Influence of Heating Temperature on Interface Separation Behavior between Ti-20 mol% Al Alloy and High Carbon Steel

Abstract

Ti-20 mol% Al (Ti-12.3 mass% Al) alloy was diffusion-bonded to high carbon steel (0.82 mass% C) at 1273 K for 3.6 ks in a vacuum. The joint had a space of a few micrometers in thickness between the Ti-20 mol% Al alloy and the steel, and several specimens separated near the interface promptly after the bonding treatment. This phenomenon is referred to as ‘interface separation’. This paper describes the influence of heating temperature on the interface separation. Diffusion bonding of the Ti-20 mol% Al alloy to the high carbon steel was carried out at 1173 to 1423 K for 0.9 to 3.6 ks in a vacuum, and then several joints were heated at a given temperature for up to 176.4 ks in an evacuated silica tube. At 1173 K, the separation phenomenon could not be confirmed even after prolonged heat treatment. This joint had four kinds of reaction regions in the vicinity of the interface, and their thicknesses increased in proportion to square root of holding time. On the other hand, the joint bonded at more than 1273 K showed the separation at the interface. As the heating temperature increased, the holding time required to induce the phenomenon became shorter. To clarify a time when the separation occurs in the diffusion bonding process, the joint with a special shape was prepared and quenched into the water from 1273 K. The generation of voids was recognized at the interface. These results suggest that the occurrence of the interface separation is associated with interdiffusion between the Ti-20 mol% Al alloy and the steel.