Abstract
The behavior of γ–β/β0 phase transition in TiAl alloy doped with β stabilizers (V, Cr, Mn) are studied by using the first principles method. It is found that alloying addition as well as anharmonic lattice vibration and disordered atomic occupation contributes to enhance the stability of cubic structure and accordingly introduce the disordered β phase into the high-temperature microstructure. The formation of low-temperature β0 phase originates from not only the stabilization of cubic structure but also the destabilization of tetragonal structure. In particular, the latter is the main reason for the premature precipitation of the hard-brittle β0 phase in the room-temperature microstructure at low nominal doping concentrations. We also find a special doping region in which the γ and the β phases are stable, while the β0 phase is unstable. The existence of this region provides an opportunity for the regulation of the contents of β and β0 phases.
Highlights
The behavior of γ–β/β0 phase transition in TiAl alloy doped with β stabilizers (V, Cr, Mn) are studied by using the first principles method
This implies that the behavior of γ–β/β0 phase transition is highly complicated, which issues a great challenge for the reasonable control of the β and β0 contents, and the modification of TiAl alloy
The formation of β phase depends on the stabilization of cubic structure firstly, which in turn comes from the contribution of β stabilizers and anharmonic lattice vibration at high temperature; secondly, it depends on the disorder of atomic occupation, which is found to further enhance the stability of cubic structure
Summary
The behavior of γ–β/β0 phase transition in TiAl alloy doped with β stabilizers (V, Cr, Mn) are studied by using the first principles method. Titanium aluminides are promising light-weight structural materials for high-temperature applications in aerospace industries, owing to their good oxidation resistance, specific yield strength and specific stiffness[1] In their microstructures there mainly exists two components, a face-centered tetragonal L 10 structure (space group P4/ mmm, γ phase) and a hexagonal D019 structure (space group P63/mmc, α2 phase)[2]. It is interesting to note that the calculated critical addition of β stabilizers for stabilizing the β0 phase is much lower than those for precipitating that phase in the alloy This implies that the behavior of γ–β/β0 phase transition is highly complicated, which issues a great challenge for the reasonable control of the β and β0 contents, and the modification of TiAl alloy. In order to achieve better modification of the alloy, a further understanding on the behavior of γ–β/β0 structural phase transition is still needed
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