Figure 1a shows the typical cross-sectional morphology of plasma sprayed NiCrBSi coating. As can be seen in Figure 1a, the uniform coating thickness is about 120 um and bonded well with the substrate. There is no apparent void or crack in the coating structure.
However, there are a small number of interfaces distributed on the cross section, which is formed up by the piled flat particles. Figure 1b showed the cross-section image of NiCrBSi coating after polishing and subsequent HNO3-HF corrosion, where the coating is obviously lamellar structure, due to the accumulation of the sprayed flat particles, which is deposited by many passes to meet the requirements of coating thickness. Melted or semi-melted particles constantly impact on the substrate to spread out through the flow, then deformate into flat particles and form a layered coating.
Figure 1. The cross section views of NiCrBSi coating and retained phases after acid accelerated corrosion.(a) Cross-sectional morphology of as-sprayed NiCrBSi coating,(b) after corrosion for 30 min,(c) after corrosion for 24 h,(d) high magnification of (c),(e) nano-sized grain region after corrosion for 24h, and(f)"fish-bone like"or "leaf-like"grain region after corrosion for 24h.
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