Properties of Low-Pressure Cold-Sprayed Coatings for Repairing of Casting Defects

Low-pressure cold spraying (LPCS) is a coating technique, in which a portable cold spray system, e.g., DYMET 304K system is used to prepare technical coatings. Usually, compressed air is used as the process gas. The LPCS process is an appropriate method for spraying of metallic-ceramic composite powder materials, e.g., Cu, Ni, Zn, Al with additions of Al₂O₃ particles in the powder blends. The main functions of the hard ceramic particles are cleaning the nozzle, activating the sprayed surface and peening the coating structure. This method has advantages for example in the field of repairing and restoration applications. For that, repairing casting defects and voids is one interesting application of the process. For these purposes, zinc-based composite materials are recommended for restoration and repairing of corrosion and mechanical damages. In this study, Zn+Al+Al₂O₃, Zn+Cu+Al₂O₃ and Zn+Ni+Al₂O₃ composite materials were investigated. Zinc and aluminum give corrosion resistance by cathodic protection whereas copper and nickel will provide also more mechanical resistance. Coating properties, such as microstructures, open-cell potential behavior and mechanical properties (hardness and adhesion strength) were investigated. The coatings have relatively dense coating structures and for corrosion resistance, zinc gives a cathodic protection for other materials in these composite coatings. Furthermore, mechanical properties are sufficient due to the relatively high hardness and adhesion to the Fe52 steel base material. These coatings have high potential in their use as repair materials for macroscopic casting defects.