Materials Science Forum Vols. 475-479

Abstract: This study was to aimed to investigate on the sliding wear behaviors at both ambient and elevated temperatures in Al/SiCp composites fabricated by the newly developed duplex process. Wear test using wear tester of pin-on-disc type was carried out under the conditions of load 100N , velocity 0.64m/s, distance 4000m. The sliding wear behaviors under the conditions of ambient temperature, 200°C and 200°C-Ar gas and microstructures were studied using OM and SEM. The results obtained from this study are as follows; Wear amount decreased with the decrease in particle size. The wear resistance at 200°C-Ar on composites was greater than those at 200°C and room temperature in the as-composites.

Abstract: Mg alloy is the lightest material of structural materials and is noticed for lightweight automotive parts because of excellent castability and damping capacity compared with Al alloy. But Mg alloy has poor corrosion resistance and high temperature creep properties. In this study, Mg matrix composites were fabricated by squeeze casting method to improve high temperature creep properties and damping capacity. The creep properties and damping capacity of hybrid Mg composites reinforced with Alborex(Aluminum borate whisker: 9(Al2O3)•2(B2O3)), graphite particle, and carbon fiber were improved in comparison with Mg alloy. Hybrid Mg composites reinforced with carbon fiber and Alborex were better than those reinforced with graphite particle and Alborex in mechanical properties, creep characteristics, and damping capacity, etc.

Abstract: The relations between interfacial properties of clad composite and process conditions are studied. Adherence on interface of two materials is most significant property of clad composite. Properties of composite material are manifestation of its microstructure, and process conditions are decisive factor to the microstructure in interfacial area. In-depth understanding about the composite’s properties is only achieved through appreciation of the mechanism by which the process conditions affect the microstructure. Aluminum and copper clad composite bars are extruded at the various process conditions. Interfacial adherence of the extruded composite is examined. Microstructure of the dispersed layer and its vicinity is investigated.

Abstract: Titanium carbide particle reinforced titanium composites were prepared by in-situ synthesis reaction between titanium and carbon liquid alloys. The phases constitute and microstructures of titanium composite have been investigated by OM, XRD, SEM and EPMA. Although it was possible to synthesize titanium carbide particle reinforced titanium composites, the morphology of in-situ titanium carbide grows into typically dendritic shape due to the compositional supercooling theory. Using computerized image analysis, the average particle size and aspect ratio of in-situ formed titanium carbide is about 28.1 ㎛ and 1.9, respectively.

Abstract: We investigated about the effects of core material(Pure Al, Al3003) on extrudability such as the maximum extrusion ratio and the bonding strength of Copper Clad Aluminum(CCA) by indirect extrusion. As a results of this experiment, the maximum extrusion ratio of Cu/Al3003 was 38, which was larger than 21.39 of Cu/Al(Cu/pure Al). It was because that the difference of flow stress between copper as the sheath material and Al3003 as the core material was smaller than that of between copper and pure aluminum under the same extrusion temperature of 623K. The bonding strength gradually increased when the extrusion ratio increased, on the other hand, the bonding strength of Cu/Al3003 was higher than that of Cu/Al under same extrusion conditions. The diffusion layer thickness that affected bonding strength was not affected by the kind of core material, but it gradually increased when the extrusion ratio increased. It was thought that Cu/Al3003 had a more intimate diffusion layer than Cu/Al had because the extrusion pressure of Cu/Al3003 was higher than that of Cu/Al under the same extrusion conditions.

Abstract: 5052 Al matrix composites reinforced with carbide particles (SiC, TiC, and B4C) were fabricated by the pressureless infiltration and the tensile properties were analyzed. The strength values in the control Al were significantly increased over those of the commercial alloy while the strain to failure of the former decreased. Strength values in the composite reinforced with carbide particles were further increased compared to the control alloys. It was observed that strengthening effect by an addition of reinforcement varied with according to reinforcement types. By relative comparison, both TiC and B4C particles may be effective reinforcement compared to SiC particles in Al matrix composites.

Abstract: Metal matrix composites (MMCs) that consisted of Al-Mg matrix reinforced with initially added BN particles were fabricated using the pressureless infiltration technique, and their oxidation behavior was investigated at 500 and 550oC in air. Initially added BN particles were partly consumed to make AlN, as another reinforcing particles. Another reaction product was MgAlB2 dispersoids. Despite of the presence of these reinforcing particles, the oxidation resistance was not good owing to the formation of MgO-rich scale due to the preferential oxidation of Mg in the MMCs. Detailed microstructures and oxidation mechanism of the prepared MMCs are proposed.

Abstract: SiCp/Zn-22 wt% Al metal matrix composites of different particulate sizes have been prepared and tensile tested at 250°C at various strain rates. Scheduled thermomechanical treatment of structural refinement was employed to enhance the ductility of the composites. Substantial ductility of over 500% elongation bas been achieved within the strain rates investigated. The highest elongations are generally obtained by the samples reinforced with large particulates. Microstructural examination of the tested samples shows significant material cavitation and particulate separation in the material after tensile deformation. It was found that the particles had a de-strengthening effect.

Abstract: Using a steady-state 2-D network model to simulate the thermal behaviour of copper and superalloy matrix composites, reinforced with different types of randomly distributed continuous fibers, the limit values of thermal conductivity are established for the analysed composites. A large number of random distributions for each matrix-fiber combination is tested to assess the accuracy of the numerical results. The influence of the type of fiber, its distribution and its proportion is shown graphically. Examples of continuous fiber metal matrix composites (continuous MMCs), such as those of copper and Incoloy 907 matrices, are studied.

Abstract: Carbon nanotubes (CNTs) combining unique mechanical and physical properties could offer a kind of nanosized reinforcements for composite materials. Incorporating of CNTs to develop advance engineering composites has become an interesting concept, but the cermets based CNTs composites have been less focused. WC-Co-CNTs nanocomposites were consolidated by spark plasma sintering (SPS) to investigate the effects of CNTs incorporation on the grain growth and mechanical properties of WC-Co nanocomposites. Experimental results show that CNTs could preserve their tubular structures in high temperature SPS process, some CNTs are surviving in the WC-Co fracture surfaces featured bridging and pulling out manner. The interaction between the CNTs and the matrix has a retardation effect of grain growth of WC, but CNTs additions could be resulted in an increase of carbon content in the binder phase that causes enhanced tendency of grain growth, either of which plays the dominated role depending on the CNTs content. The WC-10Co-0.5wt%CNTs nanocomposites possess superior hardness to toughness combinations, which hardness is about 15% and fracture toughness is about 40% higher than that of the pure nano-WC-10Co cermets consolidated under the same process.