Fe-23Cr-6Al合金在1300℃氧化时,α-Al_2O_3层的单层晶粒首先生成柱状晶,随后由于柱状晶的横向生长和外层等轴晶区的形成和扩展,氧化层晶粒的柱状特征逐渐减弱。添加RE可增大柱状晶的纵向生长速率,减小其横向生长速率和外层等轴晶的生长速率,从而增强氧化层晶粒的柱状特征。在不含RE合金的氧化层表面有较多的晶须和小晶体,表明α-Al_2O_3层生长时伴有Al离子向外扩散。认为RE阻止此扩散是影响氧化层晶粒生长、改善氧化层粘附性的一种可能原因。
When the Fe-23Cr-6Al alloy is under oxidation at 1300℃, the α-Al_2O_3 grains of single layer are formed initially as columnar crystals, and then, their columnar feature degenerated progressively owing to the columnar grains growing along transverse direction and the development of outer layer oxide consisted of equiaxial crystals. If the RE added, the growth rate of columnar grain along longitudinal direction is increased and along transverse direction decreased, as well as the growth rate of equiaxial grain of outer layer oxide also decreased. Consequently, their columnar feature become more intensive. For the alloy without RE, more crystalline whiskers and fine crystals are found on the surface of oxide layer. It may be considered that the Al ions diffusion through α-Al_2O_3 layer outwards is prevented by RE addition, and the oxide layer adherence is then improved.
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