Dispersion limit upon equal-channel angular pressing. Temperature effect

“…ECAP is an effective technology to form a UFG microstructure in aluminum alloys [98,99,107,108]. A distinct ECAP advantage is an opportunity to form a large fraction of high-angle grain boundaries (HAGB) in a fine-grained material [99,107,108]. HAGBs in the microstructure of a fine-grained material help to launch the grain-boundary sliding (GBS) effect, which, under optimal temperature-rate deformation conditions, is the main mechanism of low-temperature superplastic deformation of fine-grained materials [101,109].…”

Section: Discussionmentioning

confidence: 99%

Effect of Sc, Hf, and Yb Additions on Superplasticity of a Fine-grained Al-0.4%Zr Alloy

Нохрин¹,

Gryaznov²,

Shotin³

et al. 2022

Preprint

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The research was undertaken to study the way deformation behaves in ultrafine-grained (UFG) conducting Al-Zr alloys doped with Sc, Hf, and Yb. All in all, 8 alloys were studied with zirconium partially replaced by Sc, Hf, and/or Yb. Doping elements (X = Zr, Sc, Hf, Yb) in the alloys total 0.4 wt.%. The choice of doping elements is conditioned by possible precipitation of Al3X particles with L12 structure while annealing these alloys. Such particles provide higher thermal stability of a nonequilibrium UFG microstructure. Initial coarse-grained samples were obtained by induction casting. The UFG microstructure in the alloys was formed by Equal Channel Angular Pressing (ECAP) at 225°C. Superplasticity tests were carried out at temperatures ranging from 300 to 500 °C and strain rates varying between 3.310-4 and 3.310-1 s-1. The highest values of elongation to failure are observed in Sc-doped alloys. A UFG Al-0.2%Zr-0.1%Sc-0.1%Hf alloy has maximum ductility: at 450 °C and a strain rate of 3.310-3 s-1, relative elongation to failure reaches 765%. At the onset of superplasticity, stress–strain curves are characterized by a stage of homogeneous strain and a long stage of localized plastic flow. The dependence of homogeneous strain (eq) on test temperature in UFG Sc-doped alloys is increasing uniformly, which is not the case for other UFG alloys with eq(T) dependence peaking at 350-400 оС. Strain rate sensitivity coefficient of flow stress m is small and does not exceed 0.26-0.3 at 400-500 °C. In UFG alloys containing no scandium, m coefficient is observed to go down to 0.12-0.18 at 500 оС. It has been suggested that lower m values are driven by intensive grain growth and pore formation in large Al3X particles, which develop specifically at the ingot crystallization stage.

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“…[3][4][5] An alternative approach proposed by several experimental investigations [6][7][8][9][10][11] has indicated that green or sintered powders can be processed by ECAP, in which it is desired to retain the ultrafine structure of the powder in the consolidated extrudate. The hypothesis is that the intense plastic shear involved with ECAP would be the main mechanism for the consolidation and the densification of the green and sintered powders.…”

Section: Introductionmentioning

confidence: 99%

Equal Channel Angular Pressing of Canned 2124-Al Compacts: Processing, Experiments, and Modeling

Elkhodary

Salem

Zikry

2008

Metall Mater Trans A

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A detailed experimental and computational investigation of the influence of equal channel angular pressing (ECAP) on the microstructure and properties of precompacted 2124-Al nanostructured powder, canned in copper, was conducted. Measurements and observations were obtained by densitometry and optical, scanning, and transmission electron microscopy. Based on experimental observations, it was found that hot compacts subjected to a single ECAP pass had significant microstructural refinement and subgrain formation, and significant density changes were not attained. Green compacts, on the other hand, were observed to lose coherency under ECAP. Three-dimensional finite element modeling of the ECAP process was also conducted to further elucidate the evolution of the extrusion process, and to understand how it affects plastic strains, porosity, and thermal distributions.

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Dispersion limit upon equal-channel angular pressing. Temperature effect

Cited by 10 publications

References 4 publications

Effect of the simultaneous enhancement in strength and corrosion resistance of microcrystalline titanium alloys

Effect of the simultaneous enhancement in strength and corrosion resistance of microcrystalline titanium alloys

Effect of Sc, Hf, and Yb Additions on Superplasticity of a Fine-grained Al-0.4%Zr Alloy

Equal Channel Angular Pressing of Canned 2124-Al Compacts: Processing, Experiments, and Modeling

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