Microstructural and micro-electrochemical study of a tantalum-titanium weld interface

Overview & Synopsis

Laser welding offers an array of advantages compared to conventional fusion welding techniques, such as a higher welding speed and lower thermal distortion. However, information about the key aspects of the welding of dissimilar materials remains limited. Therefore, we chose to study the weld interface between tantalum and Ti-6Al-4V, which have good metallurgical compatibility but highly different thermophysical properties that can lead to pronounced chemical heterogeneities. An SEM analysis of the microstructure clearly revealed the formation of an unmixed zone in the melted area and a DRX analysis highlighted the presence of a beta(Ta,Ti) solid solution, tantalum islets and possibly alpha'-titanium where betagenic tantalum was absent. In terms of electrochemical behaviour, the titanium content was the main indicator of oxidation phenomena: a content greater than 50% resulted in a stable passive film, while lower Values led to an oxidation peak at approximately 1.7V vs Ag/AgCl. These results suggest that a reliable laser welding process.must promote a high titanium content in the melted area. This may be achieved through am optimized process with a heat source that shifts away from the tantalum in order to minimize tantalum levels in the melted area.