Time, stress, and temperature-dependent deformation in nanostructured copper: Stress relaxation tests and simulations

The plasticity of metallic glasses depends largely on the atomic-scale structure. However, the details of the atomic-scale structure, which are responsible for their properties, remain to be clarified. In this study, in-situ high-energy synchrotron X-ray diffraction and strain-rate jump compression tests at different cryogenic temperatures were carried out. We show that the activation volume of flow units linearly depends on temperature in the non-serrated flow regime. A plausible atomic deformation mechanism is proposed, considering that the activated flow units mediating the plastic flow originate from the medium-range order and transit to the short-range order with decreasing temperature. IMPACT STATEMENTAn atomic deformation mechanism in metallic glasses is proposed. Activated flow units mediating the plastic flow originate from the medium-range order and transit to the short-range order with decreasing temperature.

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“…The plastic deformation is accommodated in localized shear bands. The plastic strain rate within the shear bands can be expressed as [33][34][35]…”

Section: Resultsmentioning

confidence: 99%

Cryogenic-temperature-induced structural transformation of a metallic glass

Bian

Wang

et al. 2016

Materials Research Letters

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“…A review on deformation mechanism of nanocrystalline and ultrafine grained fcc metals like Ni or Cu can be found in [8,[34][35][36][37][38]. The time-dependent deformation behavior of materials is strongly influenced not only by the homologous temperature and the applied stress, but also by loading history and the microstructure, respectively [20-22, 24, 25, 31, 32, 37-42].…”

Section: Introductionmentioning

confidence: 99%

“…UFG Cu-alloys have been used as reference materials as they can be easily produced via a HPT deformation and show already a significant creep deformation at room temperature. In addition, good data sets on strain rate sensitivities and stress exponents are already available for Cu [33,37,38,[43][44][45][46][47][48][49][50][51][52][53] as well as for the investigated CuAl5 alloy investigated [53]. Furthermore, UFG materials do not show a pronounced indentation size effect and are thus nicely suited for indentation creep testing.…”

Section: Introductionmentioning

confidence: 99%

Nanoindentation creep testing: Advantages and limitations of the constant contact pressure method

Minnert

Durst

2021

Journal of Materials Research

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Different loading protocols have been developed in the past to investigate the creep properties of materials using instrumented indentation testing technique. Recently, a new indentation creep method was presented, in which the contact pressure is kept constant during the creep test segment, similar to the constant stress applied in a uniaxial creep experiment. In this study, the results of constant contact pressure creep tests are compared to uniaxial and constant load hold indentation creep experiments on ultrafine grained Cu and CuAl5. The constant contact pressure method yields similar stress exponents as the uniaxial tests, down to indentation strain rates of 10–6 s−1, whereas the constant load hold method results mainly in a relaxation of the material at decreasing applied pressures. Furthermore, a pronounced change in the power law exponent at large stress reductions is found for both uniaxial and constant contact pressure tests, indicating a change in deformation mechanism of ultrafine grained metals. Graphical abstract

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“…Though experimental means exist to extract the effective activation volume V * from the apparent activation volume V a , e.g. through repeated relaxation tests done at the same stress [7,8], numerous authors use V a as a first guide for identification of the plasticity mechanisms [9,10,11,12,13].…”

Section: Introductionmentioning

confidence: 99%

X-ray diffraction and stress relaxations to study thermal and stress-assisted annealings in nanocrystalline gold thin films

et al. 2019

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The dependence on thermal history of the plasticity mechanisms occurring in nanocrystalline gold thin films is evidenced thanks to relaxation tests combined with in-situ synchrotron X-ray diffraction. The two techniques complement one another. The activation parameters show that the films deform mainly by dislocations and give indications about their mean free paths, whereas the Bragg peak positions, widths and areas bring invaluable information on residual stress as well as on some plasticity properties, like dislocation storage inside the grains or grain rotations. For the demonstration, two sputter-deposited nanocrystalline 50 nm-thin films deposited onto stretchable substrates are studied. It is shown that an as-grown sample (at a homologous temperature of 0.22) presents a stress-assisted annealing, thus decreasing its initial defect density, whereas if a thermal annealing (three hours at 200°C, corresponding to a homologous temperature of 0.35) has been applied to the sample before the tensile test, it deforms by conventional plasticity, and the dislocations are not stored inside the grains. These mechanisms lead to different work-hardening properties. This work shows how a moderate annealing can have a profound influence on the mechanical behaviour of these thin films.

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Time, stress, and temperature-dependent deformation in nanostructured copper: Stress relaxation tests and simulations

Cited by 73 publications

References 85 publications

Cryogenic-temperature-induced structural transformation of a metallic glass

Cryogenic-temperature-induced structural transformation of a metallic glass

Nanoindentation creep testing: Advantages and limitations of the constant contact pressure method

X-ray diffraction and stress relaxations to study thermal and stress-assisted annealings in nanocrystalline gold thin films

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