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.

Bonding and Separation between Ti-15 mol% Sn Alloy and Iron Materials

“…Considering the experimental results for the Ti-15Sn alloy/iron material and Ti-20Al alloy/iron material joints, [7][8][9] it is concluded that the interface separation is attributed to the preferential diffusion of iron into the titanium alloy.…”

“…To encourage the effective use of these materials, they have been joined to themselves and other materials by various joining methods, such as diffusion bonding, 1,2) brazing, 3) friction welding, 4) and electron beam welding. 5) The authors have previously investigated the interfacial microstructures and the bonding strengths of Ti-Al alloy/iron material joints produced by diffusion bonding, [6][7][8][9] because steel is a dominant structural material in industrial products. It has been reported that, when Ti-20 mol% Al (Ti-20Al, i.e.…”

“…It is thought that the interface separation is attributed to the preferential diffusion of iron into the Ti-20Al alloy, which transforms from an α-titanium + Ti3Al duplex structure to an α-titanium single-phase structure in the vicinity of 1 273 K. [7][8][9] If this hypothesis is correct, the interface between titanium alloy, which shows an increase in the ratio of the α-titanium phase with increasing heating temperature, and carbon steel containing 0.82 mass% C has the potential to cause the separation phenomenon. To verify this, Ti-Sn alloy was selected as a binary titanium alloy.…”