Characterization of Vapor Deposited Thin Films of Magnesium and Magnesium Alloys
Open Access
- Author:
- Gresh, Robert William
- Graduate Program:
- Engineering Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 25, 2014
- Committee Members:
- Barbara Shaw, Thesis Advisor/Co-Advisor
- Keywords:
- corrosion
magnesium
thin film
film
deposition
electrochemical
structure
morphology - Abstract:
- Magnesium and magnesium-aluminum alloy thin films were created by physical vapor deposition using a dual gun electron beam physical vapor deposition (EBPVD) system for the purpose of evaluating their corrosion properties. A surface profilometer was used to measure the thickness of the films, which was then used to calculate the deposition rate. Energy dispersive x-ray spectroscopy (EDS) was used to determine the composition of thin films. The cross sections of thin films were analyzed using a field-emission scanning electron microscope (FESEM) to provide information about the structure and morphology of the films. X-ray diffraction (XRD) was used to measure the x-ray spectra of thin films and determine the phases and crystal structures present in the thin films. Electrochemical testing was conducted to determine the corrosion characteristics of the samples. The open circuit potential (OCP) was measured along with corrosion rates calculated from polarization resistance (PR) and electrochemical impedance spectroscopy (EIS) data. Magnesium films were deposited with deposition rates ranging from 9.27 to 126.60 Å/s and angles from 0° to 38°. Magnesium films with low deposition rates (less than 20 Å/s) showed a denser morphology with columns of 500-700nm diameter and a preferred orientation to the (0002) plane of the hcp magnesium structure. Higher deposition rates (40 to 126 Å/s) for magnesium films resulted in a less dense morphology with thin columns of 200-300nm diameter and a preferred orientation of the (103) plane for hcp magnesium crystal structure. The magnesium-aluminum films were produced using the two gun system with deposition rates ranging from 14.42 to 34.58 Å/s and with compositions ranging from 2.97 to 58.71 wt. % Al. The best Mg-Al film had an open circuit potential of -1.856 V and a corrosion rate of 5.85 mpy. These characteristics make this film an ideal candidate for a protective coating.