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 induc ed by creep deformation. For this purpose x-ray rocking curves and x-r ay 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 disloca tions and dislocation networks formed during deformation produce addit ional lattice misorientations. In specimens creep-deformed at 800 degr ees C in which the cuboidal gamma'-particle morphology has been preser ved, a marked difference in the frequencies of lattice rotations aroun d axes parallel and perpendicular to the tensile axis, respectively, c ould be deduced from rocking-curve broadening. This is caused by the d ifferent states of stress in the gamma-matrix channels which lie paral lel and perpendicular to the stress axis, respectively. On the other h and, after creep deformation at 950 degrees C, a directionally coarsen ed gamma/gamma' structure prevails, giving rise to a distinctly differ ent rocking-curve broadening, indicating that only the lattice misorie ntations around axes perpendicular to the stress axis are enhanced by creep deformation.