Bo-Yu Liu

Twinning-like lattice reorientation without a crystallographic twinning plane

Twinning on the plane is a common mode of plastic deformation for hexagonal-close-packed metals. Here we report, by monitoring the deformation of submicron-sized single-crystal magnesium compressed normal to its prismatic plane with transmission electron microscopy, the reorientation of the parent lattice to a ‘twin’ lattice, producing an orientational relationship akin to that of the conventional twinning, but without a crystallographic mirror plane, and giving plastic strain that is not simple shear. Aberration-corrected transmission electron microscopy observations reveal that the boundary between the parent lattice and the ‘twin’ lattice is composed predominantly of semicoherent basal/prismatic interfaces instead of the twinning plane. The migration of this boundary is dominated by the movement of these interfaces undergoing basal/prismatic transformation via local rearrangements of atoms. This newly discovered deformation mode by boundary motion mimics conventional deformation twinning but is distinct from the latter and, as such, broadens the known mechanisms of plasticity.

From “Smaller is Stronger” to “Size‐Independent Strength Plateau”: Towards Measuring the Ideal Strength of Iron

Prof. W.-Z. Han, Dr. L. Huang, Q.-J. Li, B.-Y. Liu, Prof. J. Li, Prof. E. Ma, Prof. Z.-W. Shan Center for Advancing Materials Performance from the Nanoscale and Hysitron Applied Research Center in China State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong University Xi’an 710049 , P. R. China E-mail: zwshan@mail.xjtu.edu.cn Prof. S. Ogata, Prof. H. Kimizuka Department of Mechanical Science and Bioengineering Osaka University Osaka 560-8531 , Japan Prof. S. Ogata Center for Elements Strategy Initiative for Structural Materials Kyoto University Kyoto 606-8501 , Japan Prof. Z.-C. Yang Department of Mechanical Engineering and Materials Science and Department of Bioengineering University of Pittsburgh Pittsburgh , PA 15261 , USA Prof. C. Weinberger Sandia National Laboratories Albuquerque , NM 87185 , USA Prof. C. Weinberger Mechanical Engineering and Mechanics Department Drexel University Philadelphia , PA 19104 , USA Prof. X.-X. Zhang Division of Physical Science and Engineering King Abdullah University of Science & Technology Thuwal 23955-6900 , Saudi Arabia E-mail: xixiang.zhang@kaust.edu.sa Prof. J. Li Department of Nuclear Science and Engineering and Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge , MA 02139 , USA Prof. E. Ma Department of Materials Science and Engineering Johns Hopkins University Baltimore , MD 21218 , USA

Twin Boundary Migration Creating Zero Shear Strain: In-Situ TEM Observations and Atomistic Simulations

Atomistic simulations were conducted to study the migration of \(\{ 10\bar 12\} \) twin boundary. A bi-crystal that satisfies the twin orientation relationship was constructed and a tensile strain was applied in parallel to the axis of one crystal. Under the tensile strain, the twin boundary starts to migrate but the migration (twin growth) does not produce any observable shear strain on the bicrystal. In-situ transmission electron microscopy (TEM) observations of a single crystal Mg under tension and compression confirm that during twinning and detwinning, no shear strain is produced. The specimen uniformly elongates and narrows during twinning, and widens across the width during detwinning.

Turning a native or corroded Mg alloy surface into an anti-corrosion coating in excited CO 2

Despite their energy-efficient merits as promising light-weight structural materials, magnesium (Mg) based alloys suffer from inadequate corrosion resistance. One primary reason is that the native surface film on Mg formed in air mainly consists of Mg(OH)2 and MgO, which is porous and unprotective, especially in humid environments. Here, we demonstrate an environmentally benign method to grow a protective film on the surface of Mg/Mg alloy samples at room temperature, via a direct reaction of already-existing surface film with excited CO2. Moreover, for samples that have been corroded obviously on surface, the corrosion products can be converted directly to create a new protective surface. Mechanical tests show that compared with untreated samples, the protective layer can elevate the yield stress, suppress plastic instability and prolong compressive strains without peeling off from the metal surface. This environmentally friendly surface treatment method is promising to protect Mg alloys, including those already-corroded on the surface.Magnesium alloys usually have poor corrosion resistance, which inhibits their use in the automotive and biomedical industries. Here, the authors use an environmental TEM to carbonate the natural corrosion products at the surface of magnesium alloys and form a compact and protective surface layer.

Non-Dislocation Based Room Temperature Plastic Deformation Mechanism in Magnesium

Dislocation and deformation twinning are traditionally known to be plasticity carriers of crystalline materials at room temperature. By using in-situ TEM mechanical testing technique, here we report that the plasticity of a specially orientated single crystal magnesium can be mediated neither by dislocation nor by twinning, but through a non-dislocation based process, termed as unit-cell-reconstruction. After the reconstruction, a ~7% strain is produced. The newly formed grain and its parent grain are separated by a boundary that mainly consisted of basal-prismatic interfaces. Such boundary can migrate back and forth under a cyclic loading and therefore produce a reversible plastic deformation. The reported novel mechanism may have important implications for the alloy design of magnesium.