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Deformation response of DP1200 steel was studied under high strain rate. Ferrite cracking occurs when strain rate exceeds the critical range (500–700 s−1). Cracks in ferrite propagate to martensite/ferrite interface, weakening its inhibitory effect on adjacent martensite. Thus martensitic deformation becomes the main factor of total deformation earlier to enhance the total strength.

Through Ni-carbonyl CVD process, bulk Ni material (hereafter referred as CVD Ni) with bimodal grain structures, i.e. UF grains and large grains with UF/nano twins, can be produced. In tensile test, this material demonstrated a very good combination of strength and ductility as well as a special strain hardening behavior. Upon investigating the material's hardening behavior, a critical threshold strain, ec, of 0.02 was identified for the distinct change in the strain hardening behavior. Prior to this strain level, the strain hardening rate of the CVD Ni was found always higher than that of its counterpart coarse-grained (CG) Ni; but it dropped, after this strain, to the same level as the CG material. Furthermore, through the analysis of results from Tension Unloading Reloading-in-Tension (TURT) tests, this specific strain value was also found to be significant in the change of the hysteresis loop width as well as the back stress strain hardening responsible for the material's Bauschinger behavior. Microstructural evolution examination suggests that most of the twin boundaries (TBs) initially acted as obstacles to dislocation movement providing strong dislocation back stress and hence contributing to the strong hardening behavior. From the strain level of 0.02 and onwards, however, massive detwinning was detected which is responsible for the drop in the hardening rate. Finally, dislocation cell structures, that were typically evolved from entanglements of dislocation inside CG Ni, were also found inside the detwinned large grains of CVD Ni in the high strain regime, which yielded similar strain hardening behavior as in the CG Ni material.

Thermomechanical processing determines the practical applications of metal–matrix composites (MMCs) by contributing to the interrelationship between their microstructure and properties. In this study, we investigate the changes in Al-3.0Cu-1.2Mg/SiCp (40 vol%) caused by the tension applied at high temperatures and strain rates. The study shows the microstructural changes and mechanical characteristics resulting from the cold/warm and hot rolling of the extruded material. It is observed that hot rolling has a favorable effect on the restoration of the defects formed in parts of the extruded bar. The microstructural characteristics of the composite related to the deformation-induced redistribution of the secondary inclusions in the matrix and fracture of the reinforcement particles are shown. High-temperature uniaxial tensile testing of the studied composite conducted under high strain rates (10−1 and 10−2 s−1) indicates an increase in the ductility. The decrease in the stress of the tested samples is attributed to the refined grains in the matrix after the thermomechanical processing. The testing of the given material provides the stress–strain relationships, which indirectly assist in ranking the relative formabilities of the differently processed sheets of the MMCs with a high-volume fraction of the reinforcement particles. The proposed approach may be considered for the near net-shaped manufacturing of MMCs with high wear resistance and low thermal expansion coefficients.

By the method of cold rolling, appropriate intermediate annealing and final annealing treatments, the multi-scale lamellar structure of ultrafine grains distributed in ribbons with coarse grains was produced in an Al-1.2Mn alloy, which displayed excellent combination of high strength and good ductility compared to coarse-grained and ultrafine-grained alloys. The high strength of the alloy with multi-scale lamellar structure is attributed to back stress strengthening associated with the formation of geometrically necessary dislocations and the good ductility results from the high strain hardening rate during plastic deformation. Loading-unloading-reloading tests were carried out to measure the back stresses of the alloys. The results show that the back stress of the specimen with multi-scale lamellar structure is much higher than that of the coarse-grained specimen.

To evaluate the dynamic mechanical properties of 25CrMo4 steel, the stress-strain curve of 25CrMo4 steel have been obtained by performing quasi-static and impact compression experiments at strain rates ranging from 0.001 s − 1 to 4163 s − 1 . The 25CrMo4 steel displays an obvious strain rate effect and its hardening rate changes with the strain and strain rate. It even shows softening effect at high strain rates. Further, the grains of 25CrMo4 steel show features of both body-centered cubic (BCC) and face-centered cubic (FCC) structures and are severely stretched and fragmented during impact loading, as evidenced by microscopic observations. Based on these two points, the Zerilli-Armstrong (ZA) constitutive equations have been improved reasonably. These can provide the mechanical properties of 25CrMo4 steel during impact compression loading, which can in turn be used as reference values for practical engineering analysis.

Lightweight steels containing a considerable content of Al show high specific strength and ductility, but there are some drawbacks such as low yield strength and stringer-type bands formed along the rolling direction. Here we design new duplex lightweight steel in order to complement the drawbacks, and achieve ultra-high yield strength (865 MPa), good ductility (41%). Submicron ferrite mainly affects high yield-to-tensile ratio, and high strain hardening is attributed to Lomer-Cottrell lock and planar slip, and cell structure by further deformation in austenite. These results are expected to provide a desirable possibility for applications to reinforcement components requiring high yield-to-tensile ratio.

Strain distribution and void formation sites were investigated in fine multi-layered steel sheets subjected to tensile deformation. The sheets comprised of alternating layers of ferrite and martensite wherein the layer thickness was varied but remained sufficiently thin to suppress their early fracture. Additionally, the influence of layer thickness on the deformation and fracture behavior was discussed. The elongation was not significantly enhanced with decreasing layer thickness. Furthermore, strain was inhomogeneously introduced in the sheets and continuously distributed regardless of the layers. The high strain regions were distributed more finely as the layer thickness decreased. Cracks were generated at the highly strained martensite layer, which grew to large voids. The fracture surface on the martensite layer comprised of fine dimples, while that on the ferrite layer consisted of large and shallow dimples or a cleave-like fracture surface. Therefore, the coalescence of large voids developed in the martensite layer, accompanied by the secondary voids or quasi-cleavage fracture in the ferrite layer, results in the fracture of the multi-layered steel sheets. Based on the calculation with Scheyvaerts's criterion, the critical stress of void coalescence was approximately equal in the steel sheets with 17, and 97 layers, which was why the layer thickness hardly affected the elongation of the steel sheets.

The effect of strain rate (0.001–800/s) on two commercial ferrite-martensite dual phase steels (DP600 and DP800), having different martensite contents (10.2% and 33.2%, respectively) were investigated. Microstructures of the deformed samples have been studied to understand the influence of strain rate on the micro-mechanisms of deformation in dual phase steels. The observations reveal that the volume fraction and size of the martensite play an important role in the deformation at different strain rates. Dislocation cells formed as the steels were deformed at different strain rates but the size of these cells and the extent of cell formation varied significantly with strain rate and martensite fraction. While deforming at various strain rates, martensite in DP600 was found to remain undeformed where the deformation was mainly prevalent within the ferrite grains. Although at high strain rates, extreme dislocation generation within the matrix of DP800 caused the fragmentation of martensite crystals. Secondary slip system of BCC ( 〈 111 〉 {112}) was also found to coexist with the primary slip system at higher strain rates which aided the plastic deformation at high strain rates within the ferrite grains. The difference in the martensite volume fraction and distribution in these two steels also affected the void initiation and fracture morphologies when deformed at various strain rates.

The effects of multi-axial compression (MAC) on the microstructural evolution of pure Al and Al–4 wt%Mg alloy were investigated by means of TEM and EBSD techniques. It shows that the addition of high concentration solute Mg to Al changes the grain refinement process. Most importantly, new high-angle grain boundaries form via different mechanisms for pure Al and Al–4 wt%Mg alloy: orientation splitting for pure Al and shear banding at low strain and orientation splitting at high strain for Al–4 wt%Mg alloy. In addition, the solute Mg can hinder the dislocation slip and retard the dynamic recovery during the deformation process. Consequently, the Al–4 wt%Mg alloy exhibits a slower misorientation evolution compared to pure Al, and obvious differences in hardness and microtexture evolution exist between pure Al and Al–4 wt%Mg alloy.

Microstructural changes and ferrite phase transformation under shock loading, between 8.5 GPa and 17.5 GPa, in a hot-rolled Lean Duplex Stainless Steel (commercially known as LDX 2101) were investigated in as-received and pre-deformed conditions. The latter condition was considered to distinguish classical deformation twins at high strain rates from those associated to the reversible ferrite phase transformation. Plate impact experiments were used to introduce compressive shock loading at peak stresses below and above the stress threshold of the ferrite phase transformation, 13 GPa. Effects of shock loading were also examined by compressing shocked samples quasi-statically and comparing their response with those tested in the as-received condition. The microstructural examinations revealed that the ferrite in LDX 2101 experienced a reversible phase transformation at a peak stress of ~17 GPa. The fingerprints for this transformation were {112} primary twins and {332} primary and secondary twins. In addition, the yield stress of the sample pre-shocked at ~17 GPa showed a considerable increase (⁓150 MPa) compared to the flow stress in as-received conditions.

At room temperature, the strain-rate sensitivity (SRS) was almost negligible at high strain rates in as-extruded Mg–3Al–1Zn alloy because of the exponent ( m ) of 0.008. However, SRS became remarkable with decreasing strain rate down to 10 −8 s −1 , where the m value increases up to 0.06.

Hot compression tests were carried out in temperature range of 680–880 °C and at strain rates of 0.001–1 s −1 on Ti–6V–6Mo–6Fe–3Al beta titanium alloy. The stress–strain curves showed yield point phenomena, especially at high strain rates and low temperatures. A polynomial equation was developed to relate the yield drop to the Zener–Hollomon parameter. It was found that the yield drop reaches a maximum and remanis nearly constant at high values of the Zener–Hollomon parameter (ln Z >30). The flow curves at high temperatures and low strain rates were typical of dynamic recovery. However, at low temperatures and high strain rates (27 Z

The uniaxial quasi-static and dynamic tensile tests were conducted at different strain rates (10–3 s−1, 800 s−1, 1900 s−1 and 2900 s−1) for 7050-T7451 aluminum alloy. Then, research of the strain rate hardening coefficient in the original Johnson–Cook model at different strains and strain rates showed that the coefficient is a function of strain and strain rate from the tensile experimental results. Furthermore, a modified Johnson–Cook model was proposed to describe the flow behaviors of the studied alloy based on the correction to the strain rate hardening coefficient. Comparisons between the experimental data and predicted results using the original JC model, Khan–Liu (KL) model and the modified JC model showed that a better agreement can be obtained applying the modified model than the other two models. Verifications for predicting three new high strain rates (1500 s−1, 2500 s−1 and 3500 s−1) experimental data demonstrated the modified JC model can provide an accurate description for the dynamic behaviors of the studied alloy.

In this paper, the distinct influences of pre-strain on low cycle fatigue (LCF) behavior of CP-Ti at different strain amplitudes are clarified from macroscopic and microscopic aspects. At low strain amplitude, the sample of as-received material (AR) shows pronounced secondary cyclic hardening, however, this phenomenon gradually disappears in pre-strained (PS) sample with the increase of pre-strain. As cyclic stress amplitude and mean stress of PS sample increase with the decrease of strain amplitude, the detrimental effect of pre-strain on LCF life becomes more significant at lower strain amplitude, indicating the pre-strain dependent LCF behavior. At high strain amplitude, due to the more significant cyclic softening and mean stress reduction behavior, cyclic stress amplitude and mean stress rapidly decay to the value of AR sample in the initial few cycles, indicating the pre-strain independent LCF behavior. As the reduction of LCF life is related to the increase of mean stress and stress amplitude, the asymmetry coefficient related model can be applied to predict LCF life of CP-Ti. Further TEM observation shows that at low strain amplitude, dislocation structures of AR sample are mainly composed of planar slip structures and the secondary cyclic hardening is caused by corduroy structure. After pre-strain, both planar slip and wavy slip structures are observed in PS sample, indicating that the irreversibility of the dislocation structures inherited from pre-strain causes the decrease of LCF life. At high strain amplitude, the dislocation structures introduced by pre-strain can be erased completely during subsequent cyclic deformation, consequently, dislocation configurations of AR and PS samples are composed of the same wavy slip structures.

This study shows that Mg–Mn alloys exhibit high strain-dependent damping values, which are much better than that of pure Mg in the high strain region. The high damping capacities of these alloys are attributed to the dislocation that connects to the dispersed α-Mn. However, excessive α-Mn creates an obstacle dislocation effect, which leads to the decrease in damping capacities because of the tangled dislocations. This conclusion is confirmed by the G-L theory and TEM images. Meanwhile, the dispersed phase hampers the increase of damping peaks of temperature-dependent damping capacities, and the α-Mn aggregate at grain boundaries can hinder them from sliding. The results of this study will be useful for the further development of high-damping Mg alloys.

The acoustic emission (AE) generated during tensile tests performed on Q345 steel specimens was investigated in this study. Two typical types of AE signals were obtained during the test: Type A signals with burst type waveforms in the micro-yielding and work-hardening stages and Type B signals with continuous-type waveforms during the discontinuous yielding (Luders band propagation) stage. The effects of the strain rate and notch on these two types of signals were studied. The AE energy of Type B signals increased with increasing strain rate and was much higher in notched specimens compared to unnotched ones at high strain rates. However, for Type A signals, less AE energy was generated in notched specimens than in unnotched specimens, and it showed little sensitivity to changes in the strain rate. These results were fully analyzed by relating the AE behavior to the deformation properties and transmission electron microscope (TEM) observations of the materials. Thus, the AE source mechanisms and the effects of the strain rate and notch during plastic deformation were determined for discontinuous yielding materials.

This paper develops a new constitutive model for HCP metals subjected to high strain, high strain rate and high temperature based on the theory of thermally activated dislocation motion in crystal materials. The constitutive parameters of the material are determined by a new efficient method composed of a global genetic algorithm and a local penalty-function algorithm, which guarantees that the constitutive parameters are a globally optimal solution in their theoretically allowed ranges. The application of the model to Ti6Al4V alloy shows that in the high strain rate regime, the model prediction is much more accurate than those by the Johnson–Cook and Zerilli–Armstrong models.

International audience; The development of hot rolling textures, and particularly the Brass {1 1 0} component, of two typical aeronautical alloys: Al-Cu-Li AA2050 and Al-Zn-Mg-Cu AA7050, has been investigated by EBSD and X-ray diffraction measurements after plane strain compression tests and industrial hot rolling. Systematic hot channel-die compression tests were performed to strains of 2.7 at 420-450 degrees C, on both as-homogenized alloys. Under the same processing conditions, the two alloys develop the same rolling textures showing that the presence of Li is not intrinsically responsible for the development of strong Brass components. However, it is shown, by further channel-die compression tests between 350 and 500 degrees C and up to strains of 3.9, that the deformation temperature can have a major influence: with increasing temperature {1 1 0} orientations are strongly favoured at the expense of the Copper {1 1 2} component. Numerical simulations demonstrate that previous and current experimental observations of the influence of temperature on texture development can be explained by increasing slip on non-octahedral slip systems.

This work examines the evolution of the dislocation structure in large grains of polycrystalline copper with decreasing strain amplitude. The experimental results show that (1) dislocation reversal is initially triggered by the operation of a final slip system, which is formed by the previously high strain amplitude when the strain amplitude is reduced; and (2) the region that is occupied by the dislocation reversal structures called loop patches. It is small in large grains because a more homogenous internal stress distribution induces a more uniform evolution of dislocations in large grains.

Available online: 14th of August 2009 This article has been retracted: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy ). This article has been retracted at the request of the Editor in Chief. The authors carried out all the reported experiments except for the transmission electron microscopy imaging (TEM) which was a complementary evaluation and performed by a third party. It has now come to light that the TEM images provided by this third party, (figures 4 & 5), may not be trustworthy. The authors confirm the reliability of the rest of the results and the reported conclusions. The authors would like to apologize to the readers of “Materials Science and Engineering A” for any inconvenience caused.

Deformation textures and recrystallization textures of ultrafine grains pure copper produced by asymmetrical accumulative roll-bonding (AARB) and symmetrical accumulative roll-bonding (ARB) respectively were investigated using X-ray diffraction (XRD). It was found that dominant deformation textures of copper after 98.4% strain are {1 0 0} shear texture by AARB and {2 1 1} copper texture by ARB, a mixed “deformation–recrystallization” texture is observed during the first stage of recrystallization, dominant recrystallization texture is {0 0 1} cube texture in samples produced respectively by AARB and ARB. We suggest that deformation textures and recrystallization textures are controlled by the crystal structures and deformation methods of samples, some unusual properties in ultrafine grains pure copper are possibly unstable.

Research into the production and properties of bulk nanostructured materials was first initiated in Ufa twenty years ago and has continued to the present day. This paper traces these developments and briefly summarizes some of the many achievements coming from this work. The impact of this research is examined with respect to the many publications from Russia in the field of Materials Science appearing in the scientific literature over the last ten years.

The high-cycle fatigue behavior of smooth and notched samples of ultrafine-grained titanium prepared by severe plastic deformation is compared with the corresponding properties of conventional titanium. It is shown that the combination of high strength and enhanced ductility of ultrafine-grained titanium lead to an increase of the fatigue endurance limit. Using a combination of equal-channel angular pressing and subsequent thermal and mechanical treatment, it was possible to increase the fatigue endurance limit of commercial-purity titanium by a factor of 1.5. Furthermore, it is shown that post-deformation annealing can additionally enhance the ductility of the ultrafine-grained Ti and lower fatigue-notch sensitivity particularly in comparison with Ti-6Al-4V.

Most of severe plastic deformation processes involve strain reversal. Till now quite big number of researches has been done on indirect study of its role, which discusses the effect of loading path in ultra-fine grained structure formation. This work is aimed to study directly the role of the strain reversal in grain refinement by severe plastic deformation. A 99.99% purity aluminum was processed by high pressure torsion up to 96° rotation (maximal equivalent strain ɛ ≈ 8) with two deformation modes: monotonic and reversal deformations with a step of 12° rotation (maximal equivalent strain ɛ ≈ 1). It was shown that strain reversal retarded the grain refinement in comparison with the monotonic deformation. This explains slower rate of the nanostructure formation of the SPD processes that involve strain reversal.

The effect of Mn on the damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloys has been studied. The damping vs. strain amplitude spectrum of the studied alloys could be divided into three parts. The strain amplitude weakly dependent part appears again when the microplastic strain occurs at high strain amplitude. The mechanical properties of as-cast Mg–3 wt.%Ni alloy could be improved by the addition of Mn, which is due to the refinement of α-Mg dendrites and solid solution strengthening by Mn. In addition, the corrosion resistance of the alloys could also be improved remarkably by the addition of Mn.

Experimental observations pertaining to the damage evolution in Starphire®, a soda-lime transparent-armor glass, made in the recent work of Strassburger et al. [E. Strassburger, P. Patel, J.W. McCauley, C. Kovalchick, K.T. Ramesh, D.W. Templeton, Proceedings of the 23rd International Symposium on Ballistics, Spain, April, 2007; E. Strassburger, P. Patel, J.W. McCauley, D.W. Templeton, Proceedings of the 23rd International Symposium on Ballistics, Spain, April, 2007] in a series of edge-on-impact (EOI) tests and other open literature experimental findings are used to construct a (high strain-rate, high-pressure, large-strain) ballistic constitutive model for this material. The basic components of the model are constructed in such a way that the model is suitable for direct incorporation into typical transient non-linear dynamics finite element-based software packages like ANSYS/Autodyn [ANSYS/Autodyn version 11.0, User Documentation, Century Dynamics Inc. a subsidiary of ANSYS Inc., 2007] or ABAQUS/Explicit [ABAQUS version 6.7, User Documentation, Dessault Systems, 2007]. To validate the material model, a set of finite element analyses of EOI tests was carried out and the computational results compared with their experimental counterparts. It is found that front-shapes and propagation velocities of the longitudinal and transverse waves are quite well represented by the model. The same was found to be the case for front-shapes and propagation velocities of the “coherent-damage” zones but mainly at shorter post-impact times. Discrepancies at longer post-impact times are attributed to the effects of damage-promoting target-fixturing-induced stresses and cutting/grinding-induced flaws.

The inner corner angle (ICA) is one of the major factors affecting deformation homogeneity in workpieces during equal channel angular pressing (ECAP). In this study, the effect of the ICA on the plastic deformation behavior in ECAP was investigated using the finite element method. A round ICA induces highly inhomogeneous deformation in the head, tail, top and bottom regions of the workpiece due to increasing compressive and decreasing shear deformation components. It was found that a round inner corner with an angle up to 9° is acceptable in finite element simulations for reproducing a sharp inner corner. These results can serve as a design guide for processing and dies of ECAP.

The precipitation behavior during equal-channel angular pressing (ECAP) performed at room temperature and 175 °C in an Al–Mg–Si alloy has been investigated. Dynamic precipitation was in fact observed during severe plastic deformation at both temperatures and reasons for dynamic precipitation were analyzed and compared with that in conventional static aging. The interaction between precipitates and dislocations was investigated and strengthening mechanisms were discussed.

Low cycle fatigue (LCF) behavior of the Ni–Fe-based superalloy IN718 was examined in various heat-treated conditions. The alloy was subjected to solution treatment, peak ageing, over ageing and extra over ageing to study the role of precipitates on its LCF behavior. This alloy is found to exhibit dual slope Coffin–Manson relationship in all the above heat-treated conditions examined. While the slope of the segment corresponding to the region of high strain is lower than that of the region of low strain amplitude for solution treated, peak aged and extra overaged conditions, there is reverse trend in the slope of the two segments in the overaged condition.

An Al-6061 alloy was processed by equal-channel angular pressing at room temperature for one, two, four and six passes and microhardness measurements were recorded along linear traverses on longitudinal planes in the centers of each billet. The results show the average microhardness increases significantly in the first pass although there is a region of lower hardness running in a band near the bottom surface of the billet. Additional but smaller increases in hardness occur in subsequent passes. The hardness values are distributed homogeneously throughout the longitudinal plane after ECAP through six passes although there remains a very narrow region of lower hardness within a distance of ∼0.5 mm adjacent to the bottom surface. When combined with earlier microhardness measurements taken on the Al-6061 alloy on the cross-sectional plane, the results confirm the potential for achieving excellent homogeneity after pressing through a total of six passes.

Evolution of dislocation cell microstructures during severe plastic deformation was analyzed using a modified kinetic dislocation model based on the two dimensional approach by ETMB [Y. Estrin, L.S. Toth, A. Molinari, Y. Brechet, Acta Mater. 46 (1998) 5509]. The proposed model simulated decreasing dislocation density after a maximum point and increasing misorientation angle with strain, which fits with experimental results well.

Recent advances in the analysis of strain-induced boundaries in cold working have led to a strong evolution in understanding of their nature and in nomenclature. This has impacted on the hot working domain, instigating a re-examination of microstructural behavior and pressure to revise the terminology. While hot working involves high strain rates and strains, it shares with creep the development of a steady state regime at relatively low strains. The development of substructure and response to Taylor polycrystalline constraints have essential differences from those in cold working, so the different boundary character warrants retention of their traditional names.

The literature data on dissociation widths in elemental semiconductors (Si and Ge) deformed under high-stress conditions are re-examined in the frame of a model which considers that moving dislocations are subjected to a periodic Peierls potential. It is concluded that the experimental results can be interpreted in a consistent way by considering that the mobility of a Shockley partial dislocation depends only on its core structure and not on its leading/trailing position.

Dynamic recrystallization (DRX) occurs ordinarily during low strain rate, hot deformation of low C or IF steels. Nonetheless, important processes are carried out with these materials at high strain rates, where the relevance of DRX has not been discussed. This paper shows how one can estimate a critical strain rate, above which DRX becomes unimportant in the hot mechanical behavior of IF steels, based on experiments carried out at low and moderately high strain rates.

Austenitic stainless steel of 304L type was thermo-mechanically processed to enhance special low CSL boundaries. Rolling reductions of above 60% of thickness was employed prior to annealing. It was observed that during recovery and recrystallization, twinning induced CSL boundary of Σ3 type. However, 80% of thickness reduction during grain growth regime, retarded Σ3 type grain boundary formation.

Ultrafine grained steels with grain sizes below about 1 μm offer the prospect of high strength and high toughness with traditional steel compositions. These materials are currently the subject of extensive research efforts worldwide. Ultrafine grained steels can be produced either by advanced thermomechanical processes or by severe plastic deformation strategies. Both approaches are suited to produce submicron grain structures with attractive mechanical properties. This overview describes the various techniques to fabricate ultrafine grained bcc steels, the corresponding microstructures, and the resulting spectrum of mechanical properties.

The mechanical hysteresis and the large recoverable deformation that shape memory alloys have in the pseudoelastic regime make them attractive for damping devices. The diffusion effects on the transformation temperatures in Cu–Al–Be are presented and evaluated near room temperature. The thermomechanical and aging treatments to optimize the mechanical properties of Cu–Al–Be wires for dampers through controlled grain growth are studied. In particular, the conditions to ensure the appropriate behavior without accumulative deformation against the cycle number, and in the coexistence zones, are analyzed. The pseudoelastic window of properly conditioned wires allows the use as dampers in civil engineering.

An investigation has been carried out on short crack growth behaviour of AISI type 316 stainless steel under creep-fatigue conditions at 550 °C for high strain ranges of 0.9–2.5% and 60 min hold-time using a high temperature reverse bending rig. The analysis revealed the dominant failure characteristics to be the individual initiation and growth behaviour of many minor cracks in Stage I, and their subsequent coalescence in Stage II. Increasing the strain range increases the number of minor cracks and promotes the process of minor crack coalescence. Predominantly intergranular long cracks are found to form under tensile stresses and transgranular short cracks under compressive stresses.

Composite materials typically have some degree of disorder in the distribution of particles of the second phase, leading to instances of close proximity of such particles. It is well known that under stress the two phases deform incompatibly giving rise to induced internal stresses. We show that proximity can lead to additional stresses in two different ways. First, and lesser, the incompatibility at the interface of a particle with the matrix is affected by the presence of a neighboring particle. Second, and much greater, the finite nature of the displacements associated with the incompatibility means that at close approach these displacements become significant with respect to the interparticle spacing with correspondingly large strains and stresses.

The rail steel S900A and Armco-iron have been deformed by severe plastic deformation, the microstructural evolution and the changes in microhardness have been investigated. In both materials the deformation leads to a decrease in structure size. In the case of the steel an alignment of the lamellae parallel to the shear plane and a decrease of the lamellae spacing is observed. Lamellae which have been originally not favourably aligned are heavily bent and broken into small fragments. This refinement is also reflected in the evolution of the microhardness.

Dispersing reinforcements in a ductile matrix is one method of strengthening metallic materials at high temperatures. Although this method generally strengthens the material, it is predicted that concomitant diffusion weakens it when heterogeneous stresses around the reinforcements are accommodated by rapid diffusion along the matrix/reinforcement interface. Here we show weakening with increasing volume fraction of reinforcements under low strain rates and strengthening under high strain rates using Ti/TiB(w) composites at 1473 K. The criterion of weakening or strengthening is established by the diffusional-accommodation rate considering the accommodation process of the misfit strain between the matrix and reinforcements by diffusion.

Although hot working had been defined as deformation above the recrystallization temperature (determined after cold working), it was only about 1965 that dynamic recrystallization (DRX) was confirmed to be occurring during the deformation; two decades were required to clarify the similarities to, and the differences from, static recrystallization. In classical discontinuous DRX in Cu, Ni, and γ-Fe, successive necklaces of new grains cause work softening; however in steady-state, the nuclei are uniformly distributed as reestablished dislocation structure limits growth. In high recovery metals at high strains, the grain boundary (GB) serrations meet across the elongated thinned grains thus pinching them off into almost equiaxed grains containing a substructure, thus geometric DRX.

The effect of the accumulative strain on texture evolutions in 1050 aluminum alloy processed by dissimilar channel angular pressing (DCAP) was investigated. Very high plastic strain ( e eff ∼ 19) were imparted into the materials via multiple passages ( N = 32) through the DCAP die. The intensities of the texture components after DCAP depended on the accumulative strain for low applied strain ( e eff e eff > 5.8), there was no significant change in intensity.

Variations in microstructure and chemical compositions of the metallic glasses found in the literature, as well as an overall lack of experimental data on inhomogeneous behavior of metallic glass make the evaluation of the effects of shear band/fracture behavior on mechanical properties of metallic glasses difficult. Investigating the effect of strain localization alone on inhomogeneous flow seems to be a first step in approaching this problem. Mechanical behavior of metallic glasses at room temperature and various strain rates in tension and compression was investigated. Formation of multiple shear bands was observed at high strain rates. An increase in strain rate leads to enhanced ductility in tension, whereas, the ductility of the material in compression decreases with increasing strain rate. Differences in deformation processes in tension and compression were compared.

In this paper, we report a new severe plastic deformation (SPD) technique, which combines equal channel angular pressing (ECAP) with Conform, to process ultrafine grained (UFG) materials in a continuous manner. ECAP in its original form can only process short metal bars and is labor intensive. Conform is a technique that has been used to continuously form metals into various shapes. By combining these two techniques, we were able to produce UFG structures in an Al wire and to significantly increase its strength.

The texture development of equal channel angular extrusion (ECAE) processed Al.5Cu alloy submitted to further ECAE or rolling is analyzed. Initial ultrafine-grained (UFG) or fine-grained (FG) materials obtained after ECAE are considered. Combining ECAE with rolling offers additional opportunities for texture control. In both samples, from 50 to 75% rolling reduction is sufficient to create rolling textures. Texture strength increases significantly up to 95% reduction and then decreases in both materials. The highest texture strengths are found for rolled FG samples. For UFG materials, further ECAE via route A or D create gradually weaker close to random textures. Thus simple shear activated by ECAE for some specific routes appears more effective for texture randomization than rolling. This may reflect some difference between ECAE and rolling in the mechanisms occurring during severe plastic deformation.

A novel technique for producing high-strain-rate-superplastic (HSRS) microstructure via friction stir processing (FSP) in a commercial 2024 Al has been demonstrated. A maximum ductility of ∼525% has been achieved at a strain rate of 10 −2 s −1 and 430 °C. Current results suggest that friction stir processing can be developed as a simple yet effective technique for producing microstructure amenable for superplasticity at high strain rates and/or lower temperatures and at lower flow stresses.

[ 1 12] Cu–7at.%Al single crystals as well as [ 1 23], [ 1 17] and [023] Cu–16at.%Al single crystals were cyclically deformed under constant plastic strain control at room temperature. The cyclic hardening curve of [ 1 12] Cu–7at.%Al single crystal can be divided into three stages, namely initial non-hardening stage, rapid hardening stage and saturation stage. The cyclic stress–strain (CSS) curve exhibited a plateau region in the range of γpl, from 1.1×10−3 to 4.5×10−3. The saturation stress of the plateau is about 27 MPa. The occurrence of strain burst depends on the applied plastic strain amplitude γpl. No strain burst was detected when γpl, was below 4.4×10−4 or above 1.1×10−3. The cyclic deformation and strain burst behavior of [ 1 23], [ 1 17] and [023] Cu–16at.%Al single crystals are different from that of [ 1 12] Cu–7at.%Al single crystal. The cyclic deformation of all three differently oriented Cu–16%Al single crystals is unstable with the frequent occurrence of irregular strain bursts. The specimens cyclically hardened at a very low rate and saturation was not attained at high strain amplitudes. The experimental results indicate that the crystallographic orientation has almost no effect on the cyclic deformation and strain burst behavior of Cu–16at.%Al single crystals. The evolution of slip bands during cyclic deformation in both Cu–7at.%Al and Cu–16at.%Al single crystals is similar to the development of Luders band. The percolation of slip bands along the gauge length is generally accompanied by strain bursts. The above experimental results were explained in terms of the variation of slip mode with Al content in the alloys and the corresponding strain localization during cycling.

Fine-grain high-purity alumina doped by small amounts of Zr was tested by a high strain-sensitivity creep technique at temperatures from 1273 to 1423 K and stresses from 4.2 to 35 MPa. Stress exponents close to 1 and apparent activation energies of about 235 kJ/mol were observed at lower temperatures, while both values become higher at 1423 K. Quasi-periodic instabilities in creep flow were observed in all creep tests at temperatures lower than 1423 K. Attempts to attribute it to some measuring artifacts caused by external influences were not successful. Nevertheless, more experiments are needed to ensure that they belong to the creep deformation process. The origin of their observation remains unclear.

The high strain rate behavior of two different tungsten-based composites (WBCs) has been investigated using a combination of compression Kolsky bar and high strain rate pressure—shear plate impact experiments. The two materials investigated are (a) a W/(WNiFe) “heavy alloy” containing 91 wt.% W with a WNiFe matrix/binder phase and (b) a W/Hf composite containing 72 wt.% W and Hf matrix/binder phase. For each materials, stress-strain curves are obtained in compression and shear over the strain rate range of 10 3 to 10 5 s −1 . The flow stresses observed in the W/Hf composite during these dynamic deformations are comparable to those observed in the W/(WNiFe) material, in spite of the lower tungsten content of the W/Hf composite. Further, the W/Hf composite displays approximately the same degree of strain-rate hardening as the W/(WNiFe) composite. The observed behaviorof the W/(WNiFe) composite is compared with the predictions of several phenomenological models for high-rate deformations, including the Johnson-Cook and Zerilli-Armstrong models.