Fabrication of riblet structures on a Ni-based superalloy (PWA1483) for potential drag reduction in high temperature applications based on laser optimization

We propose a new laser-based fabrication process of small-sized riblets on PWA1483 coated on a 3 mm-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 mm 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.