The Research Of Bonding Technology Of Directional TiAl Alloys

Aimed at the need of manufacture of aeroengine blades, the bonding technology and interface reaction mechanism of directional solidification TiAl-based alloy are studied. The effects of two braze alloys on interface microstructure and shear strength of the joints are analysed, and the optimum bonding parameters for each braze alloy are determined. In addition, direct-diffusion bonding is introduced to bond directional solidification TiAl-based alloy. Based on the analysis of joint microstructure and shear strength with different bonding parameters, the optimum bonding parameters are obtained. The directional growth rhythm of the joint is also discussed.The qualitative and quantitative analyses of joint microstructure were performed by means of optical microscope, SEM, XRD and microhardness, and the shear strength of the joint was tested. The results showed: for the joints using Ag-Cu-Ti braze alloy, the shear strength of the joint was up to 178MPa with the brazing temperature 870℃, the holding time 15min. The interface structure of one side was TiAl/AlCuTi/AlCu₂Ti/Ag-based solid solution/AlCu₂Ti/TiCu/Ti₂Cu(symmetrical structure). The AlCu₂Ti/TiCu/Ti₂Cu structure in the center of the joint changed to evenly distributed AlCu₂Ti phase with the brazing temperature increased. The joint was fractured in the AlCu2Ti intermetallic compound layer, because the brittle phases helped decrease the joint strength.For the joints using Ti-Zr-Ni-Cu braze alloy, the shear strength of the joint was up to 248MPa with the brazing temperature 1050℃, the holding time 10min. The interface structure of one side was TiAl/the diffusion layer of base metal and braze alloy+Ti₃Al/retained braze alloy+Ti₃Al(symmetrical structure). The joint was fractured in the diffusion layer of base metal and braze alloy, as well as in the retained braze alloy layer, because the brittle phases helped decrease the joint strength.For the direct-diffusion bonding, the joint performance was influenced by interface contact and element diffusion. The shear strength of the joint was up to 294MPa when the bonding pressure kept at 30MPa, the bonding temperature was 1200℃and the holding time was 60min. The recrystal grains at the interface...