A study on the electrodeposition of tantalum on NiTi alloy in an ionic liquid and corrosion behaviour of the coated alloy

The present paper deals with the electroplating of tantalum on NiTi alloy in the room temperature ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(tri-fluoromethylsulfonyl)imide ([BMP]Tf2N) containing TaF5 as a source of tantalum, as well as studying the corrosion behaviour of the coated alloy. The study comprised cyclic voltammetry, chronoamperometry, open circuit potential and potentiodynamic polarization measurements complemented by SEM-EDAX investigations. The results show that adherent, dense and uniform layers of Ta can be electrodeposited in the ionic liquid ([BMP]Tf2N) containing 0.25 M TaF5 and 0.25 M LiF at 200 °C. The corrosion behaviour of NiTi alloy without and with coating by a thin layer of tantalum was examined in 3.5% NaCl solutions. It was found that the coated sample shows better corrosion resistance than the uncoated one. Compared to the uncoated alloy, the Ta-coated alloy exhibits higher open circuit potential, wider passive region and higher breakdown potential.