Investigating Erosion-Corrosion and Flow-Assisted Galvanic Corrosion Behaviour of Tantalum/Tungsten.

Tantalum (Ta) and Tungsten (W) are currently used as a neutron spallation target at UKRI Rutherford Appleton Laboratory (RAL). This target suffers from frequent failures susceptibly due to erosion-corrosion phenomenon, reducing its operational life significantly. These failures prompted investigation of pure Ta and W with an overarching aim to improve the service life of RAL’s target. This study investigated erosion, corrosion, and erosion-corrosion behaviour of Ta and flow-assisted galvanic corrosion behaviour between Ta and W, using an impinging jet erosion-corrosion apparatus and potentiostat. The pure erosion experiments were performed using deionised aqueous slurry of SiC particles at a range of impact angle, concentration, and impact velocity. The pure corrosion, erosion-corrosion, and flow-assisted galvanic corrosion experiments were performed using solutions of different pH (4, 7, and 10). The potentiodynamic and potentiostatic polarisation techniques were performed in these solutions, at fixed impact velocity (5 ms-1) and variable impact angles (30° and 90°), to assess pure corrosion and erosion-corrosion rate of Ta, respectively. Zero resistance ammeter technique was performed at 90° and different flow velocities (5 ms-1 and 9 ms-1) to assess flow-assisted galvanic corrosion between Ta and W. Findings on pure erosion of Ta revealed its distinct material removal mechanism which was discussed underpinning theories of solid particle erosion and grain boundary sliding under localised indentation loading. Erosion-corrosion of Ta showed a positive synergy under all pH levels at 30° impact angle, and a negative synergy in neutral and alkaline solutions at 90° impact angle. Galvanic coupling between Ta and W increased corrosion rate of W in alkaline solutions, while Ta suffered minimum damage due to the presence of stable oxide layer on its surface. The findings of this study provide insights into erosion-corrosion and flow-assisted galvanic corrosion response of Ta and W and suggest ways to improve performance of RAL’s target.