To improve the low formability that HSS sheets exhibit at room temperature, innovative forming technologies like the hot stamping process are currently applied. In order to avoid scaling and decarburization during the heating step, metal sheets coated with a specially developed Al-Si coating are utilized. In the present work the coating characteristics in terms of morphology, surface roughness and tribological behaviour are investigated as function of heating temperature, holding time and cooling rate that are typical of hot stamping processes.
The new and fast scatterometry method called optical diffraction microscopy is compared with atomic-force microscopy by use of cross-section scanning-electron microscope images as references. The sample is a high-aspect-ratio grating with a period of approximately 1000 nm. To allow the atomic-force microscope to track all parts of the grating profile, the grating is investigated at different tilt angles. The measured quantities of the profile include sidewall angle gamma (approximately 90 degrees), groove height h (approximately 2000 nm), and degree of filling f (approximately 40%). The two methods, which respond to quite different material properties, give consistent results within standard uncertainties of u(gamma)=0.8 degrees , u(h)=15 nm, and u(f)=1%.
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