Characterization and Corrosion Behavior of Functional Gradient Hydroxyapatite Coating

Abstract

The aim of the present work is to examine the characterization and corrosion behavior of functional gradient hydroxyapatite coating deposited on titanium-based alloy by plasma spray coating process. The functionally graded coating is designed to provide the crystalline hydroxyapatite at the interface with metallic substrate and the amorphous hydroxyapatite at the outer surface. It is considered that the top amorphous layer of hydroxyapatite has higher bioactivity, and its initial dissolution will lead to bone tissue growth enhancement and bonding, whereas the underneath crystalline hydroxyapatite coating after heat treatment is expected to enhance the long-term stability of coating at the interface with metal. The heat treatment of the underneath as-sprayed coating for crystallization was performed at 700 °C for 1 h. The characterization of the coatings was performed by various techniques such as scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction analysis, surface roughness, and microhardness. It was observed from potentiodynamic scan that heat-treated coating exhibited better dissolution resistance as compared to the as-sprayed coating. Heat treatment of the hydroxyapatite coating resulted in improved crystallinity of the coating which may provide long-term stability to the coating.