Drag Reduction and Self-Cleaning of Thermal Sprayed Surfaces by the Combination of Materials with Positive and Negative Thermal Expansion Coefficients

The combination of materials with different thermal expansion coefficients allows a high-temperature- functionalization of the surface. By a lateral- and depth-selective distribution of particles with a negative thermal expansion coefficient (NTE) in a matrix-material with a positive thermal expansion coefficient depending on the temperature different surface topographies can be realized. This can be used to produce a riblet structure (shark skin) in operation condition. On the other hand, at cooling down, self-cleaning of the surface by the reversal of the deformation can be realized.

The chosen NTE-ceramic Y2W3O12 is highly hygroscopic and therefore has to be produced in-situ in the protective MCrAlY-Matrix. Therefore a feedstock powder consisting of MCrAlY, WO3 and Y2O3 was produced and deposited on the substrate by thermal spraying as well as laser cladding. To control the position of the NTE-particles nucleation centres were built by ion-implantation. In a following heat treatment the Y2W3O12-ceramic is formed in preference in these nucleation centres. First results prove the possibility to influence the microstructure of thermal sprayed composite powders by a following ion-implantation and heat treatment.