铌硅化物基超高温合金Si-Y_2O_3共渗涂层的组织及其高温抗氧化性能

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

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.

Si-Y2O3 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-Y2O3 co-deposition coatings are composed of a（Nb,X）Si2（X represents Ti,Hf and Cr elements） outer layer and a（Nb,X）5Si3 transitional layer.Some thin discontinuous（Cr,Al）2（Nb,Ti） laves phase precipitates exist between the substrate and（Nb,X）5Si3 transitional layer.EDS analyses reveal that the distribution of Y on the coatings is not uniform.The content of Y in（Nb,X）Si2 and（Nb,X）5Si3 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-Y2O3 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-Y2O3 co-deposition coatings during oxidation at 1250℃ is composed of TiO2,SiO2 and Cr2O3.Si-Y2O3 co-deposition coatings possess better oxidation resistance than simple Si deposition coatings.