a b s t r a c tWe present an experimental study of the kinematics of twist extrusion (TE) and show that TE has the following properties: (i) as in equal-channel angular pressing (ECAP), the mode of deformation in twist extrusion is simple shear. Unlike in ECAP, there are two shear planes; one of them is perpendicular and the other is parallel to the specimen axis. (ii) The following processes are present during twist extrusion: vortex-like flow with large strain gradient, stretching and mixing of metal particles. We argue that, due to these properties, TE opens possibilities for investigating and forming new microstructures. It has already been successfully used to obtain ultrafine-grained microstructures with good properties in Al, Cu and Ti alloys.
High purity Al (99.99%) was subjected to severe plastic deformation through twist extrusion at room temperature. Microstructures were examined for 1 pass and 4 passes on the cross section perpendicular to the longitudinal axis of billets using optical microscopy and electron back scatter diffraction analysis. It was shown that a vortex-like material flow was observed on the cross section and this became more intense with increasing number of the pressing. After one pass, subgrain structures with low angle grain boundaries were developed throughout the section but after 4 passes, the microstructure consisted of grains surrounded by high angle boundaries with fraction of $70% in the edge parts. The average grain size at the edge parts is refined to $1:6 mm.
Twist extrusion (TE) is one of the most popular techniques of severe plastic deformation, aiming at imparting to a material a tailored microstructure and the associated property improvement. The article provides a survey of the literature on the mechanics of TE and the effect it has on the structure, texture, and the attendant properties of various materials, including metals and alloys, powder materials, and polymers. Special emphasis is placed on vortex flow during TE and its hitherto unexplored potential for producing micro-and macrostructures that promise superior properties of the materials. In particular, the possibility of creating novel hybrid materials with chiral inner architecture is demonstrated. The survey is concluded by a presentation of examples of practical applications of TE.
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