NOVEL, MOSI2-BASED COMPOSITES WITH SURFACE COMPRESSIVE STRESSES

FLAW SENSITIVITY LIMITS APPLICATIONS OF CERAMICS IN SEVERAL STRUCTURAL APPLICATIONS. MAJORITY OF FAILURES ORIGINATE FROM SURFACE FLAWS INTRODUCED DURING SERVICE. ENHANCED RESISTANCE TO CONTACT-INDUCED DAMAGE SHOULD SIGNIFICANTLY INCREASE APPLICATION OF CERAMICS. THREE LAYER COMPOSITES CONSISTING OF SURFACE COMPRESSIVE ZONES DESCRIBED IN THIS PROPOSAL EXHIBIT EXTREMELY HIGH RESISTANCE TO CONTACT DAMAGE. EVEN AFTER INDENTING WITH A VICKER'S INDENTER UNDER 1000 N (225 LBS.) LOAD, THE STRENGTH IS RETAINED TO GREATER THAN 600 MPA (100 KSI). IN THE PRELIMINARY WORK, THIS WAS ACHIEVED IN AL(2)0(3)-ZRO(2) BY FORMING LAYERED STRUCTURES WITH OUTER LAYERS CONTAINING UNSTABILIZED ZIRCONIA AND ALUMINA. THE TECHNIQUE IS NOT LIMITED TO OXIDES. IT IS PROPOSED THAT MOSI(2)-BASED THREE LAYER COMPOSITES WITH SIC AND MULLITE AS OUTER LAYERS IS PROPOSED. STRENGTHS IN EXCESS OF 2 GPA WITH EXCELLENT DAMAGE RESISTANCE IS ANTICIPATED. THE EFFECT OF SURFACE COMPRESSIVE STRESSES WILL BE TO ENHANCE THE RELIABILITY OF STRUCTURAL CERAMICS. ANTICIPATED BENEFITS/POTENTIAL APPLICATIONS - THE DEVELOPMENT OF STRUCTURAL CERAMICS WITH EXCELLENT RESISTANCE TO CONTACT-INDUCED DAMAGE, WHICH IS THE MAIN SHORTCOMING OF CERAMICS, AND STRENGTH RETENTION TO 1400¿C WILL BE THE PRINCIPAL BENEFIT. THESE CERAMICS WILL HAVE APPLICATIONS AS WEAR PARTS, VALVE SEATS, ARMOR PLATES, CUTTING TOOLS, DIESEL ENGINE PARTS AND CERAMIC TURBINES.