HVOF thermal spraying is one of the most widely used processes for depositing coatings such as metals, cermet, ceramics, and metallic glasses, which seems more feasible due to its high cooling rates of 107 – 1010 K/s. However, in comparison with the HVOF process, the HVAF system which produces a mixture of compressed air and fuel gas in the combustion chamber has a lower spraying temperature (1600k) than HVOF (1900k) process. So, the chemical uniformity generated by controlled oxidation in the coating by HVAF can be improved. Moreover, the high particle velocity, typically over 700 m/s, of the HVAF process has been reported to provide lower porosity and improved adhesion strength in the coating than in the HVOF process. Furthermore, the use of air instead of oxygen for combustion by HVAF is expected to lower the cost of spraying and promote its competitiveness over other processes.

• Fe- based metallic glass coatings deposited by ac-HVAF have much better corrosion resistance than stainless steel, which is mainly dependent on their amorphous structure and chemical composition. Both amorphous coating and stainless steel have the Cr element, which is the element of self- passivation. For amorphous coating, the introduction of the Cr element contributes to the formation of a strong passive film of hydrated chromium oxyhydroxide. This process effectively inhibits the active dissolution of the amorphous phase and enhances corrosion resistance.