Oxide layer phase structure of MCrAIY coatings

During operation, stationary blades and vanes of gas turbines are subjected to high thermal and mechanical stresses and severe oxidation. This situation can only be controlled by a composite approach in which the base material provides the necessary mechanical properties and coatings provide protection against oxidation, corrosion and, in the case of thermal barrier coatings, a part of the heat flux. For a better understanding of the oxidation processes on standalone MCrAIY overlays as well as MCr AIY used as a bond coat, in situ X-ray diffraction measurements of the formation and composition of the oxide scale at high temperatures are presented. The phase changes during oxide scale formation are discussed. Data are presented for MCrAlY coatings with 12%AI and 3%Re at three different temperatures versus time. At 950, 1000, and 1050°C a three phase oxide layer of Cr₂0₃‘ A1₂0₃, and NiCr₂O₄ was detectable. Rhenium could not be found in the oxide layer at any of the three temperatures.