In this review the role of stress in the high temperature oxidation of metals is examined. In the introductory sections the Wagner theory of oxide growth and its modification to account for short circuit diffusion are outlined. The direct influence of oxide growth stresses on defect diffusion is then examined and shown to be a significant factor when constrained volume changes accompany the growth of the oxide layer. Methods for evaluating growth stresses are critically reviewed and the possible origins of such stresses considered in detail. The response of the oxide layer to thermally and mechanically induced stresses is considered in the last part of the review. Under tensile conditions, through-thickness cracks can readily be produced but may also heal with fresh oxide if imposed strain rates are relatively low. Spallation of the oxide is not usually found under tensile conditions but occurs frequently under compressive stresses by either a ‘buckling’ or ‘wedginq’ process. Detailed descriptions...

Stress effects in high temperature oxidation of metals

High temperature oxidation behavior and research status of modifications on improving high temperature oxidation resistance of titanium alloys and titanium aluminides: A review

The focus of this review is the state of knowledge of the oxidation behaviour in steam of alloys with potential for use as pressure parts in steam boilers. The rate of oxide growth on steam-touched surfaces and the characteristics of that oxide are of increasing interest as the quest for improvements in cycle efficiency leads to progressively higher operating temperatures and pressures. The consequences of increased rate of growth of these oxides are of concern because of implications for tube overheating and oxide exfoliation. Mitigation of such problems requires a mechanistic understanding of the influences of alloy composition and microstructure, and especially of the evolution with time of specific scale structures. Similarly, the relative effects of factors such as time, temperature and operating parameters must be understood. The oxidation behaviour of the class of ferritic steels that forms the bulk of the heat transfer surface in steam boilers is of particular importance since allo...

A review of the oxidation behaviour of structural alloys in steam

An austenitic stainless steel, which consists of by mass percent, C: not more than 0.02%, Si: not more than 1.5%, Mn: not more than 2%, Cr: 17 to 25%, Ni: 9 to 13%, Cu: more than 0.26% not more than 4%, N: 0.06 to 0.35%, sol. Al: 0.008 to 0.03%. One or more elements selected from Nb, Ti, V, TA, Hf, and Zr in controlled amounts can be included with the balance being Fe and impurities. P, S, Sn, As, Zn, Pb and Sb among the impurities are controlled as P: 0.006 to 0.04%, S: 0.0004 to 0.03%, Sn: 0.001 to 0.1%, As: not more than 0.01%, Zn: not more than 0.01%, Pb: not more than 0.01% and Sb: not more than 0.01%. The amounts of S, P, Sn, As, Zn, Pb and Sb and the amounts of Nb, Ta, Zr, Hf, and Ti are further controlled using formulas.

Austenitic stainless steel

Oxidation of Ti-6Al-4V alloy

Twenty-four ternary element additions were made to a binary TiAl alloy (Ti−34.5 wt.% Al), and the oxidation behavior was studied. As a result of the oxidation tests in air at 1173 K for 360 ks, ternary elements were classified into three groups according to their effects, namely, (a) detrimental; V, Cr, Mn, Pd, Pt, Cu; (b) neutral; Y, Zr, Hf, Ta, Fe, Co, Ni, Ag, Au, Sn, O; (c) beneficial; Nb, Mo, W, Si, Al, C, B. This classification was valid for Cr, Mn, Mo, and W under several other temperature and time conditions. The influence of the additions was very significant, the difference in the weight gain between the best and the worst alloys being approximately two orders of magnitude. As a result of detailed examinations, it was confirmed that Cr and Mn additions caused linear-oxidation behavior from the outset at 1173 K, virtually no Al2O3 barrier being formed. This is probably due to the doping of those elements in TiO2. The beneficial elements, such as Mo, Nb, W, resulted in protectiveoxidation behavior. The characteristic features of the scale on those alloys were the presence of a continuous Al2O3 layer as the second layer from the outer surface and the relatively massive precipitation of Al2O3 in the vicinity of the scale-metal interface. Also, these alloys did not show any evidence of internal oxidation. The scale types and the proposed mechanism for the innerscale formation are described.

The effect of various ternary additives on the oxidation behavior of TiAl in high-temperature air

The influence of ternary element addition on the oxidation behaviour of TiAl intermetallic compound in high temperature air

The Influence of beneficial additional elements (W, Mo, Nb and Si) on the oxidation behavior of a Ti-34.5 mass%Al alloy has been compared and their roles were studied. The relative effectiveness was in the order W, Mo, Nb, Si (the former, the better) at 1173 K. After the analyses of rate law and comparison in the Arrhenius plots of parabolic rate constants, it was clarified that the oxidation resistant temperature was increased by 100 and 200 K for the Mo (Nb) and W containing alloys respectively in comparison with the binary alloy for which the temperature was around 1000 K. The Mo, Nb and W containing alloys did not show any internal oxidation nor breakaway oxidation which was observed in the binary alloy

Role of W, Mo, Nb and Si on Oxidation of TiAl in Air at High Temperatures

The depths of internal oxidation of Ni-Al (0.5–4 wt.%) alloys oxidized in the temperature range 800–1100°C in either Ni/NiO packs or in 1 atm oxygen are virtually independent of the alloy compositi...

/pdf/enhanced-diffusion-of-oxygen-during-internal-oxidation-of-1kku5mks37.pdf

Enhanced diffusion of oxygen during internal oxidation of nickel-base alloys

Several Fe-Cr-Ni austenitic stainless steels (Cr wt.%: 13–25, Ni wt.%: 15) were oxidized in steam for 1000 hr at 500–900°C. The oxide scales were examined and categorized with respect to the chromium concentration and the grain size of the base metal. Experiments showed three conditions for the critical bulk Cr concentration and the oxidation temperature at which the oxidation behavior changed drastically. Metallographic examination showed that two of these three conditions resulted from the internal-external transition of Cr2O3 either on the metal surface or along the grain boundaries of the base metal. Attempts were made to interpret these conditions from the available oxidation theories. Atkinson's treatment was employed with some modification to incorporate the grain-boundary diffusion of Cr in the base metal. The calculation basically explained the internal-external transition for the oxidation of these steels.

Yoshiaki Shida

Papers

The effect of various ternary additives on the oxidation behavior of TiAl in high-temperature air

The influence of ternary element addition on the oxidation behaviour of TiAl intermetallic compound in high temperature air

Role of W, Mo, Nb and Si on Oxidation of TiAl in Air at High Temperatures

Enhanced diffusion of oxygen during internal oxidation of nickel-base alloys

Internal-external transition for the oxidation of Fe-Cr-Ni austenitic stainless steels in steam