Superb cryogenic strength of equiatomic CrCoNi derived from gradient hierarchical microstructure

doi:10.1016/j.jmst.2018.12.002

材料科学与技术 ›› 2019, Vol. 35 ›› Issue (6): 957-961.DOI: 10.1016/j.jmst.2018.12.002

• • 下一篇

收稿日期:2018-07-01 修回日期:2018-08-13 接受日期:2018-08-27 出版日期:2019-06-20 发布日期:2019-06-19

Superb cryogenic strength of equiatomic CrCoNi derived from gradient hierarchical microstructure

Bin Gan^a, Jeffrey M. Wheeler^b, Zhongnan Bi^c^*(), Lin Liu^a, Jun Zhang^a, Hengzhi Fu^a

^aSchool of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, 710072, China
^bLaboratory for Nanometallurgy, Department of Materials Science, ETH Zürich, Vladimir-Prelog-Weg 5, Zürich, CH-8093, Switzerland
^cCentral Iron and Steel Research Institute, No. 76 Xueyuannan Road, Beijing, 100081, China

Received:2018-07-01 Revised:2018-08-13 Accepted:2018-08-27 Online:2019-06-20 Published:2019-06-19
Contact: Bi Zhongnan
About author:
¹The authors contributed equally to this work.

摘要/Abstract

Abstract:

This work demonstrates the effectiveness of a cryogenic torsional pre-straining for significantly improving the cryogenic strength of an equiatomic CrCoNi alloy. The origin of this phenomenon is elucidated by various microstructural characterization tools, which shows that the sequential torsion and tension tests lead to the observed hierarchical microstructure through the activation of different twinning systems and stacking faults. This gives rise to the significant increase in the yield strength from 600 MPa to 1215 MPa, while the fracture strain changes from 68% to 48%. The current study reveals that the incorporation of nanotwins architecture by shear deformation may constitute a viable strategy to tune the mechanical performance and, in particular, to dramatically increase the strength while keeping a good ductility.

Key words: Medium entropy alloy, CrCoNi, Torsion, Hierarchical microstructure, Strengthening

. [J]. 材料科学与技术, 2019, 35(6): 957-961.

Bin Gan, Jeffrey M. Wheeler, Zhongnan Bi, Lin Liu, Jun Zhang, Hengzhi Fu. Superb cryogenic strength of equiatomic CrCoNi derived from gradient hierarchical microstructure[J]. J. Mater. Sci. Technol., 2019, 35(6): 957-961.

图/表 5

Fig. 1. (a) Orientation imaging microscopy map generated by EBSD showing grain structure of the center of CrCoNi MEA tensile rod, (b) EBSD map of the edge of wrought CrCoNi MEA tensile rod after a pre-torsion treatment.

Fig. 2. (a)-(d), Backscatter Electron Images of the sample with a pre-torsion treatment from the center to the edge, (e) picture of the pre-torsioned sample with a diameter of 9 mm, (f) hardness gradient in the radial direction of sample after the pre-torsion.

Fig. 3. Engineering stress-engineering strain curves of CrCoNi alloys with and without the pre-torsion treatments in the liquid N2 environments as well as that of the recrystallized CrCoNi alloys tested at room temperature.

Fig. 4. (a) SEM micrograph of the microstructure of the edge of CrCoNi MEA with pre-torsion, (b) SEM image of the edge of CrCoNi MEA after torsion and tension tests.

Fig. 5. (a) TEM bright field image of the tensile bar with a beam direction of [111], showing the intersections of slip bands with an orientation of <011 > , (b) TEM bright field image showing the presence of stacking faults, (c) TEM bright field image of the slip bands with a beam direction of [001], (d) TEM dark field image showing the high dislocations density in the slip bands, (e) a high resolution image of the region with a yellow square, (f) TEM bright field of the region containing a high density of nanotwins with a beam direction of [011], (g) the corresponding diffraction pattern showing the twinning spots, (h) a high resolution image showing the presence of nanotwins.

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Superb cryogenic strength of equiatomic CrCoNi derived from gradient hierarchical microstructure

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