Research On Process Of Vacuum Brazing For TU2 Free-oxygen Copper And Hafnium

In order to meet the requirement of the air plasma electrode, the process of vacuum brazing for TU2 free-oxygen copper and hafnium was investigated. By metallographic microscope, SEM, EDS, XRD and shearing test, the effects of different processing parameters on microstructures and properties of the joints were analyzed. The electrodes which were made of the samples after brazing were used in the process of air plasma cutting. That can verify the properties of the brazing joints and improve further the production technology.With BAg72Cu brazing filler metal, the vacuum brazing process of Hafnium and free-oxygen copper were carried out. The results show: The main microstructure of brazing joints was composed of three main areas with different patterns--the black area beside Hf, the mid area of Ag-Cu eutectic structure and the area of mountain-like or cobble-like copper based solid solution near Cu.With the increase of brazing temperature, the black area and the area of copper based solid solution both become wider, however the mid area of Ag-Cu eutectic structure become narrower. The brazing temperature influenced the shear breaking stress slightly. All the shear breaking stress of the joints are over 160MPa, and the differential value of the maximum and minimum is just 20MPa.When brazing at 815℃, the obvious cobble-like structures did not appear in the brazing joints with the extending of the holding time, instead, mountain-like structures increased and enlarged a little. Meanwhile,the black area became wider and the change of its width accorded with the Second Diffusion Law. At the same time, the effect of holding time on shear breaking stress is not significant.With the increase of the fit-up gap, the mountain-like and cobble-like structures increased and grew up. The width of the black area didn't change obviously. Copper based solid solution appeared near the black area, and some of them even became dendrites. And that led the joints breaking shear stress decreased significantly Furthermore,increasing fit-up gap would make the location of hafnium filament and base copper become difficult.The electrodes used in the air plasma cutting were good on the whole. They were cutting fast, superior in quality and have longer service life, basically reached the level of foreign high-quality electrodes. Meanwhile,the electric-heat conduction and service life of the electrodes brazed at lower temperature due to its smaller width of the black area are better than the one at higher temperature.The optimum technology parameter is: brazing temperature 815℃, holding time 35min, fit-up gap 0.10mm, heating rate 10℃/min, furnace cooling.