Chemo-Thermo-Mechanical Degradation of Multifunctional Thermal/Environmental Barrier Coating Ceramics and its Mitigation
Abstract
The broad objective of the proposed research program is to build on the successes of thecurrent ONR project in integrating experiments and theory/modeling to provide a comprehensiveand scientific understanding of calcia-magnesia-aluminosilicate (CMAS)-induced degradation ofnew multifunctional alloy environmental barrier coatings (EBCs) and its mitigation. Specifically,the objectives of the proposed research program are to study: (i) EBC ceramics alloying (solidsolutions) and (ii) engineering microstructures and grain-boundary characteristics. Advanced EBCs explored in the literature so far are non-alloyed, line-compound ceramics, and little attention has been paid to their thermal conductivities. Also, there has been little attention paid to microstructures and grain-boundary characteristics of EBCs, when it has been shown that they can play critical roles in CMAS-induced degradation of EBCs and its mitigation. Thus, the ultimate goal is to mitigate the CMAS damage in an expanded menu of technologically important multifunctional EBC ceramics that can also serve as effective thermal barriers.The proposed research is divided into two interrelated thrusts and are as follows:1. Alloying is a very powerful way to tailor the properties of ceramics. Here the alloying approach will be used to tune the EBC/CMAS high-temperature interactions and mitigate the damage.Various relevant alloy compositions in the rare-earth (RE) disilicate system will be studied: RE2Si2O7 (RE=Y, Yb, Lu, Er, Sc). The thermal conductivity of these dense alloys can also be reduced significantly, below 1 W.m.K-1, making them truly multifunctional ??? they can serve as both thermal and environmental barriers, eliminating the need for additional thermal barrier coating (TBC) layer in T/EBCs. Also, while Si-free ceramics are very attractive for EBCsapplication, they typically have high coefficients of thermal expansion (CTE) compared to that of SiC, making them unsuitable for use with SiC-based CMCs. In this context, a judicious alloying approach will be used to potentially reduce CTEs of oxide ceramics, which will open up a menu of hitherto unsuitable Si-free oxide ceramics for potential EBCs application. Relevant alloy compositions in the rare-earth aluminate perovskite system will be studied: REAlO3 (RE=Y, Gd). This makes the alloying approach highly synergistic. Powders and dense alloy EBC ceramics will be prepared, and their high-temperature interactions with CMASs of different compositions will be studied using a battery of analytical/microscopy and spectroscopy characterization techniques. Their thermal (conductivity, expansion) and mechanical (hardness, toughness, strength) properties will be measured. 2. Microstructures and grain boundaries play important roles in determining the damage and its mitigation in both CMAS-reacting and CMAS-non-reacting EBCs. However, detailed understanding of how and why this happens is lacking. Also lacking is an understanding of theeffect of the microstructure on the reactivity in the case of CMAS-reacting EBCs. Thus, select alloy EBC ceramics with tailored microstructures (grain size, morphology) and grain-boundary characteristics (chemistry, complexion) will be fabricated, and they will be subjected to attack by CMAS of different compositions and optical basicities. These will be characterized comprehensively using a battery of analytical/microscopy and spectroscopy techniques, together with appropriate chemo-thermo-mechanical modeling to gain deep insights into microstructural and grain-boundary effects on CMAS-induced damage of EBC ceramics and its mitigation.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 27, 2018
- Source ID
- N000141812647
Entities
People
- Nitin P Padture
Organizations
- Brown University
- Office of Naval Research
- United States Navy