International Journal of Materials Research Volume 100 Issue 6

International Journal of Materials Research

Volume 100 Issue 6

Contents
Journal Overview

June 11, 2013 Page range: 741-742

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Feature

Beyond fick's equations, an overview

Jean Philibert June 11, 2013 Page range: 744-749

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Abstract

Fick's equations do not allow modelling of a large number of diffusion phenomena. Several extensions are described and some applications outside the field of physical metallurgy are briefly described. Departure from Brownian motion appears to be very common, so that anomalous diffusion would actually appear as normal.

Review

The high-temperature creep properties of materials processed using severe plastic deformation

Cheng Xu, Megumi Kawasaki, Terence G. Langdon June 11, 2013 Page range: 750-756

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Abstract

Processing through the application of severe plastic deformation (SPD) is now an accepted procedure for introducing very significant grain refinement into bulk solids. Typically, experiments show that the materials processed in this way have grain sizes in the submicrometer or even the nanometer range. This exceptional grain refinement provides an opportunity for conducting creep tests at elevated temperatures and examining the occurrence of creep flow through mechanisms where the creep rate varies inversely with the grain size. The present paper describes creep experiments conducted on two different representative materials subjected to SPD processing: high-purity aluminum and an aluminum 7034 alloy. The results demonstrate that the creep behavior depends critically upon the thermal stability of the ultrafine-grain microstructures.

Nanostructuring of metallic materials by spd processing for advanced properties

Ruslan Valiev June 11, 2013 Page range: 757-761

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Abstract

During the past decade, fabrication of bulk nanostructured metals and alloys using severe plastic deformation (SPD) has been evolving as a rapidly advancing direction of nanomaterials science and technology aimed at developing materials with new mechanical and functional properties for advanced applications. The principle of these developments is based on grain refinement down to the nanoscale level via various SPD techniques. This paper is focused on recent studies of SPD processing regimes and routes enabling fabrication of ultrafine-grained metals and alloys. The paper also considers nanostructural features of SPD-processed materials that are responsible for enhancement of their properties.

Basic

Some factors affecting the creep behaviour of metallic materials processed by equal-channel angular pressing

Václav Sklenička, Jiří Dvořák, Petr Král, Milan Svoboda, Ivan Saxl June 11, 2013 Page range: 762-766

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Abstract

Very few reports describing the creep behaviour of materials processed by equal-channel angular pressing (ECAP) have shown that there are both similarities and differences between the creep behaviour of coarse-grained metals and alloys and their ultrafine-grained counterparts. This paper examines these differences and evaluates some factors affecting the creep behaviour of pure aluminium, pure copper, and the binary Al-0.2 wt.% Sc alloy processed by ECAP. It was found that the creep behaviour of pressed material depends strongly on the number of ECAP passes and successive passes result in a gradual decrease in the creep resistance which may be attributed to microstructural changes, homogenization of the microstructure and the microtexture, nanoporosity induced by the ECAP procedure and thermal instability of the pressed material during creep exposure.

The elastic–plastic transition in nanograined polycrystals

Georges Saada, Guy Dirras June 11, 2013 Page range: 767-769

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Abstract

This paper is devoted to the analysis of the specific constraints imposed on the mean free path, the nucleation and the multiplication rate of dislocations in strained polycrystals whose grain size is smaller than about 100 nanometres. It is demonstrated that the extent of the microdeformation stage, at the end of which the yield stress should be measured, is definitely larger than the generally accepted value of 0.2 % proof strain for average grain sizes smaller than 125 nanometres. This analysis is confirmed experimentally in two instances. Systematic experimental analysis of the elastic – plastic transition in these materials is a necessary requirement in order to obtain relevant values of the flow stress in these materials.

Synchrotron X-ray line-profile analysis experiments for the in-situ microstructural characterisation of SPD nanometals during tensile deformation

Michael B. Kerber, Erhard Schafler, Arkadiusz K. Wieczorek, Gabor Ribarik, Sigrid Bernstorff, Tamas Ungar, Michael J. Zehetbauer June 11, 2013 Page range: 770-774

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Abstract

There is a great interest in the understanding of mechanical properties of nanocrystalline materials, especially of those processed by severe plastic deformation, since those exhibit both high strength and considerable ductility. A special setup for X-ray line profile analysis was developed for monitoring the microstructural evolution of in-situ tensile tests of high pressure torsion deformed samples. A comprehensive evaluation procedure is presented which allows the determination of several physical microstructural parameters. This includes a careful estimation of the error of the evaluation procedure. As an example, nickel shows a slight decrease of the size of the coherently scattering domains while the dislocation density tends to increase. The dislocation arrangement exhibits strain-field-screening of neighboring dislocations and an equal amount of screw and edge dislocations.

Tensile and fatigue properties of sub-microcrystalline ultra-low carbon steel produced by hpt-straining

Yoshikazu Todaka, Hironori Nagai, Yosuke Takubo, Miki Yoshii, Masaaki Kumagai, Minoru Umemoto June 11, 2013 Page range: 775-779

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Abstract

The tensile and fatigue properties of ultra-low carbon steel after HPT-straining at a rotation-speed of 0.2 rpm under a compression pressure of 5 GPa were investigated. Elongated grains with 300 nm thickness and 600 nm length with high dislocation density were formed by the HPT-straining. The obtained Vickers microhardness was around 3.6 GPa. The engineering tensile strength of the HPT-processed ultra-low carbon steel for 5 and 10 turns was 1.9 GPa, which is similar to the value of maraging high-alloy steels. The elongation increased with strain (at 5 to 10 turns). The increase in elongation is caused by the reduction of the stress concentration due to the existence of continuously recrystallized grains. The fatigue strengths of HPT-processed specimens were twice as high as those of the 90 % cold-rolled specimen in the low-cycle fatigue region, whereas in the high-cycle fatigue region the fatigue strengths were not so different due to the high notch sensitivity of the HPT-processed specimens.

Precipitation Effects in Ultra-Fine-Grained Mg–RE Alloys

Jakub Čížek, Ivan Procházka, Bohumil Smola, Ivana Stulíková, Martin Vlach, Vladivoj Očenášek, Olya B. Kulyasova, Rinat K. Islamgaliev June 11, 2013 Page range: 780-784

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Abstract

Mg-based alloys with rare-earth alloying elements are promising hardenable lightweight materials with good mechanical properties even at elevated temperatures. Ductility and strength of these alloys can be improved by grain refinement. Ultra fine grained Mg alloys with grain size around 100 nm were successfully prepared by high-pressure torsion. Ultra-fine-grained structure can enhance diffusivity of alloying elements due to the significant volume fraction of grain boundaries. As a consequence, precipitation effects in ultra-fine-grained alloys may occur faster than in corresponding coarse-grained materials. This phenomenon was examined in this work by comparison of the precipitation sequence in Mg – Tb – Nd and Mg – Gd alloys with ultra-fine-grained structure and corresponding coarse-grained alloys.

EBSD investigation of the grain boundary distributions in ultrafine-grained Cu and Cu–Zr polycrystals prepared by equal-channel angular pressing

Milan Dopita, Miloš Janeček, David Rafaja, Jaromír Uhlíř, Zdeněk Matěj, Radomír Kužel June 11, 2013 Page range: 785-789

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Abstract

Ultrafine-grained copper and cooper–zirconium polycrystals prepared by equal-channel angular pressing following the route Bc to various strain (1, 2, 4 and 8 passes) were investigated using electron back-scatter diffraction. Equal-channel angular pressing resulted in significant grain-size reduction. The original course-grained structure evolved from prolate bands of cells/subgrains enclosed by lamellar nonequilibrium grain boundaries (after the first two passes) towards an equiaxed homogeneous microstructure with equilibrium grain boundaries (after 8 passes). Significant changes in the volume fraction and the character of grain boundaries were observed both in Cu and in Cu – Zr alloy. Pronounced evolution of twin-related boundaries (3 n grain boundaries) with strain (number of ECAP passes) was found in Cu while only a weak increase of 3 and 9 grain boundaries was observed in Cu – Zr alloys.

Acoustic emission study of the deformation behaviour of magnesium sheets

Jan Bohlen, Patrik Dobroň, Kerstin Hantzsche, Dietmar Letzig, Frantisek Chmelík, Karl Ulrich Kainer June 11, 2013 Page range: 790-795

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Abstract

In this study, acoustic emission (AE) measurements were performed during tensile testing of sheets of four magnesium alloys in different orientations with respect to the tensile axis in order to investigate the influence of microstructure and texture on the deformation behaviour. AE measurements could especially be used for analysing the activity of twinning. It was shown that the grain size has an important impact on the AE count rates which was directly related to the activity of deformation mechanisms. Small changes in the texture can significantly affect the activity of twins. It was further shown that a weak texture promotes ductility.

Mechanical properties of pure titanium and Ti-6Al-4V alloys with a new tailored nano/meso hybrid microstructure

Hiroshi Fujiwara, Tatsuya Sekiguchi, Kei Ameyama June 11, 2013 Page range: 796-799

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Abstract

Pure titanium and Ti-6Al-4V alloy powders are treated by a mechanical milling process, which is one of the severe plastic deformation processes. The mechanical milling enables to produce a nano-grain microstructure very easily and has been applied to many powder materials. The bimodal microstructure in those mechanically milled powders is composed of a nano-grain structure with a grain size of about 50 nm in the surface-near region and of a work-hardened microstructure in the core region of the powder. We applied the hot roll sintering process to pure titanium and to Ti-6Al-4V mechanically milled powders. These compacts have a hybrid microstructure that consists of nano-grain structure with grain sizes of 200 to 500 nm and a micron size meso-grain structure. The hybrid microstructure materials demonstrate enhanced mechanical properties compared to conventional materials.

In-situ SEM/EBSD observation of abnormal grain growth in electrodeposited nanocrystalline nickel

Sadahiro Tsurekawa, Tatsuya Fukino, Takashi Matsuzaki June 11, 2013 Page range: 800-805

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Abstract

An in-situ SEM/EBSD technique has been applied to observe initial-stage and late-stage abnormal grain growth in electrodeposited nanocrystalline nickel with the aim of obtaining a comprehensive understanding of the dynamics of abnormal grain growth. We found that the late-stage abnormal grain growth occurred in an anisotropic manner such that the area of faceted {001} planes increased, and the faceted interface migrated by step motion. During abnormal grain growth, low-angle boundary and low- CSL boundaries such as 3 and 9 were found to migrate more slowly than random boundaries. As a result, small grains that possessed a CSL relation with the abnormally growing grain were often embedded into the abnormal grain. Initial-stage and late-stage abnormal grain growth both obeyed a parabolic growth law.

High-temperature creep properties of Fe–Al alloys modified by Zr

Miroslav Karlík, Petr Kratochvíl, Josef Pešička, Tomáš Vlasák June 11, 2013 Page range: 806-810

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Abstract

Two Fe – Al alloys with Zr additions were prepared by vacuum induction melting and rolling at 1200 °C: a disordered (ferrite – A2) and a D0 3 -ordered one. The data are compared to a similar Fe 3 Al-based alloy with lower Zr content investigated earlier. Tensile and creep tests were performed at 600, 700, and 800 °C, where the disordered alloy maintains its A2 structure, and D0 3 -ordered alloys are transformed to B2-ordered structure. Transmission electron microscopy of the alloys crept at 600 °C showed precipitation of fine particles on dislocations, subgrain boundaries and also in the matrix. Coarsening of these particles during creep at 800 °C takes place. The particles in Fe 3 Al-based alloys are identified mostly as zirconium carbides, whereas (Fe, Al) 2 Zr precipitates were observed in the ferritic alloy. The increase of Zr content from 0.25 to 0.6 at.% does not have a significant effect on the high temperature (HT) mechanical properties of the Fe 3 Al-type aluminide, because both alloys contain the same amount of carbon. In consequence no additional volume fraction of ZrC particles could be formed. The creep resistance of the ferritic alloy is considerably lower, but this material can easily be rolled to prepare sheets for HT corrosion protection.

ALCHEMI study of chromium doped iron-aluminides

Jozef Veselý, Miroslav Cieslar, Margarita Slámová June 11, 2013 Page range: 811-813

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Abstract

Mechanical properties of intermetallic iron-aluminides are strongly influenced by thermal pretreatment, stoichiometry and additional alloying elements. In the present study samples of FeAl and FeAl alloyed with Cr annealed at different temperatures were investigated. A revised ALCHEMI technique (Atom Location by CHanneling Enhanced MIcroanalysis) was employed to study site occupancies. The orientation dependences of characteristic X-ray yields were measured. Dynamic electron diffraction conditions with the systematic row excitation (planar ALCHEMI) were used. Experimental data were fitted by a theoretical calculation based on Bloch wave method. The distribution of elements on individual sublattices was obtained and preferential occupation of Al sites by Cr was confirmed.

Intermetallic compounds at the interface between Sn–Cu(–Ni) solders and Cu substrate

Petr Harcuba, Miloš Janeček, Margarita Slámová† June 11, 2013 Page range: 814-817

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Abstract

The influence of Cu content and Ni addition on the morphology and the growth kinetics of the intermetallic compound (IMC) layer formed at the interface of liquid Sn – Cu-based solders and the Cu substrate were investigated. The effects of temperature and reaction times on IMC morphology and thickness were studied. The reaction of a Sn-1.4Cu alloy with the substrate leads to the formation of a layer of Cu 6 Sn 5 (-phase) of typical scallop morphology. At long reaction times, a Cu 3 Sn (-phase) is observed at the interface between the Cu substrate and the Cu 6 Sn 5 layer. A small nickel addition to a Sn-0.6Cu alloy significantly changes the IMC morphology, accelerates its growth kinetics, prevents the formation of the Cu 3 Sn layer and reduces the rate of substrate dissolution. The effective activation energy of growth of the IMC layer in the Sn – Cu – Ni alloy was determined.

The effect of the microstructure on elastic properties of a polycrystalline stoichiometric NiAl

Przemysław Witczak, Zbigniew Witczak June 11, 2013 Page range: 818-821

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Abstract

Elastic constants for a polycrystalline stoichiometric NiAl intermetallic obtained via different processing routes were measured using ultrasonic methods. Samples having various porosity, (0 – 0.1), texture, and 0.2 – 200 μm grain size were produced by combined operations of casting or self-sustaining high-temperature synthesis, followed by hot hydrostatic extrusion and/or hot isostatic pressing. It was shown that the bulk modulus, as a quantity independent of crystallographic texture, depends on porosity according to an exponential relationship. Elastic properties of near theoretical density materials having various grain sizes were measured under high hydrostatic pressure ranging up to 1 GPa. Parameters of the equation of state were determined. The values of bulk moduli and their first pressure derivatives for the nanostructured material under investigation and of single crystals appeared to be the same.

Ab-initio simulation of the tensile strength of silicon nanofilms

Yoshitaka Umeno June 11, 2013 Page range: 822-825

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Abstract

Investigations of the relation between atomic configuration and strength at atomic and electronic level are important not only for understanding the fundamental deformation behavior of materials but also for application of materials to nanostructured devices. In this study, simulation of tension of silicon nanofilms under tensile stress was carried out using ab initio density functional theory calculation to investigate the effect of surface structure on tensile strength. Nanofilms with various surface orientations were examined. The theoretical tensile strength of Si nanofilms with a thickness of around 1.0 nm having (100) surfaces, which are flat with dimer-row structure, was only slightly lower than that of bulk Si. In contrast, surfaces with rather high Miller indices can significantly reduce critical strain owing to surface steps, indicating that such atomic-level structure affects the strength quite strongly.

New properties of halogen plasma-treated Cu films

Vitaly Pikulev, Dries Dictus, Svetlana Loginova, Mikhail R. Baklanov June 11, 2013 Page range: 826-829

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Abstract

Luminescence activity and structure of halogen plasma-treated Cu films on Si substrate have been investigated. Peculiar photoluminescence signals in the range of 1.6 – 2.0 eV were detected both at low (from 77 to 15 K), and at room temperature. The observed luminescence peaks are not present for stoichiometric CuCl. The exposure of CuCl- and CuBr-containing layers to helium plasma, with UV-illumination, result in the formation of knots of twisted nanowires on the surface of these layers. These wires don't have luminescent activity. The accelerated degradation of luminescence of these samples in air in the presence of light illumination and ozone treatment was studied.

Applied

High-speed deformation of titanium during dynamic channel-angular pressing

Vitaly Zel'dovich, Eugeny Shorokhov, Natalya Frolova, Igor Zhgiliev, Alexey Kheifetz, Irina Khomskaya June 11, 2013 Page range: 830-833

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Abstract

A titanium sample was deformed using dynamic channel-angular pressing using a shock loading technique. The structural changes and the cracking behavior occurring during the high-speed deformation were studied by metallographic inspection. A geometrical method of determining the amount of uniform shear strain upon equal-channel angular pressing is suggested. The localized deformation leads to the appearance of adiabatic shear bands. Two types of adiabatic shear bands were observed that intersect the sample in either the longitudinal or transverse directions. The occurrence of recrystallization inside the bands indicates local heating of the material to 770 – 870 K. The morphology of the adiabatic shear bands can be described as a multilayer structure. The width of bands is up to 100 m.

Microstructural evolution of equal-channel angular pressed interstitial-free steel

Kristián Máthis, Tomáš Krajnák, Miloš Janeček, Milan Dopita, Hyoung Seop Kim June 11, 2013 Page range: 834-837

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Abstract

Equal-channel angular pressing (ECAP) belongs to advanced technologies for improving mechanical properties of materials. In the present work, the influence of the number of ECAP passes using route B C on both grain size and mechanical properties of interstitial-free steel was investigated by means of transmission electron microscopy, electron back-scattering diffraction, and microhardness testing. It was found that the grain size decreases with the increasing number of passes. At the same time, an increase in microhardness was observed. The evolution of microstructure with increasing strain imposed through ECAP, in particular the process of grain fragmentation and the formation of high-angle boundaries were also examined.

Effect of equal channel angular pressing on microstructure, texture, and high-cycle fatigue performance of wrought magnesium alloys

Julia Müller, Miloš Janeček, Sangbong Yi, Jakub Čížek, Lothar Wagner June 11, 2013 Page range: 838-842

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Abstract

The magnesium alloys AZ80 und ZK60 received from Dead Sea Magnesium in as-cast conditions were extruded at T = 350 °C using an extrusion ratio of ER = 22. The extruded bars were severely plastically deformed by equal channel angular pressing (ECAP). Multiple ECAP processing up to 8 passes was done. The ECAP-induced changes in grain size and grain size distribution were measured by transmission electron microscopy while changes in dislocation density and crystallographic textures were determined by positron annihilation spectroscopy and X-ray diffraction analysis, respectively. The strain induced by ECAP was found to influence the microstructural characteristics, in particular the grain size, the dislocation density, and the crystallographic texture, which in turn enhance (or deteriorate) the mechanical or fatigue response of both alloys.

The characteristics of superplastic flow in a magnesium alloy processed by ECAP

Roberto B. Figueiredo, Terence G. Langdon June 11, 2013 Page range: 843-846

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Abstract

It is well known that Equal-Channel Angular Pressing (ECAP) introduces an ultrafine grain size and leads to exceptional superplastic properties in a ZK60 (Mg-5.5 % Zn-0.5 % Zr) alloy. This paper presents an analysis of the flow behavior during superplastic deformation in the ZK60 alloy. It is shown that an increase in the ECAP processing temperature enhances the thermal stability of the grain structure. In addition, the optimum superplastic properties occur at higher strain rates when testing at higher temperatures thereby introducing the potential for achieving high strain-rate superplasticity.

Deformation behaviour of ultrafine-grained 7075 aluminium alloy

Pavel Lukáč, Kryštof Turba, Přemysl Málek, Miroslav Cieslar June 11, 2013 Page range: 847-850

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Abstract

Samples of a 7075 aluminium alloy were prepared by the equal-channel angular pressing (ECAP) technique. The channel had a 10 mm × 10 mm cross section and an angle of 90°. A total of six passes was performed using route B C . The ECAP processing was carried out at 120, 170, and 220 °C. The ECAP-processed samples with grain sizes between 300 and 2000 nm were machined to tensile specimens with their tensile axis parallel to the pressing direction. Uniaxial tensile tests were carried out using an INSTRON testing machine at temperatures between room temperature and 300 °C at a constant crosshead speed giving an initial strain rate of 10 – 3 s – 1 . The maximum stress decreases with increasing testing temperature. The elongation to failure increases with increasing testing temperature. The values of the yield stress, the maximum stress (ultimate tensile stress), and the elongation to failure depend also on the ECAP processing conditions.

The optimization of ECAP conditions to achieve high strain-rate superplasticity in a Zr- and Sc-modified aa 7075 aluminum alloy

Kryštof Turba, Přemysl Málek, Edgar F. Rauch, Florence Robaut, Miroslav Cieslar June 11, 2013 Page range: 851-857

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Abstract

An AA 7075 aluminum alloy with Zr and Sc additions was subjected to 6 – 8 passes of equal-channel angular pressing at 120, 170, and 220 °C in order to study the effect of the pressing conditions on the microstructural characteristics and the consequences for high-temperature mechanical properties. Using the method of electron backscatter diffraction, a decrease in pressing temperature was found to lead to a more pronounced refinement of the microstructure and a higher fraction of high-angle grain boundaries, but at the same time compromised the ability of the Al 3 (Zr, Sc) phase to stabilize the ultra-fine-grained microstructure at elevated temperatures. Optimum superplastic properties were therefore achieved after pressing at the intermediate temperature of 170 °C. The material exhibited high strain-rate superplasticity with a ductility of 650 % at an initial strain rate of 1 × 10 – 1 s – 1 .

Multilayer composite al99.99/almg3 sheets prepared by accumulative roll bonding

Margarita Slámová†, Peter Sláma, Petr Homola, Jaromír Uhlíř, Miroslav Cieslar June 11, 2013 Page range: 858-862

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Abstract

Accumulative roll bonding (ARB) allows producing ultrafine-grained sheets of high strength and has been successfully used to prepare such materials from aluminium alloys. However, due to intensive work hardening of bond-rolled AlMg3 sheets, significant edge cracking occurred. Cracking was reduced by cladding AlMg3 with aluminium. Lamellar composites were thus prepared. Their structure was studied by electron backscatter diffraction and transmission electron microscopy; hardening was evaluated by microhardness measurements and tensile tests. Composite grain sizes are coarser than in the mono-material sheets. Accordingly, the evolution of strength with ARB-cycling in both materials differs. AlMg3 composite layers exhibit less work hardening than the mono-material; the composite strength is between that of the two mono-material ARB-sheets while the ductility does not differ substantially.

Preparation of ultrafine-grained twin-roll cast AlMg3 sheets by accumulative roll bonding

Petr Homola, Margarita Slámová†, Peter Sláma, Miroslav Cieslar, Miroslav Karlík June 11, 2013 Page range: 863-866

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Abstract

Accumulative roll bonding is a method for achieving grain refinement of metallic materials by severe plastic deformation, resulting in strength superior to that of conventionally manufactured sheets. The method has been successfully used by the authors to prepare bulk ultrafine-grained sheets from pure aluminium and several twin-roll cast aluminium alloys. The present paper summarizes the results of a study aimed at monitoring the evolution of microstructure and mechanical properties during the accumulative roll bonding process of a twin-roll cast AlMg3 (AW – 5754) alloy. Moreover, the annealing behaviour of the roll-bonded sheets is compared with the behaviour of conventionally rolled counterparts.

Recovery and recrystallization behavior of aluminum processed by extrusion-preceded equal channel angular pressing

Aikaterini Zi, Ivana Stulíková, Bohumil Smola, Werner Riehemann June 11, 2013 Page range: 867-870

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Abstract

High-purity aluminum was severely plastically deformed by miniaturized extrusion-preceded ECAP as well as by cold rolling. Isochronal and isothermal annealing was performed to investigate the recovery and recrystallization behavior by measuring the development of Vickers microhardness and electrical resistivity. Both processes were found to take place which was verified by TEM and EBSD observations. The onset and course of recovery and recrystallization in cold-rolled Al were postponed to higher temperatures and time due to the lower stored deformation energy. The activation energies for recovery and recrystallization estimated from the microhardness response to isothermal annealing match well those of relevant processes, namely those of thermally activated dislocation motion, pipe-, boundary-, and self-diffusion.

Low sliding-wear resistance of ultrafine-grained Al alloys and steel having undergone severe plastic deformation

Yong-Suk Kim, Hyun Seok Yu, Dong Hyuk Shin June 11, 2013 Page range: 871-874

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Abstract

Dry sliding wear characteristics of ultrafine-grained Al alloys 1100, 5052, and low carbon ferrite-martensite dual phase steel (Fe-0.15C-0.25Si-1.11Mn-0.06V) were investigated. The Al alloys and the steel were processed by the accumulative roll bonding and the equal channel angular pressing, respectively, to produce the ultrafine-grained microstructure. Pin-on-disk wear tests were performed on the alloys at various applied loads at room temperature. Hardness and strength of the ultrafine-grained alloys increased with the increase in the accumulated total plastic strain. However, wear resistance of the ultrafine-grained alloys was not improved after the severe deformation. The low wear-resistance of the ultrafine-grained alloys was attributed to the lack of strain hardening due to unstable and non-equilibrium grain boundaries of the alloys and the cracking at the interface of the ferrite and martensite phases.

Study of the recrystallization of AW-5049 and AW-5754 twin-roll cast alloys by EBSD

Jaromír Uhlíř, Margarita Slámová†, Petr Homola June 11, 2013 Page range: 875-879

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Abstract

The paper presents the results of an investigation of the annealing response of sheets prepared from two twin-roll continuous cast aluminium – magnesium alloys. Sheets of 1 mm thickness prepared by cold rolling with 80 % reduction in thickness were annealed using an industrial regime with slow heating, holding at 350 °C and slow cooling. Hardness measurements and tensile tests allowed estimation of the magnitude of deformation recovery at different annealing stages. The evolution of the grain structure was studied by electron backscatter diffraction in a scanning electron microscope. The recrystallization in AW-5754 occurs at lower temperatures than in the AW-5049 material. The recrystallized grains are finer in the former alloy. The tensile properties of both AW-5754 and AW-5049 sheets are isotropic. Soft AW-5754 sheets exhibit less pronounced texture than AW-5049 ones.

XRD profile analysis of ECAP Cu and Cu + Zr samples

Zdeněk Matěj, Radomír Kužel, Milan Dopita, Miloš Janeček, Jakub Čížek, Tereza Brunátová June 11, 2013 Page range: 880-883

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Abstract

Technical purity copper and copper with addition of 0.18 wt.% of zirconium samples processed by equal channel angular pressing with different number of passes were studied by X-ray line profile analysis. Dislocation-induced broadening is the dominant effect determining diffraction line shape. X-ray analysis reveals increasing mean dislocation density (∼10 15 m – 2 ) with the number of ECAP passes. The character of the deformation field connected with the dislocation distribution is slightly different in pure copper than in copper with addition of zirconium and evolves significantly during 4 or 8 ECAP passes in the case of pure copper.

Stability of microstructure in silver processed by severe plastic deformation

Jenő Gubicza, Nguyen Q. Chinh, János L. Lábár, Géza Tichy, Zoltán Hegedűs, Cheng Xu, Terence G. Langdon June 11, 2013 Page range: 884-887

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Abstract

The stability of the microstructure of pure silver processed by equal channel angular pressing at room temperature was studied by transmission electron microscopy and X-ray line profile analysis. After processing by 1 pass the microstructure was stable, whereas after 8 passes a static recovery/recrystallization of the severely deformed microstructure was observed a long time after deformation when the material was stored at room temperature. This unusual behavior is attributed to the high degree of dislocation dissociation due to the very low stacking fault energy of silver. The highly dissociated dislocations may be annihilated a long time after deformation due to thermal activation assisted by stresses which evolve in the severely deformed microstructures.

Acoustic emission study of the mechanical anisotropy of the extruded AZ31 alloy

Patrik Dobroň, František Chmelík, Jan Bohlen, Kerstin Hantzsche, Dietmar Letzig, Karl Ulrich Kainer June 11, 2013 Page range: 888-891

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Abstract

The mechanical anisotropy behaviour of the extruded AZ31 magnesium alloy was investigated by in-situ measurements of acoustic emission. Specimens taken in the extrusion direction were uniaxially loaded in tension and compression at room temperature. The acoustic emission count rates were correlated with stress – strain curves and their values show local maxima at the yield point, which is linked with cooperative dislocation processes and/or with the occurrence of deformation twins, especially in compression tests. During compression tests, another acoustic emission maximum occurs after the yield point which indicates the activation of further deformation mechanisms. In this paper the acoustic emission results are presented and discussed in terms of texture evolution during plastic deformation.

Effects of shot peening on internal friction in cp aluminum and aluminum alloy 6008

Aneta Flejszar, Tomasz Ludian, Agnieszka Mielczarek, Werner Riehemann, Lothar Wagner June 11, 2013 Page range: 892-894

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Abstract

The strain-amplitude-dependent damping of bending beams of aluminum alloy 6008 and CP aluminum was measured at room temperature after different heat treatments and after shot peening. Shot peening led to an increase of damping in almost the whole measured amplitude strain range from 10 – 6 to 10 – 3 for CP aluminum. Strong ageing effects at room temperature were observed immediately after the shot peening process, namely an increase of the amplitude dependent part and a decrease of the amplitude-independent part of damping. After about 2700 h, ageing of the samples had saturated. For aluminum alloy 6008 much smaller ageing effects were found being due to compensating effects like formation of Cottrell clouds, precipitation of G.P. – zones, and the reduction of foreign atoms in solid solution. The found amplitude-dependent damping can be explained by the reversible movement of dislocations between strong pinning points like, e. g., precipitates and weak pinning points like solid solute atoms as proposed by the dislocation damping theory of Granato and Lücke. Using this model the found ageing effects can be explained by the diffusion of solid solute atoms to the dislocations.

Effects of grain growth on microhardness and coercivity in electrodeposited nanocrystalline nickel

Gabriele Vidrich, Aneta Flejszar, Agnieszka Mielczarek, Werner Riehemann June 11, 2013 Page range: 895-897

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Abstract

Nickel specimens with various grain sizes were produced by electrochemical deposition. As-deposited pure nickel had a mean grain size of 300 nm. By dispersing nanoscaled SiO 2 - and Al 2 O 3 -particles in the electrolyte it was possible to reduce the grain size by incorporation of these particles into the growing nickel matrix. The grain sizes were 150 nm and 60 nm for the Al 2 O 3 - and SiO 2 -reinforced nanocomposite, respectively. Microhardness and coercivity of all samples were measured immediately after electrodeposition and after successive isochronal heat treatments with increasing annealing temperature. Grain growth of the samples could be observed by a decrease in hardness as well as coercivity with increasing annealing temperature.

Strain release from pre-deformed Ni53.6Mn27.1Ga19.3 shape memory alloy during thermal cycling

Miroslav Frost, Alexandra Rudajevová June 11, 2013 Page range: 898-900

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Abstract

A polycrystalline Ni 53.6 Mn 27.1 Ga 19.3 shape memory alloy was deformed in compression in four steps up to a final deformation of 3.0 % at room temperature. After each deformation step the relative elongation was measured in two thermal cycles in the temperature range 300 K to 640 K, where a thermoelastic martensitic phase transformation occurs. A one-way shape memory effect and a two-way shape memory effect were observed after deformation of the alloy and their relation to other mechanical characteristics of the alloy are discussed.

Simulation of the growth kinetics of FeB and Fe2B phases on the AISI M2 borided steel: Effect of the paste thickness

M. Keddam June 11, 2013 Page range: 901-905

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Abstract

The influence of boron paste thickness on the simulated growth kinetics of Fe borides grown on the AISI M2 steel's substrate was investigated. The boron potential was varied using two boron paste thicknesses (3 and 4 mm) with time durations of 2 and 6 h, and treatment temperatures of 1223, 1253, and 1273 K. Assuming that the growth of the boride layers follows a parabolic law, a kinetic model was applied to evaluate the parabolic growth constant at each growing phase interface, the layer thicknesses of Fe borides, as well as the associated mass gain depending on the treatment parameters (process time, temperature, and boron paste thickness). The simulation results were in good agreement with experimental data taken from the literature.

High-pressure torsion deformation of a magnesium-based nanocomposite

Zoltán Száraz, Zuzanka Trojanová, Michael Zehetbauer June 11, 2013 Page range: 906-909

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Abstract

Discs of microcrystalline magnesium reinforced with Al 2 O 3 nanoparticles were deformed by high-pressure torsion at room temperature. Hydrostatic pressures from 1 to about 4 GPa were used and discs were deformed from 0.5 up to 2 rotations. The in-situ flow stress curves were obtained and transformed into resolved shear stress/resolved shear strain curves. In-situ stress – strain curves indicate some softening effects, which probably arise from recrystallisation. The evolution of microstructure was observed with methods of light microscopy and transmission electron microscopy. Radial dependence of the microstructure was also monitored with microhardness measurements. The high-pressure torsion deformation also affects the distribution of the reinforcing particles in the hexagonal matrix.

Fracture behavior of Mg–Li matrix composites

Stanislav Kúdela, Horst Wendrock, Stanislav Kúdela, Andrzej Pawełek, Andrzej Piątkowski, Klaus Wetzig June 11, 2013 Page range: 910-914

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Abstract

Deformation and fracture of Saffil fiber (SF) reinforced Mg, Mg-8 wt.% Li and Mg-12 wt.% Li composites was monitored by means of in-situ scanning electron microscopy during 3-point bend tests. Mg and MgLi matrix composites (10 vol.% SF) were prepared by the melt infiltration technique. Poor interfacial bond causes premature failure of the SF/Mg composite that is usually triggered by the debonding of perpendicular fibers at the convex composite surface. Strong interfaces in SF/Mg12Li composite result in multiple cross-breakage of aligned fibers which is indicative of their participation in the composite strengthening. Resultant composite strengthening is frustrated by massive stress relaxation of the Mg12Li matrix. Strong interfaces and fairly high strength of the Mg8Li matrix cause remarkable strengthening of SF/Mg8Li composites. The cleavage of phases in two-phase Mg8Li matrix plays an insignificant role in the composite failure.

Notifications

The 80th Birthday of Dr.-Ing. Wolfgang Eychmüller

P. Segar June 11, 2013 Page range: 915-916

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Personal

June 11, 2013 Page range: 917-918

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About this journal

The International Journal of Materials Research (IJMR) publishes original high quality experimental and theoretical papers and reviews on basic and applied research in the field of materials science and engineering, with focus on synthesis, processing, constitution, and properties of all classes of materials. Particular emphasis is placed on microstructural design, phase relations, computational thermodynamics, and kinetics at the nano to macro scale. Contributions may also focus on progress in advanced characterization techniques.
All articles are subject to thorough, independent peer review.