Electrical resistivity of metal matrix composites

Theoretical models for predicting the electrical resistivity of metal matrix composites reinforced with continuous fibers, short fibers, and particulates were developed by integrating thin slices of composite cells. The experimental electrical resistivity of aluminum, copper, and silver matrix composites was measured and compared with theoretical values derived from the models. Experimental resistivity of composites followed the trend of theoretical prediction, increasing with increasing volume fraction and decreasing size of reinforcement. Deformation regions containing residual stresses and dislocations formed around the reinforcement and raised the resistivity of composites. The magnitude of residual stresses and the dislocation density were found to depend on the type, size and shape of reinforcement, as well as the matrix type. The effective size of the deformation regions varied due to their overlapping and better fitted the calculated curves through empirical modification. Theoretical prediction of resistivity that takes into account the effect of residual stresses and dislocations, and the overlapping of deformation regions agreed reasonably well with experimental results.     

Microstructure and Mechanical Properties of Mg–7.4% Al Alloy Matrix Composites Reinforced by Nanocrystalline Al–Ca Intermetallic Particles

Mg–7.6% Al(in mass fraction) alloy matrix composites reinforced with different volume fractions of nanocrystalline Al3Ca8 particles were synthesized by powder metallurgy,and the effect of the volume fraction of reinforcement on the mechanical properties was studied.Room temperature compression test reveals considerable improvement on mechanical properties as compared to unreinforced matrix.The compressive strength increases from 683 MPa for unreinforced alloy matrix to about 767 and 823 MPa for the samples having 20 and 40 vol% of reinforcement,respectively,while retaining appreciable plastic deformation ranging between 12 and 24%.The specific strength of the composites increased significantly,demonstrating the effectiveness of the low-density Al3Ca8 reinforcement.     

石墨烯增强铜基复合材料的制备技术及发展

石墨烯由于其独特的二维结构和优异的物化性能,在改善复合材料的力学性能、电学性能和热学性能等方面具有很大的潜力,已成为金属基复合材料较理想的增强体。铜合金具有优异的导电导热性能和良好的延展性,但是其强度较低、不耐磨及高温下易变形的特点阻碍了其应用和发展。因此,结合石墨烯和铜的性能特点,将石墨烯作为增强体添加到铜中,制备性能优异的石墨烯增强铜基复合材料成为目前研究的热点之一。综述了目前石墨烯增强铜基复合材料的制备方法,并对各方法的特点进行了分析比较,提出未来可采用的制备工艺的方向以及在制备过程中面临的问题和挑战,并对其未来的研究方向进行了展望。     

Effect of Heat Input on Mechanical and Metallurgical Properties of Friction Stir Welded AA6061-10% SiCp MMCs

Metal matrix composites (MMCs) reinforced with SiC particles combine the matrix properties with those of the ceramic reinforcement, leading to higher stiffness and superior thermal stability with respect to the corresponding unreinforced alloys. However, their wide application as structural material needs proper development of a suitable joining process. In this investigation, an attempt was made to study the effect of heat input on the evolution of microstructure in weld region of friction stir welded AA6061-10% SiCp MMCs. The tensile properties of the joints were evaluated and they are related with microstructure and heat input of the process. The microstructure characterization of the weld zone shows evidence of a substantial grain refinement of the aluminum matrix and fracturing of reinforcement particles due to dynamic recrystallization induced by the plastic deformation and frictional heating during welding.     

C纤维增强镁基复合材料热成形微观组织模型

以C纤维增强镁基复合材料在高温变形过程中的物理机制为基础,建立了C纤维增强镁基复合材料高温变形时以Yada模型为基础的微观组织模型。将该微观组织模型应用于镁基复合材料的高温变形,编写C++程序求解,根据实验数据对模型进行回归,确定高温状态及半固态下微观组织模型中的特征参数值。C纤维增强镁基复合材料的热模拟实验结果和定量金相实验结果证实,初生α相晶粒尺寸的样本数据的平均相对误差为6.89%,非样本数据的平均相对误差为7.08%。模型预测精度较高,能较好地描述镁基复合材料高温塑性变形时的微观组织演变行为。     

Thermal elasto-plastic finite element modelling of the deformation behaviour of metal matrix composites considering interfacial strength

A suggestion of the strength analysis technique considering the interfacial bonding strength is very important for the design of parts and the estimation of fatigue behavior. In this paper three dimensional finite element analysis was performed during the elasto-plastic deformation of particulate reinforced metal matrix composites. Bonding strength, interface separation and matrix void growth between the matrix and reinforcements were predicted during deformation under tensile loading. The shape of the reinforcement was assumed to be a perfect sphere. The type of the reinforcement distribution was assumed as FCC array. The element birth and death method of the ANSYS program was used for estimating the interfacial bonding strength, void generation and propagation. The experimental data of the extruded SiCp/6061 AI composites were compared with the calculated results.     

Cutting forces and TEM analysis of the generated surface during machining metal matrix composites

Cutting of metal matrix composites (MMCs) has been considerably difficult due to the extremely abrasive nature of the reinforcements that causes rapid tool wear and high machining cost. An investigation was carried out to clearly understand the role played by the ductile matrix on the machining performance based on the estimation of line defects generated as a result of cutting. The microstructural studies were conducted using transmission electron microscopy (TEM) on the machined surface to reveal the deformation pattern of the work hardening matrix and its correlation with the forces generated during turning MMCs. Cracking and debonding of the reinforcement particles are the significant damage modes that directly affect the tool performance. It was found that the particle size and volume fraction affect the extent of deformation in the generated surface. Also the machining forces are correlated to the plastic deformation characteristics of the matrix material. This investigation provided valuable information on the deformation behaviour of particulate reinforced composites that can improve the performance and accuracy of machining MMCs.     

超大挤压变形对钛合金增强镁基复合材料显微组织的影响

采用粉末冶金法制备了钛合金（Ti-6Al-4V）（质量分数，下同）颗粒增强MB15镁基复合材料，经225：1的超大比热挤变形后，借助光学显微镜（OM）、扫描电镜（SEM）和透射电镜（TEM）对其显微组织进行了研究。结果表明：钛合金颗粒沿挤压方向因塑性变形而被拉长，其增强效果得到提高；超大比热挤变形能够显著细化基体晶粒，并提高复合材料的组织均匀性；此外，原镁粉表面的氧化膜经超大比变形后得到了有效的碎化和分散，具有一定的弥散强化效果，因此可充当粉末冶金制备镁基复合材料的辅助增强相。     

Fabrication and fracture toughness of macro-toughening-designed composite

lINTR0DUCTIONParticleReinforcedMetalMatrixC0mp0s-ites(PMMCs)havehighspecificstrength,spe-cificmodulus,elevatedtemperatureproperties,res1stancetowearandlowcost.However,com-paniedlowductilityandtoughnessisonemainobstacletotheirapplicationforengineeringL','j.ManystudiesonSiCparticlereinforcedalu-.minum.ll.y.['v']showthattheadditionofpar-ticlenotonlyrefinesmatrixgrainbutalsoresultsinhighdensitydislocationsinthematrixneartheinterface.Particlesblocklong-distance-slipofthedislocationsinthema…     

非连续增强钛基复合材料研究新进展

非连续增强钛基复合材料由于具有各向同性、比强度高、优良的高温强度、成本较低等特点而受到高度关注。TiC及TiB增强颗粒以其稳定的复合结构、良好的增强效果得到发展,成为非连续增强钛基复合材料的最终优选增强剂。从制备方法、增强体与基体的界面结构及复合材料的性能等方面概述了非连续增强钛基复合材料的最新研究进展。     

钴基合金-不锈钢梯度强化材料低应力多碰塑变分析

目的研究钴基合金-不锈钢梯度强化材料抵抗低应力多碰塑性变形的能力,以改善单一涂层应力集中问题。方法制备指数梯度和线性梯度涂层试样,与304不锈钢基体试样一起进行低应力多碰实验,比较分析3种材料的塑性变形量、硬度变化量与金相组织变化。结果线性梯度涂层试样的累积塑性变形量约为304不锈钢的1/2,指数梯度涂层试样的累积塑性变形量约为304不锈钢的1/3;两种涂层试样均存在循环硬化及软化现象,硬度值由表及里逐渐减小,多碰后塑性变形符合"趋表效应"。结论两种梯度涂层强化材料的抗低应力多碰塑变能力均明显优于未强化材料,且指数梯度强化材料性能优于线性梯度强化材料。     

纳米碳管增强镁基复合材料应力传递有限元分析

结合有限元的分析方法,建立了一个简化模型来模拟纳米碳管增强镁基复合材料在拉伸试验过程中的变形,研究了基体、增强体的应变和应力分布,以及界面对复合材料力学行为的影响,探讨了纳米碳管增强体与基体间的应力传递机制和断裂机理。模拟结果表明,纳米碳管整体上受力比较均匀,在轴向上的界面处出现应力集中;基体与纳米碳管在两端面的接触部位出现明显的应力集中,应力分布呈火焰状,中心大,逐渐向外围减小,在基体的其余部位应力大小则是相对均匀的,这说明复合材料的破坏是从界面处开始的,其破坏机制是界面脱开。     

Equation for the density of particle-reinforced metal matrix composites: A new approach

This paper presents a novel equation for the density of ceramic particle reinforced metal matrix composites. An overall density change occurs in composites due to the thermal mismatch between the metal matrix and the reinforcement. The thermal mismatch occurs because the coefficient of thermal expansion and the elastic properties are different for the matrix and the reinforcement. The values obtained using the proposed equation for density were compared with both the rule of mixtures for density and the experimental values obtained for aluminium and zinc alloy composites. The composite specimens were fabricated using compocasting technique (one of the types of liquid metallurgy route). The proposed mathematical model is found have better agreement with the experimental results at lower volume fractions of the reinforcement; however, some deviations were observed at higher volume fractions of the reinforcement. The proposed equation yields agreeable results for aluminium composites and fairly agreeable results for zinc alloy composites.     

有限元模拟SiC增强Al基复合材料的力学行为

采用有限元方法和轴对称单胞模型模拟了增强体(SiC)形状、体积分数以及不同基体类型对铝基复合材料力学行为的影响。模拟结果表明:增强体的加入会阻碍基体的塑性流变,使基体内发生非均匀变形,在增强体尖角处出现应力集中;椭圆柱形增强体对基体塑性变形的阻力最大,传递载荷的能力最强,因此强化效果最好。在一定范围内,随着增强体体积分数的增加,基体与增强体之间的比表面积增大,有利于载荷的传递;增强体体积分数的增加导致颗粒间距减小,几何必须位错自由运动的路径减少,复合材料的强度也随之增加。此外,不同类型基体自身的塑性流变能力不同,Al-Zn-Mg基体强度最高,在拉伸变形过程中,受到增强体的阻碍作用最大,会有更多的载荷从基体传递到增强体,以Al-Zn-Mg为基体的复合材料的强度最高。     

A Fatigue Model for Discontinuous Particulate-Reinforced Aluminum Alloy Composite: Influence of Microstructure

In this paper, the use of a microstructure-sensitive fatigue model is put forth for the analysis of discontinuously reinforced aluminum alloy metal matrix composite. The fatigue model was used for a ceramic particle-reinforced aluminum alloy deformed under conditions of fully reversed strain control. Experimental results revealed the aluminum alloy to be strongly influenced by volume fraction of the particulate reinforcement phase under conditions of strain-controlled fatigue. The model safely characterizes the evolution of fatigue damage in this aluminum alloy composite into the distinct stages of crack initiation and crack growth culminating in failure. The model is able to capture the specific influence of particle volume fraction, particle size, and nearest neighbor distance in quantifying fatigue life. The model yields good results for correlation of the predicted results with the experimental test results on the fatigue behavior of the chosen aluminum alloy for two different percentages of the ceramic particle reinforcement. Further, the model illustrates that both particle size and volume fraction are key factors that govern fatigue lifetime. This conclusion is well supported by fractographic observations of the cyclically deformed and failed specimens.     

Numerical simulation of solidification kinetics in A356/SiCp composites for assessment of as-cast particle distribution

The present work is aimed at studying the effect of solidification rate on reinforcement clustering in particle reinforced metal matrix composites (PMMCs) through numerical simulations and experimental studies. A macrotransport-solidification kinetics (MTSK) model was used to simulate the solidification kinetics of the PMMCs. The experimental validation of the numerical model was achieved through the Newtonian and Fourier thermal analysis methods. Results reveal that the MTSK model can be successfully used to predict the local microstructural scales and to evaluate the risk of cluster formation in cast particle reinforced composites.     

Study on behavior of reinforcement in molten pool for submicron composite Al_2O_3p/6061 Al during laser welding

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Role of interfacial and matrix creep during thermal cycling of continuous fiber reinforced metal–matrix composites

A uni-dimensional micro-mechanical model for thermal cycling of continuous fiber reinforced metal–matrix composites is developed. The model treats the fiber and matrix as thermo-elastic and thermo-elasto-plastic-creeping solids, respectively, and allows the operation of multiple matrix creep mechanisms at various stages of deformation through the use of unified creep laws. It also incorporates the effect of interfacial sliding by an interface-diffusion-controlled diffusional creep mechanism proposed earlier (Funn and Dutta, Acta mater., 1999, 47, 149). The results of thermal cycling simulations based on a graphite fiber reinforced pure aluminum–matrix composite were compared with experimental data on a P100 graphite–6061 Al composite. The model successfully captured all the important features of the observed strain responses of the composite for different experimental conditions, such as the observed heating/cooling rate dependence, strain hysteresis, residual permanent strain at the end of a cycle, as well as both intrusion and protrusion of the fiber-ends relative to the matrix at the completion of cycling. The analysis showed that the dominant deformation mechanism operative in the matrix changes continually during thermal cycling due to continuous stress and temperature revision. Based on these results, a framework for the construction of a transient deformation mechanism map for thermal excursions of continuous fiber composites is proposed.     

金属基复合材料制备中有害界面反应的控制和润湿性的改善工艺

介绍了液态法制备颗粒增强金属基复合材料（以SiCp／Al为例）过程中，如何控制增强相颗粒和基体之间发生的有害界面反应、改善增强颗粒与基体润湿性的常用方法。结果表明，添加Si元素、添加Ti、Zr、Nb、V等合金元素、表面涂覆和处理以及控制工艺方法和参数都可有效地抑制有害的界面反应发生和改善基体和增强相的润湿性。     

颗粒增强金属基复合材料简介

简述了颗粒增强金属基复合材料的主要特点,包括制备工艺简单、成本低廉、性能优异等.同时还介绍了基体材料、增强颗粒的作用和选用原则、界面、原位反应复合法等制备技术及应用前景.