Magnesium and titanium have positive heats of mixing. As a result they have not been found to form intermetallic compounds and they have very little mutual solubility. GM materials engineers have overcome previous limitations to produce hard corrosion resistant magnesium-titanium alloy films.
GM Global Technology Operations, Inc. (Detroit, MI) detail the process to make films of magnesium mixed with titanium in U.S. Patent 7,651,732. The films are produced by non-equilibrium alloying processes such as electron beam evaporation of magnesium and titanium ingots in a very low pressure chamber.
Such magnesium-titanium films form as single phase solid solutions. Titanium is inherently resistant to corrosion and its admixture with magnesium in solid solution provides a new composition that is less subject to intra-film galvanic corrosion. The magnesium-titanium films also provide relatively hard and strong coatings, say inventors Yang T. Cheng, Mark W. Verbrugge, Michael P. Michael Lukitsch Balogh, and Daniel E. Rodak. The films also offer high elastic modulus and hardness and have high corrosion resistance.
To prepare intermetallics compounds, target anodes of magnesium and titanium, situated in a vacuum chamber, are bombarded with separate electron beams to produce a vapor of magnesium and titanium atoms for co-deposition as a solid film on a substrate. The substrate may be at about room temperature and may be suitably cleaned or otherwise prepared to receive an adherent coating of the elements as they are deposited from the vapor mixture. By controlling the relative evaporation rates of the metals, magnesium-based films with desired titanium content may be formed. Film thicknesses of several nanometers up to a millimeter or more may be obtained depending on the requirements of the non-equilibrium, solid solution magnesium-titanium coating.
Magnesium-titanium solid solution films may be used, for example, as coatings on substrates of commercial magnesium alloys or on other metal or non-metal substrates. Nanometer scale indentation tests on magnesium-titanium solid solution films deposited on silicon yield hardness and Young's modulus values for the films. These test results indicate the elastic modulus and yield strength (based on hardness values) is significantly higher than corresponding properties of conventional magnesium alloys. Moreover, the single phase solid solution microstructure of the film is not expected to form corrosive galvanic couples within the film.