Nb-Si基原位复合材料表面包埋渗制备Si-Cr-Y共渗涂层

Co-deposition of Si-Cr-Y on Nb-Si in situ composites by the pack cementation process

通过热力学计算分析了分别使用NH4Cl和CrCl3.6H2O两种不同激活剂时,各个共渗元素的卤化物蒸汽压分压的变化,得到了实现Nb-Si基原位复合材料上Si-Cr-Y三元包埋共渗的最佳条件。采用包埋共渗法在Nb-Si基原位复合材料表面制备了Si-Cr-Y共渗涂层,研究了涂层的组织形貌、成分及其相组成。结果表明:使用NH4Cl做激活剂,通过调整包埋渗料的成分,可以在适当的温度下实现Si-Cr-Y的三元共渗。当渗料成分为12Cr-6Si-0.75Y2O3-5NH4Cl-76.25Al2O3(质量分数)时,在1350℃可以实现Si-Cr-Y三元共渗。制备的涂层具有多层结构,分为外层、内层和明显的互扩散层。互扩散层的存在,表明涂层的形成是一个连续生长过程,伴随着Cr、Si、Y元素向基体内的扩散。涂层的主要成分由Cr2(Nb,Ti)、(Nb,Ti)5Si3和HfSi2组成,Y元素的添加起到了细化涂层的作用。

In order to identify suitable pack compositions for co-depositing Cr, Si and Y to form diffusion coatings on Nb-base in situ composites by the pack cementation process, thermochemical calculation was taken to analysis the vapour pressure of halide species generated in a series of pack powder mixtures activated by NH4Cl or CrCl3·6H2O at high temperatures. The Cr-Si-Y co-depositing coating layers on the Nb-base in situ composites were prepared according to the analysis. The microstructure, phase constituents and compositional distribution in the coatings were studied. The results show that by means of carefully controlling the composition of the packs activated by NH4Cl, co-deposition of Si-Cr-Y on Nb-Si in situ composites can be achieved at the appropriate temperature. It is demonstrated that the co-depositing coating can be formed at 1350℃ with the pack power mixtures composed of 12Cr-6Si-0.75Y2O3-5NH4Cl-76.25Al2O3（mass fraction）. The coatings obtained have a multiple layer structure, consisting of an outer layer, an inner layer and a diffusion zone at the boundary between the coating and the substrate. It is suggested that the coating is formed via a sequential deposition mechanism through inward diffusion of Cr, Y and Si. The coatings are mainly composed of Cr2（Nb,Ti）, （Nb,Ti）5Si3 and HfSi2, and the microstructure of the coatings can be refined by addition of Y2O3 in the pack mixtures.