The deformation of particle reinforced metal matrix composites during temperature cycling

Superplasticity during temperature cycling of particle reinforced metal matrix composites has been studied over a range of reinforcement sizes and volume fractions. Above a critical volume and thermal cycle amplitude, the mean strain per cycle is proportional to stress and approximately proportional to cycle amplitude. For a given thermal cycle the constant of proportionality with respect to stress increases with reinforcement fraction to a maximum at around 30%; it then decreases with further increase in reinforcement. Transmission electron microscopy revealed no characteristics dislocation substructure; even after 90% strain the material was indistinguishable from its undeformed state. The experimental results confirm an internal plastic flow model for the phenomenon rather than an enhanced creep. A model of the process derived from the Lévy-Von Mises equations predicts both the effect of thermal cycle amplitude the MMC microstructure on the enhanced creep rate.     

High-temperature behavior of precious metal base composites

The high thermodynamic stability and exceptional mechanical properties of intermetallic compounds based on platinum group metals (PGMs) make them potentially exploitable as structural materials for elevated temperature service. In this study, the development of high-temperature strength was evaluated for a selection of eutectic composites based on Ru-Al, Ir-Al, Ru-Nb, Ir-Nb, and Ru-Al-Ni using compression tests. All the alloys tested were characterized by high strength at extreme tem-peratures, none more so than an Ir₈₄Nb₁₆ alloy which had a proof stress in excess of 600 MPa at 1300 ‡C. In addition, several alloys showed significant compressional ductility at room temperature. Of particular interest is the synergy of soft constituent phases in evolving strengths greater than that anticipated by simple rules of mixture. The potential of secondary phases to advance both strength and room-temperature ductility makes these composites worthy of further investigation.     

Damage initiation in metal matrix composites

The process of damage by particle cracking has been followed in a composite of A356 Al containing 20% by volume SiC. The probability of particle cracking is influenced by both particle size and aspect ratio and the results indicate that the relative importance of these factors depends on the Weibull modulus of the SiC particles. A simple model is developed to describe the process of load transfer and crack initiation in the particles. This initial model does not take into account particle interactions and the role of clustering but does provide an initial fragment to describe the damage initiation process.     

The strength of metal matrix composites

There is intensive interest in metal matrix composites (MMCs) for automotive components, and the first production applications in Japan use discontinuous fibers as the reinforcements. These fibers are randomly oriented, resulting in an MMC with isotropic properties. However, there are conflicting reports on the tensile strengths attainable. In some cases, the strength increases with increasing volume fraction(V _f) of fibers, while in other cases, there is little or no benefit. A simple method is proposed to calculate the strength of this type of MMC. It is shown that the fibers oriented perpendicular to the stress direction play a key role, and the strength depends upon the strength of the interfacial bond. Upper and lower limits of the composite strength are calculated. If the bond strength is larger than the matrix strength, the composite strength has a maximum value which increases withV _f. If the bond strength is weaker than the matrix, the composite strength has a minimum value which is either weakly dependent or even independent ofV _f. These calculations are in good agreement with examples taken from the literature of aluminum composites reinforced with either A1₂O₃, graphite, or SiC. The strength of the matrix alloy is shown to be a very important parameter: weak alloys are easily strengthened, while in certain cases, strong alloys may be weakened.     

Fabrication of metal matrix composites of

Fine fibrous titanium carbide (TiC) was processed through the self-propagating high-temperature synthesis (SHS) method and employed to fabricate aluminum matrix composites. Two consol-idation methods were investigated: (1) combustion synthesis of TiC fiber/Al composites directly using titanium powders and carbon fibers ignited simultaneously with varying amounts of the matrix metal powder and (2) combustion synthesis of TiC using titanium powders and carbon fibers followed by consolidation into different amounts of the metal matrix powder, Al,via hot isostatic pressing (HIP). In the former method, when the amount of the Al in the matrix was increased, the maximum temperature obtained by the combustion reaction decreased and the propagation of the synthesis reactions became difficult to maintain. Preheating was required for the mixture of reactants with more than approximately 5 mole pct aluminum matrix powders in order to ignite and maintain the propagation rate. Microstructural analysis of the products from the Al/C/Ti reaction without preheating shows that small amounts of an aluminum carbide phase (AI4C3) are present. In the second method, following separation of the individual fibers in the TiC product, dense composites containing the SHS products were obtained by HIP of a mixture of the TiC fibers and Al powders. No ternary phase was formed during this procedure. Formerly Graduate Research Assistant, Department of Chemical Engineering, Michigan Technological University, is with Particle Technology, Inc., Hanover, MD 21076. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

Fundamental aspects of creep in metal matrix composites

The primary characteristics of the creep of metal matrix composites (MMCs) are reviewed, including the shapes of the creep curves, the origin of the threshold stresses, and the nature of the rate-controlling processes. A detailed analysis of two representative MMCs provides no support for the concept of a constant substructure model for creep with a stress exponent (n) of 8. Analysis of the data demonstrates that creep is controlled by deformation in the matrix alloys and, as in solid solution alloys, there is a division into control by viscous glide (class A) and climb (class M), respectively. This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee.     

SiC/C-Cu复合材料的载流磨损性能

采用粉末冶金法制备SiC/C-Cu复合材料,研究SiC颗粒含量对该材料组织结构与物理性能的影响,并在HST-100载流摩擦磨损试验机上进行载流磨损试验,研究摩擦速度、电流密度与SiC颗粒含量对SiC/C-Cu复合材料磨损率的影响以及磨损机理的变化。结果表明:SiC颗粒均匀分布于铜基体中。随SiC含量增加,复合材料的硬度和孔隙率都逐渐增大,密度和导电率降低。添加SiC颗粒可增强C-Cu复合材料的抗磨损性能,材料的磨损率随摩擦速度和电流密度增加而增加,随SiC含量增加呈先降低后上升的趋势,含2%SiC(质量分数)的SiC/C-Cu复合材料具有优异的抗载流磨损性能。添加SiC颗粒可减少摩擦磨损过程中铜基体的粘着磨损,磨损机理主要为磨粒磨损和电弧侵蚀磨损。     

钛基复合材料耐磨性研究进展

钛合金因具有高比强度、高比模量、耐腐蚀、耐低温、无磁等性能特点而被广泛应用.然而,与传统钢铁材料相比,钛合金存在弹性模量低、耐热性能不足、耐磨性差等局限,阻碍其在航空航天、兵器行业等领域的推广应用.与钛合金相比,钛基复合材料可将基体钛合金高强塑性与增强体高模量、高耐磨的优势相结合,具有比钛合金更高的弹性模量、耐磨性及高...     

Acoustic emission from particulate-reinforced metal matrix composites

A systematic study of the effect of microstructural parameters on the fracture behaviour of silicon carbide particle reinforced aluminium matrix composites has been carried out. Acoustic emissions have been monitored during tensile testing, giving the size and number of emmissions as a function of strain. This has been shown to be simply related to the rate of void nucleation at the reinforcing phase. Both particle fracture and particle/matrix decohesion mechanisms can be detected. Void nucleation was observed from the onset of plastic deformation and a linear relationship between damage initiation rate and strain was found. The rate of emission increased with reiforcing particle size and volume fraction but was independent of matrix alloy composition and heat treatment. These results show that the failure strain of particulate metal matrix composites is not controlled solely by the onset of void nucleation at the reinforcing phase. Local failure processes in the matrix are shown to promote void coalescence and dominate the ductility. However, suppression of void nucleation at the particles increases the ductility. It is suggested that a critical number of fractured particles is required before failure.     

Investigation of corrosion and wear properties of Fe based metal matrix composites consolidated by sintering and hot isostatic pressing

Abstract

Many industrial applications, e.g. processing of polymers, suffer from high costs caused by corrosion and wear. Particularly the combination of both increases the requirements for the materials used. Corrosion resistant cold work steels were developed to withstand the combined attack. Resistance is achieved by a sufficient content of chromium in the metal matrix and by carbides dispersed in a martensitic matrix. A further gain in wear resistance is possible by adding hard phases to the steel to produce a particulate reinforced metal matrix composite (MMC). The common consolidation process for such MMCs is hot isostatic pressing, but they can also be processed by solid state or liquid phase sintering. This work focuses on detailed investigations of the properties in dependence on the processing route. The results show that the resulting corrosion and wear resistance depend not only on the processing method, but also on the incorporated hard phases in combination with the manufacturing method. In addition, the unreinforced metal matrices were compared to the MMC.     

Tiny tubes boost for metal matrix composites

Novel light metal matrix composites reinforced by carbon nanotubes have been produced by a Swiss research group using powder metallurgical methods. The magnesium composites exhibited a substantially higher Young's modulus than unreinforced sintered magnesium…     

铝代铅新型铜基自润滑材料的摩擦磨损性能

采用粉末松装烧结法,以A1代替Pb制备新型无铅铜基自润滑材料,研究Al含量(w(Al)为2％～12％)对该材料摩擦磨损性能的影响.结果表明:随着Al含量增加,材料硬度逐渐降低,摩擦因数呈现先降低后增加的趋势.当Al质量分数为6％时,该材料在油摩擦环境下(载荷50 N,转速900 r/min)的摩擦因数为0.089 85,磨痕宽度为1 095 μm,摩擦面较光滑、平整,具有较好的摩擦磨损性能,且自润滑层与钢背的结合强度较高;实验结果表明用Al替代Pb制备新型无铅铜基自润滑材料是可行的,为绿色环保双金属自润滑材料的研究提供了参考依据.     

Prediction of thermomechanical fatigue lives in metal matrix composites

To identify the role of silicon carbide participate reinforcement on high-temperature thermomechanical fatigue behavior of Al 2xxx-T4, experiments have been conducted under thermomechanical out-of-phase and in-phase loading conditions. A general constitutive representation, based on Eshelby’s inclusion theory, is used for the determination of volumetric average stresses and strains under cyclic loading of the metal matrix composite. This constitutive representation is used with a life prediction model, based on the matrix stress-strain behavior, which predicts contributions of fatigue, creep, and environmental damages to failure under both isothermal and thermomechanical fatigue loading. In isothermal fatigue experiments at 200 °C and 300 °C, pure fatigue damage and creep damage are the dominant damage mechanisms in the short-life regime. In the long-life regime, however, the stress levels are too low to induce considerable creep damage; so, oxidation damage becomes dominant. When fatigue damage is dominant, the model predicts a decrease in life, based on strain range, with increasing volume fraction of reinforcement. Based on stress range, improved fatigue lives are predicted with increasing volume fraction of reinforcement. The reinforced alloy exhibits longer lives when compressive hydrostatic stresses in the matrix at the high-temperature end of the cycle reduce the creep damage. Temporarily Director, Mechanics and Materials Program, National Science Foundation, Washington, DC 20550     

Aspects of fracture in particulate reinforced metal matrix composites

The tensile deformation and fracture behaviour of the aluminium alloy 6061 reinforced with SiC has been investigated. In the T4 temper plastic deformation occurs throughout the gauge length and the extent of SiC particle cracking increases with increasing strain. In the T6 temper strain becomes localised and particle cracking is more concentrated close to the fracture. The elastic modulus decreases with increasing particle damage and this allows a damage parameter to be identified. The fraction of SiC particles which fracture is less than 5%, and over most of the strain range the damage controlling the tensile ductility can be recovered, indicating that other factors, in addition to particle cracking are important in influencing tensile ductility. It is suggested that macroscopic fracture is initiated by the SiC particle clusters that are present in these composites as a result of the processing. The matrix within the clusters is subjected to high levels of triaxial stress due to elastic misfit and the constraints exerted on the matrix by the surrounding particles. Final fracture is then produced by crack propagation through the matrix between the clusters.