Eugenio Garcia (1), Hector F. Garces (2), Laura R. Turcer (2), Hrishikesh Bale (3), Nitin P. Padture (2), Sanjay Sampath (1)
Journal of the European Ceramic Society, 41, Issue 6, June 2021: 3696-3705. DOI: 10.1016/j.jeurceramsoc.2020.12.051

Keywords

Environmental barrier coatings; Air plasma spray; Ytterbium silicate; Crystallization

Abstract

A combination of characterization techniques has been used to provide new understanding of the complex crystallization behavior of as-sprayed amorphous Yb2Si2O7-based air-plasma-sprayed environmental barrier coatings (EBCs). During crystallization heat-treatment, initially a mixture of metastable α-Yb2Si2O7 and X1-Yb2SiO5 phases form, along with stable β-Yb2Si2O7 and X2-Yb2SiO5 phases. Eventually the metastable phases transform to the stable β-Yb2Si2O7 (major) and X2-Yb2SiO5 (minor) phases. The significant volume expansion associated with these transformations partially contributes towards the anomalous expansion measured in these EBCs after crystallization, but it does not account for all the measured expansion. In this context, in similar EBCs, it is also observed that the porosity increases upon crystallization heat-treatment, primarily in the form of thin, interconnected pores, which also contributes to the measured anomalous expansion. Based on this understanding, guidelines are provided for ‘near-net-shape’ crystallization of phase-pure, dense β-Yb2Si2O7 EBCs that are free of vertical cracks.

How Our Software Was Used

Dragonfly was used for segmentation and quantitive analysis of pore connectivity and pore size distribution of reconstructed data sets.

Author Affiliation

(1) Center for Thermal Spray Research, Stony Brook University, Stony Brook, NY 11794, USA.
(2) School of Engineering, Brown University, Providence, RI 02912, USA.
(3) Carl Zeiss X-Ray Microscopy, Pleasanton, CA 984588, USA.