X-RAY-INVESTIGATIONS ON CREEP-DEFORMED SINGLE-CRYSTALS OF THE NICKEL-BASE SUPERALLOY CMSX-4

X-ray investigations were carried out on undeformed and creep-deformed single crystals of the gamma'-hardened nickel-base superalloy CMSX-4 in order to obtain information about the microstructural changes induced by creep deformation. For this purpose x-ray rocking curves and x-ray topographs obtained by the method of Berg and Barrett were analyzed. In undeformed crystals, characteristic mutual misorientations of up to approximate to 30' between neighbouring dendrites were detected and characterized. The study of deformed crystals showed that the dislocations and dislocation networks formed during deformation produce additional lattice misorientations. In specimens creep-deformed at 800 degrees C in which the cuboidal gamma'-particle morphology has been preserved, a marked difference in the frequencies of lattice rotations around axes parallel and perpendicular to the tensile axis, respectively, could be deduced from rocking-curve broadening. This is caused by the different states of stress in the gamma-matrix channels which lie parallel and perpendicular to the stress axis, respectively. On the other hand, after creep deformation at 950 degrees C, a directionally coarsened gamma/gamma' structure prevails, giving rise to a distinctly different rocking-curve broadening, indicating that only the lattice misorientations around axes perpendicular to the stress axis are enhanced by creep deformation.