Acoustic emission responses with fracture behavior of APS- and HVOF- sprayed NiCrAlY coatings deposited on C263 superalloy

Thermal barrier coating systems are used to enhance the service life of aerospace hot section components. Thermally sprayed NiCrAlY bond coats serve as a critical interface between the substrate and the top ceramic coat. In the present study, a comparative analysis was carried out to evaluate the fracture and failure characteristics of atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF)-sprayed NiCrAlY coatings under acoustic emission (AE) monitoring of three-point bend test. Thermal sprayed coatings microstructural analysis showed that the porosity of HVOF-sprayed NiCrAlY coatings was 1.56 vol.%, nearly 70.8% less than the 5.35 vol.% of APS coatings, suggesting a much denser coating microstructure. A Young's modulus of 190 GPa was found for HVOF coatings in three-point bend testing, which is 10.5% greater than the 172 GPa found for APS coatings. AE monitoring results revealed that during bend test, APS coatings had a maximum of about 250 AE hits, while HVOF coatings only had about 180 hits. The decrease of 28% AE hit suggests that HVOF coatings have improved ductile fracture behavior and delayed crack propagation. Fracture surface analysis of coatings revealed ductile failure morphology in HVOF coatings and brittle cleavage patterns in APS coatings. The current research findings demonstrate the influence of thermal spray technique on structural integrity of the NiCrAlY bond coat and confirm the effectiveness of AE as a diagnostic tool.