Study on Damage Behavior of NiCoCrAlY/MSZ Plasma-Sprayed Coating in Neutral Salt Spray Environment

In order to explore the corrosion damage behavior of plasma-sprayed NiCoCrAlY/magnesia-stabilized zirconia (18~22 wt.% MgO-ZrO2, MSZ) thermal barrier and anti-ablation coatings in a salt spray environment, a series of neutral salt spray (NSS) tests for 96 h (N-2), 192 h (N-4) and 288 h (N-6) were carried out on the coatings. The microstructures, composition distributions, potentiodynamic polarization curves, bonding strengths and anti-ablation properties of the coatings before and after the NSS tests were characterized. The results show that, with the increase in salt spray time, the expansion and overflow of corrosion products (FexOy) led to more defects forming inside the coating; the porosity of the top coat (TC) of N-6 increased to 15.2% in comparison to that of the blank control sample (N-0), which was 8.5%. According to the potentiodynamic polarization curves, accelerated corrosion occurred in the coating samples after the salt spray time reached 192 h, and the corrosion current density rapidly surged from 2.2 × 10−8 A·cm−2 (N-4) to 2.2 × 10−5 A·cm−2 (N-6). Similar degradation tends could be found in the bonding strengths and mass ablation rates of the coatings due to the accumulation of loose corrosion products on the substrate, which affected the bonding states of the coatings and promoted their spalling under an oxyacetylene flame (OAF). As a result, the maximum service life of the NiCoCrAlY/MSZ coatings in the neutral salt spray environment was about 192 h. This work is instructive for studying the environmental adaptability of metal/ceramic double-layer coatings.