Passivity of AlCrFeMnTi and AlCrFeCoNi high–entropy alloys in Hanks' solution. (January 2023) - Tanji, Ayoub
Abstract: The present work studies the passivation characteristic and corrosion resistance of Al20 Cr5 Fe50 Mn20 Ti5 and Al7 Cr23.26 Fe23.26 Co23.26 Ni23.26 high–entropy alloys in Hanks' solution at 37 °C, in view of potential biomedical applications. The Al7 Cr23.26 Fe23.26 Co23.26 Ni23.26 possesses a higher corrosion resistance than Ti-6Al-4 V alloy, mainly due to the formation of a stable p–type passive film composed of Cr(OH)3, Cr2 O3, CoO, Co3 O4, and Ni(OH)2, leading to low vacancy concentration and limited ion conductivity. The Al20 Cr5 Fe50 Mn20 Ti5 exhibits an n–type passive film composed of Fe2 O3, Fe(OH)3, TiO2, and MnO2 that promotes chloride ions adsorption and diffusion–controlled corrosion, while its microstructural precipitates allowed a selective dissolution. Highlights: In 37 °C Hanks' solution AlCrFeCoNi resist corrosion better than Ti6Al4V. The low vacancy p–type passive film of AlCrFeCoNi limits ion conductivity. Strong Cr2 O3 and M–OH bond lead to AlCrFeCoNi high passivity and pitting resistance. L21 precipitates in AlCrFeMnTi lead to selective/galvanic dissolution and pitting.