Ti50Al和Ti45A18Nb合金高温初期氧化行为

EARLY OXIDATION BEHAVIORS OF Ti50Al AND Ti45A18Nb ALLOYS AT HIGH TEMPERATURE

利用SEM、XPS和AES研究了Ti50Al和Ti45A18Nb(原子分数,%)合金在900℃空气中的初期氧化行为.结果表明:Nb的加入显著提高了合金的抗氧化性.氧化90 min后,Ti50Al合金表面为粗大的富TiO_2颗粒,冷却过程中部分表层氧化膜脱落,脱落后内层为多孔、疏松的Ti和Al的混合氧化物(可能有氮化物);Ti45A18Nb合金表面生成很薄的氧化膜,其外层为细小富Al_2O_3颗粒,Nb只存在于内层(富TiO_2层)和混合层,在外层Al_2O_3内没有发现,Nb^(5+)取代TiO_2中的Ti^(4+),降低氧空位浓度从而减慢氧的向内扩散,抑制TiO_2的生成,同时促进了外层纯Al_2O_3层的形成,该层阻碍氧以及合金元素的进一步扩散.

The early oxidation behaviors of Ti50Al and Ti45Al8Nb （atomic fraction, %） alloys at 900℃ in air have been investigated. The surface morphologies of oxide films are analyzed by SEM. Oxide layers formed for different oxidation times were investigated by XPS. The changes of the layer composition with depth were analyzed by AES. Experimental results revealed that the oxidation resistance of Ti45Al8Nb was remarkably promoted by Nb addition. After oxidization for 90 min the surface of Ti50Al was covered by coarse grained titanium rich oxides, a part of the scale had spalled during cooling, and its inner part is a loose and porous structure rich in titanium, aluminium and oxygen （and probably nitrogen）. For Ti45Al8Nb after oxidization for 90 min a thin oxide film with more fined grained Al2O3 was formed on the outer surface. In the inner layer with TiO2 and other oxides Nb substituted for Ti in TiO2 as a cation with valences 5, which decreased oxygen diffusion into inner, suppressed the WiO2 growth and improved the growth of the outer pure Al2O3 layer. Al2O3 layer impeded the inward diffusion of oxygen and the outward diffusion of metallic elements.