Influence of the basic material on the structure formation of brazed joints of nickel and titanium aluminides

Making permanent joints of advanced heat-resistant materials, based on aluminides of nickel and titanium, has a great importance for the many branches of industry. Dominating method for joining is brazing. Melting a brazing alloy in the narrow gap, wetting a base material surface, alloying elements concentrations gradient at the interface result in diffusion processes, enrichment of the seam metal with elements of material being brazed. The present work gives the results of X-ray microspectral examination of structure formation peculiarities of nickel and titanium aluminide joints, produced by a high-temperature vacuum brazing using brazing alloys on the base of Pd-Ni and Ti-Zr systems. It is shown, that in brazing nickel and titanium aluminides the diffusion of aluminium from the base material into a brazed seam and fillet region is observed, thus leading to the formation of phases, respec-tively, on the base of palladium and titanium, enriched with aluminium. The structure of the brazed seam of titanium aluminides, produced by using brazing alloys on the base of Ti(Zr)-Fe system is two-phase. Concentration of aluminium in them is similar to that characteristic of the phase components (TiAl and Ti3Al) of the material being brazed. On the example of brazing of the intermetallic alloy γ-TiAl the kinetics of diffusion saturation of the seam metal with aluminium is described and it is shown, that the levelling of aluminium concentration at the interface occurs at t = 1,5 s at the gap value of 50 μm