Improvements of scale adherence on heat-resisting alloys and coatings by rare earth additions

Saito, Yasutoshi; Önay, Bülent

doi:10.1016/0257-8972(90)90086-r

Cited by 19 publications

(6 citation statements)

References 21 publications

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“…1 is valid only after a time to corresponding to a weight gain Wo, then Eq. 3 must be transformed to (W-Wo) 2 W-Wo [4] t -tokp + kl Equation 4 is more general and is preferred to Eq. 3.…”

Section: Analysis Of Scale Growth Kineticsmentioning

confidence: 99%

Chromia Scale Growth in Alloy Oxidation and the Reactive Element Effect

Pieraggi

Rapp

1993

J. Electrochem. Soc.

154

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An analysis for the kinetics of scale growth involving simultaneous cation and anion diffusion, and for anion diffusion with blocked cation diffusion, is presented and compared to experimental data in the literature. The significant reduction in sealing kinetics for the growth of chremia on pure Cr and on Fe-, Ni-, or Co-base alloys is attributed to the elimination of cation diffusion by the blocking of the cationic reaction step at the metal/scale interface. Large highly charged reactive element (RE) ions segregate at the metal/scale interface and pin the misfit dislocations whose climb otherwise serves to create interstitial cations (or annihilate vacancies). Then scale growth must proceed by oxygen diffusion over anion vacancies, corresponding to the lateral climb of misorientation dislocations (reaction at monoatomie steps) at the metal/ scale interface. This poisoned interface model provides an interpretation for the reactive element effect (REE) which is consistent with the four well-known REE characteristics.The action of reactive elements (RE) in improving the protection, especially the adherence, by chromia and alumina scales on binary and ternary alloys of Fe, Ni, and Co base is a particularly interesting and popular research subject with significant engineering importance. The early literature and its interpretation were reviewed by Whittle and Stringer. ~ Stringer, 2 Moon, 3 and Saito and Onay 4 have critiqued the more recent publications. In this paper, the authors propose a novel interpretation for the reactive element effect (REE) specifically for the growth of chromia protective scales on pure Cr, or on Fe-Cr, Ni-Cr, and Co-Cr alloys doped by a reactive element, e.g., Y, Ce, etc.Small additions [<1 weight percent (w/o)] of some chemically reactive elements (Y, Ce, La, mischmetal, and others) introduced into the alloy (or at its surface) as solutes or second phases by one of several different methods have been shown to cause certain favorable characteristics in the growth of protective chromia scales on alloys. The effective elements generally have atomic and ionic sizes which greatly exceed those for the alloys and oxide in question, so that these elements are only slightly soluble, and therefore are found or are introduced as second phases (intermetallic compound, dispersed oxide) in the alloys, and as segregated solutes in chromia. The REE also can be achieved by very thin deposits of the reactive metal oxide on the external surface 5' 6 or by ion implantation into the alloy. 7,8For the growth of a chromia protective scale on pure Cr or on an alloy of Fe-, Ni-, or Co-base, the following four effects have been demonstrated: (i) the adherence of the scale is improved greatly, especially in response to thermal cycling; (it) the parabolic scaling rate constant for steadystate growth is reduced, by as much as a factor of ten or more; (iii) for a binary alloy, the minimum concentration of chromium in the alloy required to achieve a steady-state chromia scale is reduced considerably, from about 20 to 3...

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“…1 is valid only after a time to corresponding to a weight gain Wo, then Eq. 3 must be transformed to (W-Wo) 2 W-Wo [4] t -tokp + kl Equation 4 is more general and is preferred to Eq. 3.…”

Section: Analysis Of Scale Growth Kineticsmentioning

confidence: 99%

Chromia Scale Growth in Alloy Oxidation and the Reactive Element Effect

Pieraggi

Rapp

1993

J. Electrochem. Soc.

154

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“…11: (1) to lower the scale growth rate and (2) to change the phase constituents of the scale. For chromiaforming systems, several groups [66][67][68][69][70][71][72][73] have confirmed that RE ions mainly segregated at the oxide grain boundaries by many marker experiments and TEM characterization. In this case, the segregated Y ions could block the transport of metal (M) cations and oxygen anions along the grain boundaries through a blockage effect, as shown in Fig.…”

Section: Static Oxidationmentioning

confidence: 74%

“…It has been widely reported that small amounts of Y additions in the alloys or in the protective coatings can improve the oxidation resistance remarkably [38,39,42,[64][65][66][67][68]. For instance, Zhang and Guo [38,39] reported that the introduction of 0.05-0.57 at.% Y into the silicide coating is beneficial in improving the oxidation resistance of the coating.…”

Section: Static Oxidationmentioning

confidence: 99%

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Development of silicide coatings over Nb–NbCr2 alloy and their oxidation behavior at 1250 °C

Qiao

Guo

2014

Surface and Coatings Technology

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“…Extensive investigations have been carried out during the last few decades, and numerous theories have been put forward to explain REE, as reviewed by several authors. 2,[238][239][240][241] Consistent with these reviews, existing interpretations do not provide comprehensive explanations of general application but are usually valid for specific effects in particular alloys.…”

Section: Attempts To Explain the Reementioning

confidence: 99%

The reactive element effect on high-temperature oxidation of magnesium

Czerwiński

2015

International Materials Reviews

109

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It was discovered over 75 years ago that minor additions of elements with high affinity to oxygen exert a profound effect on oxidation resistance of many metals and alloys. In this report, progress in understanding the 'reactive element effect' (REE) and opportunities created for controlling the high-temperature oxidation of magnesium alloys were reviewed. Magnesium, the lightest structural metal, exhibits high affinity to oxygen and, as opposed to heat-resistant materials, does not form a dense, slow-growing and protective oxide layer. However, additions of small amounts of reactive elements (REs) to magnesium alloys produce a number of positive effects in improving their oxidation resistance. What is of crucial importance for magnesium is that RE benefits are also extended to its ignition, flammability, evaporation and liquid-state reactivity. The mechanism by which these elements influence oxidation and other related behaviour remains, so far, unclear. Although no specific theory explaining the REE on magnesium has been developed, growth kinetics, surface morphology and internal microstructure of magnesia films and scales, doped with REs show characteristics typical for high-temperature materials that form protective oxides.

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Improvements of scale adherence on heat-resisting alloys and coatings by rare earth additions

Cited by 19 publications

References 21 publications

Chromia Scale Growth in Alloy Oxidation and the Reactive Element Effect

Chromia Scale Growth in Alloy Oxidation and the Reactive Element Effect

Development of silicide coatings over Nb–NbCr2 alloy and their oxidation behavior at 1250 °C

The reactive element effect on high-temperature oxidation of magnesium

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