催化剂及Al对TiAl合金表面Si-Al-Y共渗层组织结构的影响

Effects of activator and Al on the microstructures of Si-Al-Y co-deposition coatings on TiAl alloy

通过1 050℃下Si-Al-Y扩散共渗4h的方法在TiAl合金表面制备了Y改性Si-Al共渗层,采用SEM、EDS和XRD分析了渗剂中催化剂(AlCl3·6H2O)及Al含量对共渗层组织及相组成的影响。结果表明,催化剂含量为1%(质量分数)时未形成完整的Si-A-Y共渗层;当催化剂含量为3%,5%和8%(质量分数)时所形成的共渗层均具有多层复合结构,共渗层的内层都是由TiAl2和γ-TiAl相组成,互扩散区为富Al的TiAl相;随催化剂含量的增加共渗层外层和中间层的相组成都发生了改变;催化剂含量为3%(质量分数)时所制备的共渗层外层为大量的(Ti,X)5Si4(X表示元素Nb和Cr)和少量的(Ti,X)5Si3相;催化剂含量为5%,8%(质量分数)时所制备的共渗层外层分别为(Ti,X)5Si3和TiSi2相,中间层均为(Ti,X)5Si4及(Ti,X)5Si3相,由于TiSi2外层具有良好的抗高温氧化性能,因此催化剂含量为8%(质量分数)时适合用于Si-Al-Y共渗层的制备。Al含量对共渗层的相组成无显著影响,但改变了共渗层各层厚度。

Si-Al-Y co-deposition coatings were prepared on an TiAl alloy by pack cementation processes at 1 050 ℃ for 4 h,scanning electron microscope （SEM）,energy dispersive X-ray spectrometer （EDS）and X-ray diffractmeter （XRD）were employed to investigate the effects of pack AlCl3？？6 H2 O and Al content on the surface morphologies,microstructures and phase constitutions of the coatings.The results show that the Si-Al-Y co-deposition coating could not obtained with 1wt% activators（AlCl3？？6H2 O）in pack mixtures;all the coatings prepared respectively with （3%,5%,8wt%）activators have a multiple layer structure,which are composed of an TiAl2 andγ-TiAl inner layer,and a Al rich inter-diffusion zone;the phase constituents of outer layers and middle layers of the coatings changed with increasing co-deposition activators in pack mixtures.The outer layer of the coating prepared at 1 050 ℃ for 4 h with the pack mixtures containing 3wt% activator were main composed of （Ti,X）5 Si4 （X represents Nb and Cr）and little （Ti,X）5 Si3 phases.However,the constituent phases changed into （Ti,X）5 Si3 and TiSi2 in the out layer of the coatings prepared with 5% and 8wt% activators in pack mixtures,and the middle layer of the two coatings were composed of （Ti,X）5 Si4 and （Ti,X）5 Si3 ,and the TiSi2 out layer with the favourable performances of high temperature anti-oxidation,so the pack mixtures containing 8wt% activator was seclected for Si-Al-Y co-deposition.Al content in the pack has less effect on the phase composition of the coating,but changed the thickness of each layer.