Chromium-Based Alloys

This alloy has been investigated in detail with respect to corrosion behaviour [41,42] and contact resistance across its interfaces with the electrodes [43]. Typically, Cr 5Fe IY2O3 is a chromia former and even after long-term exposure in oxygen or air, the chromia scales are very thin. Thicker corrosion scales grow in carbon containing atmospheres (methane, coal gas) due to formation of carbides [42]. 

The fabrication of interconnect plates of Cr 5Fe IY2O3 is done by powder metallurgical methods and starts with the alloying of Cr flakes with Fe and Y2O3 by 

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Table 7.19 Oxidation data for commercial nickel-chromium-base alloys...

Niobium appears to have a slightly beneficial effect on the oxidation resistance of nickel-chromium-base alloys, although at 1 200°C the addition of niobium to Nichrome (Table 7.18) produces a much higher rate constant. Titanium on the other hand appears to have a slightly deleterious effect on oxidation resistance at low temperatures. 

Although iron sulphide also forms a eutectic with the metal this melts at 988°C, and at temperatures in the region of 700 to 800°C alloys with substantial proportions of nickel replaced by iron and a chromium level maintained at about 20% show advantages over nickel-chromium-base alloys in resistance to sulphur attack. 

Table 7.31 lists data for the corrosion of nickel and some nickel alloys by ammonia at 500°C. At higher temperatures the more complex hardened nickel-chromium-base alloys are more resistant than the binary alloys and... 

Figure 9.10 Depth profile for a non-conducting chromium oxide layer on chromium based alloy measured by rf CDMS. (A. I. Saprykin, J. S. Becker et ai, Fresenius /. Anal. Chem., 358, 145 (1997). Reproduced by permission of Springer Science and Business Media.)...

HIM) Tomashov, N. D., Ustinskii, E. P., Chernova, G. P. Study of Periodic Potential 1981 Oscillations of Chromium Base Alloys with Platinum Group Metals in Sulfuric Acid Solution Electrokhimiya 17, 969-976 (Rus.)... 

Chromium is a refractory metal having a melting point of 3375°F (1857°C). Neither chromium metal nor chromium-based alloys are widely in the hydrocarbon or chemical industries. Chromium plating is useful for aesthetic purposes, and hard chromium plating finds some use in hardface applications. It is extensively used as an alloy addition to low-alloy steels (usually for the purpose of stabilizing carbides) and in cast irons (to produce wear-resistant products) and nickel alloys (for increased corrosion resistance). Chromium is the main alloying addition in the 400-series stainless steels and is used extensively in the 200- and 300-series stainless steels. 

The metals commonly used in medical devices are stainless steel (Types 316 and 316 L), cobalt-chromium-based alloys, titanium, and titanium-based alloys. Metals are used extensively in orthopedic surgery for load-bearing devices, such as artificial joints and fixation devices (wires, pins, screws fracture plates, etc.). Other metals include tantalum, gold, and mercury alloys the latter two are used predominantly in dentistry. 

The experimental works devoted to study of materials properties in the Cr-Fe-Ni system are listed in Table 4. [2000Mie] obtained fitted equations for liquidus temperatures of steels from calculated results based on a model of interdendritic solidification. [2002His] summarized literature data on mechanical properties of high-chromiiun iron-base alloys and chromium-base alloys. This review covers data obtained up to 2002. Literature data on elastic constants of seven alloy compositions are given in [2004Li]. 

Vit] Vitek, J.M., Kozeschnik, E., David, SA., Simulating the Ferrite-to-Austenite Transformation in Stainless Steel Welds , Calphad, 25(2), 217-230 (2001) (Caleulation, Kineties, 20) [2002His] Hishinuma, A., Takaki, S., Abiko, K., Reeent Progress and Future R D for High-Chromium Iron-Base and Chromium-Base Alloys , Phys. Status Solidi A, 189(1), 69-78 (2002) (Eleetro-chemistry, Interface Phenomena, Meehan. Prop., Phys. Prop., Review, 24)... 

This is a nonmagnetic nickel-chromium-based alloy strengthened with refractory metals. The chemical composition is given in Table 15.24. It possesses excellent corrosion properties, strength, ductility, and toughness, and has outstanding structural stability. 

Stainless steels Glycer regia For austenitic iron-chromium based alloys. 

In pure Cr the benefits of rare-earth additions are extended to also provide resistance to nitridation, which seriously embrittles chromium (see Hagel 1963, Seybolt 1966, Stephens 1972 and a study by Travadze et al. 1986 of Cr—La alloys in air at temperatures between llOO C and 1400 C). These observations were repeatedly confirmed in the author s laboratory during the 1960 s, in the development of ductile, high-strength chromium-base alloys (Mills and Ryan 1965). 

Through a chemical treatment of iron-chromium based alloys, supported catalysts can be prepared in one main step from the substrate which furnishes constitutive elements of the coating. The conversion coating is a microporous physically and chemically heterogenous medium with a fractal structure. Variations of the compositional and textural properties are studied against nature of the substrate, duration of the chemical treatment and conditions of thermal or chemical post-oxidation treatment. 

Smeltzer W W, Narita T and Przybylski K, High temperature sulfidation properties of iron-chromium-base alloys , in Proc. Corrosion-Erosion, Wear of Materials in Emerging Fossil Energy Systems , Ed. By Levy AV, NACE, Houston, 1982, pp 860-872. 

On the other hand, the alloy interconnects have been used for the developers of SOFCs which operate at lower temperatures. Chromium based alloys proposed by Plansee Co. can be used at the temperatures lower than 900 "C. The high chemical stability is maintained by the dispersion of Y2O3 particles in Cr95%-Fe5% by a mechanical alloying process (Batawi etal., 1999). 

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