Fractal analysis of a new generation of HVOF sprayed coatings based on optical surface metrology

Yibo Zou; Markus Kästner; Eduard Reithmeier

doi:10.1515/teme-2016-0006

Article

Fractal analysis of a new generation of HVOF sprayed coatings based on optical surface metrology

Yibo Zou
Yibo Zou is a graduate student and research assistant at the Leibniz University of Hannover. Since 2013 he started with his research at the Institute of Measurement and Automatic Control and his research interests are surface characterization, roughness measurement and image processing.
Institute of Measurement and Automatic Control, Leibniz Universität Hannover, Nienburger Straße 17, 30167 Hannover, Germany, Tel.: +49-511-762-4284
, Markus Kästner
Markus Kästner is the group leader of Production Metrology of the Institute of Measurement and Automatic Control, Faculty Mechanical Engineering of the Leibniz University of Hannover.
Institute of Measurement and Automatic Control, Leibniz Universität Hannover, Nienburger Straße 17, 30167 Hannover, Germany, Tel.: +49-511-762-4286
and Eduard Reithmeier
Eduard Reithmeier is the director of the Institute of Measurement and Automatic Control, Faculty Mechanical Engineering of the Leibniz University of Hannover.
Institute of Measurement and Automatic Control, Leibniz Universität Hannover, Nienburger Straße 17, 30167 Hannover, Germany, Tel.: +49-511-762-3334

Published/Copyright: June 4, 2016

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From the journal tm - Technisches Messen Volume 83 Issue 6

Abstract

In this article, fractal analysis combined with roughness measurement is proposed to characterize the new generations of HVOF sprayed coatings' surface textures. Two-dimensional and three-dimensional box counting algorithms are introduced to determine the fractal dimension, which is considered as a scale-invariant parameter and is able to describe chaos and complexity of the surface. For surface roughness metrology, a confocal laser scanning microscope with different lenses is used to acquire the areal topography, providing a sequence of height maps with different image resolutions. Typical areal roughness parameters are assessed based on the international standard ISO-25178. The results show that the fractal dimension is a powerful tool to depict the nature of the surface texture of the investigated coatings. Moreover, it is found that the traditional amplitude roughness parameters depend strongly on the range of the measurement field as well as the datasets' resolution, whereas the fractal dimension is rather invariant to the scales of the measured datasets. Finally, the correlation between the fractal dimension and roughness parameters is given at the end of this paper.

Zusammenfassung

Diese Arbeit beschreibt eine Anwendung der fraktalen Analyse zur Charakterisierung der Oberflächenmikrotopographie bzw. Rauheit thermisch gespritzter HVOF (High Velocity Oxy Fuel) Beschichtungen. Basierend auf der fraktalen Dimension als skaleninvariante Kenngröße, welche mit Hilfe dimensioneller Box-Counting-Algorithmen bestimmt wird, können die Komplexität sowie die deterministischen- und stochastischen Anteile der Oberflächenmikrostruktur beschrieben werden. Zur Messdatenerfassung wird ein konfokales Laser-Scanning-Mikroskop mit unterschiedlichen Objektiven verwendet, so dass die erfassten Mikrotopographien der untersuchten Oberflächenbeschichtungen mit unterschiedlichen Auflösungen dargestellt werden können. Die Ergebnisse der Untersuchungen zeigen, dass die fraktale Analyse eine leistungsfähige Methode zur Charakterisierung der geometrischen Eigenschaften der gemessenen Oberflächen darstellt. Für Vergleichsuntersuchungen wurden zudem nach ISO-25178 genormte Rauheitsparameter ausgewertet. Neben Korrelationsuntersuchungen konnte zudem experimentell gezeigt werden, dass die ausgewerteten genormten Rauheitskenngrößen stark abhängig von den verwendeten Messfeldgrößen sowie den Bildauflösungen sind. Im Gegensatz dazu verhält sich die fraktale Dimension als Kenngröße invariant gegenüber solchen Skalierungseffekten.

Keywords: Fractal analysis; new HVOF sprayed coating; roughness measurement; box-count algorithm; optical metrology

Schlagwörter: Fraktale Analyse; HVOF Oberflächenbeschichtungen; Rauheitsmesstechnik; Box-Count Algorithmen; Optische Messtechnik

About the authors

Yibo Zou

Yibo Zou is a graduate student and research assistant at the Leibniz University of Hannover. Since 2013 he started with his research at the Institute of Measurement and Automatic Control and his research interests are surface characterization, roughness measurement and image processing.

Institute of Measurement and Automatic Control, Leibniz Universität Hannover, Nienburger Straße 17, 30167 Hannover, Germany, Tel.: +49-511-762-4284

Markus Kästner

Markus Kästner is the group leader of Production Metrology of the Institute of Measurement and Automatic Control, Faculty Mechanical Engineering of the Leibniz University of Hannover.

Institute of Measurement and Automatic Control, Leibniz Universität Hannover, Nienburger Straße 17, 30167 Hannover, Germany, Tel.: +49-511-762-4286

Eduard Reithmeier

Eduard Reithmeier is the director of the Institute of Measurement and Automatic Control, Faculty Mechanical Engineering of the Leibniz University of Hannover.

Institute of Measurement and Automatic Control, Leibniz Universität Hannover, Nienburger Straße 17, 30167 Hannover, Germany, Tel.: +49-511-762-3334

Acknowledgement

The authors would like to thank the graduate school “Multiscale Methods of Interface Coupling” in Leibniz University of Hannover for the financial support.

Received: 2016-2-11

Revised: 2016-2-22

Accepted: 2016-2-23

Published Online: 2016-6-4

Published in Print: 2016-6-28

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Articles in the same Issue

https://doi.org/10.1515/teme-2016-0006

Keywords for this article

Fractal analysis; new HVOF sprayed coating; roughness measurement; box-count algorithm; optical metrology