The influence of silicon amount on structure of Si modified aluminide coating deposited on Ti46Al7Nb alloy by slurry method

摘要

The alloys based on the intermetallic phases from Ti-Al system are materials which, on the grounds of their resistance characteristics, could be widely used in automotive and aerospace applications. The insufficient oxidation resistance of this alloys could be increased by the coating silicon modification. The technology used in this investigation was the immersion in water-based slurry containing metal powders. MHI high-Nb (14 wt %) alloy has been used as the research material for the coatings produced. The water-based slurries containing Al and Si powders have been prepared with 0-80 wt % Si content. The diffusion treatment has been done at 950°C in 4h in the Ar atmosphere. The investigation has showed that the thickness of the coatings ranged from 30 to 40 μm. The structure of the Si-modified aluminide coatings is as follows: (a) outer zone consisting of TiAl_3 phase and titanium silicides, (b) middle zone consisting of columnar titanium silicides in phase TiAl_3 matrix (c) the inner zone consisting of TiAl_2 phase. The XRD phase analysis has confirmed Ti_5Si_3 creation and, in case of the high silicon content (above 20 wt %), also other silicides: types Ti_5Si_4,TiSi_2,TiSi