Fig.1 gives the surface and cross-section BSE images of as-sprayed10Ag-BCF coating. The coating exhibits a dense and continuous splat like structure, which is closely related to full spreading and close stacking up of melted particles during impact, especially for Ag particle.According to the principle of BSE contrast imaging,a material of higheratomic mass typically exhibits a brighter contrast. Ag with a relatively high atomic number should be white in the BSE image, as shown in Fig.1(a) and(b). The relatively low melting point (961.78 C) and good plastic deformation of Ag particle have made it deposited as a shape of pancake with corona and wet well with CrsC2 grains and NiCr metal binder during deposition.
Fig.1. SEM images (BSE mode) of (a) surface and (b) cross section of as-sprayed 10Ag-BCF coating.
Fig.2 shows the cross-sectional BSE image of 10Ag-BCF coating at magnification 5000×. Except some pores in the form of black contrast regions, four greyscale contrasts dominant the presented area of 10Ag-BCF coating. The EDXA elemental mapping was conducted to determine the element distribution of these greyscale contrasts. The white strips implying high mean atomic number mainly contain Ag element and are splats of Ag. The feature that carbide grains with dark greyscale contrast surrounded by bright grey binder covers most of the area of10Ag-BCF coating, which is the typical microstructure of HVOF-sprayedCraC2-NiCr coating .A black grey particle can be obviously observed, which mainly contains Ca and F elements.
Fig.2. SEM image(BSE mode) and corresponding elemental mapping of 10Ag-BCF coating.
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