Twinning in Hexagonal Materials
A special issue of Metals (ISSN 2075-4701).
Deadline for manuscript submissions: closed (31 January 2020) | Viewed by 2582
Special Issue Editors
Interests: deformation mechanisms at fine scales (twinning, dislocation); mechanical characterization (nanoindentation, in situ tests); adapted microstructural characterizations (SEM, TEM, EBSD, AFM...)
Special Issues, Collections and Topics in MDPI journals
Interests: material characterization; mechanical testing; twinning; detwinning; dislocation slip; strain accommodation; grain boundary; titanium alloys
Special Issue Information
Dear Colleagues,
In hexagonal-close-packed (HCP) metals, slips occur mainly in <a> direction in the basal planes (B<a>), in the prismatic planes (P<a>) or in the first-order pyramidal planes (π1<a>). The hierarchy of these deformation modes changes, among other things, in function of the axial ratio c/a: so the HCPs, having a c/a < 1.633 (Ti, Zr), P<a> is the principal glide system (PGS) contrary to the HCPs with a c/a > 1.633, such as Zn or Cd, where the PGS is B<a>. The number of glide systems is therefore limited at room temperature. As a result, twinning is a primordial and particular deformation mode in HCP metals. Primordial because slips in the <a> direction do not contribute to plastic deformation along the <c> axis; <c+a> glide is therefore activated for plastic deformation (such as π1<c+a> or second-order pyramidal planes π2<c+a>) but they are rare because of their low mobility. Thus, twinning is a primary deformation mode to accommodate plastic deformation along the <c> axis. Particularly because, unlike dislocations, several characteristics are associated with twinning: it is a highly directional mechanism that reorients whole fractions of the grain and is accompanied by a marked stress relaxation. The evolution of the elastic limit shows a strong anisotropy between the directions in the plane and in the thickness. In addition, twinning shows an increase in the hardening rate and a continuous evolution of the grain microstructure with deformation. During cyclic loading or changes of loading direction, twins interact with twins, resulting in twin–twin junctions that further influence continuous twinning, secondary twinning, and detwinning. Thus, twinning is responsible for the high anisotropic stress, low deformability, texture and evolution of the microstructure of HCP metals.
This Special Issue invites researchers to submit original research and review articles on all disciplines in which the theoretical or practical problems of twinning in HCP metals are taken into account. Topics of interest include, but are not limited to:
- Atomistic calculations ab-initio type, first principles, dislocation dynamics
- Inclusion of twinning in VPSC medium or full field models
- Twin transmission by grain boundaries
- Crystal plasticity, behavioral laws that explain plastic deformation based on dislocation and twinning
- Self-consistent, fast Fourier transform (FFT), and finite element (FE) methods (like CPFEM)
- Characterization methods: EBSD, TEM; in 3D: FIB, neutrons
Dr. Jean-Sebastien Lecomte
Dr. Christophe Schuman
Guest Editors
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Keywords
- twinning
- detwinning
- HCP metals
- atomistic calculations
- crystal plasticity
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