Towards large area MAX phase coatings on steel

MAX phases are promising materials for protective coatings on steel due to their unique combination of properties like corrosion and oxidation resistance, good electrical conductivity, low friction coefficient, damage tolerance, and high temperature stability. Here the deposition of large area MAX phase coatings on steel was investigated by magnetron sputtering of a Ti2AlC compound target. It was found that the chemical composition of the produced films was different from the composition of the target. The deposited films contained about half as much Ti as the target. Consequently the dependence of the film composition on temperature and pressure was investigated. The film composition prooved to be independent of pressure but the lack of Ti increased with increasing temperature. The stoichiometry of the films was then adjusted by adding Ti to the growing coating from a separate plasma source. This method provides a pathway to stoichiometric Ti2AlC coatings with an equilibrium volume that is in excellent agreement with our ab initio calculations.