FRACTOGRAPHY OF ADVANCED SILICON NITRIDE MATERIAL FOR TURBINE APPLICATIONS

SOME CERAMICS HAVE VERY HIGH TEMPERATURE STABILITY AND STRENGTH COMPARED TO STRUCTURAL METALS AND HAVE POTENTIAL TO BE USED UNCOOLED IN ADVANCED GAS TURBINE ENGINES. ONE CANDIDATE FAMILY OF CERAMICS WITH AN ESPECIALLY GOOD COMBINATION OF THERMAL PROPERTIES AND POTENTIAL MECHANICAL PROPERTIES IS SILICON NITRIDE. RECENTLY DEVELOPED ALLOYS OF SILICON NITRIDE LOOK PARTICULARLY PROMISING, BUT REQUIRE FURTHER CHARACTERIZATION TO MAKE A REASONABLE ASSESSMENT. THE HIP SILICON NITRIDE FROM NORTON COMPANY IS PROPOSED AS AN INITIAL CANDIDATE FOR EVALUATION. THE EVALUATION WILL CONSIST OF STRENGTH TESTING OF AS-FABRICATED AND THERMALLY-AGED TEST BARS AND CONDUCTING DETAILED FRACTURE ANALYSIS TO DETERMINE THE STRENGTH-LIMITING CHARACTERISTICS OF THE MATERIAL. THIS INFORMATION WILL THEN BE USED TO ASSESS THE POTENTIAL FOR FURTHER IMPROVEMENT OF MONOLITHIC SILICON NITRIDE AND THE FEASIBILITY OF RELIABLE OPERATION UNDER GAS TURBINE CONDITIONS. THE ASSESSMENT WILL CONSIDER CERAMIC COMPOSITES AS AN ALTERNATIVE AND RESISTANCE TO CRACK PROPAGATION AS AN ALTERNATIVE TO RESISTANCE TO CRACK INITIATION.