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Abstract A severe plastic deformation is widely used to improve the mechanical properties of non-heat-treatable alloys. Thus, the investigation and modeling of microstructural evolutions of materials during large straining are of great importance. In this research, substructural evolutions of four different kinds of Al alloys namely Al-1Mn, Al-1Mg, Al-2.77Mg and Al-5Mg, have been studied using a dislocation based model and the mechanical properties of these alloys have been compared considering all microstructural parameters such as dislocation density, subgrain size, cell wall misorientation and the effect of alloying element. As a result, a simplified general equation has been expressed in order to predict the flow stress of aluminum alloys after large plastic deformation based on the influence of substructural parameters. Using this model, it is shown that magnesium is more effective to improve the strength of aluminum than manganese as an alloying element. In addition, due to higher SFE, Al-Mg alloys have more hardening rate with finer grains, accordingly. [ABSTRACT FROM AUTHOR]

Conventional Ashby plots for material selection may not appropriately describe material properties at small-length scales, new plots taking account of size effects are urgently needed for micro- or nano-mechanical design. Here, I show strength–modulus, strength–density, and size effect–Peierls stress plots for various solid materials at small scales. [ABSTRACT FROM AUTHOR]

In this work, the effect of external disturbances on the strain-rate dependent plastic deformation behavior of a Zr 57 Cu 20 Al 10 Ni 8 Ti 5 bulk metallic glass (BMG) has been examined by tailoring the geometric confinement, stress gradient, and sample size. With the external disturbances, the fracture strains of the BMG specimens become less dependence on the strain rates, and it is found that the confinement of the propagation of shear bands is the dominant deformation mechanism. This is different from previous findings in that multiplication of the shear bands also plays a critical role in accommodating the plastic deformation of BMGs with external disturbances. The present findings not only shed more light on the deformation mechanisms of BMGs under external disturbances, but also suggest that the use of external disturbances can reduce the dependence of the plastic deformation behavior of BMGs on the strain rates. [ABSTRACT FROM AUTHOR]

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]

Abstract: We report on the formation of a new bulk multimodal-grained (MGed) iron with a large true strain of 58% and high strength of 955MPa by spark plasma sintering. The new MGed structure contains fine-grained α-Fe matrix and ultrafine-grained equiaxed and acicular α-Fe enhancing phases. The large plastic strain can be attributed to the increased dislocation motion and improved shear deformation ability resulted from such MGed structure containing three different α-Fe morphologies. [Copyright &y& Elsevier]

Abstract: In this study uniaxial tension tests are conducted over a temperature range of 293–800K and a strain rate range of 0.001–2500/s using a servohydraulic testing machine and an enhanced Hopkinson technique to gain understanding of the plastic flow behavior of a DH-36 steel. Test results reveal the strong dependencies of the flow stress on strain rate and temperature. Moreover, dynamic strain aging (DSA) occurs at temperatures above 450K, causing an increase in flow stress. As the strain rate increases, the magnitude of the DSA effect reduces while the temperature range over which the DSA induced material strengthening takes place shifts to higher temperatures. Based on the experimental data, a dislocation barrier model is modified to describe the material behavior and to include the DSA effect. Good agreements between the model predictions and the experimental results are obtained. [Copyright &y& Elsevier]

Abstract: Composites with volume fraction from 10vol.% to 90vol.% were prepared by spark plasma sintering (SPS) of mixing of aluminium and metallic glass (Zr57Cu20Al10Ni8Ti5) powders with similar particle size. These materials show gradual evolution of their mechanical behaviour. First, monotonous but non linear variation of the strength is observed. That reveals two different mechanisms describing the dependence of strength with the composition and architecture. Second, stress–strain curves successively show, from low to high Al content, absence of plasticity, plasticity with intensive decrease of strength related to local damaging, and finally plasticity with work hardening. The mechanical behaviour evolutions are geometrically and analytically modelled. This reveals change in behaviour at the expected 3-dimensional percolation thresholds for a random spatial distribution of two phases. [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: 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 (Zr48Cu36Al8Ag8)99.25Si0.75-based bulk metallic glass composite (BMGC) rods ex situ dispersed with Ta particles (with a diameter of 2–4mm) have been successfully fabricated by suction casting and characterized. These Ta-added BMGCs exhibit similar thermal properties in comparison with its base alloy counterpart, with relatively high glass forming ability (GFA). The results of compression test show that a superior mechanical performance with up to 22% compressive plastic strain, 1800MPa yield strength and 1850MPa fracture strength at room temperature can be obtained for the 2mm diameter rod of the ZrCu-based BMGC with 10vol.% Ta particles. These ex situ dispersed Ta particles (20±8μm) would arrange as semi-uniform confinement zones to restrict the shear band propagation. In addition, for a given Ta particle size, higher volume fraction particles would lead to more interfacial areas, shorter inter-particle spacings, smaller confinement zone sizes than the smaller volume fraction particles, and results in presenting larger compression plasticity. [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: To investigate the tensile properties and facture toughness of high-strength structural steel of Q420 under different conditions, tensile tests and crack tip opening displacement (CTOD) tests were conducted. The test results revealed that temperature significantly influenced the fracture toughness of structural steel and that fracture toughness was significantly reduced with the decrease in temperature, resulting in brittle fractures. Prestraining increased the yield stress and tensile strength of the structural steel. However, it significantly reduced the plasticity and fracture toughness, and further increased the probability of brittle fractures. As determined by FE-analysis, temperature and prestraining facilitated brittle fractures due to the activation of the resulting near crack tip stress fields. Based on the Weibull stress fracture criterion, the temperature and prestraining effects on the fracture toughness were predicted from fracture toughness results of the virgin material at room temperature by the local approach. The prediction was in good agreement with the experimental results. It certified that the critical Weibull stress obeys the two-parameter Weibull distribution in the local approach and the fracture behavior of the prestrained material at different temperatures can be characterized by the local approach. [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 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 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: 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 deformation and fracture of quench-hardened and tempered AISI 4340 steel samples at high strain-rates were investigated. The steel samples were quench-hardened and tempered at 205, 315 or 425°C for 1h before they were subjected to high velocity impact testing. Irrespective of the tempered condition of the martensitic steel samples, failure occurred predominantly by ductile shear fracture along the path of heat waves generated in the material during impact. Adiabatic heating and the associated thermal softening were found to play a more dominant role in the deformation and fragmentation of the samples than the dislocation multiplication effect of plastic deformation. Rather than the anticipated cleavage fracture or shattering of the quench-hardened steel samples into several fragments, the test specimens showed clear evidence of ductile shear and knobby fracture modes for all tempering temperatures. The elongated dimples observed on the fracture surface of the samples tempered at 205°C show a higher aspect ratio than with the other samples. This would indicate that temperature rise along the path of the heat waves and the accompanying stress-drop appears to favor the observed dimpled fracture over the expected cleavage fracture. [Copyright &y& Elsevier]

Abstract: High Mn–Al–C steels were recently reappraised as the promising material for advanced auto body system by their excellent combination of strength and ductility over 60,000MPa% associated with microband-induced plasticity. This study was intended to examine the factors affecting the tensile properties of high Mn–Al–C steels. For this purpose, tensile tests and microstructural analyses were performed on a Fe–28Mn–9Al–0.8C steel at various conditions. As usual, strength increased and elongation decreased with decreasing the grain size. The strain hardening rate of the fine-grained steel remained unchanged to the medium strain level but that of the coarse-grained steel continuously increased to the high strain level, resulting in exceptional ductility. Fully austenitic steel obtained by high temperature solution treatment exhibited the continuous increase of strain hardening rate while that of the steel solution-treated at low temperature decreased with increasing strain due to the bimodal grain size distribution and the presence of submicron ferrite. In the strain rates of 2×10−4 s−1 to 10−1 s−1, strength was relatively insensitive to the strain rate but elongation decreased with increasing the strain rate, indicating that plastic deformation was mainly achieved by thermal activation in this strain rate range. In the temperature range of 25–450°C, both strength and elongation decreased with increasing temperature except at 300°C where serrated flow occurred with extended ductility. The flow characteristics at 300°C were rationalized in terms of dynamic strain aging associated with carbon exhaustion. [Copyright &y& Elsevier]