Iron-aluminum based intermetallics

It is also possible that the tolerance limit correlates with a boundary between an active and passive form of the iron precipitate (Hillis and Reichek, 1986). This has not been confirmed directly by metallographic examination (Aune, 1983 Lunder et al., 1985 Reichek et al., 1985), but is based on the observation that at melt compositions above the tolerance limit, iron alone (or perhaps an iron-aluminum intermetallic) drops from the melt as the metal is cooled, i.e. there is little or no reduction in the manganese level. Only at compositions below the tolerance limits is there a simultaneous reduction in both the iron and manganese content. Castings within this composition region would contain only an Fe-Mn (or Fe-Mn-Al) precipitate phase which is apparently passive as a cathodic site (Lunder et al., 1985). 

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]. 

The constituent may be anodic, cathodic, or neutral to the base metal or adjacent zone. Examples of anodic constituents are the intermetallic phases Mg Al and MgZn in aluminum alloys and Fe N in iron alloys. Examples of cathodic constituents are FeAl3 and CuAlj in aluminum alloys and Fe C in iron alloys. Examples of neutral constituents are Mg Si and MnAl in aluminum alloys and Mo C and WjC in wrought Ni-Cr-Mo alloys. 

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