Brazing Process And Mechanism Of Lamellar Ti₃Al To Itself Or To Inconel 718

Ti₃Al-based alloy has some good properities such as low density, high specific strength. But the application is limited by the poor formability. Ni-based alloy, however, has the advantage of high strength, high plasticity and good oxidation resistance, while the density of Ni-based alloy is much higher than Ti₃Al-based alloy. So the combination of the two different material would take full advantage of them in the application of aerospace. The key point is the join of Ti₃Al-based alloy with Ti₃Al-based alloy and Ti₃Al-based alloy with Ni-based alloy. In this paper, the Ti₅Si₃/Ti₃ Al composite sheets（Ti₅Si₃/Ti₃ Al for short） withTi₅Si₃/Ti₃ Al and Ti₅Si₃/Ti₃ Al with Ni-based alloy were brazed with the Ti-Zr-Cu-Ni filler material. The brazing parameters including the thickness of the filler material, the brazing temperature and the holding time were changed in the experiment. The microstructure evolution mechanism of the joints was discussed.According to the investigation, Ti₅Si₃/Ti₃ Al and Ti₅Si₃/Ti₃ Al was successfully brazed with the Ti-Zr-Cu-Ni filler material and no void or crack existed in the joint. The maximum room temperature shear strength of 224 MPa was obtained when the joints brazed with 180 μm Ti-Zr-Cu-Ni filler metal at 900 oC for 5 min. The typical microstructure was α-Ti and the eutectoid structure α-Ti+（Ti,Zr）2（Cu,Ni） in the weld, while the diffusion reaction zone consisted of α2-Ti₃ Al. The diffusion of Al atoms from Ti₅Si₃/Ti₃ Al plays an important role in the microstructure evolution of the joint. With the increase of the brazing temperature, more α-Ti appear in the joint. The shear strength of the joint increased from 224 MPa at room temperature to 405 MPa at 650 oC. owing to the improvement of the plasticity of the joint.Ti₅Si₃/Ti₃ Al and Ni-based alloy could be successfully brazed with the Ti-Zr-Cu-Ni filler material and fine joint was obtained under the appropriate parameters. The maximum room temperature shear strength of 203 MPa was obtained when the joints brazed with 180 μm Ti-Zr-Cu-Ni filler metal at 900 oC for 5 min. The typical microstructure was（Ti,Zr）2（Cu,Ni） containing α-Ti and the eutectoid structure α-Ti+（Ti,Zr）2（Cu,Ni）, the diffusion reaction zone between Ti₅Si₃/Ti₃ Al and weld is α2-Ti₃ Al, while the diffusion reaction zone between Inconel 718 and weld is complex, primarily the parallel dendrite including Ni-Cu-Ti-Al-Nb, Cr-Fe-Ni-Cu and Cr-Ni and the equiaxed grain Cr-Fe-Ti-Cu-Ni. The diffusion of Ni atoms from Inconel 718 played an important role in the microstructure evolution of the joint. With the increase of the brazing temperature, more（Ti,Zr）2（Cu,Ni） containing α-Ti appeared in the joint. The shear strength of the joint increased from 203 MPa at room temperature to 378 MPa at 650 oC, because of the improvement of the intermetallic compound at higher temperature.