Tensile Properties of Bulk Nanocrystalline Hexagonal Cobalt Electrodeposits

Karimpoor, A.A.; Erb, U.; Aust, K.T.; Wang, Z.; Palumbo, G.

doi:10.4028/www.scientific.net/jmnm.13.415

Cited by 24 publications

(30 citation statements)

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“…The quantitative information of the uniform tensile elongation (ε unif ) and ε tef is included in Table 3; (2) a strong strain hardening behavior is discerned in all plots, the degree of which is dependent on test parameters; (3) low temperature (i.e., 77 K) or slow strain rate apparently leads to a smaller ε tef , i.e., ε tef increases with increasing strain rate and temperature (see Table 3). This trend disagrees with the literature data, 9 which suggest a decreased ε tef trend with increasing strain rate in the narrow range of 1×10 Table 3), suggesting that it is susceptible to fracture process after the maximum load.…”

Section: B Tensile Characteristicscontrasting

confidence: 99%

“…Eqn. (9) suggests that the size of flaws along the sample edges and the facture toughness of nc metals will have direct impact on the measured fracture stress, and thus, ε tef values. Furthermore, as pointed out above, EDM cutting could introduce large voids into nc metals that inevitably affect their fracture toughness.…”

Section: B Strain Hardening Necking Fracture and Tensile Ductilitymentioning

confidence: 99%

“…Torre et al 2 and Karimpoor et al 9 in nc nickel and nc cobalt, respectively. Although nc cobalt has an hcp structure and distinctive slip/twinning systems compared to fcc nc metals, the inconsistent trends seen in nc nickel itself cast serious doubts on whether the tensile ductility trend is correlated with the crystallographic structure of nc materials and/or their slip/twinning systems.…”

Section: Introductionmentioning

confidence: 97%

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Controlling factors in tensile deformation of nanocrystalline cobalt and nickel

et al. 2012

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In an effort to understand and enhance the tensile ductility of truly nanocrystalline metals, we have investigated and compared the mechanical behavior, especially the tensile behavior, of hcp nanocrystalline cobalt (~20 nm) and fcc nanocrystalline nickel (~28 nm). Although both materials exhibit obvious plasticity in tension, their uniform tensile ductility, tensile elongationto-failure, and fracture behavior are drastically different. In-situ synchrotron x-ray diffraction and ultra-small angle x-ray scattering reveal distinct deformation disparity in terms of residual strain development, texture evolution, nanovoid formation, and subsequent strain hardening and strain rate hardening behavior. The dependence of tensile property on the strain rate and temperature is examined and discussed. Factors that influence the strength and ductility of nanocrystalline metals are considered and prioritized according to the current findings. A new Hall-petch relationship is proposed for nanocrystalline nickel.

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Section: B Tensile Characteristicscontrasting

confidence: 99%

Section: B Strain Hardening Necking Fracture and Tensile Ductilitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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Controlling factors in tensile deformation of nanocrystalline cobalt and nickel

et al. 2012

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“…22 This seems to indicate that stress induced grain growth is likely independent of deformation mechanisms but dependent of crystal structures for NC pure metals. Nonetheless, it is considered that the very high ductility obtained in an NC Co metal prepared by Karimpoor et al 23 is also due to complete suppression of grain growth during tensile deformation.…”

Section: Resultsmentioning

confidence: 99%

Study on nanocrystalline dual phase Ni–Co alloy with high strength and excellent ductility

Xu¹,

Dai²,

Wu³

et al. 2011

Materials Science and Technology

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In the present study, the room temperature mechanical properties of nanocrystalline Ni and Ni-75 wt-%Co alloy, prepared by pulse electrodeposition, were contrasted. Both higher strength and higher ductility were obtained for the Ni-75%Co alloy with a dual phase structure and an average grain size of 7?2 nm. By means of TEM observations of grain structures before and after tensile deformation for Ni and Ni-75%Co samples, a link between the ductility and the variation of stress induced grain growth during tensile deformation was established. Observations of TEM showed stress induced grain growth during tensile deformation, subjected to very high stresses and large strains, is very insignificant for the Ni-75%Co alloy in sharp contrast to the significant stress induced grain growth occurring in Ni. It was proposed that suppression of stress induced grain growth during tensile deformation can delay and even prohibit formation of shear banding plastic instability and thus enhances uniform strain leading to an enhanced ductility.

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“…The ultimate tensile strength and hardness of nanocrystalline pure Co are 750 MPa and 3530 MPa, while those of the coarse-grained pure Co are 210 MPa and 1700 MPa, respectively. 14,15) In addition, HPT has been applicable for achieving grain re nement in Co-Cr-Mo alloys, which have attracted wide interest owing to their spectacular mechanical properties such as high tensile strength and hardness. [16][17][18] Furthermore, inducing strain to Co-Cr-Mo alloys leads to strain-induced γ→ε phase transformation.…”

Section: Introductionmentioning

confidence: 99%

Grain Refinement Mechanism and Evolution of Dislocation Structure of Co–Cr–Mo Alloy Subjected to High-Pressure Torsion

et al. 2016

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Ultra ne-grained materials often possess superior mechanical properties owing to their small grain size. The high-pressure torsion (HPT) process is a severe plastic deformation method used to induce ultra-large strain and produce ultra ne grains. In this study, the grain re nement mechanisms in the Co-28Cr-6Mo (CCM) alloy, evolution of dislocation density as a result of HPT and its effects on mechanical properties were investigated. The dislocation density and subgrain diameter were also calculated by X-ray line pro le analysis. The microstructure of the CCM alloy subjected to HPT processing (CCM HPT ) was evaluated as a function of torsional rotation number, N and equivalent strain, ε eq . Strain-induced γ→ε transformation in neighboring ultra ne grains is observed in CCM HPT processed at ε eq = 2.25 and ε eq = 4.5. Low-angle crystal rotation around the [110] fcc direction occurs in different locations in the same elongated grain neighboring ultra ne grains, which suggests the formation of low-angle grain boundaries in CCM HPT processed at ε eq = 2.25 and ε eq = 4.5. Two possible grain re nement mechanisms are proposed. The maximum dislocation densities, which are 2.8 × 10 16 m −2 in γ phase and 3.8 × 10 16 m −2 in ε phase, and maximum subgrain diameters, which are 21.2 nm in γ phase and 36 nm in ε phase, are achieved in CCM HPT processed at ε eq = 9. HPT processing causes a substantial increase in the tensile strength and hardness owing to the grain re nement and a signi cant increase in the volume fraction of ε phase and dislocation density.

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Tensile Properties of Bulk Nanocrystalline Hexagonal Cobalt Electrodeposits

Cited by 24 publications

References 0 publications

Controlling factors in tensile deformation of nanocrystalline cobalt and nickel

Controlling factors in tensile deformation of nanocrystalline cobalt and nickel

Study on nanocrystalline dual phase Ni–Co alloy with high strength and excellent ductility

Grain Refinement Mechanism and Evolution of Dislocation Structure of Co–Cr–Mo Alloy Subjected to High-Pressure Torsion

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