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In this paper, a new treatment method, flame remelt spheroidization, is used to improve the crystallinity of hydroxyapatite (HA) powders. Based on SEM and XRD analysis, the treated powder is more crystalline than spray-dried and sintered HA powder and has higher density and a smoother surface morphology as well. In addition, coatings produced by plasma spraying the treated powder are shown to have better surface microstructure than coatings synthesized from untreated powder.

Ultrafine chromium oxide coatings were prepared by plasma spraying with ultrafine feedstock. Processing parameters of plasma spraying were optimized. Optical microscope (OM) was used to observe the microstructure of the ultrafine chromium oxide coatings. Scanning electron microscopy (SEM) was used to observe the morphology and particle size of ultrafine powder feedstock as well as to examine the microstructure of the chromium oxide coating. In addition, hardness and bonding strength of the ultrafine chromium oxide coatings were measured.The results showed that the optimized plasma spraying parameters were suitable for ultrafine chromium oxide coating and the properties and microstructure of the optimized ultrafine chromium oxide coating were superior compared to conventional chromium oxide wear resistant coatings.