High-Temperature-Functionalization of Surfaces: Drag Reduction and Self-Cleaning

Increasing requirements on technical components for high-temperature-applications (e.g., turbine blades) demand for new developments in surface engineering. The selective combination of materials with positive and negative thermal expansion coefficients (NTE) will lead to a reversible activation of the surface depending on surface temperature: The generation of a riblet structure (“shark skin”) in operation condition by thermal expansion of the matrix and shrinkage of the NTE-ceramic and self-cleaning of the surface at cool down as a result of the reversal of the process. Due to its hygroscopicity the chosen NTE-ceramic Y₂W₃O₁₂ needs to be embedded into a binder matrix. Therefore a feedstock powder consisting of MCrAlY, WO₃ and Y₂O₃ is mechanically alloyed in a high-energy ball mill. The powder is deposited on substrates by thermal spraying (VPS and HVOF) and laser cladding as well. After coating process a lateral- and depth-selective ion implantation of tungsten, yttrium and oxygen will force nucleation in predefined areas. A following heat treatment of the specimens supports the in-situ-formation of Y₂W₃O₁₂.