Ruhr-Universit├Ąt Bochum

Under conditions of low temperature (< 800┬░C) and high stress (> 600 MPa) creep, a<112> fault ribbons form in the microstructures of single crystal Ni-base superalloys. New experimental shear creep results are presented which show that a macroscopic <112>{111} shear test deforms much faster than a <110>{111} shear test. The reason is, that the two dislocation families with different Burgers vectors, which are needed in order to start the nucleation of a a<112> fault experience the same high resolved shear stress during <112>{111} shear testing.

Diffraction contrast diffraction contrast microscopy is performed to provide microstructural evidence for the presence/absence of planar faults.

Moreover, creep activation parameters n (stress exponent) and Q (apparent activation energy) are measured for the two macroscopic shear systems and are discussed in the light of previous results published in the literature.