The effect of cryogenic temperature and change in deformation mode on the limiting grain size in a severely deformed dilute aluminium alloy

Abstract

With the aim of investigating the factors that limit the production of true nanograined materials by cryogenic severe deformation, the grain structures formed in an Al-0.1%Mg alloy have been studied in plane strain compression at temperatures down to 77 K, following prior severe plastic deformation (SPD) by equal channel angular extrusion. Changing the deformation mode alone had little effect on increasing the rate of grain refinement. At the minimum cryogenic temperature (77 K) the samples still contained $30% low angle boundaries and a nanoscale high-angle boundary (HAB) spacing was only obtained in one dimension. At high strains a steady-state minimum HAB spacing was approached, irrespective of the temperature, where the rate of grain refinement stagnated. It is shown that the minimum grain size achievable in SPD is limited by a balance between the rate of compression of the HAB spacing and dynamic grain coarsening. At low temperatures this is controlled by abnormally high boundary migration rates, which are difficult to explain with existing theories of grain boundary mobility.

Microstructural response of pure copper to cryogenic rolling

“…An analysis of the literature suggests that these materials behave in a distinctly different way under cryogenic deformation conditions. For example, according to Huang and Prangnell [4], one of the key mechanisms governing grain-structure evolution in pure aluminum at cryogenic temperatures is the geometrical effect of strain per se. In other words, grains change their shape in proportion to the imposed strain, and no noticeable gross grain fragmentation/subdivision is observed.…”

“…in the cryogenic range. This approach, known as "cryogenic deformation", has recently been proposed as a means of producing bulk NC materials [4][5][6][7][8][9][10].…”

Effect of Cold Rolling on as–ECAP Interstitial Free Steel

“…[1À10] Reports indicate that irrespective of the material or SPD processing regime, a saturation in the rate of grain refinement is approached near a von Mises strain (e vM ) of 6-8 [2,4,11À15] and is ascribed to processes related to dynamic recovery. [6,11,12,16] Consequently a steady-state grain size is attained when the high-angle grain boundary (HAGB) area fraction saturates at 60 to 70 pct and its spacing converges with the low-angle subgrain boundary (LAGB) spacing. In commercially pure as-ECAP Cu, [2,3] Ni [17] and dilute Al-alloys, [5] a limit is approached when grain sizes of~0.2, 0.35, and 0.5 lm, respectively, are reached at e vM = 6 to 8.…”

Use of Local Electrochemical Methods (SECM, EC-STM) and AFM to Differentiate Microstructural Effects (EBSD) on Very Pure Copper

“…grain size for the STM field of view was of great importance. Cryogenic deformation, previously proposed to produce microcrystalline or nanocrystalline materials [23,24], was used. The samples were prepared by cryogenic rolling after cooling the sample with liquid nitrogen.…”