ACCURATE MEASUREMENT OF COATING THICKNESS ON FULLY-FINISHED NON-ORIENTED ELECTRICAL STEELS USING FIB-SEM

In this study we investigated the potential of using FIB-SEM microscopy to measure the thickness of coated layers on fully-finished, non-oriented electrical steel of NO grades. When using FIB-SEM with gallium ions (Ga+) to prepare cross-sections of layers with a thickness of a few micrometers (µm), precise ablation of the material with good spatial resolution is essential. Ga+ generated at an accelerating voltage of 30 kV enable the effective localized removal of material. The sample can be protected with a thin layer of platinum (Pt) deposited by Ga+ to prevent damage to the top layer during the initial ablation process and to achieve a smoother final cut. The result of this procedure is a clean and sharp cross-section suitable for high-resolution SEM imaging. The presented microscopic method for measuring the thickness of the coatings on fully-finished, non-oriented, electrical steel samples using FIB-SEM has proven to be repeatable, robust, specific, and has an appropriate detection limit for the thickness range of typical coated layers in non-oriented electrical steel sheet.