bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Erosion Behaviour of Conventional and Nanostructured WC-12Co Coatings Sprayed by Atmospheric Plasma
Authors: Bonache V. , Salvador M.D. , García J.C. , García V. , Sánchez Enrique , Vicent Monica
Published: December 2009

Thermal sprayed WC-Co coatings are used extensively to enhance the wear resistance of a wide range of engineering components. In this paper, erosive resistance of plasma atmospheric sprayed WC-12Co coatings has been evaluated. Solid particle erosion tests were conducted on these coatings at different angles of impact with silica and alumina abrasives of size 250 µm. Coatings have been deposited by using micrometric and nanometric agglomerated powders, employing H2 and He as plasmogen gas. In order to determine the erosion regime (ductile or brittle), the influence of impact angle on the erosion rate has been studied. Optical microscope and FESEM have been used to analyze the eroded surface. The influence of the plasmogen gas and the powder employed on the erosive behaviour of the coating has been evaluated. An attempt to connect the erosive behaviour with mechanical properties and microstructure has been made. Hardness has been determined by means of several measurements of Vickers microhardness; fracture toughness has been estimated through indentation method. Identification of phases has been made by means of X Ray diffraction.
Influence of Thermal Effects Produced by Laser Treatment on the Tribological Behavior of Porcelain Ceramic Tiles
Authors: Gutiérrez Mora F. , Domínguez-Rodríguez Arturo , Lennikov V.V. , de la Fuente G.F.
Published: December 2009

Commercial porcelain ceramic tiles have been irradiated with a laser to evaluate the thermal effects on their surface and in their tribological behavior. Different irradiation patterns were followed, varying the density of points where the laser was focused, from 25 to 150 dots per inch. Hardness and toughness were evaluated using Vickers indentations. Tribological behavior was studied using a ball-on-flat apparatus with alumina balls. An increase in the wear rate was observed in the higher irradiated samples, which can be correlated to a decrease in their toughness. A mechanism of severe wear by fracture propagation and material pullout is proposed to explain the experimental data and the observed corresponding microstucture.
Effect of the Crystalline Phase on the Brittleness Index of Glass Ceramic Surfaces
Authors: Gargori C. , Galindo R. , Tena M.A. , García A. , Monrós G.
Published: December 2009

Different crystalline phases (tetragonal zirconia, titanite, celsian, diopside, anortite, zircon, scheelite, casiterite, gahnite and spodumene) have been devitrificated into a transparent ceramic glaze by addition of oxides that acts as crystallisation agents. Microstructure, wear resistance and gloss of glass ceramic surface obtained on fired modified glazes are studied. All crystalline phases diminish the brittleness index of the original transparent glaze. Anortite stands out among reinforcing phases that produces dull surfaces associated with high roughness. On the other hand, zircon stands out among the phases that improve gloss surface together wear resistance.
On the High-Temperature Plasticity of Ceria-Doped Zirconia Nanostructured Polycrystals
Authors: de Bernardi-Martín S. , Zapata-Solvas E. , Gómez-García D. , Domínguez-Rodríguez Arturo , Guzmán-Vázquez F.J. , Gómez-Herrero Julio
Published: December 2009

Ceria-zirconia ceramic alloys with the following molar composition: 0.12CeO2-0.88ZrO2 have been sintered by high-temperature annealing. Monolithic specimens haven been crept in compression at high temperatures. Creep experiments have been rationalized to an empirical constitutive equation which is consistent with a classical Ashby-Verrall creep regime. This result has been assessed through microstructural characterization of as-received and post-mortem specimens. A pure Ashby-Verrall creep is contrary to the conventional mechanism controlling creep in other zirconia alloys. A discussion on the explanation for such mechanism is outlined.
Combined Numerical Simulation and Microstructure Characterization for Prediction of Physical Properties in Extruded Aluminum Alloys
Authors: Misiolek Wojciech Z. , Van Geertruyden William R.
Published: December 2009

The extrusion process provides conditions for non-uniform metal flow depending on strain, strain rate and temperature of deformation as well as deformation zone geometry. As a result of these conditions significant microstructure gradients are present within the extrudate. The extreme case of the microstructure gradient is a formation of the peripheral coarse grain structure (PCG). This phenomenon is present in many structural aluminum alloys extrudates and its presence should be eliminated or at least significantly reduced because of the mechanical properties and aesthetic points of view. A number of experiments, including physical and numerical simulations, were performed in order to understand and model the origin of the PCG in indirect extrusion of 6xxx alloys. These experiments included different alloy chemistry, various temperatures, extrusion ratios and extrusion speeds allowing analysis of their influence. Parallel to the experimental results the numerical simulation of the metal flow showing the origin of the metal in different extrudate location was performed using software package DEFORM TM. A review of performed research will be followed by the analysis of the results and discussion of future needs.
Numerical and Experimental Investigations of the Production Processes of Coextruded Al/Mg-Compounds and the Strength of the Interface
Authors: Kittner Kai , Awiszus Birgit
Published: December 2009

Due to a changing environmental awareness and the improved use of resources, the application of light-weight materials, such as aluminium and magnesium, becomes increasingly important and partially substitutes the utilisation of conventional materials such as steel.
However, a widespread application demands a better understanding of these materials. This concerns production processes of semi-finished products and the products itself.
Coextruded aluminium-magnesium compounds are investigated in the subproject B3 (“Experimental and numerical investigations of the interface behavior of Al-Mg compounds”) which is part of the special research area 692 – HALS at the Chemnitz University of Technology. These compounds are characterized by a very good weight-strength-ratio and allow a wide field of application, for example in automotive industry.
The compounds are manufactured in extrusion processes. The interface which is developed during the production is of special interest and the investigation of it is a shared aim of the Department of Experimental Mechanics and the Department of Virtual Production Processes. The two main tasks are the extrusion process optimisation and the microstructural, mechanical and thermal examination of the semi-finished product.
The following paper gives an overview of the performed investigations in this subproject.
Friction in Double Action Extrusion
Authors: Wang Li Liang , Zhou Jie , Duczczyk Jurek
Published: December 2009

A novel extrusion testing method, double action extrusion (DAE), to highlight the effect of friction at the die bearing in aluminum extrusion was developed. It was found that the lengths of the extrudates and extrusion force were indeed sensitive to the die bearing length and thus to the friction. FEM simulations of DAE were carried out to evaluate the shear and Coulomb friction models over a wide range of friction factors/coefficients from 0.2 to 1. The full sticking friction appeared to represent the interfacial contact between hot aluminum and die the best. The friction factor values in the shear friction model over a range of 0.3 to 0.6 commonly used to describe the contact at the billet-die interface in FEM simulation appeared to be too low. The comparison between the experimental and simulation results indicated that the shear friction model at m = 1 predicted the extrusion force the best, while the Coulomb friction model at µ = 1 predicted the extrudate lengths the best. Of the existing friction models and friction factors/coefficients, it is recommended to use the shear friction model at m = 1 to describe the friction at the billet-die interface in FEM simulation.
Computer-Aided Simulation of Metal Flow through Curved Die for Extrusion of Square Section from Square Billet
Authors: Maity Kali Pada , Rout Akshaya Kumar , Majhi Kalu
Published: December 2009

Extrusion through mathematically contoured die plays a critical role in improvement of surface integrity of extruded product. There is gradual deformation which results in the uniform microstructure. In the present investigation non-dimensional extrusion pressure and optimum die length for cosine die profile has been obtained by three dimensional upper bound method using dual stream function method for different reductions. The theoretical modeling has been validated with experiments. The experimental results are found to be compatible with the theory.
Extrusion Benchmark 2009 Experimental Analysis of Deflection in Extrusion Dies
Authors: Pietzka Daniel , Ben Khalifa Nooman , Donati Lorenzo , Tomesani Luca , Tekkaya A. Erman
Published: December 2009

In this paper experimental investigations aimed at measuring the die deformations during aluminum extrusion process is presented and discussed. A two-holes die generating two U-shape profiles with different supporting legs was produced and tested under strictly monitored conditions. The influence of die deformation on the speed, temperature distribution and distortion of the two profiles is reported and analyzed. AA6082 alloy was used as deforming material while H-13 hot-work tool steel was selected as die material. The experiments were repeated at least three times in the same conditions in order to achieve a statistical distribution of the acquired data: such data are then used as a reference for the 2009 edition of the extrusion benchmark.
FEM-Assisted Design of a Multi-Hole Pocket Die to Extrude U-Shaped Aluminum Profiles with Different Wall Thicknesses
Authors: Fang Gang , Zhou Jie , Duczczyk Jurek
Published: December 2009

Wide, thin-wall profiles exiting simultaneously from a multi-hole die during aluminum extrusion tend to have different velocities and deflect from the straight line. The pockets in front of the die orifices are often used to balance the metal flow and equalize the velocities. In practice, the effect of a pocket die design on metal flow becomes known, only after the die is manufactured and a trial extrusion run is completed. The present research was intended to demonstrate the feasibility of using FEM simulation to predict metal flow, thereby reducing or hopefully eliminating trial extrusion runs. The extrusion of U-shaped profiles with different wall thicknesses through a multi-hole pocket was taken as an example to show the scope of adjusting the die pocket to regulate metal flow. The effect of pocket shape on metal flow was evaluated. It is clear that 3D FEM simulation can indeed be effectively used to optimize die design, before the die design is finalized.
A Case Study to Solve the Problem of Wall Thickness Attenuation during Extrusion to Produce a Complex Hollow Magnesium Profile
Authors: Li Luo Xing , Zhou Jia , He X. , Zhou Jie , Duczczyk Jurek
Published: December 2009

The present case study addressed a practical problem of wall thickness attenuation during extrusion to produce a complex thin-walled hollow magnesium profile. A HyperWorks FEM software package was employed to aid in identifying the causes for the wall thickness attenuation. Recommendations were made to adjust the interspacing between the mandrels and the height of the welding chamber. The modified dies yielded much improved results in terms of velocity and hydrostatic pressure uniformity. The wall thickness of the extrudate predicted using FEM simulation was very close to experimental measurements. The case study demonstrated the feasibility of using FEM simulation as a useful tool to solve industrial problems encountered in the production of complex profiles.
Manufacturing of Carbon/Resin Separator by Die Sliding Extrusion
Authors: Hoshino Michihiko , Suzuki K.
Published: December 2009

A fuel cell will play a part of a module of power generator instead of an internal- combustion engine. It is required to improve the productivity and miniaturizing of the fuel cell. The separator in the fuel cell is an important part. The manufacturing process of carbon/resin separators usually is injection molding or compression forming. On the other hand, the authors have developed die sliding extrusion based on the friction extrusion [1] and side flow extrusion [2]. The die sliding extrusion is a kind of valuable shape extrusion [3,4]. It is applied to manufacturing fuel cell separators which have linear channels on its upper and lower surfaces in the orthogonal direction.
An Assessment of the Grain Structure Evolution during Hot Forward Extrusion of Aluminum Alloy 7020
Authors: Foydl Annika , Ben Khalifa Nooman , Brosius Alexander , Tekkaya A. Erman
Published: December 2009

The current investigation is concerned with the grain structure evolution in an Al-Zn alloy (EN AW-7020) during the hot forward extrusion process. In order to analyze that, a miniature hot forward extrusion setup was designed which allows the quenching of the extrusion butt immediately after extrusion. In order to gain a better understanding of the process, the shape of the deformed grains was analyzed and the process was simulated. The shape of these grains was indentified in two directions in the different grain zones, e.g. dead metal zone and shear zone. The FE simulations showing the different grain zones were also illustrated. Simulation results and the micrographs were quite promising to find parameters for simulation models in order to predict grain sizes with the method presented in the current research work.
Simulation of Gas and Spray Quenching during Extrusion of Aluminium Alloys
Authors: Reich Michael , Schöne S. , Kessler O. , Nowak M. , Grydin O. , Nürnberger F. , Schaper M.
Published: December 2009

After the extrusion process most aluminium alloy profiles don´t satisfy the necessary strength requirements. An increase of strength can be obtained by age hardening of hardenable aluminium alloys. Age hardening includes the three steps of solution annealing, quenching and aging and is usually carried out in a separate process after extrusion. The integration of the sub-steps solution annealing and quenching in the extrusion process results in a marked reduction of the complete process chain. The applicability of this integration depends primarily on the quenching power of the cooling module and on the quench sensitivity of the aluminium alloy. Using the finite element method the non-steady-state process of quenching the profiles after leaving the extrusion press has been simulated. The boundary conditions for quenching are varied for a gas nozzle field and a spray cooling using heat transfer coefficients based on experiments. The simulation results support the design of gas nozzle fields or spray cooling for the extrusion process of different aluminium alloys.
An Approach to Simulate Shape Distortion due to Cooling in Aluminum Extrusion
Authors: Bikass Saeed , Andersson Bjørn , Ma Xiang
Published: December 2009

Cooling subsequent to extrusion is a crucial process in aluminum extrusion value chain. Non-uniform cooling-induced shape distortion, such as deflection, twisting and etc., is a challenge for extrusion profile manufacturers. Temperature management is therefore a key to the aluminum extrusion process. Appropriate modeling, using both physical and numerical methods, can help us achieve a better temperature control in extrusion plants. In this work, finite element (FE) method was used to simulate shape distortion due to cooling and the most important challenge was to make FE models compatible to real conditions in plants. The effects of three important items I) mechanical boundary condition II) cooling source type and III) effective cooling length were examined. It was shown that for compatible prediction of distortions it was necessary to define these items similar to real life. It was also revealed that with a suitable definition of boundary conditions it is possible to use a short lab scale sample to understand mechanisms in real life profiles.
Towards Predictive Control of Extrusion Weld Seams: An Integrated Approach
Authors: den Bakker Andrew J. , Werkhoven Robert J. , Sillekens W.H. , Katgerman Laurens
Published: December 2009

Longitudinal weld seams are an intrinsic feature in hollow extrusions produced with porthole dies. The formation of longitudinal weld seams is a solid bonding process, controlled by the local conditions in the extrusion die. Being the weakest areas within the extrusion cross section, it is desirable to achieve adequate properties of these weld seams. In our research, the concept of a weld seam integrity indicator as a means of quantifying bonding efficiency is introduced. The value of this indicator depends on a number of factors: the material flow within the die weld chambers, an adequate pressure level acting on the weld planes and finally the evolution of the metal microstructure. Optimisation of the welding conditions leads to a higher value of the weld seam integrity indicator and thus to improved weld seam properties. The objective of the research presented in this paper is to assess the feasibility of this concept.
In lab-scale experiments, AA6060 and AA6082 aluminium alloy billets were formed into strips by means of the direct hot extrusion process. By utilising porthole dies a central longitudinal weld seam is formed. The effect of different geometries of the weld chamber and the processing conditions on the quality of the weld seam are investigated. Characterisation of these weld seams through mechanical testing, focusing on the ability of the weld seam area to accommodate plastic deformation following the onset of plastic instability, and microstructural analysis provides insight into bonding performance. The outcome of this characterisation provides a basis for an estimation of the weld seam indicator. Through computer modelling, the particular process conditions related to weld seam formation are calculated and correlated with the experimental results. The experimental results clearly demonstrate that weld seam formation is controlled by a combination of factors as described above. Inadequate fulfilment of these conditions, verified by the FE-simulations, is the cause of inferior weld seams, associated with low values of the weld seam integrity indicator.
Through further elaboration of the concepts presented in this work, the weld seam integrity indicator is to be developed, with the future aim of predicting the weld seam performance through finite element simulations.
Dislocation and Diffusion Deformation Mechanisms of Ultrafine Grained Materials
Authors: Kozlov Eduard , Koneva Nina , Popova N.A.
Published: December 2009

Deformation mechanisms of polycrystals as a function of the grain size in the 1nm…1cm interval are studied in this paper. The critical grain sizes are identified. Activity of dislocation and diffusion mechanisms is analyzed. The distribution of deformation in grains with different sizes within the same polycrystal is considered.
Ductility of Bulk Nanocrystalline and Ultrafine Grain Iron and Steel
Authors: Benito Josep Antonio , Tejedor Robert , Rodríguez-Baracaldo Rodriguez , Cabrera Jose María , Prado Jose Manuel
Published: December 2009

This paper reviews the ductility of nanostructured and ultrafine iron obtained using a variety of methods. Mechanical milling of powder and subsequent hot consolidation, one of the most popular methods offer high mechanical strength but poor ductility. Improvements made in the consolidation processes and the introduction of final heat treatments, in addition to new approaches such as spark plasma sintering and high pressure torsion, have increased the total plastic strain of nanostructured iron. The development of bimodal structures enables the existence of strain hardening and more uniform deformation. The paper also includes a steel study, which finds that the hardness of milled powder and the role of carbon atoms inside ferrite grains make it more difficult to improve the ductility of nanostructured samples.
Mechanical Properties of Ultrafine Grained Steels Processed by Large Strain-High Z Deformation - A Review
Authors: Narayana Murty S.V.S. , Torizuka Shiro
Published: December 2009

Ultrafine-grained steels with a grain size of about one micron offer the prospect of high strength coupled with high toughness among conventional steel compositions and are attracting the attention of researchers worldwide. Application of these ultrafine-grained steels to potential engineering structures demands extensive study of their mechanical properties. While there are many studies on the development of ultrafine-grained microstructures through various deformation processing techniques on a spectrum of compositions, fewer studies were reported on the more important aspect of evaluating their mechanical properties. This is to verify the basic assumption that the microstructural refinement at bulk level indeed improves the mechanical properties offering the prospect of a realistic replacement of the existing conventional steels in the near future. As we move towards the ultimate goal of applying these advanced high strength materials, this review article attempts to present a comprehensive picture on the mechanical properties of ultrafine-grained steels with varying carbon contents fabricated by large strain warm deformation. Finally, it is believed that time is ripe for exploring the possible applications of these materials for structural applications.
The Influence of Work Hardening, Internal Stresses, and Stress Relaxation on Ductility of Ultrafine Grained Materials Prepared by Severe Plastic Deformation
Authors: Morris David G. , Muñoz-Morris Maria A. , Gutierrez-Urrutia Ivan
Published: December 2009

Ultrafine grained materials prepared by methods of severe plastic deformation appear to show good ductility for their high strength. To a large extent this ductility enhancement, for the given strength, is shown to correspond to the fracture ductility and not the uniform ductility at maximum stress. The improved fracture ductility is often due to the refinement or removal of the coarse defects that act as sites for failure nucleation. The low work hardening rate inherent to the very fine microstructures produced by severe plastic deformation essentially condemns such materials to very low uniform ductility. Stress relaxation occurring during unloading after processing, and changes of internal stresses during reloading for mechanical testing, appear to play a significant role in determining deformation behaviour near the onset of plastic flow, and this can affect the measured uniform strain.
Structure, Strength and Ductility of As-Cast Al-Mg-Mn-Zr-Sc Alloys after Equal Channel Angular Pressing
Authors: Dobatkin Sergey V. , Estrin Yuri , Zakharov Valerij V. , Rostova T.D. , Ukolova O.G. , Tchirkova A.
Published: December 2009

The effect of equal channel angular pressing (ECAP) on the structure and mechanical properties of Al-4% Mg-1.5% Mn-0.4% Zr and Al-4% Mg-1.5% Mn-0.4% Zr-0.4% Sc alloys in the initial as-cast state was studied. The ECAP processing was shown to lead to the formation of predominantly submicrocrystalline structure with an average grain size of 850 nm in the Al-Mg-Mn-Zr-Sc alloy and 1060 nm in the Al-Mg-Mn-Zr alloy. It is remarkable that both strength and ductility of the two alloys were enhanced by ECAP. The highest strength was observed in the Al–Mg–Mn–Zr–Sc alloy (UTS = 425MPa), in combination with elongation to failure of EL=17 %.
Enhanced Ductility in Ultrafine-Grained Al Alloys Produced by SPD Techniques
Authors: Valiev Ruslan , Murashkin Maxim Yu. , Straumal Boris B.
Published: December 2009

In this work ultrafine-grained (UFG) structure was successfully produced in the commercial Al 6061 and Al-30%Zn alloys using new modifications of two severe plastic deformation (SPD) techniques, namely equal channel angular pressing (ECAP) with parallel channels (PC) and high pressure torsion (HPT) with enhanced load. Variation of SPD processing regimes made it possible not only to perform strong grain refinement but also to modify the phase composition through the formation of grain boundary (GB) segregations and precipitations. This enabled to achieve a unique combination of high strength and ductility in the Al 6061 alloy and demonstrate super-ductility in the Al-30%Zn alloy, when elongation to failure exceeded 150% at room temperature.
Factors Influencing Ductility in Ultrafine-Grained Metals Processed by Equal-Channel Angular Pressing
Authors: Figueiredo Roberto B. , Duan Zhi Chao , Kawasaki Megumi , Langdon Terence G.
Published: December 2009

The processing of bulk metals through the application of severe plastic deformation provides an opportunity for achieving exceptional grain refinement to the submicrometer or even the nanometer range. This paper examines the characteristics of metals processed by equal-channel angular pressing with special emphasis on the levels of ductility that may be attained. It is shown that the amount of ductility is dependent not only upon the composition of the material but also, and to a major extent, upon the testing temperature. Specifically, the ductilities are often low at ambient temperatures where the strength of the as-processed material is relatively high but, by contrast, exceptionally high superplastic ductilities may be achieved over short ranges of strain rate when testing at elevated temperatures.
Texture, Microstructure, and Ductility of Mg-Al-Zn Alloy after Equal Channel Angular Pressing
Authors: Serebryany Vladimir , Dobatkin Sergey V. , Kopylov V.I. , Nikolayev D.I. , Brokmeier Heinz Günter
Published: December 2009

Equal channel angular pressing (ECAP) was used for grain refinement and texture modification in the initial pressed Mg-Al-Zn alloy to study the possibility to enhance the low-temperature deformability of the material. The effect of different ECAP regimes by routes A, C, and BC on the submicrocrystalline grain formation, texture evolution, and plasticity of the alloy have been investigated. The ECAP of the alloy results in the formation of ultrafine grained structure with a grain size of 0.8-3.5 µm independent of pressing routes and regimes. The ECAP also drastically changes the axial texture by splitting the initial texture characterized by a sharp basal component to several more scattered orientations. The degree of the orientation scattering depends on the ECAP regime and route. It is proposed to estimate the effect of the texture on the yield strength and plasticity of the alloy after ECAP through generalized Schmid factors. The comparable calculated and experimental results are obtained only for yield strength.
Strength and Ductility of Nanostructured Composites with Co-Deformable Components
Authors: Han Ke
Published: December 2009

This paper reviews research on nanostructured high strength wires and strips. Such materials have sufficient ductility and they have found application in a variety of areas. The high strength of the materials is achieved by refinement of the spacing between the strengthening fibers. Due to the refined microstructure, the materials have very large interphase interface areas. Such interfaces provide very effective barriers for dislocation motions. In spite of their microstructural refinement, the materials still have sufficient ductility that gives them engineering values.
Long-Range Ordering: An Approach to Synthesize Nanoscale Ni-Mo-Based Superlattices with High Strength and High Ductility
Authors: Tawancy H.M.
Published: December 2009

It is shown that long-range ordering in certain alloys based upon the Ni-Mo system can provide a viable means for synthesizing bulk nanoscale materials combing high strength and high ductility. Three alloys were included in the study with nominal chemical compositions of Ni-27Mo, Ni-27Mo-0.03B, and Ni-27Mo-12Cr all in weight %. Ordering was induced by thermal aging at 700 oC resulting in a D1a superlattice (Ni4Mo) in the Ni-27Mo and Ni-27Mo-0.03B alloys, and a Pt2Mo-type superlattice [Ni2(Cr,Mo)] in the Ni-27Mo-12Cr alloy. During the early stages of aging, atomic order in the Ni-27Mo alloy was completed homogeneously in the matrix resulting in a nanoscale superlattice with high strength and high ductility, however, a considerable loss of ductility occurred after extended aging. The results suggested that this behavior was not related to the degree of atomic order but rather to a change in morphology resulting from a heterogeneous ordering reaction at grain boundaries promoted by strain-induced recrystallization. Although a nanoscale superlattice combining high strength and high ductility could be synthesized in the Ni-27Mo alloy by proper aging treatment, it is demonstrated that the heterogeneous ordering reaction could be suppressed by the addition of boron or chromium to improve the thermal stability of the alloy system. On the average, a combination of about 800 MPa yield strength and 40% tensile elongation at room temperature could be achieved in the alloys studied. Deformation in the ordered state is found to occur by twinning, which has been related to the crystallography of the disorder-order transformation.
Enhancement of Tensile Ductility of Severe Plastically Deformed Two-Phase Zn-12Al Alloy by Equal Channel Angular Extrusion
Authors: Purcek Gencaga , Aydin Murat , Saray Onur , Kucukomeroglu Tevfik
Published: December 2009

Tensile properties (mainly the ductility and fracture mode) of two-phase Zn-12Al alloy subjected to severe plastic deformation (SPD) via multi-pass equal-channel angular extrusion (ECAE) following route-Bc were investigated. As a result of ECAE processing, elongation to failure (as a ductility) of the alloy increased substantially and continuously with increasing the number of ECAE passes. However, the majority of the tensile strains are obtained in the state of plastic instability and therefore the uniform strains achieved along the gage length are very limited for this alloy. On the other hand, the strength of the alloy increased with increasing the number of passes up to 2, above which it decreased. The alloy sample after four ECAE passes exhibited 168% total elongation to failure at room temperature, which was 26 times higher than that of the as-cast one. This result indicates that multi-pass ECAE is effective on improving the tensile ductility of binary Zn-Al alloys. The fracture mode of the as-cast alloy samples completely changed after multi-pass ECAE and the brittle fracture behavior of the as-cast alloy was transformed into the ductile mode after processing.
The Effect of Severe Plastic Deformation on the Brittle-Ductile Transition in Low Carbon Steel
Authors: Tanaka Masaki , Higashida Kenji , Shimokawa Tomotsugu
Published: December 2009

Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the controlling process of the BDT was not changed by the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range barriers. Quasi-three-dimensional simulations of dislocation dynamics, taking into account of crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicated that the BDT temperature is decreased with decreasing in the dislocation source spacing. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries and were reemitted from there with increasing strain. It indicates that grain boundaries can be new sources in ultra-fine grained materials, which increases toughness at low temperatures.
Deformation Mechanisms of Single Crystals and Bicrystals Subjected to Equal-Channel Angular Pressing - Review
Authors: Han Wei Zhong , Li Shou Xin , Wu Shi Ding , Zhang Zhe Feng
Published: December 2009

The deformation mechanisms of various kinds of single crystals and bicrystals during the process of equal channel angular pressing (ECAP) have been paid more attention world wide. This paper reviews the recent progresses in the understanding of the deformation mechanisms of single crystals and bicrystals subjected to one-pass ECAP, and discusses the effect of initial crystallographic orientation and grain boundary on the microstructural evolution of these crystals. Based on those experimental results and analysis, it is suggested that in addition to the shear deformation along the intersection plane (IP) of ECAP die, the shear along the normal of IP also plays an important role in affecting the microstructural evolution and deformation mechanisms of these single crystals and bicrystals.
Toward Understanding Size-Dependent Plasticity of Nanolayered Metallic Composites
Authors: Zhang G.P. , Li Y.P. , Zhu X.F.
Published: December 2009

Deformation and fracture behaviors of Cu/Au and Cu/Cr multilayered composites with different length scales were investigated by using instrumented-indentation and three-point-bending methods. It is found that with decreasing the length scale (layer thickness and grain size), both multilayers tend to produce plastic instability via localized shear banding under indentation load in spite of high hardness they have, while quasi-brittle fracture under relatively low fracture stress prevails at three-point-bending test. Especially, the compressive flow stress and the tensile fracture stress exhibit inverse trend of variation with the length scales, which implies different mechanisms. Such length scale dependent deformation and plasticity were analyzed concerning size and interface effects under different stress state.
Improving Ductility in Nanostructured Materials and Metallic Glasses: “Three Laws”
Authors: Hofmann Douglas C. , Johnson William L.
Published: December 2009

Nanostructured materials and bulk metallic glasses are relatively new classes of engineering materials that have promise for unique metals applications. However, both these materials suffer from limited room temperature ductility in unconfined loading geometries. In this work, we present three experimental rules that we have observed to be necessary to toughen bulk metallic glasses. We reason that adaptations to these rules may provide the solution for toughening nanostructured composites and other brittle materials.
Enhanced Work Hardening of Cu-Based Bulk Metallic Glass Composites by In Situ Formed Nano-Scale Heterogeneities
Authors: Calin M. , Das J. , Kim K.B. , Pauly S. , Mattern N. , Eckert Jürgen
Published: December 2009

The work hardening ability under room temperature compression of ductile Cu47.5Zr47.5Al5 and Cu47Ti33Zr11Ni8Si1 bulk metallic glass-forming alloys has been studied and compared. Both alloys exhibit high fracture strength, distinct work hardening and large plastic strain. Systematic investigations on the microstructural evolution reveal the occurrence of nano-scale heterogeneities, of both structural and chemical nature, which enables multiplication, branching, and restriction of the shear bands, thus controlling the plastic instability of metallic glasses. Phase separation in the liquid state leading to chemical inhomogeneities has been revealed for as-cast Cu47.5Zr47.5Al5 samples. In the case of Cu47Ti33Zr11Ni8Si1, a composite-type microstructure with in-situ formed nano-scale precipitates embedded in a glassy matrix is responsible for the distinct work hardening recorded on the stress-strain curves. The present results support the important role of nano-scale heterogeneities for promoting efficient work hardening in Cu-based metallic glass composites.
A Simulation of the Abnormal Grain Growth in a Nano-Structural AZ31 Mg Alloy by Phase Field Model
Authors: Wu Yan , Zong B.Y. , Wang M.T.
Published: December 2009

Abnormal grain growth was simulated by phase field model in order to find ways of producing scattered a few enormous grains in a nano-structural single phase AZ31 alloy to improve its ductility. It is shown that the abnormal grain growth is controlled by the three keys factors of interface energy, strain restored energy and interface mobility. Therefore, the microstructure with scattered a few enormous grains in the nano-structural matrix can be achieved after an annealing treatment if there is a small group of specially orientated nano-size grains in the original nao-structure with local low grain boundary energy or local high strain energy or local high interface mobility. The morphology of abnormal grains is also examined as function of annealing time to optimize the microstructure.
Microstructural Origin of Superior Compressive Ductility of a Nanocrystalline Metal
Authors: Pan Deng , Kuwano S. , Fujita T. , Chen M. W.
Published: December 2009

Ultra-large compressive plasticity at room temperature has recently been observed in electrodeposited nanocrystalline nickel (nc-Ni) under micro-scale compression (Pan, Kuwano, Fujita and Chen: Nano Lett. Vol. 7 (2007), p. 2108). With aid of a TEM sample preparation technique employing focused ion beam (FIB), TEM observations on deformed nc-Ni evidenced deformation-induced microstructural evolution of nc-Ni at a variety of strain levels: Whilst the deformation increases, substantial grain growth is uncovered in the nc-Ni. No apparent ex situ evidence of intragranular dislocation activities is found in the deformed sample. As thermal diffusion plays an insignificant role in the deformation in nc-Ni at room temperature (~0.17Tm), this premium plasticity is achieved in accommodation with the grain-boundary-mediated deformation, with assistance of extensive grain growth that is mainly driven by high stresses at steady plastic flow.
Overview of the Grain Size Effects on the Mechanical and Deformation Behaviour of Electrodeposited Nanocrystalline Nickel − From Nanoindentation to High Pressure Torsion
Authors: Yang B. , Vehoff Horst , Pippan Reinhard
Published: December 2009

A summary of experimental results from nanoindentation, strain rate-controlled tension, in-situ bending and high pressure torsion on bulk electrodeposited nanocrystalline nickel, focusing on the effects of grain size on the mechanical behaviour and deformation mechanisms is presented. The interaction between dislocations and grain boundaries was locally examined by studying the dependence of nanohardness on grain size and indentation size; this is done by always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically. The grain size effects on the different deformation mechanisms of nanocrystalline nickel were revealed by strain rate-controlled tension and nanoindentation experiments, which show that with decreasing grain size the strain rate sensitivity increases and the activation volume decreases, indicating increased grain boundary mediated deformation processes in nanocrystalline nickel. Creep experiments at room temperature revealed that in nanocrystalline nickel grain boundary sliding or diffusion along the interface may dominate at lower stress levels, but with increasing stresses the deformation process is mainly controlled by dislocation creep. In-situ bending experiments in an atomic force microscope revealed directly that grain boundary mediated deformation processes play a significant role in nanocrystalline nickel, which is also supported by the observation of grain coarsening and softening of nanocrystalline nickel caused by high pressure torsion.
Experimental Evidence that the Onset of Mechanical Softening in Nanocrystalline Metals is Strain Rate Dependent
Authors: Wang Li Wei , Prorok Barton C.
Published: December 2009

This paper reports on the influence of strain rate on the onset of mechanical softening of nanocrystalline gold at room temperature. Micro-tensile testing was performed with applied strain rates on the order of 10−4 s−1 to 10−6 s−1. Our results defined a threshold strain rate, whereby plastic deformation at larger rates was dominated by dislocation processes and at smaller rates by one or more other deformation mechanisms.
Effect of Co and Mn Doping on the Martensitic Transformations and Magnetic Properties of Fe-Pd Ferromagnetic Shape Memory Alloys
Authors: Sánchez-Alarcos Vicente , Pérez-Landazábal José Ignacio , Recarte Vicente
Published: December 2009

The effect of the partial substitution of Fe by Co and Mn on the structural and magnetic properties of Fe-Pd alloys has been investigated by means of calorimetric, magnetic and neutron diffraction measurements. The addition of Mn increases both the reversible and irreversible MT temperatures whereas the addition of Co causes the opposite effect, which points out that that the compositional dependence of the transformation temperatures of the Fe-Pd alloys is not related to the Pd amount but to the e/a concentration. Furthermore, it is shown that the appearance of the BCT phase is directly related to the tetragonality of the FCT phase. On the other hand, the amount of FCT martensite that irreversibly transforms into the undesirable BCT phase is considerably reduced by both the Co and Mn doping. The substitution of Fe by Co seems to be especially interesting for magnetic field-induce strains applications since both the magnetic anisotropy and the saturation magnetization of the Fe-Pd FCT martensite are considerably increased with the Co addition.
Magnetoelastic Coupling in Ni-Mn-Ga Magnetic Shape Memory Alloy
Authors: Heczko Oleg
Published: December 2009

The role of magnetoelastic coupling in the mechanism of magnetically induced reorientation or redistribution (MIR) of twin variants is still a matter of some controversy. To evaluate this role ordinary magnetostriction of different Ni-Mn-Ga single crystals transforming to 5M (exhibiting MIR) and NM (no MIR) martensite were measured. The magnetostriction of Ni-Mn-Ga austenite is relatively low and steeply increases when approaching to martensite transformation. This is correlated to the softening of elastic modulus. Observed high field contribution of opposite sign may be due to the dependence of higher order elastic constant on magnetic field. The magnetostriction of martensite is difficult to determine as it is masked by much stronger MIR effect and indirect method must be used. The results are discussed in the frame of magnetoelastic model for MIR and compared with magnetic energy model.
The Symmetry-Conforming Theory of Martensite Aging
Authors: L'vov Victor A. , Kosogor Anna , Söderberg Outi , Hannula Simo Pekka
Published: December 2009

The Landau theory has been developed for the description of martensite aging. The characteristic features of the theory are: i) the multicomponent non-scalar character of the order parameter describing the slow reconfiguration of lattice defects after martensitic transformation (MT); ii) the complete agreement with Symmetry-Conforming Short-Range-Order principle formulated by X. Ren and K. Otsuka; iii) the applicability to the different MT-s and various defects related to aging phenomena. The physical values interpreted as the components of internal stress, which stabilizes certain variant of martensitic phase, have been composed of the components of slow non-scalar order parameter. An applicability of the developed theory to the description of influence of aging on the MT temperature and yield stress was demonstrated.
Theoretical Modeling of Magnetocaloric Effect in Heusler Ni-Mn-In Alloy by Monte Carlo Study
Authors: Buchelnikov Vasiliy D. , Sokolovskiy V.V. , Taskaev Sergey , Entel Peter
Published: December 2009

In this paper we present a theoretical model for calculation of the (positive and negative) magnetocaloric effects and magnetic properties of the Heusler Ni50Mn34In16 alloy by the classical Monte Carlo study. By the help of the proposed model the temperature dependences of the magnetization, tetragonal deformation, heat capacity, positive and negative isothermal magnetic entropy changes for magnetic field variation are obtained. All quantities are in good qualitative agreement with the available experimental data.
Fundamental Aspects of Magnetic Shape Memory Alloys: Insights from Ab Initio and Monte Carlo Studies
Authors: Entel Peter , Gruner Markus E. , Dannenberg Antje , Siewert Mario , Nayak Sanjeev K. , Herper Heike C. , Buchelnikov Vasiliy D.
Published: December 2009

Ferromagnetic Heusler alloys like Ni-Mn-Z (Z = Al, Ga, In, Sn, Sb), which undergo a martensitic phase transformation, are on the edge of being used in technological applications involving actuator and magnetocaloric devices. The other class of ferromagnetic full Heusler alloys like Co-Mn-Z (Z = Al, Si, Ga, Ge, Sn) not undergoing a structural phase transition, are half-metals (in contrast to the Ni-based systems) with high spin polarization at the Fermi level and are of potential importance for future spintronics devices. On the basis of recent ab initio calculations, we highlight the main differences between the two classes of Heusler based materials.
Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA
Authors: Righi Lara , Albertini Franca , Paoluzi Antonio , Fabbrici Simone , Villa Elena , Calestani Gianluca , Besseghini Stefano
Published: December 2009

Magnetic and structural properties in multifunctional FSMA (Ferromagnetic Shape Memory Alloys) belonging to Heusler family are frequently related to the occurrence of structural modulation in martensitic phases. The highest MFIS (Magnetic Field Induced Strain) effect has been observed in Ni-Mn-Ga alloys showing martensitic modulated structures. Depending on the composition, pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along specific crystallographic directions, accompanies the martensitic transformation. Over the years, different modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding superstructure (nM with n=3, 5, 6, 7, 12 etc). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure can be solved by applying superspace approach. The crystallographic representation of different modulated structures, obtained by structure refinement on powder diffraction data, suggests a unified description where every different “nM” periodicity can be straightforwardly represented. It will be presented an overview illustrating structural features of several displacive modulated martensitic lattices. For a specific Ni-Mn-Ga composition, the evolution of structural modulation upon temperature change will be illustrated.
X-Ray Diffraction Reciprocal Space Mapping Study of Modulated Crystal Structures in 10M Ni-Mn-Ga Martensitic Phase
Authors: Ge Yan Ling , Aaltio Ilkka , Söderberg Outi , Hannula Simo Pekka
Published: December 2009

The 10M modulated crystal structure in Ni-Mn-Ga martensitic phase with about 0.5 MPa twinning stress, was studied by X-ray diffraction reciprocal space mapping (RSM). The experimental procedure is established for collecting large range of RSM with scattering planes inclined to the surface of specimen. The investigation focused on the superlattice reflections caused by the modulation, which always appeared in two <110> directions in bulk material. The distribution of two modulation domains varies with scattering locations.