Papers by Author: L.C. Lee

Abstract: A study was carried out to investigate effects of crystallographic structure on the machining performance with polycrystalline oxygen free copper (OFC) using a single crystalline diamond (SCD) micro-tool. The SCD micro-tool used in this study fabricated with a focused ion beam (FIB) has a cutting length of around 30 µm on the primary clearance face. It was found that a change in crystallographic orientation resulted in a variation in machining force, chip thickness and shear angle, leading to a change in machined surface integrity. When a micro-size tool traverses within a grain at a machining direction aligned with a particular crystallographic orientation, the work material in front of the machining tool is found to be severely deformed. If the orientation changes to a less favorable orientation, this may lead to a much reduced shear angle, a thicker chip, striation at the chip back, higher machining forces and a degraded machined surface. This study contributes to the understanding of the physics of micro scale mechanical machining (micro-machining).

Abstract: In this study, both liquid and powder metallurgy techniques were employed to fabricate Mg nanocomposites. Comparisons were made on the physical and mechanical properties of Mg nanocomposites using these two different fabrication techniques. When similar weight fractions of carbon nanotubes (CNTs) were added to Mg using these two different techniques, the nanocomposites fabricated using powder metallurgy technique were found to be thermally more stable and has higher yield and tensile strengths than those produced using liquid metallurgy technique. The higher yield and tensile strengths were due to the presence of MgO particles which were pre-existent in the Mg powders. The MgO particles cause a hybrid reinforcement effect in the Mg-CNT nanocomposites, which surpasses the strengthening effect of the CNTs alone.