The effects of ceria on the mechanical properties and thermal shock resistance of thermal sprayed NiAl intermetallic coatings

The effects of ceria addition to thermal sprayed NiAl intermetallic coatings were investigated through micro-indentation, thermal shock testing and microstructural analysis techniques (scanning electron microscopy with energy-dispersive X-ray spectrometry and X-ray diffraction analysis). It has been found that the addition of CeO₂ to NiAl coatings reduces the tendency of brittle peeling during thermal spraying. This reduction in peeling is presumably due to the improved wetting of the substrate by the molten coating material, which leads to better coating adhesion. The addition of CeO₂ resulted in higher coating hardness and elastic modulus. The coatings containing CeO₂ also exhibited significant increases in thermal shock resistance compared with that of the pure NiAl coating. The NiAl coating containing 2 wt.%CeO₂ had the highest hardness, elastic modulus and thermal shock resistance of the four NiAl-based coatings tested. The possible mechanisms responsible for the improvement of the properties upon addition of CeO₂ are addressed.