Bulk nanostructured materials from severe plastic deformation

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

Equal-channel angular (ECA) pressing is a processing method for introducing an ultra-fine grain size into a material. In practice, it is a procedure that may be used to achieve high total strains by subjecting a sample to repetitive pressings. There is experimental evidence showing that the nature of the microstructural evolution in ECA pressing depends upon whether the sample is rotated between each passage through the die. This paper examines the shearing characteristics associated with ECA pressing for six different processing routes and reaches conclusions concerning the optimum processing procedure and the development of texture.

The shearing characteristics associated with equal-channel angular pressing

Two of the key parameters that are useful for understanding the deformation kinetics in metals with ultrafine grain (UFG) and/or nanocrystalline (nc) microstructure are the strain rate sensitivity (SRS) of the flow stress and the flow stress activation volume. In this paper, we present experimental results from our in-house tests on UFG Cu, Fe and Ta, along with those available in literature, regarding the behavior of SRS and activation volume of UFG/nc metals with face-centered cubic (fcc) and body-centered cubic (bcc) structures. The UFG metals were produced via severe plastic deformation (SPD), and confirmed using transmission electron microscopy. Our own results, as well as those in the literature, indicate that the SRS of the UFG/nc fcc metals is elevated, whereas that of UFG/nc bcc metals is much reduced compared to their coarse-grained counterparts. These trends appear to hold independent of the processing routes used to refine the grain size and of the testing method employed. The activation volumes in UFG fcc and bcc metals also exhibit different behavior. We present discussions to explain the observed trends. The implications of these findings for plastic instability are also discussed for the two lattice structures.

Effect of nanocrystalline and ultrafine grain sizes on the strain rate sensitivity and activation volume: fcc versus bcc metals

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

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.

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

A material may include grains of sizes such that at least 99% of a measured area contains grains that exhibit grain areas less than 10 times an area of a mean grain size of the measured area. As examples, at least 99% of the measured area may contain grains with grain areas less than 8, 6, or 3 times the area of the mean grain size. The grains may also have a mean grain size of less than 3 times a minimum statically recrystallized grain size, for example, a mean grain size of less than about 50 microns, 10 microns, or 1 micron. The material may be comprised by a sputtering target and a thin film may be deposited on a substrate from such a sputtering target. A micro-arc reduction method may include sputtering a film from a sputtering target comprising grains of sizes as described. A sputtering target forming method may include deforming a sputtering material. After the deforming, the sputtering material may be shaped into at least a portion of a sputtering target. The sputtering target may include grains of sizes as described. Also, the deforming may induce a strain level corresponding to e of at least about 4. Further, the deforming may include equal channel angular extrusion.

Fine grain size material, sputtering target, methods of forming, and micro-arc reduction method

The invention includes a method of forming an aluminum-comprising physical vapor deposition target. An aluminum-comprising mass is deformed by equal channel angular extrusion. The mass is at least 99.99% aluminum and further comprises less than or equal to about 1,000 ppm of one or more dopant materials comprising elements selected from the group consisting of Ac, Ag, As, B, Ba, Be, Bi, C, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, In, Ir, La, Lu, Mg, Mn, Mo, N, Nb, Nd, Ni, O, Os, P, Pb, Pd, Pm, Po, Pr, Pt, Pu, Ra, Rf, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Ti, Tl, Tm, V, W, Y, Yb, Zn and Zr. After the aluminum-comprising mass is deformed, the mass is shaped into at least a portion of a sputtering target. The invention also encompasses a physical vapor deposition target consisting essentially of aluminum and less than or equal to 1,000 ppm of one or more dopant materials comprising elements selected from the group consisting of Ac, Ag, As, B, Ba, Be, Bi, C, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, In, Ir, La, Lu, Mg, Mn, Mo, N, Nb, Nd, Ni, O, Os, P, Pb, Pd, Pm, Po, Pr, Pt, Pu, Ra, Rf, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Ti, Tl, Tm, V, W, Y, Yb, Zn and Zr. Additionally, the invention encompasses thin films.

Methods of forming aluminum-comprising physical vapor deposition targets; sputtered films; and target constructions

Described is a high quality sputtering target and method of manufacture which involves application of equal channel angular extrusion.

Stephane Ferrasse

Papers

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

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

Fine grain size material, sputtering target, methods of forming, and micro-arc reduction method

Methods of forming aluminum-comprising physical vapor deposition targets; sputtered films; and target constructions

Methods of fabricating articles and sputtering targets