Alloys with cohesive mode of scale spallation Zr, Hf

5 Alloys with cohesive mode of scale spallation +Zr, +Hf 

Compared to the reference alloy, the Zr-containing material revealed up to breakaway no broccoli effect and only minor macroscopically visible spallation at the specimen corners and edges (Fig. 7.3), in agreement with the mass change data in Fig. 7.1. The suppression of the broccoli effect by Zr has previously been related to tying up the carbon impurity into more stable carbide [12]. It should be noted that no Cr carbide formation was detected in the alloy -l-Zr . The microstructures of the scales after 1000 h oxidation are shown in Fig. 7.8. Compared to alloy MRef the alumina scale on alloy -FZr is thicker and contains zirconia inclusions and porosity in the outer part. Studies of the scale grain structure were performed using electron back-scattered diffraction (EBSD). The studies revealed (Fig. 7.9) that the alumina 

8 SEM images of the scales formed on alloy MRef (a) and alloy +Zr after 1000 h discontinuous air oxidation at 1200°C. 

The absence of the zirconia particles and the different oxide microstmcture in the inner part of the scale (Figs 7.8 and 7.9) lead to the conclusion that the 

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