Effect of annealing on dislocation structure parameters of ultrafine-grained copper: comparative study by acoustic and x-ray methods

The acoustic spectroscopy method and X-ray diffraction analysis were used to study the effect of severe plastic deformation(SPD) and subsequent annealing on the parameters of the dislocation structure of ultrafine-grained (UFG) FRTP (Fire RefiningTough Pitch) copper. To this end, the effect of SPD and subsequent annealing on the main parameters of the low-temperatureBordoni acoustic relaxation was studied in detail. Annealing was performed in the temperature range 90 – 430 C, including theprimary crystallization temperature of highly deformed copper Tann  135 C. For all states of the samples, the estimates of thedensity of mobile dislocations m, which contribute to the low-temperature dynamic relaxation, are obtained. Annealing leads to thedecrease in the dislocation density from m  1.7·1012 m-2 to m  1.5·1011 m-2. In addition to the dislocation density, an estimate ofthe 1st order Peierls’ stress 4P  19 MPa 2.5·10 G    (G – shear modulus) was also obtained from the acoustic measurements. Inparallel with the acoustic measurements, the parameters of the dislocation structure of the samples were studied by X-ray diffraction.The values of the lattice parameter, the values of microdeformation, the average size of the coherent scattering region (CSR), andalso the average density of dislocations were obtained. It turned out that the X-ray density of dislocations is two orders of magnitudehigher than the values obtained from acoustic measurements. At the same time, the data on the effect of annealing obtained by bothmethods are in qualitative agreement with each other; in particular, a decrease in the dislocation density of the same order ofmagnitude is observed.