Materials Science Forum Vols. 561-565

Abstract: The effect of calcination on the mechanical properties of hydroxyapatite and zirconia composite (HAp:ZrO2= 30:70, 50:50, 70:30 mass%) was investigated. The calcination of ball-milled mixture in air at 900°C for 0, 2 and 4 hours increased the crystallinity. Then, it was assigned that the particles form of hydroxyapatite was changed from needle-like to sphere-like by calcination. The calcined mixture was sintered by spark plasma sintering (SPS) at 1200°C with a pressure of 40MPa for 5 minutes. The calcination process caused the enhancement of flexural strength of the composite.

Abstract: MgO-CaO materials is one type of the refractories for substitution of MgO-Cr2O3 refractories that has been widely used in metallurgy and cement industries, but the application of MgO-CaO materials has been inhibited for its poor thermal shock resistance that is often improved by addition of ZrO2 but it results in increase of the cost. The present work investigated preparation of MgO-CaO materials by addition of nano-sized ZrO2. The results showed that the densification of the MgO-CaO refractories was promoted and the direct bonding rate of the materials was increased by addition of nano-sized ZrO2. The thermal shock resistance of the MgO-CaO refractories was appreciably improved by modification of the microstructure due to the formed fine CaZrO3 crystallines homogenously locating on the grain boundaries and triple points of the whole microstructure. The critical amount of ZrO2 addition for the purpose to improve thermal shock resistance was effective decreased.

Abstract: This study deals with the processing, microstructure and properties of the carbide reinforced copper matrix composites. Powder technology was used to successfully fabricate the composites. NbC particulates were used as reinforcements for copper matrix. The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the NbC particles were distributed uniformly in the matrix phase. No interface debonding and micro- cracks were observed in the composite. NbC particles were found in round shape in copper matrix composite. The composite hardness of 78 HRA was found with 60vol% NbC content. Electrical conductivity as high as 7%IACS was achieved. The wear performance and conductivity value predicts that NbC reinforced copper matrix composites can be used as sliding contact applications.

Abstract: This paper deals with the preparation of silica microcapsules containing phase change paraffin wax for thermal energy storage and the determination of their thermal properties. The spherical microcapsule samples respectively containing two types of paraffin wax (with peak melting temperature of 29.3 °C (type P1) and 35.5 °C (type P2), and the fusion heat of 140 J/g (type P1) and 153 J/g (type P2)) as core and chemically and thermally stable silica as shell, were prepared from O/W emulsion systems in the presence of polyvinyl alcohol as stabilizer, and sorbitan monooleate and poilyoxyethylene(20) sorbitan monooleate as emulsifiers. The silica shell formed via hydrolysis and condensation from tetraethyl silicate with acetate acid as catalyst. The fusion heat of the two samples is 101 J/g and 112 J/g respectively. Property of adaptable temperature of the as-made microcapsules is measured through a self-made cell model. The maximum difference between the temperature of the cell with PCM wallpaper and that of the cell with controlled wallpaper is about 1.1 °C.

Abstract: Polymer matrix composites are widely used as bearing materials for heavy load applications. Still fundamental knowledge about the wear mechanisms of these materials and the evolution in time of these mechanisms is lacking. Currently these mechanisms are only analyzed by post mortem analysis. The Laboratory Soete, based on the well-known pin-on-disc test rig, has developed a new test-setup. Instead of the standard composite specimen and steel disc, a rotating composite disc and steel pin is used to be able to have a visible composite wear track. Standard wear and friction measurements will be further combined with vibration measurements. The vibration measurements give valuable information about the pin-disc contact. The combination of all these measurements should yield valuable information on the active wear mechanisms, the occurrence of fiber and matrix fracture, fiber pull out, generated frictional heat, formation mechanisms of wear particles, and the interaction between all these effects.

Abstract: Pultruded glass fibre reinforced polyester where used to investigated the frictional behaviour of the 45° fibre orientation. Therefore, on a rebuild Pin-on-disc test rig, using composite discs and steel pins, the frictional behaviour of these materials is investigated. Due to the indicated fibre orientation, and a simple trigger mechanism, it was possible to distinguish the friction force for different fibre orientations. The classical know orientations, parallel and perpendicular to the direction of sliding provided expected results, for both cases. The ~45° orientation, which is extremely important regarding filament wounded bearings, behaved in both cases similar -- regarding friction force-- in an unexpected way. The friction force of the 45° orientation was higher in all cases, and the amount was similar to the difference between the parallel and perpendicular case. These findings yield the conclusion that the 45° orientations cannot be neglected in frictional studies, and the behaviour of weft-warp structures also determines performance.

Abstract: Metal matrix composites (MMCs) have been found to possess tremendous prospective engineering applications that require materials offering a combination of lightweight with considerably enhanced mechanical and physical properties. However, the applications of MMCs are limited by their poor machinability which is a result of their highly abrasive nature that causes excessive wear to the cutting tools. In this study, an investigation into the mechanism of the tool wear in cutting of MMCs is carried out. It is found that during cutting of an MMC, the tool cutting edge will impact on the reinforcement particles. The impacted particles will then either be dislodged from the matrix, doing no harm to the tool, or be embedded into the matrix, ploughing on the tool flank and causing excessive tool flank wear. According to this tool wear mechanism, a pressured steam jet approach is developed for the minimization of the tool wear by preventing the impacted reinforcement particles from being embedded in the workpiece matrix. Experimental tests for cutting of SiC–aluminum MMC using cubic boron nitride (KB-90) and polycrystalline diamond (KP-300) tool inserts with the aid of the pressured steam jet are conducted. The results show that from full factorial design of experiments the effect of the pressured steam jet plays a significant role on the tool wear followed by tool inserts and depth of cut. The working mechanism of the pressured steam jet method and the experimental testing results are discussed in detail.

Abstract: The high temperature mechanical properties of dual phase heavy metal of 95W-3.5Ni-1.5Fe alloy were investigated in tension. The specimens were prepared by liquid phase sintering. Yield strength decreased and ductility increased as the testing temperature was increased to 300°C, reached a plateau at between 300 and 500°C and then decreased considerably. The fracture modes of alloys when deformed at room temperature were a mixture of intergranular fracture and transgranular cleavage. As the temperature was increased, the percentage of intergranular cleavage increased, although transgranular fracture also remained. At higher temperatures, substantial reduction in ductility and in yield strength was a result of loss of bonding strength between tungsten grains and matrix phase.

Abstract: Zirconia-based ceramic composites such as ZrO2-WC, ZrO2-TiCN and ZrO2-TiN, are suitable for wire-EDM, due to their sufficiently electro-conductive secondary phases inside. Thus, the material removal technique of EDM to shape complex geometry materials economically and with high accuracy, irrespective of mechanical properties, could be successfully employed on these ceramics. Samples of these ZrO2-based ceramics were developed in laboratory and manufactured and surface finished by wire-EDM. Reciprocative dry sliding pin-on-plate experiments revealed that the ZrO2-WC composite exhibits better tribological characteristics in comparison with the composites of ZrO2-TiCN and ZrO2-TiN. Furthermore, topographies and cross-sectional views of worn surfaces were analyzed by SEM, revealing that the secondary phase inside the investigated composites governs the wear mechanism.