Morphology of Barrier Coatings and Formation of an Interphase Boundary by Brazing of Dissimilar Alloys

As established by the conducted studies of brazing dissimilar joints of Kovar with titanium alloy, applying a standard procedure of barrier nickel coating deposition on a titanium alloy by electrolytic method does not ensure its integrity during vacuum heating in the brazing mode. The structure, chemical heterogeneity of brazed joints and surface morphology of the nickel coating are studied by applying the chemical method of producing a barrier nickel coating. Proceeding from the derived investigation results, a 4-stage technology of electrolytic application for the barrier nickel coating is proposed. This coating preserves its integrity during vacuum brazing of the following dissimilar metals: BT1-0 titanium alloy with 29NK precision alloy. A detailed study of the Kovar + BT1-0 brazed joints with the application of electron microscopy and x-ray microspectral analysis confirm the formation of dense brazed seams with full penetration fillet regions with a eutectic rod- like structure, when using silver brazing filler metal.