ISSN 1063-7850, Technical Physics Letters, 2011, Vol. 37, No. 8, pp. 767–768. © Pleiades Publishing, Ltd., 2011. Original Russian Text © V.I. Betekhtin, E.D. Tabachnikova, A.G. Kadomtsev, M.V. Narykova, R. Lapovok, 2011, published in Pis’ma v Zhurnal Tekhnicheskoі Fiziki, 2011, Vol. 37, No. 16, pp. 52–55. 767 As is known, severe plastic deformation (SPD) can lead to the formation of an ultrafine-grained (UFG) structure, which is widely used to improve the mechanical properties of metals and alloys [1–5]. One of the most frequently employed SPD methods is so- called equal-channel angular pressing (ECAP). How- ever, according to experimental data [5–9], the ECAP may be accompanied by the formation of excess free volume and, eventually, nanopores. A certain level of nanoporosity can not only eliminate the strengthening achieved due to the formation of an UFG structure, but even lead to a decrease in the durability of metals under long-term test conditions. In the latter case, the characteristics of the strength on the level of micro- plastic deformation turn out to be less sensitive with respect to the negative influence of nanopores [6]. In principle, the development of nanoporosity can be reduced using a system of counterpressure at the ECAP stage. The tendency to decrease in the nanopo- rosity under the action of counterpressure was pointed out previously [7]. This Letter presents the results of an investigation of the influence of counterpressure during the ECAP stage on the development of nanop- orosity and some mechanical properties of pure cop- per (99.99% Cu). The samples of UFG copper were prepared from initial 50-mm-long rectangular blanks with 15 × 15-mm cross section and an average grain size of 1 mm, which were subjected to 12-pass ECAP in two regimes with and without counterpressure (250 MPa). The average grain size in the UFG copper upon ECAP was about 300 nm. The samples processed with coun- terpressure exhibited a tendency to further reduction in the grain size. The indicated number of passes was selected because (i) a greater number of passes did not significantly change the properties of samplers and (ii) the value of porosity was sufficient for its reliable determination [6]. The parameters of nanopores were estimated using a modified small-angle X-ray scattering (SAXS) tech- nique (using Kratky’s block-collimated MoK α radia- tion) and high-precision density measurements [5, 6]. The mechanical properties were measured at 300 K by uniaxial extension at a constant strain rate of 2.2 × 10 4 s –1 on a hard-strain tensile-testing machine using dumb-bell samples with working part dimensions of 17 × 2.5 × 1.7 mm. Nondeformed parts of the samples (in the region of clamps) were polished and used to measure the microhardness at 300 K by indentation at a 200-g load. Then, the curves of SAXS intensity versus the scat- tering angle for the copper samples processed by ECAP with and without counterpressure are presented in the figure. In the given angular interval, differences between the SAXS curves for two types of samples were at a maximum. As can be seen, the SAXS intensity is significantly smaller for the sample processed with counterpressure [cf. figure caption]. The results of data processing according to Guinier and Fornet [10] showed that, in both cases, the sizes of scattering non- uniformities were close and amounted to ~40 nm (with allowance for equiaxial shapes). At the same time, the volume fractions of these nonuniformities (with allowance for their porosity-related nature) were significantly different and amounted to ~1 and ~2% for the samples processed by ECAP with and without counterpressure, respectively. It should be noted that, in addition to scattering in the indicated interval, there Effect of Counterpressure during Equal-Channel Angular Pressing on Nanoporosity Formation in Ultrafine-Grained Copper V. I. Betekhtin*, E. D. Tabachnikova, A. G. Kadomtsev, M. V. Narykova, and R. Lapovok Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 61103 Kharkiv, Ukraine Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia *e-mail: Vladimir.Betekhtin@mail.ioffe.ru Received April 17, 2011 Abstract—Results of small-angle X-ray scattering and high-precision density measurements showed that the application of counterpressure during the equal-channel angular pressing (ECAP) of ultrafine-grained cop- per leads to a decrease in nanoporosity and an increase in mechanical properties of the ECAP-processed metal. DOI: 10.1134/S1063785011080189