Abstract
Cold spray is a promising method by which to deposit dense Fe-based metallic glass coatings on conventional metal substrates. Relatively low process temperatures offer the potential to prevent the crystallization of amorphous feedstock powders while still providing adequate particle softening for bonding and coating formation. In this study, Fe48Mo14Cr15Y2C15B6 powder was sprayed onto a mild steel substrate, using a variety of process conditions, to investigate the feasibility of forming well-bonded amorphous Fe-based coatings. Particle splat adhesion was examined relative to impact conditions, and the limiting values of temperature and velocity associated with successful softening and adhesion were empirically established. Variability of particle sizes, impact temperatures, and impact velocities resulted in splat morphologies ranging from well-adhered deformed particles to substrate craters formed by rebounded particles and a variety of particle/substrate interface conditions. Transmission electron microscopy studies revealed the presence of a thin oxide layer between well-adhered particles and the substrate, suggesting that bonding is feasible even with an increased oxygen content at the interface. Results indicate that the proper optimization of cold spray process parameters supports the formation of Fe-based metallic glass coatings that successfully retain their amorphous structure, as well as the superior corrosion and wear-resistant properties of the feedstock powder.
Highlights
Iron (Fe)-based amorphous alloys are recognized as important engineering materials due to their high strength and hardness, superior wear and corrosion resistance, and excellent soft magnetic properties, in addition to their relatively low cost (Ref [1, 2])
The results of this study demonstrate the necessity of controlling cold spray process parameters in an effort to achieve desired impact conditions and promote the coating formation of Fe-based metallic glass powders
In order to achieve this softening, both computational and experimental results indicate that cold-sprayed Fe-based amorphous powders must be heated to a temperature that is within the supercooled liquid region
Summary
Iron (Fe)-based amorphous alloys are recognized as important engineering materials due to their high strength and hardness, superior wear and corrosion resistance, and excellent soft magnetic properties, in addition to their relatively low cost (Ref [1, 2]). Researchers have been successfully establishing compositions of glassy iron alloys that will retain an amorphous microstructure under significantly lower cooling rates than early melt-spun alloys (Ref 3). At this time, iron-based bulk metallic glasses with critical cooling rates as low as on the order of 100 K/s have been found in Fe-based alloy systems containing metalloids (B, C, Si, and P) (Ref 4). Alternate material systems by which to exploit the superior properties of these amorphous alloys continue to be explored, including their use as thick corrosion and wear-resistant layers on top of crystalline metal substrates. This study is motivated by the goal of forming such material systems, including a fully amorphous Fe-based metallic glass coating on a mild steel substrate, in order to widen the assortment of their feasible industrial applications
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