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Metals
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Deformation and Transformation Twinning
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Deformation and Transformation Twinning

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 15402

Special Issue Editor

Dr. Cyril Cayron

E-Mail Website
Guest Editor
Swiss Federal Institute of Technology EPFL, Lausanne, Lausanne, Switzerland
Interests: metallurgy; EBSD; TEM; crystallography; martensitic transformations; twinning; variants; group theory
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Deformation twinning is a stress-induced lattice distortion (with or without atomic shuffles) that transforms a crystal into another crystal of same phase but with a different orientation. Deformation twinning is known from the early birth of mineralogy, and crystallographic models have been improved over the past century, from the shear modes I and II established by Mügge in 1889, to the algorithmic method proposed by Bevis and Crocker in 1968 based on the correspondence and metric tensors. For the last few decades, thanks to the progress of characterization techniques such as Electron BackScatter Diffraction (EBSD) and Digital Image Correlation (DIC), new twinning systems have been discovered or rediscovered, such as the “double twins” in magnesium alloys, and the (332) twins in some titanium alloys. Some twins are associated with abnormally low Schmid factors, or are of pure stretch type (“zero-shear”), which challenges the classical theories.

The nature of transformation twinning is different. Transformation twins are actually variants generated by a phase transformation, and the twin law results from the broken parent symmetries. This indirect relation between the twins may be confusing, and one may think that a variant can be transformed into another variant via the usual (shear) deformation twinning mechanism. This assumption is the cornerstone of the phenomenological theory of martensitic crystallography (PTMC) to explain the shape memory effect. However, there is no direct evidence that shows that such a simple shear mechanism is the correct one. A lot of important questions remain open.

All contributions are welcome in this Special Issue, including critical and constructive reviews, new surprising experimental results, even if not yet fully understood and interpreted, and new theoretical models based on classical crystallography, disconnections, phase field simulations, etc.

Dr. Cyril Cayron
Guest Editor

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Deformation twins
  • Transformation twins
  • Martensite
  • Shape memory alloys
  • EBSD
  • Crystallography
  • Lattice distortion
  • Disconnections

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Published Papers (3 papers)

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Research

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32 pages, 7683 KiB  
Article
Complements to Mügge and Friedel’s Theory of Twinning
by Cyril Cayron
Metals 2020, 10(2), 231; https://doi.org/10.3390/met10020231 - 7 Feb 2020
Cited by 13 | Viewed by 3652
Abstract
The crystallography of twinning is based on the concepts of simple shear and obliquity introduced by Mügge, Mallard and Friedel at the turn of the last century, with tensor mathematics later developed by Bilby, Bevis and Crocker in the 1960s. We propose a [...] Read more.
The crystallography of twinning is based on the concepts of simple shear and obliquity introduced by Mügge, Mallard and Friedel at the turn of the last century, with tensor mathematics later developed by Bilby, Bevis and Crocker in the 1960s. We propose a synthesis of these works by writing the three transformations (distortion, orientation and correspondence) as matrices in dyadic product forms. We show that a “normal” Friedelian mode is implicitly assumed. We introduce another mode called “tilted” that explains, with the simple twin index q = 1, some twins that were previously oddly reported with q = 2. We also interpret the type II twins, which are usually presented as the conjugate twins of type I twins, as simple shears a rational reciprocal plane, exactly as the type I twins are simple shears a rational direct plane. Finally, we explain why the term “twin” for variants inherited from a phase transformation is not appropriate, and we call for a generalization of the crystallography of twinning by considering epitaxial distortions and iso-orientation shears. Full article
(This article belongs to the Special Issue Deformation and Transformation Twinning)
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14 pages, 6086 KiB  
Article
The Effects of Recrystallization on Strength and Impact Toughness of Cold-Worked High-Mn Austenitic Steels
by Minha Park, Moon Seok Kang, Geon-Woo Park, Eun Young Choi, Hyoung-Chan Kim, Hyoung-Seok Moon, Jong Bae Jeon, Hyunmyung Kim, Se-Hun Kwon and Byung Jun Kim
Metals 2019, 9(9), 948; https://doi.org/10.3390/met9090948 - 29 Aug 2019
Cited by 22 | Viewed by 5144
Abstract
High-Mn austenitic steels have been recently developed for a storage or transportation application of liquefied natural gas (LNG) in cryogenic fields. Since the structural materials are subjected to extremely low temperature, it requires excellent mechanical properties such as high toughness strength. In case [...] Read more.
High-Mn austenitic steels have been recently developed for a storage or transportation application of liquefied natural gas (LNG) in cryogenic fields. Since the structural materials are subjected to extremely low temperature, it requires excellent mechanical properties such as high toughness strength. In case of high-Mn steels, twinning deformation during the cold-working process is known to increase strength yet may cause embrittlement of heavy deformed twin and anisotropic properties. In this study, a recrystallization process through appropriate annealing heat treatments after cold-working was applied to improve the impact toughness for high-Mn austenitic steels. Microstructure and mechanical properties were performed to evaluate the influence of cold-worked and annealed high-Mn austenitic steels. Mechanical properties, such as strength and impact toughness, were investigated by tensile and Charpy impact tests. The relationship between strength and impact toughness was determined by microstructure analysis such as the degree of recrystallization and grain refinement. Consequently, both elongation and toughness were significantly increased after cold-working and subsequent annealing at 1000 °C as compared to the as-received (hot-rolled) specimen. The cold-worked high-Mn steel was completely recrystallized at 1000 °C and showed a homogeneous micro-structure with high-angle grain boundaries. Full article
(This article belongs to the Special Issue Deformation and Transformation Twinning)
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Review

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20 pages, 7021 KiB  
Review
Review of Non-Classical Features of Deformation Twinning in hcp Metals and Their Description by Disconnection Mechanisms
by Andriy Ostapovets and Anna Serra
Metals 2020, 10(9), 1134; https://doi.org/10.3390/met10091134 - 23 Aug 2020
Cited by 30 | Viewed by 5432
Abstract
The study of deformation twinning has long history. However new, sometimes surprising, findings have shown that the phenomenon of deformation twinning still is not completely understood. During recent years, some debates are taking place in the scientific literature concerning deformation twinning mechanisms in [...] Read more.
The study of deformation twinning has long history. However new, sometimes surprising, findings have shown that the phenomenon of deformation twinning still is not completely understood. During recent years, some debates are taking place in the scientific literature concerning deformation twinning mechanisms in metals with hcp structure. These debates deal with the importance of special twin boundary dislocations named disconnections, growth and nucleation of twins, non-Schmid behavior of twinning, difference of deformation produced by twins from simple shear. They invoked new propositions for atomistic mechanisms of deformation twinning. The purpose of this review is to compare the classical theories of interfacial defects with the new findings and prove that many of these findings can be understood in terms of these well-established theories. The main attention is paid to summarizing the explanations of different phenomena in terms of disconnection mechanisms in order to show that there is no contradiction between these mechanisms and the new findings. Full article
(This article belongs to the Special Issue Deformation and Transformation Twinning)
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