Investigation of Interfaces in Remelted A356-SiC Particulate Duralcan Metal Matrix Composite

For the manufacture of Al-based metalmatrix composites, the foundry productionroute can provide less expensive products witha greater flexibility in meeting designer’s needsamong a vaviety of fablication routes. Recent-ly, a commercially produced foundry ingot,the Duralcan composite of A356 Al alloy +20

Interface-dominated mechanical behavior in advanced metal matrix composites

Metal matrix composites(MMCs)incorporate a reinforcing or functional secondary phase into a metal matrix to achieve specific properties.Of the parameters which may affect the mechanical behavior of MMCs,the structure and properties of the reinforcement/matrix interface play a crucial role.This article reviews recent developments in measuring the interfacial properties in advanced MMCs,with an emphasis on the use of micro-/nano-mechanical testing approaches.It is shown that,with the novel in situ and ex situ experimental capability,researchers can now obtain some of the critical interfacial properties as well as the effects of reinforcement/matrix interfaces on the composites’deformation and failure mechanisms that were unattainable previously by conventional methodologies.Moreover,the micro-/nano-mechanical testing platform allows for both fundamental and applied research on the composites’mechanical performance under service conditions,which is considered a promising and emerging research direction.

The Effects of Interfaces on Stress Transfer in Short Fiber Reinforced Metal Matrix Composites

In this paper, the effects of interface properties on the stress transfer between matrix and fiber in short fiber reinforced metal matrix composites (SFRMMCs) is studied with the method of the elasto plastic finite element. The interface properties include Young’s modulus, thickness and elasto plastic performances. In the calculation an interfacial layer with given thickness is introduced into the single fiber model. It is shown that, for a soft interface, the variation in interfacial properties influences the stress transfer greatly.

Distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites

The distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites wasinvestigated using cohesive zone models. It is found that the strain of the composite is concentrated in the matrix, and there is aregion with higher strain along the loading path, which can promote the formation of a void near the particles pole. The stress andstrain in matrix near the particles gradually decrease with the increase of the distance between particles. And it is calculated that thereis a critical distance within which the stress and strain fields of the neighboring particles can influence with each other. This criticaldistance increases with the increase of particle size. It is also found that the angle between the tensile direction and the center line ofparticles plays an important role in the stress and strain distribution. The model with the angle of 0° has the greatest influence on thedistribution of stress and strain in the matrix, while the model with the angle of 45° has the least influence on the distribution of stressand strain in the matrix.

INTERACTION OF PARTICLES WITH A SOLIDIFIED INTERFACE DURING SOLIDIFICATION OF METAL MATRIX COMPOSITE REINFORCED WITH PARTICLES

The interaction of particles with a solid-liquid interface during solidification of metal matrix composites has been investigated theoretically in this paper.Owing to the presence of particles in the melt,the shape of the solidification front and solute concentration field in front of solidification interface have been disturbed The thermodynamic method was employed,and a mathematical expression of the shape of the solidification interface and solute concentration field were deduced.Meanwhile,a theory is developed for evaluation of critical velocities of particles pushed by the solidification interface.A numerical simulation is done in which the critical velocity is evaluated as a function of particle size,thermal conductivity,diffusion coefficient,temperature gradient at the solidification front,the solid-liquid interfacial energy and the melt viscosity.The critical velocity is shown to be closely linked to the shape of the solidification interface and solute concentration field, and hence all the parameters also affect the shape of the solidification interface and solute concentration field of the front.

Building metallurgical bonding interfaces in an immiscible Mo/Cu system by irradiation damage alloying (IDA)

For the immiscible Mo/Cu system with a positive heat of mixing （△Hm 〉 0）, building metallurgical bonding interfaces directly between immiscible Mo and Cu and preparing Mo/Cu laminar metal matrix composites （LMMCs） are very difficult. To solve the problem, a new alloying method for immiscible systems, which is named as irradiation damage alloying （IDA）, is presented in this paper. The IDA primarily consists of three steps. Firstly, Mo is damaged by irradiation with multi-energy （186, 62 keV） Cu ion beams at a dose of 2× 1017 ions/cm2. Secondly, Cu layers are superimposed on the surfaces of the irradiation-damaged Mo to obtain Mo]Cu laminated specimens. Thirdly, the irradiation damage induces the diffusion alloying between Mo and Cu when the laminated specimens are annealed at 950 ℃ in a protective atmosphere. Through IDA, Mo/Cu LMMCs are prepared in this paper. The tensile tests carried out for the Mo/Cu LMMCs specimens show that the Mo/Cu interfaces constructed via IDA have high normal and shear strengths. Additionally, the microstructure of the Mo/Cu interface is characterized by High Resolution Transmission Electron Microscopy （HRTEM）, X-ray diffraction （XRD） and Energy Dispersive X-ray （EDX） attached in HRTEM. The microscopic characterization results show that the expectant diffusion between Mo and Cu occurs through the irradiation damage during the process of IDA. Thus a Mo/Cu metallurgical bonding interface successfully forms. Moreover, the microscopic test results show that the Mo/Cu metallurgical interface is mainly constituted of crystalline phases with twisted and tangled lattices, and amorphous phase is not observed. Finally, based on the positron annihilation spectroscopy （PAS） and HRTEM results, the diffusion mechanism of IDA is discussed and determined to be vacancy assisted diffusion.

Interface,lattice strain and dislocation density of SiC_p/Al composite consolidated by equal channel angular pressing and torsion

Powder mixture of pure A1 and oxidized SiC was consolidated into 10% （mass fraction） SiCp/AI composites at 523 K by equal channel angular pressing and torsion （ECAP-T）. The interfacial bonding of the composites was characterized by transmission electron microscopy （TEM） and high resolution transmission electron microscopy （HRTEM）. The selected area electron diffraction （SAED） for the interface was investigated. The elements at the interface were scanned by energy dispersive spectroscopy （EDS） and the EDS mapping was also obtained. X-ray diffraction （XRD） analysis was carried out for the composites fabricated by 1 pass, 2 passes and 4 passes ECAP-T. According to the XRD analysis, the influences of ECAP-T pass on the Bragg angle and interplanar spacing for AI crystalline planes were studied. The results show that after ECAP-T, the interface between A1 and SiC within the composites is a belt of amorphous SiO2 containing a trace of A1, Si and C which diffused from the matrix and the reinforcement. With the growing ECAP-T pass, the Bragg angle decreases and interplanar spacing increases for A1 crystalline planes, due to the accumulated lattice strain. The increasing lattice strain of A1 grains also boosts the density of the dislocation within A1 grains.

DETERMINATION OF MECHANICAL PROPERTIES INMICROZONE OF METAL MATRIX COMPOSTITES BY ULTRAMICROHARDNESS

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Interface and microstructure characteristics of SiC_p/2024 aluminium alloy composite

Electron microscope examination of the microstructure, interface and fracture surface of SiC particulate reinforced 2024 aluminium alloy composites produced by powder mixing and semi-solid extrusion process was presented. The microstructure of SiC p/2024 composites fabricated by the present method is characterized by uniformly distributed SiC particulates in well-densified matrix. Conventional transmission electron microscopy(TEM) reveals the interface between the SiC particulates and the aluminium matrix. It is shown that this interface provides very strong bonding which is further evidenced by the fractographic results, and that there is no apparent chemical reaction. Examination of the fracture surface indicates that the bonding strength between the SiC particulates and the aluminium alloy matrix is stronger than that of the matrix. The dimples and tearing edges on the fracture surface of composites are obviously observed.

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。

金属颗粒增强镁基复合材料制备技术及性能的研究进展

镁基复合材料具有低的密度、优异的力学性能等特点,在汽车、电子、航空航天等领域有广阔的应用前景。本文综述了国内外金属颗粒增强镁基复合材料的研究进展,详细介绍了金属颗粒增强镁基复合材料常见制备方法的特点,分析了金属颗粒增强镁基复合材料的界面结构和主要强韧化机理。最后,对金属颗粒增强镁基复合材料制备材料及工艺的发展进行了展望。

芯片用金刚石增强金属基复合材料研究进展

随着电子设备集成化程度越来越高,对高导热封装材料的需求也越来越大,金刚石增强金属基复合材料凭借其高导热性能成为研究焦点。然而,由于金刚石颗粒与金属基体之间的不润湿特性,具有高导热性的金刚石增强金属基复合材料难以制备。文中综述了金刚石增强金属基复合材料的研究进展,包括界面改性、工艺参数优化和复合材料制备方法,并指出了金刚石增强金属基复合材料目前存在的问题和今后的研究方向。

Damping capacity of BaTiO_3/Al composites fabricated by hot extrusion

To develop new type of high damping metal matrix composites, large grain size barium titanate （BaTiO3） ceramic was sintered and added into Al powder to fabricate BaTiO3/Al composites through the powder metallurgy method and hot extrusion. The damping properties of BaTiO3 ceramic, Al matrix and BaTiO3/Al composites were examined by dynamic mechanical analysis in the temperature range from 273 K to 573 K. The results show that although BaTiO3 exhibits high damping （tan δ=0.12） below 400 K, the damping capacity of 10%BaTiO3/Al （mass fraction） composites below 400 K is not increased as compared to the Al matrix. On the other hand, the damping capacity above 450 K is greatly enhanced due to the motion of dislocations at the interfaces between ceramic particles and Al matrix. The failure of exerting the intrinsic damping of BaTiO3 particles in the composites is attributed to the poor interface bonding between the particles and the matrix. The tensile strength of the composite is 42% higher than that of the Al matrix, which indicates the possibility of obtaining high strength and high damping composites via interface improvement and the addition of high volume fraction of large grain BaTiO3 particles.

Structural considerations in friction welding of hybrid Al_2O_3-reinforced aluminum composites

Comparative studies on the relationship between the welding parameters and joining efficiency in the friction welding of hybrid Al203-reinforced aluminum composites were conducted. Metal matrix composites （MMCs） with 37% （volume fraction） aluminum particle were joined by friction welding. The results show that the effects of the rotation speed on the reduction rate of particle size are greater than those of the upset pressure, and the area of the MMC weld zone decreases as the joining efficiency increases, while it is considered that the joining efficiency does not increase as the reduction rate of particle size decreases. During the macro-examination of the bonding interlace, a gray discolored region was observed on the bonding interface, and the center of the region was dark gray. After the micro-examination of the bonding interface, base metal made some second particulate formed by condensed alumina particulate but discoloration part distributed minute alumina particulate without second particulate. Consequently, it was also observed that rotational speed of 3 000 r/min and upset pressure of 63.6 MPa showed a very good.joint.

Effect of sintering temperature on the microstructure and thermal conductivity of Al/diamond composites prepared by spark plasma sintering

Spark plasma sintering was used to fabricate Al/diamond composites.The effect of sintering temperature on the microstructure and thermal conductivity（TC） of the composites was investigated with the combination of experimental results and theoretical analysis.The composite sintered at 550℃shows high relative density and strong interfacial bonding,whereas the composites sintered at lower（520CC） and higher（580-600℃） temperatures indicate no interfacial bonding and poor interfacial bonding,respectively.High relative density and strong interfacial bonding can maximize the thermal conductivity of Al/diamond composites,and taking both effects of particle shape and inhomogeneous interfacial thermal conductance into consideration can give a fairly good prediction of composites＇ thermal conduction properties.

Effects of Mg content on microstructure and mechanical properties of SiC_p/Al-Mg composites fabricated by semi-solid stirring technique

10%(volume fraction) SiCp/Al-Mg composites with different Mg contents were successfully fabricated by semi-solid mechanical stirring technique under optimum processing conditions.Effects of Mg content on microstructure and mechanical properties were studied by scanning electron microscopy(SEM),X-ray diffractometry(XRD) and transmission electron microscopy(TEM).The results indicate that SiC particles disperse homogeneously in Al-Mg matrix and interfacial reaction between Al matrix and SiC particles is effectively controlled.Distribution of SiCp reinforcement and interfacial bonding are improved by adding Mg.Additionally,the mechanical properties of composites are remarkably improved with the Mg content increasing.

A review of processing of Cu/C base plate composites for interfacial control and improved properties

The increase in both power and packing densities in power electronic devices has led to an increase in the market demand for effective heat-dissipating materials with a high thermal conductivity and thermal expansion coefficient compatible with chip materials while still ensuring the reliability of the power modules.Metal matrix composites,especially copper matrix composites,containing carbon fibers,carbon nanofibers,or diamond are considered very promising as the next generation of thermalmanagement materials in power electronic packages.These composites exhibit enhanced thermal properties,as compared to pure copper,combined with lower density.This paper presents powder metallurgy and hot uniaxial pressing fabrication techniques for copper/carbon composite materials which promise to be efficient heat-dissipation materials for power electronic modules.Thermal analyses clearly indicate that interfacial treatments are required in these composites to achieve high thermal and thermomechanical properties.Control of interfaces(through a novel reinforcement surface treatment,the addition of a carbide-forming element inside the copper powders,and processing methods),when selected carefully and processed properly,will form the right chemical/mechanical bonding between copper and carbon,enhancing all of the desired thermal and thermomechanical properties while minimizing the deleterious effects.This paper outlines a variety of methods and interfacial materials that achieve these goals.

Fabrication and fracture toughness of macro-toughening-designed composite

A macro-structure-toughened SiC particle reinforced LD2 aluminum alloy matrix (SiCp-LD2/LD2) composite was designed and fabricated based on considering the main factors which result in low room temperature fracture toughness of conventional metal matrix composites. Its room temperature fracture toughness was tested using three-point bending samples with sing1e edge notches. Compared with conventional SiCp/LD2 composites fabricated by stirring casting in case of same particle size and similar reinforcement volume fraction, this composite has a higher room temperature fracture toughness KQ. It shows strong resistance to crack propagating. The crack in it can propagate stably for a long time on the maximum load, therefore abrupt fracture occurring in most conventional composites can be avoided. Bending fractography (SEM) shows that the fracture mechanism of this material is different from SiCp/LD2 composite and the deformation of the unreinforced LD2 matrix and the SiCp-LD2/LD2 interface debonding are the main toughening mechanisms of this composite.

Enhancement of interfacial bond strength of Al_2O_(3f)/Al-15Si composite by solidification process

To build the relationship between solidification conditions and the interfacial bond strength,Al2O3f/Al-15Si composite solidified at different cooling rates were investigated by microstructure observation and mechanical testing.The results show that the interfacial bond strength of the as-cast composite is significantly enhanced after furnace-or air-cooling processes owning to the preferential nucleation and growth of the eutectic silicon on the fiber surface.The discontinuously distributed eutectic silicon on the fiber surface makes the fiber become coarse,resulting in the enhanced mechanical bond strength between fiber and matrix.However,the interfacial bond strength of the oil-cooled composite is not improved,showing that the silicon on the fiber surface is important for the improvement of the interfacial bond strength.The air-and furnace-cooled composites also have a higher tensile strength.