STRUCTURAL AND MECHANICAL PROPERTIES OF Mg/MgO AND Mg/Al_2O_3 NANOLAMINATE COATING FOR IMPLANT APPLICATIONS

摘要

Nanostructured magnesium coatings have the potential of enhancing the integration of implant to bone tissues due to their ability to regulate the functions of integrin, which modulates cell proliferation and differentiation. However, they are soft, ductile and have low wear resistance. These limitations prevent the practical use of Mg coatings for this application. However, application of Mg thin films in the form of nanolaminate coatings has been found to improve hardness as well as wear properties. In this study, Mg/MgO and Mg/Al_2O_3 nanolaminates with bilayer thicknesses (∧) 10, 20, 40, 100, 200, 1000 nm were deposited on glass substrate using the reactive pulsed DC magnetron sputtering process. The Mg/MgO nanolaminates were developed from an Mg target. (∧) was controlled by the duration of oxygen flow during the sputtering process. Values of (∧) were obtained from low angle-XRD. We found that the rate of MgO deposition significantly depends on water vapor content in the chamber and that a partial base pressure of water below 10~(-8) Torr is required to achieve repeatable results. Structure and properties of multilayered coatings were studied by X-ray diffractometry, nanoindentation, SEM and AFM. At (∧) ＜ 100 nm, MgO and Mg have preferred orientations <200> and <002> respectively, while at higher (∧), other orientations are present in the XRD patterns. The nanoindentation results showed slightly higher hardness of Mg/MgO and Mg/Al_2O_3 nanolaminate coatings compared to that of pure Mg. Nanolaminates have high ductility compared to MgO and Al_2O_3. Nanolaminate coatings at (∧) ＜ 100 nm exhibit an improvement in the mechanical properties due to the presence of interfaces which act as barrier to dislocation movement.