Decrease in the Efficiency of Diffusion-Welded Joint between Titanium and Aluminum in a Process of Use at High Temperatures

Abstract

The measurement of electric resistance has been applied to an investigation on the decrease in the joint efficiency of diffusion-welded joint between titanium and aluminum which occurs in a process of holding the joint at a high temperature. A large increase in the electric resistance of the bond which is accompanied by a remarkable decrease in the joint strength has been observed in the process of holding the joint at temperatures from 873 to 913K in a vacuum of 10^-3Pa. The activation energy for the increase in the electric resistance of the bond has been estimated to be 230 kJ/mol, which is nearly equal to that of interdiffusion in the binary system of titanium and oxygen. The electric resistance of the bond has increased more rapidly with the rise of the oxygen content of titanium base metal.
The increase in the electric resistance of the bond and decrease in the joint strength are accounted for by the formation of aluminum oxide at the interface between the aluminum base metal and intermetallic compound layer. Oxygen atoms to form the aluminum oxide are supplied from solution oxygen in titanium base metal by diffusion.