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采用Si-Cr包埋共渗法在Ti-Nb-Si基高温合金表面制备了Cr改性的硅化物涂层,共渗温度为1250和1300℃,时间为10h。利用SEM,EDS和XRD等检测手段分析了涂层的结构、元素分布及相组成等,并对涂层的形成机理进行了讨论。结果表明:Si-Cr共渗温度为1250℃时,降低渗剂中的催化剂NaF含量会降低Si和Cr的反应扩散速度并且改变了涂层的结构和相组成。催化剂NaF含量为8wt%,涂层外层由(Nb,Ti)Si2及少量(Ti,X)5Si3(X代表Nb,Cr和Hf等元素)组成,中间层由(Ti,X)5Si4组成,过渡层由(Nb,Ti)5Si3组成;降低NaF含量至5wt%,Si-Cr共渗温度仍为1250℃时,涂层外层由(Ti,X)5Si3组成,且有较多孔洞出现,中间层为(Ti,X)5Si4,而过渡层很薄。与渗Si涂层相比,Si-Cr共渗涂层中的裂纹明显减少,但在涂层外层存在较多孔洞且涂层厚度明显减小。提高包埋共渗温度至1300℃时,Cr的反应扩散速度得到提高,且在涂层外层出现了(Nb1.95Cr1.05)Cr2Si3三元相。
Cr-modified silicide coatings were prepared on Ti-Nb-Si based superalloy by Si-Cr embedding and co-infiltration with co-infiltration temperatures of 1250 and 1300 ℃ for 10h. The structure, elemental distribution and phase composition of the coating were analyzed by SEM, EDS and XRD. The formation mechanism of the coating was also discussed. The results show that when the Si-Cr co-permeation temperature is 1250 ℃, decreasing the NaF content of the catalyst in the penetration agent decreases the reaction diffusion rate of Si and Cr, and changes the structure and phase composition of the coating. The outer layer of the coating consists of (Ti, X) 5Si3 (X, Nb, Cr and Hf, etc.) The transitional layer consists of (Nb, Ti) 5Si3. When the NaF content is reduced to 5wt% and the Si-Cr co-permeation temperature is still 1250 ℃, the outer layer of the coating is composed of (Ti, The middle layer is (Ti, X) 5Si4, while the transition layer is thin. Compared with the infiltration of Si coating, cracks in the Si-Cr co-diffusion coating significantly reduced, but there are more holes in the outer coating layer and the coating thickness is significantly reduced. When the embedment temperature is increased to 1300 ℃, the reaction diffusion rate of Cr increases, and the (Nb1.95Cr1.05) Cr2Si3 ternary phase appears in the outer layer of the coating.