Papers by Author: Hui Zhao

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Authors: Hui Zhao, Zhen Liu, Zhong Han
Abstract: Characteristics of ceramic coatings on AM50 magnesium alloy by micro-arc oxidation in silicate and phosphate electrolytes have been investigated in this study. This study reveals that the thickness of the ceramic coatings increases with the treated time in both electrolytes, the growth rate of ceramic layer in phosphate is faster than that in silicate electrolyte. The surface roughness of the ceramic coating formed in phosphate electrolyte is higher than that formed in silicate electrolyte. The coatings formed in silicate, containing a thicker inner barrier layer and a thinner outer porous layer, consist of MgO, Mg2SiO4 and MgSiO3 phases. For the coatings formed in phosphate, the outer porous layer is thicker than the inner layer, it consist mainly of MgO and MgAlO4 phases.
Authors: Li Xin, Ping Liu, Hui Zhao, Sheng Long Zhu, Fu Hui Wang
Abstract: The depth distribution of the residual stress in graded (Ti, Al) N coating deposited on steel by arc ion plating was measured by the Stripping Layer Substrate Curvature Technique, and the effect of graded (Ti, Al) N and mono-layered (Ti, Al)N coating on the fatigue properties of 1Cr11Ni2W2MoV stainless steel were investigated. The depth distribution of the residual stress in mono-layered Ti70Al30N and TiN were also measured for comparison. The results show that the residual stresses in the coatings are compressive, which increase gradually from the coating/substrate interface and reach a maximum value at the middle region, then decrease until the surface. Compared with TiN and Ti70Al30N, the stress maximum value in the graded coating is nearer to the coating surface. It is also shown that the fatigue strength of the graded (Ti, Al)N and Ti70Al30N coated samples are superior to that of the uncoated substrate. The improvement of the fatigue properties for the coated samples is thought to be attributed to the hard coatings with high compressive stress.
Authors: Wei Lv, Hui Zhao, Zhong Han, Zhen Liu
Abstract: Effect of pulsed high-energy electron beam on the surface modification and the state of surface layer and wear resistance of AZ91 magnesium alloy have been investigated in this study. Optical microscope (OM) and X-ray diffraction (XRD) were employed to characterize the microstructure and phase composition of the modified surface layer. It was found that the thickness of melted layer on the surface varied with electron beam current and the numbers of pulses, the treated surface layer exhibited higher hardness than AZ91 alloy. The friction coefficient and the wear volume of AZ91 alloy after electron beam treatment decrease markedly. The wear resistance of treated samples were significantly improved, which may be attributed to high hardness as a result of grain refinement.
Authors: Hui Zhao, Zhong Han, Zhen Liu
Abstract: This study is concerned with the effect of high energy ion beam irradiation on surface properties of AZ91 magnesium alloy. The study included a characterization of ion beam surface modification zone in terms of microstructure, and mechanical properties like nanohardness, wear, and corrosion resistance of the surface layer were studied in details. Nanohardness of the modification layer was improved about 2 times as that of the as-received AZ91. The corrosion resistance of the modified layer was significantly improved in NaCl solution because of refined grains. The wear resistance of the modification layer was also improved as compared to as-received AZ91.
Authors: Hui Zhao, Chun Yan Du, Jin Hua Yang, Xiao Hui Wang
Abstract: High Current Pulsed Electron Beam (HCPEB) was employed to treat Ti-6Al-4V alloy subjected to micro-arc oxidation. The surface morphology and phase composition of surface film were investigated, as well as the wear and corrosion resistance. The results show that the coarse porous ceramic coating becomes smooth and compact after electron beam treatment. High temperature stable rutile phase increases, and low temperature stable anatase phase reduces. The friction coefficient of composite coating reduces obviously and stabilizes at 0.2, and the wear resistance is improved. The increased corrosion potential and decreased corrosion rate exhibits an enhanced corrosion resistance.
Authors: Hui Zhao, Ji Chen, Zhen Liu
Abstract: The coating formed on AM50 magnesium alloy by microarc oxidation (MAO), using DC pulse power in Na2SiO3 solution. The oxide coating contains a loose layer and a compact layer, the loose layer consisting of MgO, Mg2SiO4 and MgSiO3 phases and the compact layer mainly of the MgO phase. The curves of hardness (H) and elastic modulus (E) across the coating are similar, from the surface to the interior of the coating, H and E increase, and both of them exhibit a maximum value at the same depth of the coating. After MAO treatment, the mechanical properties, such as hardness and elastic modulus, can be improved, and the microstructure of the alloy substrate has not been changed.
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