Design of Experiments (DOE) for the Optimization of Titania–hydroxyapatite Functionally Graded Coatings

Titania–hydroxyapatite functionally graded coatings were deposited on titanium alloy substrates by plasma spraying. Because it was necessary to spray together the titania and the hydroxyapatite powders to obtain the graded system, the first target of the present study was to optimize the process parameters in order to obtain a high-quality coating. A 2³ Design of Experiments was applied to define the optimal values of plasma torch power, hydrogen flux, and spraying distance. This defined set of parameters (38 kW, 5 SLPM, and 90 mm, respectively) was used to spray the most promising graded coating, which was characterized and postheat treated.