JOPSS - Search Results

Some solute atoms induce hardening and embrittlement in body-centered-cubic refractory metals. Especially interstitial oxygen has a dramatic hardening effect in Nb, where the yield stress of oxygen-doped Nb alloys becomes more than twice as high as that of pure Nb. Conventional mechanisms cannot explain the oxygen-induced dramatic hardening since the interaction between dislocation and oxygen is relatively weak. Here, we focused on the three-body interaction of a screw dislocation with oxygen and vacancy. Our first-principles calculations revealed that the formation of vacancy-oxygen pair enhances the attractive interaction with a screw dislocation though the interaction between oxygen and dislocation is repulsive. Furthermore, this feature was found to be a unique nature of oxygen in Nb. The vacancy-oxygen pair increases the energy barrier for dislocation motion more significantly than an isolated vacancy and oxygen interstitial. We have discovered a new oxygen-induced mechanism: a unique octahedral-tetrahedral shuffling process of oxygen dominantly contributes to the dramatic hardening. Thus, the widely distributed vacancy-oxygen pairs behave as strong obstacles for dislocation motion that causes damage accumulation and successive hardening in oxygen-doped BCC alloys.

Journal Articles

Effective grain size refinement of an Fe-24Ni-0.3C metastable austenitic steel by a modified two-step cold rolling and annealing process utilizing the deformation-induced martensitic transformation and its reverse transformation

Mao, W.; Gao, S.*; Bai, Y.*; Park, M.-H.*; Shibata, Akinobu*; Tsuji, Nobuhiro*

Journal of Materials Research and Technology, 17, p.2690 - 2700, 2022/03

https://doi.org/10.1016/j.jmrt.2022.02.031

Times Cited Count：18 Percentile：80.29(Materials Science, Multidisciplinary)

Metastable austenitic steels having ultrafine grained (UFG) microstructures can be fabricated by conventional cold rolling and annealing processes by utilizing the deformation-induced martensitic transformation during cold rolling and its reverse transformation to austenite upon annealing. However, such processes are not applicable when the austenite has high mechanical stability against deformation-induced martensitic transformation, since there is no sufficient amount of martensite formed during cold rolling. In the present study, a two-step cold rolling and annealing process was applied to an Fe-24Ni-0.3C metastable austenitic steel having high mechanical stability. Prior to the cold rolling, a repetitive subzero treatment and reverse annealing treatment were applied. Such a treatment dramatically decreased the mechanical stability of the austenite and greatly accelerated the formation of deformation-induced martensite during the following cold rolling processes. As a result, the grain refinement was significantly promoted, and a fully recrystallized specimen with a mean austenite grain size of 0.5 mm was successfully fabricated, which exhibited both high strength and high ductility.

Journal Articles

Dislocation-climbing bypass over dispersoids with different lattice misfit in creep deformation of FeCrAl oxide dispersion-strengthened alloys

Ukai, Shigeharu; Yamashita, Shinichiro

Journal of Materials Research and Technology, 16, p.891 - 898, 2022/01

https://doi.org/10.1016/j.jmrt.2021.11.123

Times Cited Count：20 Percentile：84.56(Materials Science, Multidisciplinary)

The creep strain rate of FeCrAl oxide dispersion-strengthened alloys, as a promising accident-tolerant fuel (ATF) cladding of the light-water reactors, is accelerated in YAlO $_{3}$ dispersoids by two to three orders of magnitude compared with Y $_{4}$ Zr $_{3}$ O $_{12}$ dispersoid at 1273K and even occurs at an applied stress less than threshold stress for dislocation detachment. Two approaches were carried out to interpret new findings and to clarify their mechanism. By optimizing the relaxation of the dislocation line energy at the dispersoid interface, numerical analyses proved the accelerated dislocation-climbing in the YAlO $_{3}$ dispersoids. The other is a more atomistic approach. The climbing force on the dislocation induced by the stress field around the dispersoid was analyzed in terms of the Peach-Koehler relationship. The accelerated creep strain rate in YAlO $_{3}$ dispersoids is attributed to a larger climbing force induced by larger lattice misfit with less coherency in YAlO $_{3}$ dispersoid.

Journal Articles

Accumulation of radiation damage and disordering in MgAl $_{2}$ O $_{4}$ under swift heavy ion irradiation

Yasuda, Kazuhiro*; Yamamoto, Tomokazu*; Eto, Motoki*; Kawasoe, Shinji*; Matsumura, Sho*; Ishikawa, Norito

International Journal of Materials Research, 102(9), p.1082 - 1088, 2011/09

https://doi.org/10.3139/146.110564

Times Cited Count：15 Percentile：56.36(Metallurgy & Metallurgical Engineering)

Accumulation and recovery of radiation-induced damage with swift heavy ions instoichiometric magnesium aluminate spinel, MgAl $_{2}$ O $_{4}$ , has been investigated. Microstructural change and atomic disordering was examined through transmission electron microscopy (TEM) techniques, with bright-field (BF) and high-resolution (HR) TEM images, and high angular resolution electron channelling X-ray spectroscopy (HARECXS), for single crystal MgAl $_{2}$ O $_{4}$ irradiated with 200 MeV Xe, and 340 or 350 MeV Au ions. The density of core damage region, detected by BFTEM with Fresnelcontrast, increased proportionally with ion fluence at the early stage of accumulation. This result is discussed with a balance between the formation and recovery of the core damage region under irradiation, and the influence region to induce the recovery was evaluated to be 7-9 nm in radius. The structure of the core damage region is found from HR and BFTEM images to be a columnar vacancy-rich region with a low atomic density.

Journal Articles

Effect of atomic scale plasticity on hydrogen diffusion in iron; Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

Ramasubramaniam, A.*; Itakura, Mitsuhiro; Ortiz, M.*; Carter, E. A.*

Journal of Materials Research, 23(10), p.2757 - 2773, 2008/10

We present an off-lattice, on-the-fly kinetic Monte Carlo (KMC) model for simulating stress-assisted diffusion and trapping of hydrogen by crystalline defects in iron, which is supplemented by high-accuracy density functional theory calculations. Effective diffusivities obtained from KMC simulations are found to be in good agreement with theory. Our model provides an avenue for simulating the interaction of hydrogen with cracks, dislocations, grain boundaries, and other lattice defects, over extended time scales, albeit at atomistic length scales.

Journal Articles

Synthesis and characterization of copper hydroxide acetate with a layered discoid crystal

Kozai, Naofumi; Mitamura, Hisayoshi; Fukuyama, Hiroyasu; Esaka, Fumitaka; Komarneni, S.*

Journal of Materials Research, 20(11), p.2997 - 3003, 2005/11

Layered transition metal hydroxide salt (LTMHS) is a group of anion-exchangeable layered compounds. LTMHSs have lately attraced attention of researchs on anion exchange and intercalation but very limited numbers of reports have been published on their synthesis, characteristics, and application. This study reports basic properties of a layered copper hyroxide acetate synthesized by a method modified from that of the previous studies. Titration of copper acetate solution with a dilute NaOH solution to pH 6.5 and subsequent aging at 313 K yielded a layered copper hydroxide acetate. This compound has some properties similar to those of the previously known copper hydroxide acetate, Cu $_{2}$ (OH) $_{3}$ (OCOCH $_{3}$ )H $_{2}$ O. The present copper hydroxide acetate is dissimilar to the previous compound in morphology, stability of bonding between the interlayer acetate ions and the matrix hydroxides, and reaction with anions in aqueous solutions.

Journal Articles

Identification of the constitutive equation by the indentation technique using plural indenters with different apex angles

Futakawa, Masatoshi; Wakui, Takashi*; Tanabe, Yuji*; Ioka, Ikuo

Journal of Materials Research, 16(8), p.2283 - 2292, 2001/08

no abstracts in English

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Enhancing mechanical properties of medium Mn steel by warm rolling based on laminated elemental segregation

Mechanical properties of base metal and heat-affected zone in friction-stir-welded AA6061-T6 at ultra-low temperature of 20 K

First-principles analysis of the effects of oxygen, vacancies, and their complexes on the screw dislocation motion in body-centered cubic Nb

Effective grain size refinement of an Fe-24Ni-0.3C metastable austenitic steel by a modified two-step cold rolling and annealing process utilizing the deformation-induced martensitic transformation and its reverse transformation

Dislocation-climbing bypass over dispersoids with different lattice misfit in creep deformation of FeCrAl oxide dispersion-strengthened alloys

Accumulation of radiation damage and disordering in MgAl $_{2}$ O $_{4}$ under swift heavy ion irradiation

Effect of atomic scale plasticity on hydrogen diffusion in iron; Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

Synthesis and characterization of copper hydroxide acetate with a layered discoid crystal

Identification of the constitutive equation by the indentation technique using plural indenters with different apex angles