Structure stability, Laves phases

A systematic analysis of structure and stability of binary and ternary Laves phases, or Friauf-Laves phases, has been performed by Stein et al. (2004, 2005). By reviewing a large number of experimentally determined phase diagrams with Laves phases, a number of general conclusions have been obtained. These may be summarized in the following points ... 

The appearance of a perpendicular anisotropy in the mixed state of both amorphous and crystalline structure was reported by Miyazaki et al. (1997) for (Tbo.3Dyo.7)0.33Feo.67 films fabricated above 673 K (400°C) (see fig. 32). The thermal stability and the reproducibility of those films were studied also. For films prepared with substrate temperatures above 673 K (400°C), the magnetostriction changes remarkably after 3 months. This is due to ageing effects, related to the formation of the Laves phase (Tb,Dy)Fe2. 

The partial substitution of the transition element M in MjSi by a second transition metal M leads to ternary silicides of approximate composition MM Si corresponding to (M,M )2Si. Such ternaries are primarily the Si-containing E phases and V phases (Jeitschko etal., 1969 Jeitschko, 1970) and the ternary Si-containing Laves phases (Bardos etal., 1961), which were discussed in Sec. 8, as well as many other phases, which all differ by composition and crystal structure (Nowotny, 1972 a). This is exemplified by the Fe-Nb-Si system with the ternary silicides E, V, Xj, Xj, Xj and the Laves phase Nb(Fe,Si)2 with up to 25 at.% Si (Raghavan, 1987), or the Co-Nb-Si system with the ternary silicides E, T, v, Ti, v i, and the ternary Laves phase Nb(Co,Si)2 with Si contents between about 10 and 20 at.% (Argent, 1984). Finally, it is noted that other phases - in particular a phases and A13 Mn-base phases - dissolve large amounts of Si by which these phases are stabilized (Gupta et al., 1960 Bardos et al., 1966). 

The present monograph was first written as a chapter for Volume 8 of the series Materials Sdence and Technology A Comprehensive Treatment , edited by Robert W. Cahn, Peter Haasen, and Edward J. Kramer (Volume Editor Dr. Karl Heinz Matucha). Its aim is to give an overview of intermetallics, which is both detailed and comprehensive and which includes the fundamentals as well as applications. The result is an extended, critical review of the whole field of intermetallics with an emphasis on those intermetallic phases which have already been applied as functional or structural materials or which are currently the subject of materials developments. A historical introduction and a discussion of the relationship between atomic bonding, crystal structure, phase stability and properties is followed by a discussion of the major classes of intermetallics. The titanium aluminides, nickel aluminides, iron aluminides, copper phases, A15 phases. Laves phases, beryllides, rare earth phases, and siliddes are reviewed. In particular, the crystal structures, phase diagrams, and physical properties as well as the mechanical and corrosion behavior are treated. The state of developments as well as prospects and problems are discussed in view of present and future applications. The publisher has decided to publish the review as a separate monograph in order to make it accessible to a wider audience. 

Zhu] Zhu, J.H., Liaw, P.K., Liu, C.T., Effect of Electron Concentration on the Phase Stability of NbCr2-based Laves Phase Alloys , Mater. Sci. Eng. A, 239-240, 260-264 (1997) (Phase Relations, Review, Electronic Structure, 30)... 

Ste] Stein, R, Palm, M., Sauthoff, G., Structure and Stability of Laves Phases Part II - Structure Type Variations in Binary and Ternary Systems , Intermetallics, 13, 1056-1074 (2005) (Review, 249)... 

Laves P (1967) Space limitation on the geometry of the crystal stmctures of metals and intermetallic compounds. Phase transition in metals alloys. In Rudman PS, Stringer J, Jaffee RI (eds) Phase stability in metals and alloys. McGraw-HiU, New York Serezhkin VH, Mikhailov YuN, Buslaev YuA (1997) The method of intersecting spheres for determination of coordination numbers of atoms in crystal structures. Russ J Inotg Chem 42 1871-1910... 

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