ANALYSIS OF THE DISLOCATION CONTENT IN A DEFORMED CO-BASED SUPERALLOYBY TRANSMISSION ELECTRON-MICROSCOPY AND X-RAY-DIFFRACTION

The present paper compares the dislocation densities as determined in a Go-based superalloy (CoNi22Cr22W14) after creep and tensile deformat ion by Transmission Electron Microscopy (TEM) and X-ray profile analys is (XRD). After creep tests the dislocation densities obtained by both methods are in good agreement, which is the result of ii nearly homog eneous dislocation distribution. The relationship between the dislocat ion density and the flow stress meets the Taylor equation. After tensi le deformation the dislocation densities determined by TEM and XRD dif fer systematically from each other, but in both cases also a Taylor re lationship can be obtained. The constant a of the dislocation interact ion derived by TEM is much larger than in the creep tests and also tha n that of the XRD, which agrees well with the creep date. The differen ce between the TEM and the XRD results is the consequence of the dislo cation cell structure much more developed in the tensile specimens, wh ich leads to an underestimation of the dislocation density in TEM beca use of overweighting the cell interior. By fitting the Fourier coeffic ients of the X-ray diffraction line shapes with a bimodal distribution of the defect content (composite model), dislocation densities of the cell interior can be estimated that correspond well to the TEM data.