High Strength and Ductility of Nanostructured Al Alloy 2024 Subjected to High Pressure Torsion

The structure and mechanical properties of Al-based alloy 2024 after high-pressure torsion (HPT) was investigated. Alloy 2024 with homogeneous structure and grain size about 70 nm was obtained using HPT at 6 GPa pressure and 5 turns of the anvils at room temperature. The nanostructured alloy possessed very high UTS (Ultimate tensile stress) above 1100 MPa at room temperature, and superplastic behaviour at temperatures over 300°С. The microhardness of the nanostructured alloy after superplastic deformation (1.5 GPa) was greater than that after the standard treatment of the coarse-grained alloy (1.2 GPa). The influence of HPT parameters and heat treatment on the structure and deformation behaviour of the alloy was studied. The opportunity of achieving a combination high strength and good ductility in metals and alloys opens perspectives for industrial applications, particularly, in micro-systems and for high-strength items with complex geometry which could be obtained by superplastic forming.

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High Strength and Ductility of Nanostructured Al Alloy 2024 Subjected to High Pressure Torsion

Solid State Phenomena - High Pressure Technology of Nanomaterials ◽

10.4028/3-908451-22-1.85 ◽

2006 ◽

pp. 85-90

Author(s):

D. Vorona ◽

Alfred V. Sharafutdinov ◽

Nikolay A. Krasilnikov

Keyword(s):

High Pressure ◽

High Pressure Torsion ◽

High Strength ◽

Al Alloy ◽

Strength And Ductility

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Processing of Aluminium Alloys by Severe Plastic Deformation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.519-521.45 ◽

2006 ◽

Vol 519-521 ◽

pp. 45-54 ◽

Cited By ~ 2

Author(s):

Terence G. Langdon

Keyword(s):

Plastic Deformation ◽

High Pressure ◽

Severe Plastic Deformation ◽

Elevated Temperatures ◽

High Pressure Torsion ◽

Simple Procedure ◽

Superplastic Forming ◽

High Strength ◽

Ultrafine Grain ◽

Grain Sizes

Processing through the application of severe plastic deformation (SPD) has become important over the last decade because it is now recognized that it provides a simple procedure for producing fully-dense bulk metals with grain sizes lying typically in the submicrometer range. There are two major procedures for SPD processing. First, equal-channel angular pressing (ECAP) refers to the repetitive pressing of a metal bar or rod through a die where the sample is constrained within a channel bent through an abrupt angle at, or close to, 90 degrees. Second, high-pressure torsion (HPT) refers to the procedure in which the sample, generally in the form of a thin disk, is subjected to a very high pressure and concurrent torsional straining. Both of these processes are capable of producing metallic alloys with ultrafine grain sizes and with a reasonable degree of homogeneity. Furthermore, the samples produced in this way may exhibit exceptional mechanical properties including high strength at ambient temperature through the Hall-Petch relationship and a potential superplastic forming capability at elevated temperatures. This paper reviews these two procedures and gives examples of the properties of aluminum alloys after SPD processing.

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Stress- and Strain Induced Phase Transformations in Pearlitic Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.539-543.4681 ◽

2007 ◽

Vol 539-543 ◽

pp. 4681-4686 ◽

Cited By ~ 11

Author(s):

Julia Ivanisenko ◽

Witold Łojkowski ◽

Hans Jorg Fecht

Keyword(s):

Plastic Deformation ◽

High Pressure ◽

Phase Transformations ◽

Room Temperature ◽

High Pressures ◽

High Pressure Torsion ◽

Carbon Steels ◽

Coarse Grained ◽

Cold Plastic Deformation ◽

Friction Forces

An overview of the mechanically driven phase transformations taking place in nanocrystalline pearlitic steels in conditions of the severe plastic deformation (SPD), i.e. combination of high pressure and strong shear strains will be given. Conditions of the discussed experiments (room temperature and moderate strain rates) exclude any thermal origin of the observed transformations. One of them is strain induced cementite decomposition, which is a well-documented phenomenon taking place at cold plastic deformation of pearlitic steels. We explain this process taking into account friction forces at the interface between the hard cementite and ferrite. Under the high pressures and stresses higher than the ferrite matrix yield stress, the later one behaves like a viscoelastic fluid. The friction at the precipitate/matrix interface leads to two effects. One is to induce high strains on the precipitates. This leads to shift of thermodynamic equilibrium towards dissolution of the cementite. The second is wear of the cementite phase due to friction at the ferrite/cementite interface and mechanically induced drag of carbon atoms by the ferrite. This had been recently confirmed in 3D AP experiments, which demonstrated that the process of cementite decomposition starts with depleting of carbides with carbon and formation of non-stoichiometric cementite. The existing theories of atom drag by moving dislocations (ballistic models) can be regarded as one of the many possible mechanism of wear discussed by the wear theory. In that respect the process can be called athermal, as temperature indirectly influences wear processes but is not their main cause. We observed also another strain driven transformation in nanocrystalline pearlitic steel during room temperature high pressure torsion. This is a stress induced α→γ transformation, which has never been observed at conventional deformation of coarse grained iron and carbon steels. This was concluded to have occurred due to a reverse martensitic transformation.

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GRAIN REFINEMENT AND MICROSTRUCTURE EVOLUTION IN ALUMINUM A2618 ALLOY BY HIGH-PRESSURE TORSION

Jurnal Teknologi ◽

10.11113/jt.v78.9163 ◽

2016 ◽

Vol 78 (6-9) ◽

Author(s):

Intan Fadhlina Mohamed ◽

Seungwon Lee ◽

Kaveh Edalati ◽

Zenji Horita ◽

Shahrum Abdullah ◽

...

Keyword(s):

Plastic Deformation ◽

High Pressure ◽

Grain Refinement ◽

Room Temperature ◽

Rotation Speed ◽

High Pressure Torsion ◽

Applied Pressure ◽

Saturation Level ◽

Microstructural Refinement ◽

Average Grain Size

This work presents a study related to the grain refinement of an aluminum A2618 alloy achieved by High-Pressure Torsion (HPT) known as a process of Severe Plastic Deformation (SPD). The HPT is conducted on disks of the alloy under an applied pressure of 6 GPa for 1 and 5 turns with a rotation speed of 1 rpm at room temperature. The HPT processing leads to microstructural refinement with an average grain size of ~250 nm at a saturation level after 5 turns. Gradual increases in hardness are observed from the beginning of straining up to a saturation level. This study thus suggests that hardening due to grain refinement is attained by the HPT processing of the A2618 alloy at room temperature.

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