Fatigue crack initiation and growth were examined in cast and HIP'ed
\textgamma-TiAl 4522XD. It was found that fatigue crack growth rates were
higher at $750\celsius$ than $400\celsius$, but that $\Delta K_\mathrm{th}$ was
also higher. Temperature excursions between $400$ and $750\celsius$ during
fatigue crack growth resulted in retardation of the crack growth rate, both on
heating and cooling; however heating from 400 to $750\celsius$ at a $\Delta K$
that would then be below threshold did not result in complete crack arrest. It
was also found that for notches $0.6$~mm in length and smaller, initiation from
the microstructure could instead be observed at stresses similar to the
material failure stress; a microstructural initiation site exists. Secondary
cracking around borides could also be observed. A change from trans- to mixed
trans-, inter- and intra-lamellar cracking could be observed where the
estimated size of the crack tip plastic zone exceeded the colony size. Changes
in fracture surface morphology could not be related to the temperature of
fatigue crack growth, although this could be observed from the oxide scale
colouration. Compressive pre-loading of a crack results in retardation of the
crack, which could also be observed from the oxide.