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Page 8 of 18 Chong et al. J Mater Inf 2023;3:21 https://dx.doi.org/10.20517/jmi.2023.17

Figure 5. Surface morphologies and distribution of elements from EPMA of the alloy Pt Al after 100 h oxidation in air at 1,300 °C. (A)
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Surface morphology; (B1)-(B3) Pt, Al, and O map distribution, respectively; (C) Linear distribution of Pt, Al, and O.
Figure 5 shows the EPMA elemental maps of Pt Al oxidized at 1,300 °C for 100 h. Obviously, the light
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areas are fcc phase (mainly Pt), and the dark areas are Al O according to the EPMA analysis; see Figure 5A.
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The Al O layer is not fully dense. Figure 6 shows the cross-sectional EPMA of Pt Al after oxidation at
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1,300 °C for 100 h. The oxide scale on the Pt Al surface is continuous and intact, which is from 10.1 to
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13.3 μm in thickness, as shown in Figure 6A. However, the discontinuous Pt-rich layer is also observed
outside the oxide layer, which is probably due to the deposition of the Pt vapor above 1,000 °C .
[10]
Pt Al Cr 6
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Figure 7 shows the XRD patterns of the Pt Al Cr alloy after oxidation at 1,300 °C for 100 h. It reveals that
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the α-Al O is the major phase in the oxide layer with small peaks identified as Pt, indicating that Cr
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promotes the formation of α-Al O . Different from the case of Pt Al , after oxidation at 1,300 °C for 100 h,
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the Pt Al Cr alloy exhibits a smooth and dense surface. No spallation or crack is observed, and the Al O
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