Atomistic studies of <110] screw dislocation core structures and glide in γ-TiAl

The core structure of <110] superdislocations in L10 TiAl was investigated with a view to clarifying their dissociation abilities and the mechanisms by which they may become sessile by self-locking. A detailed knowledge of the fine structure of dislocations is essential in analysing the origin of the various deformation features. Atomistic simulation of the core structure and glide of the screw <110] superdislocation was carried out using a bond order potential for ?-TiAl. The core structure of the screw <110] superdislocation was examined, starting with initial unrelaxed configurations corresponding to various dislocation dissociations discussed in the literature. The superdislocation was found to possess in the screw orientation either planar (glissile) or non-planar (sessile) core structures. The response of the core configurations to externally applied shear stress was studied. Some implications were considered of the dissociated configurations and their response to externally applied stress on dislocation dynamics, including the issue of dislocation decomposition, the mechanism of locking and the orientation dependence of the dislocation substructure observed in single-phase ?-TiAl. An unexpectedly rich and complex set of candidate core structures, both planar and non-planar, was found, the cores of which may transform under applied stress with consequent violation of Schmid's law.

Atomistic studies of interactions between the dominant lattice dislocations and γ/γ-lamellar boundaries in lamellar γ-TiAl

This paper reports on atomistic simulations of the interactions between the dominant lattice dislocations in ?-TiAl (<1 0 1] superdislocations) with all three kinds of ?/?-lamellar boundaries in polysynthetically twinned (PST) TiAl. The purpose of this study is to clarify the early stage of lamellar boundary controlled plastic deformation in PST TiAl. The interatomic interactions in our simulations are described by a bond order potential for L10-TiAl which provides a proper quantum mechanical description of the bonding. We are interested in the dislocation core geometries that the lattice produces in proximity to lamellar boundaries and the way in which these cores are affected by the elastic and atomistic effects of dislocation-lamellar boundary interaction. We study the way in which the interfaces affect the activation of ordinary dislocation and superdislocation slip inside the ?-lamellae and transfer of plastic deformation across lamellar boundaries. We find three new phenomena in the atomic-scale plasticity of PST TiAl, particularly due to elastic and atomic mismatch associated with the 60° and 120° ?/?-interfaces: (i) two new roles of the ?/?-interfaces, i.e. decomposition of superdislocations within 120° and 60° interfaces and subsequent detachment of a single ordinary dislocation and (ii) blocking of ordinary dislocations by 60° and 120° interfaces resulting in the emission of a twinning dislocation.

Reading the Irishwoman: Studies in Cultural Encounter and Exchange, 1714-1960

In 1700 few Irishwomen were literate. Most lived in a rural environment, rarely encountered a book or a play or ventured much beyond their own domestic space. By 1960 literacy was universal, all Irishwomen attended primary school, had access to a variety of books, magazines, newspapers and other forms of popular media and the wider world was now part of their every-day life. This study seeks to examine the cultural encounters and exchanges inherent in this transformation. It analyses reading and popular and consumer culture as sites of negotiation of gender roles. This is not an exhaustive treatment of the theme but focusses on three key points of cultural encounter: the Enlightenment, emigration and modernism. The writings and intellectual discourse generated by the Enlightenment was one of the most influential forces shaping western society. It set the agenda for scientific, political and social thought for the eighteenth and nineteenth centuries. The migration of peoples to north America was another key historical marker in the development of the modern world. Emigration altered and shaped American society as well as the lives of those who remained behind. By the twentieth century, aesthetic modernism suspicious of enlightenment rationalism and determined to produce new cultural forms developed in a complex relationship with the forces of industrialisation, urbanisation and social change. This study analyses the impact of these three key forces in Western culture on changing roles and perceptions of Irish women from 1700 to 1960.