Kang Cheung Chan

Bio: Kang Cheung Chan is an academic researcher from Hong Kong Polytechnic University. The author has contributed to research in topics: Amorphous metal & Deformation (engineering). The author has an hindex of 37, co-authored 290 publications receiving 5461 citations.

Pulse electrodeposition of nanocrystalline nickel using ultra narrow pulse width and high peak current density

Abstract: The synthesis of nanocrystalline nickel by electrodeposition has been studied for more than 10 years. However, most attention has been on the adjustment of bath composition or development of new chemical additives. In this paper, a new method was developed to synthesize bulk nanocrystalline nickel without using any additives. Pulse plating with ultra narrow pulse width and high peak current density was employed to increase the deposition current density and the nucleation rate. At an on-time of 10 μs and an off-time of 90 μs, it was found that different surface morphologies, grain sizes, textures, and hardness were obtained at different current densities. Grain sizes ranging from 50 to 200 nm were obtained when the current density varied from 300 to 60 A dm −2 . The preferred orientation of the nickel deposit changed from a weak (2 0 0) fiber texture to a strong (2 0 0) fiber texture when the peak current density increased from 40 to 100 A dm −2 . It was obtained however that the intensity of the (2 0 0) fiber orientation decreased when there was a further increase in the current density. The hardness of the nickel deposit was also found to increase with increasing peak current density when it changed from 20 to 150 A dm −2 , but the hardness tended to decrease when the current density was above 150 A dm −2 . These experimental findings are considered to relate to the change in cathodic overpotential which affects both the grain size, the internal stress, the porosity, and the preferred orientation.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Laser Material Processing

Abstract: In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).