Crystallization behavior of plasma-sprayed lanthanide magnesium hexaaluminate coatings

LaMgAl11O19 thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying. The crystallization behavior of the coatings and the synthesis mechanism of LaMgAl11O19 powders were researched. The results showed that the plasma-sprayed coatings contained some amorphous phase, and LaMgAl11O19 powders were partially decomposed into Al2O3, LaAlO3, and MgAl2O4 in the plasma spraying process. The amorphous phase was recrystallized at a temperature of approximately 1174.9°C, at which level the decomposed Al2O3, LaAlO3, and MgAl2O4 reacted again. The resynthesis temperature of LaMgAl11O19 in the plasma-sprayed coatings was lower than that of LaMgAl11O19 in the original raw powders. The synthesis mechanism of LaMgAl11O19 powders can be summarized as follows: during the first part of the overall reaction, La2O3 reacts with Al2O3 to form LaAlO3 at approximately 900°C, and then LaAlO3 further reacts with Al2O3 and MgAl2O4 to produce LaMgAl11O19 at approximately 1200°C.