Microstructure and Residual Stress of Low-Pressure Plasma-Sprayed MCrAlY Coatings

Abstract

A low-pressure plasma spray coating process has been applied in gas turbines for use in hot parts (turbine blades, duct segments, etc. ) which are exposed to aggressive gases at elevated temperatures. Overlay coatings based on MCrAlY alloy system (M is Ni, Co or Fe) are employed commonly as oxidation-and corrosion-resistant coatings. In this paper, the microstructures and the residual stresses of five kinds of MCrAlY coatings sprayed by low-pressure plasma spray system and heat-treated at 1393 K for 2 h in Ar atmosphere were investigated by the X-ray diffraction method. It was found that the MCrAlY coatings were composed of the Ni-or Co-based solid solution and the precipitated Al intermetallic composite. Thermal and mechanical properties were also measured for investigating the characteristics of residual stress. It was confirmed by the X-ray diffraction that the residual stresses of some kinds of sprayed coatings could not be measured with high accuracy for the strongly layered structure. A convenient calculation technique for the determination of residual stress was investigated using an inherent strain model.