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P Huang - One of the best experts on this subject based on the ideXlab platform.
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Strain Rate Sensitivity and related plastic deformation mechanism transition in nanoscale ag w multilayers
Thin Solid Films, 2014Co-Authors: Qing Zhou, F Wang, P HuangAbstract:Abstract Nanoscale metallic multilayers are a promising structural material for fabricating the next generation of nanoscale devices. Even though the mechanical properties of the multilayers have been extensively studied, the interpretation for the Strain Rate Sensitivity of the multilayers is still lacking. In present study, the hardness and Strain Rate Sensitivity of Ag/W multilayers with a wide range of modulation period Λ and modulation ratio η deposited by d.c. sputtering deposition were evaluated by nanoindentation testing. X-ray diffraction and transmission electron microscopy were carried out to investigate the texture and microstructure of the multilayers. Experimental results indicated that a mechanism transition occurred as the plastic deformation of the Ag/W multilayers was accommodated by the two constituent layers together at Λ ≤ 50 nm, while the plastic deformation localized mainly in Ag layers when Λ > 50 nm. A modified rule of mixture and plastic deformation localization model was proposed to describe the variation of Strain Rate Sensitivity for the multilayers with smaller and larger Λ, respectively.
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depth dependent Strain Rate Sensitivity and inverse indentation size effect of hardness in body centered cubic nanocrystalline metals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Jiyuan Zhao, Fei Wang, P HuangAbstract:Abstract Size effects on hardness ( H ) and Strain Rate Sensitivity ( m ) of nanocrystalline (NC) body-centered cubic Mo thin film were examined under nanoindentation testing. Contrast to existing reports that there was no indentation size effect on hardness in NC metals, inverse indentation size effect (ISE) in NC Mo was observed for the first time at penetration depths ranging from 15 to 200 nm, at all the loading Strain Rates applied. In addition, the Strain Rate Sensitivity of NC Mo exhibited strong dependence on penetration depth, increasing dramatically with decreasing penetration depth. Surface effects related to two deformation mechanisms were proposed to be responsible for the observed inverse ISE on H and depth dependent m . Specifically, the mobility of screw dislocation/component and the diffusion length of interfacial diffusion were altered as the deformed region underneath the indenter was approaching the free surface, resulting in the unusual size effects in NC Mo.
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grain size dependent Strain Rate Sensitivity in nanocrystalline body centered cubic metal thin films
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Qing Zhou, Fei Wang, Jiyuan Zhao, J Y Xie, P HuangAbstract:Abstract The Strain Rate Sensitivity (m) and activation volume (v⁎) of three nanocrystalline (NC) body-centered cubic (bcc) metals, i.e., W, Mo and Ta, with various grain sizes were evaluated by nanoindentation testing. Opposite to the conventional trend that NC bcc metals exhibit reduced m as the grain size was decreased, elevated m was observed as the grain size was reduced from ~90 nm to ~30 nm for all the samples concerned. It was proposed that the unusual variation trends of m for NC bcc metals were dominated by GB-related mechanisms when the grain size drops below a critical value.
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activation volume and Strain Rate Sensitivity in plastic deformation of nanocrystalline ti
Surface & Coatings Technology, 2013Co-Authors: F Wang, T T Gao, P HuangAbstract:Abstract The mechanical behavior of coarse grained, ultrafine grained and nanocrystalline Ti, which was fabricated on single crystalline Si substRate using a d.c. magnetron sputtering system, were investigated by nanoindentation tests at a range of Strain Rates; both the Strain Rate Sensitivity and activation volume were obtained. It is demonstRated that the Rate controlling mechanisms of plastic deformation for nanocrystalline Ti differ from those in coarse grained and ultrafine grained Ti. The implications of these findings for the mechanical properties of nanocrystalline hcp metals are also discussed.
Frederic Barlat - One of the best experts on this subject based on the ideXlab platform.
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Strain hardening Rate Sensitivity and Strain Rate Sensitivity in twip steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Alexandra Bintu, Gabriela Vincze, José Joaquin De Almeida Gracio, Catalin R Picu, A B Lopes, Frederic BarlatAbstract:Abstract TWIP steels are materials with very high strength and exceptional Strain hardening capability, parameters leading to large energy absorption before failure. However, TWIP steels also exhibit reduced (often negative) Strain Rate Sensitivity (SRS) which limits the post-necking deformation. In this study we demonstRate for an austenitic TWIP steel with 18% Mn a strong dependence of the twinning Rate on the Strain Rate, which results in negative Strain hardening Rate Sensitivity (SHRS). The instantaneous component of SHRS is large and negative, while its transient is close to zero. The SRS is observed to decrease with Strain, becoming negative for larger Strains. Direct observations of the Strain Rate dependence of the twinning Rate are made using electron microscopy and electron backscatter diffraction, which substantiate the proposed mechanism for the observed negative SHRS.
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Strain Rate Sensitivity of the commercial aluminum alloy aa5182 o
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: R C Picu, Gabriela Vincze, José Joaquin De Almeida Gracio, Fahrettin Ozturk, Frederic Barlat, Antoinette M ManiattyAbstract:The mechanical behavior of the commercial aluminum alloy AA5182-O is investigated at temperatures ranging from −120 to 150 ◦ C and Strain Rates from 10 −6 to 10 −1 s −1 . The Strain Rate Sensitivity parameter is determined as a function of temperature and plastic Strain, and the Strain Rate and temperature range in which dynamic Strain aging leads to negative Strain Rate Sensitivity is mapped. The effect of dynamic Strain aging on ductility and Strain hardening is investigated. The Sensitivity of the measured quantities to the experimental method employed and their dependence on grain shape are discussed. The experimental data are compared with the predictions of a model constructed based on a recently proposed mechanism for dynamic Strain ageing. The mechanism is based on the effect solute clustering at forest dislocations has on the strength of dislocation junctions. The model is shown to reproduce qualitatively the experimental trends. © 2004 Elsevier B.V. All rights reserved.
M Q Li - One of the best experts on this subject based on the ideXlab platform.
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Strain Rate Sensitivity and Strain hardening exponent during the isothermal compression of ti60 alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: M Q LiAbstract:Abstract In this paper, the flow stress was investigated in detail during the isothermal compression of Ti60 alloy. The Strain Rate Sensitivity and the Strain hardening exponent of Ti60 alloy were calculated based on the flow stress–Strain curves. The results showed that the softening effect in the α + β two-phase region was more significant than that in the β single-phase region due to the change in the deformation heat of the alloy. An initial yield drop was observed at or above 1273 K and in the Strain Rate range of 0.1–10.0 s −1 . The β phase became the continuous phase above 1273 K, which led to little temperature dependence of flow stress. The maximum m value of 0.34 occurred at 1253 K and a Strain Rate of 0.001 s −1 during the isothermal compression of Ti60 alloy. The Strain Rate Sensitivity at a Strain of 0.7 and a Strain Rate of 10.0 s −1 decreased with increasing deformation temperature after a peak value. And the m values decreased with increasing Strain Rate. This phenomenon could be reasonably explained based on the microstructure evolution during the isothermal compression of Ti60 alloy. The Strain hardening exponent increased with increasing deformation temperature at the Strain Rates of 0.001 s −1 , 1.0 s −1 and 10.0 s −1 . The variation of Strain hardening exponent with Strain was observed to be dependent on the Strain Rate and the deformation temperature.
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the variation of Strain Rate Sensitivity exponent and Strain hardening exponent in isothermal compression of ti 6al 4v alloy
Materials & Design, 2010Co-Authors: M Q Li, Weixin Yu, Hong LiAbstract:Abstract The deformation behavior in isothermal compression of Ti–6Al–4V alloy is investigated in the deformation temperatures ranging from 1093 K to 1303 K, the Strain Rates ranging from 0.001 s −1 to 10.0 s −1 at an interval of an order magnitude and the height reductions ranging from 20% to 60% at an interval of 10%. Based on the experimental results in isothermal compression of Ti–6Al–4V alloy, the effect of processing parameters and grain size of primary α phase on the Strain Rate Sensitivity exponent m and the Strain hardening exponent n is in depth analyzed. The Strain Rate Sensitivity exponent m at a Strain of 0.7 and Strain Rate of 0.001 s −1 firstly tends to increase with the increasing of deformation temperature, and maximum m value is obtained at deformation temperature close to the beta-transus temperature, while at higher deformation temperature it drops to the smaller values. Moreover, the Strain Rate Sensitivity exponent m decreases with the increasing of Strain Rate at the deformation temperatures below 1253 K, but the m values become maximal at a Strain Rate of 0.01 s −1 and the deformation temperature above 1253 K. The Strain Rate affects the variation of Strain Rate Sensitivity exponent with Strain. Those phenomena can be explained reasonably based on the microstructural evolution. On the other hand, the Strain hardening exponent n depends strongly on the Strain Rate at the Strains of 0.5 and 0.7. The Strain affects significantly the Strain hardening exponent n due to the variation of grain size of primary α phase with Strain, and the competition between thermal softening and work hardening.
Benjamin T Britton - One of the best experts on this subject based on the ideXlab platform.
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Strain Rate Sensitivity in commercial pure titanium the competition between slip and deformation twinning
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Benjamin T Britton, Qinmeng Luan, Teasung JunAbstract:Abstract Titanium alloys are widely used in light weight applications such as jet engine fans, where their mechanical performance under a range of loading regimes is important. Titanium alloys are mechanically anisotropic with respect to crystallographic orientation, and remarkably titanium creeps at room temperature. This means that the Strain Rate Sensitivity (SRS) and stress relaxation performance are critical in predicting component life. In this work, we focus on systematically exploring the macroscopic SRS of Grade 1 commercially pure titanium (CP Ti) with varying grain sizes and texture using uniaxial compression. Briefly, we find that Ti samples had positive SRS and samples compressed along the sheet rolling direction (RD) (i.e. soft grains dominant) were less Rate sensitive than bars compressed along the sheet normal direction (ND) (i.e. hard grains dominant). We attribute this Rate Sensitivity to the relative activity of slip and twinning. Within the grain size range of ~ 317 ± 7 μ m , we observe an increase in the Rate Sensitivity, where volume fraction of { 10 1 2 } 10 1 1 > T1 tensile twins was low, and the twin width at different Strain Rates were similar. These observations imply that the macroscopic Rate Sensitivity is controlled by the ensemble behaviour of local deformation processes: the amount of slips accumulated at grain boundaries affects the SRS, which is grain size and texture dependent. We hope that this experimental study motivates mechanistic modelling studies using crystal plasticity, including Strain Rate Sensitivity and twinning, to predict the performance of titanium alloys.
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a nanoindentation investigation of local Strain Rate Sensitivity in dual phase ti alloys
Journal of Alloys and Compounds, 2016Co-Authors: David E J Armstrong, Benjamin T BrittonAbstract:Abstract Using nanoindentation we have investigated the local Strain Rate Sensitivity in dual-phase Ti alloys, Ti–6Al–2Sn–4Zr-xMo (x = 2 and 6), as Strain Rate Sensitivity could be a potential factor causing cold dwell fatigue. Electron backscatter diffraction (EBSD) was used to select hard and soft grain orientations within each of the alloys. Nanoindentation based tests using the continuous stiffness measurement (CSM) method were performed with variable Strain Rates, on the order of 10 −1 to 10 −3 s −1 . Local Strain Rate Sensitivity is determined using a power law linking equivalent flow stress and equivalent plastic Strain Rate. Analysis of residual impressions using both a scanning electron microscope (SEM) and a focused ion beam (FIB) reveals local deformation around the indents and shows that nanoindentation tested structures containing both α and β phases within individual colonies. This indicates that the indentation results are derived from averaged α/β properties. The results show that a trend of local Rate Sensitivity in Ti6242 and Ti6246 is strikingly different; as similar Rate sensitivities are found in Ti6246 regardless of grain orientation, whilst a grain orientation dependence is observed in Ti6242. These findings are important for understanding dwell fatigue deformation modes, and the methodology demonstRated can be used for screening new alloy designs and microstructures.
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local Strain Rate Sensitivity of single α phase within a dual phase ti alloy
Acta Materialia, 2016Co-Authors: Zhen Zhang, Giorgio Sernicola, F P E Dunne, Benjamin T BrittonAbstract:Abstract We have performed in-situ micropillar compression to investigate the local Strain Rate Sensitivity of single α phase in dual-phase Ti alloy, Ti–6Al–2Sn–4Zr–2Mo (wt%). Electron backscatter diffraction (EBSD) was used to identify two grains, anticipated to primarily activate a slip on the basal and prismatic plane respectively. Comparative micropillars were fabricated within single α laths and load-hold tests were conducted with variable Strain Rates (on the order of 10 −2 to 10 −4 s −1 ). Local Strain Rate Sensitivity exponent (i.e. m value) is determined using two types of methods, constant Strain Rate method (CSRM) and conventional stress relaxation method (SRM), showing similar Rate Sensitivity trends but one order higher magnitude in SRM. We thus propose a new approach to analyse the SRM data, resulting in satisfactory agreement with the CSRM. Significant slip system dependent Rate Sensitivity is observed such that the prism slip has a strikingly higher m value than the basal. Fundamental mechanisms differing the Rate Sensitivity are discussed with regards to dislocation plasticity, where more resistance to move dislocations and hence higher hardening gradients are found in the basal slip. The impact of this finding for dwell fatigue deformation modes and the effectiveness of the present methodology for screening new alloy designs are discussed.
Terence G Langdon - One of the best experts on this subject based on the ideXlab platform.
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the microstructure length scale of Strain Rate Sensitivity in ultrafine grained aluminum
Journal of Materials Research, 2015Co-Authors: A D Kammers, Jittraporn Wongsangam, Terence G Langdon, Samantha DalyAbstract:The mechanical properties of ultrafine-grained aluminum produced by equal-channel angular pressing (ECAP) are strongly influenced by Strain Rate. In this work, an experimental investigation of local Strain Rate Sensitivity as it relates to microstructure was performed using a combination of scanning electron microscopy and digital image correlation. Uniaxial tension tests were carried out at 200 °C and Strain Rates alternating between 2.5 × 10?5 s?1 and 3.0 × 10?3 s?1. The results demonstRate that the heterogeneous microstructure geneRated by ECAP has a strong effect on the microstructure scale Strain Rate Sensitivity. Deformation centered at grain boundaries separating regions of banded microstructure exhibits the greatest Strain Rate Sensitivity. Strain Rate Sensitivity is limited in deformation occurring in regions of microstructure composed of ultrafine grains sepaRated by low-angle grain boundaries. The tensile specimens all failed by shear bands at 200 °C and at room temperature they failed by necking with little plastic deformation apparent outside of the neck.
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evolution of plasticity Strain Rate Sensitivity and the underlying deformation mechanism in zn 22 al during high pressure torsion
Scripta Materialia, 2014Co-Authors: Inchul Choi, Terence G Langdon, M Kawasaki, Jaeil JangAbstract:This study explores the evolution of plasticity, Strain-Rate Sensitivity and the underlying deformation mechanism of a Zn–22% Al eutectoid alloy during high-pressure torsion processing. The experiments reveal an optimal torsional Straining condition for achieving the largest plasticity; beyond this condition the Strain-Rate Sensitivity decreases and activation volume increases. The results are discussed in terms of changes in the microstructure and the underlying deformation mechanism.
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Strain Rate Sensitivity studies in an ultrafine grained al 30 wt zn alloy using micro and nanoindentation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Nguyen Q Chinh, M Kawasaki, Tamas Csanadi, Tivadar Gyori, R Z Valiev, B B Straumal, Terence G LangdonAbstract:a b s t r a c t The characteristics of plastic deformation of an ultrafine-grained (UFG) Al-30 wt.% Zn alloy were inves- tigated using depth-sensing micro- and nanoindentation. Emphasis was placed on the effects of grain boundaries and the unusually high Strain Rate Sensitivity. It is shown that there is a close relationship between enhanced Strain Rate Sensitivity and ductility in this UFG material and this is associated with grain boundary sliding and enhanced diffusion along the Al/Al grain boundaries which appear to be wetted by Zn-rich layers.
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the effect of grain boundary sliding and Strain Rate Sensitivity on the ductility of ultrafine grained materials
Materials Science Forum, 2010Co-Authors: Nguyen Q Chinh, Tamas Csanadi, R Z Valiev, B B Straumal, Jeno Gubicza, Terence G LangdonAbstract:Most ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) exibit only limited ductility which is correlated with the low Strain Rate Sensitivity (SRS) of these materials. Recently, it was demonstRated that SPD is capable of increasing the room temperature ductility of aluminum-based alloys attaining elongations up to 150%, together with relatively high Strain Rate Sensitivity. In the present work, additional results and discussions are presented on the effect of grain boundary sliding (GBS) and SRS on the ductility of some UFG metals and alloys. The characteristics of constitutive equations describing the steady-state deformation process are quantitatively analyzed for a better understanding of the effects of grain boundaries and Strain Rate Sensitivity.
