Phase evolution in plasma sprayed Nb2O5 coatings

Resumo

© 2021 Elsevier LtdNb2O5 polymorphism and defect chemistry depend on the temperature, pressure, atmosphere composition and the initial crystallography. Plasma spray of Nb2O5 is a pathway to form coatings with in-situ metastable and nonstoichiometric phases, however so far unexplored. This study aimed to understand the phase evolution of plasma sprayed Nb2O5 coatings, and its effect on their morphology and properties. Phase evolution from H-Nb2O5 in the feedstock, to T-Nb2O5, TT-Nb2O5, N-Nb2O5, H-Nb2O5, Nb12O29 and NbO2 in the coatings depends on the plasma Ar/H2 ratio and its related enthalpy. The microstructure shows a layered distribution of nonstoichiometric phases at the splat boundaries and splat cores composed of T-Nb2O5 or TT-Nb2O5. The presence and distribution of these phases are related to the thermomechanical and electrical properties. The mechanisms driving the formation of these coatings are based on the Nb2O5 incongruent vaporization which promote retention of nonstoichiometric phases and the rapid solidification of metastable phases.

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