Topologically close-packed phase

Pope and Chu, 1993). Correspondingly, stacking sequence faults may be formed easily in topologically close-packed phases, which have been studied in detail (Khan-tha et al., 1990). A structure transformation may be induced by a mechanical stress, a has been observed for ZrFc2 with a C36/C15 transition (Liu etal., 1993). 

Because of constitutional complexity, the exact chemistries of nickel-base superalloys must be controlled carehiUy in order to avoid the precipitation of deleterious topologically close-packed (TCP) phases and extraneous carbides after long-term high temperature exposure. Heat-treatment schedules and thermomechanical treatments in the case of wrought alloys also are important to provide optimum strength and performance. 

The Laves phases - sometimes designated as Friauf-Laves phases - with an AB2 composition in the binary case form a very large group of intermetallics which crystallize with the hexagonal C14 structure, the cubic Cl 5 structure, or the dihexagonal C36 structure (Laves, 1967 Wernick, 1967 Livingston, 1992). These structures are topologically close-packed (tcp) structures (Wernick, 1967 Schulze etal., 1973 Watson and Bennet, 1984), i.e. the Laves... 

CrjSi, which is a candidate phase for high-temperature applications, and VjSi, which is superconducting at low temperatures with a comparatively high transition temperature, both crystallize with the topologically close-packed cubic, A15 structure and have been discussed in Secs. 7.7 and 7.2, respectively. 

Laves phases have what is known as a topological close-packed (TCP) structure which is often undesirable because they can act as stress risers that initiate cracks because of their hardness and morphology and because they tie up atoms needed for the more desirable coherent y phases that are involved in precipitation hardening of alloys. 

From the above MC simulation results, a suppositional concentric square column structure is constructed, which is not observed in MC simulation (Yu et al., 2007a) but can be considered as a basic block of the CMSC structure. We plot the same four architectures together forming a close-packed structure in Figure 37. Under curved confinements, the topological CMSC structure can be considered as the cross-sectional concentric circle that truncates the four close-packed square columns with the exterior radii Rex, and the center is at the common corner of the four squares. Among the four square columns, the phase structures of... 

As aluminium does not undergo vapour phase difiusion flame with FIFE it is more reasonable to investigate the reaction of sohd aluminium particles with PTFE decomposition products. As the topology of the [Ah 3] -cluster (Figure 5.27) is very much like the closed packed structure of bulk aluminium it has been investigated as a model compound to study the reaction between sohd aluminium and gaseous oxidizers such as hydrogen chloride [32] and chlorine [33]. Chaudhuri has adopted... 

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