电弧电压对低能等离子喷涂WC-Co涂层组织及性能的影响

使用烧结破碎的WC-12%Co粉末,采用轴向送粉等离子喷涂系统制备WC-Co涂层。保持电弧电流不变,增加工作气体中的氢气含量来提高电弧电压,以研究电弧电压对于涂层微观结构的影响。使用X射线衍射仪(XRD)分析WC-Co涂层的脱碳相变,使用扫描电子显微镜(SEM)观察粉末的熔化程度、扁平化状态和涂层的微观结构,使用MH-6维氏硬度计和MM200磨损试验机分别测量了涂层的显微硬度和耐磨性。结果表明,提高电弧电压有利于粉末的熔化。根据熔化程度的不同,粉末会呈现四种典型的扁平化状态。提高电弧电压促使碳化钨脱碳生成的W_2C和Co_3W_9C_4,涂层中硬质相体积增加,钴基体积减小。适当提高电弧电压有利于增加涂层的硬度和耐磨性,但过高的电弧电压会恶化涂层质量,反而降低涂层的硬度和耐磨性。     

The role of the reaction medium in the self propagating high temperature synthesis of nanosized tantalum powder

The high temperature combustion of the mixture Ta₂O₅ + 5 Mg has been investigated using a microthermocouple in the medium MgO and molten NaCl. The effect of varying the amounts of these two inorganic agents (MgO and NaCl) was examined. It was shown that using MgO as the reaction medium produces the complex oxide Mg_xTa_yO_z as an impurity in the Ta powder, whereas unagglomerated single-phase powder (particle size of 20-90 nm) of Ta was formed in the presence of NaCl. The approximate mechanism for forming the final product is discussed. The distributions of temperature, the rate of heat generation and degree of conversion in the combustion wave of the mixture Ta₂O₅ + 5Mg + NaCl were measured. The sizes of the combustion zones and the kinetics of reaction were derived.     

流化床还原碳化法制备超细WC－Co复合粉末

介绍了一种制备超细ＷＣ－Ｃｏ复合粉末的新工艺─—流化床还原碳化法。ＸＲＤ分析结果表明，该法制备的粉末由ＷＣ和Ｃｏ两相组成。Ｘ－射线小角衍射测定粉末的平均颗粒度为０．１２μｍ。将该粉末压制成形的样品在１２８０℃真空烧结１ｈ获得９９．７％理论密度的试块。     

Revealing true porosity in WC-Co thermal spray coatings

The principles underlying composite material behavior during metallographic preparation of coating cross-sections are generally not well understood. This study of the effect of extended fine polishing on apparent porosity shows that adequate polishing times, using a fine abrasive (3 μm) and low force, are required to remove prior deformation in the section surface and to reveal the true porosity of the underlying composite material. Insufficient polishing times can result in considerable underestimation of porosity. A model is described which proposes that the deformation induced in the material during grinding and polishing, even at low applied force, results in smearing of material into voids that exist in the plane of the section.     

WC-Co硬质合金烧结过程中的晶粒长大现象研究

在分析晶粒长大机理的基础上，指出在WC—Co硬质合金烧结过程中，WC晶粒的长大为正常长大和异常长大这两种方式并存，且在烧结早期WC晶粒就开始长大，并提出了可抑制WC晶粒长大的具体措施。     

Processing of In Situ Aluminium Matrix Composites by Micropyretic Reactive Sintering

In situ aluminium matrix composites were processed by the micropyretic reactions between the host aluminium matrix and powder containing nanodimensional Fe₂O₃ crystallites used as the precursor compound. Differential Scanning Calorimetric (DSC), studies have shown, use of nanosized Fe₂O₃ crystallites has decreased the initiation temperature of the in situ micropyretic reaction and the desirable reinforcements; iron-aluminide and alumina are formed during sintering. Microstructural features of the composite consist of well-dispersed reinforcements in the host Al matrix with size less than 1 µm. Wear tests performed on the composite samples have revealed coefficient of friction and wear volume can be reduced significantly by incorporating 20 vol% reinforcement.     

纳米WC-Co复合材料制备及其烧结过程

综述了纳米 WC- Co复合材料制备技术的进展并分析了烧结过程和新的烧结技术。对各种制备方法的原理、原料、工艺流程进行了介绍。     

Nanocarbon-dependent synthesis of ZrB2 in a binary ZrO2 and boron system

Thermodynamically, ZrO₂ may react with boron to form B₂O₃/B₂O₂ and ZrB₂ at room temperature. However, this reaction is incomplete at temperatures lower than 1550 °C, even with the use of metastable reactants, i.e., as-synthesized amorphous hydrous nano-ZrO₂ and amorphous boron powders. In this study, a complete disintegration of ZrO₂ was achieved by introducing nanocarbon to the binary system of ZrO₂ and boron at 1550 °C. The metastable reactants affected the temperature required for the solid-state reactions and also strongly affected the kinetics of the transformation. Single crystal and plate-like ZrB₂ particles with a uniform distribution and a size of ca. 1.0 μm in two-dimensions were obtained using 5 wt.% nanocarbon and a B/Zr molar ratio of 4.     

直接碳化原位合成WC-Co复合粉的反应过程

以偏钨酸铵(AMT)、可溶性钴盐、有机碳源为原材料,采用喷雾转化、直接碳化原位合成法,成功制备出WC-Co复合粉末。利用XRD、SEM等分析方法对粉末样品物相组成、微观形貌、粒度分布进行了研究。研究表明,由于Co对W碳化的促进作用,在900℃时,W就被完全碳化为WC,远低于W正常被碳化完全的温度;W的碳化过程主要依靠钨粉颗粒表面与含碳气氛热解后沉积在钨颗粒表面上的碳元素的反应以及碳向钨粉颗粒内部的扩散来实现,属固-固反应;由于生成W2C的自由能比WC的更低,W很快先被碳化为W2C,然后再进一步碳化为WC;W/Co/C碳化反应体系沿WCo3,Co6W6C,W2C-Co,WC-Co步骤进行反应;随着温度的升高,反应体系可不经过前两步,而直接生成W2C-Co,再进一步碳化为WC-Co复合粉。     

超细WC-Co复合粉制备及快速烧结技术研究进展

超细WC-Co复合粉是制备高性能超细/纳米晶硬质合金的重要原料之一,近年来发展了多种复合粉的制备技术。本文综述了其中的喷雾转换工艺法、化学沉淀法、原位还原碳化法、化学气相反应合成法和机械合金化法的研究和应用状况。同时简要介绍了一些新型的快速烧结技术的原理,以及这些新型的快速烧结技术制备的超细/纳米晶硬质合金上的研究进展,并对快速烧结技术在硬质合金领域发展前景进行了分析。