采用Si-Al-Y2O3包埋共渗工艺在Nb-Ti-Si基超高温合金表面制备Y改性的Si-Al共渗层, 分析了渗剂中Al粉含量对渗层组织和相组成的影响, 并研究了其在1250℃的抗氧化性能. 结果表明: 采用不同Al粉含量的渗剂在1050℃所制备的Si-Al-Y2O3共渗层均具有多层复合结构, 且渗层的内层都是由Al3(Nb, X)(X代表Ti, Cr和Hf)和 (Cr, Al)2(Nb, Ti)相组成; 当渗剂中Al粉含量为10%(质量分数)时, 渗层的外层以(Nb, X)Si2相为主, 中间层以(Nb, X)5Si3相为主; 当渗剂中Al粉含量为15%时, 渗层中间层由 (Nb, X)5Si3及Al3(Nb, X)两相组成, 而外层组成相相对于渗剂中Al粉含量为10%时的未发生变化; 当渗剂中Al粉含量为20\%时, 渗层的外层以 (Nb, X)3Si5Al2相为主, (Nb, X)Si2相弥散分布其中, 中间层则以Al3(Nb, X)为基体相, (Nb, X)5Si3相弥散分布其中, 并在其上部分布较少而下部较密集. Y在渗层中的分布不均匀, 并且随着渗剂中Al粉含量的提高, 渗层各层中的Y含量均增加. Si-Al-Y2O3共渗层的形成是一个在合金表面先沉积Al、后沉积Si的有序过程, 其生长服从抛物线规律. 在1250℃下氧化5 h后, 渗层表面生成了致密的Al2O3膜.
Si-Al-Y2O3 co-deposition coatings on an Nb-Ti-Si base ultrahigh temperature alloy were prepared by pack cementation processes at 1050℃. The effects of Al content (mass fraction) in pack mixtures on the microstructure and constituent phases of the co-deposition coatings were studied, and the oxidation-resistant performance of the coating was investigated. The results show that all coatings prepared at 1050℃with pack mixtures containing different Al contents have a multiple layer structure, and the inner layers of all coatings are composed of Al3(Nb, X) (X represents Ti, Cr and Hf) and (Cr, Al)2(Nb, Ti) phases. The outer layer of the coating prepared at 1050℃ for 10 h with the pack mixture containing 10% Al is composed of (Nb, X)Si2, and the middle layer is composed of (Nb, X)5Si3. However, the constituent phases change into Al3(Nb, X) and (Nb, X)5Si3 in the middle layer of the coating prepared with the pack mixture containing 15%Al. (Nb, X)3Si5Al2 and (Nb, X)Si2 phases have been detected in the outer layer of the coating prepared with the pack mixture containing 20%Al, and Al3(Nb, X) is the main phase constituent in its middle layer with dispersed (Nb, X)5Si3 particles in it. EDS analysis reveals that the distribution of Y in the coatings is not uniform, with its content increasing with the rising of Al content in the pack mixtures. Co-deposition of Al and Si occurs in a sequential manner during the deposition process and the growth of the coatings obeys a parabolic kinetics. After oxidation at 1250℃ for 5 h, dense Al2O3 scales have formed on the coatings, which prevent the oxygen from diffusion into the substrate effectively.
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