Effect of gas flow rate on deposition behavior of Fe-based amorphous alloys in vacuum kinetic spray process

Amorphous Fe-based coatings were fabricated on soda–lime glass substrates by the vacuum kinetic spray (VKS) method. The effects of gas flow rate on the deposition behavior, the coating microstructure, and properties were investigated. The deposition mechanism of bulk metallic glass (BMG) material was also analyzed. The as-fabricated film microstructure was studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and high resolution transmission electron microscopy (TEM). Moreover, atomic force microscopy (AFM) and a scratch tester were used to measure the surface roughness and cohesive/adhesive bonding strength, respectively. The deposition rate was drastically increased as the gas flow rate increased, and the film was significantly thicker than that of ceramics. Also, the particles underwent more severe deformation and fragmentation as the particle velocity increased, similar to a ceramic material. However, interestingly, a porous film was fabricated in contrast to a ceramic film, and the porosity increased with increasing gas flow rate. It is thought that the cohesive bonding strength was constant regardless of gas flow because of the porous coating layer, while adhesive strength significantly increased by an anchoring layer as the gas flow increased. Based on the fact that no crystalline phases except for ZrO2 were found in the coating layer, fragmentation is still an important process for successful deposition in a VKS system compared to the KS process. As a result, it can be concluded that the plasticity-accompanied fragmentation process of BMG particles resulted in a porous coating layer in contrast to the dense ceramic coating formed by the fragmentation-dominant deposition process.