Fe-based metallic glasses are promising materials in engineering applications due to their ultrahigh strength and hardness, excellent corrosion and wear resistance, superior soft magnetic property, and low material cost. However, the limited glass-forming ability (GFA) and intrinsic brittleness of these materials significantly restrict their widespread application as structural materials. Fortunately, fabricating amorphous coatings (ACs) by thermal spraying techniques, including plasma spraying, arc spraying, detonation spraying, laser processing, high velocity oxygen fuel (HVOF), and high velocity air fuel (HVAF), is an effective method to overcome the aforementioned problems and expand the applications as surface protection. In the procedure of HVOF thermal spraying, the feedstock powders are injected into a spraying gun, heated to molten or halfmolten states, accelerated toward a substrate, and then spread laterally and rapidly solidified. Among various thermal spray techniques, HVOF thermal spraying is reported to have several advantages; for instance, it is conducted at relatively low operating temperature and provides a super-high velocity, thus creates extremely dense and well-bonded coatings. Based on HVOF technique, HVAF utilizes compressed air instead of pure oxygen as the combustion-supporting media for spraying and allows considerably higher powder feed rates, thus resulting in less oxidation, higher coating density and hardness, stronger adhesion, and lower preparation cost. In recent years, attention and interest in the development of novel Fe-based ACs with low friction and superior wear resistance under various aggressive environments have increased. Because of the high hardness and reduced Young's modulus, Fe-based ACs exhibit superior wear resistance to conventional crystalline steels (CSs), hard Cr and Al2O3 coatings. Besides, the high hardness and amorphous microstructure of Fe-based ACs can be attributed to the excellent erosion-corrosion resistance in sand-containing corrosive solutions. HVOF-sprayed Fe-based amorphous composite coatings reinforced with Al2O3 particles also display a good combination of hardness and wear resistance in air and NaCl solution.
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