Amorphous steel coatings deposited by cold-gas spraying
Cold-gas spray (CGS) deposition of amorphous steel coatings starting from a commercial feedstock powder containing boron, tungsten, and silicon was investigated. Microstructural
characterization, carried out by X-ray diffraction (XRD), transmission electron microscopy, and backscattered electron diffraction (EBSD) analysis, confirmed the amorphous nature of deposited
coatings. The amorphization phenomenon is related to high-strain/strain-rate deformation with shear instability caused by very high particle kinetic energy, with a mechanism that resembles the severe
plastic deformation process. The CGS coatings were heat-treated at temperatures ranging from 650 to 850 ◦C to induce partial recrystallization. The effect of nanocrystal nucleation and growth on
the hardness of the coatings was investigated, and the hardness of heat-treated samples was found to increase with respect to as-sprayed coatings, outperforming conventional high-velocity oxy-fuel
(HVOF) deposits. Hardness was found to decrease after prolonged (<90 min) or higher temperature (>750 ◦C) exposures.