An artificially aged Al-Zn-Mg alloy with a grain size of similar to 1.3 pm was processed by equal-channel angular pressing (ECAP) and then subjected to dynamic compression at a strain rate of 4000 s(-1) in the range from room temperature to 673 K. The results show the eta' phase is refined and a eta phase is formed during the first pass of ECAP and after further processing 8 passes the GP zones are removed. An ultrafine-grained (UFG) structure with an average grain size of similar to 200 nm was obtained after 4 passes. It is shown that dynamic compressive deformation assists the precipitation process through precipitate coalescence and by changing the precipitate orientations. The dynamic compressive yield strengths and flow stresses decrease gradually to different degrees with increasing temperature except after ECAP processing for 4 passes where there is thermal stability up to 473 K. The ECAP processing significantly improves the strength of the alloy at elevated temperatures by comparison with the as-received material.

In order to investigate the early fracture of ultrafine-grained (UFG) pure copper with a partially recrystallized microstructure and simple shear texture, the evolution of surface strain was measured using in situ micro-tension with digital image correlation. The spatial distribution of voids in tensile specimens was revealed after testing using synchrotron radiation X-ray tomography. The results show that the shear fracture behavior is associated with void evolution in UFG copper and this is strongly affected by the simple shear texture produced by equal channel angular pressing (ECAP). The results have important implications for use in micro-forming. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A Ti-6Al-4V alloy was used to examine the effect of martensitic (alpha) or lamellar (alpha + beta) microstructures on grain refinement and the hcp to fcc phase transformation during HPT processing. There was significant grain refinement with grain sizes of similar to 30 and similar to 40 nm in the alpha' and alpha + beta microstructures, respectively, and with the occurrence of an allotropic hcp to fcc phase transformation in the alpha' sample after HPT. A high volume fraction of boundaries, together with a substructure containing initial defects of the martensitic sample, promotes the formation of the fcc phase during the HPT processing.

An extruded ZIC60 magnesium alloy was processed by high-pressure torsion (HPT) at room temperature for up to 5 turns under a constant compressive pressure of 2.0 GPa with a rotation speed of 1 rpm. This processing produced an average grain size of similar to 700 nm. The grain size distributions and textures were examined by electron backscatter diffraction (EBSD) and this revealed some multi-modality in the microstructure at different stages of straining with fractions of both coarse grains and ultrafine grains. EBSD analysis at the mid-radius positions of unprocessed and HPT-processed materials revealed a gradual evolution from a prismatic {10 (1) over bar0} fiber to an ultimate basal {0001} fiber texture with the c-axis parallel to the normal direction. The majority of grain boundaries had misorientations larger than 15 throughout the processing. The strain hardening tended towards a reasonable hardness homogeneity with a hardenability exponent, eta, of 0.07 up to strains of 20 and with a subsequent hardness saturation at Hv approximate to 125. (C) 2017 Elsevier B.V. All rights reserved.

Differential scanning calorimetry (DSC) was used to study the thermal stability of the microstructure and the phase composition in nanocrystalline 316L stainless steel processed by high-pressure torsion (HPT) for 1/4 and 10 turns. The DSC thermograms showed two characteristic peaks which were investigated by examining the dislocation densities, grain sizes and phase compositions after annealing at different temperatures. The first DSC peak was exothermic and was related to recovery of the dislocation structure without changing the phase composition and grain size. The activation energies for recovery after processing by 1/4 and 10 turns were similar to 163 and similar to 106 kJ/mol., respectively, suggesting control by diffusion along grain boundaries and dislocations. The second DSC peak was endothermic and was caused by a reverse transformation of alpha'-martensite to gamma-austenite. The hardness of annealed samples was determined primarily by the grain size and followed the Hall-Petch relationship. Nanocrystalline 316L steel processed by HPT exhibited good thermal stability with a grain size of similar to 200 nm after annealing at 1000 K and a very high hardness of similar to 4900 MPa.

An investigation was conducted to examine the effect of molybdenum (Mo) content on the grain size, lattice defect structure and hardness of nickel (Ni) processed by severe plastic deformation (SPD). The SPD processing was applied to Ni samples with low (similar to 0.3 at%) and high (similar to 5 at%) Mo concentrations by a consecutive application of cryorolling and high-pressure torsion (HPT). The grain size and the dislocation density were determined by scanning electron microscopy and X-ray line profile analysis, respectively. In addition, the hardness values in the centers, half-radius and peripheries of the HPT-processed disks were determined after 1/2, 5 and 20 turns. The results show the higher Mo content yields a dislocation density about two times larger and a grain size about 30% smaller. The smallest value of the grain size was similar to 125 nm and the highest measured dislocation density was -60x10(14) m(-2) for Ni-5% Mo. For the higher Mo concentration, the dislocation arrangement parameter was larger indicating a less clustered dislocation structure due to the hindering effect of Mo on the rearrangement of dislocations into low energy configurations. The results show there is a good correlation between the dislocation density and the yield strength using the Taylor equation. The a parameter in this equation is slightly lower for the higher Mo concentration in accordance with the less clustered dislocation structure.