Study On Aluminizing And Al-Si Co-Infiltration On Ti-Alloy Fabracated By EB-PVD

Ti-alloy sheet fabricated by electron beam physical vapor deposition (EB-PVD) technique was aluminized and Silicon aluminized by pack cementation. X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure of as-deposited and aluminized and Al-Si co-deposition coating. Oxidation resistance properties of these sheets were investigated by cyclic oxidation at 700℃in the air.The results showed that the as-deposited Ti-alloy sheet was composed ofα-Ti solid solution. The diffraction peaks were widen and asymmetrical. The microstructure was in a non-equilibrium state with compact and refined grains. After aluminizing at 600℃and 620℃for 6 hours, the phase construction of the aluminized coating was Al₃Ti. The interface between the coating and substrate was smooth and clear. However, as Al₃Ti phase was brittle, it was easy to create crack in the cooling process due to the heat stress. Aluminized at 700℃, the sheet was infiltrated and a small amount of aluminum-rich region appeared in a small area. After Al-Si co-infiltration, the phases of the coating were Al₃Ti and Ti₅Si₃. The interface was clear but unsmooth.By means of vacuum heat treatment, interdiffusion occurred between the coating and the matrix and the interdiffusion area showed stratified arrangement. As the heat treatment time and temperature increased, interdiffusion area extended and the aluminized coating became thinner and finally disappeared. The interfaces between inter-diffusion layers became unsmooth.50 hours cyclic oxidation results showed that cyclic oxidation kinetics curve of as-deposited Ti-alloy sheet was approximate linear. The oxide film fell off after cyclic oxidation 30h. The oxide was mainly composed of TiO₂ and the oxide film was porous with poor oxidation resistance property. By aluminizing and Al-Si co-infiltration, the kinetics curve of treated alloys was parabolic. Oxide products of Ti-alloy with aluminizing coating were Al₂O₃ and a small amount of TiO₂. Oxide products of Ti-alloy with Al-Si co-infiltration coating was a mixture of Al₂O₃, SiO₂ and TiO₂.