Disorder in alloys

Nearly all experimental eoexistenee eurves, whether from liquid-gas equilibrium, liquid mixtures, order-disorder in alloys, or in ferromagnetie materials, are far from parabolie, and more nearly eubie, even far below the eritieal temperature. This was known for fluid systems, at least to some experimentalists, more than one hundred years ago. Versehaflfelt (1900), from a eareflil analysis of data (pressure-volume and densities) on isopentane, eoneluded that the best fit was with p = 0.34 and 8 = 4.26, far from the elassieal values. Van Laar apparently rejeeted this eonelusion, believing that, at least very elose to the eritieal temperature, the eoexistenee eurve must beeome parabolie. Even earlier, van der Waals, who had derived a elassieal theory of eapillarity with a surfaee-tension exponent of 3/2, found (1893)... 

M.A. Krivoglaz and A. A. Smirnov, The Theory of Order-Disorder in Alloys, Macdonald, London, 1964. 

Radiation ordering and disordering in alloy systems have successfully been studied in high-voltage microscopes at different temperatures. 

The anti-structure disorder is encountered particularly if the two elements A and B have similar properties (comparable volumes, close electronegativity values, etc.), as happens in certain inter-metallic compounds. This is the disorder that is created during the transformation from order to long distance disorder in alloys (see Chapter 2). 

Beryllium-containing materials can be potentially harm fill if mishandled. Care must be taken in the fabrication and processing of beryUium products to avoid inhalation of airborne beryllium particulate matter such as dusts, mists, or fumes in excess of prescribed workplace limits. Inhalation of fine airborne beryllium may cause chronic beryllium disease, a serious lung disorder, in certain sensitive individuals. However, most people, perhaps as many as 99%, do not react to beryUium exposure at any level (see Beryllium and beryllium alloys). 

Tanner, L.E, and Leamy, H.J. (1974) The microstructure of order-disorder transitions, in Order-Disorder Transformations in Alloys, ed. Warlimont, H. (Springer, Berlin) p. 180. 

Krumbhaar. Solidification in the one-dimensional model for a disordered binary alloy under diffusion. Eur Phys J. B 5 663, 1998. 

Ab-initio studies of surface segregation in alloys are based on the Ising-type Hamiltonian, whose parameters are the effective cluster interactions (ECI). The ECIs for alloy surfaces can be determined by various methods, e.g., by the Connolly-Williams inversion scheme , or by the generalized perturbation method (GPM) . The GPM relies on the force theorem , according to which only the band term is mapped onto the Ising Hamiltonian in the bulk case. The case of macroscopically inhomogeneous systems, like disordered surfaces is more complex. The ECIs can be determined on two levels of sophistication ... 

B. Urban-Erbil and W. Pfeiler, Ordering and disordering in CuPt-alloys, in. .Ordering and Disordering in... 

Four of the solid solutions of Table III have excess entropies of solution which include contributions from magnetic disordering in both the alloy and in one or both of the pure components. These contributions can be quite large, and since there is no assurance... 

As an example. Fig. 8.1 shows a result from Bardi and co-workers obtained on a bimetallic AusPdClOO) single-crystal alloy [Kuntze et al., 1999]. The LEED pattern indicates a sharp (1 x 1) unit cell that corresponds to the bulk-tmncated stmcture of the substitutionaUy disordered Au3Pd alloy. Additionally, the authors determined the composition of the first outermost layer to be pure Au. These findings revealed that the (100) oriented surface of Au over AusPd alloy is not reconstmcted, which is unique, since pure Au, Pt, and Ir (100) crystals are all known to be reconstmcted in similar ways [Van Hove et al., 1981 Ritz et al., 1997]. In this case, the presence... 

This disorder decrease on alloying is in principle unexpected, because alloying introduces chemical disorder in addition to bond disorder. However, Silva et al. [14] reported results on the joint density of states as determined by EELS which showed a clear decrease in the density of tail states at 7-at.% N and showed a further increase for higher nitrogen content. 

In this section, we consider how to model a bulk (i.e., infinite) substitution-ally disordered binary alloy (DBA), in light of its intrinsic randomness. The fact that the DBA lacks periodicity means that the key tool of Bloch s theorem is inapplicable, so specialized methods (Ehrenreich and Schwartz 1976, Faulkner 1982, Yonezawa 1982, Turek et al 1996) must be used. 

Well-ordered intermetallic compounds (alloys), when processed in high-energy ball mills exhibit atomic (chemical) disordering in the early stages of ball milling [153]. Let us take as an example ordered AlRu intermetallic crystals that are of B2 type and P-CuZn structure. This structure consists of two simple cubic interpenetrating... 

H. Bakker, G.F. Zhou, H. Yang, Mechanically driven disorder and phase transformations in alloys, Prog. Mater. Sci. 39 (1995) 159-241. 

The heats of formation of equiatomic AB transition-metal alloys may be predicted by generalizing the rectangular d band model for the elements to the case of disordered binary systems, as illustrated in the lower panel of Fig. 7.13. Assuming that the A and transition elements are characterized by bands of width WA and WB, respectively, then they will mix together in the disordered AB alloy to create a common band with some new width, WAB. The alloy bandwidth, WAB may be related to the elemental bond integrals, hAA and , and the atomic energy level mismatch, AE — EB — EAt by evaluating the second moment of the total alloy density of states per atom ab( ), namely... 

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