Characterization of thin coatings using eddy current methods.

摘要

Eddy current testing is one of the non-destructive evaluation (NDE) techniques in industries, especially in aircraft, nuclear and coating industries. The eddy current method can be applied to measure electrical conductivity and thickness of thin coatings on metallic material. As a method for NDE, the eddy current evaluation is also used for detection of corrosion in airplane structures and defects in metals. Recently we also reported an application for coating surface inspection.; In this thesis, the basic theory of eddy currents is presented and compared to experimental results. A two-probe differential system having higher sensitivity and less noise than a one-probe system was developed. The measurement method is based on pulsed eddy currents with a pulse width of 1mus that allows us to scan at rates of up to 105 pulses per second. A 2D eddy current scanning system for fast inspection of coatings and the related computer program were developed. Based on the principle of induced eddy currents, a method for characterization of thin tantalum, niobium and chromium sputtered coatings on gun stainless steel is presented. The objective of this work is to find the correlation between the sputtering conditions and conductivity of coatings and to develop a system for fast inspection of coatings as a coating quality control tool during the coating process as well as in the field for determining coating degradation levels. For tantalum coatings, the relationship between beta-Ta fraction and their conductivity is analyzed. For niobium coatings, the relationship between sputtering pressure and conductivity of coatings is examined, as well as the relationship between impurity level of process gas and conductivity of coatings. For chromium coatings, the relationship between microcrack density and conductivity of coatings is analyzed. The topographic picture and destructive analysis of these samples show very good agreement with eddy current results.; Other than this work, some other applications in the eddy current field are discussed.