Applications of spatially periodic field eddy current sensors for surface layer characterization in metallic alloys

Spatially periodic field eddy current sensors such as the Meandering Winding Magnetometer (MWM) with Grid Methods provide a powerful capability to nondestructively characterize surface layers introduced during fabrication as well as those modified by service exposure. This is critical for process quality control and component condition assessment. Conformable MWM sensors provide absolute property measurements (conductivity, permeability) and dimensional data (coating thickness, proximity) over flat and curved surfaces with minimal calibration requirements. Using a three-layer (substrate, coating, air) model and an inversion algorithm, a new measurement module has been developed to estimate the thickness of a process-affected zone and to provide a measure of property variations in this zone in real time. This paper presents results for two specific process quality control applications: (1) alpha case thickness measurements in a titanium alloy and (2) characterization of shot peening for aluminum alloys. (Author)