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Journal Articles

Change in damping capacity arising from twin-boundary segregation in solid-solution magnesium alloys

Somekawa, Hidetoshi*; Basha, D. A.*; Singh, A.*; Tsuru, Tomohito; Watanabe, Hiroyuki*

Philosophical Magazine Letters, 100(10), p.494 - 505, 2020/10

 Times Cited Count:7 Percentile:54.31(Materials Science, Multidisciplinary)

The damping capacity in the vicinity of {10$$bar{1}$$2} twin boundaries was measured before and after annealing by nano-dynamic mechanical analysis. The subsequent annealing process led to a lower damping capacity in all magnesium binary alloys, which was in contrast to the results in pure magnesium. This is on account of the segregation of solute atoms in incoherent twin boundaries. The alloying elements, which have the characteristic of a low segregation energy for twin boundaries, effectively prevents the damping capacity degradation.

Journal Articles

Non-basal dislocation nucleation site of solid solution magnesium alloy

Somekawa, Hidetoshi*; Basha, D. A.*; Singh, A.*; Tsuru, Tomohito; Yamaguchi, Masatake

Materials Transactions, 61(6), p.1172 - 1175, 2020/06

 Times Cited Count:13 Percentile:66.5(Materials Science, Multidisciplinary)

The effect of grain boundary segregation on plastic deformation was investigated using the MgY solid solution binary alloy. Deformed microstructural observations revealed many traces of prismatic $$<a>$$ dislocations as well as basal dislocations. These dislocations were nucleated at grain boundaries with segregation of yttrium element. By comparison of material factors of binary alloy, the alloying elements having low critical resolved shear stress (CRSS) of non-basal plane and large grain boundary (twin boundary) segregation energy led to activation of non-basal dislocations in the vicinity of grain boundaries. The MgCa alloy had similar material factors and showed the same deformed microstructures as those of the alloys containing rare-earth element, which indicate that calcium element is an alternative alloying element.

Journal Articles

Interfacial segregation and fracture in Mg-based binary alloys; Experimental and first-principles perspective

Tsuru, Tomohito; Somekawa, Hidetoshi*; Chrzan, D. C.*

Acta Materialia, 151, p.78 - 86, 2018/06

 Times Cited Count:61 Percentile:96.47(Materials Science, Multidisciplinary)

We investigated the effect of solute elements on interfacial segregation and fracture in Mg alloys by experiments and first-principles density functional theory calculations in conjunction with interfacial fracture mechanics. Based on the assumption of brittle fracture in Mg alloys, the interfacial separation caused by segregated solutes in Mg can be efficiently described by the energy-based criterion of fracture, which is in good agreement with the fracture toughness obtained by experimental tests of Mg-M binary alloys. The electronic interaction, that is, the change in the electronic state between the interface and surface, mainly influences the ideal work of separation regardless of the type of interface. We found that IIIB ($$d^{1}$$) and IVB ($$d^{2}$$) solutes, such as Zr, show distinctive hybridization between the p band of Mg and the d band of the solute, which characterizes the strong fracture toughness of Zr-doped Mg alloys in both the calculations and experiments.

Journal Articles

Effect of alloying elements on grain boundary sliding in magnesium binary alloys; Experimental and numerical studies

Somekawa, Hidetoshi*; Tsuru, Tomohito

Materials Science & Engineering A, 708, p.267 - 273, 2017/12

 Times Cited Count:28 Percentile:80.02(Nanoscience & Nanotechnology)

The effect of alloying elements on grain boundary sliding was systematically investigated using several binary magnesium alloys via both experimental and numerical methods. The alloying element clearly affected damping properties related to grain boundary sliding, as measured by nanoindentation tests. The properties, such as damping capacity and strain rate sensitivity, apparently depended on grain boundary characteristics, i.e., the grain boundary energy. By increasing and decreasing the grain boundary energy, the alloying element was found to play a role in enhancing and suppressing grain boundary sliding, respectively. First-principles calculations revealed that lithium element had a weak bonding to magnesium due to a few operation of electric orbit. On the other hand, rare-earth elements exhibited relatively strong bonding to magnesium, because of electron interactions with the first nearest neighbor site, and tended to prevent grain boundary sliding.

Journal Articles

Effect of crystal orientation on incipient plasticity during nanoindentation of magnesium

Somekawa, Hidetoshi*; Tsuru, Tomohito; Singh, A.*; Miura, Seiji*; Schuh, C. A.*

Acta Materialia, 139, p.21 - 29, 2017/10

 Times Cited Count:26 Percentile:80.02(Materials Science, Multidisciplinary)

The effect of crystal orientation on incipient plasticity during nanoindentation was investigated by experiments and molecular statics simulation. Pop-in behavior is a result of dislocation activity, and is therefore influenced by crystal orientation. Experimental results using single crystals indicated that indentations on the basal plane had higher pop-in loads and larger pop-in displacements than those on the prismatic plane, an effect also captured by molecular statics simulation. The difference can be traced to the types of activated dislocations, with not only basal but also pyramidal dislocations active for indentations on the basal plane, but only basal dislocations triggered at the first pop-in on the prismatic plane.

Journal Articles

Effect of twin boundary on crack propagation behavior in magnesium binary alloys; Experimental and calculation studies

Somekawa, Hidetoshi*; Tsuru, Tomohito

Scripta Materialia, 130, p.114 - 118, 2017/03

 Times Cited Count:23 Percentile:74.48(Nanoscience & Nanotechnology)

The impact of alloying elements on crack propagation and atomistic phenomenon at {10$$bar{1}$$2}-type twin boundaries in magnesium was investigated via both experiments and calculations. The alloying elements clearly affected crack propagation behavior. Cracks were difficult to propagate along matrix-deformation twinning interfaces in alloys that had high fracture toughness. In such magnesium alloys, the solute atoms, e.g., silver, manganese and zinc atoms, create adhesive interactions between magnesium atoms. Closed-shell and covalent-like bonding of these kinds of solute atoms would influence strong adhesion, which impedes the nucleation of a new surface at the twin boundary.

Journal Articles

Material design for magnesium alloys with high deformability

Somekawa, Hidetoshi*; Yamaguchi, Masatake; Osawa, Yoshiaki*; Singh, A.*; Itakura, Mitsuhiro; Tsuru, Tomohito; Mukai, Toshiji*

Philosophical Magazine, 95(8), p.869 - 885, 2015/02

 Times Cited Count:22 Percentile:70.84(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Effects of alloying elements on deformation and fracture; First-principles approach to element strategy

Tsuru, Tomohito; Somekawa, Hidetoshi*; Itakura, Mitsuhiro; Yamaguchi, Masatake

no journal, , 

Mg alloys have great potential for the next generation of structural materials. Widespread application, however, has been limited because of a key weakness stemming from their hexagonal-close-packed (hcp) crystal structure. Their elongation-to-failure is extremely low due to the strong anisotropy of plastic deformation and decohesion of twin boundary in HCP metals. Recently it has been known that solute atoms alter the plastic deformation dramatically. However, the detailed mechanism is still unclear. We investigated the dislocation core structure of some typical HCP metals and the effects of solute atoms on dislocation core structure and motion in Mg especially. An initial atomic configuration is constructed by solving for the displacement field of the dislocation dipole within a periodic continuum linear elasticity theory. DFT calculations were carried out to explore the stable dislocation core structure.

Oral presentation

First-principles study on effects of alloying elements on deformation and fracture

Tsuru, Tomohito; Somekawa, Hidetoshi*; Yamaguchi, Masatake; Itakura, Mitsuhiro; Daryl, C.*

no journal, , 

We investigated the dislocation core structure of some typical HCP metals and the effects of solute atoms on dislocation core structure and motion in Mg especially. An initial atomic configuration is constructed by solving for the displacement field of the dislocation dipole within a periodic continuum linear elasticity theory. DFT calculations were carried out to explore the stable dislocation core structure. Introduction of a substitutional/interstitial solute atom changes the electronic structure near the solute. If these changes occur in the same energy range associated with the changes in the electronic structure of the dislocation during motion, strong chemical hybridization can occur between the solute atom states and those states associated with dislocation motion. DFT calculations also give some information about the tendency of twin boundary cohesion/decohesion due to the solutes.

Oral presentation

First-principles and experimental study on interfacial fracture in Mg alloys

Tsuru, Tomohito; Somekawa, Hidetoshi*

no journal, , 

Mg alloys are promising candidates for next generation of structural lightweight materials in practical use, especially for transportation equipment in terms of energy and environmental conservation. Based on the assumption of brittle fracture of Mg alloys, the interfacial separation caused by segregated solutes in Mg can be described efficiently by the energy-based criterion of fracture, which is good agreement with the fracture toughness of experimental test for Mg-M binary alloys. The electronic interaction, that is the change in electronic states between interface and surface, dominantly influences the ideal work of separation regardless of the type of interface. We found that d1 and d2 solutes such as Zr have a distinctive hybridization between p-band of Mg and d-band of solutes, which characterizes a strong fracture toughness of Zr-doped Mg alloys in both calculations and experiments.

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