Research On Process And Mechanism Of TLP Bonded IC10 Single Crystal Superalloy

With the strong demand for bonding and repairment of IC10 single crystal superalloy,the welding experiment was carried out by using transient liquid phase(TLP)diffusion bonding technology,with BNi2 + 0/3/6/9%Al(wt.%)four different types of mixtured-powder as interlayers.The influence of content of Al element in interlayers on microstructure,mechanical properties,fracture behavior and distribution of microhardness was investigated.In addition,the influence of welding parameters on microstructure,mechanical properties,fracture behavior and distribution of microhardness of IC10/BNi2 + 3%Al/IC10 joints was investigated,too.Further more,the effect of Al element on the formation and distribution of microstructure in the joints was analyzed.Finally,based on B element diffusion theory and two-phase model,some issues of TLP diffusion bonding process were calculated.When TLP bonding IC10 superalloy with the utilization of BNi2 + Al interlayer,the main reaction products in the seam were ?? phase?Cr B phase?(?-Ni + M23B6)eutectic structure and few(?-Ni + M23B6 + Co Si2)eutectic structure,and precipitated phases at diffusion affected zone(DAZ)were identified as M5{B,Si}3 and M5B3.With the increase of Al content in the interlayer,the distribution of precipitated phases in the seam was more dispersed.At the same experiment parameter,joints using the BNi2 + 3%Al interlayer reached the maximum shear strength of 570 MPa.When using BNi2 interlayer to fabricate IC10 superalloy,there was a large amount of continuous eutectic structure at the center of the joint,which reduced the mechanical properties of the joint.Once the content of Al element was excessive,as can be observed on the microstructure and fracture morphology,the wetting and spreading ability of the interlayers plunged significantly,and holes emerged,so the mechanical property deteriorated dramatically.The influence of welding parameters on IC10/BNi2 + 3%Al(wt.%)/IC10 joints was discussed.It was found that the bonding temperature had a strong influence on the formation and distribution of the reaction products in the joints.There was a great number of eutectic structure and Cr B phase at the seam,and no precipitates rich Si observed in DAZ at lower bonding temperature.While the joint could complete isothermal solidification and produce precipitates rich Si in DAZ at higher bonding temperature.The holding time also had a certain influence on the distribution of the reaction products in the seam.With the increase of the holding time,the reaction products in the seam had a certain degree of dissolution and diffusion.With the bonding temperature rising from 1040 °C to 1140 °C,the average shear strength of the joints increased from 220 MPa to 550 MPa and then decreased slightly to 480 MPa.As the holding time increased from 0.5 h to 3 h,the average shear strength of the joints increased and then was stable at that level.The elevated temperature tensile strength at 1000 °C of the IC10/BNi2 + 3%Al(wt.%)/IC10 joints were from 85 MPa to 130 MPa.The shear fracture at room temperature was a typical quasi-cleavage fracture,while the tensile fracture at high temperature indicated a mode of intergranular fracture.The hardness of each phase in the joints was measured by nano-indentation test.And the microhardness test showed that the microhardness of the seam was related to the amount and the distribution of existing precipitated phases and eutectic structure.The hardness of the non-isothermal solidification region was higher than that of the parent material and the seam matrix.The results showed that the isothermal solidification stage deviated from the standard TLP models due to the mixture of Al powder in the interlayer.It was no longer characterized by the existence of continuous eutectics and precipitated phases in the center of the joint,but the low melting point liquid phase distributed along the ?? phase boundary.As a result,the eutectic structure and Cr B precipitated along the ?? phase boundary.In the end,based on the B element diffusion theory and two-phase model,the results were calculated as following.When the bonding temperature was 1100 °C,the maximum width of liquid phase zone was 109.88 ?m,theoretical time for the completion of isothermal solidification stage was 9.4 h and the solute concentration of B element at the end of isothermal solidification stage was from 0.0271% to 0.027%.When the bonding temperature was 1140 °C,the maximum width of liquid phase zone was 118.07 ?m,theoretical time for the completion of isothermal solidification stage was 9 h and the solute concentration of B element at the end of isothermal solidification stage was from 0.024% to 0.0239%.