PREDICTING THE DETERMINISTIC EFFECTS OF COMBUSTION GAS ENVIRONMENTS ON THE STRESS-RUPTURE LIFE OF SILICON NITRIDE TURBINE COMPONENTS

ABSTRACT Silicon nitride ceramic turbine components are under intensive development by Honeywell International Inc. to enable a new generation of higher power density engines. Auxiliary power units and industrial engines are frequently used in high salt ingestion (e.g., coastal airport) operating environments, which can accelerate turbine component degradation. In order to better recognize and avoid severe degradation conditions associated with hot corrosion and oxidation of ceramic components, Honeywell developed the CERSRL code to predict the effects of duty cycle, environmental, and statistical scatter effects on tensile strength and stress-rupture lives. Predicted component life is dependent upon engine design (stress, temperature, pressure, fuel/air ratio, gas velocity, and inlet air filtration), mission usage (fuel sulfur content, location [salt in the air], and times at duty cycle power points), and material system parameters (Weibull modulus, characteristic strength, crack growth behavior, and coating [if any]). For a laboratory air oxidation environment and a specified probability of failure, the stress for rupture can be expressed as a function of a Larson-Miller Parameter (i.e., a function of temperature and rupture life). Preliminary analyses indicate that the hot corrosion and oxidation resistance of silicon nitride materials, such as NT154 and AS800, is adequate for Honeywell's initial engine applications. Inlet air filtration and protective coatings may be required to achieve required ceramic component lives in more aggressive environments