Phase, structural and microstructural investigations of plasma sprayed hydroxyapatite coatings
Limin Sun, Christopher C. Berndt, Clare P. Grey
Material Science and Engeering
Abstract
The properties and performance of plasma sprayed hydroxyapatite (Ca10(PO4)6(OH)2, i.e. HA) coatings are closely related to their manufacturing process. The objecti ve of the current study is to in vestigate the phase, structure and microstructure of the coatings and their formation mechanism due to different processing parameters. Hydroxyapatite powders were atmospherically plasma sprayed (APS) using various process parameters. The phase, structure and microstructure of the coatings were in vestigated and their microhardness measured. Both crystallinity and hydroxyl contents decreased with increasing spray power and stand-off distance (SOD), and increased from the coating interface to the surface. Crystallinity alone cannot reflect coating quality due to the existence of various forms of HA, i.e. unmelted, recrystallized and dehydroxylated, as well as the gradient structures consisting of these forms. Coating microstructure varied from a porous structure to a smooth glassy structure or a typical lamellar structure, and some newly formed nanocrystalline regions were revealed. These effects were associated with the temperature/time experiences of
particles, their cooling rates and the heat and hydroxyl accumulation during coating buildup. The coating with highest recrystallization displayed the highest microhardness.
Keywords: Hydroxyapatite; Recrystallization; Microstructural control; Thermal spray; Biomedical coatings; Phase e volution
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