| Due to the properties of heat and vibration-resisting, multi-micropore, adjustable thermal expansion property, corrosion-resisting, excellent thermal stability and large high-temperature viscosity, SiO2 glass ceramic is bonded to TC4 alloy (Ti-6Al-4V) to manufacture engine bay in aerospace fields. So far, ceramic bay is mechanically bonded to the combustor at external diameter, resulting in large negative mass. Therefore, reliable joining of SiO2 glass ceramic to TC4 alloy is expected in the present work to decrease the negative mass and improve the gas impermeability at the same time. High quality joining of SiO2 glass ceramic to TC4 alloy is successfully realized by brazing, and the optimal brazing parameters are identified as well as the bonding mechanism.SiO2 glass ceramic was brazed to TC4 alloy using AgCu/Ni composite interlayer. According to several testing methods, the typical interface structure was identified to be TC4 alloy/acicularα-Ti/Ti(s.s)+Ti2(Cu,Ni)+Ti2(Ni,Cu) hypereutectoid structure/ Ti(s.s)+Ti2(Cu,Ni)+Ti2(Ni,Cu) hypereutectic structure/Ti2(Ni,Cu)+Ti2(Cu,Ni) compounds/Ti(s.s)+Ti2(Cu,Ni)+Ti2(Ni,Cu) hypereutectic structure/Ti4O7+TiSi2/SiO2 ceramic when the joint was brazed at 970℃for 10min. Under this condition, the largest shear strength 110MPa was reached. The fracture occurred on SiO2 glass ceramic because of its lower strength than that of each interfacial layer.Based on the brazing experiments under different parameters, species of the interface products were hardly influenced by the brazing temperature, but it was not the condition for the hypereutectic structure near SiO2 /braze interface. When the brazing temperature was low, island-like Ti(s.s)+Ti2(Cu,Ni)+Ti2(Ni,Cu) hypereutectic structures were distributed at SiO2 glass ceramic side. As the temperature rised to 970℃, these structures had distributed continuously near the reaction layer at ceramic side, and they were thickened as the temperature increased to 980℃. Ti4O7+TiSi2 layer was hardly influenced by the brazing temperature. The effect of holding time on Ti(s.s)+Ti2(Cu,Ni)+Ti2(Ni,Cu) hypereutectic structures was similar to that of temperature, however, effect of time on Ti4O7+TiSi2 layer was quite different, the holding time longer, the reaction layer thicker.According to the observed interfacial microstructure, joint formation was divided into the following seven stages: physical contact of the brazed surfaces; melting of AgCu and interaction between liquid AgCu and Ni foil, TC4 alloy; formation of eutectic liquid, coexistence of Ti, Cu, Ni, Ag, and appearance of reaction products at ceramic side; dissolution of TC4 alloy, homogeneousness of liquid filler and width increase of reaction layer at ceramic side; stop of dissolution of TC4 alloy and reaction at ceramic side, formation of hypereutectoid microstructure; formation of hypereutectic microstructure Ti(s.s)+Ti2(Cu,Ni)+Ti2(Ni,Cu); solidification of intermetallic compounds on joint center. Effect mechanisms of element Ag, Cu, Ti and Ni on joint formation were studied. Among these elements, Ti is the most important. Ti dissolved from Ti alloy by eutectic reaction and diffused to ceramic side, resulting in the reaction layer formation and excellent spreading of liquid filler on SiO2 glass ceramic.Metallurgy reaction at Ti alloy side was researched. The result was that eutectic liquid tended to appear at Ti alloy side instead of Ni filler side, because diffusion coefficient of Ni to Ti is much larger than that of Ti to Ni. Concentration of Ti in the liquid filler after dwelling was obtained. Dissolution thickness X of TC4 alloy after brazing was calculated based on the concentration of Ti, and this is meaningful to control the dissolution of Ti alloy and prevent the erosion of base material.Spreading and interface reaction of liquid filler on SiO2 glass ceramic were investigated. Growth kinetics equation of reaction layer at SiO2 side was attained according to the process property of active element Ti, realizing the micro-controlling of reaction layer growth via the brazing temperature and dwelling time.
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