Fabrication and characterization of supersonic plasma sprayed Fe-based amorphous metallic coatings

The left side of the figure shows the transmission electron microscope (TEM) image of the cross-sectional of the coating. The larger crack occurred at the interface between the coating and the substrate during the ion milling process of the specimen, which was ascribed to the large difference of microhardness between the coating and the substrate. It can be clearly seen that the cross-sectional morphology of the specimen (Fig. 3(a)) contains three kinds of regions. The coating (region A) is primarily composed of amorphous phase according to the selected area electron diffraction (SAED) pattern with a diffused halo ring, and it is consistent with the results of the XRD test (the right of the figure). It also can be seen that the content of Mo in this region is a little higher than other region from the EDS analysis. Region B is a transition zone from the coating to the substrate, and can be concluded that this area is mixed a crystal structure from the SAED pattern. More Al, O elements found in this area from the EDS analysis may be caused by the sandblasted process before the spraying which makes the interface exist a little Al2O3 crystal. The SAED pattern of region C shows that the substrate is a single crystal region (BCC), and there is a small amount of Mo elements from the EDS analysis, which maybe appeared interdiffusion between elements. It is also interesting to detect that the amorphous content of coatings is as high as 90%. The change of the amorphous content keeps consistent with the change of micro-hardness (the right of the figure), illustrated that amorphous has an important role in enhancing the hardness of coatings.100