Deformation behavior of bimodal nanostructured 5083 Al alloys

Abstract

Cryomilled 5083 Al alloys blended with volume fractions of 15, 30, and 50 pct unmilled 5083 Al were produced by consolidation of a mixture of cryomilled 5083 Al and unmilled 5083 Al powders. A bimodal grain size was achieved in the as-extruded alloys in which nanostructured regions had a grain size of 200 nm and coarse-grained regions had a grain size of 1 m. Compression loading in the longitudinal direction resulted in elastic-perfectly plastic deformation behavior. An enhanced tensile elongation associated with the occurrence of a Lüders band was observed in the bimodal alloys. As the volume fraction of coarse grains was increased, tensile ductility increased and strength decreased. Enhanced tensile ductility was attributed to the occurrence of crack bridging as well as delamination between nanostructured and coarse-grained regions during plastic deformation.

The deformation and work hardening behaviour of a SPD processed Al-5Cu alloy

“…According to the model by Lavernia and collaborators [36,37], cracks follow a fast and intergranular path when running through the nanostructured grains, but are blunted and slowed down when they encounter a large and soft grain. The coarse grains in a bimodal grain structure are therefore an important reason to attain large uniform elongation in the 4P sample.…”

Mechanical Behavior of Cryomilled Ni Superalloy by Spark Plasma Sintering

“…[1] Of the UFG materials that exhibit considerable ductility, an inhomogeneous microstructure (bimodal grain size distribution) is frequently reported. [2,3] For example, in bimodal Al-Mg alloys fabricated via cryomilling, [4,5] a true strain of 6 to 8 pct in tension was obtained. The grain size distribution in this material indicated that the fine grain size is in the range of 100 to 300 nm, whereas the coarse grains centered around 1 lm.…”

Nanostructured Ti Consolidated via Spark Plasma Sintering

“…A similar approach was previously used for cryomilled materials, including Al, [15] Ni, [39] and Ti [13] alloys. A bimodal or multimodal structure can also be formed via thermomechanical treatments and again provide a high ductility.…”

“…Also in these studies, quasi-isostatic (QI) forging was used as a consolidation and secondary deformation method. Specifically, a multistep approach was adopted in this study and involved cryomilling, blending with micron-sized powders (to generate a multiscale microstructure), [15] hot vacuum degassing, and QI forging produced materials with a multimodal grain size distribution. In roomtemperature tensile tests, a YS of 840 MPa, a UTS of 902 MPa, and an elongation to failure value of 27.5 pct were measured for these samples.…”

“…The selection of a 70 pct cryomilled + 30 pct as-received mixture was motivated by numerous reports on improved ductility in bimodal and multimodal metals, [15,[34][35][36][37][38] as well as earlier experiments on QI-forged cryomilled Ni and Ti. [13,14,39,40] The blended powders were degassed in a closed stainless steel can under vacuum (~10 À3 Pa) at 623 K (350°C) to eliminate moisture and other volatile species using a Varian Turbo-V 70D (Varian Inc., Santa Clara, CA) turbo molecular pump equipped with a Terranova Model 934 vacuum gage controller (Duniway Inc., Mountain View, CA) and a tube furnace.…”