纳米晶WC-Co硬质合金的研究现状

概述了国内外纳米晶硬质合金的发展现状.纳米晶WC-Co硬质合金制备的关键技术主要包括:优质纳米晶WC粉的制备和烧结过程中WC晶粒长大的控制.综述了优质纳米晶WC粉的特点和制备技术,以及目前国内外烧结过程中控制晶粒长大采取的主要措施:添加晶粒长大抑制剂、调整烧结工艺和开发新型烧结方法.列举了合金的实际应用领域,展望了纳米晶硬质合金的发展前景.     

纳米Ni粉对WC-8Ni硬质合金性能的影响

将WC-8Ni硬质合金中的粘结剂用不同比例的纳米镍Ni粉替代,采用常规硬质合金的工艺制备出合金试样,测试其物理力学性能,研究不同比例的纳米Ni粉及不同的烧结温度对合金性能的影响.结果表明,在适当比例的纳米镍粉及烧结温度下,合金的性能得到很大的提高.     

纳米晶钨粉对液相烧结93W合金组织性能影响

采用高能机械球磨方法制备了超细钨粉,经冷等静压和1465℃分解氨气氛中液相烧结制得高密度钨合金.研究了纳米晶亚微米颗粒钨粉对烧结态93W-4.9Ni-2.1Fe高密度钨合金微观组织及性能的影响.研究表明:采用超细钨粉与低温液相烧结技术,获得了高相对密度(大于99.7%)的烧结态高密度钨合金,且细钨颗粒组织均匀分布于粘结相中;与采用亚微米颗粒钨粉的烧结态钨合金相比较,不仅微观组织弥散分布,而且具有较高的力学性能;液相烧结态钨合金的力学性能主要与原始钨粉粒度及烧结温度有关.     

纳米陶瓷微米高温合金复合涂层组织与性能

采用溶胶-凝胶化学包覆法制备纳米陶瓷微米高温合金复合粉末,用HVOF喷涂技术制备了复合涂层,采用SEM观察和摩擦磨损实验分析了复合粉末和复合涂层的组织和性能.研究表明:复合粉末是以纳米陶瓷为外壳包覆微米级高温合金颗粒核心的核壳式结构;陶瓷壳在喷涂过程中形成液相与高温合金液相熔合,烧结成致密陶瓷相,部分陶瓷在冷却过程中析出结晶体;复合涂层与基体的结合强度为59.2 MPa,摩擦系数为0.766,磨损率比纯高温合金涂层降低了32%.     

纳米陶瓷的制备概况

综述了当前纳米陶瓷的各种制备方法,介绍了从纳米粉体制备到纳米陶瓷烧结整个过程中常用的技术和方法.同时,分析了纳米陶瓷的发展前景及其制备过程中应注意的问题.     

纳米多孔铜的去合金法制备及性能研究

通过电弧炉和管式炉烧结制备不同原子比的铜锰合金前驱体,室温下在0.1 mol/L盐酸溶液中对制备出的前驱体合金进行自腐蚀制备纳米多孔铜.采用SEM、EDS、Autosorb -1等分析了样品的表观形貌、元素含量和微观孔结构.结果表明:采用去合金法得到结构均匀的三维连通纳米多孔铜片体材料,管式炉制备的Cu∶Mn原子比为3∶7的样品获得相对分布更为均匀、孔结构更为明显的多孔铜.     

纳米相复合Al-Sn合金的反应球磨制备及性能研究

利用反应球磨制备Al-SnO_2-MgH_2粉末,然后通过压制和烧结制备出高热稳纳米相复合结构Al-Sn合金。运用X射线衍射仪(XRD)和扫描电镜(SEM)等研究反应球磨制备的纳米相复合Al-Sn合金的组织和性能。结果表明:采用两步法和添加MgH_2组元的方式所制备的机械合金化(MA)Al-SnO_2-MgH_2复合粉末,经压制和600℃烧结,合金中的SnO_2几乎全部被还原成单质Sn,并呈现双尺度结构。其中,共生反应形成的纳米级Sn粒子和Al_2O_3颗粒均匀弥散地分布在Al基体中,显著提高了合金的硬度,从而使合金表现出低的摩擦系数和磨损量。     

超细碳化钨-钴硬质合金的原子力显微镜研究

以液相复合-连续还原碳化方法制备的纳米碳化钨-钴复合粉末为原料,采用低压烧结制备了性能优良的超细碳化钨-钴硬质合金.运用原子力显微镜(AFM)对超细碳化钨-钴硬质合金的表面形貌进行了观察、缺陷和粒度分析,同时对合金的力学性能进行了测试.结果表明,采用低压烧结获得的烧结试样的洛氏硬度HRA≥93.5,抗弯强度TRS≥3300MPa,平均晶粒度＜220nm.制备了具有高强度、高硬度的超细碳化钨-钴硬质合金.纳米碳化钨-钴复合粉末制备的超细硬质合金组织结构均匀,但局部仍然存在着组织缺陷,分析了产生缺陷的机理.     

超细、纳米晶WC-Co硬质合金烧结技术的研究现状

WC-Co硬质合金因高硬、耐磨而在切削、釆矿和耐磨零件等领域广泛应用。研究发现,当WC晶粒尺寸小于0.5μm时(即超细、纳米晶WC-Co硬质合金),与普通硬质合金相比,材料的硬度和强度显著提高,其韧性也同样会有所提升。因此,晶粒细化有助于改善硬质合金的力学性能,从而延长其使用寿命。长期以来,有关硬质合金性能改善方面的研究多关注于从粉体出发,即通过采用超细纳米粉体和合理烧结工艺来实现超细晶和纳米结构硬质合金的制备。然而,在合金制备过程中其致密性与晶粒长大之间往往存在较为复杂的交互作用,如何保证在烧结过程中致密化的同时抑制WC晶粒长大是提高合金性能以及保证合金质量稳定性的关键技术问题之一。本文主要阐述了高温液相烧结制备超细、纳米晶WC-Co硬质合金过程中有关致密化和晶粒长大机制之间的关联性,从烧结工艺与添加剂两方面介绍了近年来国内外的研究现状。烧结工艺具体分为常规烧结工艺(主要包括氢气烧结、真空烧结和热等静压烧结等)和快速烧结工艺(主要包括微波烧结、放电等离子烧结、高频感应热烧结等),对比了上述烧结工艺之间的不同以及总结了不同烧结工艺的优缺点。在添加剂方面,重点介绍了过渡族碳化物和稀土元素对硬质合金烧结过程中晶粒生长的抑制作用,并在此基础上阐述了超细、纳米晶WC-Co硬质合金烧结技术的未来发展趋势。     

高频回旋管微波烧结纳米陶瓷研究

在高频回旋管微波烧结系统上进行纳米陶瓷烧结研究,制备出氧化锆单元及二元纳米陶瓷样品,对不同烧结工艺制备出的样品做了密度、硬度测试,利用XRD和扫描电镜分析陶瓷样品晶粒特性,以摸索适宜的烧结工艺.探讨了高频回旋管微波烧结纳米陶瓷的可行性.     

Solid-State Sintering of Tungsten Heavy Alloys

Solid-state sintering is a technologically important step in the fabrication of tungsten heavy alloys. This work addresses practical variables affecting the sinterability: powder particle size, powder mixing, and sintering temperature and time. Compositions containing 1 to 10 micrometer (μim) tungsten (W) powders can be fully densified at temperatures near the matrix solidus. Blending with an intensifier bar provided good dispersion of elemental powders and good as-sintered mechanical properties under adequate sintering conditions. Additional ball milling increases powder bulk density which primarily benefits mold and die filling. Although fine, 1 urn W powder blends have high sinterability, higher as-sintered ductilities are reached in shorter sintering times with coarser, 5 urn W powder blends; 10 urn W powder blends promise the highest as-sintered ductilities due to their coarse microstructural W.     

高比重钨合金研究的新进展

分别从原材料、烧结工艺及其后处理、强韧化和杂质影响等方面较系统地介绍了国内外近十年来在高比重钨合金领域所取得的进展，并从这些方面详细讨论了影响高比重钨合金性能的具体因素。在此基础上对钨合金今后的发展方向提出了意见。     

高比重钨合金力学性能影响因素分析

首先考虑液相烧结工艺条件及组分对高比重钨合金微结构和各相性质的影响，再从细观力学的角度考虑高体积百分比钨合金微结构及各相性质对复合材料有效力学性质的影响，从而架起工艺条件及组分与钨合金力学性能之间关系的桥梁，为分析高比重钨合金性能从理论上建立一套方法，从材料设计和制备的角度实现对这种材料性能优化提供一种方案。并应用上述模型和方法对用粉末冶金法制备的两种不同钨含量的钨合金材料微结构和力学性能进行分析。     

Electronic mechanism of sintering: Some case studies on real systems

The paper reviews the role of electronic configuration model of condensed state in explaining the sintering behaviour of various alloys. The systems are copper base alloys, ferrous alloys containing phosphorus, tungsten based heavy alloys, Al-refractory carbide composites, 6061 Al-alloy composites, high speed steel composites and tungsten carbide based cemented carbides. These studies cover the research activities of the Powder Metallurgy Laboratory at IIT, Kanpur.     

Activated sintering of tungsten alloys through conventional and spark plasma sintering process

The sintering temperature of pure tungsten can be reduced through the addition of small amounts of transition elements. The present study deals with the activated sintering of tungsten with 1.0?wt% additions of copper, cobalt, molybdenum, iron and nickel using the spark plasma sintering (SPS) technique. The alloys were sintered at 1200°C and the mechanical properties and microstructures were compared with those of conventionally sintered alloys, sintered under vacuum condition. The high-rate sintering of SPS has led to an overall reduction in process time and also to a better densification of alloys compared with the conventional sintering process. In both the processes, nickel addition is found to be the best activator, followed by cobalt, iron, molybdenum and copper. The addition of copper and molybdenum showed only a meager increase in the relative density. The alloys, with nickel, cobalt and iron additions, sintered through the SPS process offered much higher density compared with the conventionally sintered alloys. The highest density is observed for the nickel-doped tungsten alloy, which is found to be around 90% of the theoretical density. The microhardness of the sintered alloys is found to depend on its sintered density.     

Superhard nanodisperse tungsten heavy alloys obtained using the methods of mechanical activation and spark plasma sintering

We have studied the structure and mechanical properties of nanodisperse tungsten-based heavy alloys of the W-Ni-Fe system. The temperature dependence of the density of compacted alloys exhibits a nonmonotonic character with a maximum that corresponds to the optimum temperature of sintering. The effect of the regime of solid-state pulsed spark plasma sintering (SPS) on the structure and mechanical properties of mechanically activated W-Ni-Fe heavy alloys has been studied. It is established that, using preliminary mechanical activation in a planetary ball mill and the subsequent high-rate SPS, it is possible to obtain superhard tungsten-based heavy alloys with mechanical properties that substantially exceed those of the analogous standard alloys.     

Grinding behavior of WO3, NiO,Fe2O3 by ultrasonic milling parameters control and preparation of nanocomposite powder

Tungsten-based alloys have been widely applied in various industries due to their excellent mechanical properties. Tungsten-based alloys have a high sintering temperature due to the high melting point of tungsten, so the coarse particles negatively affect the mechanical properties of the alloy. This problem can be solved by increasing the densification by reducing the sintering temperature and time by adding nanoparticles with high surface energy. Herein, we fabricated nanoparticle-sized metal oxides by ultrasonic milling to minimize the influx of impurities to improve the densification of tungsten alloys. The main parameters of the ultrasonic milling experiments were ball density and ball layer. Metal oxides prepared by ultrasonic milling showed an average particle size distribution of less than 200 nm, and metal composite powders prepared through subsequent hydrogen reduction also showed nanoparticle size distributions. We believe that this approach will enable the production of improved sintered tungsten-based alloys.     

Microstructure and microhardness of high entropy alloys with Zn addition: AlCoFeNiZn and AlCoFeNiMoTiZn

High entropy alloys were designed from equiatomic multicomponent systems using powder metallurgy including mechanical alloying and sintering. The structure and morphology of the resulting alloys were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy techniques and their hardness values were also determined in the Vickers scale. The results indicate under the milling conditions used, the AlCoFeNiZn, AlCoFeNiMoTi and AlCoFeNiMoTiZn alloys crystallized forming BCC structures whereas the AlCoFeNi alloy presented two different phases, one with FCC structure and the other one with BCC. The synthesis method resulted in alloys with grain sizes in the nano scale having values between 4.1 and 9.4 nm on the powder form up to 40.1 nm after sintering phenomenon which lead to phase transformations which were more evident in the Mo-containing alloys. In addition, the AlCoFeNiZn and AlCoFeNiMoTiZn alloys did not show Zn traces after sintering as it was suggested by chemical analyses using energy dispersive spectroscopy, suggesting it is lost by evaporation during sintering process. Mo-containing systems exhibited the highest microhardness in both milled and sintered conditions.     

Fabrication and characterization of magnesium–fluorapatite nanocomposite for biomedical applications

Recent studies indicate that there is a high demand for magnesium alloys with adjustable corrosion rates, suitable mechanical properties, and the ability for precipitation of a bone-like apatite layer on the surface of magnesium alloys in the body. An approach to this challenge might be the application of metal matrix composites based on magnesium alloys. The aim of this work was to fabricate and characterize a nanocomposite made of AZ91 magnesium alloy as the matrix and fluorapatite nano particles as reinforcement. A magnesium–fluorapatite nanocomposite was made via a blending–pressing–sintering method. Mechanical, metallurgical and in vitro corrosion measurements were performed for characterization of both the initial materials and the composite structure. The results showed that the addition of fluorapatite nano particle reinforcements to magnesium alloys can improve the mechanical properties, reduce the corrosion rate, and accelerate the formation of an apatite layer on the surface, which provides improved protection for the AZ91 matrix. It is suggested that the formation of an apatite layer on the surface of magnesium alloys can contribute to the improved osteoconductivity of magnesium alloys for biomedical applications.     

Oxidation of chromia forming molybdenum-tungsten based alloys

The oxidation behaviour of tungsten and molybdenum based, chromia-forming alloys prepared by powder sintering activated with group VIII metals has been investigated. The influences of the alloy composition, nature of the sintering agent and oxidation temperature have been studied. A good oxidation resistance is observed with palladium as sintering agent. This metal is rejected at the grain boundaries and allows a fast diffusion of chromium to the metal-oxide interface. Contrary to palladium, nickel leads to a catastrophic oxidation of the sample. The formation of a two-phase interface enriched in nickel leads to a non-protective oxide layer constituted with Cr₂O₃ and NiWO₄.Catastrophic oxidation is observed when the refractory metals are oxidised into volatile oxides, i.e. in the case of the alloys with a high molybdenum content. Contrary to molybdenum, a high tungsten level leads to high oxidation resistance, even at temperature as high as 1300°C. In this latter case, alloys are two-phase: this result has led to the investigation of the ternary section of the Cr-Mo-W system at 1300°C.