Detection of Residual Stresses and Nodular Growth in Thin Ferromagnetic Layers with Barkhausen and Acoustic Microscopy

The measurements described here showed that Barkhausen microscopy allows qualitative and quantitative determination of residual stresses in ferromagnetic thin layers. Moreover, the BEMI enables fast qualitative imaging with high local resolution of residual stress distributions in specimens. A good correlation was found between residual stress values obtained by magnetic and X-ray measurements. Reference residual stress values can be obtained by means of four-point-curvature instead of X-ray measurement. Thus, the calibration would no longer depend on the X-ray measurements bearing the big disadvantage of lower resolution and immense time efforts. Calibration by means of tensile tests is impossible because of the brittleness of the ceramic substrate. A coupling of micromagnetic and reference measuring values can be achieved by means of training with a neural network. With the help of acoustic microscopy growth defects in thein layers coud be detected and characterized. Thus, new knowle dge about the structure and properties of these defects were obtained.