Generalized planar fault energies and mechanical twinning in gamma TiAl alloys

We calculated generalized planar fault energies along 1/6〈1 1 −2](1 1 1) true- and 1/6〈1 −2 1](1 1 1) pseudo-twinning directions and correlated with the propensity for mechanical twinning in gamma TiAl alloys with different Al contents. The generalized planar fault energies along 1/6〈1 1 −2](1 1 1) increase with increasing Al content. The predicted critical twinning stresses show that hypostoichiometric TiAl undergoes twinning more readily than stoichiometric and hyperstoichiometric TiAl. The critical stresses for 1/6〈1 −2 1](1 1 1) are dramatically larger than those for 1/6〈1 1 −2](1 1 1), and thus twinning occurs through energetically favorable 1/6〈1 1 −2](1 1 1).