Morphological and Mechanical Properties of Hydroxyapatite Bilayer Coatings Deposited on 316L SS by Sol–Gel Method

Abstract

The present paper reports on the influence of the addition of TiO 2 and SiO 2 oxides as sub-layer, on the morphological and mechanical properties of the hydroxyapatite (HAP) bioceramic coatings deposited on 316L stainless steel by sol-gel method in order to improve the properties of hydroxyapatite and expand its clinical application. The stability of the sols suspensions was evaluated by measuring the time dependence of the viscosity. Annealed properties of the coatings were analyzed by XPS, XRD, SEM, and EDS. The Vickers microhardness of the coatings is obtained under the same indentation load of 10 g. The hydroxyapatite coating deposited on the surface of the 316L SS substrate exhibits a porous carbonated apatitic structure. The results clearly demonstrate that HAP-TiO 2 and HAP-SiO 2 bilayer coatings where hydroxyapatite is deposited on the surface of TiO 2 -and SiO 2 -coated 316L SS substrate systems were highly homogeneous and uniform and show higher microhardness compared to HAPcoated 316L SS. A gap of nearly 10 pct is observed. The addition of TiO 2 and SiO 2 as sub-layer of a hydroxyapatite coating results in changes in surface morphology as well as an increase of the microhardness.

Study of the mechanical behavior and corrosion resistance of hydroxyapatite sol–gel thin coatings on 316 L stainless steel pre-coated with titania film

“…In the same way, TiO 2 sol was kept closely capped and aged for 24 h at the temperature of 100°C. The effect of temperature of TiO 2 aging sol on the film morphology has been discussed and detailed in [12].…”

“…As a conclusion, we showed that the TiO 2 sub-layer significantly improves the hardness of the HAP coating. In [12] it is shown that the microhardness of the HAP coating, which is about of 459 HV (4.50 GPa) increases with the addition of the TiO 2 and SiO 2 inner layers, to reach approximately 530 HV (5.19 GPa) for the global HAP bilayer coatings. In addition, the hardness values obtained from both classic tests in microindentation and the continuous stiffness measurement mode in nanoindentation are slightly different.…”

“…In a previous work [12], we determined the hardness of the HAP single and the bi-layered coating systems by means of classical microindentation tests. The model of Jönsson and Hogmark was applied to separate the two contributions of the substrate and of the film in the measured hardness in order to determine the hardness of the film only.…”

Hydroxyapatite-Based Coating on Biomedical Implant

“…An extremely high temperature (6000-10,000°C) is applied in plasma-spray deposition can decompose the HAp properties into tricalcium phosphate, tetra-calcium phosphate, calcium oxide (CaO), and others amorphous phases [41,42]. When increasing annealing temperature from 375 to 500°C, the adhesion strength between HAp coating and the substrate increases [43,44].…”

Comparison of Mechanical and Barrier Properties of Al2O3/TiO2/ZrO2 Layers in Oxide–Hydroxyapatite Sandwich Composite Coatings Deposited by Sol–Gel Method on Ti6Al7Nb Alloy

“…Numerous studies [25][26][27][28][29] have investigated the variation of the microstructural, compositional, morphological, or surface properties of such coatings and their influence on the bioactivity, mechanical, and bonding strength. There is also another approach, consisting of the production of layered composite coatings, where the oxide layer, e.g., TiO 2 [30][31][32], ZrO 2 [32][33][34], Al 2 O 3 [26,31], and SiO 2 [30], is applied directly to the substrate and the HAp layer is deposited on top of it. This solution seems to have some advantages, e.g., better control over the composition and morphology of individual layers, as well as potentially much better isolation of the substrate in the event of dissolution of the HAp layer after implantation.…”