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論文

Hydrogen desorption spectra from excess vacancy-type defects enhanced by hydrogen in tempered martensitic steel showing quasi-cleavage fracture

齋藤 圭*; 平出 哲也; 高井 健一*

Metallurgical and Materials Transactions A, 50(11), p.5091 - 5102, 2019/11

 被引用回数:1 パーセンタイル:60.52(Materials Science, Multidisciplinary)

低温熱脱離分析法(L-TDS)と陽電子消滅法(PAS)を用い、擬へき開破壊を示す焼戻しマルテンサイト鋼中の種々のトラップサイトの中から、水素存在下塑性ひずみにより導入された格子欠陥からの脱離による水素ピークを分離し同定する試みを行った。水素の存在下において塑性ひずみを付与した鋼試験片をL-TDSにより測定することで、2つのピーク、すなわち元から存在していた脱離と新たな脱離の分離を可能にした。PASの結果からL-TDSによって新たに見出された脱離は空孔型欠陥に対応することが明らかとなった。水素存在下における塑性ひずみは、破面から1.5mm以内に形成される格子欠陥濃度を原子比で約10$$^{-5}$$オーダーまで著しく増大させた。これらの結果は、水素存在下における塑性変形がナノボイド核形成と合体をもたらし、焼戻しマルテンサイト鋼の擬へき開破壊をもたらすことを示している。

論文

Work hardening, dislocation structure, and load partitioning in lath-martensite determined by ${it in situ}$ neutron diffraction line profile analysis

Harjo, S.; 川崎 卓郎; 友田 陽*; Gong, W.*; 相澤 一也; Tichy, G.*; Shi, Z.*; Ungar, T.*

Metallurgical and Materials Transactions A, 48(9), p.4080 - 4092, 2017/09

AA2017-0020.pdf:3.33MB

 被引用回数:11 パーセンタイル:26.87(Materials Science, Multidisciplinary)

${it in situ}$ neutron diffraction during tensile deformation of lath martensite steel containing 0.22 mass% of carbon, is performed using TAKUMI of J-PARC. The diffraction peaks at plastically deformed states exhibit asymmetries as the reflection of redistributions of the stress and dislocation densities/arrangements in lath-packets where the dislocation glides are favorable (soft packet) and unfavorable (hard packet). The dislocation density is as high as 10$$^{15}$$ m$$^{-2}$$ at the as-quenched state, and then during tensile straining, the load and the dislocation density become different between the two lath-packets. The dislocation character and arrangement vary also in the hard packet, but hardly change in the soft packet. The hard packet plays an important role in the high work hardening in martensite, which could be understood by taking into account not only the increase of the dislocation density but also the change in dislocation arrangement.

論文

Composite behavior of lath martensite steels induced by plastic strain, a new paradigm for the elastic-plastic response of martensitic steels

Ung$'a$r, T.*; Harjo, S.; 川崎 卓郎; 友田 陽*; Rib$'a$rik, G.*; Shi, Z.*

Metallurgical and Materials Transactions A, 48(1), p.159 - 167, 2017/01

AA2016-0372.pdf:2.81MB

 被引用回数:16 パーセンタイル:15.64(Materials Science, Multidisciplinary)

Based on high-resolution neutron diffraction experiments we will show that in lath martensite steels the initially homogeneous dislocation structure is disrupted by plastic deformation, to produce a composite on the length scale of martensite lath packets. The diffraction patterns of plastically strained martensitic steel reveal characteristically asymmetric peak profiles in the same way as has been observed in materials with heterogeneous dislocation structures. Lath packets oriented favorably or unfavorably for dislocation glide become soft or hard. The lath packet type develops by work softening or work hardening in which the dislocation density becomes smaller or larger compared to the initial average one. The decomposition into soft and hard lath packets is accompanied by load redistribution between the two lath packet types. The composite behavior of plastically deformed lath martensite opens a new way to understand the elastic-plastic response in this class of materials.

論文

Mechanical properties and microstructure of dissimilar friction stir welds of 11Cr-ferritic/martensitic steel to 316 stainless steel

佐藤 裕*; 粉川 博之*; 藤井 啓道*; 矢野 康英; 関尾 佳弘

Metallurgical and Materials Transactions A, 46(12), p.5789 - 5800, 2015/12

PNC-FMSとSUS316鋼の異材接合に摩擦攪拌接合(Friction stir welding)を適用し、系統的に強度と組織の評価を実施した。その結果、接合欠陥の生じない健全な継手を得ることができた。なお、本研究の一部は、文部科学省原子力基礎基盤戦略研究イニシアチブにより実施された「摩擦攪拌接合によるNa高速炉心材料の新たな接合技術に関する研究」の成果である。

論文

First-principles study on the grain boundary embrittlement of metals by solute segregation, 1; Iron(Fe)-Solute(B, C, P, and S) systems

山口 正剛

Metallurgical and Materials Transactions A, 42(2), p.319 - 329, 2011/02

The microscopic mechanism of grain boundary embrittlement in metals by solute segregation has been not well understood for many years. From first-principles calculations, we show here that the calculated cohesive energy (= surface energy - grain boundary energy) of bcc Fe $$Sigma$$3(111) symmetrical tilt grain boundary is reduced by the segregation of sulfur and phosphorous, while it is increased by the segregation of boron and carbon. The rate of the decrease/increase in the cohesive energy was excellently proportional to the experimental shift in the ductile-to-brittle transition temperature of high-purity iron with increasing segregation. It indicates that the change in the cohesive energy of grain boundary plays a key role in the grain boundary embrittlement.

論文

First-principles study on the grain boundary embrittlement of metals by solute segregation, 2; Metal(Fe, Al, Cu)-Hydrogen (H) systems

山口 正剛; 海老原 健一; 板倉 充洋; 門吉 朋子*; 鈴土 知明; 蕪木 英雄

Metallurgical and Materials Transactions A, 42(2), p.330 - 339, 2011/02

The microscopic mechanism of grain boundary embrittlement in metals by hydrogen trapping (segregation) has been not well understood for many years. From first-principles calculations, we show here that the calculated cohesive energy of bcc Fe $$Sigma$$3(111) and fcc Al(Cu) $$Sigma$$5(012) symmetrical tilt grain boundaries with varying the trapping density of hydrogen can be significantly reduced by hydrogen trapping; it indicates that the reduction of the cohesive energy of the grain boundary may cause the hydrogen-induced grain-boundary embrittlement in Fe, Al, and Cu, although the possibility of hydrogen trapping at grain boundary is very different among those metals. Considering the "mobile" effect of hydrogen during fracture, more hydrogen atoms coming from solid solution state can be trapped on the gradually formed two fracture surfaces in addition to the already trapped "immobile" hydrogen atoms at the grain boundary before fracture.

論文

Mechanisms of neutron irradiation hardening in impurity-doped ferritic alloys

西山 裕孝; Liu, X.*; 亀田 純*

Metallurgical and Materials Transactions A, 39(5), p.1118 - 1131, 2008/05

Mechanisms of neutron-irradiation hardening in phosphorus (P), sulfur (S) and/or copper (Cu) doped ferritic alloys have been studied by applying a rate theory to temperature dependence of the yield strength. In P-doped alloys, neutron irradiation below 563 K brings about a remarkable increase in the athermal stress and activation energy due to more extensive dispersion of fine ($$sim$$1.7 nm) P-rich precipitates than Cu-rich precipitates. During neutron irradiation above 668 K, precipitation hardening occurs to some extent in Cu-doped and S-doped alloys, compared to small or negligible hardening in the P-doped alloys. In alloys with low to moderate contents of various dissolved impurities subjected to the high-temperature irradiation, the formation of kink pairs becomes considerably difficult. Differing dynamic interactions of dissolved and precipitated impurities with the nucleation and growth of dislocations are discussed, giving rise to irradiation hardening.

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