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Nanostructured metallic materials having nanocrystalline and ultrafine-grained structures show exceptional mechanical properties, e.g. superior strength, that are very attractive for various applications. However, superstrong metallic nanomaterials typically have low ductility at ambient temperatures, which significantly limits their applications. Nevertheless, several examples of nanostructured metals and alloys with concurrent high strength and good ductility have been reported. Such strong and ductile materials are ideal for a broad range of structural applications in transportation, medicine, energy, etc. Strong and ductile metallic nanomaterials are also important for functional applications where these properties are critical for the lifetime of nanomaterial-based devices. This article presents an overview of experimental data and theoretical concepts addressing the unique combination of superior strength and enhanced ductility of metallic nanomaterials. We consider the basic approaches and methods for simultaneously optimizing their strength and ductility, employing principal deformation mechanisms, crystallographic texture, chemical composition as well as second-phase nano-precipitates, carbon nanotubes and graphene. Examples of achieving such superior properties in industrial materials are reviewed and discussed. [ABSTRACT FROM AUTHOR]

The high strength and increased electrical conductivity of the Al alloys are highly desirable for their applications in power transmission lines. However, high strength and high electrical conductivity are mutually exclusive in metallic materials. A novel nanostructuring strategy is reported that achieves Al–Mg–Si alloys with superior tensile strength and enhanced electrical conductivity. The new strategy is based on a combination of grain refinement down to ultra-fine scale with accelerated formation of nanosized precipitates during severe plastic deformation. [ABSTRACT FROM AUTHOR]

Fracture behavior of coarse-grained and nanostructured commercially pure Ti was studied at room temperature and 250°C. Three dimensional digital elevation models of corresponding fracture surfaces were generated using an automatic fracture surface analysis system and quantitative analyses of fracture surface topography were performed. Average dimple height, crack tip opening displacement COD, and crack opening angle COA were measured. Energy required for formation of dimple structure on fracture surface, fracture toughness, and crack growth resistance were calculated using these results and fracture mechanics relations. It was shown that the correct fracture toughness can be calculated from COD measurements for the nanostructured Ti at room temperature where dislocation glide is the only active deformation mechanism and plastic rotation is insignificant. No correct fracture toughness can be calculated if other deformation mechanisms such as twinning in coarse-grained Ti at room temperature and 250°C or cooperative grain boundary sliding in nanostructured Ti at 250°C are active and plastic deformation is more significant. Advantages of application of three-dimensional analysis of fracture surfaces in fracture studies on nanostructured Ti are discussed. [ABSTRACT FROM AUTHOR]

Nanostructured materials should present a good resistance to irradiation because the large volume fraction of grain boundaries can be an important sink for radiation-induced defects. The objective of the present study is to experimentally investigate the irradiation impact on the microstructure and mechanical properties in nanostructured materials. Nickel and Cu-0.5 Al2O3 specimens were synthesized by electro deposition (ED) and severe plastic deformation (SPD). Mean grain size of the unirradiated specimen is about 30nm for the ED Ni and about 115 nm for the SPI) Ni, 590 MeV proton irradiation and 840 kcV nickel ion irradiation were conducted at room temperature. Vickers hardness measurements and transmission electron microscope observation were performed to examine the impact of irradiation on nanocrystalline materials. It appears that the irradiation induced microstructure in Ni and in Cu-0.5Al2O3, which leads to hardening, consists exclusively of stacking fault tetrahedra. Their density appears much lower than in the case of coarser grained material. These results, experimentally showing the resistance of nanostructured material to radiation damage, are presented here. [ABSTRACT FROM AUTHOR]

The effect of surface pre-treatment on electrochemical anisotropy of nanostructured Ti rods with a strong fiber texture produced for dental implants by a complex severe plastic deformation route was studied in Hank’s solution using DC and AC electrochemical tests. Ti ion release has been quantified by inductively coupled plasma optical emission spectroscopy. The HF/HNO 3 -pickling produces a similar electrochemical behaviour in both transverse and circumferential surfaces of nanostructured Ti rod. The electrochemical anisotropy of HF-pickled nanostructured Ti is considerable due to a significant difference in roughness of the prismatic and basal planes, resulting in increased release of Ti 4+ ions from basal planes. Electrochemical anisotropy is further enhanced in the presence of D-glucose in Hank’s solution. It is recommended to avoid HF-pickling of nanostructured Ti implants in favour of HF/HNO 3 -mixtures. [ABSTRACT FROM AUTHOR]

The influence of grain boundary segregation on the strength of a nanostructured austenitic stainless steel was investigated. The steel was nanostructured by severe plastic deformation at two different temperatures to form ultrafine-grained states different by microstructure parameters. It is shown that despite the difference in grain size both nanostructured steels demonstrated the same level of strength. For the first time it is directly observed that severe plastic deformation at elevated temperature leads to formation of Mo–Cr–Si rich grain boundary segregations in the steel. Considering different contributions to the material strengthening, we demonstrate that grain boundary segregations can lead to significant enhancement of the yield stress. [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]

Abstract: We present the processing, microstructure and properties of nanostructured TiNi-based shape-memory alloys synthesized by severe plastic deformation (SPD), including high-pressure torsion, equal-channel angular pressing, and multi-step SPD deformation (SPD plus cold rolling or drawing). It was found that the SPD processing did not alter the phase transformation sequence of the alloys but changed the morphology of the martensite. Also, we found that the mechanical and shape memory properties were improved by forming nanostructures in these alloys; SPD processing rendered a higher recovery stress (up to 1.5GPa) and a higher maximum reverse strain (up to 10%) of shape memory, which are desirable in various practical applications. [Copyright &y& Elsevier]

The influence of annealing regarding the structure, phase composition and microhardness of nanostructured carbon steel produced by high pressure torsion (HPT) was examined. This material which is far from thermodynamic equilibrium exhibits enhanced thermal stability and a more sluggish mechanical softening than conventional martensite obtained by quenching from elevated temperatures. [Copyright &y& Elsevier]

Abstract The influence of additional low-temperature annealing on microstructure, strength and electrical сonductivity of Al-0.4Zr alloy has been studied. The alloy was preliminarily aged by long-term annealing at 375 °С for 60 h and processed by high pressure torsion (HPT), resulting in formation of ultrafine-grained (UFG) structure. Additional annealing of the alloy with a UFG structure at 230 °С for 1 h leads to substantial enhancement of strength (the yield stress by 40% and ultimate tensile strength by 20%). The hardening effect increases with increasing the annealing time to 3 h, and then it reduces smoothly. The strength enhancement due to annealing is accompanied by an increase in the electrical conductivity. The best combination of strength (the yield stress 149 MPa, the ultimate tensile strength 163 MPa) and electrical conductivity (55% IACS) was achieved after annealing for 3 h. The experimentally obtained changes of the yield stress and electrical resistivity at 77 К due to annealing are compared with the theoretical estimates. The analysis shows that the low-temperature annealing induces additional hardening mechanism in the UFG Al-0.4Zr, which is most likely associated with the rearrangement of high angle grain boundary structure. The obtained results suggest a new way to increase simultaneously strength and electrical conductivity of UFG Al-Zr alloys by an appropriate annealing. Highlights • Extremely high hardening by annealing was found for HPT-processed Al-0.4Zr alloy. • This effect assumes action of a new hardening mechanism in the annealed state. • Hardening by annealing is associated with rearrangement of HAGB structure. • The hardening is accompanied by an increase of electrical conductivity. • This opens a new approach to improve strength and conductivity simultaneously. [ABSTRACT FROM AUTHOR]

Model Fe-Cr alloys with and without W were nanostructured by severe plastic deformation at 350˚C. Transmission electron microscopy observations of the microstructure indicate that the addition of 1 wt% of W led to a reduction of the mean grain size from 129 to 110 nm. Atom probe analyses show that only Cr and Si segregate at grain boundaries during deformation while W remains homogeneously distributed. This solid solution leads to higher mechanical strength and plasticity as compared to Fe-Cr. The origin of the beneficial effect of W on the mechanical performance is discussed. [ABSTRACT FROM AUTHOR]

The influence of microstructure evolution on microhardness and electrical resistivity of ultrafine grained (UFG) commercial purity Al under annealing at different temperatures within a range of 363–673 K was studied. The initially coarse grained Al was processed by high pressure torsion (HPT) technique for the formation of UFG structure. The microstructure was characterized by electron backscattering diffraction and X-Ray diffraction. It was shown that annealing of UFG Al at temperatures within a range of 363–473 K leads to simultaneous increase of microhardness (by 6–13%) and electrical conductivity (by 4–8% at 300 K). The correlation between microstructural features and the resulting properties were analyzed. The average width s of potential barriers at grain boundaries (GBs) in HPT-processed Al was estimated in the frame of a tunnel model. The obtained large value of s compared with the GB crystallographic width is associated with elastically distorted lattice near GBs. The obtained results suggest a new way to increase simultaneously strength and electrical conductivity of UFG Al alloys by an appropriate annealing. [ABSTRACT FROM AUTHOR]

This work is aimed at studying the features of initial Ti Grade 4 structure that affects the changes in its structure and properties during equal channel angular pressing (ECAP). A hot-rolled and martensite structure state, obtained in the process of water quenching from 950 °C were used as initial states. It has been established that ECAP of titanium in an initial martensitic state leads to the formation of a finer and more homogeneous structure than ECAP of a hot-rolled state. The share of high-angle boundaries reaches 80%, and the average size of structural fragments is 220 ± 80 nm. After ECAP at 400 °C, recrystallized grains are observed. As a result, the ECAP of titanium in the initial martensitic state leads to more significant hardening of up to 1100 ± 20 MPa compared to the hot-rolled state of –950 ± 15 MPa. This will make it possible to reduce the number of technological operations, as well as improve the strength resource for heat treatment aimed at ductility enhancement in ultrafine-grained titanium. [Display omitted] • Samples of Ti Grade 4 in the martensitic and hot-rolled state were subjected to 8 cycles of ECAP at a temperature of 400 °C. • The refinement of the structure of martensitic titanium during ECAP is more efficient than that of hot-rolled titanium. • 8 Cycles of ECAP of the sample in the martensitic state lead to an increase in strength to fracture up to 1100 ± 10 MPa. • Titanium in the hot-rolled and martensitic state after ECAP have ductile and ductile-brittle fracture patterns, respectively. [ABSTRACT FROM AUTHOR]

High-resolution electron backscatter diffraction (EBSD) was used to examine the grain structure in long rods of ultrafine-grain (UFG) commercial-purity titanium produced for medical implants. The UFG material was obtained by equal channel angular pressing (ECAP) using a Conform scheme followed by rod drawing. The microstructure was found to be bimodal consisting of relatively coarse elongated grains containing well-developed substructure and ultrafine grains. The mean grain size was ~0.3 μm, and the fraction of high-angle boundaries was ~45%. The material had a strong < 10 1 ¯ 0 > -fiber texture. An analysis of the microstructure–properties relationship showed that the increase in material strength developed during severe plastic deformation resulted from grain refinement and substructure evolution in comparable measure. [ABSTRACT FROM AUTHOR]

Abstract: Structure and mechanical properties of nanostructured Ti and TiNi, TiNbZr, TiNbTa shape memory alloys, and TiCaPCON biocompatible coatings were characterized by metallographic analysis and instrumented indentation. Discussed is the mechanism of localized deformation of the coatings deposited onto nanostructured substrates. Deformation was found to proceed inhomogeneous, through formation of shear bands during penetration of a Vickers diamond indenter into TiCaPCON coatings on the substrates with high elastic modulus especially. [Copyright &y& Elsevier]

Abstract: Long-length ultrafine-grained (UFG) Ti rods are produced by equal-channel angular pressing via the conform scheme (ECAP-C) at 200°C, which is followed by drawing at 200°C. The evolution of microstructure, macrotexture, and mechanical properties (yield strength, ultimate tensile strength, failure stress, uniform elongation, elongation to failure) of pure Ti during this thermo-mechanical processing is studied. Special attention is also paid to the effect of microstructure on the mechanical behavior of the material after macrolocalization of plastic flow. The number of ECAP-C passes varies in the range of 1–10. The microstructure is more refined with increasing number of ECAP-C passes. Formation of homogeneous microstructure with a grain/subgrain size of 200nm and its saturation after 6 ECAP-C passes are observed. Strength properties increase with increasing number of ECAP passes and saturate after 6 ECAP-C passes to a yield strength of 973MPa, an ultimate tensile strength of 1035MPa, and a true failure stress of 1400MPa (from 625, 750, and 1150MPa in the as-received condition). The true strain at failure failure decreases after ECAP-C processing. The reduction of area and true strain to failure values do not decrease after ECAP-C processing. The sample after 6 ECAP-C passes is subjected to drawing at 200¯C resulting in reduction of a grain/subgrain size to 150nm, formation of (100) fiber texture with respect to the rod axis, and further increase of the yield strength up to 1190MPa, the ultimate tensile strength up to 1230MPa and the true failure stress up to 1600MPa. It is demonstrated that UFG CP Ti has low resistance to macrolocalization of plastic deformation and high resistance to crack formation after necking. [Copyright &y& Elsevier]

We have used severe plastic deformation (high-pressure torsion straining) to achieve cold consolidation of gas-atomised Al90Fe5Nd5 powders into bulk nanostructured disks with a dispersion of fcc-aluminium crystallites within the glassy matrix with full density and hardness in excess of 3 GPa. The micro- and nanostructure of the resulting disks is presented. [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]