Microstructure and mechanical properties of diffusion bonded joints between titanium and stainless steel with copper interlayer

The solid state joining of titanium to stainless steel with copper interlayer was carried out in the temperature range of 850-950 degrees C for 7.2 ks in vacuum. The interface microstructures and reaction products of the transition joints were investigated with an optical microscope and a scanning electron microscope. The elemental concentration of reaction products at the diffusion interfaces was evaluated by electron probe microanalysis. The occurrence of difference in intermetallics at both interfaces (SS/Cu and Cu/Ti) such as CuTi2, CuTi, Cu4Ti3, chi, FeTi, Fe2Ti, Cr2Ti, alpha-Fe, alpha-Ti, beta-Ti, T-2 (Ti40Cu60-xFex; 5 < x < 17), T-4 (Ti37Cu63-xFex; 5 < x < 7) and T-5 (Ti45Cu55-xFex; 4 < x < 5) has been predicted from the ternary phase diagrams of Fe-Cu-Ti and Fe-Cr-Ti. These reaction products were detected by X-ray diffraction technique. The maximum tensile strength of similar to 91% of Ti strength and shear strength of similar to 74% of Ti strength along with similar to 7.2% ductility were obtained for the joint bonded at 900 degrees C due to better coalescence of mating surfaces. At a lower joining temperature of 850 degrees C, bond strength is poor due to incomplete coalescence of the mating surfaces. With an increase in the joining temperature to 950 degrees C, a decrease in bond strength occurred due to an increase in the volume fraction of brittle Fe-Ti base intermetallics.