Mechanical property and characterization of a NiCoCrAlY type metallic bond coat used in turbine blade

Abstract

This paper highlights some of the results obtained while studying Ni20Co18Cr12.5Al0.6Y (NiCoCrAlY) type metallic bond-coat properties of a thermal-barrier coated (TBC), AE-437A Ni base superalloy mostly employed for manufacturing compressor and stationary stator blades in aero turbines. Experiments were mainly focused in the area of evaluation of microstructure, residual stress, shear strength, hardness and with special emphasis in establishing the ductile to brittle transition temperature (DBTT) of the bond coat by using acoustic emission technique during room temperature and high temperature tensile tests. Results reveal that the residual stress was tensile in nature in the TBC layer and compressive in the bond coat as well as in the substrate. The DBTT of this bond coat is around 650 °C, which is in close proximity to the value reported in literature for CoCrAlY type of bond coat. Finite element technique was used to analyze the equivalent stresses in the bond coat, the result of which revealed the highest order of equivalent stress 800 °C, as the bond coat is ductile above 650 °C. Shear strength of the bond coat is in close proximity with that of the bond strength reported in literature for CoCrAlY and Ni22Co17Cr12.5Al0.6Y types of bond coat.