Abstract
Plasma sprayed NiCrAl/Al2O3-13wt.%TiO2 coating was fabricated and annealed at 300–900 °C in air atmosphere. The Elastic modulus (E), micro-hardness (HV) and fracture toughness (Kca) were evaluated by Vickers Indentation Fracture technique. The microstructure was studied by scanning electron microscopy. It can be concluded that with the increasing of annealing temperature, E and HV at the interface of Substrate/Bond layer (S/B) are firstly increased and retain the highest value at 600 °C then decreased with higher annealing temperatures due to the phase transformation. E of the ceramic coating rised initially with annealing temperature increasing, reached the highest value at 400 °C, and then decreased with the further increasing of the temperature. The Kca of the S/B interface firstly increased as the heating temperature increasing, confirming the crack initiation resistance increasing after annealing with the temperature below 700 °C. However, the Kca decreased for further annealing temperature, even lower than that of the as-sprayed coating. Thereby, a proper annealing temperature can improve the mechanical properties of the coating since the coating becomes denser, ceramic lamellar structure becomes ambiguous and cracks are partially healed.
Acknowledgments
The authors thank Mr. Matthiev Touzin, State Key Laboratory, Lille University, France, for the assistance in experimental work.