Papers by Author: H. Cheng

Abstract: The Co-base alloy laser cladding layer was coated on the 2738 mold steel surface by using the TJ-HL-5000 transverse-flow CO2 continuous laser. The morphology and hardness were investigated by metallography microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness tester. The metallography microscope and SEM investigations show that from interface to surface along the cross section direction, the cladding layers consist of plane crystal layer, columnar crystal layer, dendrites layer and surface cellular crystal layer, respectively. XRD results indicate that the cladding layer is made of γ-Co, Cr23C6, MoC, FeCr and Co3Mo2Si phases. The micro-hardness of the laser cladding coating was about 900-1100HV1, 3 times or more of the steel substrate. And the mechanisms of microstructure formation and strengthening are investigated.

Abstract: Thermoelectric (TE) materials are attracting renewed attention for clean energy conversion. Reducing the dimension of materials to 2D/1D (e.g. thin film and nanowire) is one major approach to achieve high figure of merit (ZT) in the existing TE materials system. Electrodeposition has been widely used in fabricating various low dimensional TE materials. However, electrodeposition behavior of CoSb3 skutterudites is rarely reported. In this work, we report the co-deposition behavior of cobalt and antimony in citric based solutions by electrodeposition. The effects of deposition potential and concentration of cobalt and antimony containing precursors were studied. The focus of the study will be on the crystalline properties and chemical composition of the deposited films.

Abstract: Skutterudite materials have received great attention because their promising properties for thermoelectric (TE) applications. Among the family of skutterudites, CoSb3 has been intensively investigated due to its large electrical conductivity and Seebeck coefficient. However, its thermal conductivity is too high to make it an effective TE material. Nanostructuring of CoSb3 has the desirable effects of reducing its lattice thermal conductivity as the point imperfections or grain boundaries can scatter phonons (heat carrier) more effectively than electrons (charge carrier). In this study, nanostructured CoSb3 was synthesized by solvothermal routes using CoCl2·6H2O and SbCl3 as precursors dissolved in anhydrous ethanol with the reaction temperature kept at 240°C. In addition to the CoSb3 phase, other Co-Sb compounds were also formed during the reaction process. In this paper, we investigated the effects of processing parameters, such as concentration of CoCl2·6H2O, SbCl3 and NaBH4 in ethanol and thermal duration of solvothermal synthesis, on the yield of CoSb3 phase.