Quasicrystalline materials

S. Joseph Poon, Electronic and Thermoelectric Properties of Half-Heusler Alloys Terry M. Tritt, A. L. Pope, and J. W. Kolis, Overview of the Thermoelectric Properties of Quasicrystalline Materials and Their Potential for Thermoelectric Applications Alexander C. Ehrlich and Stuart A. Wolf, Military Applications of Enhanced Thermoelectrics David J. Singh, Theoretical and Computational Approaches for Identifying and Optimizing Novel Thermoelectric Materials... 

Hardness was measured by Vickers indenter in PMT-3 microhardness tester at a load of 2 N. The observed sinking of compact hardness with the growth of pressure, i.e. with growing deformation (Fig. 4), is an evidence of strain softening characteristic for quasicrystalline materials [5, 6], Plastic... 

Milman, Yu.V., Lotsko, D.V., Bilous, A.M. and Dub S.M. (2001) Quasicrystalline materials. Structure and mechanical properties, Functional Gradient Materials and Surface Layers Prepared by Fine Particles Technology, Kluwer Acad.Publ. 289-296. 

Unique nanocrystalline microstructures can be produced by controlled crystallization of the fully amorphous product, including nanocrystalline precipitates homogeneously distributed in an amorphous alloy matrix. In some systems, both the strength and ductility increase in this partially crystalline state [24], Other alloys produce nanocrystalline intermetallic or quasicrystalline precipitates, providing a credible path for increasing the specific stiffness. Thus, a significant effort is required to study the kinetics of crystallization, the devitrification pathways and the microstructures and properties that may be produced upon devitrification. The potential for exploration of novel compositions and microstructures in this class of materials is clearly promising. 

Quasicrystalline powders behave while consolidation in many features like ceramic materials and are consolidated with difficulties. Usually it is performed by HIP technique, but this process takes rather much time and requires complicated equipment. In our former works [1] it was shown that the consolidation of ceramic powders is significantly easier when using high quasihydrostatic pressure that activates particle contact interaction, and high-temperature sintering requires 2-3 min. 

The deviations from the average value for the utmost points of the curve do not exceed 0.1 GPa (6 %). This result is an evidence of the fact that a porous body from the quasicrystalline powder deforms under a high quasihydrostatic pressure as porous bodies from plastic material. Thus, it is shown that the effective pressure P for the consolidation of a powder billet of Al63Cu25Fei2 in the high-pressure apparatus is... 

Thus, it is shown that the behavior of the two-phase /+P material while high-temperature sintering under high quasihydrostatic pressure is determined by the quasicrystalline /-phase. 

Rapid solidification processes are successfully used for A1 alloys to form a dispersion particles of intermetallic phases, which resist coarsening and strengthen the alloys at elevated temperatures. It has recently been shown that metastable intermetallic phases with a quasicrystalline structure, mainly of the icosahedral type, can also be produced by rapid solidification [23], As distinct from a crystalline state, translational long-range order is absent in quasicrystals, but there is rotational symmetry with 5-, 8-, 10- or 12-fold axes, which is forbidden in crystalline materials. The absence of translational symmetry in all three orthogonal directions is characteristic of the icosahedral structure [24],... 

The objectives of this Workshop, to present and discuss new results in the development and processing of metallic materials with high structural efficiency and to establish new interactions and networks between the participants, were successfully met. A number of new developments were presented and discussed at this Workshop, including recent information on titanium alloys modified with relatively small amounts of B and Si to provide dramatic improvements in strength and stiffness, and new A1 alloys strengthened with quasicrystalline precipitates for good elevated temperature properties. In addition, a current extensive update on severe plastic deformation and on nanocrystalline metals for structural applications was provided. 

Determination of crystalline and amorphous states, determination of crystal anisotropy, defects and defect structures, characterization of quasicrystalline, microcrystalline, nanocrystalline and amorphous materials... 

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