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Abstract: High-manganese austenitic TWIP steels exhibit very high strength and elongation before necking. The peculiarity of these steels is that mechanical twins form during straining due to their low stacking fault energy (SFE). These twins are usually thought to have a huge impact on the outstanding properties of the materials, either by bringing about a dynamic Hall & Petch effect and/or a composite effect. In this study, the appearance of mechanical twins during tensile straining is investigated for a Fe–20%Mn–1.2%C TWIP steel. The twinning rate was estimated by means of point counting analysis on EBSD micrographs at different strain levels. The reliability of this method is first thoroughly discussed. It is then shown that there exists a first order relationship between this twinning rate and the work hardening rate. [Copyright &y& Elsevier]

Abstract: A high strength bulk nano-crystalline Al–1Fe–(0-1)Zr alloys were processed by mechanical alloying and spark plasma sintering. The high yield strength of ∼850MPa was achieved in an Al–1Fe–0.5Zr alloy with 19% strain in compression. The high strength was attributed to the nanosized Al–Fe grains and the dispersion of fine Al6Fe particles. High temperature compressive yield strength of 455MPa and elongation of 16.7% was achieved at 250°C. [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: The effects of age-forming on microstructures and mechanical properties of 7050 Al alloy were investigated in this work. The alloy was subjected to age-forming as well as stress-free ageing at 160°C for 6, 12, 18 and 24h, and its microstructures were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). It was shown that creep might lead to grain elongation during age-forming, and the applied stress induces the coarsening of precipitates in 7050 Al alloy. The texture in the alloy was also influenced by age-forming. Consequently, the differences in microstructures result in differences in mechanical properties of age-forming versus traditional stress-free ageing. The ultimate tensile strength of age-formed samples were slightly lower than that of stress-free aged samples, while the yield strength of age-formed samples were apparently lower than that of stress-free aged samples. Specifically, the elongation of samples age-formed displays apparently decrease. [Copyright &y& Elsevier]

Abstract: We report the feasibility of fabricating ultrafine-grained ZK60 magnesium alloy sheets with a combination of superior mechanical properties at room temperature and excellent superplasticity at high strain rates by means of high-ratio differential speed (HRDSR). The ZK60 alloy processed under the optimum HRDSR condition showed a high yield strength of 378MPa and a reasonably high ductility (a total elongation of 12.3%). The major strengthening mechanisms could be attributed to the grain size and particle strengthening. Its microstructure was quite thermally stable up to 573K, such that high strain rate superplasticity could be achieved at 10−2 and 10−1 s−1. The development of high-density shear bands that occurred uniformly over the entire volume of a sample and dynamic precipitation of spherical or irregular shaped particles with the sizes of 20–32nm along the lamellar boundaries in the shear bands and on the boundaries of grains newly formed within the shear bands via continuous dynamic recrystallization, resulted in an ultrafine-grained microstructure with high thermal stability. The room-temperature mechanical properties and superplastic ability of the HRDSR-processed ZK60 were comparable to those of a magnesium alloy of a same or similar composition processed via powder metallurgy. Because the currently developed HRDSR technique is based on a rolling process and only a few processing steps are involved, its transfer to industry that demands high-performance magnesium alloy sheets is promising. [Copyright &y& Elsevier]

Abstract: Compression tests of the 50vol% TiC x /Al and the 50vol% TiB2/Al composites have been performed in the strain rate range from 1×10−4 s−1 to 1×10−1 s−1, and the effect of strain rate on the compressive behavior and the work-hardening capacity (H c) of them have been investigated. The yield strength () and the H c of both the composites are strain rate sensitive, while the ductility is insensitive to the strain rate. The ultimate compressive strength () of the TiB2/Al composites is not significantly influenced by the strain rate, while that of the TiC x /Al composite increases from 615MPa to 826MPa with the strain rate increasing. Under various strain rates, the of the TiB2/Al composite is significantly better than that of the TiC x /Al composite, while its ductility and H c are lower than that of the TiC x /Al composite. At the strain rate of 1×10−4 s−1, the of the TiB2/Al composite and the TiC x /Al composite are 1071MPa and 615MPa, respectively; while the H c of them are 0.87 and 0.99, respectively. [Copyright &y& Elsevier]

Abstract: The properties of polymers are strongly affected by their molecular structures. Therefore, three different types of polyethylene; low density, low-linear density and high density polyethylene were used in this study to experimentally investigate the dependency and attractive effect of molecular structures towards compressive properties of polyethylene over a wide range of strain rate studied. For the mechanical tests, an experimental technique based on the compression split Hopkinson pressure bar was introduced to perform high strain rate testing whereas a conventional universal testing machine was used to perform static compression testing. Additionally, two constitutive equations were employed to validate the yield behaviour of all tested polyethylene specimens under different levels of strain rates. Results indicated that the molecular structure of polyethylene did affect its mechanical properties in terms of yield behaviour, stiffness, strength, rate sensitivity, activation volume and absorbed energy, respectively. Meanwhile, the levels of strain rates also played as secondary roles that influenced the mechanical properties of the polyethylene specimens. Of the three types of polyethylene specimens, high density polyethylene recorded an excellent performance in terms of yield behaviour, absorbed energy, stiffness, and strength properties than that of other polyethylene specimens. However, low linear polyethylene showed greater rate sensitivity than that of other polyethylene specimens under both static and dynamic regions. Interestingly, both constitutive models almost agreed with the experimental results. [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 microstructure, compression property and work-hardening effect of the NiAl-matrix composite with 1.7wt.% NbB2 and Nb x C (x =1 or 2) fabricated by the combustion synthesis and hot pressing technique have been investigated in the study. The NiAl-matrix composite has strong strain rate sensitivity. The yield strength of the NbB2–Nb x C/NiAl composite decreases while the fracture strain and the work-hardening capacity (H c) increase with decreasing strain rate. A high true ultimate strength of 1472MPa, a fracture strain of 20.1% and H c =1.41 were obtained under the strain rate of 2.0×10−5 s−1. [Copyright &y& Elsevier]

Abstract: Extensive multistep forging at 950°C was applied to the cast AlCuCrFeNiCo high-entropy alloy to transform the cast coarse dendritic structure into a fine equiaxed duplex structure consisting of the mixture of BCC and FCC phases, with the average grain/particle size of ∼1.5±0.9μm. Tensile properties of the alloy in the as-cast and forged conditions were determined in the temperature range of 20–1000°C. The hot forged alloy was stronger and more ductile during testing at room temperature, than the as-cast alloy. The yield stress (YS), ultimate tensile strength (UTS), and tensile ductility (δ) of the forged condition were 1040MPa, 1170MPa, and 1%, respectively, against 790MPa, 790MPa and 0.2% for the as-cast condition. In both conditions, the alloy showed brittle to ductile transition (BDT), with a noticeable increase in the tensile ductility within a narrow temperature range. In the as-cast condition, this transition occurred between 700 and 800°C, while in the forged condition, it was observed between 600 and 700°C. With an increase in the testing temperature above the BDT, a continuous decrease in tensile flow stress and an increase in tensile ductility were observed. In the temperature range of 800–1000°C, the forged alloy showed superplastic behavior. The tensile elongation was above 400% and reached 860% at 1000°C. [Copyright &y& Elsevier]

Abstract: The present study investigated hydrogen embrittlement (HE) cracking upon indentation of high-strength steel. When an indentation test was applied to high-strength steel that included absorbed hydrogen, radial cracks initiated and propagated at the corners of the indentation impression, whereas the as-received steel with no hydrogen absorption exhibited no cracking. In addition, the length of the hydrogen-induced indentation cracks was found to be dependent on the hydrogen content in the steel. A combined experimental and computational investigation was conducted for a mechanistic study of Vickers indentation cracking caused by hydrogen embrittlement. Crack propagation was simulated based on a cohesive zone model in the finite element method and the stress intensity factor for the crack was evaluated. It was found that the simulated crack initiates at loading, and then propagates upon unloading. The value of the stress intensity factor at the indentation crack was in agreement with the threshold resistance to crack propagation for HE cracking (threshold stress intensity factor, K ISCC). This suggests that the length of the cracks can be used to evaluate the susceptibility of the steel to HE cracking. [Copyright &y& Elsevier]

Abstract: Tensile fracture behaviors and mechanisms of 2D C/SiC-BC x composite were investigated. Results showed that the 2D C/SiC-BC x composite exhibited similar tensile strength (about 250MPa), but different fracture mode and damage evolution compared to that of 2D C/SiC composite under similar monotonic tensile stress condition at room temperature. The initial modulus and fracture modulus of 2D C/SiC-BC x composite obtained under tensile cyclic loading at RT were about 98.6GPa and 54.5GPa, respectively. At high temperatures, the tensile strengths were lower than that at room temperature and behaved as a step-like stress–strain curve. [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: Strain aging in low-carbon steels is a well-known strengthening phenomenon, the typical results of which are an increase in yield stress and/or an increase in the extent of discontinuous yielding. Aging effects are generally characterized through the use of results from mechanical tests in which the strain path prior to aging (prestrain) and the strain path after aging are in the same direction. However, these tests do not completely characterize the properties of aged materials, since the effects of aging are reduced when materials are tested in directions different than the direction of prestrain. The result is anisotropy of properties which can affect the performance of industrial products. In this paper, the effect is demonstrated in two examples of industrial products made from low carbon steels, the aging of which during processing results in performance changes that are not predicted through standard tensile testing of as-fabricated products. The first example compares the effect of aging on yield strength and dent resistance of stamped hood panels on an electro-galvanized, Al killed, bake hardenable sheet steel for auto body panel applications. The second example shows the effect of aging on the anisotropy of tensile data from two American Petroleum Institute (API) grade X100 pipe steels in the as-received condition. The data show that the performance gains realized from strain-aging in the tensile tests on base material are not apparent in the tensile data from the stamped panels after aging, but the dent resistance clearly demonstrated the beneficial effect of aging. The high degree of anisotropy in the yield strength and yielding behaviors between the circumferential and longitudinal tensile data in the two pipe steels demonstrates the effect of strain path on a materials response to aging, which may occur during downstream processing or in field service. The manifestation of material properties that are dependent upon the relationship between the pre-aging strain direction and the post-aging strain direction underscores the importance of correct evaluation of mechanical performance in the design of structural components in materials which undergo aging. [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: High dense tantalum sintering components with a hardness gradient within individual grains were synthesized successfully by means of spark plasma sintering (SPS) of the nitrided tantalum particles at a pressure of 400MPa and a temperature of 950°C. High yield strength up to 1350MPa combined with 12% fracture strain was achieved in the compression tests, which can be attributed to the novel gradient composition inside the grain structure. [Copyright &y& Elsevier]

Abstract: The ductility of nanocrystalline Cu films with different thickness ranging from 40nm to 600nm was tested by uniaxial tension. The ductility of the films was determined by the changes of the statistical crack density and the electrical resistance with tensile strain. It was found that the ductility decreases with increasing the film thickness, exhibiting an inverse size effect compared to the previous results. The 40-nm-thick Cu films sustain strains up to 20% without cracks, while the 600-nm-thick Cu films fracture at only 5% with channel cracks. The effective interfacial bond strength between the films and the substrate is suggested to be responsible for the ductility of Cu films. [Copyright &y& Elsevier]

Abstract: Microstructure and creep behavior of a commercial ZrO2 dispersion-strengthened Pt alloy were investigated. Emphasis was placed on examining the correlation between the minimum creep rates and the applied stress in the temperature range of 1273–1773K. The ODS Pt alloy exhibited a highly elongated grain structure that had developed by a thermo-mechanical processing. The interfaces between ZrO2 particles and the Pt matrix were found to be incoherent. An attractive interaction appeared to be present between dislocations and ZrO2 particles. The detachment controlled dislocation creep model was used to explain the steady state creep behavior. The presence of ZrO2 inclusions was also beneficial for maintaining the grain structure and the subgrains, which then provides increased resistance to high temperature creep deformation. [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: A type of duplex aging heat treatment was developed to improve the mechanical properties at room temperature and elevated temperatures in a pre-strained Al–Cu–Mg–Ag alloy. In contrast to the conventional T8 temper at 165°C and 200°C, the hardening response of the alloy to aging was increased by duplex aging treatment, the ultimate tensile strength and yield strength of duplex aging temper were improved by approximately 3–7%, which was attributed to the fact that the recovery of dislocations occurred and the precipitation of θ′ phase was restrained effectively at high aging temperature, and more Ω precipitates were formed during secondary aging. [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: The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing ΔK) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430Mpa, 530Mpa, 21J, 24Mpam1/2 for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor ΔK The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain boundaries (GB), and steps developed on the crack plane during crack-precipitate interaction at the GB due to ultrafine grain formation. [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: Elasto-Delayed-Elastic-Viscous (EDEV), a predictive material model for ‘quasi constant-structure’ primary creep is used in developing an algorithm for predicting stress–strain diagrams at constant strain rates. The strain rate dependence of the 0.2% offset yield-strength (σ y), time to yield, and the amounts of permanent (viscous) and the recoverable (anelastic or delayed elastic) strain components of the 0.2% offset strain can also be evaluated. Six material constants required for calculations can be obtained from short-term (few seconds to a few hours), constant-stress Strain Relaxation and Recovery Tests (SRRTs). The method is illustrated by calculations made for Ni-based fcc alloy, Waspaloy at 732°C (0.62T m) and Ti-based, alpha (hexagonal)-beta(bcc) alloy Ti-6246 at 600°C (0.45T m). In the ASTM recommended strain-rate range, 5×10−5 s−1 to 1.2×10−4 s−1, σ y increases by 6% for Waspaloy and 15% for Ti-6246. In this range, the 0.2% offset strain consists of 50% delayed elastic (anelastic) strain for Waspaloy and 70% for Ti-6246. Proportional limit is governed entirely by the delayed elastic effect or the Elasto-Delayed-Elastic (EDE) regime. Intragranular dislocation creep does not play the dominant role up to yield for the materials and temperatures considered, suggesting a shift in paradigm from conventional ideas. The EDEV model, in conjunction with SRRTs (which can be realized using a single specimen), can be used as a tool for characterizing and developing new alloys and ceramics or optimizing processing including grain-boundary engineering. [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: The effect of solutes, coarse and fine precipitates on work hardening rate and microstructure refinement of cryorolled Al 6063 alloy at different strains was investigated by employing hardness measurements, tensile tests, DSC, XRD, EBSD and TEM characterizations in the present work. The presence of solute in solid solution exhibits a stronger effect on the work hardening of the materials during cryo rolling than the presence of non-coherent and coherent second phase particles. The fine precipitates are sheared and dissolved at a cryorolling strain of 2.3, while the coarse precipitates remain unaffected. The work hardening rate of solutionized material is not saturated even at a cryorolling strain of 2.3, while it is saturated at this strain for the precipitated material. The severe strain induced during plastic deformation of Al 6063 alloy produces ultrafine microstructures with improved strength and hardness. The ageing treatment of the solutionized material after cryorolling at a strain of 2.3 has improved its strength and ductility significantly as compared to precipitated materials due to the precipitation hardening and grain coarsening mechanisms, respectively. [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: In this work, a series of experiments was performed to explore the effects of anisotropy, strain rate, and temperature on microstructure change and associated mechanical response of a rolled AZ31B-H24 Mg alloy sheet under tension. Tensile tests were carried out on specimens in the 0, 45, and 90° to the rolling direction, using initial strain rates in the range of 4×10−3 to 1×10−1 s−1 at temperatures of 250 and 370°C. Results showed that variations in flow behavior under tension could be related to the changes in microstructure resulting from applied tensile conditions. Resultant microstructures, such as degree of dynamic recrystallization, grain growth, and shape of the grain, were associated with temperature, strain rate, and tensile loading direction. The initial texture influenced the variations in changes in microstructure and mechanical properties upon testing in different directions. The specimens upon testing in the 45° to the rolling direction yielded higher m-value, lower strength, and greater elongation to failure under all test conditions. [Copyright &y& Elsevier]

Abstract: This paper describes the mechanical behavior of the 6061-T6 aluminium alloy at room temperature for various previous thermal histories representative of an electron beam welding. A fast-heating device has been designed to control and apply thermal loadings on tensile specimens. Tensile tests show that the yield stress at ambient temperature decreases if the maximum temperature reached increases or if the heating rate decreases. This variation of the mechanical properties is the result of microstructural changes which have been observed by Transmission Electron Microscopy (TEM). [Copyright &y& Elsevier]

Abstract: The effect of plasma sprayed NiCr and NiCrAl coatings on the creep resistance of Nickel alloy 690 at temperature of 1033K was investigated. Experimental results showed that the coatings had a beneficial effect on the improvement of the creep resistance of substrate. However, there was almost no difference in the creep lives between the NiCr and NiCrAl coated specimens at a given stress level. The relation between the applied stress and time to rupture of the coated specimens can be estimated by using Larson-Miller equation. For the coated specimens tested at low applied stress levels, the product of the minimum creep rate and the time to rupture was a constant value. The θ projection method can be used to accurately characterize the creep behavior of the coated specimens. The variation of the creep strain along with time predicted by using θ projection method agreed well with the experimental results. [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 microstructure, texture and mechanical properties of the 1wt.% Ca-AZ31 alloy (1CaAZ31) processed by high-ratio differential speed rolling (HRDSR) were examined. After HRDSR, the grain size of the 1CaAZ31 decreased to ∼0.9μm, and (Al, Mg)2Ca particles were highly refined and uniformly dispersed into the matrix. The significant improvement in strength was attributed to the effective grain-size reduction. Contribution of the particle strengthening was relatively small. Strength of the ultrafine grained (UFG) 1CaAZ31 was sensitive to strain rate. As the result, the yield stress was as high as 412MPa at 1×10−1 s−1, while it was 292MPa at 1×10−5 s−1. The strain-rate-sensitivity of the UFG 1CaAZ31 was 0.031–0.041, which is about twice larger than that of its annealed counterpart having coarse grains (0.018). Uniform elongation of the UFG 1CaAZ31 was small compared to that of the coarse-grained 1CaAZ31 due to the reduced strain hardening ability, but its post-uniform elongation was large due to the increased strain-rate sensitivity. [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: The effect of 1, 2 and 3wt.% rare earth (RE) additions on the microstructure and creep resistance of the Mg–6Zn–3Cu alloy (ZC63) was investigated by impression creep tests in the temperature range 423–498K and under punching stresses in the range 150–700MPa for dwell times up to 3600s. The results showed that the creep strength of the base alloy was remarkably improved by RE addition. This was attributed to the grain refinement effect of RE elements, and formation of thermally stable Mg12RE, MgRE, and Cu2RE compounds which strengthen both matrix and grain boundaries during creep deformation. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the test temperature, around 0.017< σ imp/G <0.037. Based on the steady-state power-law creep relationship, the stress exponents of about 4.4–6 and 7–12.7 were obtained at low and high stresses, respectively. The creep activation energies were found to be in the range 73–78 and 122–130kJ/mol, at low- and high-stress regimes, respectively. It is suggested that the operative creep mechanism is pipe-diffusion-controlled dislocation viscous glide in the low-stress regime, and dislocation climb with some sort of back stress, similar to those noted in dispersion strengthening alloys, in the high-stress regime. [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: The static and dynamic properties of mica/polypropylene composites, with a mica content of 10, 15, 20% by weight, were studied at different levels of strain rates (from 10s−4 to 10s2), using a conventional Universal Testing Machine and Split Hopkinson Pressure Bar apparatus. The results show, that the mechanical properties of mica/polypropylene composites, in terms of yield stress, fracture strain, compression modulus and compressive strength, were greatly affected by the level of strain rates applied and mica content. It was found that the Bergström model was both consistent and reliable, in evaluating the effect of the strain hardening mechanism of the composites, in respect to the applied strain rate. The relationship between the strain rate sensitivity and the thermal activation volume of the mica/polypropylene composites were successfully obtained at various mica contents, where the results show a contradicting pattern for both parameters. [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: The influences of major factors including applied stress amplitude, inclusion size and hydrogen content on granular-bright-facet (GBF) size of high strength steels in the very high cycle fatigue regime were studied in this article. It was found that the GBF size is determined by the applied stress amplitude and material hardness. If the applied stress amplitude is lower, the GBF size is larger. When a specimen containing bigger inclusions, the applied stress amplitude to form GBF can be reduced which results in the increase of GBF size. Hydrogen has different effects on the GBF size. The related reasons were discussed. [Copyright &y& Elsevier]

Abstract: Investigations on high strain rate behavior of epoxy LY 556 under compressive loading are presented. Compressive Split Hopkinson Pressure Bar (SHPB) apparatus was used for the experimental investigations. The studies are presented in the strain rate range of 683–1890 per second. It was generally observed that the compressive strength is enhanced at high strain rate loading compared with that at quasi-static loading. During SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. Further, an analytical method is presented based on variable rate power law for the prediction of compressive strength at high strain rate loading for epoxy LY 556. Using the analytical method, high strain rate compressive stress–strain behavior is presented up to strain rate of 10,000 per second. [Copyright &y& Elsevier]

Abstract: The axial–torsional cyclic deformation behavior of polycrystalline nickel was investigated by performing fully reversed plastic strain amplitude controlled fatigue experiments at effective plastic strain amplitudes ranging from 1×10−4 to 1×10−3. Experiments were accomplished under proportional and 90° out-of-phase nonproportional loading paths. Results indicate that loading path has very little effect on the cyclic response at the lower effective plastic strain amplitude. However, at the higher effective plastic strain amplitude, significant additional hardening is induced by the nonproportional loading path. [Copyright &y& Elsevier]

Abstract: Properties of a random porous material such as pervious concrete are strongly dependent on its pore structure features, porosity being an important one among them. This study deals with developing an understanding of the material structure–compressive response relationships in pervious concretes. Several pervious concrete mixtures with different pore structure features are proportioned and subjected to static compression tests. The pore structure features such as pore area fractions, pore sizes, mean free spacing of the pores, specific surface area, and the three-dimensional pore distribution density are extracted using image analysis methods. The compressive stress–strain response of pervious concretes, a model to predict the stress–strain response, and its relationship to several of the pore structure features are outlined. Larger aggregate sizes and increase in paste volume fractions are observed to result in increased compressive strengths. The compressive response is found to be influenced by the pore sizes, their distributions and spacing. A statistical model is used to relate the compressive strength to the relevant pore structure features, which is then used as a base model in a Monte-Carlo simulation to evaluate the sensitivity of the predicted compressive strength to the model terms. [Copyright &y& Elsevier]