The Preparation Of Ordered Porous Ceramic Joint And The Application Study On The Joining Of C_f /sic Composites

Due to combining the advantages of carbon fiber and SiC matrix, carbon fiber reinforced silicon carbide matrix (Cf/SiC) composites exhibit several promising properties such as low density, high specific strength, high fracture toughness and excellent temperature resistance, which made them potentially applied in the fields of aeronautics, aerospace, military and energy. However, Cf/SiC composites are very difficult to directly shape to large or complex component because of the poor processing performance, thus the joining technology is required. Although much attention has been paid on the study of the joining technology, it is still quite far from the practical application. Aimed at the shortages of recent joining technologies, an concept named ordered nanoporous ceramic joint was put forward and studied systematically, which might be potentailly applied in the joining field of Cf/SiC composites.In this paper, the mono-dispersed silica spheres were prepared by st?ber method. The prepared silica spheres exhibit good discreteuniformity, regular shape and the concentrative particle diameter, which are neccesary for preparing the template of the ordered nanoporous materials.In this study, the ordered nanoporous ceramic joints on the Cf/SiC composites were successfully fabricated for the first time by combing template and preceramic polymer techniques. The fabrication process includes four basic steps: (1) the preparation of template joints; (2) infiltrating the polymer solution or melt into the template; (3) pyrolysis of the polymer in the template; (4) removal of the template. The achieved ordered nanoporous ceramic joints contain a homogenous pore stucture with uniform walls and the pores regularly aline at a highly wide range even in three-dimension. The performances of the joints were strongly affected by the technological parameters including the concentration of PCS solution, sintering temperature, heating rate and temperature holding time. The result shows that the optimum condition for preparing the ceramic joint are that the concentration of PCS solution, the sintering temperature, the heating rate and the temperature holding time are of about 40wt%, 1000℃, 5℃/min and 120min, respectively.Two different joining methods, named directly soaking method (DSM) and the method of soaking after the first joining (SJM), were used for the joining of the ordered nanoporous ceramic joints of the Cf/SiC composites. The result shows that the property of achieved joint component from SJM is better than that from DSM, and the bending strength of the joints from DSM and SJM is about 20.5MPa and 82.4MPa, respectively.For SJM technich, the effects of the joining temperature, the heating rate and the temperature holding time on the joining strength of the joints had been investigated, and the microstructure and the composition of the joining layer were examined by SEM and XRD, respectively. The result shows that the optimum technological parameters were 1000℃, 5℃/min and 120min. SEM and XRD analysis of the joint layer proved the successfully preparation of the dense joint structure with the composition of SiC and little amount of free carbon. It is the dense SiC layer between the joints that endows Cf/SiC joining component not only higher joining strength, but also larger potentiality at harsh temperature enviroment.