Fabrication of Riblet Structures on a Ni‐based Superalloy (PWA1483) for Potential Drag Reduction in High Temperature Applications Based on Laser Optimization

Abstract

We propose a new laser‐based fabrication process of small‐sized riblets on PWA1483 coated on a 3 μm‐thin sputtered Ni/Cr/Ni multilayer. Laser ablation was used for local material removal. Subsequent oxidation was used to provide an optimal riblet dimensions for a drug reduction and oxidation resistance. As a result of the heat treatment, a 7 μm oxide film was formed. The oxide film consists of two different oxide layers: while the upper one is formed of a dense Cr2O3 layer with NiO, Cr2NiO4, and TiO2 inclusions, the bottom one mainly consists of alpha‐Al2O3. Between the riblets, a TiO2 layer was formed on the top of Cr2O3 layer. First mechanical tests showed a promising riblet stability under the low‐cycle fatigue load, under tension, and under quasi‐cyclic bending load. The riblets also exhibit no severe failure by applying a quasi‐cyclic bending stress of 900 MPa for 200 times. Furthermore, cyclic tensile loading with a mean load of 500 MPa and an amplitude of 220 MPa corresponding to a strain range of 0.35% (stress level of R = 0.35) led to no damage of the riblet structure.