Recently, Fe-based bulk metallic glasses (BMGs) have attracted much attention because of their combinations of engineering properties, such as high strength and hardness, superior corrosion resistance, good magnetic properties, and relatively low material cost. However, Fe-based BMGs exhibit almost no plastic strain and strain hardening even in compression when tested at room temperature, which greatly restricts their applicability as prospective structural materials. To alleviate this case, one interesting idea is to direct toward improving the plasticity of such metallic glasses in terms of critical Poisson’s ratio and to date much works have been made. Another is to focus upon their unusual attributes of wear and corrosion resistance; as such, these materials as coating applications to withstand aggressive environment will be more attractive.
Coating technology is considered to be the most effective method for producing two-dimensional materials, especially for hard and brittle materials. High velocity oxygen fuel (HVOF) sprayed coatings have been widely used for industrial applications where good wear and corrosion resistance are highly needed. During HVOF thermal spraying, the feedstock powder particles were injected into a high velocity hot gas jet which was generated through combustion of oxygen and a fuel gas. Because of the high particle kinetic energy available in HVOF thermal spraying process, partially molten or “soft” particles were capable of forming dense coatings. Over the last decade, HVOF thermal spraying has been used for depositing metals, cermets and low melt ceramics, and one of the most attractive ways is the manufacture of amorphous metallic coatings, which often retain the favorable properties of metallic glasses. Up to now, a number of attempts have been made on fabrication of Ni- and Fe-based amorphous metallic coatings by means of HVOF, but a detailed evaluation on the structural characteristics and relative properties of amorphous steel coatings is still lacking. Amorphous phase is a non-equilibrium phase, so formation and retention of this phase are very difficult during thermal spraying processes. Alloys with high glass forming ability (GFA) would be favorable for forming fully amorphous phase coating. Recently, a number of Fe-based bulk metallic glasses with good GFA were found in the Fe-(Cr, Mo)–(C, B) system, in which a critical sample diameter is as large as 12 mm.
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