β→α Transformation of γ-Phase in Sintered WC-Co Cemented Carbides

Varying the morphology and the structure of γ-phase (Co-base Co-W-C solid solution) by means of altering the cooling rate and the preparing method of liquid sintered WC-Co cemented carbides samples, the mechanism of fcc→hcp transformation of γ-phase in WC-Co alloy has been explored. The results show that, the cooling rate is an important affecting factor on fcc→hcp transformation of γ-phase and the fcc→hcp transformation is mainly a diffusive type when cooling WC-Co samples above room temperature

Change in relative density of WC-Co cemented carbides in spark plasma sintering process

The relative density of WC-Co cemented carbides during spark plasma sintering（SPS） was analyzed.Based on the change in displacement of the ram in the SPS system,the relative densities in the sintering process can be achieved at different temperatures.The results indicated that densification of the samples started at near 900°C,the density rapidly reached its maximum at the increasing temperature stage,in which the temperature was lower than the sintering temperature of 1200°C,and most of the densification took place in the stage.Besides,the theoretical values were consistent with the experimental results.

Effect of stress ratio on fatigue lifetime and crack growth behavior of WC-Co cemented carbide

Two types of fatigue tests, a rotating bending fatigue test and a three- or four-point bending fatigue test, were carried out on a fine grained WC-Co cemented carbide to evaluate its fatigue crack growth behavior and fatigue lifetime. From successive observations of the specimen surface during the fatigue process, it was revealed that most of the fatigue lifetime of the tested WC-Co cemented carbide was occupied with crack growth cycles. Using the basic equation of fracture mechanics, the relationship between the fatigue crack growth rate(da/dN) and the maximum stress intensity factor(Kmax) was derived. From this relation, both the values of the threshold intensity factor(Kth) and the fatigue fracture toughness(Kfc) of the material were determined. The fatigue lifetime of the WC-Co cemented carbide was estimated by analysis based on the modified linear elastic fracture mechanics approach. Good agreement between the estimated and experimental fatigue lifetimes was confirmed.

MAGNETIC PROPERTY OF BINDER IN WC-Co CEMENTED CARBIDES

Tianjin Institute of Hard Alloy,Tianjin 300222,China ABSTRACT The effects of solutes of wolfram and carbon on specific saturation magnetization(4πσ)of cobalt have been examined on the basis of the measurement of Ana for hexagonal typeα-Co and cubic typeβ-Co.The Co-W-C solid solution simulative alloys have been fabricated according to binder composition in WC-Co cemented carbides and the effect of its component and structure on its Ana has been discussed too.It is pointed out that the Co phase structural factor must be considered as measuring the Ana of WC-Co cemented carbides.

γ-PHASE IN WC-Co CEMENTED CARBIDES

The allotropic transformation process of the γ-phase in WC-Co cemented carbides has been explored.Theconcepts of γ-grain and the γ-domain have been proposed forward:The γ-domain is the residual FCC-typeβ-Co grain that failed to transform when cooling alloy sample and γ-base is the HCP-type x-Co transformedmainly by means of diffusion,the outline of the γ-grain is consistent with the newly fromed β-Co grain formedat high temperature.The quantity and distribution of γ-grain domain are related to the cooling rate after sinter-ing and influence the alloys properties.

Coercive Force of γ-Phase in WC-Co Cemented Carbides

The influence of γ-phase composition in WC-Co cemented carbides on its specific coercive force H_(sc) hasbeen studied by analysing the imitative alloys of γ-phase. The results show that the H_(sc) of γ-phase is lower thanthat of pure cobalt, because the solute W can raise γ-phase H_(sc) but the carbon exhibits more intense negativeeffect on H_(sc). The effect is enhanced with raising the C solubilities in γ-phase.

Effects of deep cryogenic treatment on microstructure and properties of WC-11Co cemented carbides with various carbon contents

The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains are refined into triangular prism with sound edges via the process of spheroidization,but WC grain size has no evident change compared with that of untreated alloys.The phase transformation of Co phase from α-Co（FCC） to ε-Co（HCP） is observed in the cryogenically treated alloys,which is attributed to the decrease of W solubility in the binder（Co）.Deep cryogenic treatment enhances the hardness and bending strength of the alloys,while it has no significant effects on the density and cobalt magnetic performance.

Phase Analysis of Cemented Carbide WC-Co Boronised with Yttrium

Phase analysis for the coated surface with B 4C and Y 2O 3 of cemented carbide WC-20Co in vacuum-heating was carried out by high-temperature X-ray diffraction from ambient temperature to 1300 ℃. The results show that, the high-concentration active boron atoms are released from the boron-supply agent B 4C located on the alloy surface and diffused into the γ-phase, leading to forming the three-element boron-bearing compound W 2Co 21B 6 beside forming boron-bearing compounds on the blank surface. By contrast with boronising only, the element yttrium in boronization broadens the boronising temperature range during vacuum-sintering, catalyzes the decarbonisation decomposition of B 4C and promotes diffusion of active boron atoms into the bulk of WC-Co.

Manufacture of the Ultrafine Grain WC/Co Cemented Carbides by Combined Sintering Processing

A new kind of sintering process, combined sintering process. i.e. vacuum sintering plus hot isolate pressure sintering (HIP), was introduced for producing ultrafine WC-10% Co (mass fraction. so as the follows) cemented carbides. The effects of some processing parameters on the microstructure and mechanical properties of the obtained cemented carbides were studied. The results show that the rapid shrinkage and the pronounced densification of tile cemented carbides took place during the vacuum sintering stage, which is intinaately correlated with the local liquid sintering occurred during this earl} sintering stage for the high surface activity of ultrafine WC-Co powder. The way of high pressure imposing. isothermal treatment cycle during ac.acuum sintering and HIP sintering stage directly influence the densitication of compacts and the mechanical properties of the produced WC-10%Co cemented carbides.

Microstructure and mechanical properties of WC-Co-based cemented carbide with bimodal WC grain size distribution

In order to improve the wear resistance of coarse-grained WC-Co cemented carbides,the fine WC powder were used to reinforce the metallic binder.These WC-Co-based cemented carbides having bimodal WC grain size distributions were synthesized by liquid phase sintering.For comparison,the cemented carbides having unimodal WC grain size distributions were synthesized.The microstructure,hardness,fracture toughness and wear resistance of these cemented carbides were investigated.The results show that adding fine WC powder is an effective method to improve the wear resistance of coarsegrained WC-Co cemented carbides.The WC size,mean free path and fracture toughness decrease with the addition of fine WC powder,while the hardness exhibits an opposite trend.The impact-wear coefficient of bimodal distribution cemented carbides is noticeably lower than that of the unimodal one with the same hardness,which means that the cemented carbides with bimodal grain structure have better combination of hardness and impact-abrasive wear resistance.The impact-abrasive wear mechanism of the bimodal cemented carbides is that the fine WC grains prevent abrasive wear and the coarse WC grains prevent impact wear.

真空冶金法回收WC-Co硬质合金废料的研究

通过热力学计算,从理论上分析了1 550~2 000℃、压力小于1.73Pa的条件下,采用真空冶金法可以从WC-Co硬质合金废料中分离WC硬质相和钴黏结相。随后,以钴含量为3%~15%的WC-Co硬质合金废料为原料进行了钴含量对钴挥发率、纯度以及对WC粉末质量影响的研究。结果表明,钴挥发率随原料钴含量的增大先增大后减小,钴含量为8%时钴挥发率达最大值86.63%;原料钴含量对金属钴的纯度无明显规律性影响,钴含量为12%时金属钴纯度达最大值99.95%。WC粉末的XRD谱显示,当原料钴含量为3%和15%时出现钴衍射峰,有钴残留,原料钴含量为5%、8%及12%时未出现钴衍射峰,各次试验均未出现W2C相,无明显脱碳;WC粉末的SEM形貌显示,粉末呈近球形,表面光滑,粒径为1~8μm。试验制得了合格WC粉末和金属钴。

Influence of Microgrooves on Friction Properties of WC-3wt.% Co Cemented Carbide Against GCr15 Ball

Two cemented carbides of the same nominal composition(WC-3wt%Co) were prepared by two different preparation techniques,one of which had many microgrooves on the surface and the other was compact.The influence of micro-grooves on the friction properties of WC-Co cemented carbides sliding against the GCr15 ball was studied.Friction and wear tests were also carried out using modified ball-on-disk equipment at a sliding speed of 150 mm/s and normal load condition of 5 N.The result indicated that the wear track width and the GCr15 wear volume of the compact cemented carbide are much narrower than those of the porous ones,but the quality loss of the compact cemented carbide is slightly higher than that of the porous ones.The wear scars concentrate on a certain part of the compact cemented carbide,with a lot of abrasives on their surface.For the porous cemented carbide,the wear scars distribute uniformly,with only a little abrasives on their surface.The friction coefficient of the porous cemented carbide is smaller than that of the compact cemented carbide:the porous cemented carbide is about 0.4,but the dense cemented carbide is about 0.6 with some fluctuations during the stable phase.

废硬质合金的回收再生方法及研究进展

综述了国内外回收废硬质合金的主要方法及其基本原理、应用工艺条件和综合回收效果。指出物理处理和化学冶金方法相结合、机械破碎与高温热处理相结合的方法对废硬质合金具有很好的综合回收效果,是当前研究的主要方向。

硬质合金回收研究进展及发展趋势

硬质合金的使用量逐年快速增长,生产上废弃的硬质合金渐渐受到重视.改进废旧硬质合金的二次回收工艺,对资源的保护和可持续发展的意义重大.回收硬质合金的研究主要围绕节能环保、工艺简洁、回收效率和回收质量等方面展开.文中综述了国内外关于回收废旧硬质合金碳化钨和钴的研究目的,主要方法及其基本原理、应用工艺条件和综合回收效果.指出物理处理和化学处理冶金方法相结合、机械破碎和高温热处理相结合的方法对废旧硬质合金具有很好的综合回收效果,是当前研究的主要方向.最后对硬质合金回收的未来发展进行展望.

从硬质合金的硝酸浸出液中回收钴和铜

对从硬质合金碎屑的硝酸浸出液中置换回收金属钴和铜进行了研究。分别采用铁、铝和锌3种金属粉末进行还原置换,对比发现,锌粉对浸出液中钴、铜的置换效果好于铁粉与铝粉。采用锌粉分别进行水解除铁和二次置换钴试验,结果表明,在80℃、溶液pH=2的条件下,采用预先水解除铁-锌粉置换钴流程,反应4h,钴和铜的回收率最高,分别达到94%和98%。

氧化还原法回收废硬质合金

氧化还原法回收废硬质合金是一种简便环保的方法。分析了氧化还原法回收废硬质合金的原理及影响因素,指出了该方法存在的问题并提出相应的改进办法。重点讨论了氧化还原法回收废涂层硬质合金存在的问题及对策,在此基础上对氧化还原法回收废硬质合金的未来发展提出建议,为钨资源的可持续发展提供参考。

硬质合金再生料的表征及影响因素研究

针对我国硬质合金用量加大,废旧硬质合金量逐渐增长,钨资源储量和开采量日益减少等问题,以废旧硬质合金再生料为研究对象,借助扫描电镜、能谱、X射线衍射谱对再生钴粉、碳化钨粉的晶体形貌、化学成分、物相结构进行检测,并通过洛氏硬度计研究再生钨钴合金的硬度。经分析找出了再生硬质合金的问题所在,为改进废旧硬质合金回收技术与控制技术提供了一定的理论支撑。

磷酸动态浸出法处理低钴类废硬质合金的研究

研究了在少量氧化剂存在下，以磷酸为浸出介质，将含钴量较低的废旧硬质合金解体分离并予以分步回收的可行性。经实验建立了一条较合理的回收再利用工艺流程和生产线。

Applications of molten salt and progress of molten salt electrolysis in secondary metal resource recovery

Molten salt is an excellent medium for chemical reaction,energy transfer,and storage.Molten salt innovative technologies should be developed to recover metals from secondary resources and reserve metals from primary natural sources.Among these technologies,molten salt electrolysis is an economic and environment-friendly method to extract metals from waste materials.From the perspective of molten salt characteristics,the application of molten salts in chemistry,electrochemistry,energy,and thermal storage should be comprehensively elaborated.This review discusses further directions for the research and development of molten salt electrolysis and their use for metal recovery from various metal wastes,such as magnet scrap,nuclear waste,and cemented carbide scrap.Attention is placed on the development of various electrolysis methods for different metal containing wastes,overcoming some problems in electrolytes,electrodes,and electrolytic cells.Special focus is given to future development directions for current associated processing obstacles.

硬质合金废料电解回收钨及W(Ⅵ)在熔盐中的电化学行为

硬质合金在机械制造等领域应用广泛,产生的硬质合金废料逐年增加,对硬质合金废料进行回收有利于节约资源、保护环境。采用循环伏安技术考察NaCl⁃KCl⁃Na_(2)WO_(4)熔盐体系中W(Ⅵ)的电化学行为,利用扫描电镜及X射线衍射技术研究电解电压对硬质合金废料阳极溶解形貌及组织结构变化的影响。结果表明:W(Ⅵ)在NaCl⁃KCl⁃Na_(2)WO_(4)熔盐体系中的电化学还原过程是准可逆的,反应受扩散控制,750℃时扩散系数为6.252×10^(-5)cm^(2)·s^(-1)。随着电解电压的增大,硬质合金废料表面形貌由颗粒团絮多孔状转变为蜂窝状,随后表面出现黑色块状物质。通过控制电解电压可以选择性分离回收硬质合金废料中的钨、钴金属,硬质合金废料中的钛优先于钨溶解,增大电压,更换阴极电解可得到纯钨产品。