| Silicon carbide is extremely superior structural materials with a number of advantageous properties, such as a good high-temperature strength, thermal conductivity of 88W.m-1.K-1,only 3.1?3.2g.cm-3 density, low coefficient of thermal expansion, excellent thermal shock resistance, acid and alkali corrosion resistance and abrasion resistance. Therefore, SiC ceramic is widely used in the fields of aerospace, chemical filed, nuclear energy,microelectronics and transportation, et al. SiC products with features such as complicated shape or large size can be extended in practical engineering applications. Therefore, the new technology of SiC ceramic joining has important significance.In this study, the preparation of thin composite filler and its joining mechanism and properties in the joining of SiC ceramics were discussed. In addition, the interlayer materials used to join SiC ceramics and TC4 titanium alloys were also studied.Ag-Cu-Ti thin film composite fillers with 10 ?15vol% SiC, TiC or B4C ceramic particles were obtained by tape casting. The slurry with better rheological property was prepared by adjusting dispersant type, dispersant content, binder content and solid content. In this experiment, non-aqueous tape casting was used with castor oil phosphate as dispersant,methyl ethyl ketone /ethanol? volume ratio: 66:34? azeotropic mixture solution as solvent,PVB as binder. The formulation of the slurry was optimized as the following: dispersant content as 5wt.%, binder content as 2.6wt.%, the solid loading as 26vol.%. The thickness and CTE of the composite filler were adjusted by tape casting. The ceramic particles distributed uniformly in the Ag-Cu-Ti matrix and the flexibility of the composite filler can be freely cut into arbitrary shape, which is benefit for joining.The joining effects and microstructure were studied with different volume fraction of ceramic powder. The results showed thin film composite filler can be used to join SiC to SiC at 900? and holding 10 min, and no cracks, pores and other defects exist in the whole interface. TiC and Ti5Si3 phases were found at the reaction layer near SiC matrix. TiB2 and TiC was found around the B4C powder and TiC and Ti5Si3 was proved near the SiC powder.However, there was no reaction with TiC powder. When the volume fraction of the composite filler is 20%SiC, the flexural strength of the joint is up to 260± 19MPa. Ceramic powder, the thickness of the reaction layer near the based material and the interface near the ceramic powder were the main factors to the joining strength.Ta, Nb and W whose CTE is between SiC and TC4 titanium alloys, and Cu with smaller elastic modulus is as interlayer materials to join SiC and TC4 titanium alloys. As a result, Cu as interlayer material is successfully to achieve the joining. The influence of joining temperature and holding time on joint was explored. Based on the microstructure and mechanical properties, it is concluded that the thickness of the reaction layer and the thickness of the diffusion layer are the main factors affecting the joint strength. When the brazing temperature is 860? and aging time was 20min,the bending strength of the joints reach a maximum strength,149.6±10MPa. The strength of the joints was reduced to 14±6MPa after quenching at a temperature of 500? for ten times. Cu oxidation was the main reason for losing the original good plastic deformation, and resulted in the thermal stress of the joint. |
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