Papers by Author: Sheng Kai Gong

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Authors: He Fei Li, Zhao Hui Zhou, Hesnawi A, Kuo Jiang, Sheng Kai Gong
Abstract: Thermal barrier coatings with one-layered/ two-layered NiAl bond coat were produced by electron beam physical vapor deposition (EB-PVD). Compared to the TBC with one-layered bond coat, the TBC with two-layered bond coat improved the thermal cycling resistance significantly. The failure mechanism of the two-layer NiAl bond coat TBC was investigated in this paper.
Authors: Chun Xia Zhang, Fu Shun Liu, Sheng Kai Gong, Hui Bin Xu
Abstract: Two layer thermal barrier coatings (TBCs) were prepared by EB-PVD (Electron Beam-Physical Vapor Deposition) at different substrate temperatures in the range of 823 to 1123K, and their microstructure was investigated with SEM and AC impedance as a function of substrate temperature and thermal cycling time. YSZ layer of all TBCs samples is in column structure, but the grain size and growth orientation are different with substrate. In this research, impedance spectra (IS) was measured as a function of thermal cycling between 1323K and 298K for these thermal barrier coatings. Grain boundary and bulk can be distinguished from analysis of AC impedance spectroa to provide information about the relation between microstructure and electric properties.The change in IS until failure was found to be related with the thickness, microcracks and macrocracks of TGO and the change in the interfacial of TGO/YSZ.
Authors: Yong Wang Kang, Chun Gen Zhou, Sheng Kai Gong, Hui Bin Xu
Abstract: Al-Cu-Fe-Cr quasicrystalline coating was deposited on a substrate of stainless steel by low-pressure plasma spraying (LPPS) method. The corrosion behavior of such coating was studied by polarization in 1mol/l H2SO4 and 0.1mol/l NaOH solutions at room temperature. The polarization curve shows that LPPS Al-Cu-Fe-Cr quasicrystalline coating can turn to passive state both in 1mol/l H2SO4 solution and in 0.1mol/l NaOH solution. The corrosion resistance of the coating is poorer than that of bulk quasicrystal in 0.1mol/l NaOH solution. Moreover, in strong acid solution LPPS Al-Cu-Fe-Cr quasicrystalline coating has more corrosion resistance than 1Cr18Ni9Ti in some potential range ranging from -200mVSCE to -35mVSCE, but in strong alkaline solution the corrosion resistance of the coating is poorer than 1Cr18Ni9Ti.
Authors: Chang Liang Wang, Chun Gen Zhou, Sheng Kai Gong, Hui Bin Xu
Abstract: The cyclic oxidation of thermal barrier coating (TBC) specimens consisting of nickel-base superalloy, low pressure plasma sprayed Ni-24Cr-6Al-0.7Y (wt.%) bond coatings and air plasma sprayed 7.5 wt.% yttria stabilized zirconia top coatings was studied at 1050°C in air, (air + 5%H2O), O2 and (O2 + 5%H2O) respectively. The oxidation kinetics of the TBC in each test environment accords with parabolic law at the initial stage and obeys almost liner law at the final stage. The cyclic oxidation life of the TBC is 500h (1h/cyc) in O2 and (O2 + 5%H2O) and 900 h in air and (air + 5%H2O). The SEM observations indicated the oxide formed along the bond coat and top coat interface after failure at 1050°C in different environments are all consisted of Al2O3, Ni(Al,Cr)2O4, NiO and Cr2O3.
Authors: Jian Xu, Xin Qing Zhao, Sheng Kai Gong
Abstract: The effect of Mo on the oxidation behavior of TiNiAl at 1073K has been investigated. It is found that 1at.% Mo addition can increase the diffusion of Al in the alloys and promote the formation of dense and continuous Al-rich oxide layer. Therefore the oxygen diffusion can be effectively impeded and the oxidation behavior of TiNiAl is improved. The observation of the cross-sectional oxidation layer showed that beneath the top oxide scale a Mo-rich oxide layer formed. Because the oxide of Mo is volatile at high temperature, voids formed in the oxide scales during the oxidation process. 3at.% Mo addition could cause cracks between the oxide scale and the substrate, resulting in poor adhesion of the oxide scale to the substrate.
Authors: Wen You Ma, Ya Fang Han, Shu Suo Li, Yun Rong Zheng, Sheng Kai Gong
Abstract: The effect of Ru on the microstructure of a high content refractory elements nickel base Superalloy has been studied in the present investigation. The results showed that, the adding of 3%Ru did not prevent the precipitation of TCP phase during high temperature exposure, and even accelerated the formation of TCP phase,however the addition of Ru decreased the growth rate of μ phase significantly. In addition, the adding of Ru decreased the solving temperature of γ/γ′ eutectic by 5°C, and increased the tendency of γ′ rafting during high temperature exposure.
Authors: Dong Bo Zhang, Sheng Kai Gong, Hui Bin Xu
Abstract: Conventional two-layered structure thermal barrier coatings (TBCs) with different pre-oxide layer thicknesses were produced by EB-PVD onto Ni-based superalloy. The pre-oxide layer with different thicknesses was formed after vacuum heat treatment for 2 hours and before ceramic deposition by heating the bond coat to 1323K in air for different times. It has been found that with pre-oxide layer thickness increasing from 1μm to 3.1μm, the growth rate of thermally grown oxide (TGO) increased during thermal cycling test and the thermal cyclic lifetime of TBCs decreased from 730hs to 400hs Two failure modes were observed for TBCs with different pre-oxide layer thicknesses and different TGO layer growth rates.
Authors: Xiaoping Han, Yao Zhang, Sheng Kai Gong, Hui Bin Xu
Authors: Sheng Kai Gong, He Fei Li, Hesnawi A, Kuo Jiang, Li Dong Sun
Abstract: The influence of YSZ addition on isothermal oxidation behavior of EB-PVD NiAl bond coatings on Ni based superalloy was investigated. The oxidation rate of the YSZ doped bond coat is almost the same as the bond coat without the doping of YSZ. Four different areas exist on the surface of the coating after 100 h oxidation, including the spalled area, the high Al-contained area, the high Cr&Ni-contained area and the high Ti-contained area.
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