FeB and FeB/h-BN based anti-corrosive composite coatings for aluminium alloys

Purpose - The purpose of this paper is to investigate the corrosion behaviour of ferroboron (FeB) and FeB/h-BN (hexagonal boron nitride) coatings deposited onto A383 substrates by atmospheric plasma spraying. Design/methodology/approach - Potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion susceptibilities of the composite coatings. Microstructural characterizations were carried out by using scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). Findings - It was observed that the coatings resisted localized corrosion in NaCl solutions and protective oxide films on the coatings repaired themselves over the corrosion potential. Hexagonal-BN is not only a limiting factor in the corrosion of the FeB based coatings. The corrosion morphologies of the coatings are strictly dependent on pores and micro-cracks in the coating. Practical implications - The iron-based borides act as solid lubricants and have a positive influence on tribological properties such as hardness, friction and corrosion of the coating. Originality/value - Knowledge of the effects of FeB on the corrosion behaviour of thermal spray coatings is still incomplete and this is the most important obstacle to the widespread use of the coatings in engineering applications. The paper reports electrochemical test results of the coatings and discusses the morphologic effects of h-BN on the corrosion behaviour.