Phase Transformation during Plasma Spraying of Hydroxyapatite–10‐wt%‐Zirconia Composite Coating

Abstract

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.

Comparison of plasma‐sprayed hydroxyapatite coatings and zirconia‐reinforced hydroxyapatite composite coatings: In vivo study

“…After 12 weeks' implantation, the osteointegration was not observed at the surface of the HA/ZrO 2 coating, and the result is possibly related to the phase composition and contents of HA/ZrO 2 coatings. As shown in Table VII,26 the phase and phase contents of HA/ZrO 2 coating were investigated by X‐ray diffractometry (XRD) and transmission electron microscopy (TEM) with energy‐dispersive X‐ray (EDX). In comparison with HA coating, the lower contents of α‐Ca 3 (PO 4 ) 2 (α‐TCP), Ca 4 P 2 O 9 (TP), CaO and amorphous phase and the existence of CaZrO 3 were identified in the HA/ZrO 2 coating.…”

Effects of Laser Power Level on Microstructural Properties and Phase Composition of Laser-Clad Fluorapatite/Zirconia Composite Coatings on Ti6Al4V Substrates

“…In addition, many researchers have analyzed the reaction between ZrO 2 and CaO in accordance with Reaction (5) [4,24,29,51]. CaO (S) + ZrO 2(S) → CaZrO 3(S) …”

Microstructure and mechanical properties of plasma sprayed HA/YSZ/Ti–6Al–4V composite coatings

“…3. The absence of TTCP and b-TCP in the composite coatings is probably due to different degrees of decomposition of HA and the interdiffusion of HA and YSZ [17]. The thermal conductivity of YSZ (0.007 J s À1 cm K) is lower than that of HA (0.013 J s À1 cm K), which can affect the thermal diffusivity and molten state of the materials during plasma spraying.…”