活性元素Y对高Nb-TiAl合金表面硅化物渗层组织的影响

Effects of Active Element Y on Formation of Silicide Co-deposition Coatings on High Nb-TiAl Alloy

目的提高Nb-TiAl合金的抗高温氧化性能。方法采用NaF为催化剂、1080℃下Si-Y扩散共渗5 h的方法,在高Nb-Ti Al表面制备了Y改性硅化物渗层,利用SEM、EDS和XRD分析了渗剂中Y_2O_3含量对共渗层组织及相组成的影响。结果采用不同含量Y_2O_3所制备的Si-Y共渗层具有多层复合结构,共渗层的厚度随Y元素的添加呈先增大后减小的趋势,共渗层的内层均由γ-Ti Al相组成;当渗剂中Y_2O_3含量为2%和3%（质量分数）时,共渗层的外层主要为（Ti,Nb）Si_2相,中间层分为上下两层,分别为（Ti,Nb）_5Si_4相和（Ti,Nb）_5Si_3相,其中2%Y_2O_3的Si-Y共渗层有一层富Al的（Ti,Nb）_5Si_4和（Ti,Nb）_5Si_3相组成的浅表层;当渗剂中Y_2O_3含量为0%、1%和5%时,共渗层外层以（Ti,Nb）_5Si_4相为主,中间层主要为（Ti,Nb）_5Si_3相。结论稀土Y元素质量分数为2%～3%时具有明显的促渗作用,且获得的Si-Y渗层组织结构致密,但添加过量的稀土元素会抑制Si元素的吸附与扩散,使得Si-Y共渗层中产生较多的孔洞,同时渗层的组织结构发生了改变。

The work aims to improve high temperature oxidation resistance of Nb-Ti Al alloy. In this paper, Y modified silicide coating was prepared on high Nb-Ti Al surface by taking Na F as catalyst and diffusing and co-penetrating Si-Y for 5 h under 1080 ℃. Effects of Y_2O_3 content in permeating agent on co-deposition coating and its phase composition were analyzed by virtue of XRD, SEM and EDS. All Si-Y coatings prepared with different contents of Y_2O_3 were provided with a multi-layer composite structure. Thickness of the coatings firstly increased and then decreased with the addition of Y element in the pack. All inlayers of the coatings were mainly composed of a γ-Ti Al phase. The outer layers of the coatings prepared at 1080 ℃ for 5 h with the pack mixture containing 2% or 3% Y_2O_3 were mainly composed of（Ti,Nb）Si_2 phase, and the middle layer was divided into upper and lower layers composing of（Ti, X）_5Si_4 and（Ti, X）_5Si_3 respectively. Moreover, a superficial layer consisting of Al-rich（Ti,Nb）_5Si_4 and（Ti,Nb）_5Si_3 was detected in the coating prepared with 2% Y_2O_3. However, the constituent phase turned to（Ti, Nb）5Si4 in the out layer and（Ti, X）_5Si_3 in the middle layer of the co-deposition coating when the pack mixture contained 0%, 1% or 5% Y_2O_3. The coating growth can be catalyzed obviously when the content of Y_2O_3 in the pack mixtures ranges between 2%～3%. However, excess addition of rare earth element will restrain the adsorption and diffusion of Si element, and thus a number of holes will appear on Si-Y co-deposition coating and the layer structure will change.