LARGE GAP JOINING OF TI-6AL-4V ALLOY WITH MIXED POWDER INTERLAYERS

Titanium based brazing alloys containing chromium, ii on, copper, and nickel as beta stabilisers have been studied for joining the titanium alloy Ti-6Al-4V; Two of these alloys were selected for use in producin g lar ge gap joints. The first brazing allay, Ti-12Zr-14Cr-12Cu-12Ni ( type I), can be used to braze Ti-6Al-4V below its beta transus tempera ture. Joints of thickness tip to 150 mu m can be made in a normal braz ing cycle without prolonged holding. The interlayer consists of a beta titanium alloy with no precipitation of intermetallic compounds. The second brazing alloy Ti-12Zr-14Cr-6Fe-5Cu-5Ni (type 2), has to be braz ed above the beta transus temperature of Ti-6Al-4V. Its powders were m ixed with pure titanium and Ti-6Al-4V powders and the mixture was used as the joining interlayer. Interlayers 5 mm in thickness were used to produce joints for microstructural examination and mechanical testing . It was found that residual pol es in the inter layers were related t o the amount of the brazing alloy in the interlayer. A fully dense int erlayer could be obtained with 60 wt-% brazing alloy in the intel laye r. The as bonded joints revealed tensile strength equal to 50% of that of the base metal. Diffusional treatment of the joints improved the j oint efficiency to about 70%, compared with the base metal.