Corrosion-induced deceleration-to-acceleration of fatigue crack growth for deep-sea Ti6Al4V ELI titanium alloy

Abstract

The Ti6Al4V ELI titanium alloy is a promising structural material for deep-sea equipment due to the advanced mechanical properties. The damage evolution of the Ti6Al4V ELI induced by cyclic loading accompanying with marine corrosion should be quantified to achieve structural integrity design for deep-sea equipment. However, synchronous acceleration testing for fatigue and corrosion is still challenging, due to the lack of equivalent acceleration ratio between fatigue and corrosion. Here we propose a calculation algorithm to determine the corrosion acceleration ratio based on the electric charge transmission during the corrosion process. Accordingly, we design a testing equipment with controllable current through corrosive solution. The corrosive acceleration ratio is modified by controlling current intensity. Then we observe for the first time that a deceleration-to-acceleration tendency for corrosion-fatigue testing for the Ti6Al4V ELI specimens. In addition, we reveal that this inconspicuous phenomenon is attributed to the competition between the corrosion-induced crack tip blunting and the material volume degradation. These findings provide insights for assessing the Ti6Al4V ELI, thereby designing for the deep-sea equipment.