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Field-ion microscopy and molecular dynamics simulation were used for the characterization of the translation states at special grain boundaries in tungsten. It is revealed that rigid-body displacement had the component of displacement parallel to the [110] direction equal to 0 or 1 interplanar spacing. Full vectors of lateral shifts are described by broad statistical distribution. The mathematical simulation revealed two mirror-symmetry-breaking lateral translations along the $[{\bar{2}21}]$ direction of the Σ9 grain boundary corresponding to different atomic structures. It is shown that the partial disconnection with the $(a/18)[{\bar{2}21}]$ Burgers vector can be considered as the elemental carriers of grain-boundary polymorphic transformation. [ABSTRACT FROM AUTHOR]

The structure and microhardness of single crystals of nickel–tungsten alloys containing 25–36 wt % W are investigated. The temperature gradient at the crystallization front and the velocity of the crystallization front are the variable parameters of directional crystallization. It is found that, when the velocity of the crystallization front is 4 mm/min, the morphology of the cellular structure of the single crystals grown from nickel–tungsten alloys changes from square cells to hexagonal cells at a tungsten content of greater than or equal to 31 wt %. As the velocity of the crystallization front increases to 10 mm/min, no morphological transition occurs. It is shown that impurities play an important role in the formation of a cellular structure with cells of different types. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]