Nanoindentation Investigation of Ti/Fe Bimetallic Plate Welded by Vanadium Filler

This article presents a systematic investigation of microstructures and mechanical properties of Ti/Fe bimetallic plates butt welded using vanadium (V) filler. It is found that the Ti/V/Fe interface is featured by dendrite structures consisting of β-Ti, FeTi, Fe2Ti, and α-Ti phases, with a hardness ranging from 5.5 to 16.25 GPa. V weld metal (WM) mainly consists of V solid solution phase with some α-Ti precipitating along the grain boundaries. A series of intermetallics, e.g., σ-FeV and Fe2Ti, are formed at the V/Fe WM interface. V WM has relatively uniform hardness (2 to 5 GPa), but hardness fluctuation is observed at the V/Fe WM interface, from 2 to 16.3 GPa. Cracks tend to initiate and propagate along the regions rich in σ-FeV and Fe2Ti. The reheated zone (V/Fe WM) by subsequent welding passes may promote the formation of σ-FeV, responsible for the cracking. Based on the Fe-Ti-V ternary phase diagram, a schematic model is established to predict the phase transformation in these welds.