hydrogen reduced the carbonization rate, and is not beneficial to obtaining nano-sized WC. Products that satisfy the standard were obtained when WO_(2.72) reacted with CO at 850 °C, 900 °C and 950 °C for 3.0 h, 2.5 h and 2.0 h, respectively. The particle sizes of the three samples calculated from the specific surface area were 46.4 nm, 53.2 nm and 52.1 nm, respectively.     

The two dimensional microstructure characterization of cemented carbides with an automatic image analysis process

The traditional two dimensional microstructure characterization of cemented carbide, based on stereology of linear intercept method, requires tedious and subjective manual measurements. In this study, an automatic image analysis procedure with two key techniques, i.e. maximum class square error method and watershed transformation method, has been successfully developed. The image analysis for WC-16Co cemented carbides with this procedure easily acquires consistent microstructure parameters. The analysis for area weighted WC grain size, as well as the subsequent mean free path of Co binder show quite different results compared with the conventional number weighted data. It is found that for both number weighted and area weighted data, the contiguity of WC/WC grains is insensitive to the variation of either mean WC grain size or mean free path of Co binder. The mean WC grain size is linearly related to the mean free path of Co binder. The hardness of cemented carbide, having a linear relationship with the inverse square root of mean WC grain size, conforms to Chermont and Osterstock's model. Although it is too early to conclude whether number weighted or area weighted WC grain size (and subsequent mean free path of Co binder) is better, this study shows that area weighted WC grain size and the corresponding mean free path of Co binder are more suitable for Chermont and Osterstock's hardness modeling compared with number weighted WC grain size. The area weighted WC grain size and subsequent mean free path of Co binder, which have rarely been considered for microstructure characterization of cemented carbide previously, could be the key parameters for a better understanding of the microstructure evolution, as well as a better mechanical behavior modeling for cemented carbide.     

Effect of WC particle size on the microstructure and mechanical properties of Ni–Co coarse grain cemented carbide

The effect of different WC grain size additions on the microstructure and grain distribution of Ni–Co coarse crystalline cemented carbide was studied. And then the effect of grain distribution on the mechanical properties of cemented carbide was discussed. The effect of WC grain size on the grain size and coherency of cemented carbide was analyzed by microstructure. And the distribution of grains in the microstructure was investigated by the truncation method. The addition of fine (1.1–1.4 μm), medium (2.3–2.7 μm), and coarse WC (5.6–6.0 μm) particles can increase the nucleation rate of WC grains in the bonded phase. And the higher grain growth driving force can produce the theoretical limitation of nucleation and inhibit the coarsening of WC grains to a certain extent. The WC grain size has an insignificant effect on the frequency of the occurrence of super-coarse grains in coarse crystalline cemented carbide. The average grain size and super coarse grains in microstructure gradually decrease, which promotes the improvement of transverse rupture strength. The increase of the adjacent degree and the decrease of the mean free path reduce which is beneficial to the improvement of the corrosion resistance of the alloy. The best overall performance of the alloy is achieved when fine-grained WC is added.     

低成本碳黑在WC生产中的应用

采用高纯碳黑和低成本碳黑生产YG11C类WC产品。对产品的关键参数Fsss粒度、Ct(总碳)及硫含量进行对比分析得到通过两种原料制得的产品质量没有明显改变;通过合金产品批量化验证,合金产品品质未有明显改变。     

Effect of carbon content on microstructure and mechanical properties of WC-10Co cemented carbides with plate-like WC grain

Four sets of WC-10Co cemented carbides with different carbon content were prepared by adding the ultrafine WC powders as seeds during the in-situ sintering reaction among W, Co and C. The effect of carbon content on microstructure and mechanical properties were studied. The results show that the microstructure, phase composition and mechanical properties of WC-10Co cemented carbides with plate-like WC grains were seriously affected by the carbon content. The fast growth of WC grains with high carbon content could proceed the prismatic plane preferentially along the <1 0 $1(-)$ 0> directions, resulting in the high content of plate-like WC grains. The density increased with the increment of the carbon content and reached the maximum value, then, followed by a decline. The hardness and the transverse rupture strength of the alloy in the two-phase zone with carbon content of 5.91 wt% reached the maximum value. The existence of plate-like WC grains could impede the propagation of the cracks due to the decrease of the weakest carbide regions and the increase of the basal facets of broken WC crystals. In this case, more fracture energy was required to crack propagation and further improved the transverse rupture strength. Additionally, the plate-like WC was benefit to reduce the wear volume and bring about a better wear resistance. Thus, the alloy with the appropriate proportion of carbon content can obtain higher mechanical properties and wear resistance.