Evolution of the Microstructure by High Velocity Impacts of Particles by Cold Spray

Abstract

The cold spray technique is still in its innovation stage. This process is similar to other thermal coating techniques with the additional benefit of lower working temperature than the melting energy of the feedstock material. In this study, a new coating-substrate system is developed by using the 80%Ni-20%Cr feedstock powder sprayed by this technique on a superni 601 superalloy substrate. The coating microstructure depends upon both the substrate and coating material properties, and thus, coating obtained in this study has a unique microstructure. The coating microstructure developed and tested in this study by scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD) techniques is found to be suitable for boilers and incinerators. INTRODUCTIONThe cold spray coating deposition technique is a relatively new member of the thermal spray family but with the added advantage that coating particles remained in the solid state in the as-sprayed coating [1][2][3][4][5][6][7][8][9][10][11][12]. This property of the cold spray process prompted the authors to develop and study the new coating-substrate system by this process for different applications, especially for corrosive environments at temperatures near to 900 C. The study related to the cold spray process is reported in detail in the earlier publications of the authors [8,9].The base material chosen in this study for cold spraying (superni 601 grade superalloy) is for providing strength to the newly developed system, at high working temperature of boilers and incinerators. The 80Ni-20Cr (wt.%) coating composition is selected for providing elements for the formation of the corrosion resistant oxide scale at high operating temperature. Though, the coating composition is good enough for the corrosive environment, the composition is not a sole criterion for providing effective corrosion protection. The development of the required coating microstructure is equally important for this purpose. The microstructure of the coating should be able to block the transport of ionic species and elements from both the environment and the substrate. If the microstructure is not good enough,

Metallisation of polycarbonates using a low pressure cold spray method

“…In the case of the tin coatings, the aluminium particles penetrated the tin interlayer (Figure 4). It is well known that in the cold spray process, the previously deposited particles are usually compacted by successive incoming particles – a tamping effect [20]. Thus, the material layers located in the lower section of the coating are supposed to be more dense [14,21].…”

Microstructure study of cold sprayed 50%Ni–50%Cr coating on Inconel-601

“…29 The cold sprayed coatings with average hardness in the range similar to that measured for Ni-50Cr coating have shown resistance against the highly corrosive environment at elevated temperature. 23,26,28 The coating structure formed by cold spraying and the morphology of the sprayed particles present in as coated condition are examined by the SEM images in Figs. 3, 4 and 7.…”

Effect of burnishing on HVOF coated boiler steel against hot corrosion in actual boiler environment

“…The coated alloy's oxide scale spallates, as shown in BSE images (Figure 4b). Nickel and chromium oxides along with their spinels could be accountable for hindering the transference of degrading species through the applied coating [52,53]. Chromium and cobalt oxides, coupled with cobalt–chromium (CoCr 2 O 4 ) and nickel-chromium (NiCr 2 O 4 ) spinels, may have hindered CoO diffusing activities by preventing its production [28,54].…”