Ordered binary alloy

Figure 52. Various superstructures in ordered binary alloys imaged using the bright-field superlattice mode and compared to stractural models...

M. J. Richard and J. W. Cahn, Pairwise interactions and the ground state of ordered binary alloys,. dcta Metal., 19, 1263-1277(1971). 

The addition of a third element to an ordered binary alloy can modify considerably the point-defect properties for example, the behavior of FeCo-2% V is very complex, because vanadium forms a resonant virtual bound state at the Fermi level, the partial filling of which depends strongly on the state of order (Riviire et al., 1983b). Solutes (specifically Mn, Re, and Ti) have also been shown to have complicated effects in CoAl (Fleischer, 1993). 

In ordering binary alloys (intermetallic compounds), the segregation of one component to the surface should be unfavorable, as it involves the occupation of adjacent... 

Wlien 2 g > (Eaa BB binary alloy corresponds to an Ismg ferromagnet (J> 0) and the system splits into two phases one rich in A and the other rich in component B below the critical temperature T. On the other hand, when 2s g < (Eaa+ bb > system corresponds to an antiferromagnet the ordered phase below the critical temperature has A and B atoms occupying alternate sites. 

In order to control the composition of the binary alloy we use the chemical potential pj, and minimize the grand potential Cl. The densities of A and B atoms are obtained from the point distiribution function fj(r) and f2(r) as... 

The aim of the present study is precisely to investigate the thermodynamical properties of an interface when the bulk transition is of first order. We will consider the case of a binary alloy on the fee lattice which orders according to the LI2 (CuaAu type) structure. 

Vasihev MA. 1997. Surface effects of ordering in binary alloys. J Phys D Appl Phys 30 3037-3070. 

The order-disorder transition of a binary alloy (e.g. CuZn) provides another instructive example. The body-centred lattice of this material may be described as two interpenetrating lattices, A and B. In the disordered high-temperature phase each of the sub-lattices is equally populated by Zn and Cu atoms, in that each lattice point is equally likely to be occupied by either a Zn or a Cu atom. At zero temperature each of the sub-lattices is entirely occupied by either Zn or Cu atoms. In terms of fractional occupation numbers for A sites, an appropriate order parameter may be defined as... 

Figure 2.15. Relative extent of the mutual solid solubility in binary alloys of transition metals, ordered according to their group number in the Periodic Table. The group number is reported on the left and on the top of the figure.

Trends in the formation capability of binary compounds. A few general comments about the formation of intermediate phases in binary alloy systems can be made by using maps similar to those previously employed in Fig. 2.8 in order to give a summary of the mutual solubility. 

Remarks on the crystal chemistry of the alloys of the 3rd group metals. A large number of intermediate phases have been identified in the binary alloys formed by the rare earth metals and actinides with several elements. A short illustrative list is shown in Tables 5.19 and 5.20. Compounds of a few selected rare earth metals and actinides have been considered in order to show some frequent stoichiometries and crystal structure types. The existence of a number of analogies among the different metals considered and the formation of some isostructural series of compounds may be noticed. 

An equation which includes the effect of adding a magnetic term to the enthalpy of an ordered system has already been given in Section 7.3.2.3 of Chapter 7, but no details were given of how to determine the value of the magnetic interaction energy 4 5- binary alloy this involves the introduction of three magnetic... 

The first generation sintered magnets were based on the binary alloy SmCo5 and such magnets still account for the bulk of those now manufactured. However, in order to meet certain cost criteria it was soon recognised that it would be to the benefit of all to provide a less expensive type of magnet based on a modofied composition and this was first achieved by partial... 

Naturally, the fixed composition phase transformations treated in this section can be accompanied by local fluctuations in the composition field. Because of the similarity of Fig. 17.3 to a binary eutectic phase diagram, it is apparent that composition plays a similar role to other order parameters, such as molar volume. Before treating the composition order parameter explicitly for a binary alloy, a preliminary distinction between types of order parameters can be obtained. Order parameters such as composition and molar volume are derived from extensive variables any kinetic equations that apply for them must account for any conservation principles that apply to the extensive variable. Order parameters such as the atomic displacement 77 in a piezoelectric transition, or spin in a magnetic transition, are not subject to any conservation principles. Fundamental differences between conserved and nonconserved order parameters are treated in Sections 17.2 and 18.3. 

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