Metal Matrix Composite Samples Research Articles

Effect of Forging Parameters on Low Cycle Fatigue Behaviour of Al/Basalt Short Fiber Metal Matrix Composites

This paper deals with metal matrix composites (MMCs) of Al 7075 alloy containing different weight percentage (2.5, 5, 7.5, and 10) basalt short fiber reinforcement and unreinforced matrix alloy. The samples were produced by the permanent stir casting technique. The casting ingots were cut into blanks to be forged in single stage and double stage, using MN press and graphite-based lubricant. The microstructures and fatigue properties of the matrix alloy and MMC samples were investigated in the as cast state and in the single and double stage forging operations. The microstructure results showed that the forged sample had a uniform distribution of the basalt short fiber throughout the specimens. Evaluation of the fatigue properties showed that the forged samples had higher values than those of the as cast counterparts. After forging, the enhancement of the fatigue strength of the matrix alloy was so significant and high in the case of 2.5 and 5.0 wt. percentage basalt short fiber reinforced MMC, and there was no enhancement in 7.5 and 10 weight percentages short fiber reinforced MMCs. The fracture damage was mainly due to decohesion at the matrix-fiber interface.

Comparison of the Microstructure and Mechanical Properties of As-Cast A356/SiC MMC Processed by ARB and CAR Methods

Accumulative roll bonding (ARB) and continual annealing and roll-bonding (CAR) processes were used in this study for improving the microstructure and mechanical properties of the A356/10 vol.% SiC metal matrix composite (MMC) produced by semi-solid metal processing (SSM). The results showed that using the ARB and CAR processes led to the following points: (a) the uniformity of the silicon and silicon carbide in the aluminum matrix improved, (b) the Si particles became finer and more spheroidal in appearance, (c) the porosity disappeared, (d) the bonding quality between the reinforcement and the matrix improved, (e) the particle-free zone disappeared, and therefore (f) the tensile strength (TS), elongation, and formability index of the MMC samples improved. However, it was found that the CAR process is a better method for improvement of microstructure and mechanical properties of as-cast MMC compared to ARB process.

In situ synthesis of titanium diboride composites through volume combustion

Hard in situ synthesis of TiB2–Fe2B metal matrix composite (MMC) has been synthesised by volume combustion synthesis (VCS) reactions of Fe–FeTi–FeB system. VCS samples were characterised by SEM, EDX, XRD and DTA. Results show that it is possible to synthesise in situ structured MMC samples (with TiB2 and Fe2B phases) by VCS. Metallographic investigations show that Fe2B and TiB2 are found dispersed throughout the metal matrix, and other borides are present in microlevel patches dispersed in a eutectic matrix. The Fe–TiB2 composites sintered at temperature of 1200°C consist of three different regions, i.e. α-Fe, TiB2 and Fe2B regions. The increase in sintering temperature to 1400°C leads to a hypereutectic microstructure of the Fe–B binary system having TiB2 grains uniformly distributed throughout the matrix. A semiliquid phase sintering occurred by increasing eutectic phase transformation temperatures to 1400°C, which increased the efficiency of VCS. On the other hand, increasing sintering time from 1 to 3 h decreased the volume fraction of α-Fe and increased the volume fraction TiB2 phase.

Influence of processing conditions on the carbide/matrix interface in sintered composite layers

Abstract Metal matrix composite (MMC) coatings composed of nickel-based matrices and tungsten carbides (WC/W 2 C) are frequently used to solve problems of reduced life time under severe abrasive and corrosive conditions. The influence of processing conditions on the carbide/matrix interface was studied in the liquid-sintering process with a well defined temperature/time profile. Evaluation of the sintered samples by optical microscopy (OM) showed formation of an interface layer between matrix and carbides. SEM/EDS analysis indicated the formation of mixed Ni- and W-rich carbides on the interface microstructures. XRD measurements revealed the formation of Ni 3 B. The layer thicknesses were determined quantitatively by OM-image analysis. The hardness profiles across the interface were examined by nanoindentation. Furthermore, scratch tests were performed for the characterisation of carbide bonding in the matrix and evaluation of the influence of the interface layer on the single abrasion behaviour of the MMC samples. Results show that the carbide/matrix bonding and the single abrasion behaviour were dependent on the gradient of the micro-mechanical properties. Increasing processing temperature or time increased the hardness gradient and consequently decreased the bonding between carbide and matrix. Additions of chromium and iron in the matrix powder caused an improvement of the bonding and the abrasion behaviour under 2-body-condition of the MMC samples.

Diamond Turning of a Metal Matrix Composite with Ultrasonic Vibrations

ABSTRACT The objectives of this study are to develop an ultrasonic vibration device, investigate diamond turning of an aluminium-based metal matrix composite (MMC) reinforced with SiC particles with ultrasonic vibrations applied to the cutting tool, and evaluate effects of cutting parameters on the surface finish of turned MMC samples. A low-cost, small-size vibration device was designed to mount a piezoelectric transducer and cutting tool onto a low-end CNC machine. Cutting experiments were carried out using a fractional factorial design to investigate the effects of cutting parameters. The experimental results show that surface roughness of the MMC samples cut with ultrasonic vibrations is better than that of the MMC sample cut without ultrasonic vibrations. Depth of cut and cutting speed also affect the surface finish significantly. A light dispersion phenomenon, which is not reported in other articles, is observed and explained.

Ultrasonic assisted turning of an aluminium-based metal matrix composite reinforced with SiC particles

In this study, diamond turning of an aluminium-based metal matrix composite (MMC) reinforced with SiC particles was conducted with the assistance of ultrasonic vibrations. A simple and small size vibration device was designed to mount a piezoelectric transducer and a diamond insert onto a CNC machine. Turning experiments were carried out using a factorial design to investigate the effects of vibration and turning conditions on the surface finish of the turned MMC samples. The experimental results show that surface roughness of the MMC sample turned with ultrasonic vibrations is better than that of the MMC sample turned without ultrasonic vibrations. Turning with vibrations creates regular surface profiles along the turning and vibration direction, resulting in a light dispersion phenomenon, which is not reported in other articles. This phenomenon can only be observed when the pitch of the regular profiles is within a particular range. The pitch is determined by the cutting speed when the vibration frequency is fixed.

Mechanical characterisation of AA7015 aluminium alloy reinforced with ceramics

Manufacturing of metal matrix composites (MMCs) through powder metallurgy route and their characterisation are the objects of the present work. Thus a light alloy reinforced with 5% of ceramics is obtained after attrition milling of mixed powders, die pressing, lubrication of compacts and hot extrusion into 10 mm diameter bars. Since 7xxx series of aluminium alloys show high mechanical properties, AA7015 alloy was chosen as metallic matrix and B 4C, TiB 2 and Si 3N 4 ceramics were added. After process optimisation, the microstructure of these materials shows a uniform distribution of ceramics in the aluminium alloy matrix. Physical properties like density, conductivity and coefficient of linear dilatation were determined on extruded MMCs samples. Hardness and tensile strength properties on machined samples according to ISO 2740 standard were evaluated. Also wear behaviour using a pin-on disk test was studied, within a microstructure study, which was carried out using optical and scanning electron microscopy.

On composite-structure weaknesses: Part II. Computer experiments, identification, and correlation

Part II of this article concerns correlating the composite-structure weaknesses (CSWs) with the local microstructure of simulated short-fiber-reinforced metal-matrix composite (MMC) samples. The proposed analytically-numerically-based approach was employed for numerical computation of the mesoscopic stress distribution in short fibers. Nine local microstructure-related parameters are defined, which incorporate local elastic and thermal anisotropies into presentation of a local microstructure. It is found that the nine defined parameters are adequate physical parameters, which also account for synergetic interactions due to orientation-induced local anisotropies, either elastic anisotropy or thermal expansion anisotropy. By using the defined physical parameters, CSWs can be correlated with the local microstructure of simulated MMC samples. A database which collects numerical correspondences between the orientation and geometry of composite constituents and CSWs has been established for a number of simulated MMC samples. Computer experiments confirm that not only the stiffness mismatch between fiber and matrix materials, but also orientation-induced local anisotropies, exert decisive influence on the distribution of CSWs in short-fiber composites. The mesoscopic stress and strain distributions within a short fiber are critically dependent on the local evolution of elastic and thermal anisotropies of surrounding grains. Whether a CSW may become a failure origin must be evaluated in conjunction with a local damage mechanism.

On composite-structure weaknesses: Part I. Simulation, properties, and numerical approach

Composite material samples were created by means of computer simulation to duplicate short-fiber-reinforced metal-matrix composites (MMCs). Each sample contains a fairly large number of Voronoi grains and ellipsoidal short fibers, which orient and distribute in a random manner, to mimic composite microstructures for investigating the coherent interconnections of composite-structure weaknesses (CSWs) with local microstructure. It is supposed that the samples are subjected to coupled boundary traction due to mechanical loading and thermal cycling. A Kroner-Kneer structure-based model and Waldvogel-Rodin algorithm were used for numerical computations of the mesoscopic stress distribution in constituent grains. The computations are based on the grain-volume average of local fields. Polycrystal elastic/thermal properties and effective elastic/thermal properties of simulated MMC samples were predicted, respectively, in terms of micromechanics models, in favor of incorporating the influences of macroscopic material properties on the formation of CSWs. An analytically-numerically-based approach is proposed for analyzing peak mesoscopic stress and strain distributions in short fibers. Three crucial aspects constitute a kernel of the approach, i.e., (1) segmentation of short fibers, (2) establishment of the geometric relations of a short fiber to the surrounding grains, and (3) the local nature of micromechanics. The analytically-numerically-based approach takes into account the grain orientation, fiber orientation, grain geometry, fiber geometry, and macroscopic properties of simulated MMC samples. The Numerical Assessment of Computer-Imitated Weaknesses-MMCs (NACIW-MMCs) software program has been developed for performing simulation of the microstructure of short-fiber-reinforced MMCs and executing all involved numerical computations.

Effect of alternative aging process on the fracture and interfacial properties of particulate Al2O3-reinforced Al (6061) metal matrix composite

The effects of different aging processes on ductility, fracture, and interfacial properties in particulate Al2O3-reinforced Al (6061) metal-matrix composite (MMCs) were studied. Tensile tests based on relevant ASTM standards were performed to investigate the mechanical responses of specimens under different heat-treatment conditions. Scanning electron microscopy (SEM), field-emission SEM (FESEM), and transmission electron microscopy (TEM) studies were carried out to correlate fracture mechanism(s) with microstructural features. Based on the experimental results, the overall effect of heat treatment on tensile properties is similar to that in the monolithic alloy, however, the rate of recovery in fracture-related properties, such as elongation to fracture, is lower in the overaged condition for the MMC samples. To explain this “low” recovery behavior of overaged MMCs, the following observations have been taken into account: (1) a shift of the materials’ behavior from particle fracture to interface (or near-interface) debonding fracture, when moving from the underaged to overaged regime, and (2) more frequent observations of interfacial reaction products (spinel) on the fracture surface of overaged specimens. The presence/formation of spinel phase at the interface was recognized as the main cause of this behavior. Although spinel products mainly form during material processing, they may continue to form in the solid state as well. As a result, the surface morphology of the spinel phase in the underaged specimens is different from that in the overaged specimens.

Neutron diffraction measurements of residual stresses in metal matrix composite samples

The results of neutron diffraction experiments for the determination of residual stresses in metal matrix composite samples are reported. Investigated materials are Al alloys (AA2124 and AA359) with SiC particulate reinforcements. An AA2124+17% SiCp forged specimen and an AA359+20% SiCp bar, one side of which was submitted to a spark-erosion treatment, were investigated at LLB, Saclay (F) and ILL, Grenoble (F), respectively. In both cases, residual stresses were determined in both the matrix and the reinforcement, in different gauge points. As expected, for both the samples, results show that in each gauge point the main contribution is generally given by thermal microstresses. In the case of the AA359+20% SiCp bar, a slight decrease of the absolute value of residual stresses (tensile in the matrix, compressive in the reinforcement) is found, when approaching the spark-eroded face of the specimen.

Study of degraded neutron spectra through metal matrix composites using CR-39 films

Considerable interest has grown in the last decade in the use of CR-39 films in routine neutron monitoring and dosimetry. In addition, work in neutron spectrometry has been undertaken by various workers ( Decossas et al., 1984; Faermann et al., 1983; Fews et al., 1984; Turner et al., 1984). In the present study metal matrix composites (MMC) samples of Pb–Li, Pb–Cd, Al–Li and Al–B 4C were prepared by using powder metallurgy and alloying elements techniques. The density was obtained for these MMC samples in the range of 80–90% of the metal density. Degraded neutron spectra were obtained by exposing these samples to a 252Cf source housed in a camera and the detector used was CR-39 films covered with a 1 mm PE radiator. These spectra have also been validated through Monte Carlo Neutron and Photon Transport Code (1983).

Incorporation of Alumina Particles with Different Shapes and Sizes into Molten Aluminum Alloy by Melt Stirring with Ultrasonic Vibration

This paper presents the influence of particle shapes and sizes on the incorporation of Al 2 O 3 particles into molten Al-5 mass%Mg alloy by melt stirring with ultrasonic vibration. A new theoretical model of particle transfer into molten metal dealing with different shapes is proposed to estimate the difficulty in incorporation of spherical and massive particles. In the model, the particles are assumed to be spheroids with different major and minor axes. The difficulty depends on the maximum acceleration which originates from the interfacial tension: the incorporation of Al 2 O 3 particles into molten Al-Mg alloy becomes more difficult with the negative maximum acceleration increased. Four kinds of preheated A1 2 O 3 particles were added to a molten Al-5 mass%Mg alloy surface and stirred with ultrasonic vibration at 1023 K in a nitrogen atmosphere. The volume fraction of incorporated particles is related to the calculated maximum acceleration; that is, it is experimentally found to decrease as the negative maximum acceleration increased. According to the proposed model, the ultrasonic vibration makes the apparent contact angle of the A1 2 O 3 particle and the molten Al-Mg alloy improve from 1.78 to 0.87 rad. Gas defects, which are known to be a serious problem in metal matrix composites (MMC) produced by melt stirring, disappear in MMC samples formed with ultrasonic vibration. Moreover, the rotating torque for melt stirring decreases by applying ultrasonic vibration, because of the decomposition of agglomerate particles. Hence, the application of ultrasonic vibration to melt stirring is a novel candidate method of MMC production.

Quantitative characterization of metal matrix composites using histogram processing techniques

Abstract Ultrasonic nondestructive characterization of heterogeneous media is a difficult task, due to the inherent inhomogeneity of the material. Previous studies have shown that the amplitude information is not fully correlated to the material microstructure. This leads to difficulties in the interpretation of C-scan ultrasonic images. Our interest is to evaluate the concentration of spherical particles in metal matrix composites (MMC) in order to detect like porosities, aggregates and lack of particles. The aim of this work is to furnish good quantitative zero-state characterization of the material, before fatigued state determination after fatigue cycles. However, the ultrasonic resolution in such materials using 100 MHz longitudinal waves leads to information on particle aggregates and/or porosities. So, the interpretation of C-scan images is often difficult to perform. This paper deals with histogram processing techniques for local particle concentration estimation. The method is based on the study of the mean value and standard deviation of the histograms, and is efficient for studying non-fatigued MMC samples. The main benefit lies in the detection of defects like scatterers, aggregates, porosities and lack of particles, the detection of local variations in scatterer concentration and, finally, in the determination of silicon carbide particle concentration in reinforced samples. However, work still needs to be performed on the application of this technique to fatigued MMC in order to determine the feasibility of the detection of defects due to fatigue cycles.