Intermetallic systems, development

The discovery of the binary (Yb,Ca)-Cd i-QCs [19] was a remarkable milestone in the history of QCs. The reasons are apparent they offered unique opportunities for structural analyses as they exhibited negligible chemical disorder, probably because of the large differences in the chemical crystallography of the components, in contrast to more common problems with ternary intermetallics. In addition, they also represented new (Tsai) types of AC cores and of i-QCs with a structural motif different from those of the Mackay and Bergman types (above) that were better known at the time. Without doubt, such a breakthrough discovery must lead to an era of related chemical explorations or tunings. Actually, almost all of the i-QC systems developed since 2000 are Tsai types [28,29], including our own additions (below). 

Since all known QC systems, with e/a of about 1.75-2.20 [25], lie close to the approximate border between the Hume-Rothery and polar intermetallic phase regions, a reasonable starting place for development of new QC/AC systems is to study selected polar intermetallic systems with nearby e/a values. Synthetic explorations of such polar intermetallics have been significant only in the past few decades [42,45], Knowledge and insights developed about the diverse interplays between composition-structure-electronic structure-physical properties for these phases were expected to be a considerable aid to the discovery of novel QC/ACs. 

Historical Development of Interstitial Hydrides in Other Intermetallic Systems... 

Ductility of one of the constituent powders is not a requirement for mechanical alloying to occur. A number of brittle/brittle systems have been shown to form solid solutions of intermetallic compounds during milling (Davis et al. 1988, Davis and Koch 1987). In contrast to the layered morphology exhibited by ductile systems, brittle/brittle systems develop a granular morphology. While the alloying mechanism is not well understood with brittle systems it is evident that material transfer between the components plays an important role (Davis et al. 1988). 

The sub-lattice model is now the predominant model used in most CALPHAD calculations, whether it be to model an interstitial solid solution, an intermetallic compound such as 7-TiAl or an ionic solution. Numerous early papers, often centred around Fe-X-C systems, showed how the Hillert-Staffansson sub-lattice formalism (Hillert and Staffansson 1970) could be applied (see for example Lundberg et al. (1977) on Fe-Cr-C (Fig. 10.8) and Chatfteld and Hillert (1977) on Fe-Mo-C (Fig. 10.9)). Later work on systems such as Cr-Fe (Andersson and Sundman 1987) (Fig. 10.10) showed how a more generalised sub-lattice treatment developed by Sundman and Agren (1981) could be applied to multi-sub-lattice phases such as a. 

Recently a relaxation method [6,7] has been developed to measure Cp at very low temperature. As the method can change a sample temperature rapidly due to the use of a very small amount (5-30 mg) of sample for the measurement, the Cp values at the temperature can be determined rapidly and precisely from near absolute zero to 400 K [8-14]. In the present study, we have attempted to determine the y values of the intermetallic compounds of the Mg-Zn binary system by using the relaxation method. 

William B. Pearson (1921-2005) developed a shorthand system for denoting alloy and intermetallic structure types (Pearson, 1967). It is now widely used for ionic and covalent solids, as well. The Pearson symbol consists of a small letter that denotes the crystal system, followed by a capital letter to identify the space lattice. To these a number is added that is equal to the number of atoms in the unit cell. Thus, the Pearson symbol for wurtzite (hexagonal, space group PS mc), which has four atoms in the unit ceU, is hPA. Similarly, the symbol for sodium chloride (cubic, space group Fm3m), with eight atoms in the unit cell, is cF8. 

Recent development of the computational technique for electronic state of materials enables us to calculate the accurate valence electronic structure of fairly large and complicated systems from the first principles. However, it is still very important to investigate the electronic state and chemical bonding of a simple and small cluster model of metal element, because the basic imderstanding of the essential properties of the metal elements is not sufficient. It is also very useful to investigate a small cluster model in understanding various kinds of properties and phenomena of more complicated metallic materials like alloys and intermetallic compounds, because the fundamental electronic state is reflected in their properties. 

Development of Experimental Intermetallic Forming Starter Systems for the Ml Smoke (HC) Canister , AFATL-TR-71-136 (1971)... 

The properties of alloy and intermetallic compound surfaces play an important role for the development of new materials. Attention has been stimulated from various topics in microelectronics, magnetism, heterogeneous catalysis and corrosion research. The investigation of binary alloys serves also as a first step in the direction to explore multi-component systems and is of particular regard in material science as a consequence of their widespread use in technical applications. The distribution of two elements in the bulk and at the surface probably results in new characteristics of the alloy or compound as compared to a simple superposition of properties known from the pure constituents. Consequently, surfaces of bulk- and surface- alloys have to be investigated like completely new substances by means of appropriate material research techniques and surface science tools. [1-6]. 

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