Papers by Author: Wan Chang Sun

Abstract: A novel Co-WC composite coating was deposited on the surface of high speed steel (HSS) substrate by an energy-efficient method of electrodeposition. The effects of process parameters on friction and wear properties of the composite coatings were evaluated, and the worn morphologies of Co-WC composite coatings were investigated by scanning electron microscopy. Results revealed that the incorporation of WC particles can significantly improve the wear resistance of the coating. As the current density was increased to 6.5Adm^-2 and the WC concentration was increased to 35g/L, the Co-WC composite coating had the lowest friction coefficient and wear loss.

Abstract: In this research, micro-hardness and wear resistance of two types of electroless coatings were investigated including Ni-P and Ni-P-B₄C composite coatings. Dispersible B₄C particles and electroless Ni-P alloy were codeposited on carbon steel by electroless plating and then heat treated at 200, 400 and 600 °C for 1 h, respectively. The cross-section morphology and microstructure of the composite coatings were characterized. Meanwhile, the micro-hardness and tribological behavior of composite coatings were evaluated. The results showed that the Ni-P-B₄C composite coating presents better wear resistance in comparison with that of Ni-P coating. The Ni-P-B₄C composite coating with heat treated at 400 °C exhibits high micro-hardness and good wear resistance, which the highest hardness is 1200 HV, the minimum wear weight loss is 0.12 mg and the lowest friction coefficient is 0.2054.

Abstract: Ni-P-multi-walled carbon nanotubes (Ni-P-MWNTs) composite coating was successfully co-deposited on 45 steel substrate by electroless plating. The microscopic morphology of Ni-P-MWNTs composite coating was observed by SEM. The influences of CNTs concentration in plating bath on the microstructure and corrosion resistance of the composite coating were investigated. The results indicated that the deposited composite coating shows dispersed CNTs and continuous Ni-P matrix, and there are no pores and cracks and other defects at the interface between the substrate and composite coating, and the thickness of the composite coating is about 50 μm. The Ni-P-MWNTs composite coating with 0.3g/L CNTs in bath displayed the best corrosion resistance, the corrosion potential of the composite coating is-0.372V.

Abstract: Ni-B/Ni-B-B4C composite coatings on the substrate of medium-carbon steel (45#) were successfully fabricated by electroless plating in a low temperature bath. The corrosion resistance of Ni-B coating were examined by using electrochemical workstation. The results indicated that there are no pores and cracks and other defects at the interface between the substrate and composite coating. It was found that the corrosion resistance of Ni-B coating increased and then decreased with the addition of NaBH₄ increasing, and the best addition in plating bath was about 0.9 g/L. While the corrosion resistance of Ni-B coating heat-treated at 400°C with NaBH₄ addition 0.9 g/L was the worst.

Abstract: Area-selectively liquid-phase sintering (AS-LPS) method was developed to control the coarsening of Si particles in Al/60vol.% Si composites with the help of sol-gel-derived interfacial modification, achieved by pre-coating discontinuous Al₂O₃ film on Si powders. The results show that due to the local presence of less than 1 μm-thick films, Si particles can approximately preserve their as-received size and morphology after being sintered at 950 °C. Whereas, for those prepared by use of the unmodified Si powders, Si phases evolve to several hundred-micron-sized flakes, being similar to the typical eutectic Si in Al-Si casting alloys. It is assumed that the Al₂O₃-film-coated areas at Al/Si interface control the dissolution of Si into Al liquid, while in uncoated areas Al matrix and Si particles bond together by LPS, thus realizing AS-LPS.

Abstract: The growth of microarc oxidation (MAO) coatings on aluminum substrates was controlled via changing solution temperature from 10 to 60 °C. The results show that an elevation of the temperature lowers the applied voltage and the coating thickness. The coating formed in low-temperature solution demonstrates large-sized pores and contains lots of elements only originating from solute such as P, W, and V. On the contrary, numerous small-sized pores disperse homogeneously on the coating synthesized in high-temperature solution. It is assumed that the variation of solution temperature affects the dissolving capacity of the alkaline solution and the adsorptive capacity of solute anions, thus dominating the growth behaviors of MAO coating.

Abstract: Ti(C,N)-based cermets were prepared by pressureless sintering using micron-sized TiC and TiN powders as main starting materials and Ni and Co as metal binders. The fracture micrographs of Ti(C,N)-based cermets were observed by SEM. The effects of metal binder phase content on porosity and mechanical properties of Ti(C,N)-based cermets were investigated. The results show that when sintering at 1450 °C for 50min, typical core/rim microstructure is observed in the cermets, which is compact and distributed homogeneously, the density and relative density are 5.9 g/cm3 and 95.6%, respectively. Intergranular fracture is the main crack propagation mode, with a few of the transgranular fracture, and there are more dimples and tearing ridges in the fracture surface. Using the same sintering process, Ti(C,N)-based cermets with metal binder content of 10%Ni5%Co has a compact microstructure and fine grains, the metal binder phase is dispersed more evenly, the best vicker hardness, bending strength and fracture toughness of Ti(C,N)-based cermets are 15.8 GPa, 885.5MPa and 9.7 MPa·m^1/2, respectively. However, Ti(C,N)-based cermets with Ni replaced of high Co content will generate some brittle intermetallic compound, its toughness is inferior to the metal binder phase, which reduces the strength and toughness of Ti(C,N)-based cermet materials.

Abstract: The atomic diffusion and mechanical properties of as-cast AZ80 magnesium alloy after solution treatment at different time were studied by OM,SEM,EDS as well as tensile testing. The results show that the coarse β-Mg₁₇Al₁₂ phase distributed along the grain boundaries as net microstructure is almost dissolved after solution treatment, and the content of Al that in the α-Mg matrix is well distributed with the solution time prolonged. Because of the β-Mg₁₇Al₁₂ phase reducing and granulating, the function of precipitates phase strengthening was depressed and the hardness (HB) of alloy dropped obviously. However, the tensile strength(σb ) and elongation(δ) enhanced remarkably and the yield strength (σ_0.2) decreased slightly.

Abstract: Abstract. Ni-W-P-Al2O3 electroless composite coating was successfully co-deposited on 45 steel substrate using electroless plating. Optical microscope (OM), X-ray diffraction (XRD) and potentiodynamic polarization were used to analyze the morphology, microstructure and corrosion resistance of the composite coating. The results show that Al2O3 particles co-deposit homogeneously, and the structure of the composite coating as deposited is amorphous and crystallite. After heat treatment, the amorphous structure of the composite coating appears a precipitation transformation. When annealing at 400°C, because of the emergence of crystal defects brought out by the precipitation of crystal phases, the composite coating exhibits the lowest corrosion resistance. As the annealing temperature rising to 600°C, the crystalline structure continually grows up and the precipitation transformation tends to be completed. Then the crystal defects decreases which results in an improvement to the corrosion resistance of the composite coating.

Abstract: Ni-W-P-Al2O3 electroless composite coating was successfully co-deposited on 45 steel substrate using electroless plating. Optical microscope (OM), micro-hardness tester and potentiodynamic polarization were used to analyze the morphology, micro-hardness and corrosion resistance of the composite coating. The effect of Al2O3 concentration in the plating solution on the micro-hardness and corrosion resistance of the composite coating was mainly discussed. The results show that Al2O3 particles co-deposit with Ni-W-P homogeneously. The micro-hardness and corrosion resistance of the coating are improved with the increasing of Al2O3 concentration in the plating bath, and then decrease at a high Al2O3 concentration.