Effects of annealing in vacuum on the microstructure of silicon-containing calcium phosphate films deposited on a ZrNb alloy by radio-frequency magnetron sputtering

Coatings were deposited on the surface of a ZrNb alloy by radio-frequency magnetron sputtering using targets consisting of either pure crystalline hydroxyapatite (HA) or silicon-containing HA (Si-HA). The coated ZrNb samples were heated in a vacuum furnace at a pressure of 5 x 10(-5) Torr and temperature 700 degrees C for 2 h. Precursor powders of silicate-substituted HA [Ca-10(PO4)(6-x)(SiO4)(x)(OH)(2-x), x = 0, 0.5, or 1.72] were used to fabricate the targets for sputtering. The aim of this study was to analyze the effect of Si addition to HA on crystallization behavior and structure of the resulting films using transmission electron microscopy and electron diffraction patterns of selected sites. The average thickness of the films was in the range of 175-345 nm. The Si substitution in HA played a major role in the mechanisms of coating formation and crystallization behavior, which influenced the structure and crystallinity of the layers deposited by radio-frequency magnetron sputtering. Moreover, the results indicate that surface-induced crystallization of the deposited thin films is more pronounced than internal crystallization. A possible mechanism underlying the observed decrease in the crystallization rate with the increasing silicate content in the HA-based films is discussed.

Automated summary

Coatings of pure crystalline hydroxyapatite (HA) or silicon-containing HA (Si-HA) were deposited on a ZrNb alloy surface by radio-frequency magnetron sputtering. The coated samples were heated in a vacuum furnace, and the effect of Si addition to HA on the crystallization behavior and structure of the films was analyzed. The Si substitution played a major role in the mechanisms of coating formation and crystallization behavior, influencing the structure and crystallinity of the deposited layers. The surface-induced crystallization of the thin films was found to be more pronounced than internal crystallization.