Creep deformation and rupture of nickel base superalloy CM247LC under variable loading

The high temperature cyclic creep behaviour of a directionally solidified N i base superalloy has been investigated and compared with constant load cre ep data. Irrespective of whether holding time is allowed during off loading periods or not, the creep rupture lives are shorter for the cyclic creep. The effect of cyclic loading is to cause further increase in strain rate ac celeration. The frequency of load change does not have any significant effe ct on rupture time. The evolution of the particulate microstructure as well as other transient creep phenomena such as anelasticity have practically n o effect on the observed strain rate acceleration. However the presence of the shrinkage pores and presumably the variation in their size and populati on introduce some measure of scatter in the rupture lives. MST/4330.