Characterization of NiCrAlY coatings for a high strength, high conductivity GRCop-84 copper alloy

NiCrAlY top coats are currently being considered as environmental protective coatings for copper alloy liners in rocket engine combustion chambers of reusable launch vehicles. The microstructure and mechanical properties of this top coat sprayed on GRCop-84 have been characterized as a function of thermal cycling between 298 and 873 K and no obvious degradation was observed. Interfacial microsample tensile tests developed to measure coating adhesion to the substrate revealed that the interfaces were stronger than the substrate in both the as-received and thermal cycled conditions. Finite element modeling was used to analyze the stresses in the microsamples and verify the strength of the interfaces. The formation of depleted zones, devoid of Cr2Nb particles, was associated with plasma arc cleaning in a minority of the samples prepared for this study, and the presence of these depleted zones has been found to significantly decrease the adhesion of the NiCrAlY coating and to change the failure mode in thermal cycled specimens.