Effect of surface orientation on reactive wetting of sapphire by Al–Ti alloys at 1273 K

Abstract

The effect of surface orientation on the reactive wetting of sapphire by Al–Ti alloys was studied by the modified sessile drop method at 1273 K under a high vacuum atmosphere. The monocrystal α-Al2O3 (sapphire) substrates with different atomic termination surfaces were selected in this study, i.e., C (0,0,0,1), R (1 1(−),0,2), and M (1 1(−),0,0) faces. The order of wettability is R > C ≈ polycrystalline substrate > M, and the final contact angles are 65 ± 0.1° (R), 76 ± 0.2° (C), 76 ± 0.3° (polycrystalline), and 84 ± 0.3° (M), respectively. The addition of Ti does not result in the formation of the continuous reaction layer, but it may contribute to the reaction of 4Al(l)+Al2O3(s)→3Al2O(g)↑. When the interfacial bonding is mainly chemical, the wettability depends on the bonding energy between the terminal atoms of the crystal face and the atoms of the liquid phase. The higher the bonding energy, the better the wettability.