Phase aluminum-based intermetallics

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... 

In order to provide the required flame retardancy to the molding compound, an encapsulated formulation usually contains brominated resins and antimony oxide. The brominated resins used in the encapsulated formulation are mainly tetrabromobisphenol A (TBBA) based epoxy resin or brominated epoxy novolac. These bromine-containing additives were reported to cause bond degradation at high temperature through accelerated void formation in the gold-aluminum intermetallic phases (1-4). 

Al—Cu—Mg. The first precipitation hardenable alloy was an Al—Cu—Mg alloy. There is a ternary eutectic at 508 0, and there are nine binary and five ternary intermetallic phases. For aluminum-rich alloys, only four phases are encountered in addition to the aluminum soUd solution (Table 18). Several commercial alloys are based on the age hardening characteristics of the metastable precursors of 0 or S-phase, principally 0 or S. Hardening by T- and p-phases is not very effective. Alloys of greatest age hardenabiUty have compositions near the Cu Mg ratio of the S-phase. Additions of about 0.12% Mg to alloys containing as much as 6% Cu, however, significantly increase strength by refining the 0 precipitate. 

Nickel-based alloys, which form the bulk of alloys produced, are basically nickel-chrome alloys with a face-centered cubic solid-solution matrix containing carbides and the coherent intermetallic precipitate y-NijlAfTi). This latter precipitate provides most of the alloy strengthening and results in useful operating temperatures up to 90% of the start of melting. Further additions of aluminum, titanium, niobium, and tantalum are made to combine with nickel in the y phase, and additions of molybdenum, tungsten, and chromium strengthen the solid solution matrix. 

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). 

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. 

No Mutual Solubility or Intermetallic Compound Formation System The mechanical properties of interfaces can be predicted based on the form of the binary equilibrium phase diagram [103]. Weak interfaces result in phase systems which do not form compounds or exhibit solubility. This behavior results because the unlike atomic species repel each other, typical of a system like Cr-Cu (Fig. 27). The binary phase diagram shows these species do not exhibit solubility or compound formation, and that the metals do not mix in the liquid state for most compositions. Interfacial adhesion can be improved in these systems by the addition of a glue layer which reacts with both metals. For the Cr-Cu system, the glue layer can be oxygen or another metal such as aluminum. Alternatively, the adhesion can also be achieved... 

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