Brazing Of SiC Ceramic To GH783 Low Expansion Superalloy

SiC ceramic has superior mechanical and thermal physical properties such as chemical property stability,high mechanical properties,wear resistance,good anti-radiation ability and low price,etc.It's a promising structural ceramics as a key material to manufacture automobiles,spacecraft and other high-temperature structural engine components.GH783 low expansion superalloy has a high oxidation resistance and a similar thermal expansion coefficient to the SiC ceramic,which is an ideal material matched with SiC.It's significant to bonding of SiC ceramic to GH783 alloy for the future development of new high temperature,anti-oxidation structure.For example,SiC ceramic has been recognized as an promising reflector material,space remote sensing instrument can transmit high quality information from space to earth by using of GH783 alloy as the rack of reflector.In the mechanical industry,the SiC ceramics and the GH783 alloy compound materials available in manufacture the seal packing collar,the spray nozzle and the heat interchanger and so on.In this paper,the brazing of GH783 alloy and the brazing of SiC ceramic to GH783 alloy have been studied to provid a theoretical basis for the application of SiC/GH783 composite components.High frequency induction brazing and vacuum brazing of GH783 alloy to itself were carried out by use of Ag based filler metals and Ti based filler metals in this study.The Ag-based filler metals are Ag-Cu eutectic solder ,Ag-25.2Cu-10Sn and Ag-25.2Cu-10Zn,Ti-based filler metal is Ti75Cu;Vacuum brazing of SiC ceramic toGH783 alloy was carried out by use of Ag72Cu-Ti filler metals in this study.The microstructure of brazed joint was investigated and analyzed using SEM and XRD.The shearing strength of the joints was detennined.The effect of the technological parameters,adding element on interface structures and joint strength was discussed.The experiment result showed that both the Ag based filler metals and Ti75Cu filler metals have a good wetting properties for GH783.The brazed joint connected dense without pores,cracks and other welding defects.The thickness of interface reaction layer between Ag based alloy and GH783 alloy is small.The thickness of interface reaction layer between Ti75Cu alloy and GH783 alloy is great.Additions of Zn or Sn element into Ag-Cu eutectic filler material enhanced the wettability for GH783,improved the joint shear strength.Under the conditions of heating current 540～600A,heat preservation electric current 300～400A, heating time 20s,keeps warm 4s,cools 2s, the brazed GH783 alloy using the Ag-Cu eutectic solder,Ag-Cu-10%Sn and Ag-Cu-10%Zn alloy attachment shearing strength respectively is 146MPa,165MPa,187MPa.As using of Ti75Cu filler metals,shearing strength was up to 80MPa at the brazing temperature 950℃for 10min.The fracture showed that the fracture mechanism of brazed GH783 joints with Ag-Cu and Ag-Cu-10%Zn filler metal is ductile fracture,but the fracture mechanism of brazed GH783 joints with Ag-Cu-10%Sn and Ti75Cu filler metal is ductile mixed brittle.As breazing of SiC ceramic to GH783 alloy using Ag72Cu-Ti filler metals,there were interface reaction between filler metals and both parent materials.The interface reaction layer close to the ceramic is TiC and Ti-Si compounds.The interface reaction layer close to the GH783 alloy is FeTi,Fe2Ti,Ti2Co,TiNi and TiCu mixed phases.The middle part of the joint was Ag-riched phase ,Cu-riched phase and Ag-Cu eutectic phase.The thickness of reaction layer increased with the increased of the Ti content,the breazing temperature and the holding time.The amount of Ti,bonding temperature and holding time have a significant impact on brazed joint shear strength of SiC/GH783 joint at room temperature.The activity of Ti in filler metal has a direct impact on the interfacial reaction.If the activity of Ti is relatively low,the chemical reaction between the filler metal and base metal will be insufficient, even difficult,the joint strength is very low.If the amount of Ti excessive,the melting point of filler metal will increase,increase the number of intermetallic compounds,increase the brittleness of joint,lead to joint strength low,so the amount of Ti should be moderate.When bonding temperature is low,the atoms dissolution,diffusion and solid solution between the base metal and filler metal is not sufficient,its difficult to achieve a good metallurgical bonding,in particular,the reaction with SiC ceramics is insufficient,there is no continuous and effective reaction layer,which will lead to very low joint strength.When the brazing temperature is too high,the reaction generates a new layer and brittle phase,and the thickness of interfacial reaction layer will increase,leading to internal residual stress increase,which will reduce the joint strength.The impact of holding time on the joint strength of SiC/AgCuTi/GH783 is similar to brazing temperature,impliment also through interface reaction and the elements spread.When the holding time is very short,the atomic diffusion and response between the filler metal and base materials is insufficient,interfacial reaction between SiC ceramic and the GH783 is less, it is difficult to achieve effective metallurgical bonding,and thus have lower joint strength.When the holding time is too long, the interfacial reaction is too intense,the number of solid solution will reduce and the thickness of generated reaction layer will grow up,too much residual stress cause lower joint strength.Therefore there is a optimize value for the brazing temperature and the holding time. As using of Ag72Cu-Ti filler metals to braze SiC ceramic to GH783 alloy,shearing strength of the brazed joint was up to 35MPa when the content of Ti was 5wt%,brazing at 950℃for 10min.