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In this paper, various gradient structures (i.e., the ferrite grain size increases continuously with the depth) with different grain size distributions are produced in low-carbon steel by using pre-torsion deformation and thermal annealing at ~ 550 °C to 700 °C for 0.5 h. Results indicate that the grain size distribution possesses a crucial influence on mechanical properties of gradient-structured samples. The yield strength decreases steady accompanied by a gradual increase in uniform ductility and static toughness with increasing the ferrite grain size. The optimal synergy of high yield strength (σy~ 506.0 ± 3.9 MPa), promising uniform ductility (eu~ 9.6 ± 0.5%) and static toughness (Ur~ 108.8 ± 4.1 MJ/m3) is achieved by a specific gradient structure with the grain size distribution from ~ 7.2 µm at the surface to ~ 16.5 µm at the core, which is much better than that (σy~ 318.2 ± 1.6 MPa, eu~ 13.4 ± 0.4% and Ur~ 102.5 ± 4.8 MJ/m3) of its coarse-grained (CG) counterpart. Related strengthening and toughening mechanisms are also discussed.

Generally, the improvement in the strength comes at the cost of the ductility and toughness for most metallic materials. Here, an exceptional synergy of high strength (σy ~ 453.8 MPa), ductility (ef ~ 24.5%) and static toughness (Ur ~ 115.0 MJ/m3) is achieved in a low-carbon steel subjected to torsion deformation and annealing treatments, compared with that (σy ~ 282.4 MPa, ef ~ 27.3% and Ur ~ 102.9 MJ/m3) of its coarse-grained counterpart. The enhancement of mechanical properties is attributed to the formation of a specific gradient structure with a thickness of ~ 3 mm, that is, the ferrite size increases while the volume fraction of the pearlite decreases continuously with the depth from the sample surface to the core. The strengthening and toughening mechanisms of the gradient-structured low-carbon steel are also discussed.

We report that a gradient structured Zr processed by asymmetric rolling and partial annealing possesses an exceptional synergy of high strength (σy ∼ 550 MPa) and high tensile ductility (eu ∼ 10.1%) much better than that (σy ∼ 250 MPa and eu ∼ 14.2%) of its coarse-grained (CG) counterpart. This gradient structure is characterized by a gradient dislocation density distribution from the surface to the core and composed of microscale and ultra-fined elongated grains connected by low angle grain boundaries (LAGBs). These findings can provide valuable insight for designing gradient structures with excellent mechanical properties.

In the present paper, the microstructures and mechanical properties of a low-carbon steel processed by graded pre-torsion (PTO) and homogeneous pre-tension (PTE), respectively, have been investigat...

In this paper, the mechanical properties and fracture mechanisms of coarse-grained (CG) commercial-purity Ti subjected to both tensile and torsion deformations are investigated. During tensile deformation, CG Ti exhibits general excellent extendibility and ductile fracture. However, CG Ti presents absolutely brittle fracture during torsion deformation, despite its high torsion deformability. This is attributed to the specific fracture mechanism in torsion that the microcracks nucleate at the surface layer and propagate from the surface to the interior of torsion sample, which is contrast to the typical microcrack nucleation and propagation behaviors of ductile metals in tension. This study has an important significance for the design and application of metals carrying torsional load.

Gradient structures (GS) with various grain size distributions are successfully architectured in a commercial low-alloying steel by using the pre-torsion and thermal annealing routes, and the corresponding mechanical properties and hetero-deformation induced (HDI) strengthening and work-hardening are investigated. Results demonstrate that an optimal grain size distribution from ~5.0 ± 2.8 μm at the surface to 11.1 ± 4.5 μm at the center leads to the maximum HDI strengthening of ~325 MPa. The HDI work-hardening intensifies continuously with the decreased average grain size of the GS due to the formation of abundant geometrical necessary dislocations (GNDs) whose density decreases abnormally from the fine-grain surface to the coarse-grain core caused mainly by the interactions between the short-range GNDs and long-range GNDs. Thanks to the HDI strengthening and work-hardening, the yield strength increases with a reduction of uniform ductility approximately following the linear inverse rule, in stark contrast to the banana-shaped strength-ductility trade-off of monolithic materials, and an exceptional strength-ductility synergy is achieved.

Ideal metallic biomaterials for use in implants are required to meet the mechanical compatibility, i.e., low Young's modulus combined with high mechanical strength, however, these constraints are generally contradictory. Here, an exceptional combination of ultralow Youngʹs modulus of E ~45 GPa, ultrahigh tensile strength of σ b ~1185 MPa and ultrahigh elastic admissible strain of δ ~2.2% is achieved in a new high Zr-containing Ti-based alloy (Ti-50Zr-5Al-4V (wt%)), which is subjected to solution treatment and cold rolling. The ultralow Youngʹs modulus is attributed to a mixture of bcc β and orthorhombic α″ phases while the ultrahigh strength results from the solution strengthening and work hardening. This study can be of significance for developing excellent removable implant materials.

Microstructure and tensile properties of a new α/β Ti–47Zr–5Al–3V (wt%) alloy are investigated in the present study. Both α/β and β thermal annealing at 650 °C–800 °C for 1 h and subsequent aging at 450 °C for 2 h are introduced to investigate the effect of thermal annealing and aging on the microstructure and tensile properties of the Ti–47Zr–5Al–3V alloy after cold rolling. After thermal annealing, a fully equiaxed microstructure, a bi-modal microstructure and a fully lamellar microstructure are obtained with increasing the annealing temperature (650–800 °C), respectively. The 450 °C/2 h aging leads to further precipitation of extremely fine α platelets from the annealed samples. With increasing the annealing temperature, the tensile strength ( σ b ) of annealed samples increases gradually from ∼1350 to 1420 MPa, whereas the elongation to failure ( e f ) first increases and then decreases and the highest e f ∼10.6% is attained at 750 °C. For all annealed samples, the 450 °C/2 h aging leads to increased strength and decreased ductility and the 750 °C/1 h annealing plus 450 °C/2 h aging results in the best combination of ultrahigh strength ( σ b ∼1510 MPa) and good ductility ( e f ∼9.3%). The ultrahigh strength results from the strengthening of fine secondary α platelets, while the good ductility is attributed to the formation of large primary α p grains and the fine β grain size.

A novel heterogeneous medium Mn steel with a nominal composition of Fe-0.18C-7.8Mn-1.65Al-0.04Ce wt.% is successfully fabricated by introducing various nucleation energy barriers for reverse austenite in a cold-rolled specimen prior to final annealing. The obtained steel demonstrates a ferrite and austenite duplex phase with multiple morphologies (i.e., granular, block-shaped, and lath-like), dispersed grain size, and heterogeneous chemical components. The heterogeneous microstructure yields superior synergy of 1060 MPa yield strength, 1270 MPa tensile strength, and 54.5% total elongation. The tensile behavior and microstructural evolution of the fabricated heterogeneous steel are investigated in detail. The stacking fault and dislocation accumulations are found to dominate during the initial deformation stage, and granular austenite transforms into martensite in the intermediate strain stage. Finally, block-shaped and lath-like austenite undergoes a phase transformation. Moreover, the back stress caused by the heterogeneous microstructures significantly improves the yield strength and work hardening ability of the heterogeneous specimen. Therefore, the combination of successive transformation-induced plasticity (TRIP) effect, dislocation strengthening, and back stress hardening contributes to the outstanding mechanical properties of this steel.

Usually, the improvement of strength of structural materials is at the cost of ductility. Here, a superior synergy of high strength (σy ~ 526.8–582.6 MPa) and ductility (ef ~ 25.5–19.3%) is achieved in the gradient dislocation-structured low-carbon steel subjected to torsion deformation, which is much better than that (σy ~ 317.9 MPa and ef ~ 22.8%) of its coarse-grained counterpart. The enhanced strength is attributed to the back stress, grain refinement and the introduction of numerous dislocations (i.e., work hardening) whose density increases consistently with the radius along from the core to the surface. The high ductility results from the promising work hardening capacity of the gradient dislocation-structure. This study provides a practical route to developing advanced structural materials with enhanced integrated mechanical properties.

An enhanced wear resistance in vacuum has been achieved in a multi-modal-laminated TiZrAlV by using room-temperature rolling combined with subsequent thermal treatment. The sample exhibits a higher wear resistance than the nanostructured counterpart and offers a ~30% wear mass reduction as compared with the coarse-grained counterpart. The high wear resistance can be attributed to the combination of high strength and high ductility provided by the multi-modal-laminated structure. This study demonstrates that multi-modal structure can be adopted to enhance the wear resistance of nanostructured metals and alloys for engineering application. Keywords: Multi-modal structure, Wear resistance, Titanium alloys, Nanostructured materials

The formation of hierarchical structures is an effective way to optimize the mechanical properties of pure metals and simple alloys but not multi-component alloys. In this study, hierarchical structures were introduced into a quaternary TiZrAlV alloy by treating the deformed sample via recrystallization and aging treatment. A combination of high strength (σb = ∼1548 MPa), high ductility (ef = ∼6.6%), and good fracture toughness (KIC = ∼55.1 MPa.m1/2) was achieved in one hierarchically structured sample. The effects of thermal treatment on the microstructure evolution, and tensile and fracture properties of the deformed TiZrAlV were investigated.

Microstructures, thermal stabilities and microstructures and properties evolutions of a new β TiZrAlV alloy have been investigated in this paper. Various hierarchical and multiphase nanolaminated (HMN) structures have been successfully produced in the alloy via appropriate thermomechanical processing treatments. The higher thermal stability (Tp ~ 275 °C), i.e., onset temperature of phase transformation, is achieved in a specific HMN structure consisting of nanoscale acicular isothermal α″ martensites, submicroscale α plates and large microscale primary αp grains, compared with that (Tp ~ 105 °C) of its coarse-laminated counterpart without primary αp grains. For this specific HMN structure, thermal exposures at 300–400 °C lead to further precipitation of isothermal α″ martensites, which enhances evidently the strength and reduces the ductility, while the reverse transformation of α″/α to β and the coarsening of previously formed α plates concur during thermal exposures at 500–600 °C, which leads to dramatically decreased strength and increased ductility. Keywords: Thermal stability, Tensile properties, Hierarchical-laminated structure, Severe plastic deformation, Titanium alloys

The irradiation of high-energy particles always leads to the deterioration of mechanical properties of materials. Here, we report an abnormal proton irradiation-induced optimization of tensile properties, i.e. an obviously enhanced ductility with a slight decrease of strength, of a hierarchical structured TiZrAlV alloy. The optimization of tensile properties can be attributed to the lattice relaxation caused by irradiation, and the suppressed formation of vacancy clusters in the sample.

The irradiation of high-energy particles always leads to the embrittlement of metallic materials. Here, we report an abnormal irradiation toughening phenomenon in a hierarchical structured ZrTi, which results from the irradiation-induced lattice relaxation that yields an enhanced ductility with a slight decrease of strength. Positron annihilation measurements reveal that the lattice relaxation dominantly originates from a recombination of irradiation-induced interstitials (i.e., Ti atoms) with preexisting dislocation-associated vacancies. This study provides an approach to suppress the irradiation-induced brittleness in metallic materials.

High strength and ductility are the prerequisite for structural materials for wide applications. Here, a simultaneous enhancement of both the ductility and strength is reported in a hierarchical and multiphase nanolaminated (HMN) TiZrAlV prepared via thermomechanical processing treatments. An excellent combination of high ultimate tensile strength of σb ~ 1550 MPa and good elongation to failure of ef ~ 8.0% is obtained in an appropriate HMN structure that consists of nanoscale α″ martensites, submicroscale α plates, and large microscale primary αp grains, much better than that (σb ~ 1440 MPa, ef ~ 3.6%) of its coarse-laminated counterpart without primary αp grains. The present study is significant for the enhancement of strength and ductility of engineering materials via the design of hierarchical-laminated structure.

In the present study, microstructure and mechanical properties of a new β-metastable TiZrAlV prepared via thermomechanical processing (TMP) treatments have been studied. An excellent combination of ultimate tensile strength (σb ≈ 1 630 MPa) and ductility (ϵf ≈ 6.6%) has been achieved in the alloy after cold rolling, thermal annealing (665 °C/1 h), and two-step aging (650 °C/0.5 h + 450 °C/2 h). This is attributed to the formation of a refined β microstructure with grain size of ≈10 µm and a multi-modal-laminated structure that consists of large primary ap grains (2 µm, 9.5 vol%) and coarse α precipitates (300 nm, 21 vol%) and fine α platelets (50 nm, 65 vol%). The fine α platelets contribute to high strength while the large primary αp grains and the refined β grain size provide ductility.

Ti alloys that possess a fine fully lamellar structure generally exhibit high strength but limited ductility. In this study, a hierarchical and multiphase nanolaminated structure that consists of large microscale primary α p grains (~1.5 μm), sub-microscale α plates (~200 nm) and nanoscale acicular isothermal (orthorhombic) α″ martensites (~15 nm) is produced in a TiZrAlV alloy with a fine (~12 μm) β grain size through the use of severe plastic deformation (SPD) combined with subsequent recrystallisation annealing and aging treatments. This specific structure results in an excellent combination of tensile properties, e.g., an ultimate tensile strength of σ b ~1545 MPa and an elongation to failure of e f ~7.9%. The present study demonstrates an alternative route for enhancing the mechanical properties of titanium alloys with laminated structures.

A nano/ultrafine lamellar structure with micrometer-sized equiaxed grains has been produced in TiZr-based multicomponent alloys via severe plastic deformation followed by thermal annealing. The dual-morphology hierarchical structured TiZr shows a high ultimate tensile strength σUTS~1500 MPa and a large plastic strain ef~7.2%, demonstrating a good combination of high strength and ductility. The large ductility mostly results from both the nano/ultrafine lamellar structure and coarse grains that contribute to enhanced strain hardening.

In general, strength and fracture toughness are mutually exclusive in most structural materials. Here, we report a simultaneous enhancement of both the strength and fracture toughness in a hierarchical nanolamella-structured TiZrAlV that consists of lamellae with nano- and submicrometer-sized widths together with a few submicrometer- and micrometer-sized grains. The hierarchical nanolamella-structured alloy shows an excellent combination of high yield strength (σs~1438 MPa) and fracture toughness (KIC~57 MPa m1/2) as compared with its coarse-laminated counterpart. The high strength results from a lot of nanoscale lamellae in the alloy, and the enhanced fracture toughness can be attributed to both the coarse α lamellae and grains that have a high strain hardening capability and the complex strain paths caused by a hierarchical nanolaminated structure, which may enhance the resistance to crack growth and change the crack path during fracture processes.

Dual phase ( α + β )-Ti alloys with a fully fine laminated microstructure usually exhibit a high strength but a limited ductility. In the present study, a hierarchical nanolaminated microstructure consisting of lamellae with nano- and submicrometer-sized widths has been produced in a TiZrAlV alloy by employing severe plastic deformation (SPD) combined with subsequent thermal annealing. The hierarchical nanolamella-structured Ti alloy exhibits excellent combinations of tensile properties, e.g., an ultimate tensile strength σ UTS =1600 MPa and an elongation to failure e f =6.5%. The high strength can be attributed to the formation of a lot of nanoscale α lamellae in the alloy, and the enhanced ductility results mainly from both the coarse α lamellae that have a high strain hardening capability and the complex strain paths caused by a hierarchical nanolaminated structure.

Nanocrystalline metals usually exhibit a high strength but a disappointingly low ductility and toughness, which limit their practical utility. Here, we report a high fracture toughness ( K IC ~117 MPa m 1/2 ) in a hierarchical nanostructured Zr that consists of nano-, sub-micrometer- and micrometer-sized grains, which is much larger than that K IC ~78 MPa m 1/2 in coarse-grained Zr. This hierarchical nanostructured Zr shows a good combination of yield strength ( σ s ~550 MPa) and fracture toughness as compared with its coarse-grained counterpart. We expect that these results will have implications in the enhancement of fracture toughness of nanocrystalline materials and in the design of high-performance structural materials.

The elastic anisotropy, mechanical and thermal properties of semi-transition-metal borides with I4/m symmetry have been investigated using the first-principles method. Compared with other TM2B compounds, Cr2B shows the most brittle and largest shear modulus, Young's modulus, Vickers hardness, Debye temperature and minimum thermal conductivity with the relatively higher bulk modulus and fracture toughness. Due to the effect of volume, the slightly difference has been found in the order of D and min between Ta2B and W2B. Except Ti2B, TM2B compounds show weak elastic anisotropy.κmin between Ta2B and W2B. Except Ti2B, TM2B compounds show weak elastic anisotropy.

Grain refinement always leads to a high strength but a low ductility that results from a reduced strain hardening. Here, we report an extraordinary enhancement of strain hardening in fine-grained (FG) Zr with an average grain size of 2–3 μm compared with its coarse-grained (CG) counterpart, which yields a uniform elongation of ~15.5% in the same order as that (~13.2%) of the CG Zr. The unusually enhanced strain hardening in the FG Zr is attributed to the formation of nano-scale defect structures within the fine grains. The present work provides a promising way to enhance the ductility of fine- and ultrafine-grained materials without losing their high strength, and thus is of wide interest.

O DOI: 10.1002/adem.201300153 M M U Extraordinary Toughening by Cryorolling in Zr** N IC A T By Yindong Shi, Ming Li, Defeng Guo, Tengyun Ma, Zhibo Zhang, Xiaohong Li, Guosheng Zhang and Xiangyi Zhang* IO N High strength and good ductility are essential for the extraordinary work toughening behavior is observed in the applications of structural materials. However, the strength and ductility of materials are often mutually exclusive. For example, deformed materials always exhibit a hardening behavior, i.e. enhanced strength accompanied with reduced ductility. This is attributed to the mutual entanglement and blockage of high-density dislocations induced by plastic deformation, which greatly inhibit the motion of dislocations. Thermal annealing is indispensable for enhancing the ductility of deformedmaterials at the expense of their strength. Recently, studies show that dislocations in some special configurations are movable, which prevents localized shear deformation and contributes to the ductility of deformed materials. To tailor dislocation configurations in deformed materials, high-density dislocations induced by plastic deformation are indispensable. This can be achieved by suppressing the dynamical recovery of deformedmaterials using cryogenic deformation that has been successfully employed to study lowtemperature properties of materials, tailor their microstructures and mechanical properties. More recently, our studies demonstrate strain rate has a significant effect on the dislocation configurations of cryorolled Zr, and the dislocations in lamella configurations are movable under high stress and contribute to plastic deformation. Moreover, dislocation dynamics simulations show that in hcp Zr no dislocation junction forms between intersecting screw dislocations at low temperature, which results in a weak forest hardening. These studies hint a work toughening behavior, not hardening behavior, may be observed in the hcp Zr if appropriate dislocation configurations, in which dislocations are moveable under high stress, are yielded through cryogenic deformation. To unambiguously confirm this supposition through experimentally procedure, both room temperature (RT) and cryogenic deformation experiments of metal Zr with increased strain were designed and performed in this study, and an

Thermal annealing is usually employed to enhance the ductility of deformed materials, but always leads to a great loss in strength. In this study, we report an abnormal mechanical annealing behavior, i.e. a significant reduction of dislocation density with increasing compression strain, in the cryorolled Zr treated with high-pressure confinement deformation. A good combination of high strength and ductility has been achieved in the mechanically annealed sample. This unusual mechanical annealing behavior results from the motion of preexisting high-density dislocations in the cryorolled Zr under high stress. The high ductility of the mechanically annealed sample is attributed to the restoration of work hardening capability and grain boundary related deformations, while the high strength is due to the formation of nano-scale subgrains and grains in the sample. The observed mechanical annealing phenomenon can be employed to tailor microstructure and enhance the mechanical properties of deformed materials, and thus is of wide interest for the development of advanced structural materials with high strength and ductility.

In the present study, the formation process of dislocation cells in cryorolled Zr has been studied. High density dislocations were introduced into pure Zr by employing cryorolling technique. Dislocation lamellas are yielded in cryorolled Zr at a high strain rate of = 2·24 s−1, and these lamellas fragment or bend into dislocation cells during annealing processes. Instead, in the cryorolled Zr yielded at a low strain rate of = 0·59 s−1, dislocation cells form by the fragmenting or the necking of dislocation tangle regions. The formation process of dislocation cells in cryorolled Zr is dependent on dislocation configurations induced in the metal.

Dislocation configurations, e.g. dislocation tangles, cells and lamellas, in pure Zr have been tailored by cryorolling in the strain rate range of e =0.59–2.24 s −1 , demonstrating a significant effect on mechanical properties. A simultaneous enhancement in the ductility and strength is obtained in the Zr cryorolled at e =2.24 s −1 . The enhancement of ductility is due to the motion of preexisting dislocations under high tensile stress in dislocation lamella configurations yielded at the high strain rate, and the enhancement of strength results from the increase of dislocation density in the cryorolled Zr.

Metals can be strengthened by many methods, but theses strategies always result in limited ductilities. A simultaneous enhancement of strength and ductility in metals is still a great challenge. In the present study, a multimodal grain structure composed of coarse grains (∼24%), ultrafine grains (∼56%), and nanoscale grains or subgrains (∼20%) has been introduced in hcp pure Zr by employing cryorolling in the temperature range from −160 to −90 °C combined with subsequent low-temperature annealing. The multimodal structured Zr exhibits a high ultimate tensile strength (∼658 MPa) and a large uniform elongation (∼8.5%) simultaneously. The high strength results from the contribution of nanoscale and ultrafine grains, while the improved ductility is mainly derived from the improved strain hardening capability by the coarse grains that are effective in storing dislocations and complex deformation strain paths caused by the multimodal distribution of grain sizes.

Both high strength and good ductility are desirable for structural materials for their applications. Here, an outstanding synergy of high yield strength (σy∼550.6 MPa) and promising uniform ductility (eu∼9.2%) is achieved in a low-carbon steel subjected to pre-torsion deformation and thermal annealing, which is much better than that (σy∼319.8 MPa, eu∼13.1%) of its coarse-grained (CG) counterpart. The enhanced mechanical properties is attributed to the formation of a gradient structure of ∼5 mm thickness, that is, the grain size of the ferrite increases gradually with decreasing the radius along the radial direction from the surface to the core. High back stress (over 400 MPa) is invoked by the gradient structure and increases with tensile strain, which devotes to both the high strength and ductility.

In the present paper we identify by x-ray diffraction and electron microscopy the athermal formation of the fcc phase, which is beneficial for a high ductility in TiZr, after severe plastic deformation (SPD) at an ambient temperature. For true strains e ≥2.2, the lattice distortions increase, favoring more martensitic formation of the fcc phase. This coincides with the enhancement of the ductility which is attributed to the higher number of slip systems in the fcc phase than in the hcp phase.

In this study, multi-modal Zr metals composed of nano-grains (NG), ultrafine-grains (UFG) and micro-grains (CG) with various size distributions have been produced via cryorolling followed by thermal annealing. The strength of the multi-modal Zr consisting of UFG and CG follows approximately the rule-of-mixtures with the volume fraction of CG, while its ductility in the rolling direction deviates positively from the rule-of-mixtures. The 78% UFG+22% CG sample with a grain size distribution in the range of 200 nm–1.6 μm exhibits a good combination of high tensile strength ( σ b ∼650 MPa) and uniform elongation ( e u ∼13.4%), much better than that of CG Zr, σ b ∼350 MPa and e u ∼13.8%. The present study is significant for the enhancement of strength and ductility of engineering materials via the design of multi-scale structure.

Article history:Received 16 June 2011Accepted 29 August 2011Available online 6 September 2011Keywords:MicrostructureMetals and alloysMultimodal grain structureStrain rateZirconium The effect of rolling strain rate on the microstructures of cryorolled Zr before and after 450 °C annealing hasbeen investigated. With increasing strain rate, dislocation density increases and dislocation configurationchanges from dislocation cells or tangles to dislocation lamellas in the cryorolled Zr, resulting in different mi-crostructures after annealing. High-density dislocations with the lamella configurations produced at a highstrain rate of e˙ =2.24 s −1 lead to a multimodal grain microstructure in the annealed Zr sample. Themultimodal-structured Zr exhibits a simultaneous enhancement of strength and toughness as comparedwith the samples cryorolled at low strain rates and the coarse-grained Zr.© 2011 Elsevier B.V. All rights reserved. 1. IntroductionThe ultrafine and nanoscale-grained materials have been studiedextensively in pursuing high strength as described by the Hall–Petch relationship, but they often exhibit a very low ductility [1]. It'sbeen reported that the presence of a few large grains within a nano-structured matrix yields a considerable ductility, opposing to the brit-tle behavior of nanostructured metals [1,2]. These studies hint thatdeveloping multimodal grain structures is an alternative route to en-hance the mechanical properties of engineering materials. This idea issimple but difficult to be employed since a large storage of cold-workenergy in deformed metals is necessary for tailoring their microstruc-tures through controlling recrystallization [3]. However, the dynamicrecovery in deformation processes results in a substantially reducedstorage of cold-work energy. To significantly suppress the dynamicrecovery, some cryogenic deformation techniques, e.g. cryomillingand cryorolling are developed [2,3]. Using these strategies, highcold-work energy (e.g. high-density dislocations) has been stored inthe deformed materials and some multimodal-structured metalswith enhanced mechanical properties, e.g. Cu, Al and Ti [2–4], havebeen fabricated. Although the effects of deformation temperatureand strain on the formation of multimodal grain structures havebeen well studied [3,5], little is known on the effect of strain rate.Zirconium (Zr) with a hcp structure has great industrial applica-tions due to its attractive properties, such as the resistance to irradia-tion [6]. In this study, the effect of strain rate on microstructureevolutions and mechanical properties of cryorolled Zr has been inves-tigated. The mechanism for the formation of multimodal grain struc-tures in cryorolled Zr is discussed.2. ExperimentFully recrystallized pure Zr (99.95%) sheets were cryorolled, from3.0 to 0.25 mm in thickness with a reduction of ~2% per pass, in thestrain rate range of e˙ =0.59–2.24 s