On 3rd december 2018, Marie Laveissiere has defended her thesis. Awarded by the University of Toulouse, her work was supervised by both CIRIMAT laboratory (CNRS/UT3 Paul Sabatier/INP), the Science de la Matière doctoral school, and IRT Saint Exupéry.
The high quality and the relevance of Marie’s thesis contributed to get significant results as a part of SURFINNOV project.
“Elaboration and characterization of coatings prepared by Plasma Electrolytic Oxidation on TA6V titanium alloy”
About his thesis
Surface treatments are often needed for metallic materials in order to improve their performances and broaden their scope of applications. TA6V (or grade 5) titanium alloy is used in many fields (going from biomedical to aeronautical parts) because it is light and possesses good anticorrosion and thermal properties. Nevertheless its tribological behavior needs substantial improvements that a coating may provide.
The aim of this work was to prepare, using Plasma Electrolytic Oxidation (PEO), coatings on TA6V in order to improve its tribological properties. PEO is a recent and innovative electrochemical oxidation process for which growth mechanisms and accurate influence of operating parameters such as electrolyte composition or applied electrical signal, still need clarification.
Systematic study of several electrolytes led to the preparation of adherent coatings with thicknesses between 5 and 60 µm. These coatings result from both electrochemical conversion of the substrate and incorporation of compounds from the electrolyte. They are composed of an amorphous phase, its proportion depending directly on the silicates quantity in the bath, and crystalline phases formed after the important rise of surface temperature during treatment. The understanding of correlations between electrolyte and coatings have limited the formation of the soft amorphous phase and favored hard crystalline structures, leading to an optimized electrolyte.
The study of electrical parameters, such as frequency or treatment time, highlighted their strong influence on the coatings composition and morphology. The duty cycle influenced the chemical composition of the coatings, promoting the formation of crystalline alumina.
Finally coatings prepared with PEO were mechanically tested. The presence of crystalline phases allowed the increase of the coatings Vickers hardness compared to the bare TA6V. Nevertheless, due to the PEO coatings roughness, a step of mechanical polishing post-treatment appeared necessary in order to reduce the friction coefficient and wear loss. Finally, the understanding of correlations between process parameters and coatings properties, has successfully led to the preparation of a coating with promising tribological properties, namely a friction coefficient below 0.3 and a wear loss inferior to 0.01 mm3 after 100,000 cycles, demonstrating a significant improvement in surface mechanical properties of the TA6V substrate.
Developing corrosion protection solutions for light alloys by improving the tribological properties of titanium and improving surface treatments versus the temperatures required.
- Alain DENOIRJEAN, CNRS Research Director – IRCER, Limoges – Rapporter
- Gérard HENRION, CNRS Research Director – IJL, Nancy – Rapporter
- Luc LAVISSE, Lecturer – LICB, Chalon-sur-Saône – Examiner
- Catherine MABRU, Professor – ICA, Toulouse – Examiner
- Laurent ARURAULT, Professor– CIRIMAT, Toulouse – PhD Advisor
- Hélène CERDA, Research Engineer – Liebherr Aerospace Toulouse, Toulouse – Invited
M. Laveissiere, H. Cerda, L. Arurault : “Elaboration de revêtements par Oxydation Micro-Arcs sur alliage de titane TA6V”. 2016
M. Laveissiere, H. Cerda, J. Roche, L. Arurault : “Plasma Electrolytic Oxidation of TA6V for the improvement of its surface hardness”. 2017