The current understanding of the fundamentals of recrystallization is summarized. This includes understanding the as-deformed state. Several aspects of recrystallization are described: nucleation and growth, the development of misorientation during deformation, continuous, dynamic, and geometric dynamic recrystallization, particle effects, and texture. This article is authored by the leading experts in these areas. The subjects are discussed individually and recommendations for further study are listed in the final section.

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Current issues in recrystallization: a review

Pristine graphene is the strongest material ever measured. However, large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain grain boundaries that can potentially weaken the material. We combined structural characterization by means of transmission electron microscopy with nanoindentation in order to study the mechanical properties of CVD-graphene films with different grain sizes. We show that the elastic stiffness of CVD-graphene is identical to that of pristine graphene if postprocessing steps avoid damage or rippling. Its strength is only slightly reduced despite the existence of grain boundaries. Indentation tests directly on grain boundaries confirm that they are almost as strong as pristine. Graphene films consisting entirely of well-stitched grain boundaries can retain ultrahigh strength, which is critical for a large variety of applications, such as flexible electronics and strengthening components.

High-Strength Chemical-Vapor–Deposited Graphene and Grain Boundaries

Grain Boundary Complexions

Atomistic simulations were employed to investigate the structure and energy of asymmetric tilt grain boundaries in Cu and Al. In this work, we examine the Σ5 and Σ13 systems with a boundary plane rotated about the ⟨ 100 ⟩ misorientation axis, and the Σ9 and Σ11 systems rotated about the ⟨ 110 ⟩ misorientation axis. Asymmetric tilt grain boundary energies are calculated as a function of inclination angle and compared with an energy relationship based on faceting into the two symmetric tilt grain boundaries in each system. We find that asymmetric tilt boundaries with low index normals do not necessarily have lower energies than boundaries with similar inclination angles, contrary to previous studies. Further analysis of grain boundary structures provides insight into the asymmetric tilt grain boundary energy. The Σ5 and Σ13 systems in the ⟨ 100 ⟩ system agree with the aforementioned energy relationship; structures confirm that these asymmetric boundaries facet into the symmetric tilt boundaries. The Σ9 and ...

Asymmetric tilt grain boundary structure and energy in copper and aluminium

http://www.issp.ac.ru/libm/papers/153.pdf

Formation of nanograined structure and decomposition of supersaturated solid solution during high pressure torsion of Al-Zn and Al-Mg alloys

The temperature dependence of 〈111〉 tilt grain boundaries with angles of misorientation of 38·2° and 40·5° was investigated in bicrystals of both pure (99·999%) Al and the same Al doped with 10ppmGa in the temperature regime between 400 and 580°C. The grain boundary mobility for the investigated grain boundaries over the entire investigated temperature range is enhanced by minor additions of Ga. Both the activation enthalpy and the pre-exponential factor are affected by Ga doping. The orientation dependence of grain boundary mobility is strongly reduced but not completely removed. The drastic rise in grain boundary mobility by the addition of Ga to pure Al is interpreted as a consequence of a change in the boundary structure and the mechanism of boundary migration owing to a pre-wetting phase transition and formation of a liquid (or quasiliquid) Ga-rich layer on the grain boundary.

Acceleration of grain boundary motion in Al by small additions of Ga

Grain Boundary Segregation in the Cu-Bi System

http://www.issp.ac.ru/libm/papers/134.pdf

Grain boundary phase transitions and phase diagrams

This article presents the results of experimental and theoretical studies on the energy and structure of Σ3 tilt boundaries with (110) and (211) tilt axis in Cu. For both types of boundaries, a plot of the grain boundary energy versus the inclination of the boundary plane features a minimum at high inclinations against the plane of the coherent twin boundary. Along with this second energy minimum, the boundaries exhibit complex, three-dimensional structures, featuring a thin slab along the boundary plane in which Cu adopts unusual crystal structures. In the (110) tilt boundaries the slab has a rhombohedral structure (9R), while in the (211) tilt boundaries it has a body-centered cubic structure. These structures seem to be energetically favorable because they continue close-packed layers of atoms across the grain boundary.

Structure and energy of twin boundaries in copper

The temperature dependence of the contact angle θ at the intersection of Zn grain boundaries with Zn/liquid Zn-Sn boundaries have been studied. For this purpose, two Zn bicrystals were grown with {1000} tilt boundaries having misorientation angles of o=16° (small angle grain boundary) and o=60°. These boundaries possess different energies. The temperatures T w of the grain boundary wetting phase transition for these two boundaries were determined and the corresponding tie lines in the two-phase (Sn)+L field of the Zn-Sn phase diagram were constructed. Above T w the contact angle θ is 0° and a layer of liquid phase substitutes for the grain boundary. The temperature of the wetting transition (T w1 = 382±1°C) for the boundary with the high energy (o=60°) is lower than that (T w2 = 386.5±1°C) for the boundary with the low energy (o=16°). Above the temperature interval where all the grain boundaries become wetted, the solid phase may exist only as isolated single crystalline islands in the sea of melted phase.

Wolfgang Gust

Papers

Acceleration of grain boundary motion in Al by small additions of Ga

Grain Boundary Segregation in the Cu-Bi System

Grain boundary phase transitions and phase diagrams

Structure and energy of twin boundaries in copper

Tie Lines of the Grain Boundary Wetting Phase Transition in the Zn-Rich Part of the Zn-Sn Phase Diagram