The preparation and properties of Sm₂Zr₂O₇ coatings by plasma spraying

Rare-earth zirconate with lower thermal conductivity compared to zirconia ceramic is very promising new thermal barrier coating material. In this article, Sm₂Zr₂O₇ precursors were synthesised by the co-precipitation method, and the size of crystal grain was between 20 and 30 nm. Then, the precursor and the powder calcined in 1250°C were granulated by the spray dryingmethod. The adaptabilities of two kinds of powders for plasma spraying process were discussed. The results show that the crystal grain size of powder granulated directly by precursor was between 40 and 50 nm, and the one granulated by precursor calcined in 1250°C was between 150 and 200 nm. Under the same parameters of plasma spraying, the coating made by calcined powder was denser and its bond strength was higher; as the value of current dropped and secondary gas increased, the particles flied faster. To the submicron crystalline powder, the ratio of unmelted particles increased and equal-axis structures dropped, the coating'sbond strength decreased. To the nano crystallinepowder, the ratio of unmelted particles decreased and equal-axis structures increased, the coating's bond strength rose.