MICHAEL PHELAN / LONDON
New material allows higher temperature turbines with lower CO2 emissions
NASA's Glenn Research Center (GRC) has achieved a major milestone in recent testing of a coating material designed to allow an increase in engine turbine temperatures of 170°C (300°F), paving the way for more efficient engines with lower CO2 emissions.
The low conductivity thermal barrier coating (TBC) was tested as part of the materials and structures portion of Cleveland, Ohio-based GRC's Ultra Efficient Engine Technology (UEET) project.
The testing achieved the milestone of demonstrating a reduction in surface thermal conductivity of 50%, meaning the material tested absorbed 50% less heat. NASA says the UEET low conductivity TBC met several key goals, including surviving 1,200 cycles and 100 "hot hours" at a surface temperature of 1360°C, and demonstrating a post-exposure thermal conductivity 60% lower than the baseline material.
The testing was conducted on 25mm (1in) diameter test coupons using the GRC materials division's laser rigs, which give an engine-like heat flux environment for real-time monitoring of thermal conductivity.
Candidate ceramic coatings were evaluated last year, applied using a combination of plasma spray and physical vapour-deposition (PVD). Coatings were screened for conductivity and for sintering, described as "coating densification caused by high temperature".
"The next steps," says NASA, "are to finalise compositional details and optimise processing of the plasma spray and PVD coatings. Future plans include more realistic testing in high-fidelity rigs and pursuit of engine demonstrations."
Bob Draper, UEET materials manager, says: "This material has been so successful that it will quite likely enter into commercial service very quickly. An alternative use is to apply it as a thinner coating while maintaining component temperatures. This would have the effect of reducing component, subsystem and engine weight. Another use would be to apply thicker coatings on combustors or other sheet metal components, contributing to higher efficiencies with reduced cooling, or allowing less costlysubstrate materials."
Source: Flight International
