MICROSTRUCTURAL CHANGES DURING THE HIGH-TEMPERATURE CREEP OF A DIRECTIONALLY-SOLIDIFIED NICKEL-BASE SUPERALLOY

Bars of IN738LC (a 40 volume percent gamma prime strengthened alloy) were directionally solidified and given commercial heat treatment. Four specimens were tested in air at 850 degree C under constant load with an initial applied stress of 250 MPa. The tests were interrupted at different levels of strain. The results show that the major changes in interparticle spacing occur at the beginning of the test, whereas the creep rate increases most rapidly towards the end. A model based only on changes in the level of mechanical strenthening through particle coarsening cannot account for the increasing strain rate during creep.