  Cast and HIP'ed \textgamma-TiAl 4522XD is being developed for use in jet
engine low pressure turbine blades, where temperature variations occur through
the flight cycle. The effects of temperature variations on fatigue cracking
were therefore examined in this study. It was found that fatigue crack growth
rates were higher at 750C than 400C, but that $\Delta K_\mathrm{th}$ was also
higher. Temperature excursions between 400 and 750C during fatigue crack growth
resulted in retardation of the crack growth rate, both on heating and cooling.
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. 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.
