Pitting corrosion behaviour in sodium chloride solution of intermetallic centreline stringers in super duplex stainless steels

International audienceAlthough manufacturers have optimized metallurgical routes to deliver super duplex stainless steels free from intermetallic phases, a segregated zone is generally formed close to mid-thickness for flat products. This zone may contain a small amount of sigma phase particles in the form of centerline intermetallic stringers. In this paper, their corrosion behaviour is investigated in sodium chloride solution, by coupling non-electrochemical and electrochemical techniques at the global and local scales. Corrosion mechanisms at centerline intermetallic stringers is then discussed and weak points in the sample are identified

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

International audienceLaser 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