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

Abstract

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 Refining
Tough Pitch) copper. To this end, the effect of SPD and subsequent annealing on the main parameters of the low-temperature
Bordoni acoustic relaxation was studied in detail. Annealing was performed in the temperature range 90 – 430 C, including the
primary crystallization temperature of highly deformed copper Tann  135 C. For all states of the samples, the estimates of the
density of mobile dislocations m, which contribute to the low-temperature dynamic relaxation, are obtained. Annealing leads to the
decrease 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 of
the 1st order Peierls’ stress 4
P  19 MPa 2.5·10 G    (G – shear modulus) was also obtained from the acoustic measurements. In
parallel 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), and
also the average density of dislocations were obtained. It turned out that the X-ray density of dislocations is two orders of magnitude
higher than the values obtained from acoustic measurements. At the same time, the data on the effect of annealing obtained by both
methods are in qualitative agreement with each other; in particular, a decrease in the dislocation density of the same order of
magnitude is observed.