Chemically driven growth of tungsten grains during sintering in liquid nickel

Yoon, Duk N.; Huppmann, W. J.

doi:10.1016/0001-6160(79)90185-8

Cited by 114 publications

(19 citation statements)

References 6 publications

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“…Powder characteristics, including chemical purities, are listed in Table I. % W) normally ranges between 1460 ± C and 1500 ± C. 7,8,11,19 Since this temperature range is considerably above the ternary liquidus temperature of 1443 ± C 20,21 and since we wish to investigate the effects of different solid-state powder processing methods, we chose a sintering temperature of only 1450 ± C. This temperature is only a few degrees above the liquidus for the W7Ni3Fe composition and should enable us to differentiate between the effects of ball-milling and attritor-milling on the sintered microstructure. About 0.5 wt.…”

Section: Methodsmentioning

confidence: 99%

“…[5][6][7][8][9][10][11][12][13][14][15] In some of these investigations, the starting materials were either only blended [5][6][7][8][9] or blended and milled in conventional ball mills prior to consolidation and sintering, [10][11][12][13] and a few utilized high energy milling. [5][6][7][8][9][10][11][12][13][14][15] In some of these investigations, the starting materials were either only blended [5][6][7][8][9] or blended and milled in conventional ball mills prior to consolidation and sintering, [10][11][12][13] and a few utilized high energy milling.…”

Section: Introductionmentioning

confidence: 99%

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A comparison of the sintering characteristics of ball-milled and attritor-milled W–Ni–Fe heavy alloy

1996

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Blended elemental W-7 wt. %Ni-3 wt. %Fe powders were mechanically alloyed in a planetary ball mill and a heavy duty attritor. The structural and morphological characteristics of the as-milled powders were characterized by x-ray diffraction and electron microscopy techniques. A ternary solid solution of Fe and Ni in W formed in both the cases; the amount of Ni and Fe dissolved is higher in the attritor-milled powder than in the ball-milled powder. Morphologically, the W-rich particles in the attritor-milled powders were spheroidal, smaller in size, and showed a narrower size distribution than in the ball-milled condition. These differences led to increased density in the attritor-milled powder compact and significant differences in chemical composition of the matrix region and W-rich grains. Transmission electron microscopy investigations of the matrix region in the compacts revealed the presence of Fe 2 W precipitates uniformly distributed in an Ni(Fe, W) matrix.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A comparison of the sintering characteristics of ball-milled and attritor-milled W–Ni–Fe heavy alloy

1996

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“…Therefore, Yoon and Hupman (1981) proposed the diffusional coherency strain theory for motion of GBs during DP. The theory supposes a thin diffusion layer ahead of the grain boundary which is coherent with the matrix.…”

Section: Introductionmentioning

confidence: 99%

Discontinuous precipitation in copper base alloys

Kashyap

2009

Bull Mater Sci

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Discontinuous precipitation (DP) is associated with grain boundary migration in the wake of which alternate plates of the precipitate and the depleted matrix form. Some copper base alloys show DP while others do not. In this paper the misfit strain parameter, η, has been calculated and predicted that if 100 η > ± 0⋅1, DP is observed. This criterion points to diffusional coherency strain theory to be the operative mechanism for DP.

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“…We develop a velocity selection theory for this problem, including anisotropic surface tension effects. The strong diffusion interaction and coherency strain effects in the solid near the melting front lead to substantial changes compared to classical dendritic growth.The early observation of liquid film migration (LFM) were made during sintering in the presence of liquid phase [1] or during partial melting of alloys [2] (see [3] for a review). Nowadays LFM is a well established phenomenon of great practical importance.…”

mentioning

confidence: 99%

“…This process is very important in practical applications, in particular during sintering in the presence of the liquid phase [1,3]. However, despite its practical importance, experimental investigations of this process are far from the level of accuracy of the model experiments in classical dendritic growth.…”

mentioning

confidence: 99%

Velocity-Selection Problem for Combined Motion of Melting and Solidification Fronts

Brener

Temkin

2005

Phys. Rev. Lett.

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We discuss a free boundary problem for two moving solid-liquid interfaces that strongly interact via the diffusion field in the liquid layer between them. This problem arises in the context of liquid film migration (LFM) during the partial melting of solid alloys. In the LFM mechanism the system chooses a more efficient kinetic path which is controlled by diffusion in the liquid film, whereas the process with only one melting front would be controlled by the very slow diffusion in the mother solid phase. The relatively weak coherency strain energy is the effective driving force for LFM. As in the classical dendritic growth problems, also in this case an exact family of steady-state solutions with two parabolic fronts and an arbitrary velocity exists if capillary effects are neglected [5]. We develop a velocity selection theory for this problem, including anisotropic surface tension effects. The strong diffusion interaction and coherency strain effects in the solid near the melting front lead to substantial changes compared to classical dendritic growth.The early observation of liquid film migration (LFM) were made during sintering in the presence of liquid phase [1] or during partial melting of alloys [2] (see [3] for a review). Nowadays LFM is a well established phenomenon of great practical importance. In LFM one crystal is melted and another one is solidified. Both solid-liquid interfaces move together with the same velocity. In the investigated alloys systems the migration velocity is of the order of 10 −6 − 10 −5 cm/s and it is controlled by the solute diffusion through a thin liquid layer between the two interfaces [4]. The migration velocity is much smaller than the characteristic velocity of atomic kinetics at the interfaces. Therefore, both solids should at the interfaces be locally in thermodynamic equilibrium with the liquid phase. On the other hand, these local equilibrium states should be different for the two interfaces to provide the driving force for the process. It is by now well accepted (see, for example, [3,4]) that the difference of the equilibrium states at the melting and solidification fronts is due to the coherency strain energy, important only at the melting front because of the sharp concentration profile ahead the moving melting front (diffusion in the solid phase is very slow and the corresponding diffusion length is very small). Thus, the liquid composition at the melting front, which depends on the coherency strain energy and on the curvature of the front, differs from the liquid composition at the unstressed and curved solidification front. This leads to the necessary gradient of the concentration across the liquid film and the process is controlled by the diffusion in the film.If only the melting front existed, the melting process would be controlled by the very slow diffusion in the mother solid phase and elastic effects would be irrelevant. In the LFM mechanism the system chooses a more efficient kinetic path which is controlled by the much faster diffusion in the liquid film. ...

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Chemically driven growth of tungsten grains during sintering in liquid nickel

Cited by 114 publications

References 6 publications

A comparison of the sintering characteristics of ball-milled and attritor-milled W–Ni–Fe heavy alloy

A comparison of the sintering characteristics of ball-milled and attritor-milled W–Ni–Fe heavy alloy

Discontinuous precipitation in copper base alloys

Velocity-Selection Problem for Combined Motion of Melting and Solidification Fronts

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