On the rumpling mechanism in nanocrystalline coatings: Improved by reactive magnetron sputtering with oxygen

Abstract

• The O dopped nanocrystalline coating is prepared by reactive magnetron sputtering. • The doping of O significantly improves the oxidation resistance of the coating. • The surface rumpling behaviors on coatings is retarded by oxygen. Surface rumpling is detrimental to high temperature protective coatings as it shortens their lifetime and leads to adhesion losses and unexpected corrosion degradation. The driving force and mass transport mechanism behind of rumpling remains to be clarified. In the present investigation, we subjected two types of nanocrystalline coating systems to avoid the influence of interdiffusion on rumpling study. One group was an ordinary nanocrystalline coating, and the other group was designed and prepared with trace oxygen by reactive magnetron sputtering. Systematic cyclic oxidation test at 1100 °C was also carried out. Results show the ordinary nanocrystalline coating oxidized rapidly, which leads to the fast consumption of Al and the acceleration of phase transition in the coating. Meanwhile, severe surface rumpling is observed due to the stress release of nanocrystals through plastic deformation. Besides, the reactive doping of oxygen can significantly reduce the consumption process of Al in nanocrystalline coating. The rumpling is controlled due to the improvement of coefficient of thermal expansion and Young's modulus of the coating. Thereafter, the cyclic oxidation resistance is improved.