Growth mechanisms of oxide scales on ODS alloys in the temperature range 1000–1100°C

Abstract

After a short overview of the production, microstructure and mechanical properties of nickel-and iron-based Oxide Dispersion Strengthened (ODS) alloys, the oxidation properties of this class of materials is extensively discussed. The excellent oxidation resistance of ODS alloys is illustrated by comparing their behaviour with conventional chromia and alumina forming wrought alloys of the same base composition.ODS alloys exhibit improved scale adherence, decreased oxide growth rates, enhanced selective oxidation and decreased oxide grain size compared to corresponding non-ODS alloys. It is shown, that these experimental observations can be explained by a change in oxide growth mechanism. The presence of the oxide dispersion reduces cation diffusion in the scale, causing the oxides on the ODS alloys to grow mainly by oxygen grain boundary transport. As oxilde grain size increases with time, the oxide growth kinetics obey a sub-parabolic time dependence especially in the case of the alumina forming iron-based ODS alloy.Die vorliegende Arbeit gibt zunachst eine kurze Ubersicht uber Herstellung, Mikrogefiige und mechanische Eigenschaften von oxiddispersionsverfestigten (ODS-)Legierungen auf Nickel-und Eisenbasis. AnschlieBend werden die Oxidationseigenschaften dieser Werkstoffgruppe ausfuhrlich diskutiert. Die hervorragende Oxidationsbestandigkeit von ODS-Legierungen wird aufgezeigt durch Vergleich derer Eigenschaften mit denen von konventionellen chrom-und aluminiumoxidbildenden Legierungen gleicher Basiszusammensetzung.Oxidschichten auf ODS-Legierungen unterscheiden sich von dcnen auf konventionellen, dispersionsfreien Legierungen insbesondere durch bessere Haftung, reduziertes Wachstum, verbesserte selektive Oxidation und feineres Korn. Es wird gezeigt , dal3 diese experimentellen Ergebnisse durch eine Anderung der Schichtwachstumsmechanismen gedeutet werden k8nnen. Die Oxiddispersionen bewirken eine Reduzierung dcs Kationentransports in der Deckschicht, so dal3 die Oxidschichtcn auf den ODS-Legierungen nahezu ausschliel3lich durch Sauerstofftransport iiber Oxidkorngrenzen wachsen. Da die OxidkorngroRe mit zunehmender Oxidationszeit zunimmt, gehorcht die Schichtwachstumskinetik, insbesondere bei den aluminiumoxidbildenden Eisenbasislegierungen, einem subparabolischen Zeitgesetz. Introductionlmreased efficiency of processes in chemical engineering and energy conversion can in many cases only be achieved if the process temperatures are increased. This requirement necessarily leads to the demand for metallic materials which allow the design of plant or engine components operating at high temperatures, often at high stresses in corrosive environments. Oxide dispersion strengthened (ODS) alloys are due to their unique combination of superior high temperature creep and corrosion resistance poitentially suitable construction materials for components which are subjected to hostile service conditions [1]. Especially in cases where component life is limited by corrosive attack, ODS alloys offer the possibility for significan...

Kinetic Aspects of Ti2AlC MAX Phase Oxidation

“…It follows the approaches of Quadakkers, [19], Liu et al [18], and Tallman et al, [3] but with less complexity as illustrated briefly below. The time exponent from scale growth (1/n) can be shown to depend on the time exponent for grain enlargement (1/m) from the following approximate relations for scale thickness (x, Eq.…”

Correlation between the Microstructure, Growth Mechanism, and Growth Kinetics of Alumina Scales on a FeCrAlY Alloy

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Optimal conditions for alumina coating formation on the MA956 superalloy for prosthetic bearing applications

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