Treatment of MCrAlY coatings

The surface of MCrAlY coatings deposited on Inconel were treated by the pulsed electron beam of the GESA installation to improve the oxidation resistance and also the bond strength of thermal barrier coatings (TBC) deposited on the surface. Typical coatings employed for gas turbine blades are employed. The influence of electrons reflected from the surface had to be considered for the calculation of the energy deposition into the material. Due to the magnetic field in the GESA installation these electrons influence the beam current and the energy distribution inside the target. The treated MCrAlY surface shows a much better oxidation resistance because the fine grained structure of the surface layer effects the formation a stable α-Al2O3 scale already in the first stage. The scale grows slowly. Thus, an early spallation is prevented. This results also in a higher life time of the TBC deposited. The TBC is still stable after 5000 h oxidation at 950 C on air, but spalls at another untreated specimen already after 3000 h. Cyclic experiments between 950 C and room temperature show great differences. The untreated specimen spalled after 300 cycles while the treated specimen was still intact after 3000 cycles. (orig.)