Plasticity and strength of micro- and nanocrystalline materials

Malygin, G. A.

doi:10.1134/s1063783407060017

Cited by 95 publications

(40 citation statements)

References 91 publications

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“…Ductility is accomplished by the distributed and uniform multiplication and propagation of dislocations, whereas strengthening is often achieved by hindering their motion. Strength and ductility are fundamentally linked in materials, and a mechanism to improve one almost always leads to a decrease in the other (1,2). How to achieve both high strength and high ductility is still a challenge of great importance in structural materials.…”

mentioning

confidence: 99%

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Qi²,

Mishra

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

116

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In mechanical deformation of crystalline materials, the critical resolved shear stress (CRSS; τ CRSS ) is the stress required to initiate movement of dislocations on a specific plane. In plastically anisotropic materials, such as Mg, τ CRSS for different slip systems differs greatly, leading to relatively poor ductility and formability. However, τ CRSS for all slip systems increases as the physical dimension of the sample decreases to approach eventually the ideal shear stresses of a material, which are much less anisotropic. Therefore, as the size of a sample gets smaller, the yield stress increases and τ CRSS anisotropy decreases. Here, we use in situ transmission electron microscopy mechanical testing and atomistic simulations to demonstrate that τ CRSS anisotropy can be significantly reduced in nanoscale Mg single crystals, where extremely high stresses (∼2 GPa) activate multiple deformation modes, resulting in a change from basal slip-dominated plasticity to a more homogeneous plasticity. Consequently, an abrupt and dramatic size-induced "brittleto-ductile" transition occurs around 100 nm. This nanoscale change in the CRSS anisotropy demonstrates the powerful effect of sizerelated deformation mechanisms and should be a general feature in plastically anisotropic materials.lightweight alloys | metallurgy | mechanical properties | in situ TEM | nanoparticle S trength and ductility are critical performance indicators of materials; in metals, both are associated with the activities of line defects in the crystalline lattice, called dislocation plasticity. Ductility is accomplished by the distributed and uniform multiplication and propagation of dislocations, whereas strengthening is often achieved by hindering their motion. Strength and ductility are fundamentally linked in materials, and a mechanism to improve one almost always leads to a decrease in the other (1, 2). How to achieve both high strength and high ductility is still a challenge of great importance in structural materials. Recent work has demonstrated that it is possible to improve both strength and ductility simultaneously, but this has mostly been limited to systems with ultrafine microstructures, such as nanotwinned Cu or twinning-induced plasticity steels (3, 4).As the lightest structural metal, Mg suffers from limited room temperature ductility and formability due to the highly anisotropic critical resolved shear stress (CRSS; τ CRSS ) of the different slip systems (5). In Mg, which has a hexagonal close-packed structure, the τ CRSS for nonbasal (prismatic and/or pyramidal) slip is ∼10 2 τ CRSS for basal slip (6, 7). Such an extreme plastic anisotropy of A ≡ τ nonbasal CRSS =τ basal CRSS ∼ 10 2 makes nonbasal slip very difficult to trigger. Without nonbasal slip or twinning (8), basal slip alone cannot accommodate arbitrary shape changes, and excessive basal slip in combination with unrelaxed tensile stresses in the plane-normal direction leads to spatially localized damage and rapid failure. Thus, a materials design strategy could be to enhanc...

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mentioning

confidence: 99%

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Qi²,

Mishra

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

116

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“…It was found that, if the ratio of the transverse sample size to the grain size is less than three, then there is a mini mum on a yield strength-sample size curve. The min imum is a result of growth in the number of near sur face grains, which have little resistance to plastic deformation due to the dislocation outflow through the external sample surface [18][19]. The characteris tics of grain boundaries must have a significant effect on the experimental results, taking into consideration the fact that the imprint size in our nanoindentation tests is about 1-2 mm and corresponds in size to the size of subgrains.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, a decrease in grain sizes increases the proportion of the free volume within the grain boundaries, near boundary regions, and triple junctions, which is accompanied by a weakening of the atomic bonds in the material. The studies [18][19] suggest a decrease in the strength of microcrystalline materials with decreasing sample thickness below a certain value depending on the crystallite sizes. It was found that, if the ratio of the transverse sample size to the grain size is less than three, then there is a mini mum on a yield strength-sample size curve.…”

Section: Discussionmentioning

confidence: 99%

Measurement of young’s modulus and hardness of Al-50 wt % Sn alloy phases using nanoindentation

Чикова

Шишкина

Konstantinov

2013

Phys. Metals Metallogr.

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Abstract-The nanoindentation method was used to measure the Young's modulus and hardness of the phases of the alloy Al-50 wt % Sn: α aluminum and eutectic. Samples are obtained in different ways, i.e., traditionally via the transition of the melt into a homogeneous structural state by heating to a certain temper ature, followed by cooling using the cooling rate greater by the order than that of the traditional method and via the addition of 0.06 wt % Ti and 1 wt % Zr to the binary alloy. It has been found that the most significant effect of the Al-50 wt % Sn phases on the Young's modulus is the transition of the melt into a homogeneous structural state and the introduction of Zr into the melt. As part of the mathematical theory of elasticity, a numerical evaluation of the interfacial pressure that arises due to the difference between Young's modulus of α aluminum and eutectic has been performed. The calculation has showed that the extra pressure is nine times less for the alloy formed through the transition of the melt into a homogeneous structural state than for the alloy produced via a traditional way.

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“…It is believed that the unusually small activation volume in NC or UFG FCC metals implies a stronger temperature dependence of the yield and flow stress. Also based on thermal-activation theory, the temperature sensitivity factor can be expressed as [16] …”

Section: Temperature Effectsmentioning

confidence: 99%

Investigation on mechanical behaviour of ECAPed 2A12 aluminium alloy

Wang

Zhang

Wang

et al. 2015

EPJ Web of Conferences

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Abstract. In the present work, the uniaxial compressive behavior of aluminum alloy processed by equal channel angular pressing (ECAP) for 1-8 passes are investigated experimentally under both quasi-static and dynamic loading conditions via an electronic universal testing machine with a maximum load capacity of 10KN and the split Hopkinson pressure bar (SHPB). The strain hardening rate as well as strain rate sensitivity the ECAPed with different passes have been determined and compared with annealed coarse grained counterpart. The experimental results show a continuously increase of both flow stress and strain rate sensitivity for the aluminum alloy subjected to ECAP process as the pressing pass number increasing. It is proposed that the reduction in grain size plays an important role in the enhancement of flow stress and strain rate sensitivity. However, the strain hardening rate of the ECAPed materials decreases remarkably. Meanwhile, compressive experiments at elevated temperatures indicate the temperature sensitivity of the material increases as the grain size is refined into fine grain regime. Based on thermal activation theory, it is proposed that the enhanced temperature and strain rate sensitivity of ECAPed aluminum alloy can be related to the reduction in activation volume due to grain refinement.

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Plasticity and strength of micro- and nanocrystalline materials

Cited by 95 publications

References 91 publications

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale

Measurement of young’s modulus and hardness of Al-50 wt % Sn alloy phases using nanoindentation

Investigation on mechanical behaviour of ECAPed 2A12 aluminium alloy

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