Preparation and characterization of bioactive monolayer and functionally graded coatings

Hydroxyapatite powders were made by reacting orthophosphoric acid with calc ium hydroxide and dense bioactive coatings were subsequently produced by th e plasma spray technique. Three types of hydroxyapatite (flame spheroidized ) monolayer coatings and three types of functionally graded coatings were m anufactured. It was found that average microhardness values of monolayer co atings decreased as the indentation load increased. The relationship betwee n indentation load and indent diagonal length observed Meyer's law. Microha rdness and fracture toughness of coatings were affected by characteristics of feedstock powders for plasma spraying. The indentation fracture toughnes s of coatings could be significantly increased by incorporating a toughenin g phase. (C) 1999 Kluwer Academic Publishers.