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Journal Articles

Role of solute hydrogen on mechanical property enhancement in Fe-24Cr-19Ni austenitic steel; An ${it in situ}$ neutron diffraction study

Ito, Tatsuya; Ogawa, Yuhei*; Gong, W.; Mao, W.*; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.

Acta Materialia, 287, p.120767_1 - 120767_16, 2025/04

Journal Articles

Deformation behavior of ultrafine-grained TRIP steel observed by neutron diffraction

Harjo, S.; Mao, W.*; Gong, W.; Kawasaki, Takuro

Proceedings of the 7th International Symposium on Steel Science (ISSS 2024), p.205 - 208, 2024/11

Journal Articles

${it In situ}$ neutron diffraction study to elucidate hydrogen effect on the deformation mechanism in Type 310S austenitic stainless steel

Ito, Tatsuya; Ogawa, Yuhei*; Gong, W.; Mao, W.*; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.

Proceedings of the 7th International Symposium on Steel Science (ISSS 2024), p.237 - 240, 2024/11

Journal Articles

Martensitic transformation-governed Luders deformation enables large ductility and late-stage strain hardening in ultrafine-grained austenitic stainless steel at low temperatures

Mao, W.*; Gao, S.*; Gong, W.; Kawasaki, Takuro; Ito, Tatsuya; Harjo, S.; Tsuji, Nobuhiro*

Acta Materialia, 278, p.120233_1 - 120233_13, 2024/10

 Times Cited Count:1 Percentile:63.56(Materials Science, Multidisciplinary)

Journal Articles

Direct observations of dynamic and reverse transformation of Ti-6Al-4V alloy and pure titanium

Guo, B.*; Chen, H.*; Chong, Y.*; Mao, W.; Harjo, S.; Gong, W.; Zhang, Z.*; Jonas, J. J.*; Tsuji, Nobuhiro*

Acta Materialia, 268, p.119780_1 - 119780_11, 2024/04

 Times Cited Count:6 Percentile:95.55(Materials Science, Multidisciplinary)

Journal Articles

${it In situ}$ neutron diffraction revealing the achievement of excellent combination of strength and ductility in metastable austenitic steel by grain refinement

Mao, W.; Gong, W.; Harjo, S.; Morooka, Satoshi; Gao, S.*; Kawasaki, Takuro; Tsuji, Nobuhiro*

Journal of Materials Science & Technology, 176, p.69 - 82, 2024/03

 Times Cited Count:2 Percentile:0.00(Materials Science, Multidisciplinary)

The yield stress of Fe-24Ni-0.3C (wt.%) metastable austenitic steel increased 3.5 times (158 $$rightarrow$$ 551 MPa) when the average grain size decreased from 35 $$mu$$m (coarse-grained [CG]) to 0.5 $$mu$$m (ultrafine-grained [UFG]), whereas the tensile elongation was kept large (0.87 $$rightarrow$$ 0.82). ${it In situ}$ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation mechanisms. The initial stages of plastic deformation in the CG and UFG samples were dominated by dislocation slip, with deformation-induced martensitic transformation (DIMT) also occurring in the later stage of deformation. Results show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain, which is attributed to the following effects. (i) Grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the $$<$$111$$>$$//LD (LD: loading direction) austenite grains, which were the most stable grains for DIMT. As a result, most of the $$<$$111$$>$$//LD austenite grains in the UFG specimens failed to transform into martensite. (ii) Grain refinement also suppressed the autocatalytic effect of the martensitic transformation. Nevertheless, the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during deformation. The above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.

Journal Articles

Hydrogen diffusion in cerium oxide thin films fabricated by pulsed laser deposition

Mao, W.*; Fukutani, Katsuyuki; 8 of others*

International Journal of Hydrogen Energy, 50(Part D), p.969 - 978, 2024/01

 Times Cited Count:3 Percentile:22.86(Chemistry, Physical)

Journal Articles

Grain size independence of cryogenic strain recovery behavior in high-Zr $$beta$$-Ti alloy

Zhang, B.*; Xin, S.*; Huang, M.*; Mao, W.; Jia, W.*; Li, Q.*; Li, S.*; Zhang, S.*; Mao, C.*

Materials Science & Engineering A, 890, p.145898_1 - 145898_7, 2024/01

 Times Cited Count:0 Percentile:0.00(Nanoscience & Nanotechnology)

A significant increase in the recovery strain of a high-Zr $$beta$$-Ti alloy from 2.25 % to 5.5 % when decreasing the deformation temperature from 300 K to 77 K is reported in this study. It is found that the super-elasticity of this alloy is independent of the $$beta$$-grain size at 77 K. The results reveal that a coarse-grained specimen exhibited approximately the same super-elasticity as its ultra-fine grain counterpart at 77 K. The relative easiness of deformation-induced martensitic transformation and dislocation slip was substantially changed at 77 K, with a strong suppression of dislocation slip, which overshadowed the effect of grain refinement on the super-elasticity.

Journal Articles

Quantitatively evaluating the huge L$"u$ders band deformation in an ultrafine grain stainless steel by combining ${it in situ}$ neutron diffraction and digital image correlation analysis

Mao, W.; Gao, S.*; Gong, W.; Harjo, S.; Kawasaki, Takuro; Tsuji, Nobuhiro*

Scripta Materialia, 235, p.115642_1 - 115642_6, 2023/10

 Times Cited Count:9 Percentile:81.83(Nanoscience & Nanotechnology)

In the present study, a hybrid ${it in situ}$ neutron diffraction and digital image correlation measurement was performed on tensile deformation of an ultrafine grain (UFG) stainless steel exhibiting a huge L$"u$ders band deformation to evaluate the individual contribution of the austenite matrix and the deformation-induced martensite to the strain hardening during the propagation of the band. Quantitative analysis revealed that the strain hardening of the austenite matrix was insufficient to maintain a uniform deformation when the flow stress was greatly enhanced by the UFG structure. The strain hardening required for the L$"u$ders band to propagate was mostly provided by the formation of martensite and the high internal stress within it.

Journal Articles

Quantitatively evaluating respective contribution of austenite and deformation-induced martensite to flow stress, plastic strain, and strain hardening rate in tensile deformed TRIP steel

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

Acta Materialia, 256, p.119139_1 - 119139_16, 2023/09

 Times Cited Count:24 Percentile:97.11(Materials Science, Multidisciplinary)

Transformation-induced plasticity (TRIP)-assisted steels exhibit an excellent combination of strength and ductility due to enhanced strain hardening rate associated with deformation-induced martensitic transformation (DIMT). Quantitative evaluation on the role of DIMT in strain hardening behavior of TRIP-assisted steels and alloys can provide guidance for designing advanced materials with strength and ductility synergy, which is, however, difficult since the phase composition keeps changing and both stress and plastic strain are dynamically partitioned among constituent phases during deformation. In the present study, tensile deformation with ${it in situ}$ neutron diffraction measurement was performed on an Fe-24Ni-0.3C (wt.%) TRIP-assisted austenitic steel. The analysis method based on stress partitioning and phase fractions measured by neutron diffraction was proposed, by which the tensile flow stress and the strain hardening rate of the specimen were resolved into factors associated with each phase, i.e., the austenite matrix, deformation-induced martensite, and the transformation rate of DIMT after differentiation, and then the role of each factor in the global strain hardening behavior was discussed. In addition, the plastic strain partitioning between austenite and martensite was indirectly estimated using the dislocation density measured by diffraction profile analysis, which constructed the full picture of stress and strain partitioning between austenite and martensite in the material. The results suggested that both the transformation rate and the phase stress borne by the deformation-induced martensite played important roles in the global tensile properties of the material. The proposed decomposition analysis method could be widely applied to investigating mechanical behavior of multi-phase alloys exhibiting the TRIP phenomenon.

Journal Articles

Unexpected dynamic transformation from $$alpha$$ phase to $$beta$$ phase in zirconium alloy revealed by in-situ neutron diffraction during high temperature deformation

Guo, B.*; Mao, W.; Chong, Y.*; Shibata, Akinobu*; Harjo, S.; Gong, W.; Chen, H.*; Jonas, J. J.*; Tsuji, Nobuhiro*

Acta Materialia, 242, p.118427_1 - 118427_11, 2023/01

 Times Cited Count:11 Percentile:73.00(Materials Science, Multidisciplinary)

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

 Times Cited Count:16 Percentile:84.42(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

Effect of deformation-induced martensitic transformation on nonuniform deformation of metastable austenitic steel

Mao, W.; Gong, W.; Kawasaki, Takuro; Harjo, S.

Materials Science & Engineering A, 837, p.142758_1 - 142758_8, 2022/03

 Times Cited Count:5 Percentile:43.90(Nanoscience & Nanotechnology)

Journal Articles

Activity enhancement of platinum oxygen-reduction electrocatalysts using ion-beam induced defects

Kimata, Tetsuya*; Kakitani, Kenta*; Yamamoto, Shunya*; Shimoyama, Iwao; Matsumura, Daiju; Iwase, Akihiro*; Mao, W.*; Kobayashi, Tomohiro*; Yamaki, Tetsuya*; Terai, Takayuki*

Physical Review Materials (Internet), 6(3), p.035801_1 - 035801_7, 2022/03

 Times Cited Count:7 Percentile:51.82(Materials Science, Multidisciplinary)

Journal Articles

Suppressed lattice disorder for large emission enhancement and structural robustness in hybrid lead iodide perovskite discovered by high-pressure isotope effect

Kong, L.*; Gong, J.*; Hu, Q.*; Capitani, F.*; Celeste, A.*; Hattori, Takanori; Sano, Asami; Li, N.*; Yang, W.*; Liu, G.*; et al.

Advanced Functional Materials, 31(9), p.2009131_1 - 2009131_12, 2021/02

 Times Cited Count:30 Percentile:83.45(Chemistry, Multidisciplinary)

The soft nature of organic-inorganic halide perovskites renders their lattice particularly tunable to external stimuli such as pressure, undoubtedly offering an effective way to modify their structure for extraordinary optoelectronic properties. However, these soft materials meanwhile feature a general characteristic that even a very mild pressure will lead to detrimental lattice distortion and weaken the critical light-matter interaction, thereby triggering the performance degradation. Here, using the methylammonium lead iodide as a representative exploratory platform, we observed the pressure-driven lattice disorder can be significantly suppressed via hydrogen isotope effect, which is crucial for better optical and mechanical properties previously unattainable.

Journal Articles

Synthesis, structure, and pressure-induced polymerization of Li$$_{3}$$Fe(CN)$$_{6}$$ accompanied with enhanced conductivity

Li, K.*; Zheng, H.*; Hattori, Takanori; Sano, Asami; Tulk, C. A.*; Molaison, J.*; Feygenson, M.*; Ivanov, I. N.*; Yang, W.*; Mao, H.-K.*

Inorganic Chemistry, 54(23), p.11276 - 11282, 2015/12

 Times Cited Count:6 Percentile:29.14(Chemistry, Inorganic & Nuclear)

Pressure-induced polymerization of triple bonds would produce conductive conjugated double bonds. To find a metal cyanide with a low polymerization pressure, anhydrous Li$$_{3}$$Fe(CN)$$_{6}$$ is synthesized and its crystal structure is determined. The irreversible bonding between the CN$$^{-}$$ can be realized by use of the industrial apparatus. The conductivity is enhanced by more than 3 orders of magnitude, which makes the polymerized Li$$_{3}$$Fe(CN)$$_{6}$$ a potential cathode material for rechargeable lithium batteries.

Journal Articles

Growth of single-phase nanostructured Er$$_2$$O$$_3$$ thin films on Si (100) by ion beam sputter deposition

Mao, W.*; Fujita, Masaya*; Chikada, Takumi*; Yamaguchi, Kenji; Suzuki, Akihiro*; Terai, Takayuki*; Matsuzaki, Hiroyuki*

Surface & Coatings Technology, 283, p.241 - 246, 2015/12

 Times Cited Count:3 Percentile:13.17(Materials Science, Coatings & Films)

Single-phase nanocrystalline thin films of Er$$_2$$O$$_3$$ (440) has been first prepared using Si (100) substrates by ion beam sputter deposition at 973 K at a pressure of $$<$$ 10$$^{-5}$$ Pa and $${it in}$$-$${it situ}$$ annealing at 1023 K at a pressure of $$approx$$ 10$$^{-7}$$ Pa. Er silicides formed during the deposition are eliminated via the annealing, which results in the single phase and the smooth surface of the Er$$_2$$O$$_3$$ thin films. The epitaxial relationship between Si (100) and Er$$_2$$O$$_3$$ (110) is clarified by X-ray diffraction and reflection high energy electron diffraction.

Journal Articles

Overview of plasma-material interaction experiments on EAST employing MAPES

Ding, F.*; Luo, G.-N.*; Pitts, R.*; Litnovsky, A.*; Gong, X.*; Ding, R.*; Mao, H.*; Zhou, H.*; Wampler, W. R.*; Stangeby, P. C.*; et al.

Journal of Nuclear Materials, 455(1-3), p.710 - 716, 2014/12

 Times Cited Count:29 Percentile:88.91(Materials Science, Multidisciplinary)

Journal Articles

Adsorption of H atoms on cubic Er$$_2$$O$$_3$$ (001) surface; A DFT study

Mao, W.*; Chikada, Takumi*; Shimura, Kenichiro*; Suzuki, Akihiro*; Yamaguchi, Kenji; Terai, Takayuki*

Journal of Nuclear Materials, 443(1-3), p.555 - 561, 2013/11

 Times Cited Count:3 Percentile:24.61(Materials Science, Multidisciplinary)

In this work, ${it ab initio}$ calculations based on density functional theory (DFT) and generalized gradient approximation were performed to investigate the structural and electronic properties of the cubic Er$$_{2}$$O$$_{3}$$ (001) surface and H adsorption processes on this surface. Several stable adsorption sites were identified, and at the most energetically favorable adsorption sites it was found that H bonds with O atoms at the cubic Er$$_{2}$$O$$_{3}$$ (001) surface with an adsorption energy of 295.68 kJ mol$$^{-1}$$ at coverage 1/8 ML, which was inclined to decrease with the increase of H coverage ($$>$$ 1/4 ML). In addition, the calculations revealed that the dissociative H atom configurations have adsorption energies that are at least 152.64 kJ mol$$^{-1}$$ greater than the H$$_2$$ molecule configurations on the surface. These results are discussed in regard of the hydrogen isotope permeation behavior in the tritium permeation barrier in a fusion reactor.

Journal Articles

Experimental and computational studies on tritium permeation mechanism in erbium oxide

Mao, W.*; Chikada, Takumi*; Suzuki, Akihiro*; Terai, Takayuki*; Yamaguchi, Kenji

Journal of Plasma and Fusion Research SERIES, Vol.10, p.27 - 32, 2013/02

A tritium permeation barrier (TPB) is strongly required in fusion blankets for the reduction of loss of fuel and radiological hazard. However, the precise tritium permeation mechanism through the TPB coatings has not been clarified yet, because of their complicated crystal structures. To understand the microscopic mechanism, we have not only prepared and characterized nanostructured ceramic Er$$_2$$O$$_3$$ thin films, but also studied the energetics and mobility of hydrogen atom in cubic bulk Er$$_2$$O$$_3$$ using ab initio density-functional calculations. The estimated diffusion activation energy ($$E$$$$_{a}$$) of interstitial H is somewhat higher than the diffusion energy barrier observed experimentally at 873 K. It is then considered that diffusion and permeation of hydrogen and its isotopes through the Er$$_2$$O$$_3$$ coatings are likely to be dominated by the grain boundary rather than by the grain.

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