Mechanism Of Metal Matrix Composites Research Articles

Aluminium Metal Matrix Composite Reinforced With Carbon Nanotubes / Graphene – A Review

This paper includes a comprehensive review of composites filed with aluminium metal matrix. The literature study includes all aspects of the preparation methods, mechanical properties, tribological properties, erosion properties and thermal properties of corrosion and cavitation. Recent years, owing to the huge demand in various industrial applications, aluminium graphene/CNT nano-composites was gaining greater momentum. The Fabrication of metal matrix composites, strengthening mechanisms in metal matrix composites, mechanical behavior of all composites and evaluation of mechanical properties were discussed below in detail. In fact these newly developed materials have high strength, high stiffness and high hardness, whereas these materials are difficult to be machined by conventional machining processes. Keywords: Aluminium, MMC, Carbon Nanotubes, Graphene, Fabrication.

3D multiscale modeling of fracture in metal matrix composites

Abstract

Competing failure mechanisms in metal matrix composites and their effects on fracture toughness

Development of high performance Metal Matrix Composites (MMCs) requires careful microstructure design which can improve material's fracture toughness while maintaining high strength. Microstructure and constituent properties combine to determine the overall fracture toughness of MMCs through the activation of different deformation and failure mechanisms. Although the effects of key microstructural attributes on the fracture toughness of MMCs have been discussed in previous studies, their effects on the interplay between plastic deformation and crack formation, as well as their effects on the competing failure mechanisms have not been systematically studied. In this paper, an integrated experimental and analytical framework is presented to evaluate the fracture toughness of MMCs through an assessment of energy contributions in terms of plastic deformation and crack surface formation in the matrix, reinforcement particles and interface. J-integral is calculated through displacement field measurement using Digital Image Correlation method. The competition of different failure mechanisms and their relations with material deformation are quantified through an analytical model by considering the effects of reinforcement volume fraction, interfacial property and yield stress of the matrix. Calculations carried out concern 6092Al/SiCp, but the overall approach applies to other MMCs as well. Results from this work indicate that interface debonding is a beneficial failure mechanism for fracture toughness enhancement of MMCs. It not only increases the surface energy dissipation by creating tortuous crack paths, but also promotes plastic deformation in the ductile matrix which largely contributes to the toughening of MMCs. The activation of interface debonding primarily depends on the volume fraction of SiCp, the yield stress of Al and the interface bonding energy.

Competing Failure Mechanisms in Metal Matrix Composites and Their Effects on Fracture Toughness

Development of high performance MMCs requires careful microstructure design which improves material's fracture toughness while maintaining high strength. Microstructure and constituent properties combine to determine the overall fracture toughness of MMCs through the activation of different deformation and failure mechanisms. Although the effects of key microstructural attributes on the fracture toughness of MMCs have been discussed in previous studies, their effects on the interplay between plastic deformation and crack formation, as well as their effects on the competing failure mechanisms have not been systematically studied. In this paper, an integrated experimental and analytical framework is presented to evaluate the fracture toughness of MMCs through an assessment of energy contributions in terms of plastic deformation and crack surface formation in the matrix, reinforcement particles and interface. J-integral is calculated through displacement field measurement using Digital Image Correlation method. The competition of different failure mechanisms and their relations with material deformation are quantified through an analytical model. Calculations carried out concern 6092Al/SiCp, but the overall approach applies to other MMCs as well. Results from this work indicate that interface debonding is a beneficial failure mechanism for fracture toughness enhancement of MMCs. It not only increases the surface energy dissipation by creating tortuous crack paths, but also promotes plastic deformation in the ductile matrix which largely contributes to the toughening of MMCs. The activation of interface debonding primarily depends on the volume fraction of SiCp, the yield stress of Al and the interface bonding energy.

Hall-Petch relations and strengthening of Al-ZnO composites in view of grain size relative to interparticle spacing

We investigated the Hall-Petch relations in Al-ZnO composites with different matrix grain size (D) relative to interparticle spacing (L). For samples with D > L, it was found that grain refinement as described by Hall-Petch relation and particle strengthening by Orowan mechanism both significantly contribute to the strengthening of the composites. For samples with D ≤ L, variation of microhardness with grain size was found to follow a good Hall-Petch relation with an enhanced Hall-Petch slope. Our study indicates the different coupling of strengthening mechanisms in metal matrix composites with different microstructure length scales.

Length effect of carbon nanotubes on the strengthening mechanisms in metal matrix composites

In the present work, we studied the effect of the aspect ratio of carbon nanotubes (CNTs) on strengthening aluminum metal matrix composites (Al MMCs). To this end, Al samples reinforced with CNTs of various aspect ratios were produced via three different powder metallurgy methods. Microstructural examination revealed that the CNTs were uniformly dispersed in the materials with a range of aspect ratios from 6.5 to 55. The tensile results showed that the CNTs exhibited a strong strengthening effect in the composites regardless of their aspect ratios. However, the post-loading examination and quantitative analysis indicated that there was a strengthening mechanism transition for CNTs, which was closely associated with the aspect ratio or length of CNTs. The origin of such transition was explored from the viewpoint of dislocation-CNTs interaction under loading. The findings may provide a new insight in understanding the strengthening behaviors of CNT-reinforced MMCs.

Effects of reinforcement on wear resistance of aluminum matrix composites

The effect of reinforcement on the wear mechanism of metal matrix composites (MMCs) was investigated by considering different parameters, such as sliding distance (6 km), pressure (0.14–1.1 MPa) and sliding speed (230–1480 r/min). The wear mechanisms of an MMC and the corresponding matrix material under similar experimental conditions were compared on a pin-on-disc wear machine. The pins were made of 6061 aluminum matrix alloy and 6061 aluminum matrix composite reinforced with 10% Al2O3 (volume fraciton) particles (6–18 μm). The disc was made of steel. The major findings are as follows: the MMC shows much higher wear resistance than the corresponding matrix material; unlike that of matrix material, the wear of MMC is very much linear and possible to predict easily; the wear mechanism is similar for both materials other than the three-body abrasion in the case of MMC; the reinforced particles resist the abrasion and restrict the deformation of MMCs which causes high resistance to wear. These results reveal the roles of the reinforcement particles on the wear resistance of MMCs and provide a useful guide for a better control of their wear.

Processing and mechanical properties of network ceramic/steel composites by pressureless infiltration

A new style Ni-containing alumina ceramic foam based continuous three-dimensional interconnected skeleton was prepared by impregnating a polymeric sponge with aqueous ceramic slurry. Subsequently, alumina ceramic foam/steel metal matrix composites (MMCs) were prepared successfully by sand mold casting technique. The microstructure and mechanical properties of MMCs were investigated by SEM, EDS and compressive test. The results show that the depth of infiltration is about 40 μm to the bonding interface of ceramic/steel and the fracture strength σ max and plastic strain limit ɛ p of composite are 520 MPa and 11.2%, respectively. The fretting wear mechanism of MMCs is mainly performed at the oxidative wear mode with lower load/friction frequency and the predominant oxidation wear together with slight adhesive wear and abrasive wear multiple mode with higher load/friction frequency. Moreover, the infiltration bonding and continuous three-dimensional interconnected ceramic skeleton play a vital role in the stability of the bonding interface and excellent mechanical properties.

Effect of Powder Blending Ratio on Synthesis of TiB<sub>2</sub> Particles by Al-Ti-B Combustion Reaction

It is favorable to disperse fine strengthening particles under 1μm to expect the effective dispersion strengthening mechanism of metal matrix composites. In this research, TiB2 particle was synthesized in Al matrix by a combustion reaction and the influence of the powder blending ratio was examined in detail. The mole mixture ratio of Ti and B powder was fixed to B/Ti=2, and the blending ratio of Al powder was varied from 40 to 70vol%. The compacted blended powder was heated under an Ar atmosphere in an induction furnace, and heating was stopped immediately after the combustion reaction took place. The synthesized TiB2 particle became finer by increasing the blending ratio of Al, and the dispersion of particles about 0.3μm was achieved. However, large quantity of Al-Ti intermetallic compounds remained when 70vol% Al was blended, indicating that the combustion reaction was not completed in this specimen.

Strengthening mechanism of shape memory alloy reinforced metal matrix composite

A new three-dimensional model for the strengthening mechanism of metal matrix composites reinforced by TiNi shape memory alloy (SMA) fibers has been proposed. The predicted results by the present model are compared with the experimental and the predicted results by a one-dimensional model from the literature.

Quantifying thermomechanical fatigue of light-metal-matrix composites by mechanical spectroscopy

This article reviews recent progress in understanding the stress-relaxation mechanisms in metal-matrix composites (MMCs) subjected to thermomechanical fatigue. Mechanical loss, dynamic shear modulus, and permanent torsional-strain measurements have been performed with forced oscillations during thermal cycling. A transient mechanical-loss maximum, which is absent in the monolithic material, appears during cooling. It has been attributed to the development of plastic zones around the reinforcements by dislocation generation and motion, which result from the differential thermal contraction of the matrix and reinforcement. This damping maximum is strongly dependent on both measurement and material parameters. The reversible shear-modulus evolution during thermal cycling suggests that no interfacial debonding occurs. In unalloyed matrices, extended thermal-stress-induced pleasicity occurs, leading to a plateau in the shear modulus, which is recovered at low temperatures by plastic-zone overlapping and matrix strain hardening. Simultaneously measured strain-temperature loops exhibit both reversible and permanent plasticity during thermal cycling (strain ratcheting).

Young’s modulus of cast HMS 2112-C f composite—prediction and ultrasonic evaluation

Various models for the prediction of strengthening mechanism of metal matrix composites (MMCs) containing either fibres or particulates are analysed. Assuming that the matrix strengthening by dislocations could be treated as equivalent to the effect of different volume fraction of dispersoids, as well as by considering the effect of morphology of reinforcement on the Young’s modulus, an expression for Young’s modulus for MMCs has been derived. The Young’s modulus values thus predicted, using this model, have been validated by ultrasonically-derived values of Young’s modulus of an Al-alloy matrix composite containing 5, 8 and 12 wt% chopped carbon fibre (C f) dispersoids, in as cast and extruded conditions. Further, the theoretically- and ultrasonically-derived Young’s modulus of cast Al-alloy-C f composites with 5 and 8 wt%C f have been found to be comparable with the reported values of Young’s modulus for these weight fractions.

A numerical analysis of the damage mechanisms in metal-matrix composites under cyclic deformation

A model to assess the damage evolution due to reinforcement fracture was developed for particulate-reinforced metal-matrix composites subjected to cyclic deformation. The composite mechanical response was simulated by means of the finite element analysis of a unit cell and the stresses on the reinforcements were used to calculate the fraction of broken reinforcements by assuming that the reinforcement strength followed the Weibull statistics. The predictions of the model (the fraction of broken reinforcements and the cyclic stress-strain curve) were compared with the experimental observations on a 2618 Al alloy reinforced with 15 vol% SiC particulates.

Constituent damage mechanisms in metal matrix composites under fatigue loading, and their effects on fatigue life

Load controlled fatigue experiments were performed on 8-ply unidirectional ([0] 8) SCS-6-Ti-15-3 metal matrix composites (MMCs) at different temperatures, and the results were interpreted in terms of the overall three-regime framework of fatigue. The emphasis was on understanding the mechanisms and mechanics of constituent damage evolution, and their effects on fatigue life. Most tests were performed at an R-ratio of 0.1, but limited fully-reversed ( R = −1) tests were conducted. In regime 1, damage was fiber failure dominated, but the exact mechanisms were different at room and elevated temperatures. In regime 2, observation of matrix cracks and persistent slip bands provided convincing evidence of matrix dominated damage. Weak fiber-matrix interfaces contributed to crack bridging. However, fiber fracture also played an important role in regime 2; tension-tension and tension-compression tests showed similar lives on a maximum fiber stress basis, although the strain range, which primarily controls matrix crack growth, was almost double for R = −1 compared with R = 0 or 0.1. Good agreement was obtained from the different R-ratio tests, between the MMC and matrix data, and data at room and elevated temperatures, when compared based on the strain range in the tension part of a cycle. Analyses and observations of fiber pull-out lengths and fiber fractures in the matrix crack wake provided evidence of fiber damage; the analyses also helped to explain increased fiber bridging with fiber volume fraction. Issues of fatigue life prediction are briefly discussed.

Creep and thermal cycling fixture design for metal matrix composites

A creep-thermal cycling system with a constant stress cam has been designed to be inexpensive and easily fabricated in order to identify the creep and thermal-cycling damage mechanisms in metal-matrix composites (MMCs) with high ductility. The current system can be modified to be a stress thermal cycling (or fatigue) system.

Structure and properties formation of metal matrix composites

Strength properties and failure mechanism of metal matrix composites (MMCs) are determined by the degree of component interaction. MMCs have failed through the mechanism of loosely-bonded bundles in the case of insufficient interaction, by a mechanism of failure localization at optimum interaction, and in the case of excessive interaction their fracture is brittle. MMC state and the appropriate failure mechanism are defined by a characteristic parametric relationship depending on retained fiber strength and derived bond strength. A relationship is given linking these parameters with processing parameters. Experimental results allow us to introduce quantitative compatibility and interaction estimation to determine optimum processing conditions. Proposed principles are illustrated by using aluminum matrix composites reinforced with carbon, boron and silicon carbide fibers as an example.