Multilayered Thermal and Environmental Barrier Coatings for Naval Gas Turbine Engines.
Abstract
The University of Virginia proposes a three???year program of fundamental research whose objective is the design and evaluation of thermal and environmental barrier coating (T???EBC) systems for eventual use in gas turbine engines at 2700 oF. It consists of a high temperature bond coating whose coefficient of thermal expansion closely matches that of silicon carbidecomposites. Once applied the bond coat protects the underlying SiC from oxidation and steam erosion by the development of a passive thermally grown oxide whose CTE is close to that of the substrate. Since this layer is prime reliant, it must also have very good thermal shock resistance. Numerous candidates have been identified with potentially good thermal shock resistance have been identified. This part of the program will first investigate the Hf doped SiAlON system whose CTE is slightly less than SiC and which forms a TGO layer consisting of cristobalite SiO2 containing small quantities of Al2O3. By adding hafnium, we will investigate the feasibility of reducing the CTE of the TGO to match that of SiC by forcing HfSiO4 phase formation during oxidation. Theprogram will also design, develop a deposition strategy and characterize the behavior of a diffusion barrier layer for use in a 2700 oF T???EBC system. The role of this material in the coating system is to reduce the flux of oxidizing species (molecular oxygen and water vapor) that reach an underlying bond coat layer previously applied to a SiC composite. The most promising candidate identified to date is a mixed (Zr,Hf)SiO4 which has an excellent CTE match with SiC andis chemically compatible with the TGO of each of the bond coats candidates. This task will also assess the potential of multi???rare earth disilicates which have the requisite CTE and a thermal conductivity that can be reduced by adding more than one rare earth oxide. The rate of oxidizer diffusion and growth rate of the bond coat TGO determine the ultimate life of an EBC system in a gas turbine engine environment. A variety of TBC candidates have been identified based upon rare earth stabilized hafnia. A preliminary assessment indicates that rare earth (including multiple rare earths) stabilized hafnia satisfies many of the needs. A study will be conducted using spark plasma sintered test coupons to identify the CTE, thermal conductivity and steam volatility of hafnia and its rare earth stabilized variants. It will include an investigation of high entropystabilized systems which may provide property tuning options, and improved resistance to calcium magnesium aluminum silicate attack. This three-year program of fundamental research seeks support for three inter-related tasks whose objective is the design and evaluation of thermal and environmental barrier coating systems for use at 2700 oF.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 27, 2018
- Source ID
- N000141812645
Entities
People
- H.N.G. Wadley
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia