A Review of Advanced Composite and Nanostructured Coatings by Solid-State Cold Spraying Process

Abstract

Cold spraying (CS) has been widely explored over the last decade due to its low process temperature and limited thermal effect on spray materials. As a solid-state process, the inherent deficiencies of traditional thermal spraying such as oxidation, decomposition and grain growth are avoided. This article summarizes the research work on the fabrication of composites and nanostructured coatings by the promising CS process. After a brief introduction to CS and its deposition mechanisms, the preparation methods of spray powders are classified. Different methods are appropriate for particles of various properties, and the tendency is to design composite powders by combined methods in order to create coatings with specified properties. Then the co-deposition mechanism of composite particles as well as research findings on metal-metal, metal-ceramic and metal-intermetallic composite coatings are reviewed concerning the deposition characteristics, microstructure and its relation to properties. Moreover, CS has been used to deposit a variety of nanostructured materials, including metals, metal-ceramic composites, and even ceramics, retaining their nanocrystalline nature in the coating without grain growth or phase transformation. Finally, the potential applications of CS and issues to be addressed in coating deposition are discussed.

Intermetallic Phase Evolution of Cold-Sprayed Ni-Ti Composite Coatings: Influence of As-Sprayed Chemical Composition

“…Due to the solid-state deposition nature of the process and high deposition rates, CS shows notable advantages in fabricating a wide variety of multicomponent coatings with different melting points, including metal matrix composites (MMC) (Ref 6 - 10 ). In this method, either different powders are fed using dual feeding (Ref 11 ), or blended or mechanically alloyed powders are fed in a single stream, to produce dense MMC coatings (Ref 12 - 14 ).…”

“…In this method, either different powders are fed using dual feeding (Ref 11 ), or blended or mechanically alloyed powders are fed in a single stream, to produce dense MMC coatings (Ref 12 - 14 ). Fabrication of MMC coatings using CS is a relatively easier and more economical route compared to thermal spraying (Ref 6 , 7 , 9 , 15 ). Mixtures with several physical properties including reactive materials (Ref 16 , 17 ) can be sprayed without concern about reactions or phase transformations during the CS process (Ref 7 , 13 , 14 , 18 ).…”

“…Mixtures with several physical properties including reactive materials (Ref 16 , 17 ) can be sprayed without concern about reactions or phase transformations during the CS process (Ref 7 , 13 , 14 , 18 ). The composite mixture can be sprayed either in near-net shape (Ref 19 ) or easily machined to the desired shapes (Ref 6 ). In the case of intermetallic forming mixtures, post spray heat treatments (PSHT) are conducted to form intermetallic compounds (Ref 6 ).…”

Effect of Feedstock Powder Morphology on Cold-Sprayed Titanium Dioxide Coatings

“…During the initial deposition stage, due to the high kinetic energy of the powder in the spray process, the particles impacting the substrate will act as cleaning agents in a way similar to sand-blasting. Surface contaminants such as dirt, oils and native oxide layers are removed by the initial particle collisions [5][6].…”

“…The accepted hypothesis on the bonding process is that a coating is formed through the intensive plastic deformation of particles impacting a substrate at a temperature well below the melting point of the spray material. The bonding of cold-sprayed particles is associated with adiabatic shear instability, leading to large plastic strains, and occurs beyond a certain velocity [5].…”