Owing to its HCP crystallography, deformation mechanisms of magnesium involve both plastic slip and deformation twinning. In order to understand and ultimately to predict the mechanical response of Mg and Mg alloys, any effective continuum model should not only describe the intricate interaction mechanisms between plastic slip and twinning, but also be able to capture the different length scale...

Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of ext...

Deformation mechanisms and the role of interfaces in deformation twinning of a two-phase [TiAI (y)GAl (ad] 1 amellar allo\t creep deformed at elevated temperatures have been investigated. Since the multiplication of lattice dislocations \vithin both y and a2 lamellae is verl\’ limited at a lo\v stress level due to a refined lamellar microstructure, the glide of interfacial dislocations on both ...

A recently developed crystal based continuum model for twinning and phase transformations is successfully applied to Dauphiné twinning and the α (trigonal) ↔ β (hexagonal) phase transformation in quartz. Both finite element and uniform deformation simulations are performed of quartz polycrystals and several experimentally observed phenomena are qualitatively reproduced. Results are given for me...

We report transmission electron microscope observations that provide evidence of deformation twinning in plastically deformed nanocrystalline aluminum. The presence of these twins is directly related to the nanocrystalline structure, because they are not observed in coarse-grained pure aluminum. We propose a dislocation-based model to explain the preference for deformation twins and stacking fa...

– The (21̄1̄)〈111〉 twinning energy landscape of BCC Mo is determined using the density functional theory for embryos containing 2 to 7 layers. The 2-layer embryo is metastable, whereas the 3and 4-layer ones are unstable. Layer-by-layer growth starts at 5 layers. The twin boundary formation and migration energies are found to be 607mJ/m and 40mJ/m, respectively, indicating that twin partial disloc...

The role of intakes in deformation twiming of Iamellar TiAl (ywl~l (a*) crystals creep deformed at an ekvated temperature have been investigated. Since the multiplication of lattice dislocations within both y and etzlamellae is very limited as a result of a refined lamekr microstmture, the gliding of interfheii dislocations on both y/a2 and y/y interfaces (i.e. interface sliding) becomes an imp...

Title of dissertation: MODELING THE INFLUENCE OF PHASE BOUNDARIES AND OXYGEN INTERSTITIALS ON THE NUCLEATION AND GROWTH OF DEFORMATION TWINS IN THE ALPHA-PHASE OF TITANIUM ALLOYS William Joseph Joost, Doctor of Philosophy, 2015 Dissertation directed by: Professor Sreeramamurthy Ankem Professor Maija M. Kuklja Department of Materials Science and Engineering Twinning is an important deformation m...

Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highes...

We have revealed the fundamental embryonic structure of deformation twins using in situ mechanical testing of magnesium single crystals in a transmission electron microscope. This structure consists of an array of twin-related laths on the scale of several nanometers. A computational model demonstrates that this structure should be a generic feature at the incipient stage of deformation twinnin...