中颗粒钨粉高温碳化制取粗晶碳化钨粉的研制

本文叙述采用中颗粒钨粉高温碳化制取粗晶WC粉的过程,探讨碳化和球磨破碎工艺对WC的性能影响,并对用中颗粒钨粉高温碳化制取的粗晶WC粉与传统工艺制取的粗晶WC粉生产的合金性能进行比较。     

制粉温度对WC粉微观结构和合金力学性能的影响

在高温下制取的 WC 粉,结晶完整,晶内亚结构粗大,微观应变小。用不同温度制取的 WC 粉所配制的合金,其力学性能有差异,且合金中 WC 相继承了原始WC 粉末微观不均匀的规律。高温制取的 WC 粉所配制的合金具有高的冲击韧性和良好的使用性能。     

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。     

“高温粉末”WC和气压烧结对YG8硬质合金性能的影响

选择高温碳化和普通碳化两种WC粉为原料制备YG8硬质合金试样,同时对比了不同的烧结工艺,结果表明采用高温碳化的WC粉制备的合金性能有明显的提高,低气压烧结工艺对合金性能的提高也是十分有益的。     

钨粉碳化防粘涂料的研制

在生产粗颗粒WC粉时，因WC粘舟而引起舟皿非正常破损是比较常见的现象。本文对W粉碳化时WC粘舟原因进行了分析，介绍了一种既具有较好防粘效果，同时也对WC与合金性能无不良影响的W粉碳化防粘涂料。     

不同粒度WC配比对粗晶硬质合金显微组织和性能的影响

分别采用单一WC粉球磨和采用两种粒度不同WC粉混合球磨的制备工艺制取3批相同配碳量、WC平均晶粒度相近的WC-6%Co粗晶硬质合金，通过分析合金WC晶粒的粒度分布，以及合金的矫顽磁力(H_c)和断裂韧性(K_IC)，研究不同制备工艺对合金WC晶粒的粒度分布、矫顽磁力、断裂韧性的影响。结果表明：不同制备工艺对合金的WC晶粒的粒度分布、钴相分散均匀性及断裂韧性有明显的影响。WC平均晶粒度相近时，采用两种WC粉末混合球磨工艺与采用一种WC粉末球磨工艺制取的合金相比，WC晶粒的粒径离差系数分别降低8.9%、15.6%,WC晶粒分布更均匀，合金矫顽磁力提高0.2、0.4 kA/m，合金韧性提升2.5%、10.8%。     

碳化温度及抑制剂的添加对超细WC性能的影响

将同一批超细钨粉,分成两组进行配炭,一组不添加抑制剂,另一组添加一定量Cr_3C_2和VC,分别将两组样品分成若干小样,在真空和氢气气氛中,采用不同温度进行碳化,分析不同WC样品粉末性能,并将1 200℃碳化的WC样品制备成钴含量为8%的硬质合金,比较合金性能及金相组织的差异。实验结果表明:在氢气气氛下,钨粉更易于碳化,碳化速度更快,WC的结晶更完整;碳化阶段添加抑制剂会抑制WC晶粒的长粗,但也抑制了WC晶粒生长的完整性;提高碳化温度可以改善WC的结晶完整性,WC的粒度也会随温度的升高而增大。氢气气氛碳化的WC制备成合金后晶粒度比真空碳化的WC粗,合金晶粒的均匀性更好,异常长粗的晶粒少;在碳化阶段添加抑制剂可以更好的抑制合金晶粒的长粗,同时也抑制了WC粉末晶粒结晶的完整性,从而导致合金在液相烧结阶段晶粒的异常长粗。     

含板状WC晶粒硬质合金制备方法的研究

以市售W粉,Co粉和石墨粉末为原料,采用普通工艺制取WC-12wt%Co合金。合金显微组织正常,含有大量板状WC晶粒。研究表明,使用板状W颗粒粉末、提高烧结温度和延长烧结时间都有助于合金中板状WC晶粒的形成。     

以蓝钨为原料制取的粗颗粒W粉、WC粉特性的研究

本文从粉末粒度分布、微观结构以及对合金性能的影响等三方面探讨了以蓝钨为原料制取用颗粒W粉、WC粉的特性。结果表明，从W粉、WC粉的粒度分布曲线来看，蓝钨原料与黄钨原料没有什么本质区别，要制取粒度分布比较平坦、没有尖峰的粗颗粒W粉和粒度分布曲线不出现双峰的粗颗粒WC粉不能靠选择原料种类来解决；用扫描电镜观察W粉、WC粉的微观形貌时发现，用黄钨为原料制的W粉、WC粉颗粒表面存在明显微孔，而这一现象在以蓝钨为原料制得的W粉、WC粉中没有发现；与黄钨相比，以蓝钨为原料制得的WC－Co、WC－Co－Ni硬质合金具有较好的综合性能。     

碳氢协同还原-碳化法制备纳米WC粉的工艺及机理

针对传统还原-碳化工艺中WC粉颗粒长大的问题,采用碳氢协同还原-碳化法制备纳米级球形WC粉,研究了前驱体配碳比和反应温度对WC粉性能的影响。结果表明,WC粉的碳含量与前驱体的配碳比密切相关,最佳配碳比(即n(C)/n(W)值)为3.6。W转变为WC具有结构遗传性,WC粉的平均粒径与还原温度和碳化温度密切相关。随着还原温度由680℃升高至800℃,还原水蒸气与碳反应生成CO和H_2,显著降低体系中水蒸气的分压,从而抑制中间产物W颗粒的挥发-沉积长大,WC粉的平均粒径随还原温度升高而减小。碳化过程中的高温促进WC颗粒的晶界迁移和纳米W颗粒之间的烧结合并长大,WC粉的平均粒径随碳化温度的升高而增大。n(C)/n(W)为3.6的前驱体粉末经800℃还原和1100℃碳化后,得到平均粒径为87.3 nm的球形WC粉。     

Microstructure and Sliding Wear Resistance of Laser Cladded WC/Ni Composite Coatings with Different Contents of WC Particle

The aim of this article was to address the effect of WC content on the microstructure, microhardness, and sliding wear resistance of laser cladded WC/Ni composite coatings. The content of WC particle in the feed powder varied in the range of 0-80 wt.%. Experimental results showed that the laser cladded coatings exhibited homogeneous microstructure without pores or cracks. By comparing with the 45# steel substrate, the microhardness of WC/Ni composite coatings was relatively high. The microhardness of coating increased with increasing the content of WC particles. The wear resistance of WC/Ni composite coatings was strongly dependent on the content of WC particle and their microstructure. When the WC content was lower than 40 wt.% in the feed powder, the wear rate of the coatings decreased with increasing WC content. The two-body abrasive wear was identified as the main wear mechanisms. For the coatings with WC content higher than 40 wt.% in the feed powder, their wear rate increased with increasing WC content. The three-body abrasive wear and fatigue wear were the main failures. The coating with 40 wt.% WC in the feed powder exhibited the best wear resistance.     

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.     

Production of high-density Ni-bonded tungsten carbide coatings using an axially fed DC-plasmatron

Using an axial feed DC-plasmatron, mixtures of fine Ni and WC powder (1–3 μm) were plasma sprayed onto stainless steel substrates. A series of high-density Ni–WC coatings were produces with uniform distribution of WC particles. The small powder sizes coupled with the axial feed system resulted in high vaporization rates of the Ni and significant decomposition of the WC powders. The high vaporization rate of Ni followed by condensation contributes to the high density of the coatings, while the high WC decomposition rate results in low WC content and low hardness values of the coatings. Based on published data and simple energy balance equations, evaporation of as much as 20% of the Ni powder was estimated, and XRD analysis indicates decomposition of as much as 80% of the WC particles.     

斯太立合金加WC激光熔覆

研究了用双筒送粉器分别输送Stellite6和WC,WC体积含量分别为0％,9％,18％,27％,36％,45％,54％,72％和100％的高功率CO2激光熔覆性及其演变。结果表明,当WC体积低于18％时,激光熔覆不出现裂纹。WC体积分数进一步增加,熔覆层平均硬度和裂纹率增加而高宽比减小。显微组织演变可分为两段：WC体积从0％到36％为第一段,WC完全熔化并溶解,凝固组织主要由枝晶和枝晶间共晶组成,W含量分别为9．68％和21％。WC体积分数从45％到100％时为第二段,大部分WC熔化和溶解,显微组织主要由基体和沉淀于其中的W化合物组成,溶解于基体的最大W偏一为26％左右。混合粉末中WC越多,W在W化合物中的含量也越多,其最高含量可达到64．55％。     

乙二胺四乙酸在纳米WC／Co复合粉制备中的应用

本文在喷雾转换法制备WC／Co纳米复合粉的基础上,采用乙二胺四乙酸与碳酸钴复合法制备高钴含量的WC／Co纳米复合粉,突破了原有技术的钴含量质量分数上限7％的瓶颈限制。采用DSC—TG分析、SEM分析、XRD分析等方法,对乙二胺四乙酸和碳酸钴的参与反应的机理进行了研究,并确定了采用新工艺制备WC／Co纳米复合粉的相关参数。实验结果表明：乙二胺四乙酸与碳酸钴反应所得有机钴盐为一种溶解度较高的螯合物,在较低温度下煅烧可分解,适用于WC／Co纳米复合粉前驱体溶液中钴含量的调节,避免了Cl-、NO3-等杂质离子的引入。通过新的复合‘工艺制备得到了适用于高温流态化床生产的前驱体粉末,最终制备得到钴含量质量分数8％的WC—Co纳米复合粉。     

细WC配比对非均匀YG20C合金性能的影响

研究了碳化钨粗颗细粒搭配对YG20C合金的力学性能与组织结构的影响,即在WC颗粒平均粒径为25μm的合金中,加入不同比例的平均粒径为2.0μm的WC颗粒,构成非均匀晶粒硬质合金。结果表明,非均匀YG20C合金的硬度和抗弯强度随着细晶粒碳化钨含量的增加都是先升高再降低。当细颗粒碳化钨比例为20%(文中含量均为质量分数)时,YG20C合金的综合力学性能最好,硬度和抗弯强度都达到"双高",其值分别为HRA83.5和2 800 MPa,比均匀YG20C合金的硬度和抗弯强度分别提高HRA1.2和400 MPa。并且非均匀YG20C合金的冲压使用效果最佳。     

等离子熔覆添加和内生联合WC颗粒增强铁基涂层的组织和性能

采用等离子熔覆技术,以铸造碳化钨、钨铁粉、镍包石墨和铁基合金粉为原材料,在Q235钢基体上制备了外加和内生联合WC颗粒增强铁基复合涂层,通过扫描电镜和能谱分析、X射线衍射、硬度测试和磨料磨损试验对其微观组织、物相组成、硬度和耐磨性能进行了表征。结果表明,在优化的工艺参数下,可以获得与基体冶金结合良好的涂层,硬质相除外加的WC颗粒,还有内生的WC、W₂C、W₃C、Fe₃W₃C和Fe₂W₂C等;随着混合粉末中除外加WC之外的W含量增加,熔池中合金液密度增大,可以减弱外加WC颗粒下沉;当W含量达到15%时,外加WC颗粒均匀分布在涂层中,没有团聚现象发生,且在外加WC颗粒周围有细小的原位WC颗粒生成,涂层的显微硬度和耐磨损性能显著提高,涂层的平均硬度约为1300 HV0.2,耐磨性为Q235钢基体的10倍。     

Effect of adding WC powder to the feedstock of WC-Co-Cr based HVOF coating and its impact on erosion and abrasion resistance

HVOF grade powders are now commercially available and being used in large scale for different components prone to abrasion/erosion. The literature on HVOF coatings based on WC-Co powder shows that there is a huge difference in hardness between the pure WC powder and WC-Co based HVOF coatings. The objective of this study was to improve the hardness of WC based HVOF coatings by adding pure WC powder to the commercially available powder. The hardness data shows that 20% addition of WC powder will improve the hardness of HVOF coating from 1106 to 1395 Hv_0.3. Hardness increase is due to the embedding of tungsten carbide hard metal matrix. This HVOF coated sample was tested for dry sand abrasion and slurry erosion as per ASTM standards. These tests show that abrasion and erosion resistance of HVOF coated samples goes down with the addition of tungsten carbide powder even though coating hardness has gone up. To understand the negative trend, porosity and SEM studies were carried out. SEM studies show that the porosity of the HVOF coating is higher than the conventional HVOF coating. With increase in WC content (30%), the porosity of the HVOF coating increased up to 10%. The higher porosity is believed to be the reason for poor abrasion and slurry erosion resistance.     

Synthesis of Al2O3／WC powder by aluminothermic reduction and carbonization method

Al2O3/WC powder was synthesized by means of aluminothermic reduction-carbonization with metallic Al powder, yellow tungsten oxide and carbon black or graphite as raw materials under the protection of coke granules.The effects of Al2O3 content, temperature, C/WO3 molar ratio, and atmosphere on the synthesis of Al2O3/WC powder were studied. The results show that the relative content of WC and W2C is strongly influenced by the factors mentioned-above. Carbon black has higher reactivity than graphite. Al2O3-WC composite is easier to obtain under the protection of coke granules than under argon atmosphere. The CO in the coke layer can easily react witht ungsten to form WC and to transfer from W2C to WC.