Etch pits in iron

Liss, R.B.

doi:10.1016/0001-6160(59)90087-2

Cited by 3 publications

(4 citation statements)

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“…The substrate dislocation exposed to the surface preferentially dissolves to form an etch pit on the surface. 36 Although it is not necessary that a density of dislocations is identical to that of etch pits, in a worked iron, densities of etch pits are smaller than that of dislocations. The difference in the densities of etch pits and dislocations is constant, being independent of the working degree.…”

Section: Resultsmentioning

confidence: 99%

Influence of Substrate Dislocation on Passivation of Pure Iron in pH 8.4 Borate Buffer Solution

Yamamoto

Fushimi

Miura

et al. 2010

J. Electrochem. Soc.

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The influence of substrate dislocations on the passivation behavior of pure iron in a pH 8.4 borate buffer solution was investigated. Cold-rolling was employed to induce dislocation in the annealed substrate. The dislocation density on the cold-rolled substrate depended on the reduction ratio ͑Red͒ and was maximum at Red = 60%. The electric charge consumed in the passivation and the passivity-maintaining current increased with an increase in the dislocation density. Electrochemical impedance spectroscopy revealed that the dislocation exposed to the iron surface increased the donor density in the passive film and reduced the chargetransfer resistance for the film aging. It was also demonstrated by radio frequency-glow discharge optical emission spectroscopy that a thick passive film formed on the cold-rolled iron compared with that on annealed iron. These results suggest that substrate dislocations enhance the reactions at the substrate/film interface, resulting in the formation of a highly defective passive film.Industrially important metallic materials such as steels and aluminum alloys usually undergo a modification of the metallographic texture by the working process of cold-rolling. Although many metallographical studies have revealed the mechanical characteristics of materials deformed by cold-rolling, it has not been clarified that the corrosion resistance of the material's surface is degraded by rolling. The degradation of corrosion resistance seems to be mainly caused by phase transformation and alloy segregation, 1-7 though the dislocation and/or the strain of the material's substrate are also detrimental to the corrosion resistance. 8,9 However, there are no consistent changes in pitting and corrosion potentials 4,6,10,11 and in the dissolution rate for the worked steels. 3,12-14 These inconsistent results seem to be due to the differences in the working degree and the materials' compositions and phases. It is very difficult to investigate only the effect of individual metallographic textures induced by working on the corrosion behavior of alloys because alloys easily cause phase transformation and/or alloy segregation at grain boundaries. Thus, it is important to investigate each metallographic parameter with pure metals, causing no phase transformation and no precipitation.The corrosion resistance of metals strongly depends on the passive film formed on the surface. The characteristics of a passive film formed on pure iron in a pH 8.4 borate buffer solution have been investigated in detail using various techniques such as coulometry, 15,16 electrochemical impedance spectroscopy ͑EIS͒, 17-19 ellipsometry, 16,20 surface-enhanced Raman spectroscopy, 21,22 extended X-ray absorption fine structure, 23,24 X-ray diffraction, 25 and X-ray photoelectron spectroscopy. 26 Although details are still not clear completely, the iron passive film is composed of a spinel structure such as ␥-Fe 2 O 3 and/or Fe 3 O 4 , having the property of an n-type semiconductor with a donor density on the order of 10 26 m −3 17-19 a...

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Section: Resultsmentioning

confidence: 99%

Influence of Substrate Dislocation on Passivation of Pure Iron in pH 8.4 Borate Buffer Solution

Yamamoto

Fushimi

Miura

et al. 2010

J. Electrochem. Soc.

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“…is maximum at Red = 60%. The substrate dislocation exposed to the surface preferentially dissolves to form an etch pit on the surface (34). Although it is not necessary that a density of dislocations is identical to that of etch pits, in the case of a worked iron, densities of etch pits are smaller than that of dislocations.…”

Section: Metallographic Texturementioning

confidence: 99%

Effect of Cold Rolling on Passive Film on Pure Iron in pH 8.4 Borate Buffer Solution

et al. 2010

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The influence of substrate dislocations on passivation behavior of a pure iron in pH 8.4 borate buffer solution was investigated. Cold rolling was employed to induce dislocation in the annealed substrate. The dislocation density on the cold rolled substrate depended on the reduction ratio (Red) and was maximum at Red = 60%. The electric charge consumed in the passivation and the passivity-maintaining current increased with increase in the dislocation density. EIS revealed that the dislocation exposed to the iron surface increased donor density in the passive film and reduced charge transfer resistance for the film aging. It was also demonstrated by rf-GDOES that a thick passive film formed on the cold rolled iron compared with that on annealed iron. These results suggest that substrate dislocations enhance the reactions at the substrate/film interface, resulting in the formation of the highly defective passive film.

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“…Liss (13) It is often difficult to interpret the results of etch pitting of polycrystalline metals because of the much increased density of dislocations, compared with single crystals. The processes of slip and twinning are more complex and dislocations exist in bands or tangled networks rather than as discrete defects.…”

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confidence: 99%

“…In addition, nodular oxide formation, often a limiting factor in the usefulness of oxidation-resistant alloys, has been studied in iron-aluminum (9) as well as in other ferrous alloy systems (10)(11)(12)(13)(14)(15). According to Wood (16), the Cr~O3 layers that form on iron-chromium alloys and stainless steels in oxygen from 800~ up become detached from the alloys in random areas and tend to arch outwards because of the stresses that develop during oxide growth.…”

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The Influence of an Air-Formed Film on the Nucleation and Morphology of Etch Pits in Pure Iron

Spink

Ives²

1971

J. Electrochem. Soc.

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Annealing pure iron in hydrogen, followed by etching in a hydrogen atmosphere is shown to develop etch features at defects in the metal itself, rather than those of an oxide film. These features are contrasted with those reported for the same etchant on unreduced samples. The influence of an air-formed film in controlling etch morphology is discussed.The etch pitting of crystalline materials is now a well established method for pinpointing dislocations and following their movements u n d e r stress. Although much of the early work was confined to nonmetals, well authenticated examples do exist in the literature where researchers have produced etch pits at dislocation sites in metal single crystals; for example, the classical work of Livingston on copper (1) and Hibbard and D u n n on silicon iron (2). Later work included the etching of bismuth (3), tungsten (4), nickel (5), m o l y b d e n u m (6), zinc (7), cadmium (8), and niobium (9). A recent review of etching methods and etchants used has been made by Robinson (10).Subsequent research on polycrystalline metals, notably iron and iron alloys, indicated that an aging treatment was necessary in order to "decorate" the line defects with small quantities of an impurity or trace element. Suits and Low (11), for example, have shown that aging is necessary for etch pitting of dislocations in an Fe-3% Si alloy and that carbon is the principal segregating impurity. Pickering (12), again working with polycrystalline Fe-3% Si, found that a one-to-one correspondence between etch pits and dislocations is only possible when the dislocation density is below a critical value which cannot be displaced upwards by increasing the carbon content. He observed pitted areas in etched thin foils directly under the electron microscope, and saw that fresh dislocations introduced by plastic deformation were never pitted whereas aged dislocations were attacked to a degree depending on the carbon level. Pickering concluded that for a oneto-one correspondence to exist the amount of carbon in solution must be (a) equal to, or above, the level which is necessary to produce sufficiently large carbon atmospheres at every dislocation present in the alloy during aging; and (b) below that level which, by the formation of random clusters or precipitates during aging, is sufficient to cause two-dimensional nucleation of etch pits not associated with dislocations.More recently etchants have been developed which produce etch pits without an aging treatment. Liss13) developed etch pits in iron in what appear to be t Present address: Central Electricity Research Laboratories, Materials Division, Leatherhead, Surrey, England. K e y words: Surfaces, reactivity of solids, dissolution, defects in solids. glide bands. Pelessini and Alessandrini (14), also working on iron, demonstrated the increasing density of pits with work hardening, without intermediate aging treatment, on grains of all orientations.It is often difficult to interpret the results of etch pitting of polycrystalline metals because of the muc...

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Etch pits in iron

Cited by 3 publications

References 1 publication

Influence of Substrate Dislocation on Passivation of Pure Iron in pH 8.4 Borate Buffer Solution

Influence of Substrate Dislocation on Passivation of Pure Iron in pH 8.4 Borate Buffer Solution

Effect of Cold Rolling on Passive Film on Pure Iron in pH 8.4 Borate Buffer Solution

The Influence of an Air-Formed Film on the Nucleation and Morphology of Etch Pits in Pure Iron

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