Amorphous alloys glass transition

SSAR is observed when the binary diffusion couples listed in Table 2.4 are heated to an appropriate reaction temperature, TR. Examples of typical values of JR are given in Table 2.4. It is well known that amorphous metallic alloys tend to crystallize in laboratory timescales upon heating to temperatures close to their glass-transition temperature, T% [2.16]. For a typical practical timescale (e.g., minutes), one can define crystallization temperature as the temperature at which a significant fraction of an amorphous sample undergoes crystallization in the specified time. The time required for an amorphous phase to crystallize can be identified with t 2 of Fig. 2.6 (see discussion in Sect 2.1.3). In the low temperature regime (well below Tg), atomic diffusion in amorphous alloys is... 

In this chapter we present a survey of our current understanding of interrelations between the electronic and ionic structure in late-transition-polyvalent-element metallic glasses. Evidence of a strong influence of conduction electrons on the ionic structure, and vice versa, of the ionic structure on the conduction electrons, is presented. We discuss as well the consequences to phase stability, the electronic density of states, dynamic properties, electronic transport, and magnetism. A scaling behaviour of many properties versus Z, the mean electron number per atom, is the most characteristic feature of these alloys. Crystalline alloys which are also strongly dominated by the conduction electrons are often called electron phases or Hume-Rothery phases. The amorphous alloys under consideration are consequently described as an Electron Phase or Hume-Rothery Phase with Amorphous Structure. Similar theoretical concepts as applied to crystalline Hume-Rothery alloys are used for the present amorphous samples. 

From Table 2, it is clear that the variations of the glass transition temperature as a function of the composition for amorphous Pd-Ni-P alloys is small. The weak composition dependence of Tg in Pd-Ni-P alloys is consistent with previously reported results [24,25], where Tg of glassy Pdgo-xNixP2o alloys were found to be between 585 and 602 K when x varies from 0.15 to 0.8. In contrast, Tg for bulk amorphous PdxCugo-xPzo alloys increases gradually as the palladium concentration increases, as illustrated in Figure 6. 

Laser Raman spectroscopy has been used as a tool to elucidate the molecular structure of crystals, liquids, and amorphous alloys in the As-S-Se-Te system. Characteristic monomer and polymer structures have been identified, and their relative abundances have been estimated as a function of temperature and atomic composition. These spectroscopic estimates are supported by calculations based on the equilibrium polymerization theories of Tobolsky and Eisenberg (1,2) and of Tobolsky and Owen (3). Correlations between the molecular structure of the amorphous alloys and physicochemical properties such as the electron drift mobility and the glass transition temperature are presented. 

Myu] Myung, W.-N., Yang, S.-J., Kim, H.-G., Glass Transition and Viscous Flow Behavior of Amorphous Fe-M-P (M = Cr, V or Mo) Alloys , Mater. Sci. Eng., A133, 418-422 (1991) (Crys. Structure, Morphology, Experimental, Kinetics, Phys. Prop., 9)... 

Included in this section is a description of the various transformations taking place in amorphous alloys, such as structural relaxation, glass transition and amorphous-to-crystalline transition. The main techniques employed to study these transitions are described in more detail and further conclusions are given that can be drawn from the results of these studies. 

If the submicroscopic regions are amorphous and larger than about 5 nm, a polymer alloy exhibits two glass-transition temperatures. Under certain conditions, crystalline submicroscopic regions can be recognized by X-ray crystallography. 

Viscous flow sets in only above about 0.6 of the glass transition temperature 7g which for many technical interesting alloys is between 400 and 600°C. Even though amorphous metals have an atomic structure (usually described by the pair correlation function) that is similar to the corresponding alloy in the liquid state, their viscous flow resembles rather the behavior of crystalline metals than those of liquids. 

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