加钴超细WC粉加工工艺研究

以高钴含量（10％－15％wt）的、经注塑成型来制造复杂毛坯用的WC－Co热塑性喂料为例,评估了超细WC粉末的加工工艺性能。考察了VC、Cr3C2抑制剂和烧结温度对WC－（10％－15％wt）Co材料的显微组织、硬度和断裂韧性的影响。在最优化工艺条件下已生产出断裂韧性和硬度分别为10－13MPam^1/2和1500－1900kg/mm^2的高质量WC－Co材料。大致确定了用于粉末注塑成型（PIM）的、超细WC－6％Co热塑性喂料的临界粉末负载及流动性。模腔压力与所用筒动力（总压力）的关系图证明超细WC－Co喂料对于复杂几何形状压坯的制造具有足够的注塑性。     

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。     

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。     

超细WC—10Co硬质合金的显微结构与机械性能

本文对超细WC-10wt％Co-X硬质合金的机械性能进行了研究：通过喷雾干燥，用舍AMT和硝酸钴溶液来制取超细原始粉末，再用机械一化学工艺，将原始粉末还原和碳化成WC／Co粉末：直径大约为100nm的WC粉末与粘结剂Co均匀地混合，在n-已烷和球料比为5：1的条件下湿磨24小时，过后再干燥24小时，并在Imtorr压力下和1375℃二的温度下进行烧结：为了比较超细硬质合金的显微结构与机械性能，将直径为0．57μm～4μm的WC粉末与Co粉末进行混合，随后在1mtorr压力下和1375℃二的温度下烧结：添加不同数量的TaC、Cr3C2、和VC晶粒长大抑制剂到WC-10wt％Co超细硬质合金中，发现烧结后超细硬质合金中的Co相在WC晶粒的边缘快速产生：Hall-Petch类型关系说明WC—10wt％Co硬质合金的硬度是随着WC晶粒度的下降而增加，而抗弯强度则取决于Co粘结相中的溶解度。     

超细碳化钨粉末特性对金刚石锯片刀头显微结构的影响

采用超细WC粉末和工业级的Sn、Ni、Co、Cu粉末以及金刚石为原料，经真空烧结后制备成金刚石锯片刀头。用扫描电镜（SEM）观察了WC粉末和合金的形貌，用能量散射谱（EDS）测试了合金的微区成分分布。研究结果表明，超细WC粉末的添加能改善Sn-Ni-Co-Cu结合金刚石锯片刀头的显微结构，超细WC含量的增加有利于材料晶粒的细化和强度提高，Cu是烧结中产生液相和使成分偏析的重要影响因素，Co对晶粒异常生长影响很大，Sn的添加有利于晶粒的细化。     

微量钴对无金属粘结相WC硬质合金烧结致密化与WC晶粒生长行为的影响

采用Cr3C2、VC掺杂超细WC为原料和无压真空烧结工艺,通过合金微观组织结构的观察与分析,研究了添加质量分数为0.3%的Co对无金属粘结相WC硬质合金烧结致密化与WC晶粒生长行为的影响。结果表明,微量Co的存在加速了WC的烧结致密化过程,与此同时也导致了WC晶粒明显的各向异性非连续晶粒长大。在上述研究基础上,提出了一种无金属粘结相WC硬质合金的低成本制备工艺,探讨了超细硬质合金中WC晶粒生长机制,提出了超细硬质合金的质量改进建议。     

WC粉末特性对超细晶硬质合金烧结敏感性影响的研究

选取3种不同厂家生产的08型WC粉作为原料,以相同的工艺路线制备WC-6%Co硬质合金样品。通过对WC原料粉末杂质含量、粒度、物相、显微形貌、晶粒尺寸和晶格参数详细分析以及不同温度烧结后合金显微组织、WC晶粒夹粗数量和WC平均晶粒度表征,探究WC粉末特性对合金烧结敏感性的影响。研究结果表明,采用颗粒尺寸分布均匀集中、亚晶尺寸大,结晶性完整以及晶格常数与标准值差异较小的WC-C粉末作为原料可以有效的降低合金的烧结敏感性。当烧结温度从1 410℃升高到1 450℃,WC-C制备的合金中WC晶粒夹粗数量增幅较小,且WC平均晶粒度无明显变化维持在0.48μm,同时WC碳含量在6.17%～6.21%波动时,对合金中的WC晶粒夹粗影响亦相对较小。     

用喷雾转化法制备的纳米晶粉末烧结的WC—10Co硬质合金的力学性能

研究了纳米晶WC－10Co硬质合金的力学性能和显著结构。这种纳米晶WC－10Co硬质合金粉末是将含有偏钨酸铵（AMT）和硝酸钴的溶液喷雾干燥制得的纳米晶前驱体粉末再经过还原和碳化制备的。直径约100nm的WC粉末与Co炽结相混合均匀，并在1毫乇压力和1375℃下进行烧结。为了与纳米晶料WC－10Co的显微结构和力学性能相比较，将直径范围为0．57－4μm的工业用WC粉末与Co粉混合，并在与纳米晶粉末相同的条件下进行烧结，在纳米晶WC－10Co硬质合金中加入不同量的TaC、Cr3C2和VC作为晶粒长大抑制剂。为研究WC－10Co硬质合金中Co粘结相的显微结构，以WC－10Co硬质合金烧结温度下制备了Co-W-C合金。WC－10Co硬质合金随着WC粒度的减小而增加的硬度因而符合霍尔－佩奇型关系式。WC－10Co硬质合金的断裂韧性随着Co粘结相的HCP（密排六方相）／FCC（面心六方相）比的增大（由于HCP／FCC相引起的）而提高。     

超细晶料WC—Co硬质合金的剪切模压成型工艺

采用剪切模压新工艺成型，通过真空烧结制备出了超细晶粒WC－Co硬质合金。研究了不同成型剂的特性、成型剂的配比、加入量以及压制力对剪切模压成型的影响。研究结果表明，采厅剪切模压成型工艺可获得很高的成型质量，从而制备出具有较好物理力学性能的超细WC—C。因质合金。     

WC/Co粉体粒径匹配与放电等离子烧结致密化

对放电等离子烧结(SPS)不同粒径匹配的WC/Co混合粉末的收缩过程进行了系统分析.结果表明,SPS烧结不同WC粒径混合粉末时,烧结体开始收缩温度、收缩速率峰值温度和致密化完成温度基本相同;对不同Co粒径混合粉末,三种温度随Co粉初始粒径的减小而降低,即SPS烧结过程与WC粒径无关而与Co粒径密切相关.SPS致密化过程中收缩速率随温度的变化、收缩速率与相对密度的关系均与常规烧结不同,其开始收缩温度和收缩速率峰值温度均较常规烧结低,同时收缩速率峰值处所对应的相对密度也较常规烧结低.这说明在常规烧结中粉末在大量液相出现(即收缩速率出现峰值时)之前已完成很大程度的收缩致密化,而SPS烧结中大量液相出现之前粉末的收缩致密化程度较低.     

EFFECTS OF SIZE COMBINATION AND CONTACTING STATE OF RAW POWDER PARTICLES ON SPARK PLASMA SINTERED ULTRAFINE CEMENTED CARBIDES

本文采用亚微米WC粉和纳米Co粉、亚微米WC粉和高能球磨后具有纳米晶组织的微米级Co粉这两种具有不同粒径匹配的混合粉末作为原料粉末，利用放电等离子烧结（SPS）技术制备超细晶WC-10Co硬质合金。对不同原料粉末的SPS过程及烧结试样的显微组织和性能进行了系统的对比分析。实验结果表明，以两种混合粉末为原料均获得了平均晶粒尺寸在200nm以下的超细硬质合金材料，其中，采用亚微米WC粉和高能球磨的微米级Co粉利用SPS技术制备的材料相对密度达到98%以上，硬度达到HRA94.5，断裂韧性达到13.50MPa•m1/2，表明具有优良的综合性能。而采用亚微米WC粉和纳米Co粉利用SPS技术制备出的超细晶硬质合金的组织均匀性和性能较差。根据SPS技术的特殊烧结机理，对采用不同粒径匹配和结合状态的WC和Co混合粉末的SPS致密化机制进行了分析。     

电冶熔铸WC/钢复合材料中WC的溶解行为

用电冶熔铸工艺制备不同WC含量的WC/钢复合材料,研究了WC颗粒在复合材料钢基体中的溶解行为和影响因素.结果表明:随着WC含量的增加,碳化物从钢基体晶界处分布逐渐转向晶内分布;随着WC颗粒尺寸的增大,在WC颗粒与钢基体界面处形成一层反应物,它阻止了WC颗粒在钢基体中的进一步溶解,同时也提高了两相界面的结合强度.通过调整电冶熔铸工艺参数和WC颗粒的尺寸及含量,可以控制WC颗粒在复合材料中的溶解行为.     

超细硬质合金烧结过程中WC扩散-溶解-析出特征与机理研究

以08型WC与Co制成WC-10%Co试样条,脱蜡后分别于1 200﹑1 250﹑1 300﹑1 350℃进行烧结并分别保温1 h和5 h。采用扫描电镜观察烧结过程中WC晶粒形貌的变化,采用差热分析仪研究WC-10%Co的共晶温度。研究结果表明:WC-10%Co在低于共晶温度的烧结过程中发生了WC晶粒形貌由等轴形向棱边平直的多边形变化,并随着温度升高,晶粒尺寸增大。这表明在固相烧结时超细WC与钴相存在溶解析出过程,改变WC晶粒形貌并使晶粒长大。     

含板状WC晶粒硬质合金的强韧化机制研究

通过加入2.5%板状WC晶种,制备含板状WC晶粒硬质合金,研究其强韧化机制。结果表明:WC晶粒的各向异性和形状改变诱导的Hall-Petch硬化是硬质合金硬度增加的主要原因。加入板状晶种后,裂纹在扩展过程中出现了明显的穿晶断裂和Co相桥接,增加了裂纹偏转,硬质合金的抗弯强度大大提高。不同Co含量和初始WC粉体粒度制备的含板状WC晶粒硬质合金,穿晶断裂、Co相桥接和裂纹偏转对抗弯强度增加的贡献不同。     

Particle properties of submicron-sized WC–12Co processed by planetary ball milling

In this study, a conventional nano-grained tungsten carbide (WC) powder was mixed with 12 wt.% of a submicron cobalt (Co) powder in a ball mill for varying milling time periods, producing a homogeneous powder mixture which can be used to sinter near-nanocrystalline cemented carbides using short-duration sintering processes. Parameters of the wet milling process were adapted in order to maximise the mixing effect on the one hand, and to avoid particle growth during the milling process on the other. Surface analysis and microscopic examination of the milled powders showed a milling-time-dependent evolution of particle size and surface roughness. X-ray diffraction (XRD) investigation indicated a decrease of the crystallite size of WC in combination with an increase in defect density, as well as a strong increase in stacking faults in the Co. The main action of the milling mechanism is the fracturing of the WC particles. Co is distributed consistently around the WC particles. The preparation method used is a useful technique to prepare homogeneous powder mixtures of WC–Co with particle sizes below 200 nm on a laboratory scale.     

Effects of WC particle size on densification and properties of spark plasma sintered WC–Co cermet

The WC–Co cermet bulks were prepared by spark plasma sintering (SPS) using powder mixtures with different-scaled WC particles. The SPS densification process was studied by calculating the current distribution between the powder sample and the die in the SPS system. The microstructures were characterized and compared for different samples by the WC grain size, Co mean free path and contiguity of WC grains. In spite of a weak effect of WC particle size on the SPS densification stages, the WC particle size plays a significant role in the homogeneity of the cermet microstructure. Good mechanical properties of the SPSed cermet were obtained with an optimized WC and Co particle-size combination. The effects of scale combination of WC and Co particles on the microstructure hence the properties of the SPSed cermet were discussed.     

Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC–(W, Ti, Ta) C–6 wt% Co cemented carbides

This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.     

Microstructure and properties of CVD coated on gradient cemented carbide with different WC grain size

In this paper, cemented carbides with gradient surface enriched in Co phase and depleted of cubic phases were prepared by one-step vacuum sintering. The gradient cemented carbides of different WC grain size were used as the substrates of CVD coatings. The effects of WC particle size on the formation of gradient layer, microstructure and properties of the gradient cemented carbides were investigated. Besides, the influence of WC grain size and gradient layer on microstructure, growth and adhesion strength of the coatings were studied. The results showed that the thickness of surface gradient layer decreased with increasing WC particle size, which was attributed to the decreased diffusion paths and the increased diffusion distance. The interface between the surface gradient layer and the bulk was disordered due to abnormal grain growth of WC in ultrafine cemented carbide. The microhardness across the direction of the fcc-free (Face Center Cubic Free) surface layer to the bulk were similar in the three gradient cemented carbides, and could be expressed as: from the surface to the inner, the microhardness decreased firstly, then increased sharply around the interface, and subsequently dropped to the bulk level. The coating on the fcc-free surface layer was thicker than that on bulk, and the coating on the substrate with fine-sized WC grains is the thickest. The increase of the WC grain size in the substrate could improve the bonding strength of the coating. Furthermore, the presence of Co-rich layer could improve the bonding strength. However, bonding strength was poor for the grain size of ultrafine.