Research On Brazing Process And Mechanism Of High Nb Containing TiAl/GH3536 Heterogeneous Honeycomb Structure

In order to give full play to the outstanding advantages of lightweight structure and promote the application of honeycomb sandwich structure in hypersonic vehicle,in this paper,in view of the shortcomings of the current application of metal based honeycomb structure,it is proposed to use high Nb containing TiAl alloy(TAN)as honeycomb panel,GH3536 alloy as honeycomb core to prepare heterogeneous honeycomb sandwich structure,and to study the brazing process and connection mechanism of heterogeneous honeycomb structure.The evolution rule of joint interfacial structure is studied,the relationship between interfacial structure and mechanical properties is established,the mechanism of brazed joint is clarified,the joint forming,thickness of brazed joint and the erosion degree of core are regulated by reasonable adjustment of brazed process,and the mechanical properties of honeycomb joint are evaluated by mechanical property test and finite element simulation.In order to prepare TAN/GH3536 heterogeneous honeycomb structure,it is necessary to strictly control the dissolution of ultra thin wall honeycomb core base metal into liquid filler and the diffusion of low melting point elements B,Si into core alloy in amorphous BNi-2 filler.The results show that the typical interfacial structure of joints is TAN/B2+?₃/?₄+(Ni-Ti)-B/?+(Ni-Ti)-B+Cr B+G phase/GH3536.When the brazing temperature is increased or the holding time is prolonged,the thickness of?₃/?₄compound layers and the brazing seam are gradually increased,the black phase Cr B is coarsened,and the number of point(Ni,Ti)-B is reduced.In the cooling stage after brazing,slowing down the cooling rate to 2°C/min can effectively eliminate the crystal crack at the brazing seam.The main fracture mode of the joint is brittle fracture.TAN/BNi-2/GH3536 heterogeneous honeycomb joint is a T-shaped joint,and a large amount of boride is easily enriched near the base metal and the brazing angle.The basic reason for the honeycomb core erosion is the excessive dissolution of the core into liquid filler and the diffusion of element B to the core side,which leads to the precipitation of a large number of borides.Increasing the brazing temperature or prolonging the holding time has a significant effect on the erosion of the honeycomb core,and the honeycomb core appears fusing easily,while increasing the brazing thickness has little effect on the erosion of the honeycomb core.When the optimum process parameter(1080°C/5min/100?m)is selected,the erosion degree of core wall is small and the joint is well formed.The tensile strength of honeycomb joint reaches the maximum value of22.4 MPa,and its ultimate elongation is 30.7%.The test pieces of TAN/GH3536 heterogeneous honeycomb structure are well brazed.X-ray examination shows that the brazing rate is 98%,the compressive strength at room temperature is?19 MPa,and the compressive strength at high temperature(850?)is 8.8 MPa.The compression deformation process can be divided into two stages:Stage I(elastic+plastic deformation)and Stage II(honeycomb core crushing+compaction).In the simulation of flat compression deformation process,the stress of Stage I is mainly concentrated in the joint of honeycomb core and panel,and the wall of honeycomb core begins to buckle;in Stage II,the honeycomb core loses its stability and deformation,the bearing capacity of honeycomb plate drops sharply,the stress concentration extends to the joint of panel and core,and then the honeycomb core is gradually folded and compacted.