Ruslan Z. Valiev

Bulk nanostructured materials from severe plastic deformation

2. Methods of severe plastic deformation and formation of nanostructures . . . . . . . 105 2.1. SPD techniques and regimes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 2.1.1. Torsion straining under high pressure . . . . . . . . . . . . . . . . . . . . . 106 2.1.2. ECA pressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 2.1.3. Multiple forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 2.2. Typical nanostructures and their formation . . . . . . . . . . . . . . . . . . . . . . . 115

Paradox of strength and ductility in metals processed by severe plastic deformation

It is well known that plastic deformation induced by conventional forming methodssuch as rolling, drawing or extrusion can significantly increase the strength of metalsHowever, this increase is usually accompanied by a loss of ductility. For example, Fig.1 shows that with increasing plastic deformation, the yield strength of Cu and Almonotonically increases while their elongation to failure (ductility) decreases. Thesame trend is also true for other metals and alloys. Here we report an extraordinarycombination of high strength and high ductility produced in metals subject to severeplastic deformation (SPD). We believe that this unusual mechanical behavior is causedby the unique nanostructures generated by SPD processing. The combination ofultrafine grain size and high-density dislocations appears to enable deformation by newmechanisms. This work demonstrates the possibility of tailoring the microstructures ofmetals and alloys by SPD to obtain both high strength and high ductility. Materialswith such desirable mechanical properties are very attractive for advanced structuralapplications.In this work, we report on how inducing severe plasticdeformation (SPD) by equal channel angular pressing(ECAP) and high pressure torsion (HPT)

Structure and properties of ultrafine-grained materials produced by severe plastic deformation

Abstract Strain-heat methods of obtaining ultrafine-grained (UFG) metallic materials with grain sizes as small as 20 nm and peculiarities of their structure are considered. It is shown that intercrystalline boundaries are the main element of the structure of UFG materials and that they are typically in a non-equilibrium state. The formation of a special grain boundary phase, i.e. a thin near-boundary layer with high dynamic activity of atoms, has been found. This unusual structure leads to the manifestation of promising new elastic, strength, superplastic, damping and magnetic properties of UFG materials.

Plastic deformation of alloys with submicron-grained structure

Abstract The peculiarities of a submicron-grained structure formation in a series of aluminium- and magnesium-based alloys by means of a special strain-heat treatment are examined in this paper. The unusual mechanical properties of alloys displayed in this state at room temperature as well as at enhanced temperatures are found. The nature of the plastic deformation of these materials is discussed.

Deformation behaviour of ultra-fine-grained copper

Abstract Mechanical behaviour and structural changes, such as the evolution of grain and dislocation structures and the formation of slip lines and grain-boundary-sliding traces, of a submicron-grained (SMG) copper during room-temperature compression have been studied. It is suggested that the absorption of dislocations into grain boundaries (GBs) is due to the migration and sliding of some highly non-equilibrium GBs during the deformation process and is influenced by high level internal stresses. From this point of view, the unusual behaviour of SMG copper, in particular, the high yielding and flow stresses, the absence of strain hardening, high plasticity and low strain rate sensitivity, are explained. Analogies of the mechanical behaviour of SMG copper with mechanical properties of metallic materials at large plastic strains in stage IV are discussed.

Deformation behavior and plastic instabilities of ultrafine-grained titanium

Ultrafine-grained (UFG) Ti samples have been prepared using equal channel angular pressing followed by cold rolling and annealing. The deformation behavior of these materials, including strain hardening, strain rate dependence of flow stress, deformation/failure mode, and tensile necking instability, have been systematically characterized. The findings are compared with those for conventional coarse-grained Ti and used to explain the limited tensile ductility observed so far for UFG or nanocrystalline metals.

Influence of ECAP routes on the microstructure and properties of pure Ti

Abstract Equal channel angular pressing (ECAP) is an innovative technique that can produce bulk ultrafine-grained (UFG) materials in product forms large enough for structural applications. It is well known that ECAP route, defined by the sequence of orientations of the billets relative to the die during the iterative ECAP passes, significantly affects the microstructural development of the work piece. Studies reported in the literature have so far focused on fcc metals such as Al and Cu. In this work, we have studied the influence of ECAP routes on the microstructures and properties of hcp commercially-pure Ti. Three ECAP routes, conventionally defined as BA, BC and C, were used to process the Ti billets. Surface quality, microstructures, microhardness, tensile properties, anisotropy, and thermal stability were studied. The route BC is shown to be the best route for processing hcp Ti.

Deformation twinning in nanocrystalline copper at room temperature and low strain rate

The grain-size effect on deformation twinning in nanocrystalline copper is studied. It has been reported that deformation twinning in coarse-grained copper occurs only under high strain rate and/or low-temperature conditions. Furthermore, reducing grain sizes has been shown to suppress deformation twinning. Here, we show that twinning becomes a major deformation mechanism in nanocrystalline copper during high-pressure torsion under a very slow strain rate and at room temperature. High-resolution transmission electron microscopy investigation of the twinning morphology suggests that many twins and stacking faults in nanocrystalline copper were formed through partial dislocation emissions from grain boundaries. This mechanism differs from the pole mechanism operating in coarse-grained copper.

Investigations and applications of severe plastic deformation

Preface. Introduction. I: Innovations in Severe Plastic Deformation Processing and Process Modeling. Severe Plastic Deformation of Materials by Equal Channel Angular Extrusion (ECAE) R.E. Goforth, et al. Severe Plastic Deformation of Steels: Structure, Properties and Techniques S.V. Dobatkin. Application of ECAP - Technology for Producing Nano- and Microcrystalline Materials V.I. Kopylov. Severe Deformation Based Process for Grain Subdivision and Resulting Microstructures A.K. Ghosh, W. Huang. Modeling of Continual Flows in Angular Domains B.V. Koutcheryaev. Synthesis and Characterization of Nanocrystalline Tial Based Alloys O.N. Senkov, F.H. Froes. Formation of Submicrocrystalline Structure in TiAl and Ti3Al Intermetallics via Hot Working G. Salishchev, et al. Severe Plastic Deformation Processes Modeling and Workability S.L. Semiatin, et al. The Effect of Strain Path on the Rate of Formation of High Angle Grain Boundaries During ECAE P.B. Prangnell, et al. Thermomechanical Conditions for Submicrocrystalline Structure Formation by Severe Plastic Deformation F.Z. Utyashev, et al. II: Microstructural Characterization and Modeling of Severe Plastic Deformation Materials. Strengthening Processes of Metals by Severe Plastic Deformation. Analyses with Electron and Synchrotron Radiation M.J. Zehetbauer. Size Distribution of Grains or Subgrains, Dislocation Density and Dislocation Character by Using the Dislocation Model of Strain Anisotropy in X-Ray Line Profile Analysis T. Ungar. X Ray-Studies and Computer Simulation of Nanostructured SPD Metals I.V. Alexandrov. An Analysis of Heterophase Structures of Ti3Al, TiAl, Ni3Al Intermetallics Synthesized by the Method of the SphericalShock Wave Action B.A. Greenberg, et al. Structural Changes Induced by Severe Plastic Deformation of Fe- and Co-Based Amorphous Alloys N. Noskova, et al. Structure of Grains and Internal Stress Fields in Ultrafine Grained NI Produced by Severe Plastic Deformation N.A. Koneva, et al. Crystal Lattice Distorsions in Ultrafine-Grained Metals Produced by Severe Plastic Deformation A.N. Tyumentsev, et al. Grain and Subgrain Size-Distribution and Dislocation Densities in Severely Deformed Copper Determined by a New Procedure of X-Ray Line Profile Analysis T. Ungar, et al. Calculation of Energy Intensity and Temperature of Mechanoactivation Process in Planetary Ball Mill by Computer Simulation E.V. Shelekhov, et al. III: Microstructure Evolution During Severe Plastic Deformation Processing. Microstructural Evolution During Processing by Severe Plastic Deformation T.G. Langdon, et al. Characterization of Ultrafine-Grained Structures Produced by Severe Plastic Deformation Z. Horita, et al. Fragmentation in Large Strain Cold Rolled Aluminium as Observed by Synchrotron X-Ray Bragg Peak Profile Analysis (SXPA), Electron Back Scatter Patterning (EBSP) and Transmission Electron Microscopy (TEM) E. Schafler, et al. Influence of Thermal Treatment and Cyclic Plastic Deformation on the Defect Structure in Ultrafine-Grained Nickel E. Thiele, et al. Nanostructure State as Nonequilibrium Transition in Grain Boundary Defects in SPD Condition O.B. Naimark. Texture, Structural Evolution and Mechanical Properties in AA5083 Processed by ECAE L. Dupuy, et al. A TEM-Based Disclination Model for the Substructure Evolution under Severe Plastic Deformation M. Seefeldt, et al. Physical Mesomechanics of Ultrafine-Grained Metals V.E. Panin. Microstructure Evo

Structure and mechanical properties of ultrafine-grained metals

Abstract This paper describes the fabrication of several pure metals and alloys with nano-and submicrometer grain sizes by severe plastic deformation techniques, the results of their structural characterization, and provides data on their mechanical properties at ambient temperature and superplastic conditions. Special attention is paid to the relationship between the defect structures of grain boundaries and the mechanical behaviour of produced ultrafine-grained metallic materials.