Bulk nanostructured materials from severe plastic deformation

Principles of equal-channel angular pressing as a processing tool for grain refinement

https://material.karlov.mff.cuni.cz/people/janecek/studenti/FyzMetNano/Estrin_AM61_2013_782.pdf

Extreme grain refinement by severe plastic deformation: A wealth of challenging science

This overview highlights very recent achievements and new trends in one of the most active and developing fields in modern materials science: the production of bulk ultrafine-grained (UFG) materials using severe plastic deformation (SPD). The article also summarizes the chronology of early work in SPD processing and presents clear and definitive descriptions of the terminology currently in use in this research area. Special attention is given to the principles of the various SPD processing techniques as well as the major structural features and unique properties of bulk UFG materials that underlie their prospects for widespread practical utilization.

https://link.springer.com/content/pdf/10.1007%2Fs11837-006-0213-7.pdf

Producing bulk ultrafine-grained materials by severe plastic deformation

The process of grain refinement in equal-channel angular pressing

It is shown that simple shear can be considered a “near ideal” deformation method for structure and texture formation in metal-working. Equal channel angular extrusion (ECAE) is a special industrial process employed to realize this method. In comparison with traditional metal-working operations, this process has a number of advantages; the most important is that extra-large, strictly uniform and unidirectional deformations can be produced under relatively low pressure and load for massive products. The unusual effects that are observed in both the structure and physical-mechanical properties of various metals and alloys suggest many new applications of the simple shear method in materials synthesis and processing.

Materials processing by simple shear

A special deformation technique, equal channel angular extrusion, (ECAE) to control materials structure, texture and physico-mechanical properties is described in detail. The paper presents a continual analysis of stress, strain, shear planes, steady and localized flow, multipass processing which define microstructural effects and are critical for attained results. Links between macromechanics of simple shear and grain refinement are outlined.

Equal channel angular extrusion: from macromechanics to structure formation

A technique invented in the former Soviet Union and recently introduced in the United States, called equal channel angular extrusion (ECAE), produces intense and uniform deformation by simple shear and is applied to 25 × 25 × 152-mm billets of Cu 101 and Al 3003. Microcrystalline structures with a grain size of 0.2 to 0.4 µm are created during room-temperature multipass ECAE deformation for true strains lying in the range e=2.31 to 9.24. Evidence shows that intense simple shear deformation promotes dynamic or continuous recrystallization by subgrain rotation. The effects of the number of extrusion passes and deformation route for Cu 101, and the deformation route after four passes for Al 3003, are studied. Increasing the number of ECAE passes in Cu 101 causes strength to reach saturation and grain refinement stabilization after four passes (true strain of 4.68), and subgrain misorientation to increase as the number of passes increases. For multipass ECAE with billet orientation constant (route A) or rotated 90 deg between all passes (route B), two levels of structures are created inside the original grains: shear bands (first level) and very fine subgrains (second level) within the shear bands. For a billet rotation of 180 deg between passes (route C), an unusual event is observed. At each even numbered pass, shear bands nearly disappear and only subgrains are present inside the original grains. Route B gives the highest strength, whereas route C produces a more equiaxed and stable microstructure. Subsequent static recrystallization increases the average grain size to 5 to 10 µm.

Microstructure and properties of copper and aluminum alloy 3003 heavily worked by equal channel angular extrusion

Engineering aspects of ECAE as a material processing technology is considered in details. Optimization of ECAE is provided by control of contact friction, the channel geometry, strain/strain rate, billet shape, punch/tool pressures. That also includes the optimal choice of processing route and number of passes for the effective solution of certain problems. Different concepts of tool design are analyzed and possible directions of process commercialization are discussed.

Engineering and commercialization of equal channel angular extrusion (ECAE)

Submicrometer-grained (SMG) microstructures are produced in an Al–Mg–Si alloy (6061) by subjecting peak-aged and overaged billets of the alloy to intense plastic strain by a process known as equal channel angular extrusion. Two types of refined structure are distinguished by optical and transmission electron microscopy. One structure is created through intense deformation (four extrusion passes through a 90° die, e = 4.62) by dynamic rotational recrystallization and is a well-formed grain (fragmented) structure with a mean fragment or grain size of 0.2–0.4 μm. The other structure is produced by post-extrusion annealing through static migration recrystallization, resulting in a grain size of 5–15 μm. Intense deformation of peak-aged material to a true strain e of 4.62 (four passes) produces a strong, ductile, uniform, fine, and high angle grain boundary microstructure with increased stability against static recrystallization as compared to the overaged material.

Vladimir Segal

Papers

Materials processing by simple shear

Equal channel angular extrusion: from macromechanics to structure formation

Microstructure and properties of copper and aluminum alloy 3003 heavily worked by equal channel angular extrusion

Engineering and commercialization of equal channel angular extrusion (ECAE)

Development of a submicrometer-grained microstructure in aluminum 6061 using equal channel angular extrusion