Nb-Ti-Si基超高温合金表面Si-Al-Y共渗层的组织形成

Microstructure of Si-Al-Y Co-deposition Coatings on an Nb-Ti-Si Based Ultrahigh Temperature Alloy

研究了包埋共渗温度和渗剂中Al含量对Nb-Ti-Si基超高温合金表面Si-Al-Y共渗层显微组织的影响.采用组成为10Si-10Al-3Y-5NaF-72Al2O3(wt%)的渗剂,分别在1050、1080和1150℃保温10h所制备的渗层具有相似的结构,由(Nb,X)Si2(X代表Ti,Cr和Hf)外层、(Nb,X)5Si3中间层、(Cr,Al)2(Nb,X)和(Nb,X)Al3相构成的次内层及(Nb,X)2Al内层组成.在1050℃/10h所制备渗层的外层和中间层的组成相随渗剂中Al含量增加而变化,但次内层和内层的组成相不改变.当渗剂中Al含量为15wt%时,渗层外层仍为(Nb,X)Si2,但中间层却由(Nb,X)Al3和(Nb,X)5Si3两相组成;当渗剂中Al含量为20wt%时,渗层外层转变为由(Nb,X)Si2和(Nb,X)3Si5Al2两相组成.对1050℃/10h所制备的渗层(采用Al含量为15wt%的渗剂)进行1250℃/0.5h氧化,氧化膜厚度约为10μm,主要由Al2O3、TiO2和SiO2组成.

The oxidation-resistant Si-Al-Y co-deposition coatings on a Nb-Ti-Si based ultrahigh temperature alloy were prepared by halide activated pack cementation processes. SEM, EDS and XRD analyses were used to study the influences of the holding temperature and the content of A/in pack mixtures on the microstructura/formation of the coatings. The results show that the coatings prepared with the pack mixture of 10Si-10Al-3Y-5NaF-72Al2O3 （wt%） at different temperatures （1050℃, 1080℃ and 1150℃, respectively） have a similar structure, consisting of a （Nb,X）Si2（X represents Ti, Cr and Hf elements） outer layer, a （Nb, X）sSi3 mid layer, a sub-inner layer composed of （Cr, AI）E（Nb,X） and （Nb,X）Al3 phases, and a very thin inner layer consisting of （Nb,X）2Al phase. The microstructure of the coatings prepared at 1050℃ for 10h changes evidently with the content of Al in the pack mixtures （10Si-xAl-3Y-5NaF-（82-x）Al2O3 （wt%） （x=10, 15, 20, respectively））. Increasing the content of Al in the pack mix- ture to 15wt%, the constituent phases of the mid layer of the coating change into （Nb,X）Al3 and （Nb,X）5Si3, but the constituent phases remain unchanged in the outer layer, sub-inner layer and inner layer in the coating. The main constituent phases of the outer layer of the coating prepared with the pack mixture containing 20wt% Al are （Nb,X）Si2 and （Nb,X）3Si5Al2, while the constituents phases of the other layers in this coating are the same as those in the coating prepared with the pack mixture containing 15wt% AI. The scale developed on Si-Al-Y co-deposition coating which was prepared with 10Si-15AI-3Y-5NaF-67AIz03 （wt%） pack mixture at 1050℃ for 1 Oh, upon oxidation at 1250℃ for 0.5h, is about 10μm thick, and composed ofA1203, TiO2 and SiO2.