Papers by Author: K.C. Chan

Abstract: To investigate the maintainability of bulk metallic glasses (BMGs), two Lanthanum base metallic glass were first characterized by using X-ray diffraction and then machined by single point diamond turning (SPDT). With increasing depths of cut (DOC) from 1 um to 5 um, surface finish was improved. However, surface finish is not improved significantly when the DOC is further increased.

Abstract: The compressive deformation behavior of as-cast Zr55.9Cu18.6Ta8Al7.5Ni10 Bulk Metallic Glass (BMG) composite with micro-scale particles of Ta-rich solid solution embedded in an amorphous matrix was investigated in the supercooled liquid region. It was found that the apparent viscosity of the BMG is dependent on temperature and strain rate. A deviation from a Newtonian behavior was observed at high strain rate and low temperature. The experimental results can be described by a master curve based on a stretched exponential function and the free volume theory. The structural state and the thermal ability of the BMG composite after deformation are also discussed in the paper.

Abstract: In this paper, the superplastic deformation behaviour of a pulse electrodeposited Ni-SiC nanocomposite was further studied at temperatures ranging from 330 to 530oC. It was found that optimum temperature of the composite was 450oC, and the shape of its flow stress vs strain rate curves is similar to that of conventional superplastic materials. The microstructures of the composite before and after deformation were examined using SEM and TEM. Dislocations and deformation twinning were observed in the deformed samples, and there was significant grain growth during deformation. The deformation mechanisms were also discussed in the paper based on the experimental findings.

Abstract: Wear of ultra-high molecular weight polyethylene (UHMWPE) and its composites is one of the main obstacles that limit the longevity of total joint replacements. Compression molded UHMWPE/quartz composites with organosiloxane as a cross-linking agent for UHMWPE matrix, were tested in nanoindentation and nanowear. The nanomechanical properties of the composite were examined in the light of nanoindentation experiments performed with a diamond tip of nominal radius of curvature of about 150 nm under conditions of various contact loads. Results from nanowear tests show that, in addition to the nanohardness and elastic modulus, the crosslinking procedure has the most pronounced effect on the tribological properties and at 0.5 phr organosiloxane, composites reache their maximum nanowear resistance. These findings are in agreement with the results of conventional mechanical and wear tests performed on these materials.

Abstract: High strain rate superplastic (HSRS) bulging and cavitation behavior of a cold rolled Al-6Mg-0.3Sc sheet were investigated at the temperature of 798K and at the constant applied flow stress of 6.0MPa. The maximum effective strain of about 2.1 was obtained. The experimental results revealed that the cavity growth was essentially plastic - controlled. HSRS bulging limits of the sheet were further predicted based on the Marchiniak - Kuczynski model and a plastic damage approach. It is able to predict HSRS forming limits of the sheet in a reasonable agreement with the experimental findings even without assuming any initial geometrical defect.

Abstract: This study descripts processing of biphasic calcium-phosphate (BCP) and poly-L-lactide (PLLA) biocomposite implant material. The composite was obtained by mixing completely dissolved PLLA with granules of high crystalline BCP and was compacted by hot pressing using cylindrical dies at 450 K temperature and 98.1 MPa pressure, for 30 and 60 minutes. Wide-angle Xray structural (WAXS) analyses of BCP, PLLA and BCP/PLLA composite blocks were made followed by calorimetric (DSC) tests in the 320-520 K temperature range. Compression tests revealed that Young’s modulus and compressive strength of the composite increased with extended hot pressing time and were found to be within the bounds of the cortical bone values.