Papers by Keyword: Metal Matrix Composite (MMC)

Abstract: Thick alumina coatings were performed on A356-20vol.% SiCp composites by micro-arc oxidation (MAO) process with different processing time. The dry sliding wear tests were performed on A356-20vol.% SiCp composites with and without surface coating. The samples were tested by pin-on-disc wear test equipment with different applied load and sliding velocity. It is revealed that MAO coating improves resistance to wear of A356-20vol.% SiCp composites in the severe wear conditions. On the basis of the observations and analysis of the worn surface, worn subsurface, wear debris and variation of friction coefficient, the role of MAO coating layer is examined.

Abstract: Compressive behavior of 7xxx series Al metal matrix composite (MMC) powders with different ceramic contents and different particle size were investigated. As a starting powder of the experiments, ceramic contents of each starting powder were 5 and 10 wt.% and ceramic particle size of starting powder were 20 and 100 ㎛, respectively. And 7xxx Al blended powder was used for comparison. The powders were uniaxially cold-compacted using cylindrical die with a compacting pressure 250 MPa and sintered at 620oC in a dry N2 atmosphere for 60 min with heating rate of 20oC/min. In case of heat treatment condition, sintered parts were solution treated at 475oC and aged at 175oC. To reveal the effect of Al2O3 particle content and particle size on the mechanical properties of composites, compression test were conducted with constant strain rate of 1×10-3/s using sub-size cylindrical samples of 9 mm diameter. Compression test was performed 5 times and its average value was used. Then fractography analysis was conducted using scanning electron microscope.

Abstract: Micro-indentation has been widely used to evaluate the mechanical properties of materials. It has also been considered to be an important measure in the study of machinability of difficult-to-machine materials such as metal matrix composites (MMCs). Because of the complexity of deformation of an MMC and the interaction in the vicinity of contact zone between the indenter and work material, an analytical or experimental method is unable to predict the detailed deformation process. The present paper uses the finite element method to investigate the behavior of MMCs subjected to micro-indentation by a spherical indenter including the development of stress and strain fields in the MMCs during loading/unloading. Particle fracture, debonding and displacement, and inhomogeneous deformation of matrix material were explored and compared with the experimental results reported in the literature. The analysis also provides an insight for understanding the formation of residual stresses in machined MMC components.

Abstract: Aluminum matrix composites, reinforced by 0.15μm and 5μm Al2O3 particles with 40% volume fractions were fabricated by squeeze casting technique. The microstructure characterization near the interfaces of Al2O3p/1070Al composites was investigated by SADP and HREM techniques. Results showed that high-density dislocations were generated in the 5μm-Al2O3p/Al composite due to the thermal mismatch stress. In contrast, the matrix of the 0.15μm-Al2O3p/Al composite appeared to be nearly free dislocations and some “micro distortion areas” of 1-5nm were observed, which was attributed to the dispersion of fine sub-micron particles and uniform distribution of the stress near the interfaces.

Abstract: The aeroengines have been the subject of continuous development for the past fifty years with considerable improvements in fuel efficiency, power density, exhaust emissions, decreased noise and better reliability. All these changes have been brought due to incremental improvements in engine cycle, combustion, turbine cooling, acoustics and materials technology.The main challenges for the future are not only technological and economical but also related to societal concerns. For instance, noise and emissions are becoming a major concern.In terms of materials, there is a constant need for developing new affordable materials, or materials systems such as thermal barrier coatings on single crystal superalloys in order to achieve higher TET but not at the expense of increased NOx, at least in commercial engines. The use of MMC's and CMC's in some parts of the engine will become possible due to a considerable improvement in processing and lifing methodologies.

Abstract: The stir-casting method was utilized in this paper to synthesize 6063Al/Al2O3·SiO2 reinforced composites consisting of 6063Al alloy as matrix and Al2O3·SiO2 particles as additive with content of 5%, 10%, 15%, 20% (volume fraction) respectively. Al2O3·SiO2 particles were obtained from fly ash particles of Steam Power Plant and were pretreated. The shape of these fly ash particles was spheroidal and ellipsoidal. The damping behavior of 6063Al/Al2O3·SiO2 particle reinforced composites was studied by measuring the composite’s internal friction values on a Multifunctional Damping Measurement Apparatus. Under the condition of this series of experiments, 6063Al/Al2O3·SiO2 particle reinforced composites had a higher internal friction values than that of 6063Al matrix and also showed the dependency of internal friction on Al2O3·SiO2 particles volume fraction, particles dimension, vibration frequency and temperature. There was an increased trend for internal friction values with increasing the volume fraction of Al2O3·SiO2 particles and decreasing particles dimension of Al2O3·SiO2 at the same frequency and the different temperature. It has been found that in the lower frequency, the higher internal friction value was obtained. The internal friction of the composites increased with increasing temperature. In the case of lower frequency, two damping peak were observed. A low-temperature damping peak appeared at a temperature near 245°C which a high-temperature damping peak appeared near 450°C. Based on the experimental results, the damping mechanism of 6063Al/Al2O3·SiO2 particle reinforced composites was preliminary discussed. It may be concluded that the damping mechanisms associated with 6063Al/Al2O3·SiO2 reinforced composites include mainly intrinsic damping, dislocation damping and interface damping. However, only the interface damping mechanism is dominant at high temperature.

Abstract: Friction stir welding (FSW) has been generating interest in association with friction stir processing (FSP), a new technique that employs FSW tooling. FSP is being investigated as a thermo-mechanical processing tool to transform a heterogeneous microstructure into a more homogenous microstructure.
However, very little data is available on the use of FSW for processing composite materials. In this study, a novel method of local manufacture of metal matrix composites (MMCs) using FSW is proposed and its application to friction stir spot welding (FSSW) is described. Trials investigating local manufacture of aluminum oxide particulate reinforced 6063 Al by friction stirring were carried out on a modified milling machine. The results are discussed in terms of weldability and residual microstructure.

Abstract: Boron-fiber-reinforced Al-matrix composite was fabricated by a pulsed current hot pressing (PCHP) process at a pressure of 32MPa for 600s. It was found that the boron fiber and the Al-matrix were well bonded when the PCHP process was performed at a holding temperature of 773K. No interfacial reaction layer was observed along the interface between the boron fiber and the matrix when PCHP was done at 773K for 600s. Tensile deformation carried out at room temperature for the composite showed that the tensile yield stress increased with increasing volume fraction of the boron fiber in the composite. The composite with 17.2 vol.% of boron fiber presented a tensile yield stress of 600MPa. This value was about 90% the yield stress estimated by a force equilibrium equation of a composite taking into account the direction of fiber axis.

Abstract: Processing technique to produce open-cell porous titanium composite was developed. One of the outstanding benefits of porous titanium composite is both physical and mechanical properties can be controlled widely by changing the metal/ceramic fraction and cell structures. In this work, porous titanium composite was fabricated by a chemical reaction between titanium powder and boron carbide (B4C) powder. The reactions between titanium and B4C generates a large amount of latent heat and, therefore, it was a combustion and self-propagating mode. Precursors were made by compacting the starting powder blend (Ti and B4C), and heated in an induction furnace to induce the reaction. The reaction was strongly exothermic and, therefore, the precursor was sintered by its latent heat when the Ti/B4C blending ratio was appropriate. The reaction products were titanium boride (TiB and/or TiB2) and titanium carbide (TiC). By controlling the Ti/B4C blending ratio, it was possible to control the volume fraction of reaction products in titanium matrix. The combustion synthesized titanium composite was porous and its cell structure was strongly affected by the processing condition of the precursor (porosity and Ti/B4C blending ratio). High porosity with open pores was obtained with small Ti/B4C ratios and high porosity of the precursor, while the cell structure was closed and spherical with high Ti/B4C ratio. The cell-wall size was varied from several tens of microns to about 500 microns by changing the combustion temperature.

Abstract: AZ31 Mg alloy matrix composites were fabricated by squeeze casting method to improve high temperature properties in this study. The results showed that Mg composites reinforced with Alborex and Ag revealed improved high temperature properties and mechanical properties compared with Mg alloys. High temperature hardness and flexural strength were increased with reinforcement of Alborex, and further increase was obtained with addition of Ag. Also, Alborex reinforced AZ31 containing Ag Mg matrix composite exhibited greater improvement on creep properties. Therefore Mg composites reinforced with Alborex containing Ag were better than those reinforced with Alborex in mechanical properties and high temperature properties.