Corrosion behaviour of electroless NiP coating in artificial blood plasma.

Electroless NiP coatings are well known for their excellent properties and vast area of applications. In the present investigation, electroless NiP coating is applied on AISI 420 substrate, which is used for manufacturing medical instruments. As blood is a strong electrolyte, the steel, when comes in contact with blood for a long time, tends to corrode very fast. The primary objective of this work is to enhance the corrosion resistivity of AISI 420 stainless steel by the application of electroless NiP coating. The corrosion resistance of coated steel was investigated using both potentiodynamic polarisation and electrochemical impedance spectroscopy in artificial blood plasma. Detailed microstructural investigation using scanning electron microscopy (SEM), X-ray diffraction and energy dispersive X-ray spectroscopy has been done. Microhardness measurement has been performed. The SEM images revealed the coatings to be primarily amorphous and changed to crystalline when heat treated at 300°C for 2 h. Microhardness of the as-plated coating was 592 HV and increased to 677 HV after heat treatment. Corrosion rate decreased from 4.694 × 10⁻⁴ mm/year of bare steel to 4.104 × 10⁻⁵ mm/year for coated and heat-treated steel. [ABSTRACT FROM AUTHOR]