CeO2对铌硅基超高温合金硅化物渗层组织及抗氧化性能的影响

摘要

采用Si­CeO2包埋共渗工艺于1150℃在铌硅基超高温合金表面制备Si­Ce共渗层，分析渗剂中CeO2粉含量对共渗层组织、相组成及高温抗氧化性能的影响。结果表明：Si­Ce 共渗层的组织、结构与单独渗硅层的相似，由(Nb, X)Si2(X表示Ti、Hf和Cr)外层、(Ti, Nb)5Si4过渡层和富Al扩散层组成。EDS分析结果表明，Ce在共渗层中的分布不均匀，而在由原基体合金中的(Nb, X)5Si3块转变而成的富Hf (Nb, X)Si2相中含量较高。渗剂中添加CeO2不仅起到了细化渗层组织的作用，而且起到了明显的催渗作用，当渗剂中CeO2粉含量为3%(质量分数)时催渗效果更显著。Si­Ce共渗层及单独渗硅层经1250℃氧化50 h后的氧化膜均主要由TiO2与SiO2组成。但Si­Ce共渗层试样的氧化膜中TiO2棒更细小，并且在SiO2基体中的分布也更均匀，因而能显著改善氧化膜的粘附性与致密性，进而提高Si­Ce共渗层的高温抗氧化性能。%Si­Ce co­deposition coatings were prepared on an Nb­silicide­based ultrahigh temperature alloy by pack cementation processes at 1 150℃for 8 h. The effects of CeO2 content in pack mixtures on the microstructure, constituent phases and high temperature oxidation resistance of the coatings were studied. The results show that all coatings prepared with different contents of CeO2 in the pack mixtures are mainly composed of a (Nb, X)Si2 (X represents Ti, Hf and Cr) outer layer, a (Ti, Nb)5Si4 transitional layer and an Al­rich diffusion zone, which are similar to that of purely siliconized coatings. EDS analysis reveals that the distribution of Ce in the co­deposition coatings is not uniform. The content of Ce in the Hf­rich (Nb, X)Si2 phase transferred from (Nb, X)5Si3 in the base alloy is higher than that in other phases. The addition of CeO2 in the pack mixtures not only refines the microstructure of the coatings, but also obviously catalyzes the coating growth, especially when 3%CeO2 (mass fraction) is added in the pack mixtures. Both scales formed on the Si­Ce co­deposition coating and purely siliconized coating after oxidation at 1 250℃for 50 h are mainly composed of TiO2 and SiO2. However, much finer TiO2 rods are observed distributing evenly in the scale of the Si­Ce co­deposition coating after oxidation. Thus, the Si­Ce co­deposition coatings enhance the high temperature oxidation resistance due to the improved compactness of the protective oxide scale.