Experimental parameters influencing grain refinement and microstructural evolution during high-pressure torsion

Supercooled liquids with enhanced orientational order

“…Further isothermal measurements were performed on glycerol films of different thicknesses (9,15,18,26,30,55, 89 nm): the temperature of the IDE was varied in the same range as above, but in steps of 5 K. The sample was held at each annealing temperature for 2 h. The conversion rate into the OL phase, v, was estimated by fitting isothermal scans with linear decays v ¼ Dl/(t À t 0 ), where Dl is the fraction of transformed film, and t 0 indicates the onset of measurement. The value of Dl is obtained from the time evolution of the dielectric strength under the assumption that De is the sum of the contribution of the two liquid phases averaged over their volume fractions according to We ruled out the possibility that the larger values of De and of t observed in the medium-range crystalline order phase are actually induced by the presence of water or other contamination in the films.…”

“…An enhanced degree of topological order may be achieved via structural rearrangements, either by annealing below the glass transition temperature (physical aging) 17 or pressurizing 18 , which permits the nucleation of MRO regions in proximity to the quasi-crystalline clusters and the consecutive propagation of a similarly ordered structure. For some metallic glasses, this approach has allowed access to smaller, pre-existing crystalline structures, otherwise undetectable by the aforementioned experimental techniques because the structure factor of an amorphous phase containing topological order is virtually undistinguishable from the structure factor of a glass where molecules are randomly distributed 19 .…”

The microstructural characteristics of ultrafine-grained nickel

“…In practice, these treatments have the disadvantage that they are specific to any selected alloy and new treatments must be developed for each separate alloy. An alternative possibility is to attain a UFG structure through the use of a processing technique involving the application of severe plastic deformation (SPD): examples of SPD processing include equal-channel angular pressing (ECAP) [1][2][3], high-pressure torsion (HPT) [3][4][5], accumulative rollbonding (ARB) [6][7][8], friction stir processing (FSP) [9][10][11] or combinations of these techniques such as ARB followed by FSP [12] or ECAP followed by HPT [13][14][15]. An important advantage of SPD processing is that the same procedure may be used to introduce UFG structures into a wide range of metallic alloys.…”

Microstructural evolution and superplasticity in an Mg–Gd–Y–Zr alloy after processing by different SPD techniques

“…A comparison of the grain sizes obtained by ECAP and HPT is given in Table 1 [7][8][9] for some Cu and Al alloys and it is readily apparent that the grain sizes produced by HPT are much smaller than for ECAP. This difference is due primarily to the much higher strains attained in HPT processing where the ability to achieve smaller grain sizes in HPT was demonstrated in early experiments [10,11] and, in addition, it was shown more recently that, by comparison with ECAP, HPT produces a higher fraction of grain boundaries having high angles of misorientation [12].…”