Microstructural Refinement under High Plastic Strain Rates during Hydrostatic Extrusion

Abstract

High strain rates have a similar influence to large deformations on the refinement of microstructure. In both cases, at large strains and high deformation rates, a strong tendency to form microbands is observed. It was found, that the width of the microbands is very sensitive to changes of the deformation parameters. It has been observed particularly, that in severely deformed materials, the width of the microbands is reduced to nanometric dimensions. Hydrostatic extrusion, which has been used in for the deformation of copper in the current work, strain rates exceeding 2 1 3.84 10 − ⋅ ε = × s were employed. In all the samples investigated, numerous microbands were found in the microstructure. The width of microbands varied from 20 to about 400 nm. Thus, the width of some of the microbands exhibited dimensions typical of nanometric materials. Additionally, a special feature was the appearance of large areas of subgrains with an average dimension of about 200 nm. These areas were identified as recrystallized dynamically, or post-dynamically. Large misorientations were found between the microbands and the surrounding “matrix’. Such misorientation facilitates the formation of high angle boundaries, which in turn contribute to the changes of microstructure and mechanical properties. The mechanism for the creation of high misorientation in the microband areas is probably different from that operating during the process of dynamic recrystalization. The results confirm the possibility of obtaining a nanometric structure at lower deformation, but at higher strain rates.

Deformation Microstructures in Metallic Materials after Severe Plastic Deformation by Rolling with Cyclic Movement of Rolls

“…Obtained results are in accordance with literature [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Enhanced mobility of dislocations in Al and Cu due to the lack of alloying elements to hinder the dislocation movement results in weakening of grain refinement.…”

“…The second group of non-ferrous materials, which play a key role in electric engineering are copper and copper alloys. In literature the effectiveness of SPD methods has been revealed for a pure Al [7][8][9][10][11][12][13], Al-Mg alloys [13,14], pure Cu [11,[13][14][15][16][17][18][19] and Cu-Fe [20] alloys. Recent works have demonstrated [21,22] that one of the method which can be used for SPD processing is rolling with cyclic movements of rolls (RCMR).…”

“…Over the last two decades, a number of techniques were adopted to processing metals and alloys to grain refinement to nanoand sub-micrometer scale. Nanograined and ultrafinegrained materials are interesting because they have better mechanical and physical properties than the materials with micrometer grained structure [5][6][7][8][9][10]. In the group of materials which are often processed by using severe plastic deformation (SPD) are pure aluminium and aluminium alloys, which play important role in automotive and aerospace engineering due to their good corrosion resistance, good machinability and weldability.…”

The effect of strain rate on the evolution of microstructure in aluminium alloys

“…Observations of the structure of the highly deformed materials show that these elements of the microstructure strongly contribute to the formation of the nanograins, which form inside the mutually crossing microbands (Richert, 2006). Inside bands that form in the conditions of the high strain rate, the nucleation of the nanograins was also observed (Kurzydłowski et al, 2006). The presented data indicate that the increase of the rate of the deformation is enough to create the similar effects as in the range of enormous strains exerted by SPD.…”

The effect of deformation and strain rate on the microstructure refinement of the aluminium alloys (AlCu4Zr0.5 and AlZn6Mg3CuZr)

“…The data given in Refs. [5,6] indicate that the increase in the rate of deformation itself produces similar effects as enormous strains exerted in SPD methods.…”