bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen Activation Behavior of Commercial Magnesium Processed by Different Severe Plastic Deformation Routes
Authors: Leiva Daniel Rodrigo , Huot Jacques , Ishikawa Tomaz Toshimi , Bolfarini Claudemiro , Kiminami Claudio Shyinti , Jorge Alberto Moreira , Botta Filho Walter José
Published: December 2010

Severe plastic deformation (SPD) techniques are being considered as low cost processing routes for Mg alloys, aiming hydrogen storage applications. The main objective is to develop air-resistant materials, with lower specific surface area in comparison with ball-milled powders, but with still attractive H-sorption kinetics associated to the microstructural refinement. In this study, the effects of different SPD processing routes (high-pressure torsion, extensive cold rolling and cold forging) in the hydrogen activation behavior of Mg was evaluated. The results show that both microstructural and textural aspects should be controlled during SPD processing to obtain Mg alloys with good H-sorption properties and enhanced activation kinetics.
Effect of Equal-Channel Angular Pressing on the Microstructure and Superelastic Behavior of Ti-25 at. % Nb Shape Memory Alloy
Authors: Song Jie , Zhang Xiao Ning , Sun Xiao Gang , Xie Chao Ying
Published: December 2010

Microstructure and mechanical behavior of Ti-25 at. % Nb shape memory alloy processed by equal-channel angular pressing (ECAP) at 673 K have been investigated. The effect of multi-passes ECAP on the martensitic transformation temperature and superelastic recovery strain of Ti-26 at. %Nb alloy have been analyzed. It is found that the Ti-25 at. % Nb alloy exhibits superelasticity with a recovery strain of 1.6 % after one pass ECAP process. As the ECAP pass numbers increases to four passes, the superelasticity increases a little. The yielding stress (σ0.2) of Ti-25 at. % Nb alloy increases to 430 MPa and the ultimate tensile strength (UTS) is near 678 MPa after one pass ECAP process at 673 K, but the yielding stress and ultimate tensile strength increases little after four pass ECAP. The grain size decreases sharply from 100 μm to no more than 500 nm after four passes ECAP process. Effect of ECAP on the microstructure evolution and Young's modulus has been analyzed.
Effect of the High Pressure Torsion on Magnetic Properties of Amorphous Alloys
Authors: Glezer Alex M. , Plotnikova Margarita R. , Dobatkin Sergey V. , Perov Nikolai S. , Shalimova Anna V.
Published: December 2010

The effect of severe plastic deformation in Bridgman’s chamber on magnetic properties of the amorphous alloys of metal-metalloid type Ni44Fe29Co15Si2B10, Fe50Ni33B17, Fe70Cr15B15 obtained by the melt quenching was studied. The substantial alteration of saturation magnetization depending on the number of ferromagnetic and antiferromagnetic components in the alloy was revealed. It was supposed that the internal separation into nanoscaled areas enriched and depleted by ferromagnetic components took place in the amorphous matrix under the action of severe plastic deformation.
Impact of Ball Milling and High-Pressure Torsion on the Microstructure and Thermoelectric Properties of p- and n-Type Sb-Based Skutterudites
Authors: Rogl Gerda , Zehetbauer Michael J. , Kerber Michael B. , Rogl Peter , Bauer Ernst
Published: December 2010

For thermoelectrics it is important to produce thermodynamically stable bulk nanostructured materials. Ball milling/hot pressing was shown to reduce the crystallite size by a factor of 100 and to reach about 100 nm with dislocation densities of 1012 – 1013m-2. Thereby thermoelectric properties of single, double and multifilled Sb-based skutterudites were improved significantly leading to figures of merit ZT, which in some cases are twice as high as those of their microstructured counterparts. With HPT treatment the crystallite size can be decreased to even 50 nm with dislocation densities as high as 1015m-2. The small grains as well as the high dislocation density result in a further lowering of thermal conductivity holding a high potential for future enhancement of ZT.
Wear Behaviour of Al-1050 Alloy Processed by Severe Plastic Deformation
Authors: Wang Chuan Ting , Gao Nong , Wood Robert J.K. , Langdon Terence G.
Published: December 2010

An Al-1050 alloy was processed by ECAP and HPT, respectively. Dry sliding wear tests were conducted on the as-received and SPD-processed samples under various sliding conditions. A comparison of wear rate indicated that SPD processing decreased the wear resistance. Two main wear mechanisms were observed. The initial wear stage was dominated by severe platelet wear mechanism and later wear was dominated by an oxidation wear mechanism. The results show the severe wear stage of SPD-processed Al-1050 is much longer than that of the as-received Al-1050, which is attributed to the loss of work hardening capacity after SPD processing.
In Vitro Corrosion and Haemocompatibility of Bulk Nanocrystalline 304 Stainless Steel by Severe Rolling
Authors: Nie Fei Long , Wang Yan Bo , Wei Shi Cheng , Zheng Yu Feng , Wang Sheng Gang
Published: December 2010

Bulk nanocrystalline 304 stainless steel (nanocrystalline 304ss) discs had been successfully prepared by the commercial microcrystalline 304 stainless steel (microcrystalline 304ss) plate using severe rolling technique. Micro-hardness was measured to reveal the different mechanical behavior after the severe plastic deformation. The electrochemical corrosion resistance and ion release behavior after immersion of the samples were investigated in Hank’s solution for its potential use as implant and orthodontic appliance in body. Furthermore, murine fibroblast cells were indirectly employed to detect cytotoxicity by co-incubation with the extraction from the given materials. Haemocompatibility, consisting of hemolysis test and adhesion of the platelets, was also measured with fresh human whole blood and platelet-rich plasma respectively. Polarization resistance trials indicate that nanocrystalline 304ss is more corrosion resistant in the Hank’s solution, with lower current density and superficial corrosion morphologies. The release values of the biotoxic ions after immersion do not exceed the set limit and turn to be well below the critical value necessary to induce allergy and below daily dietary intake level. Cellular interaction is observed via the proliferated feature of the cell line. Hemolysis and platelet adhesion results elucidates that nanocrystalline 304ss is biological and hematologic compatible.
Simulation of Multi-Pass ECAP by 3D Finite Element Method
Authors: Bao Li , Ding Hua , Zhao Wen Juan , Mei Rui Bin
Published: December 2010

Multi-pass ECAP process of pure Al for square samples (Φ＝90º, Ψ＝37º, pressing speed of 1mm/s), was simulated by using 3D finite element method (FEM).The distribution of equivalent strain for two and four passes was compared. The results showed that route A leads to non-uniform distribution of equivalent strain during multi-pass ECAP. The distribution of equivalent strain is uniform in BC route, but the value of equivalent strain is larger in C route. The simulation results were compared with the experimental ones with previous work in the literature. The simulation also shows that equivalent strain and load increase with pass increasing.
Microstructure Evolution and the Influence of Hydrofluoric Acid Treatment on the Surfaces of Commercial Pure Ti after ECAE
Authors: Zhang Xiao Ning , Huang Cheng Long , Song Jie , Chen Bin , Ji Wei Ping , Han Pei , Xie Chao Ying
Published: December 2010

Commercial pure Ti (CP Ti) was subjected to the effects of ECAE processes at 673 K by Bc path. The initial 80~100 μm equiaxed and coarse grains were elongated along the shearing force direction of ECAE and refined to ~300 nm after the eight passes ECAE. Surface roughness of CP Ti samples and contact angle of deionized water on CP Ti surface, with coarse or ultrafine grains, modified by polish and HF treatment have been investigated. It is found that CP Ti substrates with ultrafine grains show a significantly lower water contact angle and higher surface energy compared with coarse-grains. HF treatment on pure Ti surfaces brings higher surface roughness and hydrophobicity than polish treated. These results reveal that the combination of ultrafine grains and higher surface roughness, hydrophobic allows a favorable condition for cell growth and bone generation on the surfaces of pure Ti after ECAE process.
Towards Perspective Applications of Nanostructured Ti in Medicine
Authors: Reshetnikova Tasha , Shcherbakov Andrey V. , Salakhova Milyausha R. , Khakimova Larisa
Published: December 2010

The work presents main achievements of international R&D activities of the Institute of Physics of Advanced Materials of Ufa State Aviation Technical University (IPAM USATU, Ufa, Russia) with a special attention to the innovative potential of nanostructured metals and alloys produced by severe plastic deformation (SPD) techniques. Examples of the first promising applications of bulk nanostructured materials (BNM) in medicine are considered and discussed.
Influence of ECAR Processing on OFHC Cu Material Properties
Authors: Kvačkaj Tibor , Kvačkaj Michal , Stoyka Volodymir , Kočiško Robert , Bidulská Jana , Bacso Julius
Published: December 2010

The influence of severe plastic deformation (SPD) on distribution of effective stresses, effective strains and temperatures during equal channel angular rolling (ECAR) process is mathematically simulated. Effect of ECAR processing on substructural and mechanical properties of oxygen free high conductivity (OFHC) Cu material is investigated too. Mathematical simulations in software DEFORM-3D, ECAR technology, tensile tests, EBSD analysis were used as experimental methods. Mathematical simulations of first ECAR pass referred on following results: effective normal stress had low heterogeneity with value 385 MPa, effective strain was distinguished with high heterogeneity in cross section of sample (φ=1,5-3) and temperature in deformation zone achieved value 150 °C. Mechanical properties after cold drawing were: Rp0,2 = 217 MPa, Rm = 260 MPa, Z = 63 % and after sixth ECAR pass were: Rp0,2 = 412 MPa, Rm = 426 MPa, Z = 72 %. From experiments is resulting the stabilization of mechanical properties after fourth ECAR pass were obtained.
Experimental Studies and Modelling Analysis of Commercial Purity Iron Processed by Asymmetric Rolling
Authors: Li Xiao Mei , Ding Yi
Published: December 2010

Asymmetric rolling (ASR) is one of the severe plastic deformation (SPD) processes which are prominently used to reduce grain size and refine grain structure of the metals and alloys of commercial interest. In this work, commercial purity iron processed by asymmetric rolling was experimentally studied by means of optical microscopy and transmission electron microscopy (TEM). Tensile tests were performed on the samples under different treatment conditions and the experimental results were compared with the output from the modelling analysis. Modelling results of the mechanical properties of this type of material are in accordance with the grain refinement mechanism.
Microstructure Evolution and Tensile Properties of 304L Stainless Steel Subjected to Surface Mechanical Attrition Treatment
Authors: Jiang Ping , Lu Jian , Wu Xiao Lei
Published: December 2010

A gradient nanostructured layer (GNsL) was generated on the two sides of bulk sample in 304L stainless steel by means of the surface mechanical attrition treatment. The microstructure of the GNsL was characterized via TEM observation. The prominent microstructural features involve the intersection of multi-system twin operation, subdividing the original grains into blocks, a martensite transformation mainly occurring at the interface of the twins as well, and the randomly orientated nanocrystallites at the top of surface. After annealing at 750°C for 10 min, recovery had occurred and the dislocation density was much reduced. The vast majority of the grains at the top surface were in the nanocrystalline/ultrafine range, with some recrystallization regions. The uniaxial tensile tests were performed to obtain the mechanical property of bulk samples with GNsL. The yield strength was about 2 times higher than that of the coarse-grained counterpart, but with a decrease in uniform elongation and elongation to failure as well. The relationship between the microstructure and mechanical property was discussed in detail.
Grain Size Effect on Deformation Twinning and De-Twinning in a Nanocrystalline Ni-Fe Alloy
Authors: Ni Song , Wang Yan Bo , Liao Xiao Zhou , Alhajeri Saleh N. , Li H.Q. , Ringer Simon P. , Langdon Terence G. , Zhu Yun Tian
Published: December 2010

The effect of grain size on the deformation twinning and de-twinning in a nanocrystalline Ni-Fe alloy was investigated using transmission electron microscopy. Specimens with different grain sizes were obtained by severely deforming an electrochemically deposited nanocrystalline Ni-20wt.% Fe alloy using high-pressure torsion, which resulted in continuous grain growth from an average grain size of ~ 21 nm in the as-deposited material to ~ 72 nm for the highest strain applied in this study. Results show that deformation de-twinning occurs at very small grain sizes while deformation twinning takes place when the grain size is larger than ~ 45 nm. The mechanism of the observed grain size effect on twinning and de-twinning is briefly discussed.
X-Ray Analysis of α and ω – Phases of Ti, Subjected to High-Pressure Torsion
Authors: Sitdikov Vil D. , Alexandrov Igor V. , Bonarski Jan T.
Published: December 2010

This paper presents the results of experimental X-ray structural analyses of both the evolution structure and the crystallographic one in the volume of Ti samples, subjected to the Severe Plastic Deformation (SPD), realized by torsion under high pressure equal to 6 GPa at temperature 298 K. The investigations have been carried out on the disk-shaped samples with the radius of 20 mm in an initial state (the as-received state) and in the states after 0.1, 0.5, 1 and 5 rotations by High-Pressure Torsion (HPT). In the result the evolution mechanisms of the general X-ray patterns, the volume fraction of phases, the character of preferred orientations, as well as the activity of various slip and twinning systems in α- and ω-phases, depending on the SPD degree have been found out. The received results allow explaining and forecasting the behavior of nanostructured Ti, considering the parameters of its microstructure and crystallographic texture.
Investigations on Microstructure Evolution and Deformation Behavior of Aged and Ultrafine Grained Al-Zn-Mg Alloy Subjected to Severe Plastic Deformation
Authors: Hu Wei Ping , Zhang Si Yuan , He Xiao Yu , Liu Zhen Yang , Berghammer Rolf , Gottstein Günter
Published: December 2010

An aged Al-5Zn-1.6Mg alloy with fine η' precipitates was grain refined to ~100 nm grain size by severe plastic deformation (SPD). Microstructure evolution during SPD and mechanical behaviour after SPD of the alloy were characterized by electron microscopy and tensile, compression as well as nanoindentation tests. The influence of η' precipitates on microstructure and mechanical properties of ultrafine grained Al-Zn-Mg alloy is discussed with respect to their effect on dislocation configurations and deformation mechanisms during processing of the alloy.
Grain Boundary Segregation of Carbon and Formation of Nanocrystalline Iron-Carbon Alloys by Ball Milling
Authors: Chen Yu Zeng , Herz Andreas , Kirchheim Reiner
Published: December 2010

Based on a novel defactants (defect acting agents) concept (R. Kirchheim, Acta Materialia 55 (2007) 5129 and 5139), a novel method of understanding and synthesizing NC material was proposed by introducing defactants (segregating solute atoms) into the materials to ease the formation of grain boundaries (GBs) and enhance the formation ability of nanocrystalline (NC) structures. The iron-carbon system was chosen as a model system where carbon acts as the so-called defactant. Iron powders mixed with different amount of graphite were ball milled to prepare NC iron-carbon alloys with different carbon concentrations (C0). After ball milling, the as-milled powder with relatively low carbon concentration was annealed at a certain temperature to achieve saturation of GBs by carbon atoms. The microstructures of the powders were investigated by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The mean grain sizes (D) of the powders were determined by analyzing TEM dark field images and X-ray line profiles. The results indicated that once the saturation of GBs is achieved, D of the NC iron-carbon powders will be strongly dependent on C0 and will follow a simple mass balance of carbon in a closed system, i.e. D=3ΓgbVm/(C0-Cg) with Cg the carbon concentration in grains, Γgb the grain boundary excess, and Vm the molar volume of iron. Based on the experimental results, the formation of NC iron-carbon alloys was treated in detail within the framework of the defactant concept. The increase of C0 significantly reduces the formation energy of GBs, leading to a substantial decrease of D.
Texture Evolution in Pure Copper Processed by Equal Channel Angular Extrusion with Extended Processing Routes
Authors: Li Sai Yi , Li Hao
Published: December 2010

An experimental characterization of texture evolution during equal channel angular extrusion (ECAE) of pure copper was conducted up to 8 passes considering an extended range of processing routes. These routes are featured by 0°, 45°, 90°, 135°, and 180° rotation about the billet longitudinal axis after each pass, and were designated as R0, R45, R90, R135, and R180, respectively. They were implemented using new die designs with the cross-section of the die channels as a 24-sided regular convex polygon and with die angle (Φ) of 90° and 120°, respectively. X-ray diffraction measurements show that for both die sets, the textures developed via the different routes all show orientation concentrations along fibers with the {111} planes parallel to the macroscopic simple shear plane and <110> directions parallel to the macroscopic simple shear direction, yet the locations and orientation densities of the main texture components vary significantly with the pass number and the processing route. After 4 to 8 passes, the texture is found to be the weakest via route R180 for both die sets, and strongest via R0 or R45. For a given route and pass number, the texture developed with Φ = 120° is generally weaker than its counterpart with Φ = 90°. These results thus confirm the general tendencies of texture development in face-centered cubic metals with {111}<110> slip as the dominant deformation mechanisms, albeit in a wide range of processing route or deformation history.
Effect of Multiaxial Forging on Structure Evolution and Mechanical Properties of Oxygen Free Copper
Authors: Salishchev Gennady A. , Stepanov Nikita , Kuznetsov A.V. , Zherebtsov Sergey V. , Valiakhmetov Oleg R. , Kuznetsov A.A. , Dobatkin Sergey V.
Published: December 2010

Evolution of micro- and macrostructure and mechanical properties of oxygen-free copper after MAF at room temperature was studied. MAF included sequential upsetting and drawing with total cycles number equal to 20 and maximum strain ≈50. MAF causes the formation of homogenous UFG structure with a grain/subgrain size of 0.3 m and fraction of high angle boundaries 50%, but macrostructure is heterogeneous. Rough shear macrobands areas of different orientation are observed. MAF results in significant strengthening from 280 MPa to 445 MPa, but samples remain very ductile even after large strains. Mechanisms of UFG structure formations during MAF are discussed.
Twist Extrusion: Fundamentals and Applications
Authors: Varyukhin Viktor , Beygelzimer Yan , Kulagin R. , Prokof'eva O. , Reshetov Alexey
Published: December 2010

We present a study of the kinematics of Twist Extrusion (TE) and show that the mode of deformation in ТЕ is a simple shear. Unlike in Equal-Channel Angular Pressing (ECAP), there are two main shear layers perpendicular to the specimen axis. TE has a significant commercial potential due to the following physical effects: intensive grain refinement; homogenization and mixing; intensive powder consolidation. Donetsk Institute for Physics and Engineering created a TE Center to showcase the process and educate investors. Our experience with the center has shown that the most prospective directions are producing ultrafine-grained (UFG) alloys for medical and aircraft applications.
Annealing Behavior of FeNi Alloy Processed by High-Pressure Torsion
Authors: Lee Seungwon , Horita Z.
Published: December 2010

An Fe-50at %Ni alloy was processed by high-pressure torsion (HPT) and annealed at lower homologous temperatures. Vickers microhardness and microstructural evolutions were examined with respect to the annealing time. Disks with 10 mm diameters having 0.85 mm thicknesses were subjected to HPT under a pressure of 6 GPa for 1-10 revolutions at a rotation speed of 1 rpm. The annealing after the HPT processing was conducted at homologous temperatures of ~0.3 for up to 40 days. The hardness increases with straining and saturates to a constant level of ~400 Hv at large equivalent strain. Microstructure analysis using XRD revealed that there was a peak corresponding to an α (Fe, Ni) phase.
Microstructure Evolution of Pure Nickel up to a High Strain Level during Equal-Channel Angular Pressing
Authors: Liu Fan , Zhang Yue , Wang Jing Tao
Published: December 2010

Nickel of 99.5% purity, with an initial grain size of ~23 μm, was subjected to equal-channel angular pressing (ECAP) up to a strain of ~12 at room temperature via route Bc. Mechanical properties and microstructures are investigated by tensile tests, microhardness tests, TEM, and EBSD observations. Results of mechanical properties show that yield strength and tensile strength increase as strain increase up to a max value( s~1009 MPa, b~1120 MPa) at ~8, and microhardness reaches its maximum of ~370HV after 12 passes. Analysis by TEM showed that grain size of pure nickel was severely refined from ~23 μm to several hundreds of nanometers after ECAP processing. Initial coarse grain are divided with lamellar boundaries and dislocation cell structures at low strain level, there has resulted in a homogenous and fine spacing of lamellar boundaries (~100 nm) after 4 passes of ECAP, low angle characters of those boundaries are revealed from corresponding SAED pattern; equiaxed grains of diameter with ~98 nm come out among lamellar boundaries after 12 passes.
Enhanced Thermal Stability and Mechanical Properties of Ultrafine-Grained Aluminum Alloy
Authors: Islamgaliev Rinat K. , Nikitina Marina A. , Kamalov Aidar F.
Published: December 2010

The paper reports on microstructure, strength and fatigue of ultrafine-grained (UFG) samples of the Al-Cu-Mg-Si aluminum alloy processed by high pressure torsion (HPT) at various temperatures. Application of the HPT treatment led to strong grain refinement, as well as to a raise of the mean-root square strains and dynamic precipitation. In case of optimal HPT treatment the UFG samples have demonstrated the enhanced thermal stability, an increase in ultimate tensile strength in 2.5 times and enhancement in fatigue endurance limit by 20 % in comparison with coarse-grained alloy subjected to standard treatment. It is shown that the regime of the HPT treatment governs the volume fraction of precipitates and segregations, thereby affecting a grain size and thermal stability of ultrafine-grained structure.
Microstructure and Texture of Magnesium Single Crystals Processed by ECAP
Authors: Šedá Petra , Jäger Aleš , Lejček Pavel
Published: December 2010

Equal channel angular pressing (ECAP) is a promising severe plastic deformation technique for production of ultrafine-grained bulk metals with face centered cubic (fcc) structure. However, the process is often complicated in hexagonal close packed (hcp) metals such as magnesium due to its low forming capability. In this contribution, magnesium single crystals were processed by ECAP through a single pass in order to reveal processes taking place in hcp lattice during severe plastic deformation. The microstructure and texture were investigated by SEM-EBSD. The deformed microstructure contains shear bands, recrystallized regions and mechanical twins. Activity of twinning systems and texture formation are discussed regarding different initial orientation of the single crystals.
Martensitic Transformation from Ultrafine Grained Austenite Fabricated by ARB in Fe-24Ni-0.3C
Authors: Jafarian Hamidreza , Borhani Ehsan , Shibata Akinobu , Terada Daisuke , Tsuji Nobuhiro
Published: December 2010

In this paper, martensitic transformation from ultrafine grained (UFG) austenite fabricated by accumulative roll bonding (ARB) process in a metastable austenite alloy was studied. Microstructural observations and crystallographic analysis were carried out by FE-SEM/EBSD. The results showed that elongated UFG austenite having 200-300 nm in thickness surrounded by high angle boundaries was obtained after 6 cycles of the ARB process. The martensite transformed from the UFG austenite showed characteristic morphology and texture. The martensite transformation starting (Ms) temperature increased after 1 cycle ARB, which is related to increasing amount of nucleation sites, such as low angle boundaries, introduced during early stage of ARB process. In contrast, by increasing the ARB cycles, Ms temperature decreased. Decreasing the Ms temperature could be correlated to strengthening of austenite by the ARB process.
Grain Subdivision of a Nb Polycrystal Deformed by Successive Compression Tests
Authors: Zhu Liang , Sandim Hugo Ricardo Zschommler , Seefeldt Marc , Verlinden Bert
Published: December 2010

To understand and model grain refinement in severe plastic deformation, some analysis of Nb single crystals has been carried out in previous work. To bridge the gap with normal polycrystalline materials, supplementary experiments on large polycrystals, deformed at moderate strains appear to be necessary to explain the grain subdivision step by step. In the present work, successive uniaxial compression tests have been carried out on a large grained Niobium polycrystal up to height reductions of 30% with small strain increments. Electron backscatter diffraction (EBSD) analysis was done after each compression step to characterize the evolution of orientation and microstructures. It is observed that a “rotation front” forms inside the grain and moves with increasing strain from one side to the other side of the grain. In one grain, this process results in a grain boundary affected zone in the vicinity of the grain boundary. Both static orientation evolution inside the grain and historical evolution of the average orientation have been studied, which indicates that the grain orientation rotates around one of the (110) poles at low strain.
Influence of Stacking Fault Energy on the Microstructures and Grain Refinement in the Cu-Al Alloys during Equal-Channel Angular Pressing
Authors: An X.H. , Wu Shi Ding , Zhang Zhe Feng
Published: December 2010

The microstructural evolution and grain refinement of Cu-Al alloys with different stacking fault energies (SFEs) processed by equal-channel angular pressing (ECAP) were investigated. The grain refinement mechanism was gradually transformed from dislocation subdivision to twin fragmentation with tailoring the SFE of Cu-Al alloys. Concurrent with the transition of grain refinement mechanism, the grain size can be refined into from ultrafine region (1 m~100 nm) to the nanoscale (<100 nm) and then it is found that the minimum equilibrium grain size decreases in a roughly linear way with lowering the SFE. Moreover, in combination with the previous results, it is proposed that the formation of a uniform ultrafine microstructure can be formed more readily in the materials with high SFE due to their high recovery rate of dislocations and in the materials with low SFE due to the easy formation of a homogeneously-twinned microstructure.
Mechanisms of Microstructure Refinement in Titanium during “abc” Deformation at 400°C
Authors: Zherebtsov Sergey V. , Kudryavtsev Egor A. , Salishchev Gennady A.
Published: December 2010

Mechanical behavior and microstructure evolution of commercial pure titanium during successive compressions of samples along three orthogonal directions (or so-called “abc” deformation) at 400°C and strain rate 10-3s-1 were studied. The cumulative S- curve demonstrates a steady state flow stage following the intensive strengthening. The microstructure evolution of titanium during first increments of “abc” deformation is associated with twinning and shear deformation. Further deformation results in microstructure refinement due to transformation of coincidence site lattice twin boundaries to high-angle arbitrary ones and formation of high-angle deformation induced boundaries. Another mechanism of new grains formation is continuous dynamic recrystallization.
Microstructure and Mechanical Performance of AZ31-1.7 Wt.% Si Alloy Processed by Cyclic Channel Die Compression
Authors: Guo Wei , Wang Qu Dong , Liu Man Ping , Peng Tao , Liu Xin Tao , Zhou Hao
Published: December 2010

Cyclic channel die compression (CCDC) of AZ31-1.7 wt.% Si alloy was performed up to 5 passes at 623 K in order to investigate the microstructure and mechanical properties of compressed alloys. The results show that multi-pass CCDC is very effective to refine the matrix grain and Mg2Si phases. After the alloy is processed for 5 passes, the mean grain size decreases from 300 μm of as-cast to 8 μm. Both dendritic and Chinese script type Mg2Si phases break into small polygonal pieces and distribute uniformly in the matrix. The tensile strength increases prominently from 118 MPa to 216 MPa, whereas the hardness of alloy deformed 5 passes only increase by 8.4% compared with as-cast state.
Microstructure and Toughness of an AZ80 Mg Alloy Processed by ECAP and Ageing Treatment
Authors: Yin De Liang , Chen Xin , Wang Jing Tao
Published: December 2010

An extruded AZ80 Mg alloy was subjected to ECAP and subsequent artificial ageing to investigate the influences of ECAP passes and ageing conditions on the mechanical properties. The microstructures and mechanical properties were characterized by optical microscopy (OM), scanning electronic microscopy (SEM) and uniaxial tension tests. The static toughness values were calculated to evaluate the combined effects of ECAP and artificial ageing on the toughness. It is indicated that combination of ECAP and ageing at 300oC for 8h can significantly increase the toughness of as-extruded AZ80 alloy by 43%. The remarkable twinning and uniform dimples due to the continuous precipitation should be responsible for the increased tensile toughness.
The Mechanical Performance of ARB Fabricated Hybrid Lamellar Composite of Recovered/Recrystallized Al and Precipitation Hardened Al(Sc) Layers
Authors: Quadir M. Zakaria , Al-Buhamad O. , Ferry Michael
Published: December 2010

Sheets of commercial purity aluminum and super saturated solid solution of 0.3% Sc were accumulatively roll bonded to form 64 alternating layers in a 0.5 mm thickness. The rolling was done at 350 °C to ensure dynamic recovery/recrystallization in Al layers and precipitation hardening of Al(Sc) layers during the rolling. The sheet crystallographic texture was distributed along β fibre orientations. The recrystallization texture of aluminum layers after annealed at 250-350 °C was randomly distributed. The tensile property of this novel composite has achieved a small improvement over the commercially available grades and delamination between the layers was identified as the key issue to improve in this fabrication technique.
Development of Ultra-Fine Grained Structure in an Al-5.4%Mg-0.5%Mn Alloy Processed by ECAP
Authors: Kipelova Alla , Nikulin Ilya , Malopheyev Sergey , Kaibyshev Rustam
Published: December 2010

Microstructural changes during equal channel angular pressing (ECAP) at the temperatures of 250 and 300°C to the strains ~4, ~8 and ~12 were studied in a coarse-grained Al-5.4%Mg-0.5%Mn-0.1%Zr alloy. At a strain of ~4, the microstructural evolution is mainly characterized by the development of well-defined subgrains within interiors of initial grains and the formation of fine grains along original boundaries. Further straining leads to increase in the average misorientation angle, the fraction of high-angle grain boundaries and the fraction of new grains. However, only at 300°C, the plastic deformation to a strain of ~12 leads to the formation of almost uniform submicrocrystalline (SMC) grained structure with an average crystallites size of ~ 0.5 m. At 250°C, the microstructure remains non-uniform and consists of subgrains and new recrystallized grains. The mechanism of new SMC structure formation after ECAP is discussed.
Microstructure Evolution in a Cu-Ag Alloy during Large Strain Deformation and Annealing
Authors: Shakhova Iaroslava , Sakai Yoshikazu , Belyakov Andrey , Kaibyshev Rustam
Published: December 2010

The structural changes and the strengthening of a Cu-3%Ag alloy subjected to large strain drawing and subsequent annealing were studied. The cold working was carried out at an ambient temperature up to total strain above 8. The hardness increased from 600 MPa in the initial state to about 1800 MPa with increasing the total strain. The annealing treatment at 400°C resulted in increase in the hardness to about 2000 MPa for the samples cold worked to total strains above 2. On the other hand, the hardness change of the samples annealed at 450°C dependent significantly on the preceding cold strain. Namely, annealing softening took place in the samples processed to strains below 5, while the samples processed to larger strains were characterized by remarkable hardening after annealing. The value of annealing hardening increased with increasing the previous cold strain, leading the hardness to 2500 MPa in the sample strained to 7.4. The cold worked and annealed samples were characterized by the development of lamella-type microstructure consisting of highly elongated copper grains with uniform distribution of nano-scaled silver particles having a size of about 2 nm.
Synergetic Effect of ECAP and Friction Stir Welding on Microstructure and Mechanical Properties of Aluminium Sheets
Authors: Nikulin Ilya , Kipelova Alla , Malopheyev Sergey , Kaibyshev Rustam
Published: December 2010

Friction stir welding (FSW) was used to join the submicrocrystalline (SMC) grained Al-Cu-Mg-Ag sheets produced by equal channel angular pressing (ECAP) followed by hot rolling (HR). The effect of SPD and FSW on the microstructure and mechanical properties in the zone of base metal, as well as in the stirred zone (SZ) were examined. In addition, effect of standard heat treatment on microstructure and mechanical properties in these zones was considered. A refined microstructure with an average grain size of ~ 0.6 m and a portion of high-angle grain boundaries (HAGBs) of ~0.67 was produced in sheets by ECAP followed by HR at 250°C. The microcrystalline grained structure with average grain size of ~2.3 mm was found in joint weld. The moderate mechanical properties were revealed in SMC sheets and joint welds. Heat treatment considerably increases strength of the base metal as well as the joint welds. The higher strength of the alloy after T6 temper is attributed to the dense precipitations of  dispersoids having plate-like shape which are uniformly distributed within aluminum matrix. It was observed that FSW can produce full strength weld both in the tempered and in the un-tempered conditions.
Microstructure and Properties of Cu-5.7%Cr In Situ Fibrous Composite Produced by Equal-Channel Angular Pressing and Cold Rolling
Authors: Wei Wei , Wang Fei , Wei Kun Xia , Alexandrov Igor V. , Hu Jing
Published: December 2010

The composite filament structure was produced in Cu-5.7%Cr as-cast alloy ingots, subjected to equal channel angular pressing (ECAP) and cold rolling (CR) at room temperature. Microstructure, tensile properties and electrical conductivity before and after the severe plastic deformation (SPD) processing have been investigated here. The results point out that the rotation and spreading of Cr particles took place during ECAP and the additional rolling resulting in long thin in situ filaments. The average grain size of a Cu phase is equal to about 200 nm after eight ECAP passes. The formation of finer equiaxed grains of the Cu phase has been revealed after the additional CR. The tensile strength 403 MPa and 507 MPa have been achieved after one and eight ECAP passes respectively and increased up to 517 MPa and 607 MPa after the subsequent CR deformation. The enhancement of the tensile strength and the deterioration of the electrical conductivity have been explained by the microstructure evolution of Cu matrix and the dendritic Cr phase.
Microstructure and Mechanical Properties of Ultra-Fine Grain AZ80 Alloy Processed by Back Pressure Equal Channel Angular Pressing
Authors: Zhang Nian Xian , Ding Hua , Li Ji Zhong , Wu Xiao Lin , Li Ying Long , Xia Kenong
Published: December 2010

Experiments were conducted on AZ80 magnesium alloy by using a procedure of back pressure equal-channel angular pressing (BP-ECAP) in order to achieve submicron grain size. Microstructure was effectively refined by BP-ECAP. The gain size was found around 100~500 nm after 4 passes using both route A and route Bc at pressing temperatures of 200°C and 150 °C. The grain size was much finer in comparison with the same alloy but received conventional procedure of ECAP without back pressure, which maintains around 2~3 μm after 8 passes at relatively high temperatures. Compression test results showed the yield strength increased with increasing applied pass. In addition, the samples processed using route A had a increasing of yield strength more obvious than that in samples processed using route Bc. The highest yield strength from the sample pressed by route A at 150 °C was more than twice of the yield strength in the solution-treated and forged condition.
Processing of Ultrafine Grained Cu-30%Zn Alloy through Severe Plastic Deformation Using Accumulative Roll Bonding
Authors: Hashemi Sayed Ghafar , Eghbali Beitallah
Published: December 2010

In the present research, the microstructural features of ultrafine grained Cu-30 Zn alloy via ARB at room temperature were investigated by X-ray diffraction peak profile analysis. The character of dislocations was determined by analyzing the dislocation contrast factors. The average contrast factors for the different reflections obtained by determination of the type of dislocations and Burgers vectors in crystals. Also, using the modified Williamson–Hall and Warren–Averbach procedure size parameters, the effective outer cut-off radius and density of dislocations were determined. Assuming that the grain size distribution is log-normal, the median and the variance of the size distribution of sub grains were obtained. It was found that the crystallite size is reduced substantially, while the dislocation density increases up to 2 cycles of ARB. After 2nd cycle, dislocation density decreases. This is attributed to the occurrence of dynamic restoration process which takes place during next ARB cycles.
Effect of Severe Plastic Deformation on Microstructure and Properties of Al-Cu-Mg-Ag Aluminum Alloys
Authors: Xiao Dai Hong , Song Min , Chen Kang Hua
Published: December 2010

The Al-Cu-Mg-Ag heat-resistant alloy were prepared by ingot metallurgy technology. Effects of serve plastic deformation on microstructure and mechanical properties of the alloy were investigated by microscopy, differential scanning calorimetry and hardness tester. It has been shown that serve plastic deformation in the solid solution and quenching state with aging treatment was found to be quite effective in refining the grains to 2 μm, and improving the mechanical properties and heat-resistant properties of the extruded Al-Cu-Mg-Ag alloy. Serve plastic deformation treatment accelerates the aging hardening process of the extruded alloys, increases the density of precipitate phase.
Effect of Ultrasonic Treatment on the Microstructure and Properties of Nanostructured Nickel Processed by High Pressure Torsion
Authors: Nazarova Asiya , Mulyukov Radik R. , Tsarenko Yuriy , Rubanik Vasiliy , Nazarov Ayrat A.
Published: December 2010

The effect of ultrasonic treatment on the microstructure, microhardness and thermal stability of pure nickel after high pressure torsion (HPT) was studied. It was shown that the ultrasonic treatment reduces internal stresses induced by severe plastic deformation. The higher the intensity of ultrasound in the range studied, the stronger is this effect. Also it was revealed that grain growth in nickel processed by HPT followed by ultrasonic treatment occurs at higher temperatures than that in nickel as-processed by HPT, i.e. the thermal stability of nanostructured nickel is increased.
Mechanism of Grain Refinement Induced by Severe Plastic Deformation
Authors: Kratochvíl Jan
Published: December 2010

Within the framework of crystal plasticity the grain refinement observed in metals exposed to severe plastic deformation(SPD) is interpreted as an energy minimization process. For a crystalline solid it is less energetically costly to be fragmented in small regions(subgrains) deformed by a reduced number of slip systems and fitted together by local reorientations than to be deformed by homogeneous multislip.The energy minimization enhanced by hardening tends to reduce the size of the subgrains. On the other hand, the refinement increases the area of the boundaries between the subgrains, hence, it increases interface energy. Thus, the size of the subgrains is the result of a competition between these two tendencies:the internal and dissipative energy tend to decrease the refined structural size, whereas the interface energy opposes this tendency. Moreover, the formed substructure pattern follows the orientation of the active slip systems. The effective rotation of the active slip systems, which is a basic charac-teristic of SPD processing techniques, enhances the refinement process. It is proposed that the effective rotation causes a continuous reconstruction of the substructure pattern. The hindered destruction of the previous pattern leads to an increased hardening thus reducing the size of the subgrains. The proposed approach is demonstrated in the analysis of the refinement process induced by high pressure torsion and the results are correlated with the available observations.
Nano-Crystalline Structure in Mg2Si/Mg-2.5Er-5Zn Composite on the Route of Repeated Plastic Working Process
Authors: Du Wen Bo , Wang Xu Dong , Wang Zhao Hui , Li Shu Bo
Published: December 2010

The Mg-5Zn-2.5Er matrix composite reinforced with the in-situ synthesized Mg2Si second phase particles was fabricated via repeated plastic working (RPW) process. The microstructures and the nanocrystals in the composite have been investigated using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HREM) and energy dispersive X-ray (EDX). Great deals of nanocrystals were found in the matrix, and they were around the in-situ synthesized Mg2Si. The HREM analysis showed that the size of nanocrystals was in the range of 5-10 nm, and the difference in their crystallographic orientation was bigger than 15°. It is suggested that the formation of nanocrystals in the matrix is attributed to the RPW deformation process and to the intensive stresse fields around the in-situ synthesized Mg2Si particles, which suppress the growth of nanocrystals by forming nonequilibrium grain boundaries containing disordered dislocation networks and junction disclinations.
Effect of Hydrostatic Pressure on the Microstructure and Mechanical Properties during and after High Pressure Torsion
Authors: Schafler Erhard
Published: December 2010

The presence of a hydrostatic pressure as a general feature of SPD methods is essential for achieving the high strains and the introduction of the high amount of lattice defects, which are necessary to establish new grain boundaries. Systematic investigations of High Pressure Torsion (HPT)-deformed Cu under variation of strain and hydrostatic pressure revealed marked differences between the in-situ torsional stress (torque measurement) and the post-HPT strength of the ultrafine-grained materials. These facts let assume the occurrence of relaxation processes (recovery/recrystallisation) of static character with respect to the release of the hydrostatic pressure after straining. In order to gain insight into the processes behind, a special experimental procedure was designed to simulate the hydrostatic pressure release. Investigations by X-ray line profile analysis and hardness measurement show marked influences of the pressure release on microstructure and strength. While the size of the coherently scattering domains is not strongly affected, the dislocation density decreases drastically and the arrangement of the dislocations within the subgrain structure changes to a less stress intensive one, upon the pressure release. In parallel the hardness decreases significantly and confirms the discrepancy between in-situ torque-stress and post-HPT strength.
SPD-Induced Grain Boundary Segregations and Superior Strength in UFG Al Alloys
Authors: Enikeev Nariman A. , Murashkin Maxim Yu. , Sauvage Xavier , Kazykhanov Vil U. , Valiev Ruslan
Published: December 2010

Two Al alloys (AA1570 and AA6061) in the solutionized state have been processed by HPT at room temperature to achieve a homogeneous UFG structure. After HPT, the grain size was found to have a mean value about 100 nm for both alloys. Measured yield stress values of HPT-produced UFG alloys being plotted in terms of the Hall-Petch relationship were found to exceed the plot predictions for the range of ultrafine grain size. For both alloys, Atom Probe Tomography measurements allowed to reveal segregation of solute elements along grain boundaries. The origin of the extremely high strength of the alloys nanostructured by HPT is discussed with a special attention to the influence of such segregations on the emission and the mobility of dislocations.
An Overview on the Fracture Behavior of Metals Processed by High Pressure Torsion
Authors: Hohenwarter Anton , Pippan Reinhard
Published: December 2010

Motivated by the large variety of enhanced properties of ultrafine and nanocrystalline materials such materials are under extensive investigation. Besides focusing on classical material parameters, like strength and ductility, the fracture toughness of these materials is also of great importance, especially when the damage tolerance is required. In this contribution an overview of the fracture behavior of different metals covering ultrafine-grained iron and nickel as well as a nanocrystalline steel processed via high pressure torsion (HPT) will be given. It will be shown that the specimen orientation can have a tremendous influence on the fracture behavior and toughness. Due to this toughness anisotropy an unexpectedly good combination of high strength and high fracture toughness can be achieved very often in these materials.