Alloy oxidation resistant alloys

With the problems outlined above for chromia-forming alloys, oxidation-resistant alloy development tends to focus on alumina-forming alloys. A few examples will be given to illustrate some of the potential and a few of the problems with these alloys. 

High strength Ti-l5Mo-3Nb-3AI-0-25i alloy, oxidation resistant 965 1035-1350 4 96 4-92 St ... 

The oxidation and corrosion behavior of metals and alloys has been widely investigated in a range of environments for a myriad of applications. Recently, oxidation resistant alloys have been studied particularly for SOFC interconnect applications. 

The electrical conductivity requirement for interconnect applications necessitates the use of chromia-forming (or Cr-rich spinel) oxidation-resistant alloys. One drawback of the chromia-forming alloys for this particular application, however, is the Cr volatility of the chromia or Cr-rich scale. As indicated by many studies [185-189], during high-temperature exposure Cr203 (s) reacts with 02 via the following reaction... 

Corrosion of Oxidation-Resistant Alloys nnder SOFC Interconnect... 

This chapter will provide an overview of oxidation and corrosion behavior of candidate oxidation-resistant alloys under SOFC operating conditions and discuss surface modifications for improved stability and performance of metallic interconnects. 

CORROSION OF OXIDATION-RESISTANT ALLOYS UNDER SOFC INTERCONNECT EXPOSURE CONDITIONS... 

The regenerator for a typical 10,000-barrel/day unit has an overall height of 120 ft. and an internal cross-sectional area of about 100 sq. ft. The shells are constructed of carbon steel and are protected by a 6-in. lining of insulation with a refractory surface adjacent to the flowing catalyst. All parts handling flue gas and air inside the regenerator are constructed of oxidation-resistant alloy steel. 

Z. Yang, J.W. Stevenson, and K.D. Meinhardt, Chemical interactions of barium-calcium-aluminosilicate-based sealing glasses with oxidation resistant alloys. Solid State Ionics, 160 (2003) 213-225. 

Irrespective of details of the transport processes, in the development of oxidation-resistant alloys, the aim is to evolve a composition that develops one of the slow-growing oxides as a scale. This is usually done to encourage formation of AI2O3, Si02, or Cr203 and will be discussed in Chapter 5. 

This aspect of the theory of defect structures of non-stoichiometric compounds is usually covered in the main text of books on high-temperature oxidation. The subject of doping is interesting for its own sake, and it is vitally important for the study of the physical chemistry and electrochemistry of ionic compounds. In the case of an introduction to high-temperature oxidation our opinion is that, since the control of oxidation rates by controlling the ionic and electronic transport properties of oxides by impurity solution is not generally used as a technique for the development of oxidation-resistant alloys, this subject should be dealt with in an appendix. This allows it to be covered adequately without over-emphasizing its importance. 

Alloying iron with nickel and chromium is necessary to mitigate corrosion above 900 °C. At higher temperatures, 2% A1 addition increases the alloy oxidation resistance [19,20]. The oxidation rate of austenitic stainless steels (Types 309 and 310) decreases with the addition of nickel in the alloy, while the addition of tungsten, niobium, tantalum, and molybdenum increase mechanical strength, as shown in Fig. 11.7 [3]. 

OXIDATION-RESISTANT ALLOYS 11.13.1 Reactive Element Effect (REE)... 

Superalloys are usually defined as heat- and oxidation-resistant alloys specially developed for servicing at elevated temperatures under both oxidizing atmosphere and severe mechanical stresses. Three main classes of superaUoys are distinguished ... 

Z. Yang, G. -G. Xia, G. D. Maupin, and J. W. Stevenson, Conductive Protection Layers on Oxidation Resistant Alloys for SOFC Interconnect Applications, Surf. Coat.Tech., 201 4476-83... 

It seems that the temperature range for conventional unprotected (no surface coatings) solid-solution titaniiun alloys is upper limited to about600 °C [Ble85] and that futm e development shoiald include combinations of (1) inherently oxidation-resistant alloys, (2) coatings, (3) further development of the a2 phase and y-phase aliuninides and their variants, Euid (4) the use of rapidly solidified alloys. Figure 9.6 outlines the manner in which such developments proceed naturally out of the earlier work. 

Metallic particles such as chromium can be introduced into a metal plating electrolyte (for example, nickel and cobalt), and the deposited composite can be subsequently heat treated to form high-temperature oxidation-resistant alloys. MCrAlY composites have been made by depositing 10 p,m CrAlY powder in a cobalt or nickel matrix. Heat treatment bonds... 

High chemical resist- In the composition of heat-resistant and oxidation-resistant alloys. [657] 1961... 

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