**Wolfgang Blum 1,\*, Jiˇri Dvoˇrák 2, Petr Král 2, Philip Eisenlohr <sup>3</sup> and Vaclav Skleniˇcka <sup>2</sup>**


Received: 24 September 2019; Accepted: 21 October 2019; Published: 26 October 2019

**Abstract:** During quasi-stationary tensile deformation of ultrafine-grained Cu-0.2 mass%Zr at 673 K and a deformation rate of about 10−<sup>4</sup> s−<sup>1</sup> load changes were performed. Reductions of relative load by more than about 25% initiate anelastic back flow. Subsequently, the creep rate turns positive again and goes through a relative maximum. This is interpreted by a strain rate component ˙ − associated with dynamic recovery of dislocations. Back extrapolation indicates that ˙ − contributes the same fraction of (20 ± 10)% to the quasi-stationary strain rate that has been reported for coarse-grained materials with high fraction of low-angle boundaries; this suggests that dynamic recovery of dislocations is generally mediated by boundaries. The influence of anelastic back flow on ˙ − is discussed. Comparison of ˙ − to the quasi-stationary rate points to enhancement of dynamic recovery by internal stresses. Subtraction of ˙ − from the total rate yields the rate component ˙ <sup>+</sup> related with generation and storage of dislocations; its activation volume is in the order expected from the classical theory of thermal glide.

**Keywords:** Cu–Zr; ECAP; ultrafine-grained material; deformation; dynamic recovery; transient; load change tests
