Chemical effects during the formation of various types of femtosecond laser-generated surface structures on titanium all
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Chemical effects during the formation of various types of femtosecond laser‑generated surface structures on titanium alloy C. Florian1 · R. Wonneberger2 · A. Undisz2 · S. V. Kirner1 · K. Wasmuth1 · D. Spaltmann1 · J. Krüger1 · J. Bonse1 Received: 6 January 2020 / Accepted: 26 February 2020 © The Author(s) 2020
Abstract In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil. Keywords Laser-induced oxide layer · Laser-induced periodic surface structures · LIPSS · Femtosecond laser processing · Tribology · Surface chemistry · XRD · GD-OES
1 Introduction The fabrication of laser-induced periodic surface structures (LIPSS) on metals, semiconductors, and dielectrics has been experimentally demonstrated when irradiated with linearly polarized high-intensity ultrashort laser pulses. The formation process is influenced by the materials’ optical, thermal, and mechanical properties [1–4]. Depending on the specific final application, other factors may be relevant such as the chemistry of the irradiated areas, the resulting crystallinity, and its final optical * C. Florian camilo.florian‑[email protected] * J. Bonse [email protected] 1
Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
Otto Schott Institute of Materials Research (OSIM), Chair of Metallic Materials, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany
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response [5]. In recent years, such periodic surface structures have been fabricated systematically for applications in optics, medicine, fluid transport, wetting, and tribology [5–10], exploring different laser processing parameters (fluence, wavelength, repetition rate, polarization, angle of incidence, number
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