LASER ALLOYING OF PLASMA-DEPOSITED COATINGS FOR PROTECTION AGAINST ATOMIC OXYGEN

ATOMIC OXYGEN-INDUCED DEGRADATION OF MATERIALS IN LOW EARTH ORBIT IS A PROBLEM OF GREAT CONCERN IN THE DEPLOYMENT OF SATELLITES, REFLECTORS AND MIRROR AND ANTENNA STRUCTURES. IN PARTICULAR, THE DEGRADATION OF THIN CARBON-CARBON COMPOSITE MATERIALS BY ATOMIC OXYGEN RESTRICTS THE OPERATIONAL LIFE AND BATTLE-READINESS OF THIS OTHERWISE STRUCTURALLY ADVANTAGEOUS MATERIAL. ALTHOUGH SEVERAL METHODS ARE BEING DEVELOPED TOPROTECT THIN CARBON-CARBON COMPOSITE MATERIALS FROM ATOMIC OXYGEN ATTACK, NO METHOD HAS PROVEN SUCCESSFUL, IN PART BECAUSE OF THE DIFFERENTIAL THERMAL EXPANSION EXPERIENCED BY COATINGS AND IN PART BECAUSE OF LOW BONDING ENERGIES BETWEEN A COATING AND THE CARBON-CARBON SURFACE. A TWO STEP PROCESS IS BEING INVESTIGATED FOR DEPOSITING A GRADED OXIDATION-RESISTANT COATING ONTO CARBON-CARBON COMPOSITE MATERIALS USING PLASMA SPRAY TECHNIQUES FOLLOWED BY LASER SURFACE ALLOYING. THE INNOVATION OF THIS SYSTEM INVOLVES THE VERSATILITY OF THE COATING METHOD, THE PROVEN ABILITY OF PLASMA SPRAY TECHNOLOGIES TO LAYDOWN EXTREMELY THIN COATINGS ON CARBON-CARBON COMPOSITE MATERIALS, AND THE CONTROL OVER COMPOSITION AND MICROSTRUCTURE AFFORDED BY LASER SURFACE ALLOYING. PLASMA-SPRAY MATERIALS ARE BEING EVALUATED; OPTIMAL PLASMA DEPOSITION AND LASER ALLOYING PARAMETERS DETERMINED; AND MATERIALS FABRICATED AND TESTED UNDER CYCLIC CONDITIONS.