Creep Life Properties of High-Temperature Protective-Coated Systems.

Abstract

The low-pressure plasma spray coating process has been established in gas turbines and is used for some parts, such as turbine blades and duct segments, which are exposed to corrosive gases at high temperatures. Overlay coatings based on the MCrAlY alloy system (M is Ni, Fe or Co) are commonly employed as oxidation-and corrosion-resistant coatings. Mechanical properties, such as short-time tensile strength and creep-rupture lives, of CoCrAlY-and CoNiCrAlY-coated systems were investigated at high temperature and compared with the uncoated substrate IN738LC. Tensile properties of the MCrAlY-coated IN738LC at room temperature (293K) were affected by the high strength and low ductility of MCrAlY coatings. Fowever, the tensile properties at high temperature (1123K) were not affected by the coatings for an increase in ductility of MCrAlY coatings. Also, there was no difference of creep lives between the MCrAlY-coated systems and the uncoated substrate IN738LC. This was because creep cracks initiated and grew inside the substrate in all cases and the creep crack initiation due to coatings could not be observed. It appears to be possible to select MCrAlY coatings without causing marked effects on the creep lives of the substrate at high temperature.