Atomic structure and thermal stability of nanostructured Y-Fe alloys

Weißmüller, J.; Krauss, W.; Haubold, T.; Birringer, R.; Gleiter, H.

doi:10.1016/0965-9773(92)90076-a

Cited by 102 publications

(41 citation statements)

References 8 publications

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“…The functional form of this relationship is a signature of thermodynamic stabilization, and is widely observed in experimental data on this subject. 27,[32][33][34]37 Such scaling is an inherent consequence of Eq. ͑8͒, where the…”

Section: Equilibrium Equationsmentioning

confidence: 99%

“…͑2͒, it is evident that the grain boundary energy can be reduced by enhancing the solute excess, and if the magnitude of this reduction is sufficient to drive ␥ to zero, the grain boundaries can apparently exist in equilibrium. Extremely fine nanocrystalline grain sizes have been realized in a variety of binary alloy systems, for example Y-Fe, 32 Ni-P, 33 Pd-Zr, 27,34 and Fe-Zr. 35 Because the elements composing these alloys are highly immiscible with a large positive heat of mixing, these systems are classified as strongly segregating, with high assumed values of H seg ͑Ն0.5 eV͒ that can substantially reduce the grain boundary energy via Eq.…”

Section: Introductionmentioning

confidence: 99%

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Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys

2009

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A free-energy function for binary polycrystalline solid solutions is developed based on pairwise nearestneighbor interactions. The model permits intergranular regions to exhibit unique energetics and compositions from grain interiors, under the assumption of random site occupation in each region. For a given composition, there is an equilibrium grain size, and the alloy configuration in equilibrium generally involves solute segregation. The present approach reduces to a standard model of grain boundary segregation in the limit of infinite grain size, but substantially generalizes prior thermodynamic models for nanoscale alloy systems. In particular, the present model allows consideration of weakly segregating systems, systems away from the dilute limit, and is derived for structures of arbitrary dimensionality. A series of solutions for the equilibrium alloy configuration and grain size are also presented as a function of simple input parameters, including temperature, alloy interaction energies, and component grain boundary energies.

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Section: Equilibrium Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys

2009

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“…Then the driving force for grain boundary migration becomes zero and the grains ought to be stable. 9) An additional advantage of this approach is that the segregating element does not cause any additional strengthening as long as its solubility in the matrix is sufficiently low. Atomistic simulations by Millet et al 10) support this concept, but only a few systems such as YFe, 9) and NiW, NiB and NiS 10) have so far shown experimental promise.…”

Section: Introductionmentioning

confidence: 99%

“…9) An additional advantage of this approach is that the segregating element does not cause any additional strengthening as long as its solubility in the matrix is sufficiently low. Atomistic simulations by Millet et al 10) support this concept, but only a few systems such as YFe, 9) and NiW, NiB and NiS 10) have so far shown experimental promise. Also, it appears that direct experimental evidence for zero free grain boundary energies, i.e., the absence of grooving at grain boundaries intersecting a free surface, does not exist.…”

Section: Introductionmentioning

confidence: 99%

Hall–Petch Breakdown at Elevated Temperatures

Schneibel¹,

Heilmaier

2014

Mater. Trans.

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The HallPetch effect responsible for the strength of fine-grained and ultrafine-grained (UFG) metals is almost exclusively measured at room temperature. One reason for this is that at elevated temperatures grains tend to coarsen, and this negates the strengthening. The grains may, however, be stabilized by small volume fractions of fine dispersoids. These dispersoids cause direct Orowan strengthening and, by stabilizing the so-called Zener grain size, indirect strengthening due to HallPetch. We show that for most metals the critical Zener grain size above which HallPetch strengthening is more important than Orowan strengthening is lower than, and sometimes even considerably lower than 1 µm, i.e., in the range of UFG metals. Breakdown of the HallPetch relationship, which occurs at elevated temperatures once mechanisms weaker than Hall Petch start to control the strength, is best studied for grain sizes well above this critical grain size. The HallPetch breakdown due to either Coble creep or grain size-dependent dislocation creep is modeled. We present model calculations for copper and verify our approach by comparing with experimental results for ferritic steels containing nanoscale dispersions.

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“…(1). In most existing studies of nanostructure stability, the selection of an appropriate alloying element has been based on empirical considerations believed (or assumed) to correlate with GB segregation, including size mismatch [6][7][8][9][10] , low bulk solubility 7,8,[11][12][13][14][15] , or cohesive energy [16][17][18] . However, some of the more successful experimental systems with stabilized nanostructures have relatively modest values of ∆H seg , including Ni-W (∆H seg ~ 10 kJ/mol) 19,20 and Pd-Zr (∆H seg ~ 31 kJ/mol) 21 .…”

Section: Introductionmentioning

confidence: 99%

Estimation of grain boundary segregation enthalpy and its role in stable nanocrystalline alloy design

2013

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Grain boundary segregation provides a method for stabilization of nanocrystalline metals -the selection of an alloying element that will segregate to the boundaries can lower the grain boundary energy, attenuating the driving force for grain growth. The segregation strength, relative to mixing enthalpy, of a binary system determines the propensity for segregation stabilization. This relationship has been codified for the design space of positive enthalpy alloys; unfortunately, quantitative values for the grain boundary segregation enthalpy exist in only very few material systems, hampering the prospect of nanocrystalline alloy design. Here we present a Miedema-type model for estimation of grain boundary segregation enthalpy, with which potential nanocrystalline phase-forming alloys can be rapidly screened. Calculations of the necessary enthalpies are made for ~2500 alloys and used to make predictions about nanocrystalline stability.Abstract Figure: Fig. 1

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Atomic structure and thermal stability of nanostructured Y-Fe alloys

Cited by 102 publications

References 8 publications

Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys

Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys

Hall–Petch Breakdown at Elevated Temperatures

Estimation of grain boundary segregation enthalpy and its role in stable nanocrystalline alloy design

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Atomic structure and thermal stability of nanostructured Y-Fe alloys

Cited by 102 publications

References 8 publications

Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys

Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys

Hall&ndash;Petch Breakdown at Elevated Temperatures

Estimation of grain boundary segregation enthalpy and its role in stable nanocrystalline alloy design

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Product

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Hall–Petch Breakdown at Elevated Temperatures