ENVIRONMENT-RESISTANT COATINGS FOR TI-ALLOYS

THE NICOCRAIY COMPOSITES ARE EXTENSIVELY USED FOR OXIDATION PROTECTION OF NI-BASE SUPERALLOYS. HOWEVER, FOR HIGHER TEMPERATURE TI-ALLOYS, THIS OVERLAY WILL REACT WITH THE SUBSTRATE THUS DEFEATING THE INTENDED PURPOSE OF THE COATING. THIS PROJECT EXPLORES THE DEVELOPMENT OF A COMPOSITE COATING WHERE AN INTERMEDIATE NITI LAYER IS INTERPOSED BETWEEN THE TITANIUM ALLOY AND THE NICOCRAIY OVERLAY. THE DUCTILE NITI LAYER CAN ACCOMMODATE INTERFACIALSTRESSES GENERATED DUE TO THE THERMAL EXPANSION MISMATCH BETWEEN THE BASE MATERIAL AND THE PROTECTIVE COATING. IN ADDITION TO NITI BEING COMPATIBLE WITH TITANIUM, IT IS EXPECTED TO BE COMPATIBLE WITH THE NICOCRAIY LAYER AS WELL. THE ESTABLISHMENT OF THIS COMPOSITE COATING APPROACH WILL RESULT IN A RATHER QUICK AND EASY ADAPTATION OF THE WELL-EXAMINED AND APPLIED NICOCRAIY COATING TO TITANIUM ALLOYS, THUS ENHANCING THEIR CAPABILITY FOR HIGH-PERFORMANCEGAS TURBINE APPLICATIONS. THE NICOCRAIY COMPOSITES ARE EXTENSIVELY USED FOR OXIDATION PROTECTION OF NI-BASE SUPERALLOYS. HOWEVER, FOR HIGHER TEMPERATURE TI-ALLOYS, THIS OVERLAY WILL REACT WITH THE SUBSTRATE THUS DEFEATING THE INTENDED PURPOSE OF THE COATING. THIS PROJECT EXPLORES THE DEVELOPMENT OF A COMPOSITE COATING WHERE AN INTERMEDIATE NITI LAYER IS INTERPOSED BETWEEN THE TITANIUM ALLOY AND THE NICOCRAIY OVERLAY. THE DUCTILE NITI LAYER CAN ACCOMMODATE INTERFACIALSTRESSES GENERATED DUE TO THE THERMAL EXPANSION MISMATCH BETWEEN THE BASE MATERIAL AND THE PROTECTIVE COATING. IN ADDITION TO NITI BEING COMPATIBLE WITH TITANIUM, IT IS EXPECTED TO BE COMPATIBLE WITH THE NICOCRAIY LAYER AS WELL. THE ESTABLISHMENT OF THIS COMPOSITE COATING APPROACH WILL RESULT IN A RATHER QUICK AND EASY ADAPTATION OF THE WELL-EXAMINED AND APPLIED NICOCRAIY COATING TO TITANIUM ALLOYS, THUS ENHANCING THEIR CAPABILITY FOR HIGH-PERFORMANCEGAS TURBINE APPLICATIONS.