  We investigate the scatter in the cycles to crack initiation for
conventionally cast specimens of the superalloy RENE 80 in total strain
controlled low cycle fatigue (LCF) tests at 850{\deg}C. The grains at the
location of crack initiation are investigated using electron backscatter
diffraction (EBSD) measurements with scanning electron microscopy (SEM). This
results in determination of maximal Schmid factors for the slip system that
lead to the initiation of the LCF surface crack. It is shown using stress -
life and strain - life models, that taking into account the Schmid factor
considerable reduces the scatter in LCF life prediction. This is used to
propose a probabilistic model for LCF life based on random grain orientations.
Using Mote Carlo simulation, we determine the probability distribution for the
maximal Schmid factor in an uniaxial stress state under isotropic random
orientations of the grain. This is used to calculate failure probabilities
under the above mentioned model and to compare them with experimental data.
Based on extreme value statistics, it is discussed whether a high maximal
Schmid factor can be considered as causally related to an early initiation of
an LCF crack and we present some rather surprising experimental evidence. In
the last section conclusions are formulated and future directions of research
are outlined.
