Papers by Author: C.Y.H. Lim

Abstract: In this study, pure aluminum reinforced with interconnected galvanized iron mesh and Ni particulates was synthesized using an innovative disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of composite samples showed uniform distribution of Ni and Al-Ni based intermetallic particulates in the matrix material, good interfacial integrity of aluminum matrix with iron mesh and Ni particulates and the presence of minimal porosity. Results of thermal mechanical analysis indicate a decrease in the average coefficient of thermal expansion of the aluminum matrix with the use of hybrid reinforcements. Mechanical characterization also revealed that the coupled use of galvanized iron mesh and Ni particulates lead to an improvement in the hardness, dynamic modulus, 0.2% yield strength and UTS but ductility was adversely affected. An attempt is made to correlate the use of hybrid reinforcements with the improved properties exhibited by the synthesized composites.

Abstract: This paper explores the wear characteristics of nanocrystalline Mg-5%Al-5%Nd, synthesized by mechanical alloying. Pin-on-disc unlubricated sliding wear tests were conducted against a hardened tool-steel counterface under loads of 10 and 30 N, and within a velocity range of 0.2-5.0 m/s. Despite its appreciably superior mechanical properties, the nanostructured alloy did not exhibit the expected improvement in wear resistance when compared to its conventional microngrain- sized counterpart; in fact, the former performed worse when testing conditions became more severe. Scanning electron microscopy (SEM) suggested that extensive delamination in the nanocrystalline alloy was the primary reason for its high wear rates. This wear mechanism was promoted by the presence of MgxNd dispersiods, which were found only within the nanocrystalline material. These compounds likely resulted from the long duration (20 hrs) of ball-milling, which was the mechanical alloying technique employed to reduce the grain size of the final alloy.

Abstract: In the present study, two sets of powder metallurgy copper samples, with grain sizes of 99 nm and 63 nm, respectively, were investigated under different tribological conditions. The wear behavior of these materials was studied through a pin-on-disc configuration using sliding velocities of 0.5, 1 and 2 m/s with normal loads of 10 and 30 N. The finer-grained copper was able to outperform (by between 4- to 16-fold) its coarser-grained counterpart under severe test conditions, but no advantage was observed when conditions were milder. Scanning electron microscopy revealed the dominant wear mechanisms to be oxidative wear under mild sliding, with a transition to adhesive wear with increases in sliding speed and normal load.