Study On Brazing Process Of A Fourth Generation Nickel-based Single Crystal Superalloy

Nickel base single crystal superalloy has been widely used in advanced aeroengine hot end components.With the continuous innovation and development of the aviation industry,the fourth-generation nickel-based single crystal superalloys have begun to be applied in engineering,and the related processing and preparation technologies are also developing,the development of high-quality brazing technology is one of the key points.In this paper,the brazing experiments of the fourth-generation nickel-based single crystal superalloys were carried out under different processes,and the microstructure and mechanical properties of the samples were observed,the effects of different processing parameters on microstructure evolution,element distribution and mechanical properties of brazed joint were analyzed.The wetting behavior of solder alloy on the surface of the base metal alloy was evaluated by the seat drop method.The obvious wetting rings were formed at the front of the wetted interface at different temperatures and the wettability angle was less than 20°,which meant that the solder had good wettability.Then the brazing experiment was carried out on the base metal alloy with solder alloy,and a compact and complete brazed joint was obtained.The brazed joint was mainly composed of the non-isothermal solidification zone(NSZ),isothermal solidification zone(ISZ)and base metal(BM).There are a lot of eutectic compounds in the NSZ.The eutectic compounds were identified by EPMA,EDS and TEM,and the solidification sequence of the compound was summarized;The ISZ was mainly composed of γ and γ’ phase composition.In addition,EPMA technology combined with a ternary phase diagram was used to analyze the characteristic elements in the base metal alloy.The segregation of Si and Ru was found,but they were still dissolved in the γ solid solution.The microstructure of brazed joints under different process parameters was analyzed.The results show that with the increase of brazing temperature or brazing time,the volume fraction of borides in the joint decreased,the width of ISZ increased,the distribution of Ni,Co,Cr,W in the joint became more and more uniform.In addition,with the increase of brazing temperature,the position of the boride gap was gradually changed from γ solid solution transformation γ and γ′ phase.Compared with the brazing temperature,the brazing time has little effect on the above.The high temperature tensile and endurance properties of brazed joints under different process parameters were tested.The results show that the tensile strength and endurance life of brazed joints increases with the increase of brazing temperature or brazing time,and the maximum tensile strength of joints brazed at 1290 °C for 60 min was 766 MPa,the maximum endurance life was 1421 hours;The fracture location occurred in the center of the joint without obvious necking and plastic deformation;With the extension of endurance life,the fracture mode changes from quasi cleavage fracture mode to mixed fracture of quasi cleavage fracture and microporous polymerization.The cracks begin with micropores and brittle phases,extend to sub-grain boundaries,and finally fracture.The experimental results are helpful to better understand the microstructure characteristics of the fourth-generation single-crystal nickel base superalloy and provide references for further optimizing the process parameters of brazed joints.