Fatigue crack growth testing of Inconel 718 has been carried out at the temperatures 550 C and 650 C. The tests were conducted using a mix of hold times and pure cyclic loading, referred to as block tests. From the test results, the existence of an embrittled volume or damaged zone in the vicinity of the crack tip has been revealed. It has been found that the evolution of this damaged zone can be sufficiently well described using a power law function with an exponent n=0.25. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11