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Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P398
Structural Relaxation of Damage Structure in Creep-deformed Single Crystal
Superalloy SC16 Measured by Means of X-Ray Diffraction
Gerhard Schumacher 1 , Nora Darowski 1 , Ivo Zizak 1 , Hellmuth Klingelhöffer
2 , Wolfgang Neumann 3
1 Hahn-Meitner-Institut Berlin, Glienicker Straße 100, D-14109 Berlin – 2 Bundesanstalt
für Materialforschung und prüfung, Unter den Eichen 87, 12205 Berlin – 3 Institut für
Physik, Humboldt-Universität zu Berlin, Newtonstraße 15, 12489 Berlin
Nickel base single crystal superalloys are widely used as structure materials in land base
gas turbines as well as in air-craft turbines. Their excellent creep and fatigue properties
at high temperatures are due to the special microstructure of the material consisting
of cuboidal Gamma-prime-precipitates with L12 lattice structure which are coherently
embedded in the Gamma fcc solid solution phase. The Gamma-Prime precipitates
serve as obstacles for the dislocations produced during deformation. The stability of
microstructure under creep-deformation is therefore important for the understanding
of mechanical properties at high temperatures. We therefore studied the changes in
microstructure in model single crystal superalloy SC16 during exposure at high, constant
temperature after thermomechanical load at 1223 K to 15 % tensile creep strain
in [001] direction under tensile load of 150 MPa.
X-ray measurements have been performed using the 6-circle diffractometer at the
KMC-2 beamline at BESSY using an X-ray energy of 8 kV. Measurements have been
performed in the [100] direction, i.e., perpendicular to the axis of pre-strain. Structural
relaxation of gamma prime crystal lattice at 1173K has been determined by measuring
the position and linewidth of the 100 superlattice reflection. The lattice misfit between
gamma and gamma prime phase has been determined by measurement of the 200
intensity profiles.
Considerable changes in width and position of 100 superlattice reflection and in
Gamma/Gamma-Prime lattice misfit were found. The results will be compared with
measurements on the same material (15 % strain) measured in [001] direction, i.e.,
along the axis of creep-deformation [1].
The results are discussed in the frame of a dislocation model: Plastic deformation
creates dislocations which arrange differently at differently oriented interfaces [2]. The
stress induced by these dislocations partly relaxes during thermal treatment by rearrangement
of dislocations.
[1] G. Schumacher, N. Darowski, I. Zizak, H. Klingelhöffer, and W. Neumann, THER-
MEC2006, 5th int. conf. on processing and manufacturing of advanced materials, July
4-8 (2006) Vancouver, Canada, Materials Science Forum, in press.
[2] W. Chen, N. Darowski, I. Zizak, G. Schumacher, H. Klingelhöffer and W. Neumann,
Nucl. Instr. Meth. B 246 (2006) 201.
Work supported by DFG Schu 1254/3-4 and Ne646/5-3