铌硅化物基超高温合金Si-Y2O3共渗涂层的组织及其高温抗氧化性能

采用Si-Y₂O₃包埋共渗工艺在铌硅化物基超高温合金表面制备Y改性的硅化物涂层, 研究其在1250℃的恒温氧化性能. 采用扫描电镜(SEM)、能谱(EDS)与X射线衍射(XRD)分析Si-Y₂O₃共渗涂层氧化前后的物相组成和组织变化. 结果表明：涂层具有明显分层的结构, 由外至内依次为(Nb,X)Si₂(X表示Ti, Hf和Cr)外层和(Nb,X)₅Si₃过渡层, 在过渡层与基体之间有不连续分布的细小(Cr,Al)₂(Nb,Ti)块状沉淀. EDS分析表明, 涂层中的Y分布是不均匀的, (Cr,Al)₂(Nb,Ti)相的Y含量为0.94at%左右, 而(Nb,X)Si₂和(Nb,X)₅Si₃相的Y含量为0.46at%～0.57at%. 经1250℃分别氧化5, 10, 20, 50和100h后, Si-Y₂O₃共渗涂层保持其原始的相组成, 并在其表面形成以TiO₂、 SiO₂和Cr₂O₃组成的致密混合氧化膜, 且与基体结合良好.

Microstructure and High Temperature Oxidation Resistance of Si-Y_2O_3 Co-deposition Coatings Prepared on Nb-silicide-based Ultrahigh Temperature Alloy by Pack Cementation Process

Si-Y_2O_3 co-deposition coatings on Nb-silicide-based ultrahigh temperature alloy were prepared by pack cementation processes. The co-deposition holding temperatures were 1050℃, 1150℃ and 1250℃, and the holding times were 5, 10, 15 and 20h, respectively. The microstructure and isothermal oxidation resistance of the coatings were studied. The results show that all Si-Y_2O_3 co-deposition coatings are composed of a (Nb,X)Si_2 (X represents Ti, Hf and Cr elements) outer layer and a (Nb,X)_5Si_3 transitional layer. Some thin discontinuous (Cr,Al)_2(Nb,Ti) laves phase precipitates exist between the substrate and (Nb,X)_5Si_3 transitional layer. EDS analyses reveal that the distribution of Y on the coatings is not uniform. The content of Y in (Nb,X)Si_2 and (Nb,X)_5Si_3 phases is about 0.46at%-0.57at% while that in (Cr,Al)_2(Nb,Ti) is about 0.94at%. After oxidation at 1250℃ for 5, 10, 20, 50 and 100h respectively, the retained Si-Y_2O_3 co-deposition coatings still possess double layers structure with their original constituent phases and combine tightly with both scale and substrate. The dense scale developed on Si-Y_2O_3 co-deposition coatings during oxidation at 1250℃ is composed of TiO_2, SiO_2 and Cr_2O_3. Si-Y_2O_3 co-deposition coatings possess better oxidation resistance than simple Si deposition coatings.