放电等离子烧结制备超细WC基硬质合金

采用纳米碳化钒(V8C7)粉末作为晶粒抑制剂及放电等离子烧结(SPS)方式制备超细WC基硬质合金.X射线衍射结果表明:超细WC基硬质合金主要由WC和Co3C两相组成,随着温度的升高,WC的衍射峰逐渐向小角度偏移.扫描电镜结果表明:SPS和纳米V8C7粉末对超细WC基硬质合金的微观组织具有重要影响.SPS使超细WC基硬质合金在较低温度下(1200℃)实现致密化;纳米V8C7粉末可以有效抑制超细WC基硬质合金中WC的晶粒长大,1200℃时WC的晶粒尺寸约500 nm.力学性能结果表明:1200℃时超细WC基硬质合金具有较高的性能(相对密度99.5%,洛氏硬度93.2,断裂韧性12.5 MPa·m1/2).     

原始WC粉末粒度组成对超细硬质合金组织及性能的影响

分别采用两种工艺制备的Fsss粒度相近的WC粉末为原料,在不同球磨时间下制备WC-10%Co-0.3%Cr_3C_2-0.5%TaC试样于1 450℃下烧结,对比两种合金的微观结构和常规性能。结果表明:采用粒度分布较窄、不含WC团聚颗粒的WC粉末为原料,经10 h球磨就能得到微观组织结构均匀的超细硬质合金;采用粒度分布较宽、含有大量WC团聚颗粒的WC粉末为原料,需要50 h球磨才能得到微观结构较为均匀的超细硬质合金,球磨时未被破碎的WC团聚颗粒烧结时会长大为WC晶粒团聚体,或者是粗大WC晶粒,会降低合金的抗弯强度值;原始粉末粒度组成对超细硬质合金的矫顽磁力、密度和硬度影响较小。     

WC/Co纳米复合粉质量特性的研究

本文探讨了喷雾转换法制备WC/Co纳米复合粉的生产工艺特点、粉末的物理化学特性以及在超细合金中的应用效果。各方面的实验数据表明:WC/Co复合粉中WC碳化完全、粒度细而均匀,钨钴元素达到分子级均匀混合,Co对WC形成纳米级包覆,粉末颗粒外形多呈球状,球体由部分合金化的WC/Co粒子聚合而成,粒子之间存在明显的烧结颈,其亚晶尺寸在100nm以下。复合粉经强化球磨后制取的超细合金较传统工艺制备的合金的WC相晶粒更加均匀,具有更好的物理力学性能和更高的使用寿命。即使不添加抑制剂,复合粉制备的合金仍具有晶粒细而均匀的特点。     

超细结构WC-η涂层的制备及其耐熔锌腐蚀性能

以钨氧化物、钴氧化物和炭黑为原料,采用创新的原位反应技术快速合成超细WC-η复合粉,在优化的工艺条件下制备复合粉中只含有WC和Co6W6C相,粉末平均粒径为260 nm。复合粉经团聚造粒制备得到具有高致密性和良好流动性的热喷涂粉末,以此粉末作为喂料,利用超音速火焰喷涂技术制备得到超细结构的WC基涂层,其平均显微硬度(HV0.3)达到(14060±340)MPa,孔隙率仅约为0.3%。熔融锌腐蚀结果表明,制备的超细结构WC基涂层具有良好的耐熔锌腐蚀性能,其腐蚀机制主要是锌液沿微裂纹扩散导致涂层自表层向内部出现缓慢的溶解腐蚀,并逐渐形成贯穿性裂纹而引起涂层材料的大块剥落。     

高压扭转纳米结构Al-Mg铝合金的微观结构演变和位错组态

利用透射电镜（TEM）和高分辨透射电镜（HRTEM）研究高压扭转大塑性变形纳米结构Al-Mg合金的微观结构演变和位错组态。结果表明：对尺寸小于100 nm的晶粒,晶内无位错,其晶界清晰平直;而尺寸大于200 nm的大晶粒通常由几个亚晶或位错胞结构组成,其局部位错密度高达10^17 m^-2。这些位错是1/2〈110〉型60°位错,且往往以位错偶和位错环的形式出现。在高压扭转Al-Mg合金的超细晶晶粒中,用HRTEM同时观察到分别由0°纯螺型位错和60°混合位错分解产生的Shockley部分位错而形成的微孪晶和层错。这些直接证据证实,通常存在于FCC纳米晶中由晶界发射部分位错而产生孪晶和层错的变形机制,同样可以存在于超细晶FCC金属中。基于实验结果,分析了高压扭转Al-Mg合金中的局部高密度位错、位错胞、非平衡晶界、层错和孪晶等对晶粒细化的作用,提出了相应的晶粒细化机制。     

优质粗晶WC碳化工艺研究

采用二步碳化法制备出了优质粗晶WC粉末,该粉末具有化合碳高,游离碳低,为单一相,有害杂质含量少,晶粒均匀,晶内亚晶尺寸均匀,不含显微缺陷,较低的位错密度等特性,并解决了WC炸裂问题.已用该粉末作原料为用户批量提供性能优异的硬质合金.     

湿磨时间对超细WC粉末晶体学参数的影响

超过60 h的长时滚动湿磨是目前国内制备超细晶硬质合金最常用的工艺。本文探讨湿磨时间对超细WC粉末晶体学参数的影响规律,旨在论证上述湿磨工艺的合理性。采用滚动湿磨工艺制备WC-0.47Cr3C2-0.28VC-7Co超细混合料,采用Williamson-Hall法和Rietveld拟合法对X射线衍射图谱进行分析。结果表明,与WC原料相比,湿磨50 h和68 h后,WC晶粒尺寸由原始态54 nm分别减小至45 nm和40 nm,降低幅度分别为17%和26%;微观应变由原始态0.16%分别增加至0.17%和0.18%,增加幅度分别为6%和13%,增加幅度不明显;晶格常数a由原始态0.290 43 nm同步减小至0.290 40 nm,晶格常数c由原始态0.283 96 nm分别增加至0.283 97 nm和0.284 01 nm,增减幅度非常小。WC晶体微观应变的小幅变化不会对烧结过程中WC晶粒生长驱动力产生明显影响,适当延长湿磨时间以改善Co在超细WC–Co基混合料中分散均匀性的工艺具有合理性。     

高密度纯钨的低温活化烧结工艺及其致密化行为

采用溶胶喷雾干燥-煅烧-氢热还原法制备了BET粒径为0.21μm的超细纯钨粉末,并利用球磨处理进一步活化粉末。研究了超细纯钨粉末形貌及其性能随球磨时间的变化特征,探索了未球磨、球磨5h及球磨10h3种超细纯钨粉末烧结致密工艺,此外还详细研究了纯钨烧结体组织形貌、晶粒尺寸及显微硬度等性能随烧结温度及球磨时间的变化规律。结果表明,球磨处理对超细纯钨粉末的烧结起到了极大的活化作用,由球磨10h粉末制成的压块在1900℃下烧结2h其致密度即可达97.3%,比传统微米级纯钨粉末制成的压块达到相同烧结致密度的温度降低了600℃以上。同时,球磨处理可以大幅降低钨粉的起始烧结温度和再结晶温度,获得组织更加均匀细小、力学性能(硬度)更加优良的钨烧结体。     

碳化温度对超细WC粉末性能与合金性能的影响

本文探讨了碳化温度对超细WC形貌、粒度、亚晶尺寸等粉末性能的影响和不同碳化温度制备的超细WC粉末对合金强度、硬度、微观结构等合金性能的影响。粉末样品的制备采用钨粉与炭黑的混合物为试验原料,在中频电炉中,分别于1 450、1 480、1 520℃碳化,利用Fsss粒度仪、SEM电镜、马尔文激光粒度分布仪、X射线衍射仪等仪器对粉末样品进行分析检测;制备的粉末样品加入细钴粉按照6%配成合金,采用1 410℃与1 450℃两个烧结温度制备成合金试验样品,测维氏硬度,抗弯强度,用金相显微镜观察合金的组织结构,比较不同碳化温度制备的超细碳化钨在不同的烧结温度下制备的合金性能与组织结构的差异。研究表明:碳化温度对超细碳化钨各项性能及超细合金各项性能有较大的影响,温度在1 480℃以下,单颗粒与单颗粒之间的烧结长大比较微弱,单颗粒内部的亚晶长大也很微弱,但当温度升高到1 520℃,亚晶尺寸有明显升高,粉末结晶更趋完整。低温碳化的超细碳化钨,结晶不完整,缺陷较多,粉末活性高,容易长粗,矫顽磁力降幅较大,造成合金的微观结构不均匀。高温碳化的超细碳化钨在1 410℃烧结制备的合金试样的综合性能与微观结构要优于1 450℃烧结制备的合金试样。     

超细钨铜合金粉末在金刚石工具中的应用研究

采用超细钨铜合金粉末和单质钨、铜粉末热压烧结成两组金刚石胎体块,利用硬度计,排水法,万能实验机,扫描电镜和锯切实验等测试分析手段分别分析测量了胎体的硬度、致密度、抗弯强度、断口形貌和锯切性能。实验结果表明:在高钨基胎体配方中添加超细钨铜合金粉末比添加单质钨、铜粉末可以显著提高胎体的硬度10 HRB左右,改善胎体合金使之均匀化,在本实验配方中,干切硬花岗岩时,高钨基胎体配方中添加超细钨铜合金粉末比添加单质钨、铜粉末切割平稳,形成胎体和金刚石有效的磨损匹配,可以显著提高工具的使用寿命30%左右。烧结温度范围内,添加合金粉的胎体抗弯强度均比添加单质钨、铜粉末低100 MPa左右,这主要是使用的超细钨铜粉末的氧含量较高所致。     

Influence of phase components of tungsten oxide on homogeneity of ultrafine tungsten powder

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氧化钨相成分对超细钨粉均匀性的影响

研究了通过传统氢还原工艺制备超细钨粉末过程中氧化钨原料相组成对超细钨粉均匀性的影响。结果表明：单一相组成的氧化钨能制得超细而均匀的钨粉,多种相组成的氧化钨,由于其在还原过程中存在不同的还原路径和还原速度,制得的钨粉虽细但不均匀。     

Effect of process parameters on induction plasma reactive deposition of tungsten carbide from tungsten metal powder

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中国超细晶硬质合金及原料制备技术进展

超细晶硬质合金是WC晶粒度≤0．5μm的硬质合金,这类合金具有高强度和高硬度的优异性能。目前由超细晶硬质合金制备的高效刀具已经广泛用于航空航天、核能、汽车、发电设备、新能源和电子通讯等现代制造业。主要对中国超细晶硬质合金原料（例如超细碳化钨粉、钴粉、复合粉）和超细晶硬质合金制备技术、性能及表征方法作了系统的阐述。最后对超细晶硬质合金制备技术进行了展望。     

Influence of fabricating process on microstructure and properties of spheroidal cast tungsten carbide powder

A super-high temperature furnace was developed to fabricate spheroidal cast tungsten carbide powder with excellent flowability and fine feathery structure in a large scale. Optical microscope and scanning electron microscope were taken to characterize the morphology and microstructure of cast tungsten carbide powder. X-ray diffractometry was used to analyze the phase composition of powders involved. It is found that the carbon potential in the furnace and feeding speed play an important role on the microstructure, morphology and properties of the spheroidal cast tungsten carbide powder. As carbon potential is between 0.3% and 0. 9% in the furnace, cast tungsten carbide powder with hardness over 2800( HV0.5), flowability over 7.1 s/50 g and tap density over 10.3 g/cm^3 is obtained.     

钴粉粒度对超细硬质合金性能的影响

目前在硬质合金领域,钴粉是硬质合金最佳的粘结剂,钴粉性能对合金性能有一定的影响,但研究钴粉性能对硬质合金性能及结构影响的论文较少。实验选取了从0.78～4.61μm不同粒度级别的钴粉,按YF06合金牌号配料,从压坯压力、压坯中钴粉分布以及合金的物理性能和金相组织结构等方面探讨了钴粉粒度对超细硬质合金性能及结构的影响。结果表明:随着钴粉粒度增粗,压坯的压制压力增大,但钴粉粒度对超细混合料压坯中的整体钴分布影响不明显;粒度1.0～1.5μm钴粉比其他粒度级别的钴粉制备的超细硬质合金的整体物理性能更佳;钴粉粒度对超细硬质合金的组织结构也有一定的影响,大于3μm的粗钴粉容易造成超细合金中出现钴池,钴粉太细有则可能造成钴相分布不均。     

Defect Control of the WC Hardmetal by Mixing Recycled WC Nano Powder and Tungsten Powder

Tungsten metal powder was added to recycled WC nano powder to control the macro and micro defects of WC hardmetal. The macro and micro defects caused by the excess carbon in the recycled WC powder were markedly removed after the addition of tungsten metal powder ranging from 2 to 6 wt%. The density and hardness of the WC hardmetals also increased due to the removal of defects after adding the tungsten metal powder. The density and hardness of WC hardmetals with the addition of W metal powder ranged from 8 to 12 wt% increased linearly as the W metal powder content increased due to the formation of a new (Co- and W-rich WC) composition. The surface morphology of the WC hardmetals was observed via field emission scanning electron microscopy, and a quantitative elemental analysis was conducted via X-ray fluorescence spectrometry and energy dispersive X-ray analysis. The density and hardness of the WC hardmetals were respectively measured using an analytical balance and a Vikers hardness tester. The effect on the defects in the recycled WC hardmetals through the addition of the tungsten metal powder was discussed in detail.     

A facile pathway to prepare ultrafine WC powder via a carbothermic pre-reduction followed by carbonization with CH4-H2 mixed gases

In the present work, ultrafine tungsten carbide (WC) powder with a high purity has been prepared by first roasting yellow tungsten trioxide (WO₃) and carbon black powder under argon atmosphere followed by the further carbonization reaction with CH₄-H₂ mixed gases. The effects of C/WO₃ molar ratio, CH₄ percentage in the CH₄-H₂ mixed gases on the phase composition, morphology and particle size of the products were discussed. The results revealed that when the C/WO₃ molar ratios were 2.5 and 2.6, nano tungsten carbide powder with the average particle sizes of 93 nm and 77 nm could be prepared. Whereas, when the C/WO₃ molar ratio was in the range of 2.7–3.5, the finally prepared WC has the particle size of 446–192 nm, and became smaller with the increase of C/WO₃ molar ratio. The percentage of CH₄ should be <15% to prepare WC with a low free carbon content. From the results of thermodynamic calculation, X-ray diffraction (XRD), FE-SEM, and infrared carbon‑sulfur analyzer, it was concluded that ultrafine tungsten carbide powders with a high purity could be successfully prepared by this method.     

Influence of carbide grain size and crystal characteristics on the microstructure and mechanical properties of HVOF-sprayed WC-CoCr coatings

Nanostructured WC-CoCr coatings play a significant role in industrial sectors including petrochemical and aerospace fields. However, their fracture toughness requirements still need to be further improved because of more decarburization of conventional nano scale WC grains. In the study, three representative types of WC-CoCr powders were selected to illustrate the dependence of the microstructure and mechanical properties of HVOF-sprayed coatings on the carbide grain size and their crystal characteristics in the starting powders. It is demonstrated that the ultrafine powder causes excessive decomposition of the WC phase to W₂C phase when compared to submicrostructured and nanostructured powders, owing to the WC grains with a higher density dislocation. The present study implies the critical role of apparent twin characteristics within WC grains in enhancing the microhardness and fracture toughness of the nanostructured coating. The coating deposited with nanostructured powders exhibits the best comprehensive properties, which include low decarburization, superior microhardness and fracture toughness.     

蓝钨与紫钨氢还原法生产超细钨粉的比较

在相同的工艺条件下,比较了蓝钨与紫钨氢还原法生产的钨粉的性能差别.结果表明:与蓝钨相比,紫钨生产的钨粉粒度更细更均匀,并且钨粉粒度受装舟量和氢气流量的影响较小.并从原料的微观结构和氢还原机理两方面分析了造成不同原料生产的钨粉粒度和均匀性差别的原因.