MCrAlY coating obtained by electroless plating for Thermal Barrier System

Improvement in efficiencies of gas turbines can be achieved by increasing the gas inlet turbine temperature. So, due to the high temperatures, turbine blades are cooled with tapped air in the compressor (active cooling) and protected from oxidative and corrosive attacks with coatings. Coatings such as MCrAlY are typically used to improve components’ high temperature properties. Various processing routes have been studied to produce MCrAlY coatings, including plasma spray and electrolysis methods. Plasma spray involves different problems of cohesion and uniformity, where the blade reaches complex geometries. Electrolysis methods suffer in maintaining a homogeneity of the electric field applied in all points of the blade with consequent non-homogeneous coatings. The possibility of obtaining such coatings through a new route, that avoids the problems mentioned above, is quite interesting. A potentially attractive processing route is the electroless autocatalytic process since this has the advantage of permitting nondirectional deposition. We have investigated MCrAlY deposition purely by an electroless autocatalytic process. The electroless plating technique was used to convey metallic particles of chromium, aluminum, and yttrium into the nickel coating. The chemical-physical behavior of metal particles in the electroless bath was studied and the influence of process parameters on the coating characteristics is discussed. Different bath stirring methods were tested with the aim of establishing the optimal experimental conditions for the deposition process. SEM and EDS analysis was conducted in order to study the formation of the coating, the inclusion of the metallic particles into the nickel matrix and the homogeneity of the obtained coating. Thickness was evaluated by weight gain measurements and observations by SEM in cross section.