SEM observation of casting defects

At a higher magnification of the scanning electron microscope, the casting defects of the three samples are as shown in the figure.

As shown in Figure (a), there are particles distributed in the casting defect area, and the particle surface is bright, which may be foreign matters different from the metal matrix; As shown in Figure (b), the substances in the casting defect area with different contrast colors from the substrate are connected into one piece, and the specific type of the substance cannot be qualitatively determined at this time; As shown in Figure (c), the casting defect area is densely distributed with very obvious particles, and the boundaries between different particles are clear. As the specific types of the above three casting defects can not be accurately identified, it is necessary to conduct composition analysis with the help of energy spectrometer.