23. Mechanical Properties of Ti₂AlNb and Ti₂AlZr Intermetallics: A First Principles Study

The first principles density function theory (DFT) within generalized gradient approximation (GGA) has been utilized to explain the structural stability and mechanical properties of the of Ti₂AlNb and Ti₂AlZr intermetallics. The structures of these intermetallics are similar to B2, D0₁₉ and O phases. The calculated equilibrium constants for the above phases match very well with experimentally reported values. The D0₁₉ and O phases in Ti₂AlNb display nearly close value of formation energy/atom. In contrast, formation energy/atom of the B2 phase in Ti₂AlNb is lower than that of D0₁₉ and O phases. This shows that D0₁₉ and O phases are more stable than B2 phase. The decreasing order of formation energy/atom in Ti₂AlZr is B2, D0₁₉ and O phases. The stability criteria in terms of elastic constants reflect that all the three phases in both the intermetallics are stable. The G/B ratios of all the three phases in both the intermetallics indicate that these phases are ductile. In addition, anisotropy is also present in all the three phases. Interestingly, the degree of anisotropy is significantly high for highest symmetry B2 phase.