Post-Process Treatments on Supersonic Cold Sprayed Coatings: A Review

Abstract

Cold Gas Dynamic Spray or Supersonic Cold Spray, or simply ‘Cold Spray’, is an emerging technology for rapidly building thin films, thick coatings and large-scale additive manufacturing at relatively low temperatures. In a cold spray process, particles are accelerated to supersonic speeds by a propellant gas and impact a substrate, thus producing a strong bonding with the substrate and subsequently forming a deposit via layer-by-layer buildup. The scalability and low cost of this method make it promising for many applications in industry, such as metal component surface repair/enhancement/restoration and functional coatings for electrical, thermal, biomedical, energy storage, and nuclear plant applications. However, cold sprayed deposits usually require post process treatments to further modify their microstructures and mechanical properties in order to obtain the desired performances. A number of studies have been carried out on this topic. Here, recent progress in different post process treatments on cold sprayed deposits is reviewed, including heat treatment, friction-stir processing, shot peening, and laser re-melting. The effects of these post treatments on the microstructure, residual stress and mechanical properties of cold sprayed deposits are discussed.

The Influence of the Powder Characteristics on 316L Stainless Steel Coatings Sprayed by Cold Gas Spray

“…The resistance on tensile testing and the hardness of Ag irregular powder CGS sprayed coatings were higher than the Ag spherical shape, even after heat treatment [17]. Some mechanisms collaborate to the adhesion of the particles to the substrate as listed by Sun et al [18]: the adiabatic shear instability (ASI), caused by the high velocity of the powder particle, breaks the natural oxide film on the surface of both the particle and the substrate and the progressive plastic flow of the materials enables metallic bonding at atomic scale through direct contact between the adjacent fresh metal surfaces; mechanical interlocking, interfacial mixing, local melting and diffusion [19][20][21][22][23].…”

“…The CGS hardness values should be compared to other thermally sprayed 316L coatings: 190 HV [48] for flame spraying, 270 HV [48] and 312 HV [49] for HVOF, 325 HV for arc spraying [50], and 262 HV for APS [49]. The CGS process characteristics of lower temperature and higher velocity of particles than other processes justify its higher coating hardness, since its higher particles' velocity promotes the increasing in hardness due to their plastic strain hardening [51], and the relative low temperature prevents the material recrystallization, thus enabling the ASI mechanism, as explained by Sun et al [18]. In addition, all the coatings show a hardness in the range to that reported for 316L bulk materials, 350 HV 0.3 , approximately.…”

The Role of Substrate on Thermal Evolution of Ag/TiO2 Nanogranular Thin Films

“…The functionalities of metal/oxide thin films depend on the physical properties of the constituents and on the microscopic interactions at the film/substrate interface. Several factors such as the morphology, composition, crystalline phase and porosity of the materials may be controlled by synthesis methods such as cold gas dynamic spray [1], jet printing [2], supersonic cluster beam deposition (SCBD) [3,4], sol-gel methods [5][6][7][8], magnetron sputtering [9][10][11][12] and dip-coating [13]. Post-deposition annealing treatments can further tweak the film behaviour, bringing the substrate properties into play.…”

Friction stir processing of austenitic stainless steel cold spray coating deposited on 304L stainless steel substrate: feasibility study

“…Previous studies showed that heat treatment or hot isostatic pressing could signi cantly improve the mechanical properties of cold spray deposits [15,[20][21][22][23][24]. In these processes, the high temperature enhance the material diffusion through the particle-particle interface and lead to formation of joint grains between neighbor particles.…”

“…At present, many articles devoted to the friction stir processing of cold spray despots are available in literature [20,[33][34][35][36][37][38][39][40][41][42]. The major part of these works deal mainly with FSP treatment of relatively soft materials like aluminum and copper alloys [33][34][35][36][37][38].…”