Experimental investigation of vacancy effects in pure metals

Novikov, I. I.; Roshchupkin, V. V.; Semashko, N. A.; Fordeeva, L. K.

doi:10.1007/bf00825700

Cited by 7 publications

(4 citation statements)

References 1 publication

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“…Our calculations indicate that the vacancy formation energy in Ti is about 2 eV, in good agreement with previous calculations [17,20,22], but significantly higher than the experimental value of 1.2-1.55 eV [51][52][53]. The low experimental value is hard to reconcile with the measured diffusion activation energy in ultra pure samples of 3.14 eV [3], which is expected to be the sum of the vacancy formation and vacancy migration energy.…”

Section: Discussionsupporting

confidence: 83%

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First principles study of normal and fast diffusing metallic impurities in hcp titanium

Bernstein

Shabaev

Lambrakos

2015

Computational Materials Science

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a b s t r a c tThe diffusivities of metallic impurities in hexagonal close packed (hcp) Ti vary widely, with some species showing normal diffusion and others diffusing anomalously fast. Based on a transition-state theory model for impurity diffusion mediated by vacancies, self, and impurity interstitials, we find that the diffusion rate will be limited primarily by the formation energies of the various defects. We use density functional theory to calculate these defect energies, including the formation energies of vacancies, self interstitials, and metallic impurities in substitutional and interstitial positions in hcp Ti. We find that for normal diffusers the vacancy mediated diffusion mechanism dominates, while for fast diffusers the dominant mechanism is hopping directly between interstitial sites. The activation energy for the latter mechanism is significantly lower than that for vacancy mediated diffusion, explaining the large diffusivities and low activation energies observed experimentally for these fast diffusing impurities.Ó 2015 Published by Elsevier B.V.

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Section: Discussionsupporting

confidence: 83%

“…Our vacancy formation energy results are in agreement with other theoretical predictions [17,20,22], which are higher than the vacancy formation energy measured in experiment [51][52][53]. Similarly, the formation energy of an interstitial defect of element…”

Section: (X ¼ Ti) Discussed In the Previous Section And E Nà1supporting

confidence: 91%

First principles study of normal and fast diffusing metallic impurities in hcp titanium

Bernstein

Shabaev

Lambrakos

2015

Computational Materials Science

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“…Of notable significance are the following: (i) there is a large difference (> 0.5 eV) in the vacancy formation energy in Ti from experiments [12][13][14] and first-principles predictions; 11,[15][16][17] (ii) self-diffusion coefficients and activation energies from measurements are scattered (see details later); [18][19][20] (iii) existing studies of vacancy migration are incomplete, and hence the anomalous energy pathway for vacancy migration within a Ti basal plane with double saddle points, the subject of the present work, has not been reported. 11,16 Numerous experimental difficulties render determination of diffusion properties in hcp materials challenging, with the most daunting issues being specimen purity, the availability of radioactive tracer elements, and large experimental uncertainties.…”

Section: Introductionmentioning

confidence: 99%

Anomalous energy pathway of vacancy migration and self-diffusion in hcp Ti

et al. 2011

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An anomalous energy pathway with energetically-equivalent double saddle points for vacancy mediated self-diffusion within an hcp-Ti basal plane is unveiled by density functional theory.Examination of migration pathway and phonon force constants suggests that the migrating atom tries to follow the bcc-hcp phase transition via the Burgers shear deformation. We propose that the formed energy local minimum with a bcc-like atomic environment between the two saddle points originates from the existence of high-temperature bcc phase and is a feature of Group IV hcp metals with bcc-hcp phase transition. Computed diffusion coefficients are in favorable accord with experiments for hcp Ti. PACS numbers: 66.30.Fq, 63.20.dk, 82.20.Db 2

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“…If we start with a pure metal crystal, at 0 K, it has no lattice defect and it has some intrinsic enthalpy value. As we increase the temperature of this pure metal crystal, an equilibrium concentration of vacancies form (Damask and Dienes, 1971;Miedema, 1979;Novikov et al, 1980;Kobelev and Khonik, 2018). Conceptually we can visualize that the enthalpy of the system is increasing as there is heat of formation associated with each vacancy.…”

Section: Introductionmentioning

confidence: 99%

Microstructural engineering through high enthalpy states: implications for far-from-equilibrium processing of structural alloys

Mishra¹,

Gupta²

2023

Front. Met. Alloy

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Metallic materials derive their strength and ductility from their microstructural features. The general principle of alloying is not only to control the phases present in the alloys, but also how the alloying elements can help in microstructural control during the processing of materials. The overall thermodynamic framework of using free energy to explain the stability of an alloy has two significant terms, enthalpy, and entropy. Engineering alloys are processed by several far-from-equilibrium processes. During the processing, the materials are in metastable states. The metastability can also be purposely enhanced through alloy design. This paper provides a perspective on how “high enthalpy states” can be used to tailor the microstructure to overcome the conventional strength-ductility tradeoff. The emergence of new manufacturing processes also provides unique opportunities to design alloys to maximize the potential of such processes. A few illustrative examples are presented to tie the historical use of high enthalpy states and point to future opportunities. Co-development of advanced materials for disruptive new manufacturing processes can be enhanced through integrated computational materials engineering approaches.

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Experimental investigation of vacancy effects in pure metals

Cited by 7 publications

References 1 publication

First principles study of normal and fast diffusing metallic impurities in hcp titanium

First principles study of normal and fast diffusing metallic impurities in hcp titanium

Anomalous energy pathway of vacancy migration and self-diffusion in hcp Ti

Microstructural engineering through high enthalpy states: implications for far-from-equilibrium processing of structural alloys

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