Barkhausen noise and eddy current microscopy - a new scanning probe technique for microscale characterization of materials

The need for an accelerated development of new materials and surfaces raises expectations in lateral homogeneity and quantitative exactness of the characteristic material properties. The interest is focused on microstructure characterization, detection of micro-imperfections and evaluation of the local distribution of residual stresses, mechanical hardness and coating thickness. These requirements meet with the development of high-resolution NDT methods such as Barkhausen Noise and Eddy Current MIcroscopy (BEMI) at IZFP. BEMI enables locally high-resolved non-destructive materials testing by means of Barkhausen noise and eddy current analysis: The sample is scanned with a miniaturised inductive probe which serves as Barkhausen noise pick-up and eddy curremt inductive sensor. Characteristic quantities are derived from the measured data and mapped as 2-D or 3-D images allowing the recognition of defects as small as 5µm. The device is controlled by a modular measuring system which is split into modules for positioning, data acquisition and evaluation. Two additional software modules enable contact-less, quantitative testing of sensitive surfaces. This way, thin coatings can be characterized regarding their microstructure, thickness, internal stresses and heat-treatment condition. The efficiency of this device was demonstrated on many materials as solids stacks of several thin films. The BEMI testing device achieves an accuracy of 10 nm for the thickness of thin films on a variety of substrates.