The oxidation behaviour of metals and alloys at high temperatures in atmospheres containing water vapour: A review

This paper is a brief review of the extensive literature relating to the formation of protective α—Al2O3 scales on alloys at high temperature. Emphasis is placed on the proposed mechanisms of scale growth based on observations of scale morphologies and microstructures, inert-marker experiments and the distribution of oxygen isotope tracers within thermally-grown oxides. Attention is also given to the determination of ionic-transport mechanisms by electrochemical methods and to the effects of reactive elements such as yttrium in modifying ionic-diffusion processes.

The formation of aluminum oxide scales on high-temperature alloys

A family of inexpensive, Al2O3-forming, high-creep strength austenitic stainless steels has been developed. The alloys are based on Fe-20Ni-14Cr-2.5Al weight percent, with strengthening achieved through nanodispersions of NbC. These alloys offer the potential to substantially increase the operating temperatures of structural components and can be used under the aggressive oxidizing conditions encountered in energy-conversion systems. Protective Al2O3 scale formation was achieved with smaller amounts of aluminum in austenitic alloys than previously used, provided that the titanium and vanadium alloying additions frequently used for strengthening were eliminated. The smaller amounts of aluminum permitted stabilization of the austenitic matrix structure and made it possible to obtain excellent creep resistance. Creep-rupture lifetime exceeding 2000 hours at 750 degrees C and 100 megapascals in air, and resistance to oxidation in air with 10% water vapor at 650 degrees and 800 degrees C, were demonstrated.

https://science.sciencemag.org/content/sci/316/5823/433.full.pdf

Creep-resistant, Al2O3-forming austenitic stainless steels.

Thermal barrier coatings (TBCs) have been in use in aeroturbine engine hot sections for over 20 years. The initial applications were driven by the need to suppress component degradation caused by excessive thermal gradients in vane airfoils. A TBC is essentially a layered, multimaterial structure that must withstand harsh temperature, environmental, thermal cycling, and stress conditions for an extended number of aircraft takeoffs and landings. A description of the TBC materials systems presently in use is presented, together with a summary of current understanding of materials and failure issues in TBCs.

Thermal Barrier Coatings for Aeroengine Applications

With the reduction in solid oxide fuel cell (SOFC) operating temperatures into the range 650–800°C, cost effective metallic materials, in particular high temperature oxidation resistant alloys, have become promising candidates, in place of ceramic counterparts, for construction of interconnects in SOFC stacks. For a lifetime of thousands of hours, the alloys must demonstrate excellent surface, structural and electrical stability, and compatibility with other components in SOFC stacks in a very challenging environment. The present paper provides a critical review of metallic interconnects for SOFCs with a focus on recent progress in materials development, as well as advances in understanding materials degradation and interfacial phenomena under the SOFC operating conditions. It also attempts to provide guiding principles for the development of optimised, cost effective metallic interconnect materials that can demonstrate satisfactory life time stability and performance.

M. Oliveira

Papers

High temperature oxidation of Fe13CrxAl alloys in vapour mixtures

High temperature oxidation of fe-13cr-xal alloys in air water vapor mixtures