Temperature Dependence of Lattice Distortion in Strongly Creep-Deformed Single Crystal Superalloy SC16

Specimens of single crystal superalloy SC16 have been pre-deformed at 1223 K to strain of 15 % under tensile load of 150 MPa. The profiles of the 001 superlattice reflection of the γ’ precipitate phase as well as the profiles of the 002 reflections of the fcc matrix phase and of γ’-precipitate phase have been measured between RT and 1073 K by means of X-ray diffraction (XRD). From these measurements the lattice distortion of the γ’ precipitates and the lattice misfit between γ and γ’ phase have been determined as a function of temperature. The width of the 001 reflection as well as the lattice misfit decreased as a function of temperature. The results are ascribed to the anisotropic arrangement of dislocations at the γ/γ’ interfaces and to the different thermal expansion coefficients of the γ- and γ’-phase. A comparison of lattice misfit with previous measurements on moderately strained specimens suggests that the measured changes in lattice structure are predominantly created in stage I of creep-deformation.