Critical review of corrosion protection by cold spray coatings

Abstract

Cold spray is a high deposition rate coating process, in which solid powder particles are accelerated to velocities ranging between 300 and 1200 m s − 1 through a de Laval nozzle, impact and adhere to a substrate or previously deposited coating. The powder feedstock remains well below its melting temperature during deposition. Therefore, cold spray is categorised among solid state deposition methods, and offer significant advantages as compared to other traditional thermal spray techniques.Particles/substrate interaction during high velocity impact and the resultant bonding is fundamental, and determines physical and mechanical properties of the coating/substrate system. Numerous experimental and computational efforts have been carried out to provide a better understanding of the bonding mechanism in cold spray. [1][2][3][4][5][6][7][8][9][10][11][12] These efforts raised the consciousness that adhesion only occurs when the powder particles exceed a critical impact velocity. The knowledge of critical velocity is a key point to determine the optimised spraying parameters, and reduce the manufacturing cost by increasing the deposition efficiency. Experimental investigations show that the critical velocity depends on the spray material properties, 13,14 particle temperature, size distribution, surface oxidation [15][16][17][18] as well as substrate nature and properties. 19,20 The exact bonding mechanism is still a matter of debate. However, adiabatic shear instability is known as the predominant bonding precursor in cold spray. Adiabatic shear instability occurs at the particle substrate interface during impact. A strong pressure field is introduced as a result of particle impact on the substrate. Consequently, a shear load is generated, which accelerates the material laterally. This causes localised shear straining, which, under critical conditions, leads to adiabatic shear instability. Experimental results show that the minimal particle impact velocity needed to produce shear localisation at the particles/substrate interface, correlates quite well with the critical velocity for particle deposition by the cold spray process in a number of metallic materials. The initiation of adiabatic shear instability is usually described by thermal softening in competition with strain and strain rate hardening. During high strain rate deformation, strengthening occurs as a result of dislocation generation and movement. On the other hand, heat generated by plastic work softens the material. At a certain point, softening dominates the material response and results in the flow stress breakdown and onset of adiabatic shear band formation. 21 This phenomenon often leads to material jet formation in the powder particle or both particle and substrate (shown in Fig. 1), that is a precursor of adhesion in cold spray.The success of the cold spray process mainly depends on proper acceleration of the powders to an impact velocity window, set by the critical and erosion velocities. 3,22

Cold gas spray coatings: basic principles corrosion protection and applications

“…The fine powders, with narrow size distribution and containing low oxygen content are usually more suitable and desirable 90 . Also, the plastic deformation can occur more easily depending on the crystalline structure 1, 40,52,90 .…”

“…The fine powders, with narrow size distribution and containing low oxygen content are usually more suitable and desirable 90 . Also, the plastic deformation can occur more easily depending on the crystalline structure 1, 40,52,90 . All these effects on the coating formation are described in literature 1, 42 and some studies show that they have high influence in the corrosion protection performance 62 .…”

Fatigue life enhancement of cast Mg alloy by surface modification in cold spray process

“…Studies reported that the fatigue and corrosion properties of Mg alloys can be improved by surface modification in CS method [12][13][14][15][16][17][18] by employing different coating materials, which has higher strength and better corrosion resistance. Aluminum and its alloys (AA) have shown to be an excellent coating material for coating the surface of the Mg alloy parts [19]. When AA comes in contact with air a thin aluminum oxide layer is made which protects the substrate from penetration of the oxygen which in turn results better oxidation resistance.…”

Prospects of Low-Pressure Cold Spray for Superhydrophobic Coatings

“…At the same time, this increases the range of methods used for superhydrophobic coatings production.Superhydrophobic surfaces (SHS) are actively studied across a wide range of applications and industries. As a rule, with the unique water-repelling feature of these surfaces, their use is associated with the ability to reduce wear of metal surfaces due to corrosion in the aquatic environment [16][17][18][19]. Superhydrophobic surfaces can minimize the interaction between metal substrates and corrosive substances and provide better anti-corrosion properties by reduction of contact time with water [16][17][18]20,21].…”

“…As a rule, with the unique water-repelling feature of these surfaces, their use is associated with the ability to reduce wear of metal surfaces due to corrosion in the aquatic environment [16][17][18][19]. Superhydrophobic surfaces can minimize the interaction between metal substrates and corrosive substances and provide better anti-corrosion properties by reduction of contact time with water [16][17][18]20,21]. Often it facilitates self-cleaning potential taking advantage of low water adhesion [16,18,19,[22][23][24].…”