bluuebunny/crossref_metadata_2025 huggingface dataset:
Machining and Mechanical Characterisation of PM Materials for Valve Seat Inserts
Authors: Jesus Filho E.S. , Salgado Lucio , de Jesus S.L. , Rossi J.L. , Colosio Marco Antonio , Santos José Carlos
Published: March 2009

This article shows some fabrication aspects related to the obtention of sintered valve seat insert. This insert was made of a mixture of high-speed steel powders and iron powders plus NbC. This is a new development aiming the substitution of Co alloys currently used for valve seat inserts. The physical properties, mechanical properties and machining behaviour are discussed. The machining characteristics in terms of tool wear, cutting forces and chips morphology of the insert was compared to available commercial insert. The machining results indicate that the material under development has potential for commercial application and shows good machining evidences, in terms of equivalent cutting forces for ceramic tool. In addition, the machining using hard metal tool was susceptible to hardness variation observed for the material under development. Therefore, the machining tests point out the necessity for a microstructure homogenisation of the obtained material.
Modelling Strain Induced Precipitation of Niobium Carbonitride during Multipass Deformation of Austenite
Authors: Sellars C.M. , Palmiere Eric J.
Published: March 2009

A new model of strain induced precipitation in niobium microalloyed austenite is proposed. This is based on the experimental observation of formation of microbands during hot deformation of iron – 30% nickel, which remains austenitic to room temperature. Precipitates are preferentially nucleated on nodes in the dislocation network in the microbands. This geometry enables features of earlier models to be simply explained, and facilitates extension of the model to multipass deformation. It is shown that the model captures all the essential features of previous experimental observations on microalloyed C – Mn steels. Currently, sensitivity analysis of the model and systematic experimental work are being undertaken to quantitatively validate the model.
Influence of Boron on Dynamic Recrystallization and Continuous Cooling Transformation of High Strength Interstitial Free Steels
Authors: Kim S.I. , Paik D.J. , Lee Young Seog , Choi Shi Hoon
Published: March 2009

The paper examines the effect of boron (B) on the dynamic recrystallization and continuous cooling transformation (CCT) behavior in Nb-Ti microalloyed high strength interstitial free (IF) steels. For this purpose, two Nb-Ti microalloyed IF steels containing 0.003wt.% and 0.0005wt.% B, respectively, and one IF steel without B were chosen. The dynamic recrystallization behavior was investigated using hot compression testing. The character of the austenite to ferrite transformation during continuous cooling was studied by dilatometry test and CCT diagrams for the IF steels have been constructed. It was found that the initiation of dynamic recrystallization is delayed as the amount of boron increases. Addition of B retards the austenite to ferrite transformation as well. Under cooling rates of 0.5 and 1oC s-1, which correspond to slow cooling rates in the hot strip mill, the addition of B leads to the development of acicular ferrite and bainite phases. On the other hand, at similar cooling conditions the B free IF steel was observed to have a polygonal ferrite microstructure.
Ferrite Grain Size Refinement in Vanadium Microalloyed Structural Steels
Authors: Hernandez D. , López Beatriz , Rodriguez-Ibabe J.M.
Published: March 2009

The addition of small quantities of vanadium in structural steels produces a significant refinement in the final ferrite microstructure. There are two different mechanisms contributing to refinement: enhancement of grain boundary ferrite nucleation and intragranular nucleation. The contribution of each mechanism depends on the vanadium content and heat treatment of the steel. In this study the contribution of both refining mechanisms has been evaluated for two V-microalloyed steels subjected to different heat treatments. The results confirm that this refinement is based on the enhancement of ferrite nucleation through particle-stimulated nucleation mechanisms, while other aspects, as the influence of vanadium slowing down the austenite-ferrite transformation kinetics, seem to exert a minor effect.
Precipitation Strengthening in a Low Carbon Nb-Microalloyed Steel
Authors: Bai D.Q. , Hamad F. , Asante J. , Hansen S.
Published: March 2009

Among modern weldable high strength steels, low carbon microalloyed steels have been widely used for linepipe, construction, and automobile industries. One of the major technical components to successfully produce these steels is to effectively use precipitation strengthening. In the present paper, the effect of an aging treatment on the microstructure and mechanical properties of a low carbon Nb-microalloyed steel is analyzed.
Application of Niobium in Quenched and Tempered High-Strength Steels
Authors: Hulka Klaus , Kern A. , Schriever U.
Published: March 2009

This article offers an overview on the ways and means of the application of Nb in
quenched and tempered high-strength steel plates. Thereby, the outstanding role of Nb to control the austenite microstructure during rolling or heat treatment and to contribute to effective precipitation hardening is discussed. It is shown, that Nb is very effective to retard the transformation processes during quenching. For high-strength constructional steels with up to 1100 MPa yield strength and for wear resistant steels, the improvement in strength and toughness properties in Nb microalloyed steels as compared to Nb-free steels is pointed out. A remarkable effect is the improvement in toughness and brittle fracture resistance due to a very fine microstructure and finely dispersed Nb carbonitrides in a martensitic microstructure. Fields of application for the new Nb microalloyed high-strength structural steels are presented too.
Characterisation of Niobium Carbide and Carbonitride Evolution within Ferrite: Contribution of Transmission Electron Microscopy and Advanced Associated Techniques
Authors: Courtois Eglantine , Epicier Thierry , Scott Colin
Published: March 2009

Niobium is a strong carbide forming element which is often used in microalloyed steels to control the grain size during thermomechanical treatments and to provide strengthening through precipitation processes. A detailed microscopic investigation is one of the keys for understanding the first stages of the precipitation sequence, thus Transmission Electron Microscopy (TEM) is required. The main difficulty of TEM studies is due to the nanometre scale dimensions of the particles, which makes their detection, structural and chemical characterization delicate. Model Fe- (Nb0.06%,C0.05%) and Fe-(Nb0.05%,C0.03%,N0.03%) ferritic alloys subjected to isothermal annealing treatments have been investigated. High Resolution TEM (HRTEM) and conventional TEM (CTEM) were used to characterise the morphology, nature and location of precipitates. Volume fraction measurements and a statistical approach to the determination of precipitate size histograms have been investigated using Energy Filtered TEM (EFTEM) and High Angle Annular Dark Field (HAADF) imaging. Chemical compositions were quantified by Electron Energy Loss Spectroscopy (EELS). The evolution of precipitate composition with time and temperature is compared with previous simulations obtained from new thermodynamic models based on equilibrium boundary conditions.
Interfacial Structure and Strength of Ceramic/Metal Couples
Authors: Naka Masaaki , Schuster Julius C.
Published: March 2009

SiC reacts with metals at high temperatures, and forms metal carbide, metal silicide and metal carbosilicide depending on metal. The interface structure is formed by the diffusion path between SiC and metal. The diffusion path between SiC and metal is described on the tie-lines of the corresponding M-Si-C (M:Metal) ternary phase diagram. The interfacial strength of SiC/Metal depends on the thickness of reaction zones at SiC/Metal couple. Although the increase of thickness of reaction zone improves the interfacial strength of SiC/Metal couple, the increase of internal stress and crack in the reaction zone degrades the strength of the couple. The interfacial strength of SiC/Metal couple yields the maximum at a thickness of reaction zone.
Characterization of Grain Boundaries in Recrystallized L12-Type Intermetallic Alloys
Authors: Kaneno Yasuyuki , Takasugi Takayuki
Published: March 2009

Microstructural feature of the recrystallized Co-based (Co3Ti) and Ni-based (Ni3(Si,Ti) and Ni3Fe) ordered alloys with L12 structure was investigated by the electron backscatter diffraction (EBSD) method, with emphasis on grain boundary character distribution (GBCD). For comparison, the GBCDs of the recrystallized Co-Ni, Ni-Fe and 70/30 brass disordered alloys, and also copper, nickel and aluminum pure metals with A1 (fcc) structure, which have widely different stacking fault energies, were also determined. The frequency of Σ3 boundary for the Co-based alloys was higher than that for the Ni-based alloys, regardless of ordered L12 alloy or disordered fcc alloy, indicating that the frequency of Σ3 boundary was primarily dominated by stacking fault energy. Furthermore, the effect of ordering energy on structure and energy of the grain boundaries including Σ3 boundary in the ordered L12 alloys was discussed.
In Situ X-Ray Diffraction Measurement of Electrodeposition Process in Molten Salts
Authors: Kajinami Akihiko , Deki Shigehito , Umesaki Norimasa , Sato Masugu , Myochin Munetaka
Published: March 2009

In-situ X-ray diffraction (XRD) method has been developed for the observation of elctrodeposition process in molten NaCl-2CsCl salt to investigate the mechanism of pyrochemical process of nuclear fuel reprocessing system. In this paper, the scattered X-ray beam from electrodepositing nickel in NaCl-2CsCl melt was measured by the reflection mode at BL19B2 beamline of SPring-8 as the preliminary experiment. The time dependence of the electrodepositing nickel in NaCl-2CsCl melt at 923K was investigated by the in-situ XRD measurements.
Study on Morph-Genetic Materials Derived from Natural Structure
Authors: Zhang Di , Fan Tong Xiang , Sun Bing He , Wang Tian Chi , Xie Xian Qing , Okabe Toshihiro
Published: March 2009

Synthesis of morph-genetic materials derived from biological structures by rapid, high temperature conversion represents a novel technology of advanced materials processing. The resulting morph-genetic materials exhibit unique macro- and microscopic cellular morphologies. In addition, based on the porous character of some natural plants, there is a further possibility of compounding the resulting morph-genetic materials with molten metal or polymer to produce morph-genetic composites with interpenetrating networks. Thus, the morph-genetic materials will be endowed with new use values, such as good mechanical properties, and friction behaviors, etc.
Study of the Nanometric Grain Size Distribution in Iron Compacts Obtained by Mechanical Milling
Authors: Lluma Jordi , Benito Josep Antonio , Roca Antoni , Cabrera Jose María , Prado Jose Manuel
Published: March 2009

A study has been carried out on the grain size distribution of cylindrical compacts obtained by consolidation of iron powder severely deformed by mechanical milling. Consolidation has been performed in two consecutive steps: cold and hot conditions. The hot one was done at two temperatures, namely 425 and 475°C. After milling, the iron powder has a grain size of 8 nm (± 4 nm) with an average hardness of 800 HV. After hot compaction the grain size increases up to 50 nm, especially at 475°C where a small fraction of grains reach larger values than the average. The grain size was evaluated by two different techniques, X-Ray Diffraction and Transmission Electron Microscopy. Results showed some differences between both methods. The advantage of using TEM is that grain size distribution, and not only the average size, can be obtained. Small discs were also obtained from the compacted specimen in order to fracture them on a “ball on three balls” equipment. The fracture behaviour of the samples was then studied by SEM.
Influence of Cu on the Mechanical Properties of an Al-4.4wt%Mg Alloy after ECAP
Authors: Verlinden Bert , Popović M.
Published: March 2009

Two Aluminium alloys, type AA5182 and AA5182+1.2wt% Cu, have been studied. The second alloy in solution treated condition is 18% stronger than the first one. During ageing at 150°C or 200°C it shows a characteristic fast increase in yield strength during the first minutes of ageing, followed by a 'plateau'. Both materials have been deformed in an ECAP die (4 and 8 passes) at 200°C and the microstructure, hardness and mechanical properties in compression at room temperature have been investigated. Although in none of the two materials a true sub-micron grain size was obtained at 200°C, a fair combination of strength and strain hardening was observed. The AA5182+Cu alloy, when ECAP’ed after a solution treatment and quenching, shows an increase in strength of about 20% compared to the AA5182 reference alloy. A post-ECAP annealing at 200°C does not lead to a further increase in hardness or strength. An analysis of the substructure and the mechanical properties during ECAP led to the conclusion that the precipitates formed during ECAP at 200°C do not directly contribute to the higher strength of alloy AA5182+Cu, but they contribute indirectly by slowing down the recovery.
Deformation Twins Formed in Nanocrystalline Materials
Authors: Zhu Yuntian T.
Published: March 2009

Deformation twins have been oberved in nanocrystalline (NC) Al synthsized by cryogenic ball-milling and in NC Cu processed by high-pressure torsion under room temperature and at a very low strain rate. They were found formed by partial dislocations emitted from grain boundaries. This paper first reviews experimental evidences on deformation twinning and partial dislocation emissions from grain boundaries, and then discusses recent analytical models on the nucleation and growth of deformation twins. These models are compared with experimental results to establish their validity and limitations.
Grain Boundary Diffusion-Controlled Processes and Properties of Bulk Nanostructured Alloys and Steels
Authors: Kolobov Yu.R. , Ivanov Konstantin V.
Published: March 2009

The experimental and theoretical investigations of grain boundary diffusion processes have been performed using metals and alloys in nanostructured state produced by severe plastic deformation and the respective polycrystalline counterparts. The main features of diffusioncontrolled mechanisms of plastic deformation observed by the creep of nanostructured metals are considered. The use of severe plastic deformation treatment and of the effect of activation of diffusion-controlled processes for enhancing the properties of nanostructured steels and alloys designed for engineering and medical applications (nanostructured titanium-bioactive coating composite included) is described and examples are offered.
Microstructural Evolution during Friction Stir Welding of Ultrafine Grained Al Alloys
Authors: Sato Yutaka S. , Urata M. , Kurihara Y. , Park S.H.C. , Kokawa Hiroyuki , Ikeda Kazutaka , Tsuji Nobuhiro
Published: March 2009

Recently, several metallic materials with ultrafine-grained structures and characterized by high strength and toughness have been developed. When these ultrafine-grained materials are practically used, welding and joining processes are required. However, conventional fusion welding processes result in deterioration of the good mechanical properties of these ultrafine-grained materials due to the drastic grain growth of the ultrafine grains. On the other hand, friction stir welding (FSW) is a solid-state joining process having lower heat-input than fusion welding processes, enabling formation of a fine grain structure in the stir zone. Thus, this process would effectively alleviate deterioration of mechanical properties of the ultrafine-grained materials. The authors applied FSW to ultrafine-grained Al alloys and then examined the microstructural features associated with hardness in the friction stir welds. The present paper reviews microstructural evolution of ultrafine-grained Al alloys, produced by equal channel angular pressing (ECAP) and accumulative roll-bonding (ARB), during FSW.
Developing a Model for Grain Refinement in Equal-Channel Angular Pressing
Authors: Xu Cheng , Furukawa Minoru , Horita Z. , Langdon Terence G.
Published: March 2009

It is now recognized that processing by equal-channel angular pressing (ECAP) leads to very significant grain refinement in polycrystalline materials with the as-pressed grains typically having sizes within the submicrometer range. Furthermore, the materials produced by ECAP exhibit many useful properties including a high strength at ambient temperatures and, if these ultrafine grains are retained to elevated temperatures, a potential for superplastic forming. This paper examines the fundamental characteristics of grain refinement by making use of two sets of experimental observations: experimental data obtained from the pressing of aluminum single crystals through one pass of ECAP and hardness measurements taken on polycrystalline aluminum for samples subjected to ECAP for up to a total of eight passes. These experimental results are used to develop a microstructural model that provides a satisfactory explanation for the grain refinement occurring in ECAP.
Monotonic and Cyclic Behavior of Ultrafine Grain Metals:Overview
Authors: Vinogradov Alexei
Published: March 2009

The available to date experimental results are reviewed with regard to the common aspects and features of monotonic and cyclic stress-strain behavior of various ultra-fine grain materials produced by severe plastic deformation (SPD). Some possible mechanisms of plastic flow and degradation during monotonic and cyclic testing are discussed from the standpoint of initial SPD structure and its evolution upon loading. The role of two strengthening mechanisms – dislocation accumulation and grain reduction - is highlighted. The key importance of grain boundaries for the mechanical behavior, strain localization and fracture of ultra-fine grain metals is argued and the experimental evidence is presented on the significance of grain boundary sliding in their plastic deformation. The results of phenomenological modeling of the monotonic and cyclic response of ultra-fine grain metals are presented in terms of dislocation kinetics and a satisfactory agreement with experimental data is demonstrated.
Effect of the Temperature of Accumulative Roll Bonding on the Microstructure and Properties of Twin-Roll Cast AA8006 Alloy
Authors: Homola Petr , Slámová Margarita , Karlík Miroslav , Čížek Jakub , Procházka Ivan
Published: March 2009

Accumulative Roll Bonding (ARB) does not require any special equipment and enables the production of large amounts of ultra-fine grained (UFG) materials. Grain refinement is thermally stable in materials with finely dispersed particles such as twin-roll cast (TRC) aluminium alloy sheets, favourable materials for manufacturing UFG sheets. The results of a study of the effect of ARB temperature on bonding quality, structure and properties of TRC AA8006 sheet are presented. Examinations by light and transmission electron microscopy, positron annihilation spectroscopy (PAS), hardness and tensile tests were used in the study. After two cycles at 200°C, mean grain size of 0.4 - 0.8 μm is achieved, but areas with extremely fine grains of 0.1 to 0.3 μm in diameter are also observed. Hardness increases significantly after two cycles and it rises a little in subsequent cycles. Processing at higher temperatures (up to 350°C) results in better bonding but it produces smaller increase in hardness. Significant increase of dislocation density is observed by PAS after the first cycle at 250°C but it does not continue during subsequent cycles. Partial recrystallization occurs in samples processed at temperatures above 250°C explaining the smaller increase in hardness. Softening level depends on both ARB temperature and number of cycles. The thermal stability of refined structures produced by ARB at 250°C is better than these formed at higher temperatures.
Microstructure and Mechanical Properties Resulting from Conventional Cold Extrusion of Equal Channel Angular Extruded Aluminium Alloy AA6101
Authors: Nagarajan D. , Uday Chakkingal , Venugopal P.
Published: March 2009

Severe plastic deformation processes like equal channel angular extrusion (ECAE) have been widely investigated for their ability to produce nano/ ultra fine-grained microstructures. It is well known that submicron sized grains/ sub grains can be produced in most Al alloys using this technique. However, industrial applications of ECAE will depend heavily on the advantages conferred by this process when it is used as an intermediate processing step prior to conventional forming. In the current investigation, the influence of pre processing by ECAE on subsequent post processing by conventional cold extrusion has been investigated. ECAE extrusion was carried out on cylindrical specimens of AA 6101 using an ECAE die with a die angle of 120 degrees. Extrusion was carried out for three passes using two different processing routes. The ECA extruded specimens were subsequently subjected to conventional cold extrusion. The differences in extrusion pressures, which have a strong influence on industrial applications, were noted. Changes in microstructure and mechanical properties were also determined. The obtained results of mechanical properties and microstructure evaluation show that for high strains (strain ε ≈ 2.01), ECAE through some processing routes can be effectively used as an intermediate processing step prior to conventional cold extrusion to obtain a product with enhanced mechanical properties.
Hydrostatic Extrusion as a Method of Grain Refinement in Metallic Materials
Authors: Kurzydlowski Krzysztof Jan
Published: March 2009

The paper describes hydrostatic extrusion (HE) as a method of grain refinement of metallic materials down to the nanometric scale. The main features of this method are: (a) large strain, (b) very high strain rates (even greater than 104 s-1), and (c) deformation homogeneity. HE offers also the opportunity of obtaining bulk materials in a variety of forms (rods and wires of complex cross-sections, small tubes). The study undertaken on 4 materials (aluminium, aluminium alloy, copper and titanium) has shown that significant grain refinement , down to nanometric scale in the case of titanium and aluminium alloy, occurred during HE processing. This grain refinement produces significantly improved mechanical properties. It has been found that HE offers good prospects for the production of nano-structured metals and alloys.
Deformation Mechanics Associated with Formation of Ultra-Fine Grained Chips in Machining
Authors: Sevier Michael , Lee Seongeyl , Shankar M. Ravi , Yang Henry T.Y. , Chandrasekar Srinivasan , Compton W. Dale
Published: March 2009

The deformation field associated with chip formation in plane strain (2-D) machining has been simulated using the finite element method (FEM), with the objective of developing 2-D machining as an experimental technique for studying very large strain deformation phenomena. The principal machining parameters are the tool rake angle, cutting velocity and the friction at the toolchip interface while the deformation field parameters are strain, strain rate and temperature. The relation between rake angle and the shear strain in the deformation zone is studied for the low-speed cutting of lead. This correspondence is validated by comparison with measurements of the deformation parameters made by applying a Particle Image Velocimetry (PIV) technique to highspeed photographic image sequences of the deformation. It is shown that plastic strains in the range of 1-15 can be realized in a controlled manner by appropriate choice of the rake angle. The unique capabilities offered by 2-D machining for studying micro- and nano- mechanics of large strain deformation, and the creation of ultra-fine grained materials are highlighted in the context of these results.
Continuous Grain Refinement Using Severe Torsion Straining Process
Authors: Nakamura Katsuaki , Neishi Koji , Kaneko Kenji , Nakagaki Michihiko , Horita Z.
Published: March 2009

This study presents a new rapid continuous process for grain refinement in metallic materials through severe plastic deformation (SPD). The new process, designated in this study the severe torsion straining process (STSP), is applicable to a wide range of alloys based on aluminum, magnesium and copper including carbon steel. This process consists of producing a local heated zone in a rod and cooling both sides of the heated zone by spray water while rotating one end with the other. Thus, torsion strain is introduced in the local heated zone. The STSP can be continuous because the straining is achieved while the rod is shifted along the longitudinal axis of the rod. Furthermore, the process requires no die, suggesting a potential for commercialization of grain refinement through SPD. In this study, STSP was applied to an Al-Mg alloy and a Mg-Al-Zn alloy. It is shown that STSP is effective for both alloys so that the grain size is reduced to ~1.5 μm for the Al alloy and ~0.9 μm for the Mg alloy. Tensile testing showed that the strength is increased with a minimal decrease in uniform elongation. There is a critical ratio between rotation speed and moving speed, which defines the feasibility of STSP operation without breaking the rod. The grain size tends to be lowered as the ratio is close to the critical value.
Application of High Pressure Torsion to Bulk Samples
Authors: Sakai Genki , Nakamura Katsuaki , Horita Z. , Langdon Terence G.
Published: March 2009

High pressure torsion (HPT) is a well-known procedure to impart severe plastic deformation (SPD) into metallic materials. It was reported that HPT produces grain sizes finer than those using other SPD processes such as equal-channel angular pressing (ECAP). However, the application of HPT has been restricted to thin disk samples. In this study, an HPT process was developed for use with bulk samples. This process is designated as Bulk-HPT for comparison with conventional Disk-HPT. Cylindrical samples of an Al-3%Mg-0.2%Sc alloy having dimensions of 10 mm in diameter and 8.6 mm in height were prepared for Bulk-HPT. The samples were strained under a pressure of 1 GPa for 2 turns at room temperature. Microstructural observations revealed that the samples contained regions having a grain size of ~130 nm. Tensile testing showed a superplastic ductility ~480 % at 673 K with an initial strain rate of 3.3x10-2 s-1.
Differences in Structural Evolution in Single- and Dual-Phase Materials during Severe Plastic Deformation
Authors: Pippan Reinhard , Vorhauer A. , Wetscher F. , Faleschini M. , Hafok Martin , Sabirov I.
Published: March 2009

Severe plastic deformation (SPD) has been applied to two classes of metallic materials, single phase and dual phase materials. The applied shear strain has been varied between 1 and 1000 and the homologous temperature between 0.08 and 0.4. The deformation experiments are performed by high pressure torsion (HPT). The resulting microstructures were investigated by backscattered electron imaging, orientation image microscopy, and in selected cases by transmission electron microscopy. It will be shown that the behavior of single phase material is relatively uniform. With increasing strain, the size of the structural elements decreases and reaches a saturation between a shear strain of 10 to 100. The temperature and the alloying are the main parameters, which controls the saturation size of the structural elements (grains). The behavior in the dual phase materials is more complex, it varies from simple homogenisation, fragmentation of one phase, to desintegration and supersaturation of the phases.
Formation of Supersaturated Solid Solutions in Al Alloys with Transition Metals Upon Shear under Pressure
Authors: Brodova I.G. , Bashlykov D.V. , Shirinkina I.G. , Lennikova I.P.
Published: March 2009

Metallographic, X-ray diffraction and electron microscopy were used to study the phase compositions and structure of rapidly solidified the Al- alloys transition metals (Zr, Fe, Cr) subjected to severe plastic deformation (SPD) by torsion under a high quasi-hydrostatic pressure. It was established that upon SPD a number and a size of aluminides decrease with increasing a degree of deformation. For example, the maximum effect of deformation - induced dissolution of the particles are observed in the case where they have a dendritic structure and are about one μm in size. Upon SPD the supersaturation of α-phase increases by a factor of 2.5. (for rapidly solidified Al-Cr and Al-Cr-Zr alloys) and by a factor of 10 (for rapidly solidified Al-Fe alloy). After SPD all alloys have submicrocrystalline (SMK) Al-based matrix with grain size of 100-200 nm and high hardness of 2 GPa.
The thermal stability of SMK deformed materials and some specific features of post deformation phenomena as an aging and a recrystallization were investigated.
Deformation Behavior of Fine Grained Al-Mg Alloy under Biaxial Stress
Authors: Noda Masafumi , Funami Kunio
Published: March 2009

The grain boundary sliding and the formation of slipped bands and cavitations during biaxial tensile deformation were examined in fine grained Al-Mg alloy. Biaxial tensile testing was conducted with cruciform specimens at initial strain rates of 10-4 to 101s-1. It was found that at the same equivalent strain conditions, the number of cavities under biaxial tension is significantly greater than that under uniaxial tension. A greater prevalence of slipped bands and grain separations were clearly observed under biaxial stress than under uniaxial stress. It was suggested that development of slipped bands resulted from the formation of elongated cavities and multiple deformed bands under biaxial stress. Additionally, the m-value under biaxial stress remained at about 0.3 over a wide range of strain rates. The effects of grain separation and formation of cavities were related to the motion of grain boundary sliding, grain size and loading conditions.
Elaboration by Severe Plastic Deformation, Microstructural and Mechanical Study of Cu/X (X =Ta or Nb) Nanofilamentary Wires for Use in High Field Magnet
Authors: Vidal Vanessa , Thilly Ludovic , Lecouturier Florence
Published: March 2009

Nanofilamentary wires consisting of a Cu matrix reinforced by body centred cubic (bcc) nanofilaments were produced by successive hot extrusion and large strain drawing. Effects of this severe plastic deformation on the microstructure and the mechanical properties of two systems, Cu/Ta and Cu/Nb/Cu “co-cylindrical” structure, are presented and compared with the nanofilamentary Cu/Nb wires.
Mechanical Behaviour of Nanostructured Iron Fabricated by Severe Plastic Deformation under Diffusion Flow of Nitrogen
Authors: Yurkova A.I. , Byakova A.V. , Belots'ky A.V. , Milman Yu.V. , Dub Sergey N.
Published: March 2009

Specific features of mechanical behaviour of ultra fine grained iron subjected to friction treatment with nitriding (FN) were clarified by comparison with that induced by friction treatment (FT) with air. Mechanical parameters such as Young’s modulus, nanohardness, and plasticity characteristic δA were found to be of high sensitive both to the scale of grain structure and to iron modification by nitrogen. Young’s modulus tends to decrease and Hall-Petch low fails to describe correlation between grain structure and hardness for submicro-grained and nanocrystalline iron. Hall-Petch coefficient, ky, decreases as grain size decreases within submicro-grained and, then, nano grained sections and it takes even negative value in nano grained section modified by nitrogen. Parameter δA is found to be dependent on combination of hardness and Young’s modulus, resulting in its variation with decreasing the grain size. The presence of secondary nanocrystalline Fe4N phase fundamentally changes mechanical behaviour of nanocrystalline iron, leading to strengthening the grain boundaries and triple junctions.
Influence of Processing Parameters on Texture and Microstructure in Aluminum after ECAP
Authors: Zhilyaev Alexandre P. , Oh-ishi Keiichiro , Raab Georgy I. , McNelley Terry R.
Published: March 2009

The influence of strain path during equal-channel angular pressing (ECAP) has been evaluated in pure aluminum by orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). The material was examined after four pressing operations by route BC in a 90° die, or eight pressing operations by route BC in a 135° die. The von Mises equivalent strains were essentially the same for these two ECAP procedures. The microtexture data indicate that the distortion during ECAP corresponds to a simple shear in a direction approximately parallel to diechannel exit and on a plane perpendicular to the flow plane. For both procedures the OIM data reveal prominent meso-scale band-like features. Lattice orientations in each band correspond to a texture orientation but the particular combinations of orientations depend upon ECAP die angle. High-angle boundaries in the structure correspond to interfaces between the bands.
Severe Plastic Deformation of Commercially Pure Titanium by Rotary-Die Equal Channel Angular Pressing Method
Authors: Watazu Akira , Shigematsu Ichinori , Ma Aibin , Nishida Yoshinori , Kwon Yong Jai , Suzuki Kazutaka , Imai Tsunemichi , Saito Naobumi
Published: March 2009

The commercially pure titanium cylindrical samples with a diameter of 11.5mm and a length of 24mm were processed by a new severe plastic deformation process, called the rotary-die equal channel angular pressing (RD-ECAP), under the condition of 773K, 2.4mm/s punch. By the RD-ECAP, ECAP processes of 1-4 passes were possible without sample removal and the temperature of cp-titanium could be simply controlled. After the RD-ECAP process, the cp-titanium samples had no crack. Fine-grained microstructures were observed in the sample on Y plane. Therefore the samples processed by RD-ECAP were expected to have high mechanical strength.
Metal Flow at Equal Channel Angular Pressing with Backpressure
Authors: Raab Georgy I.
Published: March 2009

In the present paper a flow pattern of aluminum alloy and copper was investigated by grid procedure, using 2D-modeling and experimental data for ECAP using backpressure. The most important parameters that influence upon flow pattern and deformed state of billets were revealed. We found the most optimal radii of intersecting channels to press the billets, having 16х16 mm in section, from the aluminum alloy and copper in backpressure conditions.
Microstructure and Properties of Ti Rods Produced by Multi-Step SPD
Authors: Latysh V.V. , Semenova Irina P. , Salimgareeva G.H. , Kandarov I.V. , Zhu Yuntian T. , Lowe Terry C. , Valiev Ruslan
Published: March 2009

This paper studies the effect of combined SPD treatment on microstructure and mechanical properties of semi-products out of CP Ti. The combined processing, consisting of equal-channel angular pressing and further thermomechanical treatment, produced ultrafine-grained rods out of Grade 2 CP Ti with a diameter of 6.5 mm and a length of up to 1 m. It was established that the formation of homogeneous ultrafine-grained structure in Ti rod with α-grain size of about 100 nm allowed to enhance yield stress by 200% in comparison with initial annealed state.
Creep and Mechanical Properties of a Commercial Aluminum Alloy Processed by ECAP
Authors: Xu Cheng , Langdon Terence G.
Published: March 2009

A commercial spray-cast aluminum alloy, having a composition of Al-11.5% Zn-2.5%
Mg-0.9% Cu-0.2% Zr, was processed by equal-channel angular pressing (ECAP) to give an ultrafine-grained microstructure with a grain size of ~0.3 μm and a fracturing of the rod-shaped MgZn2 precipitates. The mechanical properties of the alloy were investigated using microhardness testing at ambient temperature and tensile testing at a temperature of 673 K. In addition, creep tests were conducted using a double-shear testing facility at temperatures from 473 to 673 K. The results show the microhardness decreases with increasing numbers of passes in ECAP and high strain rate superplasticity is achieved after processing by ECAP at 473 K for 6 or 8 passes. A maximum elongation of >1000% was recorded at a strain rate of 10-2 s-1 when testing at 673 K. The creep tests show the creep rates are faster in the as-pressed material than in the as-received material when testing at the same applied stress and testing temperature.
Microstructure Development during Equal Channel Angular Extrusion of an Al-3%Cu Alloy
Authors: Mazurina I. , Goloborodko Alexandre , Kaibyshev Rustam , Miura Hiromi , Sakai Taku
Published: March 2009

Microstructural evolution during equal channel angular extrusion (ECAE) was investigated in a coarse-grained dilute aluminum alloy, Al-3%Cu, at a temperature of 250oC. Scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD) and optical metallography (OM) was used to reveal the structural changes in the alloy deformed up to a strain of ε=12. The microstructural evolution at initial and moderate stages of deformation is characterized by the formation of low angle boundaries and deformation bands with moderate misorientations in grain interiors. With further deformation the number and the misorientation of the deformation bands increase, finally leading to the subdivision of original grains by these bands and then the development of fine grains with an average size of about 6 μm at ε=12. The evolution of deformation bands in initial grain interiors and their role on new grain formation are discussed in detail.
Anelasticity and Structural Stability of ECAP Processed Al-Mg-Si Alloys Investigated by Mechanical Spectroscopy
Authors: Amadori Stefano , Pasquini Luca , Bonetti Ennio , Cabibbo Marcello , Scalabroni C. , Evangelista E.
Published: March 2009

Mechanical spectroscopy was employed to investigate the microstructure evolution of a Zr-modified 6082 Al-Mg-Si alloy and the same alloy with Sc addition after ageing and following severe plastic deformation through equal channel angular pressing. Measurements of the internal friction and dynamic young modulus have been performed in isothermal and isochronal runs in the frequency range 0.1 - 104 Hz. The anelasticity spectra reveal in the temperature range 470-870 K both structural and anelastic relaxation processes. Two structural damping maxima connected with
inverse temperature trend of the modulus occur in the alloys submitted to equal channel angular pressing, the first one is strongly suppresed by Sc and Zr addition. An anelastic relaxation peak whose strength depends on the nature and morphology of precipitates and dispersoids and on the deformation and ageing condition was observed in all samples investigated. The high background damping occurring before the first structural damping maximum is analyzed with reference to a superplastic behavior of the equal channel angular pressing processed alloys.
Severe Plastic Deformation of a Commercial Aluminium-Lithium Alloy (AA8090) by Equal Channel Angular Pressing
Authors: Llorca-Isern Nuria , Gonzalez P.A. , Luis-Pérez C.J. , Laborde I.
Published: March 2009

The enhanced mechanical properties of crystalline materials are linked to very small grain sizes. The AA8090 is a commercial aluminium lithium alloy is referred in the metallurgical literature by its superplastic behavior linked as well to nano-grains as obtained by ECAP. On this research-work in progress, the 8090 aluminium alloy is studied after being processed in a 400 kN ECAE press up to nine passes through a 90º angle-die at 150 °C following Route A (constant path) at a processing speed of 10 mm/min. The room temperature mechanical properties of the extruded alloy are investigated through hardness measurements and tensile tests. Elastic measurements have been carried out by means of nanoindentation and ultrasonic testing, showing that both texture and nanostructuration of the processed alloy influence on the elastic constant of the processed material. In order to understand the mechanisms involved in the SPD-ECAP process, microstructural characterisation of the alloy has been carried out using different high resolution techniques such as Transmission Electron and Atomic Force Microscopy. TEM results have also been used in order to evaluate grain size evolution. From this analysis it is possible to see that after 4 passages the initial grains have already a high degree of dislocations. Among the characterisation techniques, AFM in the surface potential mode has been used to evaluate discontinuities in the matrix and /or decohesion between matrix and precipitates. After nine ECAP passages, no signs of decohesion at the interface have been observed neither using FEG-SEM nor using AFM.
Principals of Indirect Equal Channel Angular Drawing for Processing of Ultrafine Grained Materials
Authors: Shan Ai Dang , Park Jong Woo , Moon In Ge
Published: March 2009

In this paper indirect ECA drawing method was supposed to be feasible for application. This method will ensure same deformation degree as that in ECAP while keep the size of the billet unchanged so that multiple processing can be done. With this method, materials with both rectangular and round section can be processed and there is no limit to the length of the materials. Die configuration was set up and the equations for relationship among die parameters, billet parameters and its properties, drawing forces and applying pressures are given.
Fine-Grained Structures Associated with Deformation Twin and Its Influence on Tensile Behaviours in a Cold-Rolled Fe-Ni Alloy
Authors: Morikawa Tatsuya , Moronaga Taku , Higashida Kenji
Published: March 2009

Fine-grained structures in Fe-36mass%Ni Invar alloy have been investigated by using transmission electron microscopy (TEM). Particular attention has been paid on the role of deformation twinning in the formation of fine-grained structures and its influence on tensile stressstrain behaviours of rolled specimens.
In Fe-Ni Invar alloy with a moderate stacking fault energy, deformation twin did not appear in usual cold-rolling at room temperature (RT), where a kind of cell walls was formed and the Cu-type texture was observed. On the other hand, twinning was occurred by rolling when specimens were cooled to liquid nitrogen temperature (LNT) immediately before the rolling. In such case, a fine lamellar structure was developed and the brass-type texture appeared. However, the lamella boundaries did not coincide with any crystallographic planes, and they were intersected with the bands of deformation twin. Specimens rolled by 90% in thickness reduction exhibited tensile stressstrain behaviours similar to those observed in specimens with SPD structures. In particular, specimens rolled at LNT showed high yield strengths and non-uniform deformation.
Constructing the Predictive Models of Friction Coefficient Using Cylindrical Compression Testing
Authors: Hsu Yuan Chuan , Yang Tung Sheng , Sung S.Y. , Chang Sheng Yi
Published: March 2009

In this study, the predictive model of friction coefficient using cylindrical compression was constructed through combining the finite element method and neutral networks. Namely, the related data of the materials characters, cylinder compression bulging, and how they were associated with friction coefficient was obtained by the finite element method. Based on those analysis data, the relationship model, reflecting the relationship among the materials characters such as strength coefficient and strain-hardening exponent, the compression bulging such as reduction height, expanding in upper ending, expanding in bottom ending, maximum expanding in outside diameter
and the friction coefficient in workpiece/die interface, was constructed. Finally, the cross verification between finite element analysis, prediction by neutral network model and the experiments of cylindrical compression testing and ring compression testing are repeatedly checked to ensure the accuracy and reliability of the constructed model. Results of the current study indicate that their
errors are extremely limited, and the developed predictive system is reliable and feasible.
Surface Finishing of Plastic Injection Mold Steel with Ball Burnishing and Spherical Polishing Processes on a Machining Center
Authors: Shiou Fang Jung , Chiu Ju Te
Published: March 2009

This study investigates the possible ball burnishing and spherical polishing surface finish process of a freeform surface plastic injection mold on a machining center. The optimal plane polishing parameters were determined by utilizing the Taguchi’s orthogonal array method for plastic injection molding steel PDS5. Five polishing parameters, namely the speed of the polishing ball, abrasive material, feed, stepover distance and the depth of penetration were selected as the experimental factors of Taguchi’s Design of Experiment to determine the optimal plane polishing parameters, which have the dominant influence on surface roughness. The optimal plane polishing parameters have been determined after conducting the experiments of the Taguchi’s L18 orthogonal table. The optimal plane polishing parameters for the plastic injection mold steel PDS5 were the combination of the polishing speed 18,000 rpm, the abrasives of aluminum oxide (Al2O3) with grid no. 5000, the feed of 100 mm/min., stepover distance of 60μ m, and the depth of penetration of 240
μ m. The surface roughness Ra of the specimen can be improved from about 1.125μ m to 0.067μ m using the optimal ball burnishing parameters for plane burnishing. The surface roughness Ra of the burnished specimen can be further improved from about 0.067μ m to 0.023μ m using the optimal polishing parameters.
In Situ Optical Determination of Fraction Solid of Al-Si-Mg Alloys
Authors: Steinbach Sonja , Ratke Lorenz
Published: March 2009

In this paper we report on a new optical technique to measure in situ the fraction solid during solidification. The technique utilizes the extreme properties of silica aerogels, being optically transparent in the visible and near infrared. From measured brightness time profiles the fraction solid can be derived using a suitable theoretical approach. The technique is tested on a technical AlSiMg alloy (A357) solidified directionally in the furnace facility Artemis. The results are compared with the well known theoretical expressions of the lever rule and the Scheil relation. The measured fraction solid as a function of temperature agrees well with model of Scheil which shows the capabilities of the new technique.