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UM E-Theses Collection (澳門大學電子學位論文庫)

Title

A study on nanocomposite hydroxyapatite coatings on Ti6Al4V fabricated by electrophoretic deposition and laser surface treatment

English Abstract

Due to their low density, high mechanical strength and corrosion resistance, titanium alloys are often used as implants in orthopedic surgery and dentistry. In order to improve the bone bioactivity and osteointergration of metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. Plasma spraying is currently the only commercial process in service for fabricating HA coatings on the metallic implants, but long term stability of plasma sprayed coatings could be a problem because of high degree of porosities, poor bond strength, non–stoichiometric composition, non–uniformity and amorphous structure. In view of these shortcomings, electrophoretic deposition (EPD) and laser surface treatment (LST) have been attempted for fabricating HA–composite coatings. Different contents of HA and iv multi-walled carbon nano-tube (CNT) nanoparticles were used to produce composite coatings on Ti6Al4V substrate and CNTs act as the reinforcement for enhancing hardness of the coating. Due to the good bonding ability to Ti6Al4V substrate, TiO2 nanoparticles was also added to HA/CNT to serve as the interfacial bonding material. Moreover, hydrothermal treatment was also applied to pre–grow the TiO2 layer on the Ti6Al4V substrate as an interfacial layer followed by subsequent EPD of HA/CNT coating. By laser surface treatment (LST), HA with Ti, TiO2, and ZrO2 were used to fabricate the composite coatings by a 2.3-kW diode laser for improving hardness and achieving strong metallurgical bond. Surface morphology, compositions and microstructure of the specimens fabricated by EPD and LST were investigated by scanning electron microscope, energy dispersive spectroscopy and X–ray diffractometry respectively. Moreover, the corrosion behavior of various coated specimens in Hanks’ Solution at 37 oC was studied by means of open circuit potential measurement, and potentiodynamic polarization technique. Moreover, surface hardness and adhesion strength were evaluated, and the bioactivity was also determined by immersing the specimens in Hanks’ Solution at 37 oC for 4 weeks. For both EPD and LST, the HA-composite coatings show higher corrosion resistance than that of the substrate as reflected by nobler open circuit potential and lower corrosion current density. The adhesion strength of HA-composite coatings fabricated by EPD was higher than that of plasma sprayed HA coating. The enhanced properties of coatings by EPD were attributed to the nanostructure of the coatings resulting in minimal imperfections. LST specimens possess strong metallurgical bond. v Comparing two fabrication methods (EPD and LST), the electrophoretically deposited HA coating with 10 wt% TiO2 and 5 wt% CNT on Ti6Al4V shows no micro-cracks, high adhesion strength and corrosion resistance without compromising to bioactivity. LST can produce coatings with high hardness, improved corrosion resistance and strong metallurgical bond, but it compromises to decrease in bioactivity due to decomposition of HA. For the utility of HA composite coatings is in vivo implantation, so bioactivity is the most important factor, thus HA coating with 10 wt% TiO2 and 5 wt% CNT on Ti6Al4V makes the best coating with good bioactivity and acceptable surface and mechanical properties.

Issue date

2011.

Author

Zhang, Bo Kai

Faculty

Faculty of Science and Technology

Department

Department of Electromechanical Engineering

Degree

M.Sc.

Subject

Biomedical materials

Hydroxyapatite coating

Laser therapy

Supervisor

Kwok, Chi Tat

Files In This Item

TOC & Abstract

Full-text

Location
1/F Zone C
Library URL
991007340439706306