TBC Characterization Using Magnetic and Electric Field Sensors

Recent advances in magnetic and electric field sensors have enabled accurate measurements of bond coat and top coat material properties and thicknesses. This paper reviews current methods of using electric and magnetic field sensors for coating assessment in separate measurements and in a hybrid magnetic-electric sensor construct. Magnetic field (inductive) sensors can be used to characterize gas turbine components by providing critical information about the thickness and condition of the metallic bond coat and thickness of the top coat. Electric field (capacitive) sensors can be used to characterize ceramic top coats by providing information about the thickness, condition, and surface roughness of the top coat. Using multivariate inverse methods and precomputed model-derived databases, multiple unknown coating properties are estimated simultaneously and independently. The capability to independently estimate four unknowns with one sensor and as many as six unknowns with both sensors together enables practical application of this technology for manufacturing quality and in-service condition assessment. Together, these two sensors can provide an effective method of nondestructively characterizing both metallic and ceramic coatings on turbine components.