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.     

Machining of aluminium based metal matrix composites

Although metal matrix composites (MMCs) are generally regarded as extremely difficult to machine, it is also acknowledged that their machining behaviour is not fully understood. The work reviewed here confirms this widely held view but also suggests that the machinability of these materials can be improved by appropriate selection of the reinforcing phase, its volume fraction, size, and morphology as well as the composition and hardness of the matrix material. Cemented carbide tools can be used to machine some of the less abrasive materials at slow speeds but if higher production rates are required or the more abrasive materials are to be machined, polycrystalline diamond tooling is required.     

Micro-mechanical modeling the densification behavior of titanium metal matrix composites

Vacuum hot pressing has been used for the development of Ti-MMCs using foil–fiber–foil method, and a unified micro-mechanical model has been presented to determine the densification behavior. The effects of processing conditions on the consolidation, together with microstructural evolutions of the materials have been investigated. The explicit representation of fiber array, which is coupled with deformation behavior of matrix materials, is modeled in finite element simulation to determine the effect of geometrical arrangements on densification process. The approach is then used to model the densification behavior of porous plastic materials using the parameters obtained, and comparisons are made with experimental data. As shown by the results, either increasing temperature or pressure leads to increasing densification rate but the conditions should be determined by the precisely controlled geometrical arrangements with processing conditions. Further experimental investigation of the densification behavior of SiC/Ti–6Al–4V composites using thermo-acoustic emission analysis has been performed, and the results obtained are compared with the model predictions. Good comparisons are achieved.     

Micromechanical analysis of thermoelastoplastic behavior of metal matrix composites

A micromechanics model based on the variational asymptotic method for periodic composites was developed using an incremental formulation to capture the coupled thermo-elasto-plastic behavior of metal matrix composites. Taking advantage of the small size of the microstructure, a variational statement of the unit cell through an asymptotic expansion of an functional of energy change was formulated to calculate the effective instantaneous tangential elasto-plastic matrix and thermal stress matrix of the composite materials. An iterative homogenization and localization technique was proposed to simulate the nonlinear thermo-elasto-plastic behavior of metal matrix composites. This model was implemented using the finite element method. For validation, a numerical example was examined to demonstrate the application and accuracy of this theory and companion code.     

Pitting behavior of SiCp/2024 Al metal matrix composites

The effects of the volume fraction of SiC particulate reinforcements and the concentration of chloride ions in solution on the localized corrosion characteristics of SiCp/2024 Al metal matrix composites (MMC) were investigated. A scanning micro reference electrode (SMRE) technique was employed to study the dynamic process of pitting initiation and development on the surface of the composites at open-circuit potential. Potentiodynamic polarizations were performed to characterize the electrochemical behavior of the MMCs. The morphology of the localized attack on the MMC sample after corrosion tests were examined by scanning electron microscopy (SEM). The results of electrochemical measurement showed that the composites were less resistant to pit initiation than the corresponding unreinforced metrix alloy. Increase in the volume fraction of SiCp reinforcement in the SiCp/2024 Al composites resulted in a significant decrease of pitting potential. In situ potential mapping of active centers on the surfaces of the composites revealed that local breakdown of passivity and initiation of micro pitting corrosion could take place even at an open-circuit potential which was more negative than the pitting potential, and the number of active centers on the surfaces of the composites increased as the volume fraction of SiC particulates in MMCs increased. Micro-structural analysis indicated that pitting attack on the composites mainly occurred at SiCp-Al interfaces or inclusions-Al interfaces.     

Microstructure-based modeling of the deformation behavior of particle reinforced metal matrix composites

A review is provided of the use of analytical models and two dimensional (2D) and three dimensional (3D) microstructure based FEM models to accurately predict the properties of particle reinforced composite materials. It is shown that analytical models do not account for the microstructural factors that influence the mechanical behavior of the material. 2D models do capture the anisotropy in deformation behavior induced by anisotropy in particle orientation. The experimentally-observed dependence of Young's modulus and tensile strength is confirmed by the 2D microstructure-based numerical model. However, because of the 2D stress state, a realistic comparison to actual experimental values is not possible. A serial sectioning process can be used to reproduce and visualize the 3D microstructure of particle reinforced metal matrix composites. The 3D microstructure-based FEM accurately represents the alignment, aspect ratio, and distribution of the particles. Comparison with single particle and multiparticle models of simple shape (spherical and ellipsoidal) shows that the 3D microstructure-based approach is more accurate in simulating and understanding material behavior.     

Fracture in ceramic-reinforced metal matrix composites based on high-speed steel

A series of metal matrix composites based upon M3/2 high-speed steel was produced by a powder metal sintering route. Hard ceramic titanium carbide or niobium carbide additions and a self-lubricant in the form of manganese sulfide, were added as a basis for achieving improved wear resistance and reduced friction. After sintering, the composites were given a full standard high-speed steel heat treatment and subjected to mechanical tests. All three particulate additions had a deleterious effect on three-point bend strength, particularly in the case of MnS addition, mainly due to the ease of initiating cracks at or near to the particulate additions. Bend strengths were further reduced by the simultaneous addition of both MnS and either TiC or NbC especially when a high volume fraction of approximately 25 vol % MnS was added. Single, low volume fraction (8%) additions, of TiC, NbC, or MnS, had little effect on fracture toughness and KIC values were comparable to those found in the baseline M3/2 steel. Slight improvements in fracture toughness shown to occur in the 7.74% NbC composites were attributed to energy dissipation caused by the effects of crack branching during crack propagation. Composites with the higher volume fraction additions of MnS and ceramic carbide gave poor fracture toughness by forming MnS/carbide clusters which provided an easy path for crack propagation. © 1998 Chapman & Hall     

金属基复合材料热弹塑性变分渐近细观力学模型

基于变分渐近法建立具有周期性微结构的金属基复合材料（MMCs）细观力学模型及相应的增量方程,以准确预测其典型的热弹塑性行为和初始屈服面。利用细、宏观尺度比很小的特点,对单胞变分能量泛函变化进行渐近扩展,计算得到有效瞬时弹塑性刚度矩阵和热应力矩阵;利用迭代均质化及局域化技术模拟MMCs的非线性热弹塑性性能,并通过有限元技术实现相应的数值模型。算例分析表明:该模型能较好地预测MMCs的初始屈服面,并模拟热弹塑性耦合行为,研究成果为MMCs的进一步研究和实际应用提供了技术支撑。      

Investigation of the low-speed impact behavior of dual particle size metal matrix composites

SiC-reinforced aluminum matrix composites were manufactured by powder metallurgy using either single or dual particle sized SiC powders and samples sintered under argon atmosphere. Quasi-static loading, low-speed impact tests and hardness tests were used to investigate mechanical behavior and found that dual particle size composites had improved hardness and impact performance compared to single particle size composites. Sample microstructure, particle distributions, plastic deformations and post-testing damages were examined by scanning electron microscopy and identified microstructure agglomerations in SPS composites. Impact traces were characterized by broken and missing SiC particles and plastically deformed composite areas.     

Fatigue of metal matrix composites

One unidirectional and two laminated 6061-0 A-B composite plates were tested under various cyclic loading conditions. Three types of material response to cyclic loading were identified; No evidence of damage at relatively low cyclic loads, damage accumulation caused primarily by growth of long matrix cracks parallel to the fibers in off-axis layers at higher loads, and sudden localized failure of the fibers. Quantitative analysis of the results shows that the extent of internal damage, demonstrated by a reduction in axial elastic modulus, depends on the applied stress range and is independent of mean stress. The stress range at which damage first starts to appear coincides with the shakedown range of the laminate.

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Résumé On a testé sous des conditions de contrainte cyclique variable des plaques constituées d'une part par des alliages 6061-0 A-B unidirectionnels et d'autre part du même alliage composite bilaminé. On a identifié trois types de réponse du matériau aux contraintes cycliques, à savoir la non-évidence d'un dommage pour des cycles de charge à faible amplitude relative, une accumulation du dommage causé principalement par la croissance de longues fissures matricielles parallèles aux fibres dans les couches éloignées du plan médian à des contraintes plus élevées, et une fissure soudainement localisée des fibres. L'analyse quantitative des résultats montre que 1'extension du dommage interne telle qu'elle est dóntree par une réduction du module axial d'élasticité, dépend de l'amplitude des contraintes appliquées et est indéndante de la contrainte moyenne. L'amplitude de contrainte auquelle un dommage commence à apparaître coíncide avec l'amplitude de l'adaptation plastique du laminé telle qu'établie par le théorème de Melan.

     

Thermal expansion characteristics of cast Cu based metal matrix composites

Like any other metal/alloy, copper and its alloys also soften at elevated temperatures. Reinforcing with ceramic or carbon fibres is one of the suggested solutions to overcome this. Very limited literature is available on Cu based metal matrix composites (MMCs); none of these pertain to liquid phase fabrication. Hence, a systematic investigation was carried out on MMCs based on copper, with alumino-silicate fibres and carbon fibres as reinforcements. The MMCs thus produced exhibit a uniform distribution of reinforcement in the matrix. Coefficient of thermal expansion (CTE) values are lower than that of pure copper.     

Modeling and simulation of the effect of fiber breakage on creep behavior of fiber-reinforced metal matrix composites

A theoretical model and computer simulation methodology was developed to predict the effect of fiber fracture on creep behavior of continuous fiber-reinforced metal matrix composites. Initially, a single fiber model was developed based upon the fiber statistical characteristics and a shear-lag analysis to establish the computation simulation route. Then, the methodology was extended to predict the creep behavior of a multiple fiber composite. A failure criterion was also incorporated in the model to predict the rupture life of the composite. A parametric study was also conducted to investigate the effects of properties of the constituents on the longitudinal creep behavior of the SCS-6/Ti composite.     

A modification of the Mori-Tanaka estimate of average elastoplastic behavior of composites and polycrystals with interfacial debonding

A modification of the Mori-Tanaka method is proposed to evaluate the average elastoplastic behavior of composites and polycrystals in a virtual matrix. The virtual matrix is an elastic material in which real matrix material and inhomogeneities are embedded, and its volume vanishes as a limit after homogenization. With regard to elasticity, depending on the choice of material properties of this virtual matrix, many kinds of average moduli between the classical bounds can be predicted. In this paper, we extend the application of this method to elastoplastic materials. Furthermore, Weng’s approximate model of interfacial debonding between the inclusions and the matrix is installed, because of its very simple criterion for the initiation of debonding to simulate progressive debonding phenomena. Several numerical examples without interfacial debonding show the applicability of the virtual matrix concept to elastoplastic materials. The characteristics of the model and its overall behaviors are described through the use of typical numerical simulations with debondings. Finally, comparisons with experimental results including debondings demonstrate the eligibility of the proposed method and models, and the application of the present method to designing a hybrid FRP is overviewed.     

High-speed turning experiments on metal matrix composites

The hard abrasive ceramic component which increases the mechanical characteristics of metal matrix composites (MMC) causes quick wear and premature tool failure in the machining operations. The aim of the paper is to compare the behaviour of high rake angle carbide tools with their diamond coated versions in high-speed machining of an Al₂O₃Al 6061 MMC. The influence of the cutting parameters, in particular cutting feed and speed, on tool wear and surface finish has been investigated. The higher abrasion resistance of the coatings results in increased tool life performances and different chip formation mechanisms.     

Aluminium based metal matrix composites for improved elevated temperature performance

Abstract

The thermal performance of six commercially available particulate reinforced metal matrix composites (MMCs) has been investigated, including the effects of continuous thermal exposure and thermal cycling on ambient and elevated temperature tensile properties, toughness, and fatigue. Additionally, accelerated creep tests and thermal cycling tests under load were carried out. Some aspects of the performance of these MMCs were very promising, particularly strength up to 200°C and good retained strength after extended exposure at up to 260°C, while resistance to creep and thermal cycling under load was generally not as good. The results were used as a basisfor selected tests on some development MMCs aimed at improvements to particular aspects of thermal performance. The use of 2618 type aluminium alloys as a matrix for powder route SiC reinforced MMCs, in place of 2124, had no significant effect, but initial results suggest that the use of ultrafine oxides as reinforcement in aluminium alloys may improve strength above 200°C.     

金属基复合材料的发展及应用

本文主要论述了金属基复合材料 (MMCs)的类型、制备、发展、应用及其回收再生 ,目前 ,在MMCs发展和应用中 ,SiC和Al2 O3颗粒增强铝基复合材料仍占主要地位。本文着重介绍了颗粒增强铝基复合材料的性能及其成型加工特性。     

Forging behaviour and properties of metal matrix composites based on mechanically alloyed AI-Mg-Li alloy

Abstract

A range of Al-Mg-Li-C MMCs (25 vol.-% of 3 μm SiC particles) were produced by mechanical alloying and powder processing at Aerospace Metal composites, Farnborough. Upset forging trials were conducted at 350 and 550°C and 0.01 and 0.1 S^-l. No SiC particle cracking or wedge cracking at grain boundary triple points was observed. Forging at 550°C caused some edge cracking and a coarser grain structure. Large billets of varying composition were forged to ～15 mm thick plate at 350°C and 0.0l S-^l or 550°C and 0.l S^-l. Monotonic testing showed the MMCs to exhibit high stiffnesses at moderate strength levels but rather low ductility and fracture toughness. Significant strengthening was found to accrue from dispersion hardening (C content) and solid solution strengthening (Mg and Li solutes). A link was found between lower proof stress and coarser grain structure after forging at 550°C. Fracture toughness K_1C was found to decrease with increasing yield strength which was attributed to higher strain concentrations in the smaller crack tip plastic zone.     

金属基复合材料的高应变速率超塑性

综述并评论了金属基复合材料的高应变速率超塑变形机制，描述了金属基复合材料在高应变速率超塑变形中的一些理化现象，说明了变形过程中的各种影响因素，总结了具有高应变速率超塑性能的金属基复合材料及其性能，并指出了在金属基复合材料的高应变速率超塑性研究方面的不足。     

Fabrication of CuSiC metal matrix composites

A CuSiC MMC heatspreader will offer high thermal conductivity between 250 and 325 W/mK and corresponding adjustable thermal expansion coefficient between 8.0 and 12.5 ppm/°C. The primary challenge of CuSiC manufacture was to prevent reaction between copper and silicon carbide during high temperature densification, which dramatically degraded the thermal conductivity. In this study, the key issue addressed was the Si attack of Cu at the temperatures necessary for CuSiC fabrication (850 to 1200°C). Decomposition of SiC in contact with copper will dissolve Si in Cu causing a dramatic decrease of Cu thermal conductivity. This diffusion of Si into Cu can be prevented by the application of reliable barrier layers to diminish mass transport through the diffusion path and thereby minimizing the chemical interaction. A reliable barrier coating was identified and used to fabricate the CuSiC composites. The CuSiC composites were then characterized by SEM, TEM, XRD and XPS. Chemical analysis and thermal conductivity by laser flash diffusivity measurement illustrated the effectiveness of the barriers. A CuSiC composite having thermal conductivity of 322.9 W/m-K was successfully fabricated.