Effect of Zr and Ta inserts on bonding strength and interracial microstructures of Ti/steel clads

Abstract

Bonding strength and interfacial microstructures of Ti/steel clads using Zr and Ta inserts have been investigated from the viewpoint of diffusion barrier effect of carbide laver formed at the interface. Diffusion bonding was performed at 1 073 to 1 273 K for 3.6 and 14.4 ks in a vacuum. TiC layer, as a diffusion barrier, is observed at the interface in the Ti/low carbon steel (structural steel, SS400) clad bonded at 1 073 K and 1 173 K without Zr and Ta inserts. However, the clad bonded at 1 273 K has no TiC barrier layer, and thus microstructural change resulting from the diffusion of Fe and Ti atoms into each parent material is observed. Although Zr insert is used in order to produce the carbide layer showing diffusion barrier effect at 1 273 K, such a layer cannot be obtained because of eutectic reaction between the steel and the insert. On the other hand, Ta insert leads to the formation of reaction layer consisting of TaC and Ta2C in the clad bonded at 1 273 K. This clad shows the highest bonding strength in the present study. Therefore, Ta insert makes it possible to retain diffusion barrier effect of carbide layer at the temperature of 1 273 K and improves the bonding strength of the Ti/SS400 steel clad as well. The advantages of Zr and Ta inserts for Ti/high carbon steel and Ti/stainless steel clads are also discussed.