Development of NiCrAlY alloys for corrosion-resistant coatings and thermalbarrier coatings of gas turbine components

The demand for improved efficiency and power output of energy conversion sy stems has lend to an increase of gas inlet temperatures in modem land-based gas turbines. The resulting increase of component surface temperature lead s to an enhanced oxidation attack of the blade coating, which, in stationar y gas turbines, is usually of the MCrAlY (with M = Co and/or Ni) type. Cons iderable efforts have been made in the improvement elements. In the present paper, the effect of systematic composition variations, especially of the high temperature properties of MCrAlY coatings by additions of minor alloyi ng yttrium, silicon, and titanium additions, on the protective properties o f MCrAlY coatings are presented. The coatings were applied to a steel subst rate by low-pressure plasma spraying. Then, free-standing MCrAlY-bodies wer e machined from the coating. Isothermal and cyclic oxidation tests were car ried out in the temperature range 950 degrees C-1100 degrees C. The effect of systematic variation of titanium and silicon contents on oxidation and m icrostructural 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).