Corrosion resistant intermetallics

Lead-tin (Pb-Sn) [L54D00 - L55099] Usual 5-10 wt.% Sn Historically 4 wt.% Sn Tin increases mechanical strength, forms corrosion-resistant intermetallics, and improves melt fluidity during anode casting Cobalt electrowinning (500 A.m b... 

In addition to the alloys in Table 4.21, Ni-Sn and Ni-Ti alloys also possess useful corrosion resistance. Ni-Sn alloys are extremely brittle and, because of this, are used only as electrodeposited coatings. Ni-Ti alloys over a wide range of compositions have been studied, of which perhaps the intermetallic compound NiTi (55 06Ni-44-94Ti) has attracted the most interest. 

The vast array of intermetallic compounds seems limitless, although it is finite. The number of binary compounds alone is in the thousands, and the number of ternary compounds is much larger. Still larger is the number of quaternaries, quin ternaries, and so on, ad infinitum. Not all of them are useful, of course, and there are many compounds having the same hardnesses as others. These overlapping cases are usually separated when other properties—such as corrosion resistance, toughness, or cost—are taken into account. 

Researchers have tried to fabricate plates using many different metals— mainly, stainless steel, aluminum alloys, titanium alloys, nickel alloys, copper alloys, intermetallic alloys, and metal-based composites such as carbon fiber-reinforced aluminum alloys, carbon fiber reinforced copper alloys, etc. [26]. Although Ta, Hf, Nb, Zr, and Ti metals show good corrosion resistance and chemical stability [6], the cost of fhese metals is too high for them to be used as materials in metal plates. That is why relatively cheaper iron-based alloys, particularly stainless steel, have been popularly studied as plate material. In the following secfions, we will infroduce sfainless sfeel (SS) and SS plates, which have been extensively investigated and show promise for the final applications [6,11]. 

Physical Properties. An overview of the metallurgy (qv) and solid-state physics of the rare earths is available (6). The rare earths form alloys with most metals. They can be present interstitially, in solid solutions, or as intermetallic compounds in a second phase. Alloying with other elements can make the rare earths either pyrophoric or corrosion resistant. It is extremely important, when determining physical constants, that the materials are very pure and well characterized. All impurity levels in the sample should be known. Some properties of the lanthanides are listed in Table 3. 

Has 21% Cr, 13% Mo, 3% W, 3% Fe, 60% Ni and suitable for use in oxidizing environments corrosion resistance better than C-276, C-4 in oxidizing media, better pitting resistance inferior to C-276, C-4 in reducing media and with respect to crevice corrosion Superior to C-22, C-276, super thermal stability attributed to the ternary system, Ni-Cr-Mo devoid of W, Cu, Ti and Ta Similar to C-276 in composition except for Cr level being 16-21% alloy is solution annealed at 1200°C and rapidly cooled to prevent precipitation of intermetallic phases thermal behavior not as good as Alloy 59 and its corrosion resistance was less than 59 1.6% Cu has been added to C59 lower corrosion resistance and thermal stability than Alloy 59... 

Steel phases have an influence on the rate of corrosion. Ferrite has a weak resistance to pitting. The presence of martensite can increase the hydrogen fragilization of steel. Intermetallic phases as Fe2Mo in high Ni content alloys can influence the corrosion resistance. The precipitate CuA12 in aluminum alloys the series 2000 is more noble than the matrix, with corrosion around the precipitate. The majority of case histories reported in the literature have involved austenitic stainless steels, aluminum alloys, and to a lesser degree, some ferritic stainless steels and nickel-based alloys.31... 

Intermetallic Coatings for Electrical Insulation and Corrosion Resistance on High Temperature Alloys, Surface Modification Technologies IX, eds., TS. Sudarshan, W. Reitz, and J.J. Stiglich, The Minerals, Metals and Materials Society, Warrendale PA, 1996, pp.151-166. 

Proc. JSCE Symp. "Corrosion Resistance of Intermetallic Compounds at High-temperature Environment Ed. by A Takei, (1994). 

Since many years the intermetallic phases based on aluminides have been an important topic for research and development, because of their high melting points, low densities and excelent corrosion resistance at high temperatures. Especially, nickel aluminides have been of great interest as coating materials for several high temperature applications. 

Ni and A1 both being interesting materials for the MCFC, we have investigated pure Ni and various Ni alloys including the intermetallic NiAI for their corrosion resistance under fuel cell conditions [1,3-6]. 

Aluminides based on the intermetallic phases Ni3Al and Fe3Al are considered both as structural materials and as coatings for high temperature applications [1-6]. Their excellent corrosion resistance is due to their forming a dense, protective alumina scale. Alumina, especially ot-Al203, shows low rate constants even at temperatures above 1000°C [7]. Unlike chromia, which is formed on conventional stainless steels and nickel base alloys, alumina does not evaporate above 1000°C [8] and it is even stable in oxygen deficient atmospheres. 

Ohashi et al. (1987) investigated the effect of Co substitution in Nd-Fe-B magnet alloys and found that corrosion resistance of the corresponding magnets was markedly improved. This was attributed by these authors to the segregation of the Co atoms into the Nd-rich phase where it led to the formation of an Nd-Co(Fe) intermetallic compound. The improved corrosion resistance was ascribed to the disappearance of free Nd metal, associated with the eutectic composition. 

Finally, it is noted that much interest is concentrated on the development of intermetallic alloys for use as blades in flying gas turbines. This application is most demanding and it is not clear whether all the problems with strength, ductility, toughness, and corrosion resistance can be solved at economic costs. Less-high-technology applications may be more reward-... 

Casting aluminum around steel components has been used where properties such as high strength, corrosion resistance, good heat transfer, or good electrical conductivity are required of a fabricated article. The surface is first prepared by the formation of an iron-aluminum intermetallic onto which the aluminum can be cast. Good adhesion is obtained in this manner, but coating thickness is limited by the difference in expansion coefficients. 

Nitride layers are produced after treatment in a salt bath or in a gas atmosphere by inward diffusion, usually below 600°C. Unlike transformation hardening, which is effected by lattice distortion as a result of embedded carbon atoms, nitriding and boriding provide the surface with an exceptional increase in hardness by the formation of an intermetallic bonding layer. These bonding layers also increase the general corrosion resistance, but they are so thin that they can break by mechanical point loading. 

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