Ceramic turbine components research and development. Part 1. Ceramic rotor-blade development. Final report

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Abstract
The principal objective of this program was to develop (through design, analysis and laboratory spin testing) the design techniques for uncooled ceramic rotor blades. Present-day materials, fabrication techniques and system operating conditions were assumed in the program. The unique compound curvature dovetail attachment concept was generated and two configurations of this concept were generated for detailed study. In addition a three-piece blade assembly consisting of ceramic blade/superalloy intermediate piece/metal disk was conceived. An additional important design feature was the use of a compliant layer pad between ceramic and metal contact surfaces. Silicon nitride root forms of two preliminary root designs with flat surface dovetails and of the two configurations with compound curvature dovetails were manufactured and spin tested to failure with very encouraging results. A statistical assessment of failures was conducted by combining results from finite element stress analysis and the statistical mechanical properties of Norton NC 132 silicon nitride. This provided a failure prediction method that correlated well with the spin test results. The significant influence of surface finish that translates to surface flaw severity and orientation was dramatically illustrated in this study and points to the need for improved methods of manufacturing ceramic components for gas turbine application.

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