Papers by Author: Yang Wu Mao

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Authors: Shu Jie Li, Yang Wu Mao, Yue Hui He
Abstract: Joining of ceramics is of importance from both technical and economical points of view. Brazing is a widely used process to join ceramics. In order to increase the working temperature and weld strength of joints, a high temperature brazing process using Ni-Cr-SiC powders (consisting of Ni, Cr and SiC powders) as filler to join recrystallized SiC ceramic has been investigated. The obtained optimized technological parameters are joining temperature of 1360°C, holding time of 5min and filler mass of 280mg. Under these conditions the maximum relative bending strength of joints, 70.5%, is achieved. Microstructure and phase analysis reveals that interdiffusions and chemical reactions take place in the weld zone. A reaction layer, of which the major phase is Ni2Si, exists between the welding base material SiC ceramic and the filler reaction product layer, called as interlayer, of which the major phase is Cr23C6.
2394
Authors: Yang Wu Mao, Shu Jie Li, Yan Zhang
Abstract: Joining of ceramics is of importance from both technical and economical points of view. Joining of recrystallized SiC ceramic to itself has been realized by hot pressing reaction joining process using Ni-51Cr powders (consisting of Ni+51wt%Cr powders) as filler. The optimized technological parameters have been obtained by orthogonal experiment, which are joining temperature of 1150°C, holding time of 20min, joining pressure of 10MPa and cooling rate of 0.25°C/s. The most effective factor to influence the weld strength is joining pressure within the range of testing. Under the optimized conditions, the maximum relative bending strength of joint, 70.7%, is achieved. The microstructure and phase composition of the weld zone were examined by SEM, EDX and XRD. The results show that interdiffusions and chemical reactions take place in the joining process. A reaction layer, which is mainly composed of Ni2Si and Ni3C with a little Cr, exists between the welding base material SiC ceramic and the filler reaction product layer called as interlayer, which is mainly composed of Ni2Si and Cr.
2398
Authors: Yang Wu Mao, Shu Jie Li, Lian Sheng Yan
Abstract: Joining of SiC ceramic to graphite is important from both technical and economical points of view. High temperature brazing of recrystallized SiC ceramic to high strength graphite has been realized using Ni-51Cr (consisting of Ni + 51wt% Cr powders) powders as filler. The obtained maximum three-point bending strength of joints is 32.3MPa, which is equal to 80.8% of the strength of the graphite. Microstructure and phase analysis reveals that interdiffusions and chemical reactions take place in the weld zone. A reaction layer and an interlayer form in the interfacial area. The reaction layer, of which the thickness is about 60-100μm, is contacted with the SiC ceramic. The interlayer with the thickness of about 200μm exists between the graphite and the reaction layer. The reaction layer is mainly composed of Ni2Si, while the interlayer is mainly composed of Cr23C6 and Ni2Si.
1600
Authors: Shu Jie Li, Xiao Kun Yuan, Ting Zhang, Yang Wu Mao, Lian Sheng Yan
Abstract: In order to contribute to the development of the joining technique of Cf/SiC, joining of SiC ceramic to high strength graphite was investigated. This joining has been successfully realized by reaction joining process using a preceramic polymer, polysiloxane, mixed with the active additive Al-Si powder as joining material. The weld strength is strongly affected by the technological parameters and the ingredient ratio (polysiloxane:Al-Si powder). The optimized factors have been obtained by orthogonal experiments, under which the achieved three-point bending strength of the joints is 96.8% of the strength of the welding base material graphite. The microstructure and composition of the weld zone were analyzed by SEM, EDX and XRD. The results show that the joining material has transformed into a densified interlayer with the thickness of about 15μm. Also, diffusion takes place in the interfacial area, which contributes to a sound interfacial bonding. The interlayer is composed of SiC, Al2O3 and Si.
2092
Authors: Hong Li Liu, Wen Wu Zhong, Yang Wu Mao
Abstract: The SiOC foam ceramics were prepared using polyurethane sponge and polysiloxane as raw materials. The effects of the pyrolysis temperature, the concentration of polysiloxane solutions, and the content of SiC nano-powder on compression strength of the SiOC foam ceramics have been investigated respectively. The optimum compression strength of SiOC foam ceramics is obtained at the pyrolysis temperature of 1250°C and the concentration of solution PSO of 0.8 g/ml. Adding SiC nano-powder into PSO can effectively increase compression strength of samples, and the maximum compression strength, 20.8 MPa, is obtained when the content of SiC nano-powder is 5 wt%. Microstructural study reveals that the foam ceramics have an open, uniform and interconnected porous structure with high porosity of 80%.
920
Authors: Shu Jie Li, Min Jian Song, Yun Ling Xia, Yue Hui He, Yang Wu Mao
Abstract: Carbon fiber reinforced CMCs (ceramic matrix composites) are promising high temperature structural materials for aeronautical and astronautical industries. But the engineering application of the materials strongly depends on the joining technique. As a fundamental research, high strength graphite can be used to simulate carbon fiber. The study of wettability of graphite by liquid metals contributes to the development of joining technique of carbon fiber reinforced CMCs. The wettability of graphite/Ni plus Cr system was investigated using the sessile drop method. The contact angle was determined by high temperature photography. The microstructure and composition of the interfacial zone were analyzed by SEM, EDX and XRD. The contact angle of graphite/Ni plus Cr system decreases with increasing the Cr content. It becomes zero, when the Cr content reaches 50wt%. The wetting of graphite/Ni plus Cr system is chemical wetting. The contact angle of the system decreases with increasing the wetting temperature or prolonging the holding time. The higher the Cr content, the more remarkable the effects of the temperature and the holding time on the contact angle are. Microstructure and phase analysis reveals that inter-diffusions and interfacial reactions take place in the wetting process. The reaction products include Cr3C2. The formation of Cr3C2 contributes to the interfacial bonding and results in the accumulation of Cr in the interfacial zone.
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