The properties of metallic cobalt

Betteridge, W.

doi:10.1016/0079-6425(79)90004-5

Cited by 143 publications

(64 citation statements)

References 100 publications

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“…Similar to crystallite size behaviour, further milling (after 10 hours) does not induce significant changes (± 6%) of lattice strain, but reached a saturation level of strain (~ 0.31% by Rietveld analysis). This is in agreement with the results of the surface energy (Table 1) 210.97 * The value of Ω = Aσ is calculated using the reported value of σ = 2.766 J/m 2 for polycrystalline cobalt structure [15].…”

Section: X-ray Diffractometry Analysis Of Milled Cobalt Samplessupporting

confidence: 78%

X-Ray Powder Diffraction Studies of Mechanically Milled Cobalt

Yeo

Amirah

Metselaar

et al. 2012

AMR

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Abstract. The allotropic phase transformation of cobalt powder prepared by high-energy ball milling was investigated as a function of milling time. Measurement of crystallite size and microstrain in the powder systems milled for different times were conducted by X-ray diffractometry. The X-ray diffraction (XRD) peaks were analyzed using the Pearson VII profile function in conjunction with Rietveld method. X-ray diffraction line broadening revealed that allotropic transformation between face-centred-cubic phase (fcc) and hexagonal close-packed phase (hcp) in cobalt is grain size dependent and also on the accumulation of structure defects. The results showed that the phase formation of cobalt depends on the mill intensity that influences of both the grain size and the accumulation of structure defects. However, this theory alone is not adequate to explain the effects in this work. It was found that the total surface energy (Ω) theory satisfactorily explains the phase transformation behavior of cobalt. The smaller value of surface energy (Ω) of the fcc crystal than the hcp phase when size decreases may alter the qualitative aspects of the phase formation. IntroductionHigh energy ball milling (BM) is an effective method for preparation of amorphous and nanocrystalline metal powders [1,2]. Several studies have revealed that nano-sized particles of some metals and alloys often showed anomalies in their behaviour with regard to phase transformation and phase stability, which are remarkably different from that in bulk materials [3]. It is well reported [4][5][6][7] that the allotropic phase transformation in cobalt is grain-size dependent. This theory alone is not adequate to explain the effects in this work since both phases found to occur at a range of grain size. Others reported that phase transformations occurring in cobalt when subjected to ball milling is found to be dependent on the milling intensity [8,9]. The result shows that with different milling intensities, a single fcc phase, single hcp phase or mixture of fcc and hcp phases could be formed. However, in this work, it was found that even at the same mill intensity the phase formation depends on milling time. The present work on the phase transformation of cobalt may be well explained according to Ram [10] theory of a further reduction of particle size below a critical value, which may modify its crystal structure and/or morphology in a manner that the latter is stable with a minimal value of its internal energy. At this scale, the fcc-Co will stabilize with a smaller value of total surface energy (Ω) over the hcp-Co structure. Therefore it is highlighted that the Ω plays a crucial role at this point. Based on these early literatures, it would appear that careful compositional and process control must be exercised in order to produce optimum results. It is strongly believed that the usefulness application of allotropic transformation to cobalt superalloy will be confined to specialized areas.

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Section: X-ray Diffractometry Analysis Of Milled Cobalt Samplessupporting

confidence: 78%

X-Ray Powder Diffraction Studies of Mechanically Milled Cobalt

Yeo

Amirah

Metselaar

et al. 2012

AMR

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“…The deposit was 0.2 mm thick but scale-up to bulkier thickness is presumably a straightforward extrapolation. The deposit exhibited an unusually faulted microstructure indicative of a high concentration of stacking faults/microtwins, which is consistent with the low stacking fault energy of cobalt [14]. The narrow grain size distribution based on measuring about 1000 grain diameters (including twins) on several dark field images showed a mean grain size of 12 nm.…”

Section: Electrodeposited Nanocrystal-line Metalssupporting

confidence: 57%

Recent progress in improving ductility of ultra-high strength nanostructured metals

2004

Met. Mater. Int.

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Until very recently, the reported tensile ductility of ultra-high strength nanocrystalline metals was disappointingly low. This article presents a brief overview of recent progress in identifying a group of nanostructured bulk elemental metals that offer not only gigapascal strength but also decent ductility. These include electrodeposited nanocrystalline or nano-twinned metals, and consolidated full-density nanocrystalline metals. Our own recent studies of these interesting nanomaterials, extending our previous/parallel success in optimizing the properties of bulk nanostructured metals prepared via severe plastic deformation, also demonstrated unprecedented tensile plastic strains.

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“…Co-Ni alloys have low stacking fault energy with an approximate value of 31 and 18.5 kJ/m 2 for the hcp and fcc structures in pure Co, respectively. [31] Thus, the conversion between the two structures easily occurs via stacking fault formation. [32] These characteristics result in easier phase transformation in Co-Ni alloys [33] and provide the possibility of strain-induced phase transformation from hcp to fcc.…”

Section: Discussionmentioning

confidence: 99%

Strain-Induced Reverse Phase Transformation in Nanocrystalline Co-Ni Alloys

Jin

et al. 2014

Materials Research Letters

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A strain-induced reverse phase transformation from a hexagonal close-packed phase to a face-centered cubic phase was observed under tension at room temperature in electrodeposited nanocrystalline Co-Ni alloys with an average grain size of 15 nm. Such reverse phase transformation was previously observed only on heating. Investigation by transmission electron microscopy suggests a close relationship between the reverse phase transformation and grain growth during the tensile deformation.

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The properties of metallic cobalt

Cited by 143 publications

References 100 publications

X-Ray Powder Diffraction Studies of Mechanically Milled Cobalt

X-Ray Powder Diffraction Studies of Mechanically Milled Cobalt

Recent progress in improving ductility of ultra-high strength nanostructured metals

Strain-Induced Reverse Phase Transformation in Nanocrystalline Co-Ni Alloys

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