Microstructure and thermal cycling behavior of plasma-sprayed LaMgAl11O19 coatings

In this study, LaMgAl11O19 (LMA) thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying with different spraying powers. The effects of spraying power on the amorphous phase content, microstructure and porosity of the coatings were investigated using X-ray diffraction and scanning electron microscopy. The thermal expansion behavior, microhardness and bonding strength of the coatings were also studied. Results indicated that the amorphous phase content of the coatings increased with the spraying power increasing, while the porosity of the coatings exhibited an opposite trend. Coating with high amorphous phase content suffered large volume shrinkage and exhibited low thermal expansion coefficient (TEC). Bonding strength and microhardness of the coatings increased with the spraying power increasing from 22 to 32 kW and then decreased from 32 to 42 kW. Thermal cycling behavior of LMA coatings at 1100 degrees C was also investigated. Spallation of the TBCs was mainly correlated with the formation of thermally grown oxides and mismatch of TECs between the topcoat and the substrate, which were influenced by the microstructure and the amorphous phase content of the coatings. The longest lifetimes were achieved on LMA coating deposited at 32 kW, owing to its relatively low amorphous phase content and the highest bonding strength.