R-based amorphous alloys

Thermal stability 121 5.1. History of R-based amorphous alloys 183... 

It is shown in sect. 3.1 that Mg-based amorphous alloys are obtained in Mg-Ni—R and Mg-Cu-R and that glass formation is independent of the kind of R element. It is important to know the influence of the atomic size of R on the Vickers hardness (H ) of Mg-R-M amorphous alloys. Figure 75 shows the change in of the amorphous Mg65Cu2sRio alloys with the kind of R element, together with the data of their atomic radii (S.G. Kim 1992). Although exceptional values are observed only for Eu and Yb, which also have significantly different atomic sizes, there is a tendency for to increase from about 180 for R=La to about 310 for the R element with the smallest atomic radius. 

In the literature several models have been described in which amorphous alloys are, considered to be relatively stable if certain requirements are fulfilled. In many of the alloys Aj that can be obtained in the amorphous state there is a substantial difference in size between the metallic radii of the components (r > rg). In addition, the composition of many amorphous alloys made by means of liquid quenching is close to X = 0.2. This led Polk (1970) to propose a stability criterion for amorphous alloys in which the size difference in atomic radii and the asymmetry in composition is of prime importance. This stability criterion is based on the possibility of obtaining a higher packing density when the holes available in the dense random packing of the larger A atoms are filled by the smaller B atoms. In recent years it has... 

Goldman, M. E., Unlu, N., Presuel, F. M, Shiflet, G. J., Scully, J. R. 2004. Amorphous Metallic Coatings with Tunable Corrosion Properties Based on Al-Co-Ce-(Mo) Alloy Compositions. In CORROSION/2004. NACE, Houston, Texas, Paper No. 4276. 

Lucente, A. M. and Scully, J. R. 2007b. Pitting of Al-based amorphous-nanocrystalline alloys with so Ae- easttaaD.oc[y i3Xs.ElectrochemicalandSolidStateLeners, 10,C39-C43. 

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