Fig. 1 shows the distribution of Vickers hardness on the cross-section of metallic glass coatings formed by gas tunnel type plasma spraying. In this case, the plasma current was 300 A. The spraying distance was L= 50 mm, and the traverse number was 16.
The coating thickness was 180um. The Vickers hardness of metallic glass coatings is aroundHv50= 900–1150, wherever measured in the cross-section of the coating. This hardness was similar to that of the bulk type of Fe-based metallic glass.
The average Vickers hardness on the cross-section of metallic glass coating slightly increased with an increase in the distance from the surface (Hv50= 1020–1080). This is thought to result from the thermal condition affecting the amorphous phase of the coating for the different coating conditions, such as the sprayed particle temperature, cooling rate of the coating near the substrate, and so on. Also, lower porosity of about 2.5% seems to lead to the higher hardness of metallic glass coating.
At higher current of 400 A, a high hardness thick coating (about 200um) was obtained (Hv50= 1050–1080). And the porosity became lower value of 2.1% at 400 A. The coating would be high density due to high temperature effect at highe plasma current. This is a reason of higher hardness of metallic glass coating. Also, the plasma current affects the cooling rate of the coating when the particle is deposited on the substrate. In the case of higher current, large power gives higher cooling rate of the deposit metallic glass powder.
Fig.1. Distributions of Vickers hardness of Fe-based metallic glass coating, deposited at plasma current of 300 A.
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