Statistical Analyses of the Strengths of Particulate Reinforced Metal Matrix Composites(PRMMCs)Subjected to Multiple Tensile and Shear Stresses

For design and application of particulate reinforced metal matrix composites(PRMMCs),it is essential to predict the material strengths and understand how do they relate to constituents and microstructural features.To this end,a computational approach consists of the direct methods,homogenization,and statistical analyses is introduced in our previous studies.Since failure of PRMMC materials are often caused by time-varied combinations of tensile and shear stresses,the established approach is extended in the present work to take into account of these situations.In this paper,ultimate strengths and endurance limits of an exemplary PRMMC material,WC-Co,are predicted under three independently varied tensile and shear stresses.In order to cover the entire load space with least amount of weight factors,a new method for generating optimally distributed weight factors in an n dimensional space is formulated.Employing weight factors determined by this algorithm,direct method calculations were performed on many statistically equivalent representative volume elements(SERVE)samples.Through analyzing statistical characteristics associated with results the study suggests a simplified approach to estimate the material strength under superposed stresses without solving the difficult high dimensional shakedown problem.

High-temperature tribological performance of functionally graded Stellite 6/WC metal matrix composite coatings manufactured by laser-directed energy deposition

Wear-driven tool failure is one of the main hurdles in the industry.This issue can be addressed through surface coating with ceramic-reinforced metal matrix composites.However,the maximum ceramic content is limited by cracking.In this work,the tribological behaviour of the functionally graded WC-ceramic-particlereinforced Stellite 6 coatings is studied.To that end,the wear resistance at room temperature and 400°C is investigated.Moreover,the tribological analysis is supported by crack sensitivity and hardness evaluation,which is of utmost importance in the processing of composite materials with ceramic-particle-reinforcement.Results indicate that functionally graded materials can be employed to increase the maximum admissible WC content,hence improving the tribological behaviour,most notably at high temperatures.Additionally,a shift from abrasive to oxidative wear is observed in high-temperature wear testing.

Effect of porosity on damping behavior of aluminum matrix-fly ash composites

The hollow sphere fly ash/6061Al composite with about 43% porosity in volume fraction (produced by the addition of hollow sphere fly ash particles) was fabricated by squeeze casting technique. Using the same technique, the fly ash/7075Al composite with all the porosity in hollow sphere fly ash infiltrated by molten aluminum was fabricated for partially studying the effect of porosity on the damping behavior of the fly ash/Al composites. The resonant damping capacity of the 'porous' fly ash/6061Al composite reached (20.2-26.9)×10-3 and was about 8 times of the value tested by forced vibration method (in the frequency range 0.2-2 Hz). However, the damping capacity of the as-received 6061Al and the 'dense' fly ash/7075Al composite were consistent by the two testing methods and were in the range of (1.1-7.7)×10-3. The effect of temperature on the damping behavior of the materials was also studied. The related damping mechanisms have also been discussed in light of data from the characterization of microstructure and damping capacity. Due to the inferior mechanical properties of the fly ash particles, the tensile strength of the FA/Al composites was lower than that of the corresponding aluminum alloy matrix and was 70.1 MPa and 180.6 MPa for the 'porous' fly ash/6061Al and 'dense' fly ash/7075Al composite, respectively.

Materials and Process Aspects of Selective Laser Melting of Metals and Metal Matrix Composites: A Review(Invited Paper)

Selective laser melting(SLM) is currently the subject of major research studies with the objective to directly manufacture high performance metal alloys and metal matrix composite(MMC) parts by consolidating metal and its composite powders.The successful fabrication of the parts by SLM is related with proper selection of materials and processing parameters to provide sufficient densification and consolidation of the powder materials and generate suitable microstructures and mechanical properties.It is also important to minimize or eliminate typical issues such as porosity,balling effect,and thermal stress associated with the powder melting and consolidation at high temperature conditions during SLM process.This paper presents the fundamental material and process aspects,address the technical issues,and review the recent research development in the SLM of metal and MMCs.

Thermal Analysis of Metal Foam Matrix Composite Phase Change Material

In this paper,CPCM(Composite Phase Change Material)was manufactured with metal foam matrix used as filling material.The temperature curves were obtained by experiment.The performance of heat transfer was analyzed.The experimental results show that metal foam matrix can improve temperature uniformity in phase change thermal storage material and enhance heat conduction ability.The thermal performance of CPCM is significantly improved.The efficiency of temperature control can be obviously improved by adding metal foam in phase change material.CPCM is in solid-liquid two-phase region when temperature is close to phase change point of paraffin.An approximate plateau appears.The plateau can be considered as the temperature control zone of CPCM.Heat can be transferred fiom hot source and be uniformly spread in thermal storage material by using metal foam matrix since thermal storage material has the advantage of strong heat storage capacity and disadvantage of poor heat conduction ability.Natural convection promotes the melting of solid-liquid phase change material.Good thermal conductivity of foam metal accelerates heat conduction of solid-liquid phase change material.The interior temperature difference decreases and the whole temperature becomes more uniform.For the same porosity with a metal foam,melting time of solid-liquid phase change material decreases.Heat conduction is enhanced and natural convection is suppressed when pore size of metal foam is smaller.The thermal storage time decreases and heat absorption rate increases when the pore size of metal foam reduces.The research results can be used to guide fabricating the CPCM.

PROCESSINGTECHNIQUESANDCHARACTERIZATIONOFCERAMICFIBERREINFORCEDALUMINIUMCOMPOSITES

论述了铝基复合材料的制造过程，着重用于涂覆、粉未冶金法与液压金属浸润法制造的材料。用扫描电镜观察材料截面，并用弯曲试验与微硬度试验测试材料的力学性能。结果表明，用液态金属浸润制造的材料性能较好。其原因是由于空隙与纤维束的减少，纤维与基体结合较好。三点弯曲试验表明，随着增强物的增加，弹性模量也增加。此外，还进行了一系列的微硬度试验。

增强体表面改性在高导热金属基复合材料中的应用

随着电子技术的高速发展和电子器件的更新换代,电子封装材料的性能需求越来越高。金属基复合材料,尤其是铝基和铜基复合材料具有高导热、低膨胀、高稳定性等特点,是具有广阔应用前景的电子封装材料。然而,金刚石、石墨烯、硅等增强体与基体的润湿性差,或者在高温下与基体发生有害的界面反应,限制了此类高导热金属基复合材料的开发和应用。本文简述了金属基复合材料的界面研究进展,结合影响金属基复合材料界面结合的因素,提出了几种改善界面结合的方法。增强体表面改性是改善金属基复合材料界面的重要途径之一,常用工艺有磁控溅射法、化学气相沉积法、溶胶凝胶法、化学镀法等;最后,对增强体表面改性在高热导金属基复合材料中的应用进行分析和展望。

金属基热界面材料研究进展

随着芯片向小型化、集成化和高功率化发展,其在工作时产生的热量增多,若产生的热量不能及时传递到外部,会严重影响电子元件的性能和使用寿命。热界面材料是电子元件散热结构中重要的组成部分,其主要作用是填充电子元件与散热器之间的空气间隙,使电子元件产生的热量快速转移,降低界面热阻。综述了现有热界面材料的种类和特点,详细介绍了金属基热界面材料的类型与性能特征、研究现状及存在的问题等,并对低熔点金属基热界面材料的发展进行了展望。

陶瓷基复合材料与金属异种材料焊接技术的研究现状

陶瓷基复合材料因具有良好的抗高温性能,被广泛应用于航空航天、核能等工业领域。随着工程应用中对结构件性能要求越来越高,陶瓷基复合材料与金属材料之间的焊接技术成为陶瓷基复合材料领域的研究热点。本文综述了陶瓷基复合材料与金属之间的焊接技术的研究现状,包括钎焊、扩散焊、自蔓延高温合成焊和熔化焊,可以为陶瓷基复合材料与金属之间的焊接技术研究提供参考。

随机源对颗粒增强金属基复合材料力学性能影响的多尺度分析及实验验证

20%(体积分数)SiC_(p)/2009Al复合材料的准静态拉伸实验结果表明,其失效应变等力学参数具有明显的分散性。采用多尺度有限元的方法研究了两类随机源对20%SiC_(p)/2009Al宏观力学性能的影响。通过对一系列含随机源的细观多颗粒代表体积单元模型进行准静态拉伸模拟,得到了材料失效应变和断裂能各自的随机分布特征及两者之间的相关性特征,然后结合宏观试样模型,实现了实际材料内不同区域材料性能随机性的表征。研究表明,宏观有限元结果与实验数据的吻合性较好,且由于考虑了随机源的影响,宏观有限元结果还能够很好地模拟失效应变等的分散性特征。

高热导率材料的发展和应用

概述了高热导率材料的分类、优缺点、制备方法和应用,包括陶瓷基封装材料、聚合物基封装材料和金属基封装材料。重点论述了金属基复合材料的应用和分类,金属层合板轧制工艺的研究,Cu/MoCu/Cu-Cu-MoCu-Cu(CPC)金属基层状复合材料的发展等。

金属基复合材料强度的影响因素

过去 30年里金属基复合材料虽然得到了广泛的研究与发展 ,但其性能一致性差的问题制约了其应用 ,因此复合材料的性能设计受到了普遍的关注。强度是材料在工程应用上重要的衡量指标 ,对强度影响因素的研究对复合材料的性能设计至关重要。本文着重分析了复合材料中基体合金化、增强体、基体与增强体的相容性、界面。

电子封装材料的研究现状及发展

根据电子封装材料的特点及要求,介绍了几种封装材料,详细地阐述了金属基复合封装材料的性能特点、制备方法、应用背景及存在的问题。并展望了电子封装材料的发展前景。

二氧化锡颗粒增强银基复合材料的电阻率

根据复合材料的传导理论ｇ－ＭｅＯ系金属基复合材料电阻率的计算模型，并与Ａｇ－Ｓ的实验结果进行了对比。结果分析表明，颗粒增强金属基复合材料的电阻率不仅与基体和颗粒材料的电阻率及颗粒的体积分数有关，还与颗粒粒度及在基体中的分布状态有关。

镁基复合材料制备工艺研究进展

综述主要的镁基复合材料制备工艺,介绍粉末冶金法、搅拌铸造法和原位反应自生增强法等制备方法,分析各工艺的优点及存在的问题,展望镁基复合材料制备工艺的发展前景。

单壁纳米碳管/纳米铝基复合材料的增强效果

用半连续氢电弧法和活性氢等离子蒸发法分别制备出单壁纳米碳管(SWNTs)和纳米Al粉体,然后用提纯后的SWNTs和纳米Al粉体制备出SWNTs含量(质量分数)分别为0、2.5％、5.0％、7.5％和10.0％的单壁纳米碳管/纳米铝基块体复合材料。SWNTs对高强度纳米Al基体具有显著的增强作用,当SWNTs含量小于5.0％时,材料的硬度随着SWNTs含量的提高线性上升。其中5％SWNTs和纳米Al的复合增强效果最好,其硬度可达2.89GPa,大约是粗晶Al(0.15GPa)的20倍。当SWNTs含量超过5.0％时,增强效果开始缓慢的下降。讨论了单壁纳米碳管增强纳米铝基复合材料的强化机制。

金属基固体自润滑材料的研究概况

金属基固体自润滑材料是材料科学研究领域的一个重要发展方向 ,因其在特殊条件下具有优良的摩擦学特性而受到人们的广泛关注。为促进该类材料的研究与应用 ,作者综述了某些金属基固体自润滑材料的研究概况 ,重点介绍了其摩擦学特性或相关物理力学性能 。

钨纤维增强金属玻璃复合材料弹穿甲钢靶的实验研究

为具体研究钨纤维增强金属玻璃复合材料的力学特性及其穿甲自锐特征,开展了相应的准静态和动态力学实验,并用火炮开展了复合材料弹体撞击钢靶的穿甲实验,同时利用金相分析对材料失效模式进行了较系统的识别和分类,并同静动态实验数据进行比较分析,最后开展了材料自锐剪切失效的机理讨论。实验获得了复合材料的静动态力学特性及其自锐穿甲的形貌,相关分析显示,材料的变形具有明显的应变率效应,在复合材料弹体侵彻/穿甲过程中,弹体的破坏方式主要表现为局域化的剪切变形和断裂,并呈现出4种自锐剪切失效模式,增强钨纤维也表现出3类失效破坏模式。

新一代高导热金属基复合材料界面热导研究进展

热物理性质不同的材料之间存在界面热阻,界面热阻对热传输过程产生极大的影响,并在很大程度上决定了复合材料的导热性能。金刚石颗粒增强金属基复合材料(Metal matrix composites,MMCs)充分发挥了金刚石的高热导率和低热膨胀系数的优点,有望获得高的热导率以及与半导体相匹配的热膨胀系数,可满足现代电子设备在散热能力上提出的越来越高的要求,作为新一代电子封装材料已引起广泛关注。界面热导(界面热阻的倒数)既是决定复合材料导热能力的关键因素,也是研究的难点,复合材料制备工艺、界面改性方式(金属基体合金化或金刚石表面金属化)以及改性金属种类均会影响界面热导。详细论述了界面热导理论及实验研究的最新成果,并对金刚石/金属复合材料在未来研究中面临的主要问题进行探讨。

纳米氧化锌改性聚四氟乙烯的研究

以纳米氧化锌为填充剂,通过乳液共混方法制备了纳米氧化锌改性聚四氟乙烯复合材料。实验确定了较理想的复合工艺,能够在成本基本不变的条件下明显改善复合材料的多项性能。另外,通过扫描电镜观察了复合材料的微观结构,研究了纳米氧化锌颗粒的粒度分布,分析了复合材料的性能随增强体加入量的变化规律,在此基础上,探讨了纳米氧化锌改性聚四氟乙烯的机理。