Development of NiCrAlY Alloys for Corrosion-Resistant Coatings and Thermal Barrier Coatings of Gas Turbine Components

The demand for improved efficiency and power output of energy conversion systems has lead to an increase of gas inlet temperatures in modern land-based gas turbines. The resulting increase of component surface temperature leads to an enhanced oxidation attack of the blade coating, which, in stationary gas turbines, is usually of the MCrAlY (with M = Co and/or Ni) type. Considerable efforts have been made in the improvement of the high temperature properties of MCrAlY coatings by additions of minor alloying elements. In the present paper, the effect of systematic composition variations, especially yttrium, silicon, and titanium additions, on the protective properties of MCrAlY coatings are presented. The coatings were applied to a steel substrate by low-pressure plasma spraying. Then, free-standing MCrAlY-bodies were machined from the coating. Isothermal and cyclic oxidation tests were carried out in the temperature range 950°C–1100°C. The effect of systematic variation of titanium and silicon contents on oxidation and micro structural stability was studied by characterization of the coating and the corrosion products using light and electron optical microscopy and by secondary neutrals mass spectrometry (SNMS).