Some aspects of the structure of cobalt and nickel binder phases in hardmetals

Mingard, Ken; Roebuck, B; Marshall, Jessica; Sweetman, Gillian

doi:10.1016/j.actamat.2010.12.004

Cited by 79 publications

(33 citation statements)

References 25 publications

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“…2b, it can be discerned that areas with similar crystallographic orientations are larger than the WC grains and the individual Co regions. It suggests a large Co skeleton that penetrates the WC network, in agreement with previously reported findings [37].…”

Section: Grinding-induced Phase Transformation In the Co Phasesupporting

confidence: 82%

“…In order to characterize the structural changes induced by grinding in the Co-phase, two complementary characterization techniques: transmission electron microscopy (TEM) and electron back-scatter diffraction (EBSD), are employed in this study. They have previously been proven to be well-suited to characterize structural changes in cemented carbides [26][27][28][29][30][36][37][38][39]. Specifically, we report nearsurface cross-sectional analyses of ground specimens, showing metallurgical alterations of the binder phase and correlate the results to grinding-induced changes (e.g., microcracking and residual stresses).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

Yang

Roa

Schwind³

et al. 2017

Materials Characterization

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The metallic binder phase dictates the toughening behavior of WC-Co cemented carbides (hardmetals), even though it occupies a relative small fraction of the composite. Studies on deformation and phase transformation of the binder constituent are scarce. Grinding represents a key manufacturing step in machining of hardmetal tools, and is well-recognized to induce surface integrity alterations. In this work, metallurgical alterations of the binder phase in ground WC-Co cemented carbides have been assessed by a combination of electron back scattered diffraction and transmission electron microscopy techniques. The Co-base binder experiences a martensitic phase transformation from fcc to hcp crystal structure, predominantly in the first 5 μm below the surface.The hcp fraction decreases gradually along a depth of 10 μm. Surface Co displays severe plastic deformation under the highest strain, resulting in formation of nanocrystalline grains in the first micrometer below the surface. Microstructural refinement within the binder phase is observed even at greater depth. Stacking faults were detected in most of the refined grains. The metallurgical alterations of the binder phase modify the local stress distribution during grinding, which affects the discerned subsurface microcracking. The resulting residual stress profile is the sum of multiple subsurface changes, such as phase transformation, severe plastic deformation and grain refinement, where it is discerned that the depth profile of the transformed hcp-Co fraction coincides with the grinding-induced residual stress profile. The hcp fraction decreases gradually along a depth of 10 μm. Surface Co displays severe plastic deformation under the highest strain, resulting in formation of nanocrystalline grains in the first micrometer below the surface. Microstructural refinement within the binder phase is observed even at greater depth. Stacking faults were detected in most of the refined grains. The metallurgical alterations of the binder phase modify the local stress distribution during grinding, which affects the discerned subsurface microcracking. The resulting residual stress profile is the sum of multiple subsurface changes, such as phase transformation, severe plastic deformation and grain refinement, where it is discerned that the depth profile of the transformed hcp-Co fraction coincides with the grinding-induced residual stress profile.

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Section: Grinding-induced Phase Transformation In the Co Phasesupporting

confidence: 82%

Section: Accepted Manuscriptmentioning

confidence: 99%

Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

Yang

Roa

Schwind³

et al. 2017

Materials Characterization

View full text Add to dashboard Cite

show abstract

“…On the other hand, strain-hardening response (loading curve) is variable, indicating its dependence on crystal orientation and local phase arrangement. Here it should be noticed that binder phase within hardmetals usually form regions of a single-crystallographic orientation up to 50 times greater than the mean size of the WC grains [30]. In this Fig.…”

Section: Resultsmentioning

confidence: 99%

Mechanical deformation of WC–Co composite micropillars under uniaxial compression

Tarragó

Roa

Jiménez‐Piqué

et al. 2016

International Journal of Refractory Metals and Hard Materials

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“…Marcador no definido.]. WC grains are hexagonal (with two basal (0001) and three prismatic {101 � 0} planes) and they form well-faceted triangular prism shape with cobalt binder [36,37].…”

Section: Resultsmentioning

confidence: 99%

“…It has to be recalled that cobalt grains are much larger than the mean free path [37], usually with a size of a few tenths of microns, and therefore the cobalt mean free path is not a parameter of the cobalt phase but of the average separation between carbides.…”

Section: D) Mean Free Pathmentioning

confidence: 99%

Focused ion beam tomography of WC-Co cemented carbides

Jiménez‐Piqué

Turon-Viñas

Chen

et al. 2017

International Journal of Refractory Metals and Hard Materials

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The microstructure of three different grades of WC-Co cemented carbides has been reconstructed in three dimensions after sequential images obtained by focused ion beam.The three-dimensional microstructual parameters are compared against the well-know two-dimensional parameters of grain size, phase percentages and mean free path. Results show good agreement with the exception of individual grain recognition, which could not be univocally segmented. In the case of mean free path, the three-dimensional image depicts a more realistic image of the metal interconnections in the composite.For the grade with coarser grain size, the obtained tomography is translated in a finite element modelling mesh, and elastic residual stresses are estimated from sintering to room temperature. Calculated thermal stresses agree with experimental results and show significant local variations in their value due to the complex microstructure of cemented carbides.

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Some aspects of the structure of cobalt and nickel binder phases in hardmetals

Cited by 79 publications

References 25 publications

Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

Mechanical deformation of WC–Co composite micropillars under uniaxial compression

Focused ion beam tomography of WC-Co cemented carbides

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