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A polycrystalline coarse-grained Ni with 98.4 wt% purity was deformed plastically to the strain of 1.2 at the strain rate of ~10 4 s −1 using a Dynamic Hopkinson Plastic Deformation technique. The microstructure investigations indicate the ability of this loading method to process very fine microstructure with high dislocation density and large fraction of low-angle grain boundaries. It turned out that there is a transition in the mechanisms which determine the flow stress during the impact test. In the beginning of deformation viscous dislocation drag dominates, while at the end of the impact test the velocity of the individual dislocations is low due to the high dislocation density, therefore the obstacle hardening determines the flow stress. Accordingly, the flow stress measured in-situ during impact test is in good agreement with the values determined ex-situ after deformation. The main contribution to the flow stress is given by dislocations. [ABSTRACT FROM AUTHOR]

The sharing role of microstructural micro-constituents on hot deformation behavior of a 60/40 duplex brass was investigated through hot compression testing at predetermined temperatures in the range of 400–800 °C under the strain rates ranging from 0.001 to 0.1 s −1 . The hot working parameters (strain rate sensitivity, and apparent activation energy, Q ) were determined for different conditions of the applied thermomechanical processing. Assuming the Hyperbolic Sine functional behavior to analysis the deformation behavior of the alloy and also applying the rule of mixture in order to determine the share of each phase in strain accommodation, the interaction coefficients of alpha phase, P, and beta phase, R, were precisely estimated. The results indicate that the experimental material exhibits usual Dynamic Recrystallization (DRX) behavior such as single-phase materials; but in comparison to the conventional alloys DRX is postponed at 500 and 600 °C. Moreover, it is seen that the deformation mechanism at different temperatures has been severely depend on the order–disorder transformation of the beta phase in mixture. In fact this transformation is considered to play the main role in beta phase recrystallization retardation. However, at lower Zener Holloman ( Z ) values, the strain accommodation is mainly taken place in beta phase and the chief deformation mechanism is believed to be grain boundary sliding (GBS). Accordingly there crystallization of alpha phase is limited due to the lower strain accommodation. In contrast, at higher Z values, the alpha phase controls the governing deformation mechanism and the dynamic recrystallization of alpha grains may well lead to the microstructural grain refinement. [ABSTRACT FROM AUTHOR]

Fracture is the ultimate continuum of a material. Hence, it is possible that the fracture features contain the signature of the whole deformation process undergone due to variation in triaxial state of stress under tensile deformation. The two dimensional fracture features were correlated with the stress triaxiality ratio where initial inclusion content was unaltered. In order to test that, many tensile experiments of a superalloy were carried out at different notch geometries and fractographic investigation was done extensively to correlate the fracture features (ie., fractured grain size, extent of tearing ridge, dimple diameter and dimple number density) with the tensile properties. [ABSTRACT FROM AUTHOR]

Repetitive upsetting (RU), a newly developed SPD technique, was employed to process AZ91D magnesium alloy plates at 400 °C for 0, 2, 4 and 8 passes. The microstructure and texture evolution of the plates after RU were investigated and correlated with the mechanical performances at room temperature. Results show that the initial coarse grains are effectively refined, however an abnormal grain coarsening appears after 8 passes of RU. A compression texture and a shear texture, induced by specific local strains, are observed within the RU-processed plates. Both the ultimate tensile strength (UTS) and elongation to fracture of the RU-processed AZ91D alloy are improved with the increase of RU passes, exhibiting a maximum increase of 35.8% and over 75%, respectively. The yield strength (YS) increases steadily in the first 4 RU passes and then decreases slightly after another 4 passes. The mechanical anisotropy is discussed from the perspective of texture and Schmid factor. [ABSTRACT FROM AUTHOR]

During processing of age-hardenable AA 6xxx series alloys for automotive applications the sheets may experience significant time spans between solution heat treatment at the aluminium supplier and age hardening upon the final paint bake cycle at the carmaker. Natural ageing during these pause times and intermediate deformations by sheet levelling or forming operations both affect materials properties of autobody sheet. In the present study we explore the impact of a combination of natural ageing and pre-straining on the tensile properties and the in-plane anisotropy of alloy AA 6016. Materials properties are modelled with the help of a nano-scale material model called NaMo, which consists of a precipitation model simulating the formation of clusters and phases upon natural ageing as input to a mechanical model simulating the evolution of yield strength and work hardening as a function of natural ageing and pre-straining. Plastic anisotropy is modelled by polycrystal-plasticity simulations under consideration of latent hardening to account for strain path change effects introduced by the pre-straining. [ABSTRACT FROM AUTHOR]

A novel approach for development of high strength and ductile beta titanium alloys was proposed and successfully applied. The microstructure of the designed alloys is fully composed of a bcc β-Ti phase exhibiting dendritic morphology. The new Ti 68.8 Nb 13.6 Cr 5.1 Co 6 Al 6.5 (at%) alloy (BETA tough alloy) exhibits a maximum tensile strength of 1290±50 MPa along with 21±3% of fracture strain. The specific energy absorption value upon mechanical deformation of the BETA tough alloy exceeds that of Ti-based metallic glass composites and commercial high strength Ti-based alloys. The deformation behavior of the new alloys was correlated with their microstructure by means of in-situ studies of the microstructure evolution upon tensile loading in a scanning electron microscope. [ABSTRACT FROM AUTHOR]

The effect of extensive grain refinement through equal-channel angular processing (ECAP) at 300 °C on the mechanical properties was examined in a Zr-modified 5083 aluminum alloy. It was shown that any increase in the yield stress (YS) by increasing the number of pressings was attributed to additional contributions from three strengthening mechanisms: (i) grain boundary strengthening related to the size of the crystallites bounded by deformation-induced high-angle boundaries (HAB), (ii) dislocation strengthening related to highly increased dislocation density and (iii) solute strengthening related to promoting dynamic strain aging (DSA) by intense plastic straining. Grain size strengthening is the primary contributor to the increase in the YS as a result of ECAP. Dislocation strengthening plays an important but minor role in strengthening the alloy after ECAP. No ECAP effect on the dispersion strengthening was observed. However, a dispersion of nanoparticles was found to cause an increase in the YS through grain refinement and the accumulation of lattice dislocations during ECAP. It was found that the deformation-induced low angle boundaries (LABs) play an insignificant role in the strengthening of the material. [ABSTRACT FROM AUTHOR]

Abstract: Experimental evidence has illustrated that micropillar deformation is highly stochastic, as the stress–strain curves are manifested by multiple strain bursts. Although initial theoretical works employing gradient plasticity can predict the stress–strain response of individual pillars, they cannot capture the stochastic effects observed for multiple same diameter specimens. This article presents simulations that are not only in precise qualitative and quantitative agreement with experimental stress–strain curves for varying diameter pillars, but can also account for the observed stochasticity in same diameter micropillars. This is accomplished by implementing gradient plasticity within a cellular automaton, while allowing the yield-stress to randomly vary within the micropillar. In concluding, it is shown that the aforementioned numerical code can also capture the stress drops and size dependent strengthening observed in metallic glass nanopillars. [Copyright &y& Elsevier]

Abstract: The present work reports the effect of annealing treatment on detwinning deformation in Mg alloy AZ31 and pure Mg that have pre-strained twins. It shows that appropriate annealing enhances, rather than reduces, the yield strength of the pre-strained AZ31, but it does not cause any strengthening of the pre-strained pure Mg. STEM–EDS mapping shows that both Al and Zn segregate to twin boundaries in the pre-strained AZ31 after the annealing process. It is proposed that it is the pinning of twin boundary by segregated solute atoms that results in an increased activation stress for detwinning deformation and, hence, annealing hardening. [Copyright &y& Elsevier]

Disparity in hot ductility of a γ′ precipitation strengthened nickel-base superalloy, IN 738 LC, subjected to non-equilibrium heating and compressive and tensile stresses, was investigated. The alloy, which shows considerable hot ductility at temperatures ranging from 1160°C to 1250°C under compressive loading, exhibits zero ductility under tensile loading within this temperature range. The difference is attributed to the fact that while compressive loading permits plastic deformation in spite of non-equilibrium liquid phase dissolution of γ′ precipitates in the alloy, the occurrence of the liquation reaction results in inhibition of plastic deformation under tensile loading. Accordingly, while grain refinement through strain-induced dynamic recrystallization occurred under compressive loading, within the same temperature range, the formation of new grains was prevented under tensile loading. This behavior is crucial during high temperature processing of γ′ precipitation strengthened nickel-base superalloys. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, extremely high strength was obtained in medium carbon steel having a carbon content of 0.35% by weight through cold drawing. Experimental results showed that the tensile strength of the steel increased by nearly three folds from the original value ~615MPa to 1810MPa corresponding to drawing strain of 3.0. To reveal the mechanisms that govern the strengthen increase, the microstructural evolution was analyzed during cold drawing, with respect to the change of the deformation resistance (measured by micro-hardness) of micro-constituents (i.e., primary or proeutectoid ferrite and pearlite) in the material. The proeutectoid ferrite became elongated and, at the same time, increasingly hardened while the pearlite maintained equiaxed shape after initial drawing. With the increase of the drawing strain, the pearlite was stretched parallel to drawing direction, accompanied by an increase in the 〈110〉 texture intensity and dislocation density in the ferrite phase. Under heavy drawing, a laminate structure formed, consisting of alternating pro-eutectoid ferrite and pearlite both parallel to the drawing direction. The 〈110〉 texture intensity in the ferrite phase became saturated as ε>1.2. High density dislocation zones further spread in the ferrite phase. The interlamellar spacing between ferrite and cementite phases in the pearlite decreased. Based upon these observations, mechanistic models were constructed to provide insight into the deformation and strengthening mechanisms of this steel. [Copyright &y& Elsevier]

Abstract: A detailed investigation of the microstructure and mechanical properties has been conducted in pure nickel deformed to high strains using accumulative roll bonding (ARB). Samples have been investigated after different numbers of ARB cycles and the results have been compared with data for nickel processed by other deformation techniques, with particular focus on conventional rolling. It is found that the structural evolution in ARB-processed nickel is rapid at low strains followed by a slower evolution as the strain approaches ultrahigh levels. Comparing samples processed by ARB and by conventional rolling to an identical nominal strain, the microstructure after ARB is more refined and contains a greater fraction of high angle boundaries. This enhanced refinement is attributed to the geometric accumulation of shear-strain influenced volumes as a result of the ARB process and large-draught rolling conditions. Based on the observations, it is suggested that the key strengthening mechanisms in deformed nickel are grain boundary and dislocation boundary strengthening, and that the strength–microstructure relationship can be expressed by a single parameter equation: σ−σ 0=k 2 d av −0.5, where k 2 is a constant and d av is the average boundary spacing in the deformed microstructure. [Copyright &y& Elsevier]

Abstract: Angular Accumulative Drawing (AAD) is a new powerful tool that produces wires with enhanced properties and microstructure. The AAD is characterised by a complex strain path history resulting from various deformation modes. Its main purpose is to produce wires that represent increased strength and ductility due to controlled deformation inhomogeneity. This paper discusses the effect of processing routes and parameters on inhomogeneity of deformation as well as microstructure, and finally on the properties of wires. Investigated materials were: aluminium, copper, low carbon and microalloyed steels. Also, it is shown that the complex strain path history can be effectively controlled by computer simulation. [Copyright &y& Elsevier]

Abstract: The medium-Mn steel with an ultrafine grained duplex microstructure was achieved by intercritical annealing treatment. The deformation microstructures of the UFG duplex steel during tension were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). With increasing tensile strain the volume fraction of austenite phase decreased gradually. TEM observations showed that during tensile straining a lamellar-type structure was gradually formed in austenite grains and the lath thickness decreased due to phase transformation from austenite to martensite, while little change was found in ferrite grains except for a slight increase in dislocation density. The strain-induced martensite transformation obeyed the Kurdjumov–Sachs (K–S) orientation relationship. The different deformation behaviors of austenite and ferrite grains did different contributions to the tensile flow stress and the strengthening mechanisms were discussed based on experimental results. [Copyright &y& Elsevier]

Abstract: High strain rate tensile tests were conducted for three advanced high strength steels: DP780, DP980 and TRIP780. A high strain rate tensile test machine was used for applying the strain rate ranging from 0.1/s to 500/s. Details of the measured stress–strain responses were comparatively analyzed for the DP780 and TRIP780 steels which show similar microstructural feature and ultimate tensile strength, but different strengthening mechanisms. The experimental observations included: usual strain rate dependent plastic flow stress behavior in terms of the yield stress (YS), the ultimate tensile strength (UTS), the uniform elongation (UE) and the total elongation (TE) which were observed for the three materials. But, higher strain hardening rate at early plastic strain under quasi-static condition than that of some increased strain rates was featured for TRIP780 steel, which might result from more active transformation during deformation with lower velocity. The uniform elongation that explains the onset of instability and the total elongation were larger in case of TRIP steel than the DP steel for the whole strain rate range, but interestingly the fracture strain measured by the reduction of area (RA) method showed that the TRIP steel has lower values than DP steel. The fractographs using scanning electron microscopy (SEM) at the fractured surfaces were analyzed to relate measured fracture strain and the microstructural difference of the two materials during the process of fracture under various strain rates. Finally, constitutive modeling for the plastic flow stresses under various strain rates was provided in this study. The proposed constitutive law could represent both Hollomon-like and Voce-like hardening laws and the ratio between the two hardening types was efficiently controlled as a function of strain rate. The new strength model was validated successfully under various strain rates for several grades of steels such as mild steels, DP780, TRIP780, DP980 steels. [Copyright &y& Elsevier]

Abstract: Brittle low-strength and low-toughness pressable dental ceramic can be reinforced by ductile elongated gold-particles (GP). A customized crown structure can be adequately strengthened by distributing GP only in critical sections of the crown, where high tensile stresses are experienced. In the present study, a non-uniformly structured ceramic–matrix composite with excellent interfacial bonding, twofold fracture toughness and strength at desired locations, is fabricated using pressable dental ceramic and GP. The layout pattern and sequence of different GP/ceramic powder mixtures, high-temperature flow properties of these mixtures during hot-pressing and the sample mold geometry are used to control the distribution and locations of GP for selective toughening and strengthening. Nano-crystalline structures of the pressable ceramic–matrix and the nano-scaled interfacial region around GP have been revealed by high-magnification field-emission scanning electron microscopy. Toughening and strengthening mechanisms of the elongated GP including residual stresses from composite processing and ductile fracture of GP are discussed together with SEM observations. Bulk flexural strength and local micro-indentation fracture and deformation characteristics of the selective-toughened ceramic/metal composite have been compared to those of the monolithic pressable ceramic to validate the toughening and strengthening mechanisms. [Copyright &y& Elsevier]

Abstract: Constrained groove pressing (CGP) process is one of the favorable severe plastic deformation methods to fabricate ultra-fine grain sheet materials. In this paper, commercial pure aluminum sheet was subjected to CGP process using conventional and covered sheet casing (CSC) methods. Three dies with different groove lengths and angles (t =1mm and θ =45°; t =1.8mm and θ =45°; t =1mm and θ =53°) were designed and manufactured. Mechanical properties including strength, elongation to failure and hardness are obtained and discussed. The influences of these two methods and die groove angle on specimen strain behavior and required force value are analyzed by the finite element method in plain strain condition. The results show that the CSC method leads to better hardness distribution, uniform strain dispersal and finer surface quality as compared to conventional method. Moreover, the new method is a good candidate for substituting the conventional CGP process. [Copyright &y& Elsevier]

Abstract: This work explored a novel severe plastic deformation scheme, through-width vibration rolling, to continuously produce high-strength aluminum sheet. As-processed AA6061 (Al–Mg–Si) alloy sheet was directly subjected to ageing treatment, by which the yield strength up to 480MPa and the ultimate tensile stress of 491MPa could be obtained. [Copyright &y& Elsevier]

Abstract: Titanium alloys containing a majority volume fraction of the low temperature HCP α-phase have been known to display yield and creep strength asymmetries when deformed under uniaxial conditions at room temperature. This behavior has only been documented in materials alloyed with significant concentrations of aluminum (<∼10at%); however, little work has examined the phenomenon in commercial purity alloys. In this study, the yield strengths of two commercial purity titanium alloy sheet materials (Grade 1 and Grade 4) are examined under tensile and compressive loading conditions. Yield strength asymmetry has been observed and has been found to be dependent on alloy composition and crystallite distribution relative to the deformation axis. [Copyright &y& Elsevier]

Abstract: Transformation Induced Plasticity (TRIP) steels exhibit a better combination of strength and ductility properties than conventional high strength low alloy (HSLA) steels, and therefore receive considerable attention in the automotive industry. In this work, the tensile mechanical behaviors of TRIP-aided steels were studied under the condition of the quasi-static and high deformed rates. The deformed specimens were observed by scanning electron microscope (SEM) along the tensile axis. The threshold strain of microvoid formation was examined quantitatively according to the evolution of deformation. The results showed that: the yield and tensile strengths of TRIP steels increase with the strain rate, whereas their elongations decrease. However, the threshold strain for TRIP steels at high strain rate is larger than that at low strain rate. Comparing with the deformed microstructure and microvoids formed in the necking zone of dual phase (DP) steel, the progressive deformation-induced transformation of retained austenite in TRIP steels remarkably increases the threshold strain of microvoid formation and furthermore postpones its growth and coalescence. [Copyright &y& Elsevier]

Abstract: Uniaxial tensile properties influenced by the dynamic recrystallization (DRX) behavior of the partially strain-hardened magnesium AZ31 sheets (H24) containing scores of twins were investigated and compared to those of fully annealed ones (O) with absence of twins. For this purpose, a series of uniaxial tensile tests were carried out for the H24 and O materials at temperatures ranged from room temperature to 300°C and at strain rates between 10−3 and 10−1 s−1. At 150 and 200°C, the H24 material exhibited higher yield strength without much loss in elongation compared to those of the O material; this trend was attributed to the continuous DRX along or around grain boundaries as well as extensive twin-aided DRX inside grains. In addition, the post-deformation hardness value of the H24 material showed higher than that of the O material. On the other hand, at higher temperatures of 250 and 300°C, it was observed that twins shown in the H24 material were disappeared even prior to deformation, resulting in the similar grain structure and mechanical property values to those of the O material, e.g., discontinuous DRX associated with grain boundary bulging. Finally, the initiation of DRX was rationalized in terms of microstructure morphology, deformation temperature and strain rate, and then modeled in the context of strain hardening rate analysis. A comparison of experimental results and predictions for both H24 and O materials showed that the model can provide a reasonable prediction of critical strain to initiate DRX. [Copyright &y& Elsevier]

Abstract: The millimetre scale W balls reinforced Zr-base bulk metallic glass composite was prepared using infiltration technique. The compressive deformation behaviours of the composite at two strain rates of 1×10−4 s−1 and 1×10−2 s−1 were investigated. The enhanced plasticity is attributed to the effect of W balls, which constrain shear bands propagation and promote the formation of multiple shear bands. The properties of the composite depend evidently on the strain rates. The high strain rate leads to the higher strength and larger plasticity. [Copyright &y& Elsevier]

Abstract: Polycrystalline magnesium was compressed under different strain rates (0.001, 800, 1000, 2000, and 3600s−1) to investigate its dynamic mechanical properties, and microstructural characterization was performed to uncover the deformation mechanism. The results show that yield strength is insensitive to strain rate, while ultimate strength, fracture strain, and work hardening rate are highly sensitive to strain rate. Three deformation regimes (I, II, and III) were observed on the quasi-static and dynamic stress–strain curves. These regimes show respectively increasing work hardening rate in the early stage of plastic deformation, constant work hardening rate in the intermediate plastic deformation region, and decreasing work hardening rate in the end region right before fracture. Different deformation mechanisms operate for the quasi-static and dynamic loading conditions. Microscopically, twinning/detwinning is the dominating mechanism for quasi-static testing, while dynamic recrystallization and twinning/detwinning are the dominating mechanisms for dynamic testing. Analytic constitutive models were derived for predicting the dynamic stress–strain relations. The analysis indicated that different factors were in effect for different loading strain rates. The stress–strain relations were primarily affected by strain hardening for quasi-static testing; by strain hardening, strain rate hardening, and thermal softening for dynamic testing with ; and by strain hardening, damping, and thermal softening for dynamic testing with , respectively. [Copyright &y& Elsevier]

Abstract: β-Type titanium alloys with composition of Ti–24at% Nb–(0, 2, 4)at% Zr were prepared and subjected to aging treatment for different durations. The addition of Zr suppressed the formation and growth of isothermal ω phase during aging treatment, and therefore the investigated Ti–Nb–Zr alloys with different Zr content performed various deformation mechanisms, mechanical properties and super-elastic effects with the changes of aging time. The isothermal ω phase exerted inhibitory effects on twinning and stress-induced martensitic transformation. Desirable properties were obtained in Ti–Nb–Zr alloy by adding suitable Zr content and processing short time aging treatment. Ti–24at% Nb–2at% Zr alloy subjected to aging treatment at 573K for 7.2ks exhibited an ultimate tensile strength of 710MPa, an elongation of 13%, a Young''s modulus of 64GPa, and a super-elastic recovery strain of 4.3%. Ti–24at% Nb–4at% Zr alloy subjected to aging treatment at 573K for 1.8ks, 3.6ks, and 7.2ks performed a low Young''s modulus of 62GPa and ultimate tensile strength around 600MPa. [Copyright &y& Elsevier]

Abstract: The effects of high pressure torsion (HPT) processing at different temperatures on flow stress and hardness distribution of a 2024 Al alloy were studied. Using in situ torque measurements versus equivalent strain the flow stress of the material followed three distinct deformation regions at room temperature. In the first region the strength increases with strain and after taking a maximum at an equivalent strain of ∼8, the strength decreases with further straining in the second region. The third region appears at an equivalent strain of ∼22 or higher as a steady state where the strength remains unchanged. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) analysis were conducted on selected samples and influential effects of precipitates on flow stress and hardness were examined. It is proposed that restoration process in the second region of deformation and saturation region of deformation can significantly be affected by deformation temperature and aging precipitates. HPT deformation at −196°C did not show any decrease in second region of deformation instead the strength is increased exponentially until the strain of ∼35 where saturation region of deformation starts. Nano sized grains of 50–70nm were observed in saturation region of deformation with more than three folds increases in hardness. [Copyright &y& Elsevier]

Abstract: 55vol.% B4C/Al composites reinforced with 3μm and 20μm particles respectively were prepared by squeeze casting. Effect of particle size on quasi-static and dynamic compression behaviors of the composites was investigated. The results show that the quasi-static compression strength of the composite with 3μm particles is almost twice that of the composite with 20μm particles. The reason is that the connectivity architectures of the composite with small particles are more stable than that of the composite with big particles due to the enhancement of in situ matrix by geometrically necessary dislocation. In addition, the dynamic compression strength and the fracture strain first increase with the increasing impact velocity and then decrease when the impact velocity is increased from 28m/s to 33m/s for the composite with 20μm particles, and no similar phenomenon occurs for the composite with 3μm particles. The size-dependent architecture stability of the connected reinforcement is the main contribution to the different dynamic deformation behaviors of the composites during adiabatic compression. [Copyright &y& Elsevier]

Abstract: The composites consisting of amorphous matrix reinforced with crystalline dendrites offer extraordinary combinations of strength, stiffness, and toughness and can be processed in bulk. Hence, they have been receiving intense research interest, with a primary focus to study their mechanical properties. In this paper, the temperature and strain rate effects on the uniaxial compression response of a tailored bulk metallic glass (BMG) composite has been investigated. Experimental results show that at temperatures ranging between ambient to 500K and at all strain rates; the onset of plastic deformation in the composite is controlled by that in the dendrites. As the temperature is increased to the glass transition temperature of the matrix and beyond, flow in the amorphous matrix occurs readily and hence it dictates the composite''s response. The role of the constituent phases in controlling the deformation mechanism of the composite has been verified by assessing the strain rate sensitivity and the activation volume for deformation. The composite is rate sensitive at room temperature with values of strain rate sensitivity and activation volume being similar to that of the dendrites. At test temperatures near to the glass transition temperature, the composite however becomes rate-insensitive corresponding to that of the matrix phase. At low strain rates, serrated flow akin to that of dynamic strain ageing in crystalline alloys was observed and the serration magnitude decreases with increasing temperature. Initiation of the shear bands at the dendrite/matrix interface and propagation of them through the matrix ligaments until their arrest at another interface is the responsible mechanism for this. [Copyright &y& Elsevier]

Abstract: The mechanical properties of deformed AZ31 Mg alloy at high temperature of 450–600°C with a strain rate of 3s−1 were investigated by tensile tests. The zero strength of AZ31 Mg alloy was emerged at a mushy state (600°C), while the zero ductility was appeared at 575°C, just below the solidus temperature. The abnormal coarsening of the grains happened at the temperature of 525–575°C and some molten grain boundaries were observed at 600°C. Finally the morphology and crack propagation of fracture surface were also discussed. [Copyright &y& Elsevier]

Abstract: Strength change in anisotropic principal axis directions of an over-aged aluminum 2024 (Al 2024) alloy subjected to equal channel angular pressing (ECAP) was studied. This alloy was subjected to several stages of severe plastic deformation by ECAP. Various strength values were measured using the tension test, the small punch (SP) test and Rockwell and Vickers hardness tests. The SP test was employed due to the size limitation for the tension test specimen in the transverse direction of the ECAP sample. In a previous paper , we proposed equations that can assess the tensile strengths in the anisotropic principal axis directions of an anisotropic material using SP test data and showed that the proposed strength assessment equations were very accurate. These equations were used in this study. As the amount of plastic deformation by ECAP increased, the tensile strength in the longitudinal direction of the ECAP-processed Al 2024 alloy was increased. However, considerable change of strength, which is generally predicted, was not observed in this study. In the result of the tensile strength in the transverse direction, the strength even decreased after an equivalent plastic strain of approximately 3.0. It was argued that this decrease was due to the dynamic recovery of the dislocation density during or after ECAP processes at 150°C. This argument was supported by comparison with the results of the tension test and the hardness test. Based on the results of this study, the strength of an ECAP material must be assessed for both the longitudinal and transverse directions. [Copyright &y& Elsevier]

Abstract: The Bauschinger effect of three commercially produced medium carbon bar steels representing different microstructural classes with similar tensile strengths and substantially different yielding and work-hardening behaviors at low-strain was evaluated at room temperature and in situ at temperatures up to 361°C. The influence of deformation at dynamic strain aging temperatures as a means to produce a more stable dislocation structure was evaluated by measuring the resistance to strain reversal during in situ Bauschinger effect tests. It was shown that the three medium carbon steels exhibited substantial increases in strength at dynamic strain aging temperatures with the peak in flow stress occurring at a test temperature of 260°C for an engineering strain rate of 10−4 s−1. Compressive flow stress data following tensile plastic prestrain levels of 0.01, 0.02 and 0.03 increased with an increase in temperature to a range between 260°C and 309°C, the temperature range where dynamic strain aging was shown to be most effective. The increased resistance to flow on strain reversal at elevated temperature was attributed to the generation of more stable dislocation structures during prestrain. It is suggested that Bauschinger effect measurements can be used to assess the potential performance of materials in fatigue loading conditions and to identify temperature ranges for processing in applications that utilize non-uniform plastic deformation (e.g. shot peening, deep rolling, etc.) to induce controlled residual stress fields stabilized by the processing at temperatures where dynamic strain aging is active. [Copyright &y& Elsevier]

Abstract: The effects of Al addition on dynamic flow response of the fully austenitic high Mn steel were investigated by conducting high strain rate compression tests on Fe–22Mn–xAl–0.6C steels (x =0, 3, 6 in wt.%). While dynamic yield strength of the 0 Al steel and the 3 Al steel were comparable, the 6 Al steel exhibited the highest one. Meanwhile, strain hardenability of the 0 Al steel was the highest and that of other two steels was nearly same. Under the present dynamic loading, no obvious dynamic recrystallization by adiabatic heating was observed in all steels. Fully compressed microstructures revealed (a) ɛ-martensite and mechanical twin bands for the 0 Al steel, (b) multi-layer deformation bands and mechanical twin bands for the 3 Al steel, and (c) a variety of dislocation configurations such as the directional slip traces, tangled dislocations, and incomplete dislocation cells for the 6 Al steel. These findings inform that dynamic flow of the 0 Al steel was associated with both TRIP and TWIP, and that of other two steels was dominated by dislocation gliding – mainly, planar glide for the 3 Al steel and the combination of both planar glide and wavy glide for the 6 Al steel. The dynamic flow response of the present steels was discussed in terms of the stacking fault energy affected by the Al content and adiabatic heating during dynamic loading and of the strain rate effect on the critical stress for mechanical twinning. [Copyright &y& Elsevier]

Abstract: Mechanical properties and morphology of cylindrical indium nanopillars, fabricated by electron beam lithography and electroplating, are characterized in uniaxial compression. Time-dependent deformation and influence of size on nanoscale indium mechanical properties were investigated. The results show two fundamentally different deformation mechanisms which govern plasticity in these indium nanostructures. We observed that the majority of indium nanopillars deform at engineering stresses near the bulk values (Type I), with a small fraction sustaining flow stresses approaching the theoretical limit for indium (Type II). The results also show the strain rate sensitivity and flow stresses in Type I indium nanopillars are similar to bulk indium with no apparent size effects. [Copyright &y& Elsevier]

Abstract: Recent research suggests that extraordinary combinations of strength and ductility can be achieved in the so-called δ-TRIP steels, which contain ferrite, bainite and austenite. A part of the reason for the ductility of almost 40% elongation at a strength of some 900MPa, is believed to be the optimal stability of the austenite to plastic deformation. We demonstrate here that mechanical stabilisation plays an important role in preserving the austenite to large plastic strains. [Copyright &y& Elsevier]

Abstract: In this work, the role played by plastic straining on the FCC(γ)→HCP(ɛ) strain induced transformation (SIT) ɛ-martensite in a Co–Cr–Mo–0.05C alloy was investigated. It was found that alloy plastic deformation at room temperature promotes the development of ɛ-martensite giving rise to the formation of intragranular striations. Moreover, aging at 800°C of pre-strained specimens initially promotes SIT ɛ-martensite. This is followed by a time plateau (1h) delay after which isothermal ɛ-martensite develops. Apparently, prior plastic straining leads to increasing incubation times for the onset of the isothermal ɛ-martensite transformation. In addition, tensile specimens containing various amounts of isothermal ɛ-martensite were tested all the way to fracture and their respective stress–strain properties were experimentally determined. Comparisons between experimental and simulated flow curves using the rule of mixtures indicated some deviations in the simulations at volume fractions above 0.25 ɛ-martensite. In contrast, predictions of yield and tensile strength were in good agreement with the experimental outcome. In particular, linear trends were exhibited by both, the yield and tensile strength as a function of the volume fraction of ɛ-martensite. Finally, the alloy elongation remained nearly constant with the volume fraction of ɛ-martensite in the range of the 0.15

Abstract: The effect of tensile strain rate on deformation microstructure was investigated in Ti-6-4 (Ti–6Al–4V) and SP700 (Ti–4.5Al–3V–2Mo–2Fe) of the duplex titanium alloys. Below a strain rate of 10−2 s−1, Ti-6-4 alloy had a higher ultimate tensile strength than SP700 alloy. However, the yield strength of SP700 was consistently greater than Ti-6-4 at different strain rates. The ductility of SP700 alloy associated with twin formation (especially at the slow strain rate of 10−4 s−1), always exceeded that of Ti-6-4 alloy at different strain rates. It is caused by a large quantity of deformation twins took place in the α phase of SP700 due to the lower stacking fault energy by the β stabilizer of molybdenum alloying. In addition, the local deformation more was imposed on the α grains from the surrounding β-rich grains by redistributing strain as the strain rate decreased in SP700 duplex alloy. [Copyright &y& Elsevier]

Abstract: A high Mn TWIP (TWinning Induced Plasticity) steel (0.6C–22Mn steel) and an Al-added TWIP steel (0.6C–18Mn–1.2Al steel) were fabricated, and their microstructures, tensile properties, and cup formability were analyzed to investigate effects of Al addition on deformation mechanisms in tensile and cup forming tests. The twinning was not only more homogenous but also less intense in the 0.6C–18Mn–1.2Al steel than in the 0.6C–22Mn steel. This aspect was confirmed by tensile stress-strain curves, where the strain hardening was lower in the 0.6C–18Mn–1.2Al steel. The tensile test results indicated that the 0.6C–22Mn steel had the better tensile strength and elongation than the 0.6C–18Mn–1.2Al steel. However, cracks were formed on cup sides of the 0.6C–22Mn steel when exposed to the air for seven days after the cup forming test. This was because a small amount of twinning took place as loads applied during the cup forming test were faster and larger than those of the tensile test, and because the stress was concentrated on the cup side. In the 18Mn–Al steel, on the other hand, the cracking did not occur due to lower stress concentration on the cup side because many twins were homogeneously formed inside most of austenite grains. [Copyright &y& Elsevier]

Abstract: The effect of Mg addition on strengthening of aluminium alloys was studied by monotonic, cyclic and single reversal deformation in high pressure torsion. The results show the extent of strengthening varies between these three processing methods and are dependent on Mg content. There is a relatively low hardness increment in commercially pure aluminium, slightly higher hardness increment in an Al–1Mg alloy and significant hardness increment in an Al–2Mg alloy. The difference of strengthening due to strain paths is discussed in terms of geometrically necessary dislocations. [Copyright &y& Elsevier]

Abstract: The influence of ZrC content on the tensile deformation behavior and fracture strength of ZrCp/W composites in a temperature range of 800–1400°C was investigated. Both of the non-linear feature of the stress–strain curve and the rupture strain of the composites decreased with increasing ZrC content from 20 to 50vol% in all the tested temperatures. The maximum ultimate tensile strength of each ZrCp/W composite was found in the temperature range of 1000–1200°C. With increasing ZrC content from 20 to 50vol%, the maximum ultimate tensile strength of the ZrCp/W composite was decreased due to the porosity increase and the plasticity decrease of the composite although ZrC enhanced the tungsten matrix via load transferring and blocking dislocation movement in tungsten matrix. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an experimental investigation into the strength, deformation, and fracture behaviour of textile-reinforced concrete (TRC) subjected both to low and high-rate tensile loading ranging from 0.0001 to 50s−1. High strain rates were achieved using a high-rate servo-hydraulic testing machine. The effect of the addition of short fibres on the static and dynamic response of TRC has been investigated, and the microstructure of both composite and fibre was observed after the tests using an ESEM. An increase in tensile strength, strain capacity, and work-to-fracture was observed for strain rates up to 0.1s−1 with increasing strain rate. The addition of short glass fibres increased the tensile strength and first crack strength of the TRC. For high-speed tests (rates above 5s−1) an increase in the tensile strength, first crack strength and work-to-fracture was also observed, but at the same time there was a decrease in the strain capacity. The tests at high loading rates showed a pronounced effect of the specimen length on the measured mechanical properties: with increasing gauge length the tensile strength and strain capacity decreased, while the work-to-fracture increased. [Copyright &y& Elsevier]

Abstract: Nano-grain evolution in an austenitic stainless steel (SUS 316) during multidirectional forging (MDF) was investigated at temperatures of 77K and 300K. The flow stress during MDF and the room-temperature hardness increased significantly with increasing cumulative strain. The initial grains were subdivided by mechanical twinning and martensitic transformation. The formation of packets, which are composed of lamellar-structured mechanical twins with a spacing of 10–300nm, enhanced grain fragmentation. The packet size ranged from 40nm to 100nm depending on the MDF temperature and the cumulative strain. Tensile tests at ambient temperatures revealed a maximum proof strength of 2.1GPa. While the proof strength increased with cumulative strain, the plastic strain at fracture was approximately 10% independent of the cumulative strain over ∑Δɛ =2.4. [Copyright &y& Elsevier]

Abstract: The effects of sensitisation-induced martensitic transformation on the tensile behaviour of 304 austenitic stainless steel have been investigated. Yield strength is reduced by sensitisation, but ultimate tensile strength is nearly unaffected. Strain-hardening behaviour is changed by sensitisation, too. Although sensitisation may induce martensite formation near grain boundary, twin boundary, and austenite/martensite interface, the sensitisation-induced martensite does not exert a great influence on tensile behaviour in the 304 steel. In the unsensitised condition, martensitic transformation in the steel bulk induced by prior deformation and liquid-nitrogen immersion also does not change strain-hardening behaviour in the present steel. [Copyright &y& Elsevier]

Abstract: 304L stainless steel specimens are pre-strained to 0.15 or 0.5 and are then deformed at strain rates ranging from 2000s−1 to 6000s−1 at temperatures of 300°C, 500°C and 800°C using a compressive split-Hopkinson pressure bar. The results show that for both values of the pre-strain, the flow stress increases with increasing strain rate, but reduces with increasing temperature. At deformation temperatures of 300°C or 500°C, the flow stress in the 0.5 pre-strained specimen is higher than that in the specimen pre-strained to 0.15. However, at a temperature of 800°C, the two specimens exhibit a similar level of flow stress. Transmission electron microscopy (TEM) observations reveal that the strengthening effect observed in the specimens deformed at 300°C or 500°C is the combined result of dislocations, mechanical twins and martensite transformation. However, at a deformation temperature of 800°C, the strengthening effect is the result primarily of dislocation multiplication. The volume fraction of martensite transformation decreases with increasing strain rate and temperature. In addition, both the dislocation density and the twin density increase with increasing strain rate, but decrease with increasing temperature. Finally, the quantitative analysis results indicate that the flow stress varies with the square root of the dislocation density, the twin density and the volume fraction of martensite, respectively. [Copyright &y& Elsevier]

Abstract: This study was focused on improving the plastic properties of FeSiBP bulk metallic glasses (BMGs) by adding small amount of Cu (0.1–0.6%). BMGs with significant plastic strain of up to around 3.1% and a strength of 3.3GPa were obtained in our investigation. Multiple shear bands and related shear ledges were observed on the deformed specimen. The high plasticity is attributed to the nano-scale inhomogeneity that results from phase separation, which can hinder the propagation of shear bands, in effect promoting multiple shearing. The characteristic size of the α-Fe nanoparticles embedded in the glassy matrix changed with Cu content. Our results indicated a dependence between the plastic behavior and the size of the α-Fe nanoparticles. A higher Cu content resulted in an increase in the size of the α-Fe nanoparticles. Of all the samples tested in our investigation, the (Fe0.76Si0.096B0.084P0.06)99.9Cu0.1 alloy exhibited the best plastic properties. [Copyright &y& Elsevier]

Abstract: Using a commercial, electrodeposited copper film of 12μm thickness, tensile tests, fatigue tests and static loading tests were performed. The elastic modulus, two types of yield strengths, tensile strength and strain-hardening exponent were obtained. Fatigue tests were performed at four levels of mean stresses and cyclic plastic strain and ratcheting strain (monotonic plastic strain) were measured continuously during the tests. Irrespective of mean stress, fatigue life can be well represented by the maximum stress. The monotonic plastic strain at fracture is nearly constant, irrespective of fatigue life or mean stress. Based on the results obtained, the reason why fatigue life can be well represented by the maximum stress is discussed. [Copyright &y& Elsevier]

Abstract: This paper investigated the influence of pre-strain on the mechanical properties and fitness-for-service of the API 5L X65 pipeline subjected to large plastic deformation. Axial tensile pre-strains of 1.5, 5 and 10% were applied to plate-type tensile specimens extracted from the longitudinal direction of the pipe body prior to mechanical testing. Tensile test results revealed that yield strength and tensile strength increased with increasing tensile pre-strain. The rate of increase of the yield strength was greater than that of the tensile strength. Pre-strain up to 5% had little effect on decreasing the CTOD and Charpy impact along the LS notch direction. Charpy impact energy along the TL notch direction considerably decreased with increasing tensile pre-strain. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for-service code, API RP 579. [Copyright &y& Elsevier]

Abstract: The microstructure and mechanical properties of heavily cold-worked CuAgZr alloys are investigated to understand the development of strain in these alloys. Heat treatments increase strain and if applied intermediately between large strains of cold deformation this happens to be valid even for comparable stress levels. This study is focused on the state after the heat treatment in order to show the impact of the microstructure in the mentioned state on the development of the mechanical properties. The microstructure of the samples is inhomogeneous after heavy plastic deformation and also after annealing in the order of the recrystallisation temperature. At this temperature a certain fraction of Ag that has been dissolved during deformation reprecipitates and strengthens the material again. In addition, annealing causes the formation of twins, which is considered as origin of an raised elastic modulus. [Copyright &y& Elsevier]

Abstract: Micro-truss cellular materials have enhanced weight-specific properties due to the efficient arrangement of their internal load-bearing ligaments. The present study addresses the incorporation of in-situ work-hardening as a microstructural design strategy in deformation-formed micro-truss materials. First, the tensile properties of the starting perforated precursor material were used to develop a simple analytical model to characterize the plastic strain introduced during fabrication and the range of accessible cellular architectures that can be formed. Second, the flow stress of the individual struts during forming was used to develop a model for predicting the inelastic buckling resistance of the micro-truss struts. The result is a model capable of defining the regions of strength-density material property space that are achievable for a perforation-stretched micro-truss, based simply on the tensile properties of the starting precursor sheet. [Copyright &y& Elsevier]

Abstract: The results of an investigation of microstructural evolution during quasi-static and dynamic deformation of a Fe–10Ni–0.1C steel containing small amounts of V and Mo are reported. In the as-received condition, the steel has a lath martensite microstructure with a mean lath size of ∼150nm, and MC carbides dispersed in it with a mean size of ∼20nm. During dynamic deformation (strain rates of 1×103 s−1 to 4×103 s−1), depending on strain and strain rate, shear localization occurs and is accompanied by an optically visible shear band (∼20μm wide). In the situation where the localization process is in its early stages (lower rates, lower global height strains, or both), the microstructure shows severe local deformation within the band but the initial microstructure is still discernible. With progression in severity of localization, there is clear and reproducible evidence for a central region (∼6–8μm wide) within the shear band composed of ∼300nm size equiaxed grains. Electron microscopy characterization of these grains confirms the presence of both, austenite, with a low dislocation content, and heavily dislocated and/or twinned ferrite. Composition measurements from the individual grains confirm partitionless transformation. When the test conditions are further intensified, a crack “chases” the shear band, with the crack running either partway or all the way through the band and therefore through the sample. Examination of the resulting fracture surfaces provides evidence for the presence of a thin liquid film layer (perhaps 10–20nm or less) at various locations within the shear band that presumably has no shear resistance. Together, these observations provide a microstructural footprint for how deformation progressed during shear localization, a sense for the accompanying thermal profile within the shear band, and evidence for the intensity of localization in this alloy in the condition it was examined. [Copyright &y& Elsevier]

Abstract: The tensile behavior of a two-dimensional woven carbon/silicon carbide composite has been characterized both by monotonic and loading/unloading tests. The composite shows markedly non-linear behavior with evident hysteresis loops, appreciable residual strains and continuously decreasing moduli. Both the loop width and residual strain have a continuous acceleration with applied stress, implying the composite failure precedes matrix cracking saturation. The shape of hysteresis loops is characterized by an initial parabolic region followed by a linear region. The preexisting matrix microcracks in as-processed specimens and multiple microcracks accompanied by extensive fiber pull-out in the failed specimens were observed, indicating large thermal residual stresses and relatively weak interfacial bonding exist in the present composite, respectively. Then the interfacial sliding stress and residual stress were quantitatively derived from the hysteresis analysis, and further used to predict matrix cracking stress and stress–strain behavior. Excellent agreement between predictions and experimental results was obtained. [Copyright &y& Elsevier]

Abstract: In the present work, dynamic tests have been performed on AISI 1018 CR steel specimens by means of a split Hopkinson pressure bar (SHPB). The standard SHPB arrangement has been modified in order to allow running tensile tests avoiding spurious and misleading effects due to wave dispersion, specimen inertia and mechanical impedance mismatch in the clamping region. However, engineering stress–strain curves obtained from experimental tests are far from representing true material properties because of several phenomena that must be taken into account: the strain rate is not constant during the test, the specimen undergoes remarkable necking, so stress and strain distributions are largely non-uniform, and the temperature increases because of plastic work. Experimental data have been post-processed using a finite element-based optimization procedure where the specimen dynamic deformation is reproduced. Optimal sets of material constants for different constitutive models (Johnson–Cook, Zerilli–Armstrong and others) have been computed by fitting, in a least mean square sense, the numerical and experimental load–displacement curves. [Copyright &y& Elsevier]