Showing papers on "Metal matrix composite published in 2004"

Study on bulk aluminum matrix nano-composite fabricated by ultrasonic dispersion of nano-sized SiC particles in molten aluminum alloy

Abstract: Lightweight metal matrix nano-composites (MMNCs) (metal matrix with nano-sized ceramic particles) can be of significance for automobile, aerospace and numerous other applications. It would be advantageous to produce low-cost as-cast bulk lightweight components of MMNCs. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten metal. This paper presents a new method for an inexpensive fabrication of bulk lightweight MMNCs with reproducible microstructures and superior properties by use of ultrasonic nonlinear effects, namely transient cavitation and acoustic streaming, to achieve uniform dispersion of nano-sized SiC particles in molten aluminum alloy A356. Microstructural study was carried out with an optical microscope, SEM, EDS mapping, and XPS. It validates a good dispersion of nano-sized SiC in metal matrix. It also indicates that partial oxidation of SiC nanopartilces results in the formation of SiO2 in the matrix. Mechanical properties of the as-cast MMNCs have been improved significantly even with a low weight fraction of nano-sized SiC. The ultrasonic fabrication methodology is promising to produce a wide range of other MMNCs.

Review of recent studies in magnesium matrix composites

Abstract: In this paper, recent progress in magnesium matrix composite technologies is reviewed. The conventional and new processes for the fabrication of magnesium matrix composites are summarized. The composite microstructure is subsequently discussed with respect to grain refinement, reinforcement distribution, and interfacial characteristics. The mechanical properties of the magnesium matrix composites are also reported.

Microstructure and microhardness of SiC nanoparticles reinforced magnesium composites fabricated by ultrasonic method

Abstract: The use of ultrasonic non-linear effects to disperse nano-sized ceramic particles in molten metal has been studied and nano-sized SiC particle reinforced AZ91D magnesium composites were fabricated. The microstructure of the composites was investigated by high-resolution scanning electron microscopy (SEM), X-ray photo spectroscopy (XPS), and high-resolution X-ray diffractometer (XRD) techniques. Experimental results show a nearly uniform distribution and good dispersion of the SiC nanoparticles within the magnesium matrix, although some of small agglomerates (less than 300 nm) were found in matrix. Detailed study reveals that the SiC nanoparticles were partially oxidized. The microhardness of composites have been improved significantly compared to that of pure AZ91D. The interaction between SiC nanoparticles and the matrix was investigated. The interaction between ultrasonic waves and nanoparticles was also discussed. The ultrasonic fabrication methodology is striking to rapidly produce a wide range of nano-sized particles reinforced metal matrix composites.

Synthesis and characterization of plasma spray formed carbon nanotube reinforced aluminum composite

Abstract: A trend has been perceived in the field of composite materials to employ carbon nanotubes as reinforcement in synthesizing composites of unique properties. In this endeavor, free standing structures of Al-based nanostructured composite with carbon nanotubes as second phase particles has been synthesized by plasma spray forming technique. Optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy has been carried out to analyze the composite structure and to verify the retention of carbon nanotubes. Besides, density and microhardness measurements have been performed to understand the effect of carbon nanotube reinforcement on the mechanical properties of the composite. The characterization affirms the presence of unmelted and chemically unreacted carbon nanotubes in the composite. Moreover, the composite experienced an increase in relative microhardness due to the presence of carbon nanotube.

Implants based on engineered metal matrix composite materials having enhanced imaging and wear resistance

Abstract: This invention relates to an implantable medical device to treat a patient. The implantable device can be an orthopedic device such as a spinal implant including, but not restricted to, a disc or nucleus pulposus prosthesis, a spinal rod assembly, or a bone fixation plate. The orthopedic device can be formed to include a metal matrix composite that provides enhanced wear and diagnostic imaging techniques. In other forms, the present invention provides an implantable medical device that includes a porous metal matrix composite that can deliver a therapeutic composition to a patient. In still other forms, the present invention provides an implantable electrical device or lead formed to include a metal matrix composite that provides lower polarization and interfacial impedance and allows enhanced sensing of the physiological signals.

In situ fabrication of Al3Ti particle reinforced aluminium alloy metal–matrix composites

Abstract: Titanium tri-aluminide (Al 3 Ti) particles were dispersed homogeneously into a castable aluminium alloy matrix by the aluminothermic reduction of hexafluorotitanate (K 2 TiF 6 ) under different conditions. Al 3 Ti particles in different morphologies and sizes were produced by changing the fabrication conditions, such as composition of the flux, the temperature and holding time. The coarsening and growth of the Al 3 Ti particulates are principally affected by other elements present in the flux during fabrication. The effects of the temperature and holding time, alloying elements and the composition of flux on the dispersion of the reinforcement were examined by using SEM and X-ray diffraction techniques. The observed results are explained in terms of the different growth behaviour of the Al 3 Ti particles under different conditions. The dispersion of the Al 3 Ti particles and the Al/Al 3 Ti interfacial bonding are explained by the solidification of aluminium.

Fabrication of TiB2 and TiB2–TiC particulates reinforced magnesium matrix composites

Abstract: A TiB 2 particulate reinforced magnesium matrix composite (MMCs) was fabricated by adding a TiB 2 –Al master alloy processed via self-propagating high-temperature synthesis (SHS) reaction in Al–Ti–B system into molten magnesium and using the stir casting technique. The results showed that the TiB 2 –Al master alloy and TiB 2 /Mg composite contained a certain amount of transient TiAl 3 phase. When the Al–Ti–B system was incorporated with an appropriate C, TiB 2 and TiC reinforcing phases were simultaneously synthesized and the TiAl 3 phase was almost completely eliminated.

High strain rate response of aluminum 6092/B4C composites

Abstract: Aluminum 6092/B 4 C p (boron carbide) metal-matrix composites (MMC) fabricated by two different powder consolidation routes, extrusion and sintering/hot isostatic-pressing (HIPing), were made and tested over a wide range of strain rates (10 −4 to 10 4 s −1 ). The strength of these MMCs increases with increasing volume fraction of particulate reinforcement. Strain hardening is observed to increase with increasing volume fraction of reinforcement at lower strains ( 5 μm) considered. Finally, the Li–Ramesh model captures the observed high-rate behavior exhibited by these powder-consolidated composites.

Effects of carbon fiber/Al interface on mechanical properties of carbon-fiber-reinforced aluminum-matrix composites

Abstract: Carbon-fiber (CF)-reinforced aluminum-matrix composites were prepared by spreading fibers and squeeze casting. The interface structure of Cf/Al composites was examined using high-resolution transmission electron microscopy (HRTEM) and electron spectroscopy for chemical analysis (ESCA). Aluminum carbide (Al4C3) interfacial reaction products were observed to nucleate heterogeneously from carbon fibers and to grow toward the aluminum matrix in the form of lath-like crystals after heat treatment. The growth of aluminum carbide was anisotropic, since it was faster along the a- and b-axes of the basal plane than along the c-axis. Both the tensile strength and the elongation of composites decline with an increased duration of heat treatment. The results of ESCA revealed that approximately 1 pct of carbide enhanced interface bonding. However, increasing the content of brittle carbides to over 3 pct after heat treatment degraded the mechanical properties of composites.

Effect of Porosity on Mechanical Properties of Metal Matrix Composite: An Overview

Abstract: Keliangan di dalam tuangan komposit matriks logam (KML) adalah satu kecacatan yang boleh mempengaruhi kekuatan bahan terutamanya di dalam KML bertetulang partikel. Merujuk kepada kajian lepas, faktor-faktor pembentukan keliangan adalah berpunca daripada gelembung-gelembung udara yang memasuki leburan matriks logam, wap air yang terdapat pada permukaan partikel, gas yang terperangkap semasa proses pencampuran, evolusi hidrogen dan pengecutan tuangan semasa pemejalan. Namun, kebanyakkan kajian menunjukkan punca utama pembentukan keliangan adalah parameter proses tuangan. Kandungan keliangan yang paling minima akan menentukan sifat optimum tuangan KML. Secara umumnya, peningkatan kandungan keliangan akan mengurangkan sifat mekanikal KML seperti kekuatan tegangan, modulus Young, nisbah Poisson dan muatan redaman. Kesan pengurangan ini berlaku disebabkan oleh proses kegagalan yang berpunca daripada kehadiran lompang keliangan. Kata kunci: Keliangan, tuangan kacau, sifat mekanikal, tuangan komposit matriks logam, silikon karbida Pososity in cast metal matrix composite (MMC) has been known as a defect affecting the enhancement of strength, particularly in particle-reinforced MMC. From previous reviews, among the causes of porosity formation are air bubbles entering the melt matrix material, water vapour on the particles surfaces, gas entrapment during mixing process, evolution of hydrogen, and shinkage during solidification. Many studies had revealed that casting parameters are the main factors affecting porosity formation. Optimum properties of cast MMC are attained with least porosity content. Generally, increasing content of pososity will decrease the mechanical properties of MMC such as tensile strength, Young’s modulus, Poisson ratio, and damping capacity. This presence of porosity decreased the mechanical properties of cast MMC as the failure process is initiated from the voids formed. Key words: Porosity, stir casting, mechanical properties, cast metal matrix composite, silicon carbide particle

Three-dimensional characterization of the microstructure of a metal-matrix composite by holotomography

Abstract: The method of holotomography was applied to investigate the microstructure of a metal–matrix composite (MMC) consisting of an AA6061 aluminium matrix reinforced with 20 vol.% Al 2 O 3 particles. Various statistical functions characterizing the Al 2 O 3 particles and the matrix were evaluated, which facilitate a better understanding of the correlation between microstructural features and the overall physical properties of the composite. The shape of the particles is approximated by an ellipsoid and their spatial distribution is described in terms of the pair-distribution function of particle centers and the two-point probability functions of the component phases. The investigated statistical functions emphasize the existence of a short-range correlation in the microstructure, which has a correlation length of about two times the average nearest-neighbor distance. To understand better the influence of the particle shape on different statistical descriptors a comparison between the real microstructure and a system of random hard-spheres is presented.

Processing of TiNi SMA fiber reinforced AZ31 Mg alloy matrix composite by pulsed current hot pressing

Abstract: Magnesium alloy matrix composite reinforced by continuous TiNi shape memory alloy (SMA) fiber was fabricated by pulsed current hot pressing (PCHP) of TiNi SMA fibers sandwiched with a pair of AZ31 Mg alloy plates, and its microstructure and mechanical properties were examined. The Mg alloy plates with 20 vol.% of the TiNi fibers were readily hot pressed into a composite at the temperature of 773 K for a total processing time of 0.6 ks. During the processing, the thickness of the preform composed of Mg plates and TiNi fibers decreased drastically at the temperature between 400 and 650 K, resulting in the bonding between the fiber and the matrix plates occurred. As a reaction occurred insubstantially in the vicinity of the boundary between Mg alloy plates and TiNi fiber, no homogeneous interfacial reaction layer was formed. The tensile yield stresses of the composite deformed in tension at 373 and 423 K were higher by about 68 and 87 MPa than that at 293 K, respectively. At the test temperature range, both the yield stress and elongation of the composite increased with increasing temperature. At temperatures higher than 373 K, the specific strength of the composite was higher than that of AZ31 Mg alloy.

Metal matrix composites, and methods for making the same

Abstract: Metal matrix composite inserts and methods of making the same. The inserts are useful in making metal matrix composite articles.

Fabrication of carbide-particle-reinforced titanium aluminide-matrix composites by laser-engineered net shaping

Abstract: TiAl-based titanium aluminide alloys and their composites reinforced with ceramic particles are considered to be important candidate materials for high-temperature structural applications. Laser-engineered net shaping (LENS) is a layered manufacturing process, which involves laser processing fine powders into three-dimensional components directly from a computer-aided design (CAD) model. In this work, the LENS process was employed to fabricate carbide-particle-reinforced titanium aluminide-matrix composites using TiC and gas-atomized Ti-48Al-2Cr-2Nb powders as the feedstock materials. The composites deposited by the LENS process were susceptible to solid-state cracking due to high thermal stresses. The microstructures of the laser-deposited monolithic and composite titanium aluminide materials were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) analysis, electron-probe microanalysis (EPMA), and X-ray diffraction (XRD) techniques. Effects of the LENS processing parameters on the cracking susceptibility and microstructure were studied. Crack-free deposits were fabricated by preheating the substrate to 450 °C to 500 °C during LENS processing. The fabricated composite deposits exhibit a hardness of more than twice the value of the Ti-6Al-4V alloy.

Particle reinforced metals of high ceramic content

Abstract: It is commonly considered that, in ceramic particle reinforced metals, the volume fraction of ceramic should not exceed 30% if the composite is intended for structural applications: otherwise its toughness and ductility generally become unacceptably low. Particle reinforced metal matrix composites produced by infiltration provide a material with which this assumption can be tested. We first present a summary of recent results from our laboratory showing that aluminium matrix composites containing 50% or more ceramic particles can be tough, strong and relatively ductile, despite the high ceramic loadings. We then discuss toughening mechanisms that can explain the mechanical properties displayed by these composites, to highlight the importance of the particle strength distribution on the composite fracture toughness.

The mechanical behavior of magnesium alloy AZ91 reinforced with fine copper particulates

Abstract: In this study, a hybrid composite based on magnesium alloy AZ91A reinforced with copper particulates was fabricated using the disintegrated melt deposition (DMD) processing technique followed by hot extrusion. Microstructural characterization of the as-extruded composite sample revealed a near uniform distribution of the copper particulates and other intermetallic phases through the magnesium alloy metal matrix, good integrity at the copper–magnesium alloy matrix interfaces and evidence of minimal porosity. Mechanical property quantification revealed that addition of copper particulates resulted in a significant increase in elastic modulus, 0.2% offset yield strength and ultimate tensile strength of the composite material. However, ductility of the composite was marginally affected when compared to the unreinforced monolithic counterpart. The overall mechanical properties of AZ91A/Cu composite were found to be higher than the silicon carbide particulate reinforced AZ91 composite, even for higher volume fractions of the particulate reinforcement. Influence of copper in the matrix of magnesium alloy AZ91A is examined in light of intrinsic microstructural features and mechanical properties of the composite.

Strength and fracture toughness of interpenetrating graphite/aluminium composites produced by the indirect squeeze casting process

Abstract: Graphite/aluminium composites with an interpenetrating network microstructure were produced by the indirect squeeze casting process. Porous isotropic graphite preforms with about 14.5 vol.% porosity were infiltrated either with AlSi7Ba or AlSi12. Flexural strength and fracture toughness were determined at room temperature and 300 °C before and after thermal cycling. The composites exhibit a significantly higher mechanical strength and fracture toughness than the graphite preforms. The infiltration with aluminium alloys enhances the flexural strength by a factor of two up to about 120 MPa and increases the fracture toughness from 0.94 to 1.93 MPam 1/2 . At 300 °C, no decrease in flexural strength of the composites is observed. Thermal cycling results in a slight reduction of the mechanical properties for graphite/AlSi7Ba composites, while graphite/AlSi12 composites show no decline in strength and toughness, respectively. The effect of aluminium composition and thermal cycling on the mechanical properties are explained by means of a crack bridging model.

6061 Al reinforced with zirconium diboride particles processed by conventional powder metallurgy and mechanical alloying

Abstract: The homogenous distribution of the reinforcement phase is an essential condition for a composite material to achieve its superior performance. Powder metallurgy (PM) can produce metal matrix composites in a wide range of matrix reinforcement compositions without the segregation phenomena typical of casting processes. Particularly, mechanical alloying can be used to mix the matrix and reinforcement particles, enhancing the homogeneity of the reinforcement distribution. This work investigates the production of aluminium 6061 reinforced with zirconium diboride by mechanical alloying followed by cold pressing and hot extrusion, and compares the results with the same composite produced by conventional PM and hot extrusion. The incorporation of the ZrB2 particles produces only a small increase in the material hardness, but a small decrease in the UTS when conventional PM is employed. Mechanical alloying breaks the reinforcement particle clusters, eliminates most of the cracks present in the surface of the reinforcement particles, decreases its size and improves its distribution. This enhancement of the composite structure, in addition to the metallurgical aspects promoted by mechanical alloying in the matrix, brings approximately 100% improvements in the composite UTS and hardness, compared with the composites obtained by PM.

The effect of thermal exposure on the interface and mechanical properties of Al18B4O33w/AZ91 magnesium matrix composite

Abstract: The effect of high temperature exposure on the interface and tensile properties of Al 18 B 4 O 33 w/AZ91 magnesium matrix composite fabricated by squeeze casting was studied. The interfaces of the composites were examined using transmission electron microscopy, and the mechanical properties were evaluated by tensile tests. The interfacial region was composed of MgO which was formed by the reaction between the Al 18 B 4 O 33 whisker and the Mg matrix. An thin and uniform interfacial reaction layer with a thickness of 10–20 nm formed during squeeze casting could act as a barrier to prevent the further reaction between Al 18 B 4 O 33 whisker and Mg alloys. The interfacial reaction rate was very low during thermal exposure below the liquidus temperature of AZ91 matrix alloy. Only after exposure above the liquidus temperature of the AZ91 matrix alloy for a long period, the thickness of the interfacial layer increased obviously. However, the interfacial reaction rate was much slower than that in the Al 18 B 4 O 33 w/Al–Mg composites. The interfacial reaction kinetics was controlled by the seepage of Mg and release of Al and B along the narrow diffusion channels between the fine MgO particle. The composite did not show a degradation in the tensile properties after exposure below the solidus temperature of AZ91 for long periods, suggesting that the Al 18 B 4 O 33 w/AZ91 magnesium matrix composite could be subjected to long-term service at elevated temperature.

Effect of microstructural complexity on the hot deformation behavior of aluminum alloy 2024

Abstract: Powder metallurgy (P/M) aluminum alloy 2024 (Al-2024) reinforced with SiC whiskers is difficult to shape-form because of microstructural complexities introduced by rapid solidification and whisker additions. In the present investigation, four forms of Al-2024, viz. ingot, wrought, P/M, and P/M with 20 v/o silicon-carbide whiskers (SiC w ) were examined to understand the influence of structural complexity on the hot deformation microstructural mechanisms. The analyses using the concepts of activation energy and dynamic stability criteria revealed that the safe hot working window of Al-2024 narrows as the microstructural complexity increases. This experimental observation was also explained on the basis of information theory. Safe processing window identified for the composite was validated using scaled-up extrusion experiments and the influence of processing conditions on microstructural control was demonstrated.

Stability and response to rolling of the interfaces in cast Al-SiCp and Al-Mg alloy-SiCp composites

Abstract: Aluminium matrix composites reinforced with unoxidized or oxidized SiC particles and varying Mg concentrations have been prepared using stir casting technique. The extent of interfacial reactions and composition of the reaction products, formed at the Al–SiC interfaces in as-cast form, and after heat treatments at 893 K (620 °C) or 925 K (652 °C) for 4 or 20 h, have been studied on the surfaces of bulk samples, and those of the SiC particles extracted from the composite by electro-chemical leaching. Alloying of Al matrix with 0.5 or 1 wt.% Mg and its segregation at the interfaces has been found to be effective in restricting the formation of the Al 4 C 3 at the interfaces during casting. Reaction of Mg and Al with SiO 2 on the surfaces of oxidized SiC, leads to the formation of MgO and MgAl 2 O 4 crystals, which act as diffusion barrier between Al and SiC at the interfaces. At the same time, it is evident that the depletion of SiO 2 film by reaction with Al or Mg leads to the formation of Al 4 C 3 during high temperature exposure. Cold or hot rolling leads to cracking of a large fraction of SiC particles in the as-cast as well as heat-treated composites, while Al–SiC interfaces severely embrittled by formation of Al 4 C 3 also crack, because of inherent weakness to shear.