Microstructure evolution and its effect on corrosion behavior during cold rolling of Ti–Nb–Ni sheet as bipolar plates substrate for PEMFC

In this work, hot rolled Ti–Nb–Ni sheet with thickness of 1.8 mm was subjected to cold rolling with different reductions (20 %, 40 %, 60 %, 75 % and 85 %). Microstructure evolution and corrosion resistance of sheets with and without being cold rolled were investigated. Mechanical twins are generated for 20 % and 40 % cold rolled sheets, while dislocation slip becomes dominant for reductions larger than 40 %. Typical TD-split basal texture was observed in all of specimens. Corrosion resistance of the sheets in solution of pH = 3 H₂SO₄ with 0.1 ppm F⁻ at 80 °C were evaluated. All the sheets possessed corrosion current densities lower than 1 μA cm⁻², meeting the requirement of Department of Energy. Hot rolled sheet possessed the noblest OCP (−0.212 V), lowest corrosion current density (0.15 μA cm⁻²) and steady state current density (0.012 μA cm⁻²), as well as the largest polarization resistance of all the sheets (749.1 kΩ cm²). Besides, corrosion resistance for cold rolled sheets becomes inferior with reduction increasing. This can be attributed to increased dislocation density which provides more available active sites and deteriorates corrosion resistance with reduction increasing. Therefore, to obtain desirable corrosion resistance in PEMFC environment, Ti–Nb–Ni sheets with microstructure possessing massive dislocations should be avoided.