Biocompatibility of hydroxyapatite (HAp) coatings have led to its use in a wide range of applications in both dentistry and orthopaedics. The plasma spraying method is the most commonly used method for the production of Hap (Ca 5 (PO 4 ) 3 OH) coatings on Ti alloys. When HAp is injected into the plasma jet, several phases can coexist under the effect of a temperature gradient occurring in the bulk of the particle. The amounts of residual compounds, amorphous and recrystallized phases are related to the conditions of spraying such as gas flow rates, feed rate, spray distance, plasma current and cooling effect. Plasma-sprayed HAp coatings were analyzed by X-ray diffraction and electron microscopy.

Zircon (ZrSiO 4 ) is a technologically important oxide ceramic material known for its high refractoriness and chemical stability. It shows excellent thermal shock resistance as a result of its very low thermal expansion coefficient and a low heat conductivity coefficient. Plasma spraying is a convenient method to produce large area coatings with high growth rates, necessary for many applications. ZrSiO 4 is among the least expensive spraying materials for refractory applications. In this study, a single-step process was used to prepare mullite/zirconia ceramic composites by plasma spraying zircon/alumina mixtures. Mixtures of ZrSiO 4 and Al 2 O 3 powders with Al 2 O 3 to SiO 2 molar ratios of 3:2 were milled for 2 h in a zirconia medium using a ball mill. The as–milled powders were dried in the furnace and sintered at 1300 and 1350 °C for 2h then crushed to a size less than 100 μm. The powders were sprayed by an atmospheric plasma spray gun (Metco 3MB) using C/C+SiC ceramic matrix composite substrates. Scanning electron microscopy (SEM) was used to analyze the microstructures of the powders and plasma coatings. The phase composition analysis of the powder showed the presence of alumina and zircon. After plasma coating, alumina, zircon, and zirconia phases were determined.