Theory of transformation-mediated twinning

Song Lu; Xun Sun; Yanzhong Tian; Xianghai An; Wei Li; Yujie Chen; Hualei Zhang; Levente Vitos

doi:10.1093/pnasnexus/pgac282

Theory of transformation-mediated twinning

PNAS Nexus. 2022 Dec 7;2(1):pgac282. doi: 10.1093/pnasnexus/pgac282. eCollection 2023 Jan.

Authors

Song Lu¹, Xun Sun^{1

2}, Yanzhong Tian³, Xianghai An⁴, Wei Li¹, Yujie Chen^{4

5}, Hualei Zhang², Levente Vitos^{1

6

7}

Affiliations

¹ Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Brinellvägen 23, Stockholm, SE-10044, Sweden.
² State Key Laboratory for Mechanical Behavior of Materials, Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China.
³ Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 10819, China.
⁴ School of Aerospace, Mechanical & Mechatronic Engineering, The University of Sydney, Camperdown Sydney, NSW 2006, Australia.
⁵ School of Mechanical Engineering, University of Adelaide, Adelaide, SA 5005, Australia.
⁶ Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Box 516, SE-75121, Sweden.
⁷ Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Budapest H-1525, Hungary.

Abstract

High-density and nanosized deformation twins in face-centered cubic (fcc) materials can effectively improve the combination of strength and ductility. However, the microscopic dislocation mechanisms enabling a high twinnability remain elusive. Twinning usually occurs via continuous nucleation and gliding of twinning partial dislocations on consecutive close-packed atomic planes. Here we unveil a completely different twinning mechanism being active in metastable fcc materials. The transformation-mediated twinning (TMT) is featured by a preceding displacive transformation from the fcc phase to the hexagonal close-packed (hcp) one, followed by a second-step transformation from the hcp phase to the fcc twin. The nucleation of the intermediate hcp phase is driven by the thermodynamic instability and the negative stacking fault energy of the metastable fcc phase. The intermediate hcp structure is characterized by the easy slips of Shockley partial dislocations on the basal planes, which leads to both fcc and fcc twin platelets during deformation, creating more twin boundaries and further enhancing the prosperity of twins. The disclosed fundamental understanding of the complex dislocation mechanism of deformation twinning in metastable alloys paves the road to design novel materials with outstanding mechanical properties.

Keywords: martensitic transformation; metastable alloy; stacking fault; twinning.