Reliability of a Conceptual Ceramic Gas Turbine Component Subjected to Static and Transient Thermomechanical Loading

A three year program to evaluate the feasibility of using monolithic silicon nitride ceramic components in gas turbines was conducted. The use of ceramic materials may enable design of turbine components which operate at higher gas temperatures and/or require less cooling air than their metal counterparts. The feasibility evaluation consisted of three tasks: 1) Expand the material properties database for candidate silicon nitride materials, 2) Demonstrate the ability to predict ceramic reliability and life using a conceptual component model and 3) Evaluate the effect of proof testing on conceptual component reliability. The overall feasibility goal was to determine whether established life and reliability targets could be satisfied for the conceptual ceramic component having properties of an available material. Fast and delayed fracture reliability models were developed and validated via thermal shock and tensile experiments. A creep model was developed using tensile creep data. The effect of oxidation was empirically evaluated using four-point flexure samples exposed to flowing natural gas combustion products. The reliability- and life-limiting failure mechanisms were characterized in terms of temperature, stress and probability of component failure. Conservative limits for design of silicon nitride gas turbine components were established.