Vacuum Brazing TC4Titanium Alloy With Ti-based Amorphous Filler

TC4(Ti-6Al-4V) is the most widely used titanium alloy currently, which hasthe (α+β) two-phase structure and excellent mechanical properties. So it has greatsignificance to find a reliable connection process. Vacuum brazing has manyadvantages such as firmly joints, no impurity gases affects during the weldingprocess, small welding stress and deformation after welding. Amorphous filler haslow melting temperature, good molten spreadability and corrosion resistance.Therefore amorphous filler was chosen to instead of the traditional crystalline fillerin vacuum brazing TC4titanium alloy. This paper used three kinds of amorphousfillers in vacuum brazing of TC4titanium alloy, one was the traditional amorphousfiller Ti37.5Zr37.5Ni10Cu15,its joint was firmly, but brittle. The others amorphousfillers were Ti35Zr35Ni10Cu15Sn5and Ti35Zr35Ni10Cu15Al5, respectively, whichelements Sn and Al were added. The brazing temperature was expected to be lower,the welding quality could be improved effectively and joint brittleness reduced at thesame time.The XRD and DSC curve of the filler showed that three kinds of fillers hadamorphous structure, and the melting point which added Sn and Al was reduced. Thebrazing temperature were920oC,940oC and960oC, respectively, hold heating for20and40minutes. Then cooled to the room temperature in the furnace. By usingmetallographic microscopy, XRD, SEM, EDS, microhardness and electronicuniversal material testing machine, the weld interface morphology, phasecomposition and mechanical property were analysed.The TC4alloy was brazed with three kinds of fillers respectively. By increasingthe brazing temperature and extending the holding time, it made a contribution to thediffusion of elements between TC4and the filler, reduced the number ofintermetallic compounds inside of the welding line. There were a large number ofintermetallic compounds appeared in the welding line at920oC,which were CuTi2,AlNi and NiCu through XRD and EDS. Seriously affected the quality of weldingline. At the brazing temperature of940oC, the welding line of Ti35Zr35Ni10Cu15Sn5 was composed of acicular α-Ti and eutectoid structure, the welding line ofTi37.5Zr37.5Ni10Cu15and Ti35Zr35Ni10Cu15Al5appeared a large number of brittleintermetallic compounds. At the brazing temperature of960oC, the welding line wasall formed by eutectoid structure and lamellar α+β organizations. If the holding timewas extended to40minutes, coarse grains appeared in the welding line when usingthe Ti37.5Zr37.5Ni10Cu15as the filler, the quality of the welding line would be seriouslyreduced.