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We investigated the tensile properties of gradient nanograined Cu and CuAl samples prepared by plastic deformation. Tensile tests showed that the gradient nanograined Cu-4.5Al sample exhibits a uniform elongation of ~22% without any cracks, while the uniform elongation of the gradient nanograined Cu sample is only ~18%. Numerous mechanical twinning retards the softening of the nanograins and accommodates a high tensile ductility in the gradient nanograined Cu-4.5Al sample. This work indicates that mechanical twinning is a potential deformation mechanism to achieve high tensile ductility of nanograined materials.

Fatigue behaviors of two Cu samples with different volume fractions of gradient nanograined (GNG) surface layer, prepared by surface mechanical grinding treatment, are investigated under stress-controlled high-cycle fatigue tests. With increasing the volume fraction of GNG layer from 4.3% to 13%, the fatigue endurance limit (at 107 cycles) of GNG Cu is enhanced from 88 to 98 MPa, much higher than that of coarse grained counterpart. Large volume fraction of GNG layer effectively postpones the extension of abnormal grain coarsening from a deeper subsurface layer to the topmost surface and thereby retards the initiation of surface fatigue crack.

We investigated the low-cycle fatigue behavior of a novel nanotwinned 316L stainless steel consisting of nanotwinned austenitic grains embedded in the matrix with characteristic dislocation arrangements. We excitingly found that the α\prime-martensitic transformation is activated traversing twin lamellae to undertake the localized deformation of nanotwinned grains at high strain amplitudes. These α\prime-martensite nuclei are mainly originated from the intersections between “zigzag” slip bands and twin lamellae. Thanks to the effective release of stress/strain localization by the α\prime-martensitic transformation within nanotwins, the fatigue strength and fatigue life in the low-cycle regime are simultaneously enhanced.

The residual stress significantly influences the cyclic stress response of the hierarchical nanostructured materials. An obvious tension-compression asymmetry with minimum stress in compression larger than maximum stress in tension was observed in gradient nanograined (GNG) Cu under strain-controlled high-cycle fatigue tests, which gradually diminished with increasing cycles or after being annealed at a low temperature. The observed asymmetric response is primarily induced by the presence of the residual compressive stress in the GNG surface layer. The longer fatigue life can be achieved in GNG Cu with a higher residual stress, compared to that of annealed GNG Cu. Obvious tension-compression asymmetry was observed in cyclically deformed gradient nanograined Cu under strain control, caused by the residual compressive stress in the GNG surface layer.

Both nanotwinned and nanograined samples were prepared in a CuAl alloy by means of plastic deformation. Tensile tests showed that the nanotwinned sample exhibits a high yield strength of ~357 MPa and a considerable uniform elongation of 18% while the nanograined sample has ultra-high strength of ~758 MPa with a very limited uniform elongation of 1.4%. The lower yield strength and higher ductility in the nanotwinned sample were discussed based on its deformation mechanism.

By means of plastic deformation and subsequent annealing of a Fe-Mn alloy, strain-induced ɛ martensite laths transform into austenite nano-scale twins in the form of bundles. This provides a potential approach to prepare bulk nano-twinned materials that are expected to exhibit high strength and good ductility. The transformation mechanism from ɛ martensite laths to austenite nano-scale twins is discussed.

Microstructural evolution of gradient nanograined (GNG) Cu was investigated under strain-controlled cyclic deformation. Mechanically driven abnormal grain coarsening initiated from the ultrafine grained subsurface layer and eventually extended to the nanograined top surface with increasing cycles. Abnormal grain coarsening and the formation of dislocation patterns sustain the cyclic plastic strain and postpone the formation of extrusions/intrusions at the top surface, contributing to the enhancement of overall cyclic properties of GNG Cu.

Nanotwin lamellae orientation effect on tensile properties of nanotwinned grains strengthening stainless steels was investigated. It is found that the nanotwinned grains with twin lamellae oriented roughly parallel to loading direction exhibit the much higher strengthening effect (at least a GPa higher) than the nanotwinned grains containing twin lamellae inclined to loading direction, which is related to the anisotropic strengthening mechanisms of nanotwins.

The fatigue damage behavior of a novel nanotwinned stainless steel consisting of nanotwinned austenitic grains, nanograins and dislocation structures was investigated. It is found that the nanotwinned grains can effectively suppress the generation of persistent-slip-bands-like shear bands and nucleation of fatigue cracks in comparison with the other two deformed regions. Such better fatigue damage resistance of nanotwinned grains is mainly ascribed to the higher microstructural stability of them without obviously structural coarsening.

A bulk solid solution Cu-5Ag alloy consisting of nanotwins and nanograins was prepared by means of dynamic plastic deformation at liquid nitrogen temperature. Continuous precipitation of Ag occurs in the nanotwins which exhibit higher thermal stability than the nano-grains upon annealing. A tensile strength of 870 MPa and an electrical conductivity of 78% International Annealed Copper Standard are achieved in the annealed nanostructure Cu-5Ag alloy which is strengthened with nanotwins and nanoscale precipitates.

Introducing high density of nanotwins (NT) into metals is regarded an effective strategy to achieve superior mechanical properties. Our study shows that heterogeneous structured 304 austenitic stainless steel comprising of NT and micrometer-sized grains with a lower strength exhibits a comparable fatigue strength and larger fatigue limit/strength ratio, compared to its counterpart comprising of grains with NT and dislocation structures, distinct from the traditional fatigue view. Such superior high-cycle fatigue resistance arises from a weakened strain-localized fatigue mechanism where some NT grains co-deform plastically with a large volume fraction of surrounding microsized grains with enhanced dislocation slipping and martensitic transformation.

A randomly oriented copper embedded with nanotwin bundles was prepared by means of dynamic plastic deformation at cryogenic temperature. The subsequent cold rolling at room temperature induced shearing of nanotwin bundles, and resulted in a lamella structure after 90% thickness reduction. The volume fraction of copper-type rolling texture of the rolled nanotwinned copper is about 24.9±4.9 vol%, much less than the rolled coarse-grained (~76 vol%) and ultrafine grained ones. Detailed microstructure and texture characterizations show that the weaker texture is attributed to the evolution of nanotwin bundles retarding the formation of texture during cold rolling.

The plastic co-deformation behavior at the homophase interfaces between the hard nanotwinned grain inclusions and the soft recrystallized matrix grains in a duplex-microstructured AISI 316L austenitic stainless steel is examined through the analysis of long-range orientation gradients within the matrix grains by electron backscatter diffraction and transmission electron microcopy. Our analysis reveals that the mechanical accommodation of homophase interfaces until a macroscopic strain of 22% is realized within a small area of soft grains (about four grains) adjacent to the homophase interface. The activation of deformation twinning in the first two grain layers results in the occurrence of a ‘hump’ in the orientation gradient profile. We ascribe this effect to the role of deformation twinning on the generation of geometrically necessary dislocations. The smooth profile of the orientation gradient amplitude within the first 10 grain layers indicates a gradual plastic accommodation of the homophase interfaces upon straining. As a consequence, damage nucleation at such interfaces is impeded, resulting in an enhanced ductility of the single phase duplex-microstructured steel.

The work hardening behavior of nanotwinned austenitic grains in a novel type of nanotwinned austenitic stainless steels was investigated. Multiple Shockley partial dislocation activities in the nanotwinned grains could trigger occurrence of stacking faults and strain induced martensitic transformation before necking, resulting in an increase in work hardening rate. Consequently, the fully recovered nanotwinned austenitic stainless steel exhibits a uniform elongation of ~ 13% at the strength of 950 MPa.

Nano-twinned austenite grains were characterized in an austenitic stainless steel by using nanoindentation. The nano-twinned austenite grains exhibit identical elastic modulus with the micro-sized recrystallized austenitic grains. Nanoindentation hardness of the nano-twinned grains is about 4.5 GPa, ∼1.0 GPa higher than that of the recrystallized grains, but lower than that of the nano-sized grains with the comparable size owing to the presence of twinning partial dislocations.

A novel type of nanotwinned austenitic stainless steel consisting of the nanotwinned grains embedded in coarsened nano-sized grains and recrystallized matrix was synthesized. Potentiodynamic polarization measurements indicate that the nanotwinned samples exhibit a higher passive ability in the acidic solution and a comparable pitting resistance in chloride solution in comparison with that of their coarse grained counterparts. The effects of the microstructure, specifically the presence of nanotwinned grains, on the corrosion resistance are discussed. The nanotwinned austenitic stainless steel possesses an excellent combination of strength and ductility as well as corrosion resistance.

Two types of austenitic stainless steel samples were prepared by means of dynamic plastic deformation followed by annealing: nanotwinned austenitic grains embedded in recrystallized austenite matrix and martensitic/austenitic duplex microstructures. Annealing at 923 K induced martensitic reversion while most nanotwinned grains are stable. An enhanced strength–ductility combination is observed in the annealed nanotwinned samples which exhibit a uniform elongation of ~21% and a yield strength of ~900 MPa, in contrast to a uniform elongation of ~12% with comparable strength in the martensitic/austenitic samples.

A bulk nanostructured CuCrZr alloy consisting of nanotwins and nanograins was prepared by dynamic plastic deformation at liquid nitrogen temperature. A tensile strength of 700 MPa and an electrical conductivity of 78.5% International Annealed Copper Standard are obtained in the nanostructured CuCrZr alloys processed by means of this one-step deformation without aging treatment. The reason for the increased strength without the sacrifice of its high electrical conductivity was discussed.

The microstructure, hardness and tensile properties of a modified 9Cr−1Mo steel processed by dynamic plastic deformation (DPD) to different strains (0.5 and 2.3) have been investigated in the as-deformed and annealed conditions. It is found that significant structural refinement and a high level of strength can be achieved by DPD to a strain of 2.3, and that the microstructure at this strain contains a large fraction of high angle boundaries. The ductility of the DPD processed steel is however low. Considerable structural coarsening of the deformed microstructure without pronounced recrystallization takes place during annealing of the low-strain and high-strain samples for 1 h at 650 °C and 600 °C, respectively. Both coarsening and partial recrystallization occur in the high-strain sample during annealing at 650 °C for 1 h. For this sample, it is found that whereas coarsening alone results in a loss of strength with only a small gain in ductility, coarsening combined with pronounced partial recrystallization enables a combination of appreciably increased ductility and comparatively high strength.

The passive behavior of a bulk nanostructured 316L austenitic stainless steel consisting of nanometer-sized grains (NG) and nano-twin bundles (NT) are investigated. The electrochemical results indicate that the spontaneous passivation ability and growth rate of passive film are improved. The X-ray photoelectron spectroscopy (XPS) shows that a Cr 0 -enriched layer forms at the passive film/metal interface. More nucleation sites afforded by the nanostructures and the enhanced diffusion rate of charged species across the passive film are believed to be responsible for the improved passive ability. The PDM model is introduced to elaborate the microscopic process of passivation.

With surface mechanical grinding treatment, a gradient nanograined (GNG) surface layer is produced on a bulk coarse-grained (CG) pure Cu, where the grain size increases gradually from 20 nm (topmost surface) to micrometer scale. Microhardness measurements of the GNG/CG sample after tension revealed that tension induces softening for grains smaller than 165 nm and induces hardening above this size. This critical size agrees with the strain-induced saturation grain size of Cu subjected to severe plastic deformation.

The deformation behaviour of ultrafine-grained hexagonal close-packed Ti processed by dynamic plastic deformation was investigated using electron microscopy techniques. Results show that the deformation twinning propensity in ultrafine-grained Ti decreases monotonously while the number of dislocations having the component increases with decreasing grain size, indicating that the transformation of the deformation mechanism from twinning to slip occurs and that the twinning mechanism does not change within the observed grain size range. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Cyclic deformation was studied in Cu samples with a gradient nanograined (GNG) surface layer. Compared with the coarse-grained sample, the Cu samples with a GNG surface layer exhibit a greatly enhanced fatigue limit under stress-controlled cyclic deformation. The cyclic deformation induced an abnormal grain coarsening that initiated from the subsurface layer and grew along 45° to the stress axis toward the top surface layer, where the fatigue cracks were formed.

The scanning electron microscopy transmission Kikuchi diffraction technique was used to characterize the microstructure of ultrafine-grained Ti processed by dynamic plastic deformation at room temperature. Contrary to the general conception that twinning plays little role in the plastic deformation of ultrafine-grained hexagonal close-packed Ti, nanocrystalline { 1 1 2 ¯ 2 } and { 1 0 1 ¯ 2 } deformation twins were widely observed in the material. The observation provides insight into the deformation mechanisms and mechanical behaviour of nanostructured metals with hexagonal close-packed structures.

A surface layer with a gradient decrease in twin density has been produced in a Fe–Mn austenitic steel, which corresponds to a gradient drop in hardness from 5.3 GPa in the top surface to 2.2 GPa in the coarse grained core. The dependence of hardness on the twin thickness was determined, showing a weaker strengthening effect of twin boundaries than that of conventional grain boundaries in this alloy. Superior strength–ductility synergy was observed in tensile tests of the gradient nanotwinned layer.

A novel strategy for strengthening austenite steels is introduced by using the unique strengthening effect of nanoscale twins. Austenite grains containing multiple nanoscale twins can be strengthened to a yield strength of a few GPa with very high work-hardening rates. Compared with the conventional dual-phase steels, several austenite steels strengthened by using ultra-strong nanotwinned austenite grains exhibit a superior strength–ductility synergy. Perspectives on future development of the nanotwinned austenite steels and the nanotwin strengthening strategy are presented.

Bulk dynamic plastic deformation (DPD) materials comprise a composite structure of nanoscale twin bundles and nanoscale grains. The tribological properties of DPD-processed pure nano-Cu have been investigated in this study and compared with conventional coarse-grained (CG) Cu under both monotonic and repeated frictional sliding. We demonstrate that DPD nano-Cu and CG Cu exhibit steady-state mechanical characteristics after repeated frictional sliding that are similar to those seen in nanotwinned (NT) Cu produced by pulsed electrodeposition. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The tensile properties of mixed structures with microsized recrystallized grains and nanotwin bundles in a Cu-Zn alloy prepared using dynamic plastic deformation (DPD) and subsequent thermal annealing were investigated. A better strength-ductility combination was found in the partially recrystallized samples of the mixed structures with finer recrystallized grains and thinner nanotwins. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The microstructures and mechanical properties of a Cu-Zn alloy subjected to dynamic plastic deformation (DPD) at liquid nitrogen temperature (77 K) were investigated. The planar dislocation activities, deformation twinning and shear banding dominate the plastic deformation of samples with different strains, respectively. Twin boundary spacing decreases with strain and nearly saturates when the strain exceeds 1.2. Shear bands occur within high-density twin region at higher strains, inside which nano-sized grains are formed. Tensile tests show that the DPD brass exhibits a high strength and a limited tensile ductility. Deformation twins play an important role in the strengthening while the appearance of shear bands obviously reduces the ductility of materials. (C) 2009 Elsevier B.V. All rights reserved.

Multiple deformation twinning occurs in deformed metals and alloys under suitable conditions, resulting in the formation of twin/matrix (T/M) lamellar structures which act as precursors for strain-induced structural refinement on the nanometer scale. Four possible mechanisms for nanoscale structural refinement via T/M lamellae in various face-centered cubic metals are identified, including fragmentation of T/M lamellae, formation of secondary twins, twin–twin intersection and shear banding. The effects of processing conditions and material parameters on nanoscale twinning are analyzed.

We report an enhanced fracture toughness of bulk Cu sample processed by dynamic plastic deformation with a composite microstructure of nanoscale grains and embedded nanoscale twin bundles. The improvement in fracture toughness is mainly due to the embedded twin bundles which generate elongated deep fracture dimples that consume much higher fracture energy.

The effects of strain, strain rate and temperature on deformation twinning in a Cu-Zn alloy were systematically investigated by means of transmission electron microscopy. With increasing strain, the average twin layer thickness (lambda) decreased slightly while the average twin boundary spacing (Delta) decreased significantly; both saturated at the same value when strain exceeds 1.2. Variations of lambda. with strain rate and temperature were analyzed by using the Zener-Hollomon parameter, Z, and it was found that a larger Z leads to a smaller lambda. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

[Li, W. L.; Tao, N. R.; Lu, K.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Liaoning, Peoples R China.;Tao, NR (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Liaoning, Peoples R China;nrtao@imr.ac.cn

[Li, Y. S.; Zhang, Y.; Tao, N. R.; Lu, K.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Tao, NR (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;nrtao@imr.ac.cn

Based on strain-induced grain refinement, a novel surface mechanical attrition treatment (SMAT) technique has been developed to synthesize a nanostructured surface layer on metallic materials in order to upgrade their overall properties and performance without changing their chemical compositions. In recent several years, the microstructures and properties of surface layer were systematically investigated in various SMAT metals and alloys, including b.c.c., f.c.c. and h.c.p. crystal structures. Different grain refinement approaches and nanocrystalline formation mechanisms were identified in these deformed materials, involving dislocation activities, mechanical twinning and interaction of dislocations with mechanical twins. The properties of the surface layer were measured by means of hardness, tensile, fatigue and wear tests. The enhanced properties of the surface layer are mainly attributed to the strain-induced grain refinement. In this work, we reviewed the microstructures and properties of surface layer in the SMAT materials.

A nanostructured surface layer was formed on a pure iron plate by means of surface mechanical attrition treatment (SMAT). It was found that a SMAT iron sample developed a nitrided layer twice as thick as that on a coarse-grained sample under the same gaseous nitriding conditions (500 °C for 2 h), which is attributed to the fast diffusion of nitrogen along grain boundaries in the nanostructured iron. The nitrided layer of SMAT sample exhibited a high hardness and an excellent wear resistance.

A nanostructured surface layer on a pure iron sample was prepared by surface mechanical attrition treatment (SMAT). The thermal stability of SMAT sample was investigated at different temperatures with or without a high magnetic field (H =12T). It was found that a high magnetically annealing enhanced grain growth at the early stage of annealing, and produced a uniform nanocrystalline grain structure. After homogeneous grains developed, further grain growth became restrained.

The effect of dynamic plastic deformation on the microstructure of a modified 9Cr - 1Mo steel has been investigated in comparison with the effect of quasi- static compression. It is found that the boundary spacing after dynamic plastic deformation is smaller and the hardness is higher than those after quasi- static compression. The microstructure after dynamic plastic deformation is however less stable than the microstructure after quasi- static compression. Annealing at 675 and 700 degrees C leads to structural coarsening and recrystallisation in each sample, but with recrystallisation occurring faster in the sample annealed after dynamic plastic deformation. The lower thermal stability of the microstructure produced by dynamic plastic deformation is attributed to a higher driving force for recrystallisation in the dynamically deformed material.

The microstructure evolution and deformation behavior of an as-cast Al–7Mg alloy with severe Mg segregation zones distributed on grain boundaries and in interdendrite regions subjected to dynamic plastic deformation (DPD) at both room and liquid nitrogen temperatures have been studied. At low strains, the deformation of the material is found to be mainly through the formation of deformation bands. At high strains, globular ultrafine grains form in the materials due to continuous dynamic recrystallization, which is also the dominant grain refinement mechanism. After deformation to strain of 1.0, the Mg segregation zones are deformed into fine parallel bands distributing along the deformation bands. Moreover, it is revealed that Al8Mg5 particles and the Mg segregation can enhance the formation of deformation bands even in grains with a stable orientation, namely those with one of the {101} planes perpendicular to the compression direction, which can reduce the inhomogeneity of the deformation structure. © 2015. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

By means of surface mechanical attrition treatment (SMAT), nanostructured (NS) surface layers were fabricated on a pure iron plate and a low carbon steel plate. Cr diffusion behaviors in the NS Fe phase and the SMAT low carbon steel were investigated. Experimental results showed the activation energy of Cr diffusion in the NS Fe is comparable to that of the GB diffusion, but the pre-exponential factor is much higher. A much thicker Cr-diffusion surface layer was obtained in the SMAT low carbon steel plate than in the coarse-grained one after the same chromizing treatment. The much enhanced diffusivities of Cr in the SMAT samples can be attributed to numerous GBs and triple junctions with a high excess stored energy in the NS surface layer.

Flaw-free bulk Cu specimens with a high density of nano-scale mechanical twins were produced by means of dynamic plastic deformation at liquid nitrogen temperature. The nano-twinned Cu exhibits a tensile yield strength of 600 MPa and an elongation-to-failure of 11%. The significant strengthening originates from the effective blockage of glide dislocations by numerous twin boundaries and dislocations.

The deformation microstructure of face-centered cubic cobalt subjected to surface mechanical attrition treatment was studied as a function of strain levels. Strain-induced gamma --> epsilon transformation and twinning deformation were evidenced by transmission electron microscopy and were found to progress continuously in ultrafine and nanocrystalline grains as the strain increased. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A nanostructured surface layer was formed on an Inconel 600 plate by subjecting it to surface mechanical attrition treatment at room temperature. Transmission electron microscopy and high-resolution transmission electron microscopy of the treated surface layer were carried out to reveal the underlying grain refinement mechanism. Experimental observations showed that the strain-induced nanocrystallization in the current sample occurred via formation of mechanical microtwins and subsequent interaction of the microtwins with dislocations in the surface layer. The development of high-density dislocation arrays inside the twin-matrix lamellae provides precursors for grain boundaries that subdivide the nanometer-thick lamellae into equiaxed, nanometer-sized grains with random orientations.

The formation kinetics of e-Fe3–2N phase in a nanocrystalline α-Fe, which was processed by surface mechanical attrition treatment, is found to be obviously increased with respect to that in the coarse-grained form. This can be attributed to the much enhanced heterogeneous nucleation rate at numerous grain boundaries in the nanocrystalline α-Fe.

A nanocrystalline (nc) surface layer of about 10 μm thick was fabricated on a low carbon steel plate by means of surface mechanical attrition treatment. The grain size is about 15 nm in the top surface layer, and it increases with an increase of depth from the treated surface. Nanoindentation measurements indicated that hardness is enhanced in the nc surface layer relative to the matrix. Experiments show that the friction coefficient decreases and the wear resistance increases with the nc surface layer. The improvement in friction and wear properties may be attributed to the harder nc surface layer which reduces the degree of plowing and micro-cutting under the lower load and the degree of plastic removal and surface fatigue fracture under the higher load, respectively.

Surface mechanical attrition treatment (SMAT) technique was developed to synthesize a nanostructured surface layer on metallic materials for upgrading their overall properties and performance. In this paper, the grain refinement process during SMAT was investigated in materials with low stacking fault energies (SFE, Inconel 600 alloy and AISI 304 stainless steel) by means of transmission electron microscopy and high-resolution electron microscopy, respectively. Grain subdivision was performed by the interaction of mechanical microtwins with dislocations in Inconel 600. For AISI 304 stainless steel with a lower SFE, twin-twin intersections subdivide initial grains into refined blocks with sizes ranging from nanometers to submicrometers. Such grain subdivision processes of the interaction of microtwins with dislocations or microtwins obviously differ from those observed in the high SFE materials in which dislocation interactions predominate the grain refinement.

[Zhang, Y.; Tao, N. R.; Lu, K.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Lu, K (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;lu@imr.ac.cn

A nanocrystalline surface layer was fabricated on a pure Fe plate by using an ultrasonic shot peening (USSP) technique. The USSP induced surface nanocrystallization products were characterized by means of X-ray diffraction (XRD) and transmission electron microscope (TEM). Experimental evidences showed that after USSP treatments, the initial coarse-grained structure in the surface layer was refined into equiaxed ultrafine grains (about 10nm) with random crystallographic orientations. The grain refinement mechanism during USSP treatments is discussed.

The microstructure, texture and mechanical properties have been studied in PM2000 compressed via dynamic plastic deformation to a strain of 2.1. It is found that dynamic plastic deformation results in a duplex 〈111〉 + 〈100〉 fibre texture and refines the initial microstructure by nanoscale lamellae, which substantially increases the strength of the material, but decreases its thermal stability. In the as-deformed microstructure, the stored energy density is found to be higher in 〈111〉-oriented regions than in 〈100〉-oriented regions. Recovery during annealing at 715 °C reduces the energy stored in the deformed microstructure. This reduction is more pronounced in the 〈111〉-oriented regions. Orientation-dependent recrystallisation takes place in the recovered microstructure, leading to strengthening of the 〈111〉 fibre texture component at the expense of the 〈100〉 fibre texture component.