THICKNESS GAUGING OF COMPLEX COATINGS ON TURBINE COMPONENTS

THE PRINCIPAL OBJECTIVE OF THIS PROJECT IS TO CRITICALLY EVALUATE TWO ALTERNATIVE TECHNIQUES FOR NON-DESTRUCTIVE MEASUREMENT OF COMPLEX COATINGS ON TURBINE COMPONENTS, NAMELY EDDY CURRENT AND BETABACKSCATTER. THE COATING EVALUATION WOULD BE CARRIED OUT ON INDIVIDUAL COMPONENTS AND ON ACTUAL PARTS INSTALLED IN ENGINES. ACHIEVEMENT OF THESE OBJECTIVES WOULD PERMIT COATING PROCESS MONITORING OF TURBINE PARTS DURING MANUFACTURE AND ACCEPTANCE TESTING AND ALSO SHOULD ENABLE ASSESSMENT OF REMAINING LIFE ON COATED TURBINE PARTS AT SELECTED SERVICE INTERVALS. BOTH INSPECTION TECHNIQUES ARE EMPIRICAL AND COMPARATIVE METHODS WHICH REQUIRE APPROPRIATE STANDARDS FOR CALIBRATION OF THE INSTRUMENTATION. THESE STANDARDS SHOULD BE SPECIFIC WITH REGARD TO MATERIAL SUBSTRATE AND COATING COMPOSITION AND APPROPRIATE AGING WOULD BE NECESSARY FOR IN SITU PART TESTING ON ENGINES FOLLOWING PERIODS IN SERVICE. A KEY PART OF THE PROJECT WOULD THEREFORE BE SELECTION AND VALIDATION OF THE NECESSARY STANDARD SAMPLES. THE INITIAL MATERIAL CONDITION AND COMPOSITION OF BOTH COATING AND SUBSTRATE MAY BE SIGNIFICANTLY MODIFIED DURING SERVICE, BY THERMAL AND ENVIRONMENTAL EFFECTS. ALTHOUGH BOTH MEASUREMENT TECHNIQUES MAY BE CONSIDERED COMPLEMENTARY, NEWER OR POTENTIAL NEW DEVELOPMENTS MAY EXTEND THE RANGES OF EACH TECHNIQUE.