Fe-Cr-Al合金氧化膜形成机理电子理论研究

Electronic theoretical study of the mechanism of the oxide scale formation of Fe-Cr-Al alloy

通过自编软件建立了Fe-Cr-Al合金表面、氧化膜/基体界面模型,采用递归法计算了合金元素在Fe-Cr-Al合金表面、氧化膜/基体界面的环境敏感镶嵌能、亲和能、结合能、态密度等电子结构参数.从电子层次系统研究了Fe-Cr-Al合金氧化膜的形成机理、稀土元素和杂质硫对氧化膜形成过程及黏附性的影响机理.研究表明Fe-Cr-Al合金中Al的偏聚驱动力远大于Y,Cr.氧化初期氧从合金表面向合金内部扩散,合金内部Al向合金表面扩散,使合金形成富铝、氧表面层;氧与Al间的亲和力较大(亲和能低),氧原子容易与Al结合生成Al2O3保护膜;合金中加入Y后,Y在合金表面偏聚,抑制Al向合金表面扩散,氧化膜的横向生长得到有效控制,从而避免氧化膜皱褶形貌的发生,提高氧化膜的黏附性;合金内部的S通过扩散汇集在基体/氧化膜界面,S使界面区原子的总能增高,总态密度降低,减小了界面的稳定性,进而削弱氧化膜与合金基体的结合力.

The atomic structure models of the surface,the interface of oxide scale and bulk of Fe-Cr-Al alloy were set up by using corresponding computer programming, and the electronic structure parameters（environment-sensitive embedding energy,affinity energy,total energy and total density of states） of alloying elements on the surface,the interface of oxide scale and bulk of Fe-Cr-Al alloy,were calculated by the recursion method.The formation mechanism of the oxide film,the influences of sulfur and rare earth metals on the adhesion of oxide film of Fe-Cr-Al alloy and on the formation course of the oxide film were studied systematically on electronic level.The results show that the driving force of Al atom to segregate on to the surface was larger than that of Cr and Y atom.This leads to the inward diffusion of O atoms and the outward diffusion of Al atoms at the early stage of oxidation,resulting in a surface layer rich in Al and O atoms.The affinity force between oxygen and Al was larger（the affinity energy being lower）,oxygen is easy to combine with Al atoms to form Al2O3 oxide scale.Yttrium is segregated to the surface,which inhibits the diffusion of Al to the surface of Fe-Cr-Al alloy.The lateral growth of oxide film is effectively controlled,the occurrence of the convoluted morphology of the scale is avoided,the adhesion of the oxide film to the Fe-Cr-Al matrix is increased by the addition of Y.The diffusion of impurity S to the interface of Fe-Cr-Al matrix and Al2O3 oxide scale increases the total energy of the interface,decreases the total density of states,which reduces the stability of the interface,weakens the cohesion of Fe-Cr-Al matrix and Al2O3 oxide scale.