Particle Reinforced Metal Matrix Composites Research Articles

Dynamic Effects in Elastothermodynamic Damping of Hollow Particle Reinforced Metal-Matrix Composites

The Metal-Matrix Composites (MMCs) containing hollow spherical reinforcements are under active development for the applications such as space structures, submarine hulls etc. where weight is of critical importance. When these materials are subjected to a time varying strain field, energy is dissipated because of the thermoelastic effect (Elastothermodynamic Damping or ETD). The quasi-static ETD analysis for the MMCs containing hollow spherical particles has been reported in literature. The entropic approach, which is better suited for composite materials with perfect or imperfect interfaces, is used for the analysis. In the present work, the effect of inertia forces is carried out on ETD of hollow particle-reinforced MMCs. For given particle volume fractions (Vp), the inertia forces are found to be more significant at higher value of thermal parameter (ΩT1) (alternatively, frequency of vibration if reinforcement radius is fixed), large cavity volume fraction (Vh) and low value of the parameter B1.

The effects of pore and second-phase particle on the mechanical properties of machining copper matrix from molecular dynamic simulation

The subsurface damage and surface integrity of a spherical diamond indenter sliding against a face-centred cubic copper (100) surface considering the pore and second-phase particle effects is investigated by means of molecular dynamic simulations of nanoindentation followed by nanomachining. In this investigation, we establish an analytical model for pore healing, and provide a criteria to determine whether or not pore can be healed. The results show that with increase of machining distance pore becomes smaller and then closes due to machining-induced compressive stress, resulting in low material damage and strong structure stability. Compared to free pore workpiece, machining force slightly relies upon the existence of pore and second-phase particle while friction coefficient strongly depends on the existence of that. In addition, particle induces work hardening due to Lomere-Cottrel lock and dislocation slip during machining metal matrix composites. It is helpful to understand the relation of machining performance and material parameter for obtaining higher surface integrity and lower subsurface damage during machining porous metals and particle reinforced metal matrix composites.

Tailored reinforcement/matrix interface and thermodynamic mechanism during selective laser melting composites

The simulation of thermodynamic behaviours of reinforcing particles and reinforcement/matrix interface during selective laser melting of particle reinforced metal matrix composites was presented. The transition from powder to solid phase, the surface tension and the density change were taken into account. It showed that the operating temperature and the resultant turbulent intensity increased with increasing the applied linear energy density, giving rise to the high instability of the molten pool. The gravity and capillary forces play a crucial role in the rearrangement and the attendant distribution state of the reinforcing particles. The particle morphology and distribution state in the as processed parts were experimentally studied, which were in good agreement with the results predicted by simulation.

Numerical simulation of mold filling and particulate flow of A356/SiCp indirect squeeze casting

In this investigation, a mathematical model based on the dispersed phase model and multiphase flow principle was introduced, and applied to simulate the mold filling and particulate flow of particulate reinforced metal matrix composites casting. Experiments of spiral-square shaped indirect squeeze castings of A356/50 µm SiCp were conducted to validate the established model. The SiCp fractions in the casting different locations were quantitatively measured with micro digital image analysis system and were compared with the simulation results. It was found that particulate fractions and distribution patterns at different locations were quite different along the filling distance. The experimental and simulated results about the SiCp distribution in the castings show acceptable agreement. Further, the effect of fluid flow and particulate trajectories on the particulate distribution was analyzed and discussed. The research has shown the validity of application of the model for practical particulate reinforced Al-based composites casting.

On the statistical determination of strength of random heterogeneous materials

This paper introduces a numerically-based methodology for determining the load-bearing capacity of particulate reinforced metal matrix composites (PRMMC) under both monotonic and cyclic loading. A multi-scale approach combining shakedown analysis with homogenization was used to evaluate the influence exerted by the composite structure on the global behavior of PRMMCs. The results were interpreted using statistical methods in order to take account of the randomness associated with the composite structure of the material. The general work flow of the approach can be summarized as follows: first, a large number of representative volume elements (PRMMC) were constructed from real material images using an in-house code. Next, lower bound limit and shakedown problems were solved via the interior-point method. Finally, results were converted to their corresponding macro quantities and evaluated statistically. With this approach we investigated a representative PRMMC structure, WC/Co, with two different binder contents and scrutinized the contribution of the composite structure over composite strength.

Effects of solution treatment on microstructure and mechanical properties of powder thixoforming 6061 aluminum alloy

A novel processing technology for the preparation of particle-reinforced metal matrix composites, powder thixoforming, is proposed and a 6061 matrix alloy was prepared using this method to study the effects of solution treatment on its microstructure and mechanical properties. The results indicate that the microstructural evolution includes two stages during solutionizing at 535°C. The first stage involves the quick dissolution of the eutectic phase and the resulting rapid coarsening of both the primary particles and secondarily solidified grains within a period of 0–3h. The second stage is regarded as the normal growth at a slow rate that starts from 3h. Owing to the large interdendritic eutectic phase, the microstructural evolution of the permanent mold cast alloy is slower than that of the powder thixoforming. The tensile properties of the powder thixoforming 6061 alloy initially increased from 0h to 3h owing to the reduction of the harmful eutectic phase, increased solid-solution strengthening, and composition homogenization. It then decreased due to grain coarsening. After being solutionized at 535°C for 3h, the tensile properties attained the highest values, with an ultimate tensile strength of 223MPa, a yield strength of 178MPa, and elongation of 13.8%. These values represent increases of 23.9%, 79.8%, and 72.5%, respectively, as compared to the as-powder-thixoformed alloy. Simultaneously, the general fracture regime changed from intergranular mode to a mixture of intergranular and transgranular modes and finally to a transgranular mode. The solution time had similar effects on the mechanical properties of the permanent mold cast alloy, most of which were lower than those of the powder thixoforming alloy.

The effect of rotating magnetic field on the microstructure of in situ TiB2/Cu composites

Nano ceramic particulate reinforced metal matrix composites are confronted with the problem of particle aggregation emerging in the process of solidification. It sharply deteriorates the mechanical properties of the composites. In order to improve the microstructure and particle distribution, in situ TiB2/Cu composites were prepared using Ti and Cu-B master alloys in a vacuum medium frequency induction furnace equipped with a rotating magnetic field (RMF). The effect of RMF magnetic field intensity employed on the microstructure and particles distribution of the TiB2/Cu composites were investigated. The results show that with the applied RMF, TiB2 particles are homogeneously distributed in the copper matrix, which significantly improves the mechanical properties of TiB2/Cu composites. The mechanism of RMF may be ascribed to the following two aspects. On the one hand, the electromagnetic body force generated by appropriate RMF drives forced convection in the equatorial plane of composite melt during solidification. On the other hand, a secondary flow in the meridional plane is engendered by a radial pressure gradient, thus making a strong agitation in the melt. These two effects result in a homogenous dispersion of TiB2 particles in the copper matrix, and hence excellent properties of TiB2/Cu composites were obtained.

Effects of Interfacial Features on Yield Strength of Particle Reinforced Metal Matrix Composites

The effective model assumption based on the average field theory has been modified and extended to investigate the effects of interfacial parameters including the bonding strength and interfacial thickness on the yield strength of particle reinforced composites. The formulation is applied to a model case of SiC particle reinforced Al matrix composite. The theoretical results agree well with the experimental ones of the SiC/Al composite produced by a PM route. The modified theoretical model can effectively predict the interfacial behavior and provide the preparation of SiC/Al composites with scientific foundation to control the interfaces.

Effects of Processing Parameters on Properties of SiCp/Al Composites

The effects of hot pressing and hot extrusion temperatures on the properties of 12%SiCp/6066Al (volume fraction) composites fabricated by powder metallurgy have been studied. The experimental results indicate that the hot extrusion, an essential stage of powder metallurgy to produce this sort of particle reinforced metal matrix composites, can redistribute SiC particles in metal matrix and refine the matrix grain size, and that the hot pressing can improve the interfacial cohesion strength between SiC particles and metal matrix. When hot-pressed at temperatures slightly higher than the solidus temperature of the composite and hot-extruded at lower temperatures, the composites are stronger due to the high metal matrix strength and interfacial cohesion. The optimum parameters of hot pressing and hot extrusion in the composites are 560 and 430 °C, respectively.

Machinability of a silicon carbide particle-reinforced metal matrix composite

This study reports extensive simulation and experimental studies on the theory underlying the cutting behavior of the representative PRMMC, SiCp/Al. The principle and different phenomena associated with the cutting of SiCp/Al composites have been studied.

An analytical approach to modeling stress–strain relationship of particle–reinforced metal matrix composites

An analytical model was established to simulate the stress–strain curves of particle–reinforced metal matrix composites by the classical stress equilibrium equation and secant modulus method, where particle cracking and matrix tearing were taken into consideration. The stress–strain curves of the composites predicted by the model fit the experimental curves very well. The stress–strain relationship of the matrix affected by the particles is predicted exactly, and it is found that the yield stress of the matrix is influenced obviously by the particle content. The yield strength of the composites is also predicted by the model, and the results fit the experimental data very well.

Interfacial strength and deformation mechanism of SiC–Al composite micro-pillars

A comprehensive understanding of the interfacial properties in particle-reinforced metal matrix composites (PRMMCs) requires an accurate determination of the cohesive strength of the interface. In this study, micro-pillars containing a slanted SiC/Al interface were fabricated, and were tested by uniaxial compression. The interfacial shear strength was found to be 133±26MPa, consistent with values predicted by numerical simulations. The stress–strain response of the composite pillars was characterized by shorter strain bursts and more significant strain hardening, as compared with their monolithic Al counterparts. These observations were interpreted by grain fragmentation and dislocation pile-up at the SiC/Al interface upon deformation.

An immersed particle modeling technique for the three-dimensional large strain simulation of particulate-reinforced metal-matrix composites

The standard numerical integration of the immersed meshfree Galerkin weak form based on mismatching overlapping integration cells and high-order quadrature rules is very time consuming and requires a large memory in the three-dimensional case. The method even becomes numerically infeasible for the large-scale nonlinear problems in general industrial applications. In this paper, the immersed meshfree Galerkin method is improved with a stabilized particle integration scheme to solve the 3D composite solid problems efficiently. The present immersed particle method introduces a smoothed displacement field to the immersed Galerkin formulation leading to a direct and consistent implementation of a stabilized formulation without the evaluation of the second-order derivatives in the meshfree approximations. Neither numerical viscosity nor artificial control parameters are included in the present formulation for the stabilization. A cube of particulate-reinforced aluminum-matrix composite under large strain is analyzed using an explicit time integration scheme to demonstrate the accuracy and the applicability of the proposed modeling technique to the three-dimensional nonlinear simulation of composite solids.

Enhanced thermal conductivity and flexural properties in squeeze casted diamond/aluminum composites by processing control

A practical and feasible approach is demonstrated to dramatically enhance thermal conductivity of the diamond particle reinforced aluminum matrix composites by means of optimized squeeze casting for fabricating metal–matrix composites with good adhesive interface as well as minimum thermal boundary resistance. By controlling the processing route, the architecture of diamond–aluminum interface was tuned, and therefore the thermal conductivity was amazingly found to be enhanced by 89% (from 321 to 606W/(m·K)), which was the highest value reported in the scientific literature to date for diamond/aluminum composites using squeeze-casting method. Meanwhile, the bending strength was increased by 124% (from 98 to 220MPa). This study offers an easily scalable and low-cost route to construct a wide range of particle reinforced metal matrix composites with significant enhancement of thermal performance.

Abrasive Water Jet Machining of Aluminum-Silicon Carbide Particulate Metal Matrix Composites

Particle Reinforced Metal Matrix Composites (PRMMC's) have proved to be extremely difficult to machine using conventional manufacturing processes due to heavy tool wear caused by the presence of the hard reinforcement. This paper presents details and results of an investigation into the machinability of SiC particle reinforced aluminium matrix composites using Abrasive Water Jet Machining (AWJM). Al-SiC MMC specimens, prepared with stir casting method. The surface roughness of the composite material for these different compositions are examined and compared. The influence of the ceramic particle reinforcement on the machining process was analyzed.

Effect of Magnesium Addition on Processing the Al-0.8 Mg-0.7 Si/SiC<sub>p</sub> Metal Matrix Composites

Metal matrix composites (MMCs) play a vital role in today’s engineering industries. Stir casting is one of the most inexpensive methods for the production of particulate reinforced metal matrix composites. However there are few problems encountered in stir casting such as the problem of poor wettability of the reinforcement particles in the matrix metal. The reinforcement particles have the tendency to either settle at the bottom of the crucible or they tend to float at the top of molten metal. This is due to the greater surface tension of the molten metal. Various techniques are available to improve the wettability of the ceramic particles in metal matrix which includes Particle treatment, Particle coating and Addition of alloying agent. In this work, Magnesium (Mg) was used as the alloying element to improve the wettability of SiC particles in the Al matrix. Mg is used to reduce the surface tension of molten aluminum (Al) thus promoting proper wetting. To understand the effect of Mg on improving the wettability of SiC in aluminum matrix, different weight percentages of SiC particles reinforced aluminum alloy 6061(AA6061) based MMCs were fabricated in stir casting method by adding Mg as alloying element. The cast specimens were subjected to microstructural analysis, tension tests and hardness tests. Results showed that addition of Mg with SiC in AA6061 matrix significantly improved the wetting between Al and SiC; subsequently MMCs possessed enhanced mechanical properties.

Numerical simulation on magnetic assembled structures of iron-based metallic particles within MMCs by a homogeneous strong magnetic field

Particle-reinforced metal matrix composites (MMCs) have excellent physicochemical properties as structural materials. The morphology and distribution control of reinforcement particles during the fabrication of MMCs are difficult-but-critical-to-achieve required properties of the materials. This research demonstrates a possibility to quantitatively control the distribution of particles in the metal matrix by applying a magnetic field. A 2D numerical model is developed and applied to evaluate the behaviour of Fe-based metallic particles in aluminum MMCs. By combination of 2D simulation with intersectional directions, this model also provides some hints for 3D practice. The assembled structure is found to be governed by the external magnetic field orientation, magnetic flux density and magnetic susceptibility of the particles. Both behaviours of particle agglomeration and dispersion are quantitatively characterized in different conditions. By using a strong magnetic field, it is found that assembled structures of weakly magnetic particles can be effectively manipulated. Therefore, it can be expected to fabricate particle-enhanced metal matrix composites/ceramics/glass with substantial improvements in physical and chemical properties by using a magnetic field.

Fabrication of functionally graded composites using a homogenised low-frequency electromagnetic field

A characteristic feature of functionally graded materials is the continuous spatial change of their mechanical, thermal or electrical properties. Deliberate controlling of the spatial distribution of reinforcement in the metal matrix composite is one way of these materials. The article describes the theoretical basis and experimental verification of a new method using a homogenised low-frequency electromagnetic field to produce particle-reinforced metal matrix composites with a controlled distribution of reinforcement. The method developed allows for obtaining local reinforcement of the composite casting, analogous to radial centrifugal casting. The article describes the methodology for designing a casting system, which allows such control of the electromagnetic field distribution in the liquid casting, which makes it possible to obtain the desired reinforcement distribution. Experimental verification of the method developed was carried out using the example of a sleeve made of AlSi12CuMg alloy reinforced with SiC particles at the outer wall.

Influence of interfaces on the mechanical behavior of SiC particulate-reinforced Al–Zn–Mg–Cu composites

In particulate-reinforced metal matrix composites (MMCs), geometrically necessary dislocations (GNDs) form in the vicinity of reinforcement/matrix interfaces. In this study, the hardness distribution across the interface was studied using nanoindentation with high spatial resolution, for composites treated under different aging conditions. The size of the GND punched zone, as determined from the hardness measurement, was found to be in agreement with that estimated by transmission electron microscopy (TEM). Mechanical characterization of bulk composites revealed a reduction in failure strain with decreasing punched zone size, while the strength of the composites was found to depend more on the intrinsic strength of the matrix alloy. These observations were interpreted in terms of the load transfer capacity between the matrix and reinforcement through the interface.

Fracture Mechanics Characterization of Sintered 30 Vol.-% Al<sub>2</sub>O<sub>3</sub>/TRIP Steel Composites Using SENB Miniature Samples

Ceramic particle reinforced metal matrix composites (PRMMCs) combine the strength and brittleness of ceramics with the toughness of a metallic matrix. In order to use these materials in construction and operational design their fracture mechanical behavior must be evaluated. In this study, a 30 vol.-% Al2O3 reinforced austenitic TRIP steel processed by powder metallurgical technique was investigated using precracked miniature SENB-specimens in 3-point-bending. An elastic-plastic analysis by means of the J-integral method in combination with optical crack observation showed the materials ability of stable crack growth, i. e. R-curve behavior. In addition to the mechanical tests microstructural studies were performed, whereby particle debonding and fracture as well as martensitic phase transformation and crack bridging within the matrix were identified as fracture energy dissipating mechanisms.