Figure 1 shows the XRD patterns of MoSi2-ZrB2 coatings after oxidation at 1250℃for 60 h.As shown in Figure 1, the oxidized MoSi2-ZrB2 coatings mainly consist of MoSi2, Mo5Si3, SiO2 and ZrSiO4. Figure 2 demonstrates the surface morphologies of MoSi2-ZrB2 coatings after oxidation at 1250℃for 60 h. The surface of the mz40 sample is loose and undulate, as shown in Figure 1a. It can be observed from Figure 1b that the surface of mz43 sample is much denser. As shown in Figure 1c, the mz45 sample displays a uniform, dense and integrated surface.
Figure 1.XRD patterns of MoSi2-ZrB2 coatings after oxidation at 1250 ℃ for 60h.
Figure 2. Surface morphology of MoSi2-ZrB2 coatings after oxidation in air at 1250 ℃ for 60h:(a) mz40,(b) mz43 and(c) mz45.
Figure 3 shows the cross-sectional morphologies of MoSi2-ZrB2 coatings after oxidation at 1250℃ for 60 h. According to the XRD results and EDS analysis (as listed in Table 1), the coating consists of the black SiO2, the black-gray MoSi2, the gray-white Mo5Si3 and the white ZrSiO4. Moreover, some cracks and holes are observed in all coatings, and they are filled with black SiO2 phase. Figure 3d shows the microstructure of the failure edge of the mz40 sample after oxidation. The oxides of the edge of mz40 sample are confirmed to be TiNbO4 and SiO2 according to EDS analysis, which is the typical oxides of Nb-Si based alloy at high temperature .
Figure 3. Cross-section morphology of MoSi2-ZrB2 coatings after oxidation in air at 1250 ℃ for 60h:(a) mz40,(b) mz43,(c) mz45 and(d) the failure edge of the mz40 sample.
Table 1. The EDS results of constituent phase of the oxidized mz45 sample (a.%).
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