Papers by Author: Hong Song Zhang

Abstract: Effect of substrate conditions, including material type, thickness and radius of substrate, on residual stresses of plasma spraying YSZ / Sm₂Zr₂O₇ TBCs was analyzed through finite element method in this paper. Results show that all residual stresses increse with incresing of thermal expansion coefficient of substrate.Substrate thickness has slight effect on radial residual stress, and it has no effect on axial residual stress and shear stress. Effect of substrate radius on radial stresses can be almost neglected when it is over 18mm. Effect of substrate radius on axial stresses can also be ignored.

Abstract: Effect of substrate conditions, including material type, thickness and radius of substrate, on residual thermal stresses of plasma spraying Sm2Zr2O7/YSZ TBCs was analyzed through finite element method in this paper. The radial and shear stresses of the coating decrease with increasing of distance from the center to edge, and they decrease abruptly at the edge of the specimen, while the axial residal stress increase abruptly at the edge of substrate. All residual stresses increase with increasing of thermal expansion coefficient of substrate. The thickness of substrate has slight effect on the radial residual stress, axial residual stress and shear stress are almost uneffected by substrate thickness. The optimum thickness of substrate is 10mm. Radius of substrate have no effect on radial stress when it is greater than 28mm.

Abstract: In this article the finite element software was used to analyse the values for compressive strength of X-cor sandwich. During the analysis, the failure criteria and materials stiffness degradation rules of failure mechanisms were proposed. The failure processes and failure modes were also clarified. In the finite element model we used the distributions of failure elements to simulate the failure processes. Meanwhile the failure mechanisms of X-cor sandwich were explained. The finite element analysis indicates that the resin regions of Z-pin tips fail firstly and the Z-pins fail secondly. The dominant failure mode is the Z-pin elastic buckling and the propagation paths of failure elements are dispersive. Through contrast the finite element values and test results are consistent well and the error range is -7.6%~9.5%. Therefore the failure criteria and stiffness degradation rules are reasonable and the model can be used to predict the compressive strength of X-cor sandwich.

Abstract: Effect of substrate conditions, including material type, thickness and radius of substrate, on residual thermal stresses of plasma spraying Sm₂Zr₂O₇ TBCs was analyzed though finite element method in this paper. The radial and shear stresses of Sm₂Zr₂O₇ decrease with increasing of distance from the center to edge along radius of specimen, and they decrease abruptly at the edge of the specimen, while the axial residal stress increase abruptly at the edge of substrate. All residual stresses increase with increasing of thermal expansion coefficient of substrate. The thickness of substrate has slight effect on the radial residual stress, and axial residual stress and shear stress are almost uneffected by thickness of substrate. The optimum thickness of substrate is 10mm. Radius of substrate have no effect on radial stress when it is greater than 28mm, and radius of substrate has no effect on axial stress and shear stress of Sm₂Zr₂O₇ TBCs.

Abstract: Y2Ce2O7 ceramic material was prepared by solid reaction at 1600°C for 10h. The phase composition, microstructure and thermal conductivity of this material were investigated. XRD results reveals that single phase Y2Ce2O7 with fluorite structure was synthesized. Microstructure of Y2Ce2O7 was dense and no other unreacted oxides or interphase existed in the interfaces between grains. Because of phonon scattering by oxygen vacancies and difference in atomic mass between substitutional atoms and host atoms, thermal conductivty of Y2Ce2O7 is lower than that of 8YSZ, which implies that this ceramic can be used as novel candidate materials for thermal barrier coatings in the future.

Abstract: In this study, by changing Z-pin’s insertion parameters, the X-cor sandwich was prepared with vacuum curing molding process. The effects of Z-pin’s insertion angle, insertion density and diameter on compression, shear and tension properties were studied. The results show that Z-pin’s insertion parameters can significantly affect the mechanical properties of X-cor sandwich. The compression properties of X-cor sandwich are reduced, while shear properties are improved by the increase of Z-pin’s insertion angle. As Z-pin’s insertion angle increases the tension modulus increases while the tension strength firstly increases and secondly decreases. The mechanical properties increase with the increase of Z-pin’s insertion density and diameter. Compared with the foam core sandwich, the mechanical properties of X-cor sandwich are significantly improved in both modulus and strength.

Abstract: This paper reviews the theory of thermal conduction of ceramic materials with the aim to reduce further the thermal conductivity of plasma sprayed thermal barrier coatings. Methods of reducing thermal conductivity of plasma sprayed thermal barrier coatings including seeking for alternative ceramic materials to 8YSZ, addition of some dopants, preparing nanostructured coating and double-ceramic-layer coating are advised. It is indicated that the combination of colouring plus nanostructured and double-ceramic-layer coating of new ceramic candidate materials of lower thermal conductivity should be an very important research direction in future.

Abstract: The forming mechanism of Dy2Ce2O7 prepared by solid reaction using CeO2 and Dy2O3 as reactants was analyzed by X-ray diffraction method. It is indicated that there is almost no solid solution reaction between Dy2O3 and CeO2 before 1300°C, the Dy3+ cations enter the crystal lattice of CeO2 and substitute sites of Ce4+ cations in the range between 1300°C and 1400°C which resulted in the formation of Dy2O3-CeO2 solid solution. The Dy2O3-CeO2 solid solution transformed gradually into Dy2Ce2O7 after 1400°C and pure Dy2Ce2O7 can be obtained at 1500°C. No other intermediate phases were found in the whole process.

Abstract: Pyrochlore structure oxide (La0.5Sm0.5)2(Zr0.9Ce0.1)2O7 was prepared by mixing the appropriate amounts of ZrO2, La2O3, Sm2O3 and CeO2, followed by reacting at 1600°C for 10 h. It was shown that the thermal conductivity was much lower than that of 8YSZ, which was mainly ascribed to the oxygen vacancies and lattice strain in lattice of (La0.5Sm0.5)2(Zr0.9Ce0.1)2O7.