Correlation of feedstock powder characteristics with microstructure, composition, and mechanical properties of La2Ce2O7 coatings produced by plasma spray-physical vapor deposition

Abstract

By virtue of plasma spray-physical vapor deposition (PS-PVD) process, coatings in possession of columnar structures can be obtained by suitable processing parameters coupled with specially designed powder feedstock. In this paper, the influence of powder characteristics on the La2Ce2O7 (LC) coating microstructures was investigated by using three kinds of feedstock powders with same PS-PVD processing parameters. It was found that small agglomerated feedstock, weak binding strength, and small primary particle sizes can enhance the feedstock evaporation rate, thus obtaining well columnar structured coatings. X-ray diffraction (XRD) patterns revealed that except for a very small amount of La2O3 the main phase of all the coatings is LC. The La/Ce atomic ratios reduced in the coatings compared to the feedstocks, especially the coatings with better columnar structure. Super-lattice patterns were observed by transmission electron microscope (TEM), which means that the LC phase is supposed to be pyrochlore structure. Furthermore, the mechanical properties evaluated by nano-indentation tests indicated that both the hardness and Young's modulus of each coating show negative correlations with the porosity inside the columns.