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Adherent functional graded hydroxylapatite coatings produced by sputtering deposition techniques

G. E. STAN1,*

Affiliation

  1. National Institute of Materials Physics, P.O. Box MG-7, Bucharest-Magurele, 077125, Romania

Abstract

The aim of this paper was to study the influence of crystallization heat treatments up to 750°C, upon the integrity and structure of hydroxylapatite thin films. Two different types of hydroxylapatite coatings were investigated: abrupt structures prepared by magnetron sputtering and respectively functionally graded structures deposited by a co-sputtering technique. A clear dependence was noticed between adherence values and annealing temperature and was correlated with the SEM, XRD and FTIR results. X-ray diffraction and FTIR measurements showed that the hydroxylapatite coatings annealed at 400°C were less crystalline, similar to biological apatites. Over 550°C, the apatite coatings obtained were well crystallized and preferentially oriented on (002) HA crystal plane. The adherence of HA coating increased with annealing the temperature up to 550°C due to diffusion phenomena. At 550°C the adhesion test results indicated better adhesion values in case of functionally graded structures (> 85 MPa) in comparison with abrupt ones (~ 70 MPa). At 750°C an adherence decreasing occurred for both types of structures. This is mainly due to the effect of a significant thermal stress owed to the mismatch of the thermal expansion coefficients between the crystallized HA and Ti substrate. The presence of rutile lines in XRD spectrum suggests an increasing of the diffusion phenomena and a strong substrate oxidation at the HA/Ti interface with annealing temperature..

Keywords

Biomaterial; coatings; hydroxylapatite; sputtering techniques; functionally graded materials (FGM); pull-out adherence.

Submitted at: July 31, 2009
Accepted at: Aug. 7, 2009

Citation

G. E. STAN, Adherent functional graded hydroxylapatite coatings produced by sputtering deposition techniques, Journal of Optoelectronics and Advanced Materials Vol. 11, Iss. 8, pp. 1132-1138 (2009)