Experimental study on etching method for fabricating cooling passages in combined-cycle-engine wall

An etching method as a fabrication technique for cooling passages in a combined-cycle-engine wall was investigated. A nickel-based heatproof alloy, which is a candidate material for the walls of combined cycle engines, is hard, and machining of thin cooling passages in a large area is difficult. By the use of this etching method with photographic print, a large area can be easily processed at the same time. As this nickel-based heatproof alloy is also corrosion resistant, ferric chloride solution, a conventional etching solution, cannot be used for such etching. Thus, the authors chose an electrochemical technique for dissolving the nickel-based heatproof alloy and applied it for processing of the passages on the nickel-based heatproof alloy plate. In this experiment, the passages were carved on the entire surface of the plate, the size of which was 350mm × 220 mm. The passages at the edge of etched plate were observed to be deeper than those in the center area, and the ribs between passages at the edge were narrower than those in the center area. It was suggested that these phenomena occurred due to the uneven current distribution on the plate.