Science Underpinning TBC Design for Durability in Aggressive Environments
Abstract
The aims of this research were the scientific understanding of the environmental degradation of thermal barrier systems by molten deposits, as relevant to the US Navy aircraft and marine engines, and the application of this understanding to develop mitigation strategies. The program had two thrusts, one addressing molten deposits of calcium-magnesium alumino silicates (CMAS), and the other corrosive sulfate/vanadate (S/V) melts resulting from salt ingestion combined with fuel contaminants. In principle, both types of deposits can penetrate the coating and reduce its compliance upon freezing, leading to thermomechanical damage, but also attack thermochemically the TBC by dissolving the barrier oxide and reprecipitating undesirable phases. The program successfully elucidated the mechanisms and identified mitigating strategies for both problems. The proposed CMAS mitigation is based on reaction with a rare earth zirconate layer, which leads to the precipitation of solid phases in sufficient volume to inhibit the capillary-driven flow of CMAS into the pore spaces of the coating. The approach for S/v relied on reducing the Y activity by co-doping with Ta. The latter compositions also offer phase stability at considerably higher temperatures than 7YSZ and attractive toughness.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 2008
- Accession Number
- ADA487929
Entities
People
- Carlos G. Levi
Organizations
- University of California, Santa Barbara