Influence of Diffusion Processes on the Structure of Brazed Joints of Titanium Aluminides

Abstract

During high-temperature brazing, diffusion processes occur, and the metal of the brazed joints may differ from the initial composition of the brazing filler metal. This is especially pronounced when brazing titanium aluminide (47XD). X-ray microanalysis established that when using a filler metal that does not contain aluminium, seams are formed in the brazed joints of the 47XD alloy, in which aluminium is determined. Due to the diffusion processes during brazing, the chemical composition and structure of the brazed seams are similar to that of the base metal. In this regard, it is necessary to conduct systematic studies of the structure and, using the mathematical apparatus, establish the mechanism for forming brazed joints.

Results of investigations of chemical heterogeneity of the brazed joints on titanium aluminide produced by using eutectic filler metals of the Ti-Zr-Fe system and the high-temperature vacuum brazing process are presented. The effect of the diffusion processes occurring at the filler metal–base material interface on the chemical composition and morphology of the brazed seams is shown. Investigation of the kinetics of diffusion saturation of filler metal with aluminium suggests the mechanism of formation of a two-phase structure of the seams, close to that of the base material, which requires holding for 1.0 h. It is shown that levelling of the aluminium concentration at the interface with the base material occurs during t = 1.5 s at a gap width of 50 µm.