Figure 6 shows the surface morphologies of specimens oxidized for 2 h at 850, 950, 1000, and 1100 C. At a low temperature 850 C, the oxide scales have fifine grains with directionality, but they are not uniform, as shown in Fig. 7a. The directionality may be related to grinding deformation on the specimen surface. Oxide grains with a fifine size tend to congregate along grinding marks, leading to the formation of an undulating oxide layer on the surface. As the temperature elevated, the surface oxide scale crystals grow and the surface becomes flflat and smooth.

Figure 6 shows the surface morphologies of specimens oxidized for 2 h at 850, 950, 1000, and 1100 C. At a low temperature 850 C, the oxide scales have fifine grains with directionality, but they are not uniform, as shown in Fig. 7a. The directionality may be related to grinding deformation on the specimen surface. Oxide grains with a fifine size tend to congregate along grinding marks, leading to the formation of an undulating oxide layer on the surface. As the temperature elevated, the surface oxide scale crystals grow and the surface becomes flflat and smooth.