Dissolution of Plasma-Sprayed Wollastonite Coatings: The Effects of Microstructure Coupled with Stress

Abstract

Wollastonite coatings are deposited on the U-shape titanium alloy coupons by atmospheric plasma spraying at substrate temperatures of room temperature and 400 °C, respectively. The effects of applied stresses and microstructure on the dissolution behavior of wollastonite coatings have been investigated. The dissolution rate is characterized by the ion concentration changes of Ca, Si, and P in the SBF solution. The coatings deposited at room temperature show higher porosity and lower crystallinity, and further higher dissolution rate is observed, compared with the coatings deposited at a substrate temperature of 400 °C. Applied tensile stresses promote the coating dissolution. The effect of compressive stresses on the dissolution of coatings depends on the balance between the hindrance effect and the promotion action caused by the debonding and/or peeling off. The stress condition cannot change the phase transformation process when the substrate crystal structure is adverse for the apatite precipitation.