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Journal ArticleDOI

A quantitative demonstration of the grain boundary diffusion mechanism for the oxidation of metals

01 May 1982-Philosophical Magazine (Taylor & Francis Group)-Vol. 45, Iss: 5, pp 823-833
TL;DR: In this article, the authors report measurements of the oxide scale thickness and oxide grain size as a function of time during the oxidation of high-purity nickel in the temperature range 500-800°C.
Abstract: Below 1000°C the oxidation of nickel cannot be controlled by the diffusion of ions through the bulk crystal lattice of the pure oxide, because the measured oxidation rates are several orders of magnitude faster than would be predicted on this basis. Short-circuit diffusion through oxide grain boundaries or dislocations has usually been held responsible, but there has hitherto been no proper quantitative confirmation of this mechanism. We report measurements of the oxide scale thickness and oxide grain size as a function of time during the oxidation of high-purity nickel in the temperature range 500–800°C. All the oxidation experiments were carried out in pure oxygen at a pressure of one atmosphere. The measured parabolic oxidation rate constants have been compared with those calculated from grain boundary diffusion data obtained in our previous work, using a grain boundary diffusion model for the oxidation process. The quantitative agreement between measured and calculated oxidation rates shows c...
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TL;DR: In this paper, a review of recent advances in understanding the mechanical behavior of metallic glasses, with particular emphasis on the deformation and fracture mechanisms, is presented, where the role of glass structure on mechanical properties, and conversely, the effect of deformation upon glass structure, are also described.

2,858 citations

Journal ArticleDOI
TL;DR: In this paper, first principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c.
Abstract: First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.

1,646 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the intrinsic correlation between hardness and elasticity of materials correctly predicts Vickers hardness for a wide variety of crystalline materials as well as bulk metallic glasses (BMGs).

1,632 citations

Journal ArticleDOI
TL;DR: On the bicentenary of the publication of Poisson's Traité de Mécanique, the continuing relevance of Poissons's ratio in the understanding of the mechanical characteristics of modern materials is reviewed.
Abstract: In comparing a material's resistance to distort under mechanical load rather than to alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by ½ and -1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt.

1,625 citations

Journal ArticleDOI
TL;DR: The role of deformation twinning in fracture of hexagonal close-packed metals is reviewed from a theoretical point of view in this paper, where strength and ductility are correlated with the intrinsic physical and metallurgical variables.
Abstract: The role of deformation twinning in fracture of hexagonal close-packed metals is reviewed from a theoretical point of view. Strength and ductility are correlated with the intrinsic physical and metallurgical variables. The importance of c + a slip and of both “tension” and “compression” twins as independent modes for a generalized polycrystalline deformation is emphasized. Effects of slip-twin and twin-twin interactions on crack initiation and high-order twinning are reviewed. The competitive role of twin nucleationvs crack initiation is discussed. Shortcomings of our current understanding of the role of twinning are indicated, and some futher studies are recommended.

1,556 citations

References
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555 citations

Journal ArticleDOI
TL;DR: The Mechanismus des Diffusionsvorgangs is still weitgehend unbekannt as discussed by the authors, i.e., the Diffusion of mindestens einem der beiden Bestandteile durch die Anlaufschicht is notwendig.
Abstract: 1. Problemstellung. 2. Ableitung einer Gleichung zur Berechnung der Anlaufgeschwindigkeit aus Affinität, elektrischem Leitvermögen und Überführungszahlen. 3. Formeln für die Auswertung von Anlaufverauchen. 4. Elektromotorische Kräfte in Anlauf schichten. 5. Das System Silber—Schwefel. 6. Das System Kupfer—Sauerstoff. 7. Das System Silber —Halogen. 8. Anlaufvorgänge und Fehlordnungstheorie. Zusammenfassung. 1. Problemstellung. Wird Metall in einer Atmosphäre von Sauerstoff, Schwefel oder Halogen erhitzt, so bedeckt es sich in vielen Fällen mit einem dichten Überzug, einer Verbindung aus Metall und Metalloid. Für den weiteren Re^ktionsverlauf ist offenbar die Diffusion von mindestens einem der beiden Bestandteile durch die Anlaufschicht notwendig. Wenn die Diffusion allein zeitbestimmend ist, so ergibt sich die Reaktionsgeschwindigkeit proportional der Oberfläche und umgekehrt proportional der Dicke der jeweils vorhandenen Anlaufsschicht [Gleichung (24)]. Experimentelle Belege hierfür finden sich in den Arbeiten von G. TAMMANN und Mitarbeitern1), N. B . PTT.T.TNQ und R. E. B E D W O B T H 8 ) , J . S. Dumsr3), K . FISCHBECK4), W. F E I T K N E C H T 8 ) u. a. Der Mechanismus des Diffusionsvorgangs ist heute noch weitgehend unbekannt. Von den meisten Autoren wird angenommen, dass die Metalloidatome aus der Gasphase durch die Anlaufschicht zur Metallphase diffundieren. Mit gleichem Recht lässt sich jedoch auch die entgegengesetzte Auffassung vertreten, dass Metallatome nach der Seite des Metalloids wandern, zumal die Metallatome häufig kleiner als die Atome von Sauerstoff, Schwefel oder Halogen sind. Letztere

514 citations

Journal ArticleDOI
TL;DR: The product of the grain boundary diffusion coefficient and width, D′δ, has been measured directly for the diffusion of 63Ni along grain boundaries in high-purity NiO as discussed by the authors.
Abstract: The product of the grain boundary diffusion coefficient and width, D′δ, has been measured directly for the diffusion of 63Ni along grain boundaries in high-purity NiO. These measurements have been made at an oxygen pressure of 1 atm in the temperature range 500–800°C, and also at an oxygen pressure of 7 × 10−6 atm at 700°C. At po 2 = 1 atm, D′δ is given by D′δ = 3·0× 10−8 exp {−1.78(eV)/kT} cm3 S−l. The width of the boundary, δ, is estimated to be 7 × 10−8 cm and in this region near the boundary the concentration and mobility of Ni vacancies are greater than in the bulk. The measured values of D’δ confirm quantitatively that the rate of oxidation of Ni to NiO at 500–800°C is controlled by the diffusion of Ni along grain boundaries in the NiO scale.

269 citations

Journal ArticleDOI
01 Jun 1970
TL;DR: In this article, the formation of new nickel oxide upon boundaries of columnar grains where nickel diffusing through the oxide crystals, meets oxygen, diffusing along grain boundaries is identified as the primary cause of this stress.
Abstract: The oxidation of nickel near 1000°C is accompanied by the generation of stresses parallel with the metal-oxide interface and of magnitude (~1500 psi) sufficient to elongate nickel rod, increase sheet area, and sharpen the angle of bend of ells and helices. A primary cause of this stress is identified with the formation of layers of new nickel oxide upon boundaries of columnar grains where nickel, diffusing through the oxide crystals, meets oxygen, diffusing along grain boundaries. Classical parabolic growth of the scale gives way to a slower quasilinear rate when the major site of new oxide formation is abruptly shifted to a system of grain boundaries lying close to the metal surface and created by recrystallization of the oxide under the influence of stress and high temperature. Another source of stress in the scale arises from the constantly changing area of the metal-oxide interface when oxidation is occurring upon curved metal surfaces. This stress reinforces that generated by deposition of material at oxide grain boundaries when the surface is convex and opposes it when the surface is concave.

251 citations

Journal ArticleDOI
TL;DR: In this paper, diffusion profiles of 63Ni tracer in single crystals of NiO following anneals at 522°-1000°C have been determined by a radio-frequency sputter-sectioning technique.
Abstract: Diffusion profiles of 63Ni tracer in single crystals of NiO following anneals at 522°-1000°C have been determined by a radio-frequency sputter-sectioning technique. The profiles were analysed in terms of diffusion in the NiO lattice, D1, together with a contribution from dislocations in low-angle grain boundary arrays. The lattice diffusion coefficient and the diffusion coefficient for Ni diffusion in a dislocation, Dd,at an oxygen pressure of 1 atm are given by : D1=0.022 exp {−59 000/RT} cm2 s−1 (522°–1400°C), and Dd=0.26 exp {−46 000/RT}cm2 s−1 (522°-800°C), where the activation energies are in cal mole−1. Diffusion in the dislocation takes place by a vacancy mechanism within a vacancy-rich pipe of radius ∼10−7 cm surrounding the dislocation.

160 citations