Effect of Alumina Additions on Microstructural Aspects of the to α Transformation in Tantalum (V) Oxide
Tantalum (V) oxide (Ta2O5) has potential applications as part of an environmental barrier coating system for Si3N4-based turbine components. However, at elevated temperatures, Ta2O5 undergoes a phase transformation from the orthorhombic () phase to the tetragonal phase (α), which is undesirable because of the associated volume change. The purpose of the present work was to study the effect of alumina additions (0–5 wt%) on the to α transformation temperature, and associated modifications to the Ta2O5 microstructure. Sintered microstructures were characterized using SEM (scanning electron microscopy), and XRD (X-ray diffraction) was used to identify the phases present at room temperature. It was found that for undoped Ta2O5, transformation of the low-temperature -phase begins at ∼1300°C, and leads to extensive microcracking of the sintered sample. For samples containing alumina, an increase in the transformation temperature was observed. The solubility limit of alumina in Ta2O5 was between 1 and 3 wt%; for samples in which this was exceeded, the AlTaO4 second and phase particles were seen to be highly effective at inhibiting grain growth.
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Document Type: Research Article
Affiliations: Center for Advanced Materials and Nanotechnology and Department of Materials Science & Engineering, Lehigh University, Bethlehem, Pennsylvania 18015
Publication date: 2005-09-01