Cold spray is a solid-state coating deposition technology which has recently been applied as an additive manufacturing process to fabricate individual components and to repair damaged components. In comparison with fusion-based high-temperature additive manufacturing processes, cold spray additive manufacturing (CSAM) has been shown to retain the original properties of the feedstock, to produce oxide-free deposits, and to not adversely influence underlying substrate materials during manufacture. Therefore, CSAM is attracting considerable attention from both scientific and industrial communities. Although CSAM is an emerging additive manufacturing technology, a body of work has been carried out by various research groups and the technology has been applied across a range of manufacturing areas. The purpose of this paper is to systematically summarize and review the CSAM-related work to date.

Cold spray additive manufacturing and repair: Fundamentals and applications

Microstructure and corrosion performance of a cold sprayed aluminium coating on AZ91D magnesium alloy

Today, cold gas dynamic spray (CGDS) technology has thrived with considerable capabilities for manufacturing various technological depositions. The deposition conditions have been developed through many years and that have led to produce ample experimental data which is available in the literature. But, recent research and development activities also reveal innovative findings regarding various deposition conditions. This paper contains a review of experimental deposition procedures for the cold spray additive manufacturing. Details of processing conditions are reported and classified into various categories of baseline working conditions, specific processing including deposition of nanotechnological components, composites-based structures and hybrid coating with substrate deposition. Available substrate treatments and their contributions on the deposition capability were also included. A large collection of experimental data from the literature is addressed in the Section 7.

Cold gas dynamic spray technology: A comprehensive review of processing conditions for various technological developments till to date

When describing the cold-spray process, one of the most widely used concepts is the critical velocity. Current models predicting critical velocities take the temperature of the sprayed particles explicitly into account, but not the surface temperature (substrate or already deposited layers) on which the particle impacts. This surface temperature is expected to play an important role, since the deformation process leading to particle bonding and coating formation takes place both on the particle and the substrate side. The aim of this work is to investigate the effect of the substrate temperature on the coating formation process. Experiments were performed using aluminum, zinc, and tin powders as coating materials. These materials have a rather large difference in critical velocities that gives the possibility to cover a broad range of deposition velocity to critical velocity ratio using commercial low-pressure cold-spray system. The sample surface was heated and the temperature was varied from room temperature to a high fraction of the melting point of the coating material for all three materials. The change in temperature of the substrate during the deposition process was measured by means of a high speed IR camera. The coating formation was investigated as a function of (1) the measured surface temperature of the substrate during deposition, (2) the gun transverse speed, and (3) the particle velocity. Both single particle impact samples and thick coatings were produced and characterized. Both the particle-substrate and interparticle bonding were evaluated by scanning electron microscopy (SEM) and confocal microscopy.

Effect of Substrate Temperature on the Formation Mechanism of Cold-Sprayed Aluminum, Zinc and Tin Coatings

Cold spraying (CS) is a relatively new material deposition technique based on the phenomenon of high-velocity particle/substrate impact. In this process, the powder is accelerated to supersonic speed in specially developed supersonic nozzles in which air, nitrogen or helium is usually employed as a powder carrier gas. In the absence of melting, oxidation and thermal decomposition of a particle in-flight during CS, the deposited coatings demonstrate low residual stresses and preserve the initial phase composition of the source material, which are important advantages for spraying temperature sensitive powders including nanostructures and nanocomposites. In the present paper the review in the field of development of cold spray technology is performed. Different scientific and technological aspects of CS such as surface activation, nozzle geometry, powder preheating, powder injection, control of spatial resolution of particle flux and proper selection of spraying parameters are discussed.

Cold spraying: From process fundamentals towards advanced applications

Cold spray process is an emerging technique that produces high density coatings. Particles (1 to 50 μm in diameter) are carried by a supersonic gas stream through a de Laval nozzle and, finally, impact on a substrate with high kinetic energy. Low gas temperatures (

Critical particle velocity under cold spray conditions

The Cold Gas Dynamic Spray process uses the kinetic energy of unmelted sprayed particles to produce coatings. The most important element of the cold spray system is the nozzle used to accelerate the particles. Consequently, the nozzle design optimisation is a key to improve the coating quality and reduce the spraying costs. In this study, an axi-symmetric two-dimensional mathematical model is presented and used to predict the flow inside a cold spray nozzle as well as the particle velocity in the vicinity of the nozzle exit. The model results are compared with those obtained using the one-dimensional isentropic theory and with particle velocity measurements made on a commercial cold spray system. The study shows that the particle exit velocity depends on the type, stagnation temperature, and pressure of the propellant gas. The comparisons show that the proposed model is more accurate than the one-dimensional theory. It allows predicting accurately the behavior of the particles in the cold spray jet even in the presence of shock waves. Following this work, the design of new nozzles for specific applications using this mathematical model can be considered.

Cold spray modeling and validation using an optical diagnostic method

La projection cold spray utilise principalement l’energie d’impact des particules pour former des revetements denses. L’etalement et l’adhesion des particules etant lies a l’energie cinetique et donc a la vitesse des particules, il est primordial de maximiser leur acceleration pour obtenir un rendement de depot eleve. Ce transfert de quantite de mouvement peut etre optimise en modifiant les parametres de fonctionnement du systeme de projection mais egalement en choisissant une distance tuyere-substrat adequate. Cet article decrit un modele 2D mis en œuvre avec le logiciel de CFD Fluent pour simuler le comportement d’un flux de particules de titane dans un ecoulement supersonique. Ses resultats montrent que les particules n’atteignent pas leur vitesse maximale en sortie de tuyere mais environ 90 mm en aval de celle-ci. C’est donc a cette distance que le substrat doit etre place pour optimiser la projection. La precision de ces calculs est confirmee experimentalement et les variations significatives d’epaisseurs des depots montrent l’influence drastique de la distance de tir sur le rendement de depot.

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François Raletz

Papers

Critical particle velocity under cold spray conditions

Cold spray modeling and validation using an optical diagnostic method

Optimisation de la distance de tir en projection cold spray