Twinning induced nanostructure formation during cryo-deformation

M Klimova,G Salishchev,D Molodov,G Dyakonov,S Zherebtsov

doi:10.1088/1757-899x/63/1/012157

Abstract

In the present work the influence of cryo-rolling to a true strain ε=2.66 on twinning and formation of ultrafine-grained/nanostructure in commercial-purity titanium and Fe-0.3C- 23Mn-1.5Al TWIP steel was quantified using scanning and transmission electron microscopy. Different influence of twinning on the kinetics of microstructure refinement and nanostructure formation in titanium and steel was revealed. In titanium twin boundaries during deformation transform into arbitrary high-angle grain boundaries thereby promoting the microstructure refinement to a grain/subgrain size of 80 nm. In steel twinning has less pronounced influence on the microstructure refinement. However, very fine grains/subgrains with the size of 30-50 nm was observed in the microstructure after rolling at 77K to a true thickness strain of 2.66.

Highlights

According to the well-known definition [1] any SPD process is associated with a very high straining of a material via various deformation methods
In the hexagonal close packed (HCP) metals and some steels with low stacking-fault energy (SFE) a prompt microstructure refinement occurs by twinning due to a formation of a large number of high-angle boundaries in the very beginning of deformation [e.g. 3, 4]
The major conditions/causes for the deformation twinning in titanium and TWIP steel are quite different: low symmetry of HCP crystalline lattice in titanium and low stacking fault energy in steel [4, 11]

Summary

Introduction

According to the well-known definition [1] any SPD process is associated with a very high straining of a material via various deformation methods. The main attention of researchers is focused both on the way to attain a high level of strain and on the microstructure of severely deformed metallic materials. The grain microstructure of some metals and alloys refines quite readily even after relatively small strain. In the hexagonal close packed (HCP) metals and some steels with low stacking-fault energy (SFE) a prompt microstructure refinement occurs by twinning due to a formation of a large number of high-angle boundaries in the very beginning of deformation [e.g. 3, 4]. Twinning can be considered as a tool promoting formation of ultrafine-grained or nanostructure at a relatively small strain by utilizing the conventional metal-forming methods. The microstructure with a grain size between 100 and 200 nm could be obtained via sheet rolling at room temperature to a true strain of ε ≈ 2.66 [3]

Objectives

Results

Discussion

Conclusion