When it came to purchasing a new measurement device to perform meaningful corrosive investigations, the ability to measure polished and strongly reflective surfaces with steep flanks in true colour information is mandatory for the Christian Doppler Laboratory for Localized Corrosion. 

The Laboratory, part of the Montan-Univeristy, Leoben, Austria, particularly focuses on the evaluation and measurement of pit and degradation depths via surface and roughness measurement. Results are used for further R&D activities, which are targeted at the development of new measures to strengthen corrosive resistance of metallic components.

Irrespective of the type of corrosion, attacked surfaces usually show steep flanks and strongly varying reflection properties. With the objective of strengthening corrosion resistance, the laboratory was looking for an instrument that meets clearly specified requirements. Joachim Haberl from the scientific staff describes the requirements: “We were looking for an instrument that is able to measure polished and literally glassy surfaces and flanks of more than 80°. We wanted a system that offers true colour visualization to make sure that surfaces are measured effectively. Also, we expected a system providing high resolution measurements on mechanically polished surfaces with a roughness Ra > 50nm. Also, the measurement of large measurement fields had to be provided.”

Today, the Laboratory works with InfiniteFocus, a high resolution optical 3D measurement device from Alicona. Based on the principle of Focus-Variation, the instrument meets all requirements of the scientific staff. Measurements reach a vertical resolution of up to 10nm even at steep flanks and strongly varying reflection properties. Additionally, InfiniteFocus simultaneously captures the entire surface topographic information in combination with its true colour information. Both, the topographic and colour information are registered to the 3D data file.

InfiniteFocus is mainly used to analyse mechanically influenced corrosion, e.g. stress corrosion cracking, corrosion fatigue cracking or erosion corrosion. Pitting corrosion, crevice corrosion and selective corrosion are further fields of interest. “We mainly use the system to measure metallic components such as stainless steels, nickel-base alloys, titanium or aluminium alloys” says  Joachim Haberl. 

So, for example, to measure  erosion corrosion, the instrument provides profile analysis to measure depth and area analysis to reveal deep voids as distinctive characteristics. Conventional computations such as the calculation of the average depth are not as meaningful as the actual numerical verification of a void’s depth. Values as average data are less representative since they do not comprise any information about the deepest degradation depth. The Christian Doppler Laboratory for Localized Corrosion uses measurement results for further computations of degradation rates. Haberl comments: “Compared to other systems we tried, InfiniteFocus is by far the most suitable instrument to deal with complex corroded surfaces. One of its most distinctive features is the ability to gain numerical information with registered true colour information.”