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The unique nonuniform deformation characteristic of high-pressure torsion was used to produce nanostructures with systematically varying grain sizes in a copper disk, which allows us to study the grain-size effect on the deformation mechanisms in nanostructured copper using a single sample. The as-processed copper disk has 100–200 nm grains near its center and 10–20 nm grains at its periphery. High densities of full dislocations (2×1016/m2) were distributed nonuniformly in large grains, implying that dislocation slip is the dominant deformation mechanism. With increasing dislocation density, the dislocations accumulated and rearranged, forming elongated nanodomains. The originally formed nanodomains remain almost the same crystalline orientation as their parent large grains. Further deformation occurred mainly through partial dislocation emissions from nanodomain boundaries, resulting in high density of nanotwins and stacking faults in the nanodomains. The elongated nanodomains finally transformed into equiaxed nanocrystalline grains with large-angle grain boundaries. The results suggest that grain boundary rotation and grain boundary sliding might play a significant role in the formation of large-angle grain boundaries in nanocrystalline grains. These experimental results show that different deformation mechanisms operate at different length scales and confirm unambiguously the deformation mechanisms of nanocrystalline grains predicted by molecular dynamic simulations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ultrafine-grained Al alloys produced by high-pressure torsion are found to exhibit a very high strength, considerably exceeding the Hall–Petch predictions for ultrafine grains. This phenomenon can be attributed to the unique combination of ultrafine structure and deformation-induced segregations of solute elements along grain boundaries, which may affect the emission and mobility of intragranular dislocations. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and the spectrum of grain boundary misorientations were studied in Armco iron, following high pressure torsion (HPT) deformation, by means of transmission electron microscopy (TEM) and orientation imaging microscopy (OIM). It was found that HPT deformation results in the formation of an equiaxed grain structure with a mean grain size of 270 and 130nm using a shear strain of γ=210 and 420, respectively. The misorientation spectra in HPT iron have a bimodal character with maxima in low (at 1–2°) as well as in high misorientation angle ranges. A marked increase in the fraction of special boundaries (Σ3–Σ45) was revealed as a result of HPT. The microstructural changes due to HPT are discussed and compared with those obtained during conventional deformation modes. [Copyright &y& Elsevier]

Shows the conveniences for the preparation of bulk nanocrystalline materials by severe plastic deformation (SPD) using a Ti-Ni-Cu alloy possessing the shape-memory effect and a Nd-Fe-B alloy, which is a hard magnetic material. Indication that the SPD of amorphous rapidly quenched alloys results in an abrupt decrease in their crystallization temperature; Formation of finer nanocrystalline structure.

Emission of lattice dislocations from grain boundaries (GBs) specified by deformation-distorted structures with periodic fluctuations of misorientation in deformed ultrafine-grained (UFG) materials is theoretically described. It is theoretically revealed that (i) the dislocation emission from deformation-distorted GBs is significantly enhanced as compared to that from structurally equilibrated GBs; and (ii) the enhancement effect depends on the parameters specifying the deformation-distorted GBs. The influence of deformation-distorted GBs as dislocation sources on the tensile ductility of UFG materials is discussed. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, much progress has been made in the studies of nanostructured Al alloys for advanced structural and functional use associated both with the development of novel routes for the fabrication of bulk nanostructured materials using severe plastic deformation (SPD) techniques and with investigation of fundamental mechanisms leading to improved properties. This review paper discusses new concepts and principles in application of SPD processing to fabricate bulk nanostructured Al alloys with advanced properties. Special emphasis is placed on the relationship between microstructural features, mechanical, chemical, and physical properties, as well as the innovation potential of the SPD-produced nanostructured Al alloys. [Copyright &y& Elsevier]

Superplastic behavior of the ultrafine-grained (UFG) Ti–6A1–4V alloy produced by high pressure torsion (HPT) has been studied. High elongations (more than 500%) have been observed in this alloy during tensile tests at relatively low temperatures and high strain rates. At the same time, the superplastic behavior of this alloy has several specific features such as the relatively low values of strain rate sensitivity of flow stress and significant strain hardening. Moreover, it was shown that the alloy, processed by HPT, demonstrates an outstanding room temperature strength about 1500 MPa after superplastic deformation. [Copyright &y& Elsevier]

Abstract The static-annealing behavior and evolution of the microstructure-strength relationship of severely-deformed commercial-purity titanium Grade 4 over the temperature range of 50–850 °C (0.16–0.57 T m , where T m is the melting point) were established. The severely-deformed material was obtained via equal-channel angular pressing (ECAP) using the Conform (ECAP-C) technique at 200 °C to an effective accumulated true strain of 8.4. The resulting ultrafine structure was stable to 400 °C. The excellent thermal stability was concluded to be associated with a strain-aging effect, i.e., the enhanced diffusion of solutes within this temperature interval resulting in the formation of solute atmospheres at/near dislocations. At 450–500 °C, rapid growth of strain-free grains occurred, which eliminated the severely-deformed microstructure and promoted softening. This process was deduced to be controlled primarily by grain-boundary energy and therefore was interpreted primarily in terms of grain growth rather than discontinuous recrystallization expected in this temperature range. A further increase in annealing temperature to 600 °C led to normal grain growth. Analysis of the microstructure-strength relationship suggested a significant influence of mechanical twinning on yield strength of the fully-annealed material. At 600 °C and higher temperatures, dissolution of constituent iron-rich particles was observed. This promoted a partial α → β transformation at the temperatures noticeably below the typical beta-transus of pure titanium (~880 °C). This phenomenon resulted in the precipitation of nanoscale β particles which imparted substantial strengthening. Water quenching of the material annealed at 850 °C gave rise to a β → α′ martensitic transformation. The latter process was governed by exceptionally strong variant selection and thereby provided a nearly-ideal restoration of crystallographic orientations of parent α-grains. [ABSTRACT FROM AUTHOR]

The Zr 62 Cu 22 Al 10 Fe 5 Dy 1 bulk metallic glass (BMG) was subjected to high pressure torsion (HPT) at room temperature. The state after HPT processing demonstrates presence of large number of heterogeneities in amorphous structure – shear bands. Nanoindentation was used to study the effect of HPT processing on deformation behavior and strain rate sensitivity ( m ). It was found that HPT significantly affects mechanical behavior of BMG during nanoindentation. Decrease in hardness and Young's modulus was observed after HPT. At the same time HPT processing led to an increase in m from 0.014 for the as-cast material to 0.036. The lack of serration flow and shear bands around imprints was observed in addition to above mentioned changes. A much less localized deformation mode under nanoindentation along with an increase in values of strain rate sensitivity of HPT-processed state in comparison with the initial state imply homogeneous deformation behavior after processing. The observed drastic changes in deformation behavior and structure can be explained as the formation of a highly-heterogeneous amorphous structure resembling nanoglasses in result of HPT processing. [ABSTRACT FROM AUTHOR]

The high pressure torsion (HPT) of Ti–4 wt. % Fe and Ti–4 wt. % Co alloys has been studied. Before HPT, the samples were annealed above and below the temperature of eutectoid transformation. After quenching, the first samples contained a mixture of α and β phases. The latter samples contained a mixture of α-Ti saturated with Fe or Co and respective intermetallic phases TiFe. During HPT the high-pressure ω-phase formed in all samples. The amount of ω-phase was higher when the initial samples contained the α+β mixture then in the case of α+TiFe or α+Ti 2 Co mixture. Most probably, the martensitic β→ω transformation occurs easier than the α→ω one. The amount of ω-phase was higher in Ti–Fe alloy than in the Ti–Co alloy for both initial states. It seems that cobalt additions disadvantageously change the lattice parameters in Ti for martensitic β→ω and α→ω transformations. The phase transformations with mass transfer (diffusive ones) also take place by HPT of Ti–Fe and Ti–Co alloys. Both α-based solid solutions partially decomposed after HPT. After HPT, the lattice parameters of α-phase containing cobalt or iron changed towards those of pure α-Ti. It has been observed for the first time that the composition of TiFe phase also changes after HPT. [ABSTRACT FROM AUTHOR]

The Zr 62 Cu 22 Al 10 Fe 5 Dy 1 bulk metallic glass is studied in the as-cast state and in the state after processing by high-pressure torsion at temperatures of 20 °C and 150 °C. According to the data from X-ray diffraction and transmission electron microscopy, the structural state of the samples depends weakly on the conducted processing. At the same time, magnetic measurements reveal well recordable changes in paramagnetic susceptibility induced by the processing of the samples. It is assumed that, because of high-pressure torsion deformation, there occurs a noticeable change in the material electronic structure, which leads to a change in the full susceptibility of the samples. The performed studies demonstrate that paramagnetic susceptibility may be an indicator of a change in the structural state of paramagnetic amorphous metallic substances. [ABSTRACT FROM AUTHOR]

This paper reports on a study of the relationship between microstructure, mechanical behavior and impact toughness of the UFG Grade 5 Ti alloy. The mechanical behavior and impact toughness of the Grade 5 Ti alloy in a coarse-grained state, and in an ultrafine-grained (UFG) state produced by equal-channel angular pressing (ECAP) with subsequent deformation-and-thermal treatments via extrusion and warm upsetting in isothermal conditions, were studied extensively. It is shown that a strong refinement of α -grains (less than 250 nm) in the alloy by ECAP and extrusion leads to high strength but with low values of the uniform elongation and lower impact toughness. It is demonstrated that, in order to increase the impact toughness of UFG Ti alloys, it is possible to use approaches realizing ductility enhancement associated with an increase of the strain hardening capacity. An enhancement in the impact toughness of the UFG alloy through an increase in the uniform tensile elongation of the sample is achieved by the preservation of the ultrafine size of α -grains (about 800 nm) with predominantly high-angle boundaries and a decrease in the dislocation density due to recovery and dynamic recrystallization during warm upsetting. [ABSTRACT FROM AUTHOR]

Electron backscatter diffraction was applied to examine the microstructure developed in commercial-purity titanium subjected to equal channel angular pressing at 200 °C to a true strain of 8.4. The microstructure was characterized by a mean grain size of 0.4 μm and fraction of high-angle boundaries of 55%. However, it also contained a significant fraction of relatively coarse (>1 μm) remnants of original grains. A microstructure-properties analysis indicated that strengthening effect of ECAP was essentially contributed by substructure. [ABSTRACT FROM AUTHOR]

Different with common grain refinement dominated by dislocation activities, grain subdivision induced by sequential activation of multiple twinning was observed in a Mg-Gd-Y-Zr magnesium alloy via high-pressure torsion. Deformation bands were evolved from large primary twin bands, which contained refined grains through localized multiple twinning. Nanometer-scaled amorphous bands were also observed within deformation bands in Mg alloys for the first time. These observations indicate that localized deformation via multiple twinning and the consequent formation of deformation bands are potential routes to grain refinement in rare earth-magnesium alloys. [ABSTRACT FROM AUTHOR]

In this work, X-ray scattering methods were applied for a quantitative characterization of the microstructure of an aluminum alloy of the Al–Mg–Si system during dynamic aging realized through the high pressure torsion technique. A qualitative and quantitative phase analysis of the alloy was performed, together with Al alloy lattice parameter determination. From the reflections broadening the effective size of the coherent scattering domains and the lattice microstrain were determined in the framework of the Halder–Wagner approach. Using the method of small-angle X-ray scattering, the quantitative characteristics of the size, shape and spatial distribution of the secondary phase particles formed in the Al alloy during dynamic aging were established. In order to validate the obtained results, the method of small-angle X-ray scattering was preliminarily tested on similar samples after artificial aging and compared with the results from small-angle neutron diffraction widely known in literature. [ABSTRACT FROM AUTHOR]

Peculiarities of structure and mechanical behaviour of amorphous Ti 50 Ni 25 Cu 25 alloy were the focus of this research. The melt-spun ribbons of amorphous Ti 50 Ni 25 Cu 25 were subjected to high pressure torsion (HPT) at temperatures of 20–150 °C in order to modify their structure and mechanical behaviour. Some features of obtained HPT-processed samples were compared with initial state with the help of x-ray diffraction (XRD), transmission electron microscopy (TEM) and nanohardness testing. Analysis of structural data and mechanical behaviour allowed us to assume that severe plastic deformation (SPD) processing of melt-spun Ti 50 Ni 25 Cu 25 alloy might lead to the formation of the structure similar to the new kind of noncrystalline state – “nanoglass” state. [ABSTRACT FROM AUTHOR]

• Equiaxed grains of Ti–2Fe–0.1B alloy transformed into lamellar structure after hydrogenation. • 0.3 wt% hydrogen addition led to the increase of β phase from 4.95% to 30.1%. • The addition of 0.3% H enhanced the yield strength of Ti-2Fe-0.1B alloy. • Flow stress of hydrogenated Ti-2Fe-0.1B alloy decreased extremely during hot compression. [Display omitted] A low-cost Ti-2Fe-0.1B alloy with high performance was manufactured and hydrogenated in this study. The effect of 0.3 wt% hydrogen addition on microstructure evolution, compression deformation behavior at room and high temperature of Ti–2Fe–0.1B alloy has been investigated. Results indicated that lamellar α L structure along with martensite α′ are formed after hydrogenation compared with initial equiaxed grains, and the fraction of β phase increased from 4.95% to 30.1%. Obvious phase transformation α eq →α H + β H , β→β H during hydrogenation and β H →α + δ, α H →α + δ during subsequent cooling occurred. The hydrogenated Ti-2Fe-0.1B alloy is characterized by hardening effect during compression deformation at room temperature along with the loss of ductility due to the solid solution strengthening by hydrogen atoms and presence of hydride δ. However, peak flow stress of hydrogenated Ti-2Fe-0.1B alloy decreased from 49 MPa to 29 MPa extremely during compression deformation at 973 K, which can be attributed to the high volume of β phase induced by hydrogenation, as well as the promotion of dynamic recovery and dynamic recrystallization. [ABSTRACT FROM AUTHOR]

Abstract: Grain boundaries in ultrafine grained (UFG) materials processed by severe plastic deformation (SPD) are often called “non-equilibrium” grain boundaries. Such boundaries are characterized by excess grain boundary energy, presence of long range elastic stresses and enhanced free volumes. These features and related phenomena (diffusion, segregation, etc.) have been the object of intense studies and the obtained results provide convincing evidence of the importance of a non-equilibrium state of high angle grain boundaries for UFG materials with unusual properties. The aims of the present paper are first to give a short overview of this research field and then to consider tangled, yet unclear issues and outline the ways of oncoming studies. A special emphasis is given on the specific structure of grain boundaries in ultrafine grained materials processed by SPD, on grain boundary segregation, on interfacial mixing linked to heterophase boundaries and on grain boundary diffusion. The connection between these unique features and the mechanical properties or the thermal stability of the ultrafine grained alloys is also discussed. [Copyright &y& Elsevier]

Commercially pure (CP) Ti was subjected to a complex severe plastic deformation (SPD) processing route consisting of equal channel angular pressing, swaging and drawing, resulting in the formation of a homogeneous ultra-fine-grained (UFG) microstructure showing a very high strength. The significant anisotropy of mechanical properties found in the processed rod is related to a very strong crystallographic texture developed during SPD processing. The features of plastic deformation of the UFG CP Ti are discussed with respect to its crystallographic texture. [ABSTRACT FROM AUTHOR]

We report a significant grain size effect on the phase transformation in a Ti–36Nb–2.2Ta–3.7Zr–0.3O alloy during severe plastic deformation. For grain sizes larger than the submicrometer range, the body-centered cubic β phase transformed to hexagonal ω phase when deformed by high-pressure torsion under a relatively low pressure of 3GPa and at room temperature. However, a reverse ω to β transformation was observed under the same deformation conditions when the grain sizes were less than 100nm. [Copyright &y& Elsevier]

Abstract: The high-cycle fatigue behavior of smooth and notched samples of ultrafine-grained titanium prepared by severe plastic deformation is compared with the corresponding properties of conventional titanium. It is shown that the combination of high strength and enhanced ductility of ultrafine-grained titanium lead to an increase of the fatigue endurance limit. Using a combination of equal-channel angular pressing and subsequent thermal and mechanical treatment, it was possible to increase the fatigue endurance limit of commercial-purity titanium by a factor of 1.5. Furthermore, it is shown that post-deformation annealing can additionally enhance the ductility of the ultrafine-grained Ti and lower fatigue-notch sensitivity particularly in comparison with Ti-6Al-4V. [Copyright &y& Elsevier]

Abstract: Microstructure evolution in severely deformed Cu has been investigated using high-energy synchrotron light during in situ high-pressure torsion (HPT) at room temperature. Relative changes in broadening of Bragg peaks and crystal lattice expansion were studied in the loading–unloading regime of torsion straining. Experimental results revealed fast relaxation (on the order of hundred of seconds) that occurred due to annihilation of HPT-induced crystal lattice defects, which were generated directly during deformation. The kinetics of relaxation is probably diffusion-controlled; therefore, the enhanced diffusivity can be explained by extremely high excess vacancy concentration, which is usually achieved at thermal equilibrium near the melting point. [Copyright &y& Elsevier]

Abstract: It was shown that introducing an ultrafine-grained (UFG) microstructure in pure metals as well as some alloys leads to strongly enhanced fatigue properties. The cyclic deformation behavior of UFG Ti-6Al-4V ELI (extra low interstitials) alloy is studied by both strain and stress controlled fatigue tests using plastic strain amplitudes between 3×10−4 and 5×10−3 and stress amplitudes ranging from 550 to 670MPa. The UFG microstructures were obtained by equal channel angular pressing (ECAP) with different number of passes followed by a subsequent thermomechanical treatment (TMT). When compared to the conventional grain (CG) size counterpart, the UFG alloy exhibited a pronounced enhancement in the fatigue life in the S–N (Wöhler) diagram. It was also shown that additional UFG processing prior to TMT did not result in any further improvement of the fatigue resistance. Furthermore, microstructural investigations revealed a high cyclic stability of the UFG microstructure. [Copyright &y& Elsevier]

Abstract: The microstructure and hardness of binary Al–Zn and Al–Mg alloys were studied both in the as-cast state and after high-pressure torsion (HPT) with 5 torsions (shear strain about 6). The size of (Al) grains and of reinforcing second-phase precipitates decreases drastically after HPT and reaches the nanometre range. During HPT, the Zn-rich supersaturated (Al) solid solution decomposes and closely approaches the equilibrium state corresponding to room temperature. The decomposition of Mg-rich supersaturated (Al) solid solution is less pronounced. In the as-cast state the hardness of the supersaturated solid solutions increases with increasing Zn and Mg content due to solid-solution hardening. However, after HPT the work hardening and Hall–Petch hardening due to the decreasing grain size compete with softening due to the decomposition of a supersaturated solid solution. As a net effect, severe plastic deformation results in softening of the binary Al–Zn and Al–Mg alloys. Softening is more pronounced in the Al–Zn alloys where HPT leads to almost full decomposition of the supersaturated solid solution. [Copyright &y& Elsevier]

Abstract: Microstructure development during severe plastic deformation by simple shear is modeled using a disclination model for substructure formation incorporated into the viscoplastic self-consistent (VPSC) polycrystal model. The strain incompatibilities between a homogeneous effective medium and a grain calculated by the VPSC model are assumed to result in an accumulation of disclinations at junctions of the grain. These disclinations are then relaxed by the growth of low-angle dislocation boundaries from the junctions. These boundaries split the grain into smaller, misoriented volumes which with further deformation can lead to its subdivision into new grains. The evolution of misorientation angles between the newly formed grains and the parent with applied straining agrees reasonably well with experimental misorientation angle distributions for geometrically necessary boundaries. Accounting for subgrain boundaries and grain subdivision results in textures after large strains that are more diffuse and lower in intensity than those predicted using standard VPSC modeling. [Copyright &y& Elsevier]

The effect of severe plastic deformation by high pressure torsion (HPT) on radio frequency plasma nitriding of X5CrNi1810 steel was investigated. The results reveal that HPT enhances the effect of nitriding at 350 °C leading to doubling of the nitrided layer thickness. This layer was shown to consist of expanded austenite and possibly some iron nitrides. [Copyright &y& Elsevier]

Abstract: Evolution of the microstructure and mechanical properties of Al–30wt.% Zn alloy after the severe plastic deformation (SPD) by the high-pressure torsion has been investigated in detail in dependence on the increasing deformation degree. SPD leads to the gradual grain refinement and decomposition of the Al-based supersaturated solid solution. Measurements of the microhardness reveal a successive softening of the alloy with the increased deformation degree. [Copyright &y& Elsevier]

Abstract: A coarse-grained (CG) Al6061 alloy after solution treatment is subjected to high pressure torsion at room temperature resulting in the formation of a homogeneous ultra-fine grained (UFG) microstructure with average grain size of 170nm. Tensile tests are performed at room and liquid nitrogen temperatures for both CG and UFG conditions. Analysis of the surface relief of the tested specimens is performed. The effect of microstructure on the mechanical properties and on the deformation behavior of the material is discussed. [Copyright &y& Elsevier]