DEVELOPMENT OF OXIDATION PROTECTION COATINGS FOR NB/NB5SI3 IN-SITU COMPOSITES

RECENT STUDIES AT THE AIR FORCE MATERIALS DIRECTORATE (WL/MLLM) HAVE SHOWN THAT NB-NB5SI3 BASED IN-SITU COMPOSITES HAVE THE POTENTIAL FOR PROVIDING AN ACCEPTABLE BALANCE IN LOW-TEMPERATURE TOUGHNESS AND HIGH-TEMPERATURE STRENGTH/CREEP RESISTANCE, AND THEREFORE, ARE ATTRACTIVE CANDIDATES AS HIGH-TEMPERATURE STRUCTURAL MATERIALS FOR ADVANCED AEROSPACE APPLICATIONS. HOWEVER, CATASTROPHIC OXIDATION AND EMBRITTLEMENT OF THESE MATERIALS LIMIT THEIR USEFULNESS IN ENGINE APPLICATIONS. UES, THEREFORE, IS PROPOSING AN SBIR PROGRAM TO DEVELOP OXIDATION-PROTECTIVE COATINGS FOR THE NB-NB5SI3 COMPOSITE SYSTEM, USING PHYSICAL VAPOR DEPOSITION, SPECIFICALLY, THE SPUTTER DEPOSITION PROCESS. THE REQUISITE ROLE OF THE PROTECTIVE COATINGS IS TO PROVIDE (A) A RESERVOIR FOR A PROTECTIVE, OXIDE SCALE FORMATION ON THE SURFACE, AND (B) A REASONABLE SUBSURFACE DIFFUSION BARRIER AROUND THE BASE ALLOY. THE PHASE I TECHNICAL OBJECTIVES ARE (A) TO DEMONSTRATE THE POTENTIAL OF THE SPUTTER DEPOSITION PROCESS FOR OBTAINING HIGHLY CONTROLLED, REPRODUCIBLE, DEFECT-FREE, UNIFORM COATINGS OF MOSI2 AND MO(GE,SI)2, AND MULTILAYER COATINGS OF (NB,MO)5SI3/MO5SI3/MOSI2 ON A SELECTED NB-NB5SI3 BASE ALLOY, AND (B) TO EVALUATE THE EFFECTIVENESS OF THE COATINGS IN FORMING A PROTECTIVE SURFACE OXIDE SCALE UNDER STATIC OXIDATION CONDITIONS.