Formation of ZTA-composite ceramic coatings with high fracture toughness and fatigue-resistance on aluminium substrates by plasmaelectrolytic oxidation

• Applicant: Professor Dr.-Ing. Thomas Lampke
• Subject Area: Coating and Surface Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 500196783

Plasma electrolytic oxidation (PEO) is an innovative process for the production of ceramic protective coatings. Complexly shaped aluminium components can be qualified for application fields requiring high resistance against wear and corrosion. Furthermore, the construction with lightweight materials contributes to resource efficiency. A limiting factor for application fields is the reduced fatigue strength resulting from PEO due to the brittle nature of the oxide coating. However, since cyclic stresses are present in most application fields and especially in moving systems, it is necessary to increase the damage tolerance of the coatings and thus the service life of the coated component. Bulk ceramic materials meeting high requirements on the fatigue strength are usually based on zirconium oxide due to its higher fracture toughness when compared to aluminium oxide. Therefore, the aim of the proposed project is to improve the fatigue strength of plasma electrolytically oxidized aluminium substrates by forming crack-tough, damage-tolerant composite ceramic layers consisting of Al₂O₃/ZrO₂. To achieve this goal, stable REACh-compliant Zr-containing electrolytes are being developed to enable the production of these coatings using PEO. The complex interrelationships between the PEO process (electrolyte composition, electrical regime and treatment time) and the composition of the composite ceramic layers (volume fraction, phase distribution of the ZrO₂ compounds) are systematically investigated using optical emission spectroscopy and a process diagnostics software developed in previous DFG projects, which combines and evaluates optical, electrical and spectral process information. In feedback with microstructural, micro and macro-mechanical analyses, fundamental insights can be gained regarding the effective relationships between the coating microstructure and their fracture mechanical properties as well as the resulting fatigue strength of coating aluminium substrate system. The focus is on a comprehensive understanding of the incorporation mechanisms of ZrO₂ phases into the alumina coating as a function of the PEO process regime as well as the influence evaluation of the zirconia phases on the crack initiation under cyclic loading and the local crack toughness in correlation with the coating microstructure and the damage tolerance of the composite ceramic layers.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Lisa Winter