Microstructural parameters in large strain deformed Ni polycrystals as investigated by synchrotron radiation

Dislocation densities, arrangements and long-range internal stresses in col d worked polycrystalline nickel were determined by X-ray diffraction profil e analysis using synchrotron radiation. Torsionally deformed samples were s canned across the diameter of the specimens with a focal spot of 300 mu m p roviding strain dependent results in good correlation with residual electri cal resistivity data. On cold rolled specimens with different deformations, scanning measurements across single grains with a focal spot of less than 50 mu m were carried out, in order to inform on the features of the deforma tion induced substructure. At small deformations including stage III, the d islocation densities and internal stresses are uniform within single grains while at higher deformations in stages IV and V, the dislocation density a nd internal stresses exhibit correlated fluctuations. In analogy to Cu, in stage IV these fluctuations could be identified as polarized tilt walls (PT W) formed from polarized dipole walls (PDW) whereas in stage V, as a differ ence to Cu, only PDWs and pile-ups of dislocations at the grain boundaries were found. It is suggested that the differences to Cu arise from the enhan ced presence of deformation induced vacancies in Ni, enabling stronger effe cts of static recovery through dislocation climb to take place in between s ingle passes of rolling deformation.