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

https://doi.org/10.1016/j.jmst.2023.07.036

The yield stress of Fe-24Ni-0.3C (wt.%) metastable austenitic steel increased 3.5 times (158 551 MPa) when the average grain size decreased from 35 m (coarse-grained [CG]) to 0.5 m (ultrafine-grained [UFG]), whereas the tensile elongation was kept large (0.87 0.82). 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.

Heat-induced structural changes in magnesium alloys AZ91 and AZ31 investigated by in situ synchrotron high-energy X-ray diffraction

Liu, X. J.*; Xu, P. G.; Shiro, Ayumi*; Zhang, S. Y.*; Shobu, Takahisa; Yukutake, Eitaro*; Akita, Koichi*; Zolotoyabko, E.*; Liss, K.-D.*

Journal of Materials Science, 57(46), p.21446 - 21459, 2022/12

https://doi.org/10.1007/s10853-022-07917-y

Mictomagnetism and suppressed thermal conduction of the prototype high-entropy alloy CrMnFeCoNi

Yang, J.*; Ren, W.*; Zhao, X.*; Kikuchi, Tatsuya*; Miao, P.*; Nakajima, Kenji; Li, B.*; Zhang, Z.*

Journal of Materials Science & Technology, 99, p.55 - 60, 2022/02

https://doi.org/10.1016/j.jmst.2021.04.077

High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices, differing from traditional alloys. Here, we investigate magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering. Direct-current (dc) and alternating-current (ac) magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions in the entire temperature region and three anomalies are found at about 80, 50, and 20 K, which are related to the paramagnetic to antiferromagnetic transition, the antiferromagnetic to ferromagnetic transition, and the spin freezing, respectively. The electrical and thermal conductivities are significantly reduced compared to Ni and the temperature dependence of lattice thermal conductivity exhibits a glass-like plateau. Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.

Atomistic simulations for the effects of stacking fault energy on defect formations by displacement cascades in FCC metals under Poisson's deformation

Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro; Kawabata, Tomoya*; Suzuki, Katsuyuki*

Journal of Materials Science, 54(16), p.11096 - 11110, 2019/08

https://doi.org/10.1007/s10853-019-03688-1

Synthesis of multilayered composite nanotube heterostructure; SiC-SiO, C-SiO, and C-SiC-SiO nanotubes

Taguchi, Tomitsugu; Shamoto, Shinichi

Journal of Materials Science, 47(10), p.4363 - 4369, 2012/05

https://doi.org/10.1007/s10853-012-6290-9

Three types of composite nanotube heterostructures (two double-layered and one triple-layered structure) are synthesized by simple heat treatment, forming SiC-SiO, C-SiO, and C-SiC-SiO composite coaxial nanotubes. These multilayered composite nanotubes consist of several components with different electrical properties, for example, metal, semiconductor and insulator components. In particular, C-SiC-SiO triple-layered nanotubes with metallic, semiconducting and insulating layers are synthesized for the first time. These multilayered nanotubes can be expected to find applications in nanoscale heterostructure electronic and optical devices.

High-temperature pyrolysis of ceramic fibers derived from polycarbosilane-polymethylhydrosiloxane polymer blends with porous structures

Kita, Kenichiro; Narisawa, Masaki*; Nakahira, Atsushi*; Mabuchi, Hiroshi*; Ito, Masayoshi*; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of Materials Science, 45(1), p.139 - 145, 2010/01

https://doi.org/10.1007/s10853-009-3905-x

The polymer blends of polycarbosilane (PCS) and polymethylohydrosiloxane with high molecular weight (PMHS-h) were prepared by freeze-drying process. Melt viscosity, themogravimetric analysis, and gas evolution from the polymer blends were analyzed. The polymer blend of HSah15 (15 mass% PMHS-h to PCS) was melt-spun to fiber form, curing by thermal oxidation and pyrolyzed at various temperatures up to 1773 K. The fibers were investigated by tensile tests, FE-SEM observation, and XRD (X-ray diffraction) analysis. After pyrolysis at 1273 K, there were amounts of pores in the cross sections of the fiber derived from HSah15, and after pyrolysis at 1773 K, no remarkable -SiC crystal were formed on the outside surface of the fiber derived from HSah15.

Carcinogen adsorbent prepared from DNA complex by -ray irradiation

Furusawa, Kazuya*; Kita, Erika*; Saeki, Toshihiko*; Nagasawa, Naotsugu; Nishi, Norio*; Dobashi, Toshiaki*

Journal of Biomaterials Science; Polymer Edition, 19(9), p.1159 - 1170, 2008/09

To insolubilize DNA for preparing a novel carcinogen adsorbent, effects of -ray irradiation on aqueous solutions of mixtures of DNA with cross-linking biopolymers (CBP): gelatin, bovine serum albumin, carboxymethyl cellulose and hydroxyethyl-cellulose, O-[2-hydroxy-3-(trimethyl ammonio)-propyl], chloride have been studied. DNA-CBP hybrid gels were successfully prepared from aqueous mixtures of DNA with CBP in a limited range of irradiation dose. Gel fraction (Gf) and swelling ratio (S) of the hybrid gels were measured. The Gf and S of hybrid gels increased and decreased, respectively, with increasing irradiated dose. Adsorption of one of carcinogen, acridine orange, was also examined for the gels. From the experimental results, the optimum condition for preparing insolubilized homogeneous DNA gels was determined.

Synthesis of a minute SiC product from polyvinylsilane with radiation curing, 2; Ceramization process of radiation cured polyvinylsilane

Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito; Tanaka, Shigeru; Narisawa, Masaki*; Okamura, Kiyohito*; Ito, Masayoshi*

Journal of Materials Science, 42(1), p.130 - 135, 2007/01

https://doi.org/10.1007/s10853-006-1041-4

We have synthesized minute SiC products from polyvinylsilane (PVS), which is a liquid organosilicon polymer, with radiation curing. Since there is a close relationship between the properties of obtained SiC products and pyrolysis condition, it is important to investigate the ceramization process of PVS in order to find out the optimum pyrolysis condition. In this paper, the ceramization process of the PVS cured by -ray irradiation at room temperature was investigated by gas analysis, thermogravimetric analysis, density measurement, and so on. It was found that the ceramization of -ray cured PVS starts above 500K, and that drastic organic-inorganic conversion occurs in the temperature range of 700-1100K. According to the results of the changes of mass and density, it was found that the volume shrinkage of PVS during the curing and pyrolysis processes is 80%. The SiC obtained by pyrolysis at 1573K showed the density of 2.50g/cm and microvickers hardness of 31.6GPa.

Synthesis of a minute SiC product from polyvinylsilane with radiation curing, 1; Radiation curing of polyvinylsilane

Idesaki, Akira; Sugimoto, Masaki; Tanaka, Shigeru; Narisawa, Masaki*; Okamura, Kiyohito*; Ito, Masayoshi*

Journal of Materials Science, 39(18), p.5689 - 5694, 2004/09

https://doi.org/10.1023/B:JMSC.0000040077.94183.ac

Irradiation effect of -ray on polyvinylsilane (PVS), which is a liquid organosilicon polymer, was investigated and the optimum curing condition to synthesize a minute SiC product with radiation curing was discussed. Room temperature and liquid nitrogen temperature (77K) were examined as the irradiation temperature. In both cases, the cured PVS maintaining its formed shape could be obtained by -ray irradiation under vacuum, and the cured PVS in solid state at room temperature was obtained by irradiation with dose of above 3-4MGy. It was found that the efficiency of crosslinking in case of the irradiation at room temperature is higher than that in case of irradiation at 77K. The PVS injected into a mold was irradiated by -ray with dose of 3.6MGy at room temperature under vacuum, and pyrolyzed at 1273 K in Ar gas atmosphere. As a result, minute SiC products which had similar shapes to the mold and the sizes of 30-60m were obtained.

The Toughness of free-standing CVD diamond

Davies, A. R.*; Field, J. E.*; Takahashi, Koji; Hada, Kazuhiko

Journal of Materials Science, 39(5), p.1571 - 1574, 2004/03

https://doi.org/10.1023/B:JMSC.0000016153.90600.a6

A four-point bend test was used to determine the fracture toughness of mechanical grade and di-electric (optical) grade chemical vapour deposited (CVD) diamond. The validity of the test was first confirmed by measuring the toughness of alumina and confirming the results with literature values. The toughnesses of both types of CVD were similar; 8.51.0 and 8.30.4 MPa () respectively. This is higher than the value of 3.40.5 MPa () measured for diamond by Field and Freeman, 1981 using an indentation technique. It is suggested that this is primarily due to differences in surface roughness. There were enough samples to make a preliminary study of the effect of temperature and these data are reported.