Efforts to improve the performance of modern gas turbine engines have imposed increasing service emperature demands on structural materials. Through active cooling, the useful temperature range of nickel-base superalloys in current gas turbine engines has been extended, but the margin for further improvement appears modest. Because of their low density, high-temperature strength, and high thermal conductivity, in situ toughened silicon nitride ceramics have received a great deal of attention for cooled structures. However, high processing costs have proven to be a major obstacle to their widespread application. Advanced rapid prototyping technology, which is developing rapidly, offers the possibility of an affordable manufacturing approach.
Researchers at the NASA Lewis Research Center, in cooperation with a local university and industry, are developing actively cooled and functionally graded ceramic structures. The objective of this program is to develop a cost-effective manufacturing technology and the analytical modeling capability to predict thermomechanical stresses in burner rig tests of thermal-barrier-coated, actively cooled, in situ toughened silicon nitride turbine nozzle vanes under simulated engine conditions. In the initial studies, green and sintered bodies of silicon nitride plates with cooling holes were successfully fabricated through the use of a Sanders prototype molding machine for mold detail fabrication, ceramic gel casting, and conventional sintering techniques. A two-dimensional analytical model was developed to optimize the cooling hole geometry and spacing, and to reduce thermal stresses.
Silicon nitride (Si3N4) plate with cooling holes.
Lewis contact: Dr. Ramakrishna T. Bhatt, (216) 433-5513,
Ramakrishna.T.Bhatt@grc.nasa.gov
Author: Dr. Ramakrishna T. Bhatt
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Programs/Projects: HITEMP
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