Abstract
Based on the recent analysis of various databases, cold spray (CS), the newest method among thermal spraying technologies, has received the unabated attention of hundreds of researchers continuously since its invention in the 1980s. The significance of CS lies in the low process temperature, which usually ensures compressive residual stresses and allows for the formation of coatings on a thermally sensitive substrate. This paper concerns the low-pressure cold spray (LPCS) variant employed for forming metal matrix composites (MMCs) with high ceramic contents and all-ceramic coatings. At the very beginning, the influence of LPCS process parameters on deposition efficiency (DE) is analysed. In the next part, the most useful feedstock powder preparation techniques for LCPS are presented. Due to the combination of bottom-up powder production methods (e.g., sol-gel (SG)) with LCPS, the metal matrix that works as a binder for ceramic particles in MMC coatings can be removed, resulting in all-ceramic coatings. Furthermore, with optimization of spraying parameters, it is possible to predict and control phase transformation in the feedstock material. Further in the paper, differences in the bonding mechanism of metal–ceramic mixtures and ceramic particles are presented. The properties and applications of various MMC and ceramic coatings are also discussed. Finally, the exemplary direction of CS development is suggested.
Highlights
Cold gas dynamic spraying, known as kinetic spraying or cold spraying (CS), was originally developed in the mid-1980s as a coating deposition process by A
Luo et al [125] found that the grain size of the NiCrAl matrix in the cBN–NiCrAl composite powder prepared by mechanical alloying decreased to a few tens of nanometres with increasing mechanical alloying duration (Figure 9)
Further CS experiments should be concentrated on the following challenges: (i) selecting optimal parameters for powder preparation to CS; (ii) applying of ceramic or metal–ceramic powder material modifications or CS process optimization, e.g., new nozzle design, to spray highly coherent coatings without vacuum or further postspraying heat treatment (PSHT); (iii) balancing work hardening with toughness and ductility of metal matrix composites (MMCs) coating by CS parameters adjustment mainly for additive manufacturing applications; (iv) tailoring the ratio, size, concentration, and distribution of ceramic phase in the deposited MMC coating; (v) analyzing nonmetallic substrates preparation method, e.g., surface texturing, for improved bonding; (vi) selecting parameters to control the phase transition, e.g., amorphous to anatase in the spraying process or intermetallic formation in PSHT
Summary
Known as kinetic spraying or cold spraying (CS), was originally developed in the mid-1980s as a coating deposition process by A. While improving the CS process, Papyrin’s team successfully deposited a wide range of pure metals, metal alloys, and metal–ceramic composites on a variety of substrate materials and demonstrated the feasibility of cold spraying for various applications. To safeguard this innovative technology in other continents, a U.S patent on CS was issued in 1994 [6], and a European one in 1995 [7]. Several parameters are influencing the CS process, including, powder and substrate material, particle morphology, oxidation level and spraying temperature, which decide about the coating formation and deposition efficiency as well [8,9,16]. Modern applications of LPCS divided into metal–ceramic composite and al–ceramic coatings are discussed
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