Influence of coating structure on the bonding strength of plasma-sprayed AT13/NiCrAl composite coatings

The dual powder feed plasma spraying process was used to design the structure of Al₂O₃-13 wt%TiO₂(AT13)/NiCrAl composite coatings, and optimized both process parameters and coating microstructure. The effects of coating structures (different layered and dispersion structures) on the microstructure, porosity, and bonding strength of the composite coatings were systematically investigated. The relationship between the internal structure and the bonding strength of the composite coatings was elucidated. Results reveal similar primary phases across all five coatings, with a total thickness of 310 ± 20 μm. Laminate structured coatings exhibited well-defined, tightly bonded layers with interlocking interfaces and minimal porosity. The five coatings exhibited porosity values of 4.22 % (C1 coating: two-layer structure produced via sequential layer spraying), 3.42 % (C2 coating: four-layer structure produced via sequential layer spraying), 3.10 % (C3 coating: four-layer structure produced via simultaneous powder feeding), 2.88 % (C4 coating: dispersed structure produced via simultaneous powder feeding), and 4.37 % (C5 coating: eight-layer structure produced via mixed powder), and bonding strengths of 25.1 MPa, 21.2 MPa, 23.6 MPa, 26.5 MPa, and 19.5 MPa, respectively. Dispersion-structured coatings demonstrated superior bonding performance, attributed to uniform phase distribution enabling effective energy dissipation. However, they exhibited susceptibility to internal crack propagation. In contrast, laminate structures introduced phase interfaces that mitigated stress concentration and suppressed crack propagation, albeit at the expense of increased weakly bonded interfacial regions.