Processing of architectured structures for transpiration cooling – MOSART

The MOSART project aims at combining two processing techniques, EBM (Electron Beam Melting) as additive manufacturing and partial powder sintering, in order to develop a transpiration system which is robust, adjustable in terms of permeability and oxidation resistant for the walls of combustion chambers of civil and military aircraft engines. The objective is to design and optimize a multi-layer material with a porous type layer onto an architected substrate. While the porous layer, owing to its random morphology, can ensure an uniform distribution of cooling jets, the role of the architected substrate is to ensure structural strength while maximizing the cooling efficiency by an internal network of capillaries. The increase in the material life and reduction in the amount of air used for cooling would be expected by using a transpiration wall with respect to mutliperforation. In this project, such fully metallic systems include a porous layer obtained by powder sintering, combined with an architectured substrate manufactured by EBM.

EBM is a technique where the powder is locally molten via an electron beam to build 3D structures of complex geometry. This type of process called " additive manufacturing ", is particularly convenient for cooling problems, because it allows the integration of channels, grooves and ridges within massive parts. In design, the shapes can be optimized as much from a mechanical point of view, by distributing the matter around the stress fields, as from a hydraulic point of view, by setting the operating channels from the flow calculations. With the conventional techniques for producing usual multi- perforated plates, such as drilling or welding in the case of TRANSPLY ® or Lamilloy ®, such a geometrical complexity is impossible to achieve. However, EBM, as the other additive manufacturing techniques do not allow to achieve a refinement of morphological geometries such as those obtained by conventional sintering of metallic powder particles.

The advantage of a mixed solution (porous surface finish) is to provide a greater flexibility of design, to ensure both an effective transpiration close to the wall through the porous layer and to provide a structural integrity and an optimum internal cooling within the architected substrate. This porous surface finish can be manufactured by different processes which will be studied in this project. The most promising is the partial sintering of powder. It consists in a compaction at room temperature of the powder over the substrate, followed by a thermal treatment which aims at (i) sintering of metallic powder particles partially in order to keep an intrinsic porosity (around 40%); (ii) metallurgically bonding the porous coating to the substrate.

The project is divided into three technical Tasks. The first one is to develop the building blocks related to the manufacturing process of the multi- layer system in nickel-based superalloy (powder sintering, EBM manufacturing and joining). The flow investigation through the overall transpiration system is conducted in Task 2, both in terms of experimental characterization and modelling. An optimization Task will improve the system based on previous developments in order to test the selected solution in realistic conditions of use (isothermal and cyclic oxidation, structural behaviour).