TiAl合金表面Si-Al-Y共渗层的组织及高温抗氧化性能

通过在1050℃下Si-Al-Y扩散共渗0~4 h在TiAl合金表面制备了Al、Y改性的硅化物抗氧化渗层, 分析了共渗层的结构及相组成, 并对其组织形成机理及高温抗氧化性能进行了研究。结果表明: 1050℃共渗4 h所制备的共渗层具有多层结构, 由外向内依次为TiSi₂外层、(Ti,X)₅Si₄及(Ti,X)₅Si₃(X表示Nb, Cr)中间层、TiAl₂和γ-TiAl内层及富Al的过渡层, 其中Y元素主要富集于共渗层的外层和中间层。不同时间共渗的结果表明, Si-Al-Y共渗层的形成是一个在基体表面先沉积Al, 后沉积Si的有序过程。经1000℃高温氧化20 h后共渗层表面形成了由TiO₂外层及SiO₂·Al₂O₃次外层组成的致密氧化膜; Y的氧化物主要存在于氧化膜与残余共渗层的界面处, 能够有效地增强膜层的附着力。

Microstructure and High Temperature Oxidation Resistance of Si-Al-Y Co-deposition Coatings Prepared on TiAl alloy by Pack Cementation Process

In order to improve the oxidation resistance of TiAl alloy, Al and Y modified silicide coating were prepared by pack cementation process at 1050℃ for 0-4 h. The formative mechanism and oxidation behavior of the coating were studied. The results show that the coating prepared by co-depositing Si-Al-Y at 1050℃ for 4 h has a multiple layer structure: an outer layer composed of TiSi₂, a middle layer composed of (Ti,X)₅Si₄ and (Ti,X)₅Si₃ (X represents Nb and Cr elements), an inner layer composed of TiAl₂, γ-TiAl phases and a Al-rich inter-diffusion zone. Y mainly existed in the outer layer and middle layer of the coating. The coating formation process followed a sequent deposition mechanism, with Al deposited at the initial stage and Si deposited at the later stage. After oxidation at 1000℃ for 20 h, a dense scale composed of a thin TiO₂ outer layer and a thick SiO₂·Al₂O₃ inner layer is formed on the co-deposition coating. During the oxidation process, the excessive Y₂O₃ particles form in the interface of the scale and the substrate, which might promote the adherence of the scale effectively.