Interplay between thermodynamic and kinetic stabilization mechanisms in nanocrystalline Fe-Mg alloys

Amram, Dor; Schuh, Christopher A.

doi:10.1016/j.actamat.2017.11.014

Cited by 57 publications

(25 citation statements)

References 34 publications

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“…The milling process results in micron-sized powders comprised of a homogeneous α-Fe solid solution supersaturated with Au, with a grain size of about 10 nm, similar to other nanocrystalline alloys prepared by this route [28]. We then performed in-situ x-ray diffraction (XRD) experiments at elevated temperatures to study the microstructure evolution and phase transformation in the powders as a function of time and temperature (see Supplementary Materials [24] for complete experimental details).…”

Section: Main Textmentioning

confidence: 89%

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Higher Temperatures Yield Smaller Grains in a Thermally Stable Phase-Transforming Nanocrystalline Alloy

Amram

Schuh

2018

Phys. Rev. Lett.

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Grains in crystalline materials usually grow with increased thermal exposure. Classical phenomena such as recrystallization may lead to a purely temporary decrease in the grain size, while recent advances in alloy design can yield thermally stable nanocrystalline materials in which grain growth stagnates. But grains never shrink, since there is a lack of interfacegenerating mechanisms at high temperatures, which are required to decrease the grain size if such was the system's thermodynamic tendency. Here we sidestep this paradigm by designing a nanocrystalline alloy having an allotropic phase transformation-an interface-generating mechanism-such that only the high-temperature phase is stabilized against grain growth. We demonstrate that for an Fe-Au alloy cycled through the α↔γ transformation, the hightemperature phase (γ-Fe) has a stable fine grain size, smaller than its low-temperature counterpart (α-Fe). The result is an unusual material in which an increase in temperature leads to finer grains that are stable in size.

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Section: Main Textmentioning

confidence: 89%

“…To find such a system, we populate the stability map for Fe in Fig. 2 with several metallic solutes which were recently used in nanocrystalline Fe-based alloys [25][26][27][28][29]: Zr, Ni, Mg, Cr, and Au. Upon the α→γ transformation most solutes shift their position on this map, but remain within the same stability zone.…”

Section: Main Textmentioning

confidence: 99%

Higher Temperatures Yield Smaller Grains in a Thermally Stable Phase-Transforming Nanocrystalline Alloy

Amram

Schuh

2018

Phys. Rev. Lett.

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“…Recent work exploring the competing mechanisms between kinetically and thermodynamically stabilized NC alloys has focused on understanding and harnessing the phase transition kinetics to enable true stability [33,[36][37][38]. Huang et al showcased the importance of this interplay through a detailed study on the Fe 91 Ni 8 Zr 1 α → γ where they observe that grain growth is constrained by the reverse austenite (γ) transformation.…”

Section: Introductionmentioning

confidence: 99%

Understanding Thermodynamic and Kinetic Stabilization of FeNiZr via Systematic High-Throughput In Situ XRD Analysis

Hernández–Rivera

Fudger

Hornbuckle

et al. 2020

Metals

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The role of kinetically and thermodynamically driven microstructural evolution on FeNiZr was explored through in situ XRD analysis. A statistical approach based on log-likelihoods and composite link model was used to fit and extract important data from the XRD patterns. Best practices on using the statistical approach to obtained quantitative information from the XRD patterns was presented. It was shown that the alloyed powder used in the current study presents more thermodynamic stability than previously reported ball-milled powders. Based on hardness values, it was shown that mechanical strength is expected to be retained at higher processing temperatures. Lastly, a 2-dimensional heat transfer model was used to understand heat flow through the powder compacts.

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“…The interplay between thermodynamic and kinetic reasons of the stability of NG alloys has been also discussed [102][103][104][105][106] (see also References 107 through 111). However, in the present paper only thermodynamic aspects will be discussed in a novel way.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic Stability of Nano-grained Alloys Against Grain Coarsening and Precipitation of Macroscopic Phases

Kaptay

2019

Metall Mater Trans A

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Thermodynamic conditions are derived here for binary alloys to have their grain boundary (GB) energies negative, ensuring the stability of some nano-grained (NG) alloys. All binary alloys are found to belong to one of the following three types. Type 1 is the unstable NG alloy both against grain coarsening and precipitation of a macro-phase. Type 2 is the partly stable NG alloy, stable against coarsening but not against precipitation. Type 3 is the fully stable NG alloy, both against coarsening and precipitation. Alloys type 1 have negative, or low-positive interaction energies between the components. Alloys type 2 have medium-positive interaction energies, while alloys type 3 have high-positive interaction energies. Equations are derived for critical interaction energies separating alloys type 1 from type 2 and those from type 3, being functions of the molar excess GB energy of the solute, temperature (T) and composition of the alloy. The criterion to form a stable NG alloy is formulated through a new dimensionless number (Ng), defined as the ratio of the interaction energy to the excess molar GB energy of the solute, both taken at zero Kelvin. Systems with Ng number below 0.6 belong to alloy type 1, systems with Ng number between 0.6 and 1 belong to alloy type 2, while systems with Ng number above 1 belong to alloy type 3, at least at T = 0 K. The larger is the Ng number, the higher is the maximum T of stability of the NG alloy. By gradually increasing temperature alloys type 3 convert first into type 2 and further into type 1. The Ng number is used here to evaluate 16 binary tungsten-based (W-B) alloys. At T = 0 K type 3 NG alloys are formed with B = Cu, Ag, Mn, Ce, Y, Sc, Cr; type 2 is formed in the W-Ti system, while type 1 alloys are formed with B = Al, Ni, Co, Fe, Zr, Nb, Mo and Ta. For the WAg system the region of stability of the NG alloys is shown on a calculated phase diagram, indicating also the stable grain size.

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Interplay between thermodynamic and kinetic stabilization mechanisms in nanocrystalline Fe-Mg alloys

Cited by 57 publications

References 34 publications

Higher Temperatures Yield Smaller Grains in a Thermally Stable Phase-Transforming Nanocrystalline Alloy

Higher Temperatures Yield Smaller Grains in a Thermally Stable Phase-Transforming Nanocrystalline Alloy

Understanding Thermodynamic and Kinetic Stabilization of FeNiZr via Systematic High-Throughput In Situ XRD Analysis

Thermodynamic Stability of Nano-grained Alloys Against Grain Coarsening and Precipitation of Macroscopic Phases

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