SURFACE STRENGHTHENING OF ADVANCED CERAMICS BY A THIN COMPOSITE SKIN

THE OBJECTIVE OF THIS PHASE I SBIR PROJECT IS TO DEMONSTRATE THAT A MONOLITHIC CERAMIC CORE-COMPOSITE SKIN STRUCTURE HAS SIGNIFICANTLY INCREASED FRACTURE TOUGHNESS AS COMPARED TO THE CORE MATERIAL, WHILE SUBSTANTIALLY MAINTAINING ITS FLEXURAL STRENGTH. THE CORE MATERIAL IS REACTION BONDED SILICON NITRIDE, A FORMABLE AND RELATIVELY INEXPENSIVE STRUCTURAL CERAMIC. THE COMPOSITE SKIN IS A CHEMICAL VAPOR INFILTRATION PROCESSED SIC MATRIX WITH SIC, SI3N4, OR ALUMINOSILICATE FIBER REINFORCEMENT. A FURTHER OBJECTIVE IS THE DEVELOPMENT OF A LOW COST MICROWAVE-BASED FABRICATION PROCESS, FOR WHICH PHASE I FEASIBILITY WILL BE DEMONSTRATED VIA MICROWAVE IN SITU NITRIDING OF THE GREEN RBSN CORE. ANTICIPATED BENEFITS: THIS CORE-SKIN STRUCTURE APPROACH IS EXPECTED TO PROVIDE COMPOSITE BEHAVIOR WITHOUT THE EXPENSE OF FABRICATING THICK SECTION COMPOSITES. IF SUCCESSFUL, THIS WOULD MAKE THE CERAMIC CORE-COMPOSITE SKIN STRUCTURES COST-EFFECTIVE FOR SUCH COMPONENTS AS COMBUSTOR LINERS, HOT SECTION COMPONENTS AND NOZZLES IN AEROSPACE AND COMMERCIAL TURBINE ENGINES.