Multi-component alloys

Q. Han, J. D. Hunt. Numerical modelling of the growth of a cellular/dendritic array in multi-component alloys. Mater Sci Eng A 255 192, 1997. 

DICTRA (Diffusion simulation software) (Borgenstam et al. 2000). DICTRA (coupled with Thermo-Calc) is a software for the simulation of diffusion in multi-component alloy systems (processes which can be simulated are for example the homogenization of alloys, micro-segregation during solidification, carburizing, and decarburizing, of steels, etc.). 

In the case of multi-component alloys and compounds, the surface composition may also change in addition to surface relaxation and reconstruction. For instance, the first layer of (100) plane on the surface of a nickel-aluminiim alloy enriches itself with aliuninum whose atomic size is larger than nickel. Such an enrichment of some constituents on the soUd surface is called surface segregation [Van Hove, 1993]. It is abo known that surface active minor impurities of oxygen, phosphorus and sulfur in metallic iron segregate to the clean siirface of iron [Nii-Yoshihara,... 

Chapter 10 provides an exhaustive description of how these techniques can be applied to a large number of industrial alloys and other materials. This includes a discussion of solution and substance databases and step-by-step examples of multi-component calculations. Validation of calculated equilibria in multi-component alloys is given by a detailed comparison with experimental results for a variety of steels, titanium- and nickel-base alloys. Further selected examples include the formation of deleterious phases, complex precipitation sequences, sensitivity factor analysis, intermetallic alloys, alloy design, slag, slag-metal and other complex chemical equilibria and nuclear applications. 

Clearly CALPHAD has now come of age and is at a watershed where complex phase equilibria calculations can now be performed as a routine operation and yet have also been placed on a sound physical basis. Computer programmes exist which can perform complex calculations on a PC and which can therefore be operated at any location without extensive prior expertise. Furthermore, it is possible in many cases to predict phase equilibria in multi-component alloys to a degree which is close to that expected from experiment (see Chapter 10). It is therefore a branch of science that is mature and, indeed, has already entered the next stage of development, which emphasises the need to concentrate on extending its range of applicability. 

Equation (5.21) assumes ternary interactions are small in comparison to those which arise from the binary terms. This may not always be the case and where evidence for higher-order interactions is evident these can be taken into account by a further term of the type Gijit = x< xj Xk Lijk, where Lijk is an excess ternary interaction parameter. There is little evidence for the need for interaction terms of any higher order than this and prediction of the thermodynamic properties of substitutional solution phases in multi-component alloys is usually based on an assessment of binary and ternary terms. Various other polynomial expressions for the excess term have been considered, see for example the reviews by Ansara (1979) and Hillert (1980). All are, however, based on predicting the properties of... 

This accounts for the moves to combine a theoretical CVM treatment with a CALPHAD optimisation technique which include an excess term (see Section 7.6.4). However, CVM then becomes just another optimisable model and it is not yet clear whether there is any gain in predictability in the higher-order systems when adopting this procedure for multi-component alloys, even if vibrational entropy can be properly included. 

Only after at least these three steps are taken can a database then be considered as an assessed database and used with confidence in an application involving a complex multi-component alloy. 

Aluminium alloys form one of the most widely used groups of materials in existence. They make products which are often cheap and can be applied to many different areas. Extensive work has been done on the experimental determination of binary and ternary phase diagrams, mainly during the mid-part of this century, and researchers such as Phillips (1961) and Mondolfo (1976) have produced detailed reviews of the literature which provide industry standard publications. However, although some important Al-alloys are based on ternary systems, such as the LM2S/ 356 casting alloy based on Al-Mg-Si, in practice they inevitably include small amounts of Cu, Mn, Fe, Ti etc., all of which can significantly modify the castability and properties of the final product. The situation is further exacerbated by the use of scrap material. It is therefore useful to be able to predict phase equilibria in multi-component alloys. 

QUANTITATIVE VERIFICATION OF CALCULATED EQUILIBRU IN MULTI-COMPONENT ALLOYS... 

The procedure described above is simple to model in a computer programme and has a number of significant advantages (1) The Scheil equation is only applicable to binary alloys and is not easily derived with multiple k values, which would be necessary for a multi-component alloy. A calculation as described above can be applied to an alloy with any number of elements. (2) The partition coefficients need not be constant, which is a prerequisite of the Scheil equation . (3) The Scheil equation carmot take into account other phases which may form during such a solidification process. This is handled straightforwardly by the above calculation route. 

Metallization. In the fabrication sequence described in Table I, metal layers are used as conductive paths between points on the same integrated circuit or as contact points between the IC and its package. The metal layers may be single component, multi-component alloys or multilayered thin films depending on the application. The methods used for depositing the metal are... 

Possibility for the preparation of multi-component alloys with concentrations of elements much higher than their equilibrium values. This is due to the fact that the film composition is mainly determined by the relative contents of components in the stream of sputtered atoms and by the adhesion factor, but is not defined by thermodynamic equilibrium. 

Generalization of this formula to multi-component alloys is straightforward... 

In this endeavor synchrotron spectroscopy has played an important role in understanding the effect of fundamental parameters such as electronic density of states and short-range atomic order. The primary advantages of using the synchrotron are (1) the ability to probe these parameters in situ while the interface is under electrochemical control and (2) the fact that these can be measured with element specificity. The latter is particularly useful when investigating multi-component alloy clusters. In addition, this technique lends itself to systems with limited long-range order, which is typical for these nanoclusters used in fuel-cell electrode interface. This chapter describes some recent results with in-situ X-ray absorption spectroscopy, which has provided a direct probe into the variations of the Pt i/-band vacancy (normalized with respect to number of surface atoms) between... 

Before the present work, insufficient data were available in the literature for phase equilibria of systems based on Ti-B. There is a large body of data in literature on the properties of titanium-boride materials, but there is no systematic information regarding the specific role(s) of candidate alloying elements. Thus, the present effort was undertaken to explore the role of alloying additions through the study of phase equilibria and alloy properties, as well as their interrelation, from the binary Ti-B system to the Ti-rich portions of ternaries Ti-Al-B and Ti-B-X, further to quaternaries Ti-10 at.% Al-B-X (where X = Si, Ge, Sn, Zr, V, or Nb) and to some multi-component alloys. 

The PC/PEST blends were first described in 1966. The first, three-component blends were disclosed in 1972 (see Table 1.64). Many multi-component alloys comprise PC and PEST. From between them, these with PPE are particularly important — see the following Part. 

The use of grids cast from the above multi-component alloys did reduce the need for battery maintenance but did not eliminate it altogether. So the battery industry chose two basic approaches to achieve the goal set by the automobile industry, i.e., to devise maintenance-free... 

The onset of crystallization in the Vitreloy 1 alloy shown in Fig. 1.3 was based on the detection of a crystalline volume fraction of 10 " by conventional methods. There are two different curves for the onset of crystallization in Fig. 1.3. For the solid curve, which was obtained using classical nucleation theory, the effective diffusion constant was taken to be proportional to the reciprocal of the viscosity, which was considered to be of the VFT form. The dotted curve was obtained by the use of an Arrhenius form of expression for the effective diffusion constant, which was found to fit better at lower temperatures near Tg (Masuhr et al. 1999). This discussion shows that for understanding the kinetics of crystallization in multi-component alloys considerable improvisation becomes necessary. 

Him] Himemiya, T., Wolczynski, W, Sohdification Path and Solute Redistribution of an Iron-Based Multi-Component Alloy with Solute Diffusion in the Solid , Mater. Trans., 43(11), 2890-2896 (2002) (Phase Relations, Calculation, 12)... 

Man] Residual electrolytic extraction 950-1225°C multi-component alloy... 

Smi] Equihbration with Methane-H2 mixtures 997-1318°C < 0.005 mass% C, 0.0-0.8 mass% Nb in multi-component alloy... 

The most important elemental constituents of amorphous semiconductors are Si and Ge in Group IV P, As, Sb and Bi in Group V and the chalcogenides (S, Se, and Te) in Group VI. Elements, compounds, or multi-component alloys varying widely in composition can be prepared in amorphous form variously by cooling a melt or condensing a vapor. 

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