Predicting grain refinement by cold severe plastic deformation in alloys using volume averaged dislocation generation

Abstract

The grain refinement during severe plastic deformation (SPD) is predicted using volume averaged amount of dislocations generated. The model incorporates a new expansion of a model for hardening in the parabolic hardening regime, in which the work hardening depends on the effective dislocation free path related to the presence of non shearable particles and solute-solute nearest neighbour interactions.These two mechanisms give rise to dislocation multiplication in the form of generation of geometrically necessary dislocations and dislocations induced by local bond energies. The model predicts the volume averaged amount of dislocations generated and considers that they distribute to create cell walls and move to existing cell walls/grain boundaries where they increase in the grain boundary misorientation. The model predicts grain sizes of Al alloys subjected to SPD over 2 orders of magnitude. The model correctly predicts the considerable influence of Mg content and content of nonshearable particles on the grain refinement during SPD.

Evolution of microstructure and mechanical properties of an as-cast Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy processed by high pressure torsion

“…These 3 mm disks were mechanically ground to ~50 μm in thickness and further ion-milled by a Gatan plasma ion polisher with an incidence angle of 15 o . The average grain sizes of HPT-processed samples were determined from TEM images using the modified line intercept method [18], and the grain size D was taken as D=1.455 ̅ , where ̅ is the average line intercept [19,20].…”

Al–Mg–Cu based alloys and pure Al processed by high pressure torsion: The influence of alloying additions on strengthening

“…The grain size of pure (≥99.98%) Ni deformed by HPT (P=9GPa, N=5) increased from 200nm in the centre ( eq ε ≅ 4.2) to 400nm at the edges ( eq ε ≅ 5.8) [7], and other studies using 0.3mm thick disks showed finer grain sizes of 200nm (P=7GPa, N=5) [36] and 260nm (P=6GPa, N=5) [6] at the periphery (equivalent strain of about 7); and for CP Ti Grade 4 subjected to HPT (P=6, N=10), the grain size is about 160nm [37]. All of the above mentioned grain sizes were recalculated by the method described in [38] and these pure metals attained a much finer grain size than high purity Al or our HPT processed Al-1050 alloy.…”

Hardening of pure metals by high-pressure torsion: A physically based model employing volume-averaged defect evolutions

“…To fully exploit the capabilities of SPD we need quantitative models that are able to predict the microstructure development during the process and predict resulting mechanical properties based on processing and materials parameters [19,25,26,27,28,29].…”