Effect of heat treatment on microstructure and property of plasma-sprayed lanthanum hexaaluminate coating

Abstract

Amorphous phase is commonly found in LaMgAl11O19 (LMA) coating prepared by atmospheric plasma spraying. In order to improve their performance, the as-sprayed LMA thermal barrier coatings on a nickel-based DZ125 substrate were heat-treated at 900, 1000 and 1100 °C for 5–20 h, respectively. The effect of heat treatment on the microstructure, porosity, phase composition, and crystallization behavior of the LMA coatings was investigated using scanning electron microscopy, X-ray diffraction, differential scanning calorimetry analysis. Samples before and after heat treatment for 20 h were thermally cycled at 1127 °C. Results indicated that the annealing of the as-sprayed LMA coating prior to thermal cycling is preferable to promote the crystallization of amorphous phase. Variations in microstructure, phase composition and thermal cycling lifetime of LMA coatings have been correlated to the heat treatment. Heat treatment at 900 °C improved the lifetime of LMA coatings, whereas their thermal cycling performance did not significantly improved when the aging temperature increased to 1000 or 1100 °C. The corresponding mechanism had been explored by tracing the microstructure and thermo-physical properties evolutions during thermal annealing process.