Papers by Keyword: Alumina

Abstract: Tribological fatigue failure of the machined PEEK shaft was investigated through the one-point type rolling contact fatigue test between a PEEK shaft and an alumina ball, in order to explore fatigue fracture mechanism of frictional parts working at high frequency in various mechanical elements. Due to Hertzian contact of cyclic compressive stress, the subsurface crack occurred within approximately 300 μm depth from thesurface and propagated along the rolling direction. After that, the subsurface crack propagation direction changed toward the surface. The flaking occurred on the raceway of the PEEK shaft when the subsurface crack reached to the PEEK shaft surface.

Abstract: The objective of this experiment was to investigate deformation behavior of friction welded aluminium AA6063/alumina. Effect of welding speed on microstructural change and temperature gradient were determined. The result showed effects of welding speed on temperature and grains flow. Microstructures at the interfaces in all conditions exhibited recrystallised grains and hot deformation characteristic. Areas of Heat affected zone (HAZ) decreased with increasing welding speed. Hardness of recrystallised AA6063 grains decreased approximately by 30%. Increasing in amount of deformation increased the fully welded interface areas improving bonding strength of the weld.

Abstract: Microwave processing of ceramics has attracted much research interest because of its significant advantages over the conventional one. Most researchers compared processes that occurred during the microwave and conventional heating at the same temperature and time. The enhancements found in the former method are indicated as a microwave effect which is usually used for explaining the phenomena in microwave processing. Numerous recent studies have been focused on the effect to elucidate the microwave interaction mechanism with materials. This paper will present effect of very high microwave frequency to hardness of sintered alumina. The sintering results were taken from a series of experiments to study the microwave effect on properties of alumina. Microwave sintering was performed by using the 300 GHz microwave sintering system. Some possible physical mechanisms are also discussed.

Abstract: The anodizing of aluminum is a common technique used to produce decorative and protective high quality film. This process results in significant volume of industrial sludge containing considerable amounts of colloidal aluminum hydroxide, which is a problem in the disposal of these industrial wastes due to the environmental impact. This paper aims at the treatment of theses residues, which were heat-treated at the temperatures of 200°C, 1000°C and 1400°C. After each treatment, the residues were put to the X-Ray Difraction and the X-ray Fluorescence analysis. In evaluating these results, it was found a gradual increase of the percentage of alumina at 1400°C to achieve 93%. With the acquisition of ceramic mass with a high content of alumina, the objective being to make a refractory to coat the petroleum refining pipes, thereby solving an environmental problem from the aluminum industry, presenting an alternative to the petroleum industry. These residues were compacted and immersed in land and sea petroleum for 30 days, after this period its mechanical properties were analyzed to study its response to the contact with the petroleum, where it was found that these remained kept.

Abstract: Indentation in brittle solids involves many complex phenomena related to cleavage and contact, as well as intrinsic stress singularities, which are almost impossible to capture with traditional continuum approach and FEA at mesoscale. In case of a two-phase ceramic composite [1–3] the number of unknown material and interfacial constants, that have to be calibrated experimentally, increases rapidly [4, 5]. In this paper, nanoindentation in zirconia-toughened alumina (ZTA) is modelled using discrete (peridynamical) approach

Abstract: Two types of CuFe matrix composites with different reinforcements: silica and alumina particulates were developed using powder metallurgy. The mechanical properties were determined from Brinell hardness and flexural strength. The dry sliding friction and wear performance of the composites were investigated by the friction test. The results indicated that mechanical properties of alumina were superior to those of silica. The friction tests of the composites showed that the alumina reinforcement particle provides better braking performance. A wear track examination of composites showed that same abrasive wear. Our results indicated that composites with alumina reinforcement particles of high compatibility are to be preferred for braking performance.

Abstract: In order to improve the wetting ability of metal to ceramic, silica coatings on alumina/ mullite ceramics were prepared with tetraethyl orthosilicate (TEOS) by sol-gel method. The preparation processing was optimized. Furthermore, the interactions between the aluminum melt and the ceramic with or without silica coating were investigated. The results showed that the silica coatings could be successfully prepared. The molten aluminum melt reacted with silica, and alumina was formed at the interface between ceramic and metal. The ceramic (alumina/ mullite) substrates could be infiltrated by aluminum melts due to the existence of mullite. The silica coatings conduced to the infiltration and improved the combination between the ceramic and aluminum at the interface.

Abstract: Cermet while maintaining the excellent properties of ceramic materials, but also have the advantages of a metal material, is an important new engineering materials. In this paper, prepared by calcination of alumina - aluminum metal-ceramic composite material powder, and its characterization as a basis to provide raw materials for preparing high performance metal ceramic material. According to the research, with the calcination temperature is increased, the rate of change gradually increase the weight of aluminum. Calcined at a temperature of 600¡æ, the oxidation of aluminum surface the best. With the firing time increases, the rate of change in the weight of aluminum powder showed an increasing trend. When 8h, oxidation of aluminum surface better. Through this experiment, process optimization can be found in the calcination temperature was 600¡æ, calcination time is 8h, the best coating effect aluminum surface, coating evenly, clean interface, the reaction layer thickness of about 700nm, the prepared package type composite powders the best results.

Abstract: This work focuses in the corrosion and wear properties of titanium reinforced with 1% wt. alumina particles, produced by a combination of colloidal techniques and powder metallurgy. The alumina particles were added to control the grain growth of titanium during sintering, and simultaneously to increase hardness and wear resistance. Colloidal techniques permitted a homogeneous dispersion of alumina particles on the surface of fine Ti particles by the formulation of stable aqueous suspensions that were further processed by spray-dry to obtain spherical granules with improved compressibility. Ti-alumina samples were produced by uniaxial pressing of granules and vacuum sintering leading to materials with homogeneous microstructure, a reduction of grain size higher than 50 % with respect to pure titanium, and a sensible increase in hardness. But the addition of ceramic particles can also have an influence on the corrosion behavior that is one of the most interesting properties of titanium alloys, and on wear resistance, that is one of the drawbacks of Ti. Moreover, the study of simultaneous action of wear and corrosion (tribocorrosion) is an area of highest interest in applications like biomedical or automotive. The corrosion behavior was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PP) in NaCl at two concentrations (0.9 % and 3.5 %) and temperatures (37 oC, and room temperature). Tribocorrosion tests were performed using a reciprocating ball-on-plate tribometer where a 10 mm diameter alumina ball was used as counter material, and 10 N normal load was applied during 30 min in the same concentrations and temperatures of NaCl as in the static corrosion tests. The results showed a clear improvement of wear resistance on the composite without reducing the corrosion behavior in both conditions.

Abstract: The main function of a bone graft is to support bone in growth, to induce bone healing, and to facilitate bone regeneration. Synthetic bone grafts are used since it can be easily modified according to the properties needed for a good bone substitute. For this study, a hydroxyapatite-alumina biocomposite was fabricated via sintering at 1000 °C. Hydroxyapatite (HAp) was extracted from porcine bones by means of calcination. Amounts of HAp, alumina, and starch were varied to determine the compositional effects in mechanical properties and biocompatibility. The produced biocomposites were found to be compact and solid with minimal pores at the surface. Also, surface grains vary in sizes. Compression tests were done and the calculated maximum stresses range from 45.46 to 219.02 MPa. The sample with 80wt% HAp-10wt% alumina-10wt% starch has the best compressive strength. While the three-day immersion test using simulated body fluid yielded positive results as the samples were found to be stable with the highest weight loss being only 2.36%.