This study aims to explore phase transformation in plasmasprayed hydroxyapatite (HA) ؉ 10 wt% ZrO 2 -8-mol%-Y 2 O 3 composite coating, using separately prepared HA and ZrO 2 -8-mol%-Y 2 O 3 coatings as a control. Changes in the phase and chemistry of the coatings are characterized by X-ray diffractometry, with lattice-constant measurement (Cohen's method), and by transmission electron microscopy. Experimental results show evidence of diffusion, in the liquid state, of calcium ions from the HA matrix into the ZrO 2 . This behavior causes the formation of the following structural features in the composite coating: (i) a CaO-doped ZrO 2 solid solution (ZrO 2 -7.7 mol% Y 2 O 3 -4.4 mol% CaO); (ii) a mixture of ZrO 2 and CaZrO 3 having a crystal-orientation relationship; (iii) an amorphous phase containing elements of calcium, phosphorus, zirconium, and yttrium; and (iv) a remaining CaO-poor HA matrix (Ca 10؊x (HPO 4 ) x (PO 4 ) 6؊x (OH) 2؊x ; x ؍ 0.06). Rationales for the greatly decreased impurity phases of CaO and Ca 4 P 2 O 9 found in the composite coating are discussed.
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