Abstract
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.
Highlights
Amorphous metals are drawing attention in several engineering fields owing to their unique physical, mechanical, and thermo-mechanical properties
The aim of this paper is to explore the potential deposition of amorphous iron-based coatings by Cold-gas spray (CGS), starting from commercially available powders with a chemical composition optimized for its glass-forming ability, investigating the effect of the very high kinetic energy content of solid particles on the crystallization tendency, even in the absence of extremely high cooling rates
The first consequence of this was that the crystallization kinetics were slow, as demonstrated by the solidus temperature (1200 °C), exceptionally low for a Fe-based alloy, suggesting that this composition was close to the deep eutectic of the Fe–C–B system, that greatly promotes the formation of the amorphous metal because of the high thermodynamic stability and ordering of the liquid phase [28]
Summary
Amorphous metals are drawing attention in several engineering fields owing to their unique physical, mechanical, and thermo-mechanical properties. Bulk MGs are manufactured by different techniques, all including a rapid quenching step, yielding materials characterized by a short-range order but typically endowed with very limited ductility and with negligible plastic behavior in compression [9]. For these reasons, commercial applications of this class of materials are not yet consolidated. Represent the starting point for new functional materials with potential interesting applications in different fields of engineering
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