Y_2O_3对铌硅化物基超高温合金硅化物渗层组织的影响

采用包埋共渗工艺在铌硅化物基超高温合金表面制备了Si-Y2O3共渗层,共渗温度为1050℃,共渗时间为10h。利用SEM,EDS和XRD等方法分析了渗剂中Y2O3添加量对渗层结构、组织形貌及其成分分布的影响,并与相同包埋渗温度和时间下单独渗Si渗层的组织进行了对比。结果表明:在渗剂中添加不同含量Y2O3后的渗层具有相似的结构,均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)层,(Nb,X)5Si3过渡层和富Al扩散区。与单独渗Si渗层相比,渗剂中添加Y2O3没有改变渗层表层的相组成,但抑制了渗层中孔洞的产生,使相同包埋渗温度和时间处理后Si-Y2O3共渗层的组织较单独渗Si渗层的更为致密。EDS能谱分析结果表明,Y在渗层中的分布是不均匀的,在靠近过渡层与基体界面处的Y含量较高,并由内向外逐渐递减。随渗剂中Y2O3含量增加,渗层中的平均Y含量出现先增加后降低的规律。当渗剂中Y2O3的加入量为1%~2%(质量分数)时,Y2O3具有明显的催渗作用。

Effect of Y_2O_3 on Microstructure of Silicide Coatings on Nb-silicide-based Ultrahigh Temperature Alloy

Si-Y_2O_3 co-deposition coatings on an Nb-silicide-based ultrahigh temperature alloy were prepared by pack cementation process at 1050℃ for 10h. The structure, phase constituents and compositional distribution of coatings were investigated by SEM, EDS and XRD and compared with those of the coating prepared by depositing Si under the same conditions. The results show that no evident new phases form on the surface layer of Si-Y_2O_3 co-deposition coating. Coatings prepared with different content of Y_2O_3 (in the range of 0.5%-5%, mass fraction) in the pack mixtures have the similar structure, which is composed of a (Nb, X)Si_2 (X represents Ti, Hf and Cr elements) layer, a (Nb, X)_5Si_3 transitional layer and an Al-rich diffusion zone. The Si-Y_2O_3 co-deposition coatings are more compact than the simple Si deposition coating. EDS analyses reveal that the distribution of Y in the coating are not uniform. The Y content appears the highest in the place near the interface between substrate and transitional layer and it gradually decreases from the substrate to the coating surface.Furthermore,the Y concentration in the coating firstly increases and then decreases with the increase of the content of Y_2O_3 in pack mixtures. The coating growth can be catalyzed obviously when the content of Y_2O_3 in the pack mixtures ranged from 1% to 2% (mass fraction).