Showing papers on "Metal matrix composite published in 2010"

Investigation of particle size and amount of alumina on microstructure and mechanical properties of al matrix composite made by powder metallurgy

Abstract: Al matrix composite is well known, in which Al2O3 is the most widely used reinforcement. The aim of this study is to investigate the effect of alumina particle size and its amount on the relative density, hardness, microstructure, wear resistance, yield and compressive strength and elongation in Al–Al2O3 composites. To this end, the amount of 0–20 wt.% alumina with average particle sizes 48, 12 and 3 μm was used along with pure aluminum of average particle size of 30 μm. Powder metallurgy is a method used in the fabrication of this composite in which the powders were mixed using a planetary ball mill. Consolidation was conducted by axial pressing at 440 MPa. Sintering procedure was done at 550 °C for 45 min. The results indicated that as the alumina particle size is reduced, density raises at first, then, declines. Moreover, as the alumina particle size decreases, hardness, yield strength, compressive strength and elongation increase and factors such as wear resistance, microstructure grain size and distribution homogeneity in matrix decreases. For instance, as the alumina particle size gets smaller from 48 to 3 μm at 10 wt.% alumina, hardness rises from 50 to 70 BHN, compressive strength improves from 168 to 307 MPa and wear rate rises from 0.0289 to 0.0341 mm3/m. On the other hand, as the amount of alumina increases, hardness and wear resistance increase and relative density and elongation is decreased. However, compressive and yield strength rise at first, then drop. For example, if the amount of alumina with 12 μm particle size increases from 5 to 10 wt.%, hardness increases from 47 to 62 BHN and compressive strength rises from 190 to 273 MPa. Nevertheless, erosion rate after 300 m decreases from 0.0447 to 0.0311 mm3/m.

In vitro corrosion resistance and cytocompatibility of nano-hydroxyapatite reinforced Mg–Zn–Zr composites

Abstract: Due to good biocompatibility and mechanical properties, magnesium (Mg) and its alloys are considered promising degradable materials for orthopedic applications. In this work, a Mg metal matrix composite (MMC) was fabricated using Mg-2.9Zn-0.7Zr alloy as the matrix and 1 wt% nano-hydroxyapatite (n-HA) particles as reinforcements. In vitro corrosion behavior and cytocompatibility of a Mg-Zn-Zr/n-HA composite and a Mg-Zn-Zr alloy were investigated. In contrast with the Mg-Zn-Zr alloy, the MMC has better properties. The average corrosion rate of MMC is 0.75 mm/yr after immersion in simulated body fluid (SBF) for 20 days, and the surface of MMC is covered with white Ca-P precipitates. The electrochemical test results show that the corrosion potential (E(corr)) of MMC increases to -1.615 V and its polarization resistance (R(p)) is 2.56 KOmega with the addition of n-HA particles. The co-cultivation of MMC with osteoblasts results in the adhesion and proliferation of cells on the surface of the composite. The maximum cell density is calculated to be (1.85+/-0.15) x 10(4)/l after 5 days of co-culture with osteoblasts. The average cell numbers for two groups after culturing for 3 and 5 days (P<0.05) are significantly different. All the results demonstrate that the Mg-Zn-Zr/n-HA composite can be potentially used as biodegradable bone fixation material.

In situ fabrication and microstructure of Al2O3 particles reinforced aluminum matrix composites

Abstract: Al2O3p/Al composites were prepared by direct melt reaction process. The thermodynamics of in situ chemical reactions between molten aluminum and CeO2 powder was studied. The XRD results show that the components of the as-prepared composites consist of Al2O3 and Al phases. For the as-cast composite specimens, SEM, EDX, TEM and SAD were used to analyze the reinforcement phases and interface characters of composites. The results show that the in situ generated Al2O3 particles, whose sizes are 100–200 nm, have various irregular shapes and disperse uniformly in matrix. TEM observation shows that the interface between particle and matrix is clean. Furthermore, there is no fixed orientation relationship between Al2O3 particles and aluminum matrix. Only [ 1 2 ¯ 10 ] / / [ 111 ] orientation parallel relationship with low exponent is found. Therefore, the composites have isotropic properties. Besides characters mentioned above, there are large amount of high density dislocations and the generated extensive fine subgrains around Al2O3 particles. These features are favorable for improving composite performances. As a result, the composites are comprehensively strengthened not only by Al2O3 particles, but also by the high density dislocations and fine subgrains.

A Comparative Study on the Microstructures and Mechanical Properties of Al 6061 Alloy and the MMC Al 6061/TiB2/12P

Abstract: Al 6061 alloy is widely used for commercial applications in the transportation, construction and similar engineering industries. It possesses excellent mechanical properties in addition to good corrosion resistance due to which the alloy finds extensive application in naval vessels manufacturing. Al-TiB2 composite is a metal matrix composite (MMC) that can be manufactured using the in-situ salt-metal reaction. With TiB2 as the particulate addition the properties of Al 6061 alloy can be greatly improved. A comparison of the mechanical properties and the microstructure of Al 6061 alloy with Al–TiB2 metal matrix composite containing 12% by weight TiB2p manufactured through the in-situ process was presented.

Application of ARB process for manufacturing high-strength, finely dispersed and highly uniform Cu/Al2O3 composite

Abstract: In the present work, accumulative roll bonding (ARB) process was used as an effective alternative method for manufacturing high-strength, finely dispersed and highly uniform copper/alumina metal matrix composite (MMC). The microstructural evolution and mechanical properties of the Cu/15 vol.% Al 2 O 3 composite during various ARB cycles are reported. The produced MMC by nine ARB cycles showed a homogeneous distribution and strong bonding between particles and matrix without any porosity. Also, it was found that when the number of cycles increased, not only did elongation increase but also the tensile strength of the composite improved by 2.5 times compared to that of the annealed copper used as the original raw material. Strengthening in the produced composites was explained by strain hardening, grain refinement, reinforcing role of particles, uniformity, bonding quality and size of particles. The findings also revealed that after the first cycle, hardness rapidly increased, then dwindled and finally saturated by further rolling.

A novel approach for development of surface nanocomposite by friction stir processing

Abstract: A new approach was used to produce Al–10%Al2O3 surface nanocomposite on Al2024 substrate. This novel approach involved air plasma spraying of Al–10%Al2O3 powder to produce Al–10%Al2O3 coating on substrate. The coated material was then subjected to friction stir processing (FSP) to distribute Al2O3 particles into the substrate. Microstructure and mechanical properties of samples were investigated by optical microscopy (OM), scanning electron microscopy (SEM), micro-hardness and wear measurements. As a result, it was found that the Al2O3 particles were distributed uniformly inside the substrate with an average penetration depth of about 600 μm. The surface nanocomposites produced in this way had excellent bonding with the substrate. The micro-hardness of the surface nanocomposite was ∼230 Hv, much higher than ∼90 Hv for Al2024 substrate. The surface nanocomposites also exhibited lower friction coefficient and wear rate. It was found that the addition of Al2O3 nanoparticles to the Al2024 matrix alloy affect the mechanism of wear.

Fabrication and properties of mechanically milled alumina/aluminum nanocomposites

Abstract: The reinforcement agglomeration in nanocomposites is a key issue that needs to be solved in order to fully benefit of the gain in strength and ductility associated with the decrease in reinforcement size from microscale to nanoscale. In this study, mechanical milling has been used successfully to disperse nanometric alumina (n-Al 2 O 3 ) in an aluminum matrix. Al 2 O 3 /Al nanocomposite powders have been produced for various alumina sizes and concentrations. The 10 vol% n-Al 2 O 3 /Al powders display hardness values near five times higher than pure unmilled Al. A decrease in the Al 2 O 3 particle size from 400 to 4 nm has increased the nanocomposite powder hardness by 11%. The microhardness and compression properties of an Al 2 O 3 /Al nanocomposite compact consolidated by hot pressing were measured. Comparison with modeled values and literature results indicates that the higher experimental yield strength obtained with the addition of n-Al 2 O 3 versus micron size Al 2 O 3 is due to in situ matrix strengthening.

Friction Stir Processing of Particle Reinforced Composite Materials

Abstract: The objective of this article is to provide a review of friction stir processing (FSP) technology and its application for microstructure modification of particle reinforced composite materials. The main focus of FSP was on aluminum based alloys and composites. Recently, many researchers have investigated this technology for treating other alloys and materials including stainless steels, magnesium, titanium, and copper. It is shown that FSP technology is very effective in microstructure modification of reinforced metal matrix composite materials. FSP has also been used in the processing and structure modification of polymeric composite materials. Compared with other manufacturing processes, friction stir processing has the advantage of reducing distortion and defects in materials. The layout of this paper is as follows. The friction stir processing technology will be presented first. Then, the application of this technology in manufacturing and structure modification of particle reinforced composite materials will be introduced. Future application of friction stir processing in energy field, for example, for vanadium alloy and composites will be discussed. Finally, the challenges for improving friction stir processing technology will be mentioned.

Characterization of Stir Cast Al—Cu—(fly ash + SiC) Hybrid Metal Matrix Composites

Abstract: Metal matrix composites are engineered materials with a combination of two or more dissimilar materials, (at least one of which is a metal) to obtain enhanced properties In the present investigation Al-45% Cu alloy was used as the matrix and fly ash and silicon carbide (SiC) as reinforcements The hybrid metal matrix composite was produced using conventional foundry techniques The fly ash and SiC were added in 5%, 10%, and 15% by weight (equal proportion) to the molten metal The hybrid composite was tested for fluidity, hardness, density, mechanical properties, impact strength, dry sliding wear, slurry erosive wear, and corrosion The microstructure examination was done using scanning electron microscope to assess the distribution of particulates in the aluminum matrix The results show that there is an increase in hardness with increase in the particulates content The density decreases with increase in fly ash and SiC content The tensile strength, compression strength, and impact strength increases

Material selection method in design of automotive brake disc

Abstract: An automotive brake disc or rotor is a device for slowing or stopping the motion of a wheel while it runs at a certain speed. The widely used brake rotor material is cast iron which consumes much fuel due to its high specific gravity. The aim of this paper is to develop the material selection method and select the optimum material for the application of brake disc system emphasizing on the substitution of this cast iron by any other lightweight material. Two methods are introduced for the selection of materials, such as cost per unit property and digital logic methods. Material performance requirements were analyzed and alternative solutions were evaluated among cast iron, aluminium alloy, titanium alloy, ceramics and composites. Mechanical properties including compressive strength, friction coefficient, wear resistance, thermal conductivity and specific gravity as well as cost, were used as the key parameters in the material selection stages. The analysis led to aluminium metal matrix composite as the most appropriate material for brake disc system.

A new technique for dispersion of carbon nanotube in a metal melt

Abstract: A major issue in achieving the best potential of carbon nanotube (CNT)-reinforced metal matrix composites is to disperse homogeneously CNTs within the matrix of magnesium–aluminum alloys. In order to address this issue, we have developed a new approach by adding multi-walled CNTs (MWCNTs) into a magnesium–aluminum alloy matrix. This could trigger significant de-bundling of the nanotubes within the molten alloy. Also, we have characterized mechanical properties of the CNT-blended matrix, such as microstructure, matrix/nanotube interface, and dispersion of the nanotubes, by employing optical microscopy, scanning electron microscopy, atomic force microscopy and X-ray diffractometer. This method remarkably facilitated a uniform dispersion of nanotubes within the magnesium alloy matrix as well as a refinement of grain size. No significant reaction was observed between the nanotubes and the metallic matrix. Finally, we observed a maximum tensile strength at 210.3 MPa and an elongation rate of 8.56%, which represents an increase of 30.8% and 124.1%, respectively, over the parental alloy. Together, our study establishes a new approach to disperse carbon nanotubes in a metal matrix, which could be applicable for CNT materials with higher potential.

The influence of Cu rich intermetallic phases on the microstructure, hardness and tensile properties of Al–15% Mg2Si composite

Abstract: This study was undertaken to investigate the effect of different concentrations of copper (0.1, 0.3, 0.5, 1.0, 3.0, and 5.0 wt.%) on the microstructure, hardness and tensile properties of an in situ cast composite (Al–15% Mg2Si). The microstructural study of the composite showed both primary and secondary Mg2Si phases in all specimens and intermetallics containing Cu (Q and θ phases) were visible at high Cu contents. Hardness and tensile tests demonstrate that the addition of Cu increases both hardness and ultimate tensile strength (UTS) values. But that a reduction in elongation occurs with the addition of Cu (≥1% Cu). A study of the specimen's fracture surfaces via scanning electron microscope (SEM) revealed that all specimens with large facets of primary Mg2Si particles succumb to brittle fracture. These brittle phases can initiate cracks, but Cu rich intermetallics phases, produced from the segregation of Cu on eutectic cell boundaries, appear to be the favored path for crack propagation.

Microstructure evolution and mechanical properties of a particulate reinforced magnesium matrix composites forged at elevated temperatures

Abstract: SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were cut into cylindrical billets, and then forged at different temperatures (320, 370, 420, 470 and 520 °C) at a constant RAM speed of 15 mm/s with 50% reduction. The microstructure evolution of the composites during forging was investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The texture of the forged composites was measured by neutron diffraction. Mechanical properties of the composite at different forging temperatures were tested by tensile tests at room temperature. It was found that a strong basal plane texture formed during forging, and the intensity of basal plane texture weakened as forging temperatures increased. The particle distribution in the composite was significantly improved by hot forging. Typical microstructures were obtained after forging at different temperatures and the composite with different microstructures offered different mechanical properties during tensile test.

Comparison of nanostructured Al/B4C composite produced by ARB and Al/B4C composite produced by RRB process

Abstract: In the present study, Al/B 4 C composites were produced and compared in the form of sheets, through accumulative roll bonding (ARB) and repeated roll bonding (RRB) processes. The microstructure of the composites fabricated by both the methods, revealed by scanning electron microscopy (SEM), showed the B 4 C particles properly distributed in the aluminum matrix. The average grain size of the ARB processed composite was about 186 nm by linear intercept method, based on transmission electron microscopy (TEM) observations. Mechanical properties of the Al/B 4 C composites produced by two methods were investigated by tensile and hardness tests. The results showed that the tensile strength and hardness of the ARB and RRB processed composites increase with the number of cycles. However, the tensile strength and hardness of the ARB processed composite are much higher than those of the RRB processed composite. The tensile test results revealed that the elongation of the ARB processed composite is lower than that of the RRB processed composite.

Optimization of Stirring Parameters Through Numerical Simulation for the Preparation of Aluminum Matrix Composite by Stir Casting Process

Abstract: The flow behavior of the fluid has a significant effect on the particle distribution in the solid-liquid mixing vessel. The stir casting process is generally conducted in a closed crucible, in which the flow pattern is invisible. Therefore, numerical simulation is a forceful tool to guide the experimental research. In the present study, the fluid flow in the stirred crucible during stir casting has been simulated using finite element method. The effects of some important stirring process parameters, such as the blade angle, rotating speed, the diameter of the impeller, and the stirrer geometry, on the flowing characteristics of the molten matrix have been investigated in order to achieve the effective flow pattern to uniformly disperse the ceramic particles in the molten matrix. The simulation results show that the process parameters have significant effects on the flow behavior of the fluid in the stirred crucible. The various combinations of these parameters are beneficial to generate a suitable condition for the composite casting. Further experimental investigation reveals that the present work can provide a guide for the industrial preparation of aluminum matrix composite with a uniform particle reinforcement distribution by stir casting process.

Cu-based metallic glass particle additions to significantly improve overall compressive properties of an Al alloy

Abstract: We report the development of a novel light-weight Al (520) alloy-based composite reinforced with particles of a Cu-based (Cu 54 Zr 36 Ti 10 ) metallic glass by mechanical milling followed by induction heated sintering. The consolidation of the composite is performed at a temperature in the super-cooled liquid region of the metallic glass just above its glass-transition temperature ( T g ). Metallic glasses are a promising alternative reinforcement material for metal-matrix composites capable of producing significant strengthening along with a «friendly» sintering behavior. The mechanical milling procedures were properly established to allow reduction of the size of the metallic glass particles and their uniform distribution in the matrix. Microstructural observation of the composite did not reveal any porosity. The interface between the glassy particles and the matrix remained free of such defects. The fully dense consolidated composite showed a drastic gain in specific yield strength under compression relative to the matrix alloy and appreciable plasticity at fracture.

Constitutive flow behavior and hot workability of powder metallurgy processed 20 vol.%SiCP/2024Al composite

Abstract: Constitutive flow behavior and hot workability of the powder metallurgy processed 20 vol.%SiC(P)/2024Al composite were investigated using hot compression tests. The modified Arrhenius-type constitutive equations were presented with the values of material constants in consideration as a function of strain. Dynamic material model (DMM) and modified DMM were used to construct the power dissipation efficiency maps, and Ziegler's instability criterion and Gegel's stability criterion were used to build instability maps. The presence of finer SiC(P) and more boundaries resulting from smaller 2024Al powders shifted the dynamic recrystallization domain of the 2024Al matrix to higher strain rate and lower temperature ranges and decreased the peak value of power dissipation efficiency. Large instable regions were found in the form of flow localization and cavitations located at the matrix/SiC(P) interfaces and within the SiC(P) clusters. By comparison, the Gegel's stability criterion was more sensitive to the instability zones than the Ziegler's instability criterion for this material. (c) 2010 Elsevier B.V. All rights reserved.