Effects of Vacancies on Deformation Behavior in Nanocrystalline Nickel

Yuasa, Motohiro; Matsumoto, Hiroshi; Hakamada, Masataka; Mabuchi, Mamoru

doi:10.2320/matertrans.mra2008115

Cited by 11 publications

(5 citation statements)

References 42 publications

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“…The results consistently indicate lower yield points for the samples with higher concentration of vacancies. This corresponds to previous works which indicated that the presence of vacancies can decrease the yield point during any mechanical testing [21][22][23][24]. The observed difference in the initial stiffness (Figure 1, inset) is due to the different surface roughnesses.…”

Section: Resultssupporting

confidence: 87%

“…The effect of non-equilibrium vacancies on the mechanical response of metals is complex, ranging from strengthening effects due to Cottrell atmospheres, to dislocation motion impacted by climb and jog formation [20] and to weakening effects previously reported to impact dislocation nucleation [21][22][23][24]. Mukherjee et al [25] used two-dimensional models of nanoindentation tests and showed annihilation of vacancies in the compression zones and enlargement of vacancies in the tension zones under the indenter.…”

Section: Introductionmentioning

confidence: 98%

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Effect of vacancies on incipient plasticity during contact loading

Salehinia

Perez

Bahr

2012

Philosophical Magazine

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Atomistic simulations and experimental nanoindentation tests were used to examine the effect of vacancies on the inception of plastic deformation in Ni. Molecular dynamics have shown the effect of vacancy position on the yield load and demonstrate a variety of mechanisms which are responsible for the inception of plastic deformation during indentation. In cases where the vacancy position is close to regions of high shear stresses the nucleation of dislocations is related to the location of a vacancy; however, homogeneous nucleation of dislocations is also observed for vacancy-containing crystals. Complementary experiments have been used to demonstrate the effect of indenter size on the onset of yielding in the presence of vacancies. Both the simulations and experiments show that larger indenter tips increase the chance of weakening the material in the presence of vacancies.

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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 98%

Effect of vacancies on incipient plasticity during contact loading

Salehinia

Perez

Bahr

2012

Philosophical Magazine

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“…Point defects, which have a great impact on the mechanical properties and plastic deformation of nanocrystalline metals, have also been studied [14]. It was found that the yield stress and fracture stress for nanocrystalline Ni containing more vacancies were lower than those for the one containing fewer vacancies, and an increase in GB energy due to vacancies in the GB was suggested to enhance GB fracture.…”

Section: Introductionmentioning

confidence: 99%

“…The creep mechanisms caused by intergranular dislocation slip (Weitzman creep), intergranular diffusion of vacancies (Nabarro-Herring creep)[35], and vacancy diffusion along the GB (Coble creep)[11] are all not consistent with the situation in this study. Studies have shown that GB deformations can be enhanced by vacancies in GBs because the creep rate for the vacancy-rich cell unit is more than twice that for the normal cell unit in the nanocrystalline NiW alloy[14]. The formation of deformation-induced vacancies at the GBs could be correlated with the Shockley partial dislocations and the initial vacancy concentration.…”

mentioning

confidence: 99%

Initial Vacancy-Dependent High-Temperature Creep Behavior of Nanocrystalline Ni by Molecular Dynamics Simulation

Cui,

Shao,

Shi

et al. 2024

Coatings

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Nanocrystalline metals possessing excellent mechanical strength have great potential to replace traditional metal materials as structural materials, but their poor resistance to creep deformation seriously restricts their engineering applications at high temperatures. The high-temperature creep behavior of nanocrystalline Ni with different volume fractions of initial vacancies ranging from 0% to 10% was studied systematically by molecular dynamics simulation in this study. The results showed that the steady-state creep displacement first increased and then decreased with increasing initial vacancy concentration, reaching the maximum when the initial vacancy concentration was 6%. The microstructural characteristics, such as quantity increment and distribution of the vacancies, the number and types of dislocations, and shear strain distribution during creeping, were analyzed in detail. The deformation-induced vacancies formed at the grain boundary (GB) in the initial creep stage, and their variation trend with the initial vacancy concentration was consistent with that of the creep displacement, indicating that the initial vacancy-dependent high-temperature creep behavior of nanocrystalline Ni was mainly determined by the rapidly increasing number of vacancies at the GB in the initial creep stage. Afterwards, the deformation-induced, vacancy-assisted 1/6{112} Shockley partial dislocation activities dominated the creep deformation of nanocrystalline Ni in the steady-state creep stage. The results can provide theoretical support for expanding the application of nanocrystalline metals from the perspective of crystal defect engineering.

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“…Another important factor affecting the dislocation emission is the grain boundary characteristics such as defects, grain boundary segregation, and misorientation. However, there are only a few studies on the effects of the grain boundary characteristics on the mechanical properties of nanocrystalline metals [14,15].…”

Section: Introductionmentioning

confidence: 99%

Softening due to disordered grain boundaries in nanocrystalline Co

Yuasa

Hakamada

Nakano

et al. 2013

J. Phys.: Condens. Matter

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Nanocrystalline Co consisting of fcc and hcp phases was processed by electrodeposition, and its mechanical properties were investigated by hardness tests. In addition, high-resolution transmission electron microscopy observations and molecular dynamics (MD) simulations were performed to investigate the grain boundary structure and dislocation nucleation from the grain boundaries. A large amount of disorders existed at the grain boundaries and stacking faults were formed from the grain boundaries in the as-deposited Co specimen. The as-deposited specimen showed a lower hardness than did the annealed specimen, although the grain size of the former was smaller than that of the latter. The activation volume of the as-deposited specimen (=1.5b(3)) was lower than that of the annealed specimen (=50b(3)), thus indicating that nucleation of dislocations from grain boundaries is more active in the as-deposited specimen than in the annealed specimens. The MD simulations showed that dislocation nucleation was closely related to a change in the defect structures at the boundary. Therefore, it is suggested that a significant amount of defects enhance changes in the defect structures at the boundary, resulting in softening of the as-deposited specimen.

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Effects of Vacancies on Deformation Behavior in Nanocrystalline Nickel

Cited by 11 publications

References 42 publications

Effect of vacancies on incipient plasticity during contact loading

Effect of vacancies on incipient plasticity during contact loading

Initial Vacancy-Dependent High-Temperature Creep Behavior of Nanocrystalline Ni by Molecular Dynamics Simulation

Softening due to disordered grain boundaries in nanocrystalline Co

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