Development of a durable ice protective coating for use on rotorcraft

Ice protective coatings could revolutionize the aviation industry as they could assist or even replace traditional ice protection systems that increase the vehicle weight and power requirements. A major problem for many potential ice protective coatings is durability. This paper explores whether erosion resistant titanium aluminum nitride coatings (TiAlN) can be made ice protective by reducing both surface roughness and coating defects (such as pin holes or scratches). Cathodic arc physical vapor deposition was used to deposit TiAlN on 304 stainless steel. The coatings were polished post deposition using a vibratory polisher to achieve the highest quality coating to date (surface roughness of 12.6 nm). Aircraft representative impact ice adhesion strength testing was conducted using an instrumented centrifugal adhesion testing rig. The test results demonstrated that TiAlN coatings can be made ice protective. Coatings with a surface roughness of 12.6 nm were found to have an ice adhesion strength of 1.4 psi at −8 °C, with a droplet impact velocity of 60 m/s, icing cloud density of 0.9 g/m³, and a droplet median volumetric diameter of 20 μm. The research conducted not only demonstrated the capability to reduce ice adhesion strength by reducing surface roughness, but also showed that as TiAlN coatings became smoother (surface roughness varying from 1690 nm to 12.6 nm) the dependence of ice adhesion strength on temperature decreased. The result presented demonstrates that aircraft ice adhesion strength is a highly mechanical phenomenon as the ice interacts with the surface morphology.