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The effect of substrate temperature on the microstructure, mechanical properties and dissolution behavior of wollastonite coatings is investigated. The crystallinity of as-deposited coatings increases with increasing substrate temperature, whereas the porosity shows only a little variable tendency. The Knoop hardness and elastic modulus increase with the substrate temperature up to 400 °C firstly, and then a decrement is observed with the temperature further increasing to 600 °C. The dissolution rate characterized by the pH changes and the ion concentration changes of Ca, Si and P in SBF decreases with the increase in the substrate temperature. It can be concluded that increasing the substrate temperature is a feasible method to improve the mechanical properties and to decrease the dissolution rate of wollastonite coatings. However, the bioactivity of coatings deposited on preheated substrates is superior to those on non-preheated ones, which presumably results from their different phase compositions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]