Dual nanoprecipitation and nanoscale chemical heterogeneity in a secondary hardening steel for ultrahigh strength and large uniform elongation

Wang, S.*; Wang, J.*; Zhang, S.*; Wei, D.*; Chen, Y.*; Rong, X.*; Gong, W.; Harjo, S.; Liu, X.*; Jiao, Z.*; et al.

Journal of Materials Science & Technology, 185, p.245 - 258, 2024/06

https://doi.org/10.1016/j.jmst.2023.10.048

Nanoprecipitates and nanoscale retained austenite (RA) with suitable stability play crucial roles in determining the yield strength (YS) and ductility of ultrahigh strength steels (UHSSs). However, owing to the kinetics incompatibility between nanoprecipitation and austenite reversion, it is highly challenging to simultaneously introduce high-density nanoprecipitates and optimized RA in UHSSs. In this work, through the combination of austenite reversion treatment (ART) and subsequent flash austenitizing (FA), nanoscale chemical heterogeneity was successfully introduced into a low-cost UHSS prior to the aging process. This chemical heterogeneity involved the enrichment of Mn and Ni in the austenite phase. The resulting UHSS exhibited dual-nanoprecipitation of Ni(Al,Mn) and (Mo,Cr) C and nanoscale austenite stabilized via Mn and Ni enrichment. The hard martensitic matrix strengthened by high-density dual-nanoprecipitates constrains the plastic deformation of soft RA with a relatively low fraction, and the presence of relatively stable nanoscale RA with adequate Mn and Ni enrichment leads to a marginal loss in YS but keeps a persistent transformation-induced plasticity (TRIP) effect. As a result, the newly-developed UHSS exhibits an ultrahigh YS of 1.7 GPa, an ultimate tensile strength (UTS) of 1.8 GPa, a large uniform elongation (UE) of 8.5 percent, and a total elongation (TE) of 13 percent. The strategy of presetting chemical heterogeneity to introduce proper metastable phases before aging can be extended to other UHSSs and precipitation-hardened alloys.

Grain orientation dependence of deformation microstructure evolution and mechanical properties in face-centered cubic high/medium entropy alloys

吉田 周平*; Fu, R.*; Gong, W.; 池内 琢人*; Bai, Y.*; Feng, Z.*; Wu, G.*; 柴田 曉伸*; Hansen, N.*; Huang, X.*; et al.

IOP Conference Series; Materials Science and Engineering, 1249, p.012027_1 - 012027_6, 2022/08

https://doi.org/10.1088/1757-899X/1249/1/012027

This study revealed characteristics of the deformation behavior in high/medium entropy alloys (HEAs/MEAs) with face-centered cubic (FCC) structure. A CoNi alloy and a CoCrNi MEA having low and high friction stresses (fundamental resistance to dislocation glide in solid solutions), respectively, but similar in other properties, including their stacking fault energy and grain sizes, were compared. The MEA exhibited a higher yield strength and work-hardening ability than those in the CoNi alloy at room temperature. Deformation microstructures of the CoNi alloy were composed of coarse dislocation cells (DCs) in most grains, and a few deformation twins (DTs) formed in grains with tensile axis (TA) nearly parallel to 111. In the MEA, three microstructure types were found depending on the grain orientations: (1) fine DCs developed in TA//100-oriented grains; (2) planar dislocation structures (PDSs) formed in grains with other orientations; and (3) dense DTs adding to the PDSs developed in TA//111-oriented grains. The results imply difficulty in cross-slip of screw dislocations and dynamic recovery in the MEA, leading to an increase in the dislocation density and work-hardening rate. Our results suggest that FCC high-alloy systems with high friction stress inherently develop characteristic deformation microstructures advantageous for achieving high strength and large ductility.

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.*; 服部 高典; 佐野 亜沙美; Li, N.*; Yang, W.*; Liu, G.*; et al.

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

https://doi.org/10.1002/adfm.202009131

有機-無機ハロゲン化物ペロブスカイトは非常に柔らかいために、圧力などの外部刺激により格子定数を容易に変化させることができ、有用な光電特性を引き出すのに有効である。一方でこの特性は、多少の加圧でも、格子を歪ませてしまい、光と物質の相互作用を弱め、それによる性能の低下を引き起こす。そこで本研究では、代表的な物質であるヨウ化メチルアンモニウム鉛に対して圧力効果および同位体効果を調べ、それらが格子歪を抑制することが分かった。このことは、それらが、これまで得られなかったような光学的,機械的特性を持つ物質を得る手段として有効であることを示している。

High stereographic resolution texture and residual stress evaluation using time-of-flight neutron diffraction

徐 平光; Harjo, S.; 小島 真由美*; 鈴木 裕士; 伊藤 崇芳*; Gong, W.; Vogel, S. C.*; 井上 純哉*; 友田 陽*; 相澤 一也; et al.

Journal of Applied Crystallography, 51(3), p.746 - 760, 2018/06

AA2018-0163.pdf:3.0MB

https://doi.org/10.1107/S1600576718004004

Neutron diffraction texture measurements provide bulk textures with excellent grain statistics even for large grained materials, together with the crystallographic parameters and microstructure information such as phase fractions, coherent crystallite size, root mean square microstrain, macroscopic/intergranular stress/strain. The procedure for high stereographic resolution texture and residual stress evaluation was established at the TAKUMI engineering materials diffractometer. The pole figure evaluation of a limestone standard sample with a trigonal crystal structure suggested that the obtained precision for texture measurement is comparable with the oversea well-established neutron beam lines utilized for texture measurements. A high strength martensite-austenite multilayered steel was employed for further verification of the reliability of simultaneous Rietveld analysis of multiphase textures and macro stress tensors. By using a geometric mean micro-mechanical model, the macro stress tensor analysis with a plane stress assumption showed a RD-TD in-plane compressive stress (about -330 MPa) in martensite layers and a RD-TD in-plane tensile stress (about 320 MPa) in austenite layers. The phase stress partitioning was ascribed to the additive effect of volume expansion during martensite transformation and the linear contraction misfit during water quenching.

Progress in bulk texture measurement using neutron diffraction

徐 平光; Harjo, S.; 伊藤 崇芳*; 森井 幸生*; Gong, W.; 鈴木 裕士; 秋田 貢一; 鈴木 徹也*; 友田 陽; Lutterotti, L.*

JPS Conference Proceedings (Internet), 8, p.031022_1 - 031022_6, 2015/09

https://doi.org/10.7566/JPSCP.8.031022

The current status of bulk texture measurements both using angle dispersive neutron diffraction and time-of-flight neutron diffraction at JAEA was briefly reviewed, then the effect of sample orientation coverage in the time-of-flight neutron diffraction on the reliability of reconstructed pole figure on the reliability of reconstructed pole figure was simply compared after the simultaneous Rietveld texture analysis. The similar texture results obtained at different orientation coverage levels suggests that it is possible to reduce the sample rotation times reasonably during the bulk texture measurement.

Male-sterility induced by -ray irradiation of African nightshade ( L. ssp. ) seed

Ojiewo, C. O.*; Agong, S. G.*; 村上 賢治*; 田中 淳; 長谷 純宏; 桝田 正治*

Journal of Horticultural Science & Biotechnology, 80(6), p.699 - 704, 2005/11

アフリカンナイトシェード( L. spp. )はアフリカでよく消費される葉野菜であるが、発芽から開花・結実までの期間が短いことから葉の収量が比較的少ない。つまり、生殖生長の開始後、花粉や種子,果実の発達に養分が送られるため、葉に対する養分の転流が少なくなることが原因である。本研究では、雄性不稔性を利用することによって、養分の転流を葉に向けることにより収量を増加させることを考え、線の種子照射により得られたさまざまな変異体を調査した。照射種子の発芽率,生存率,種子稔性並びに雄性不稔変異体誘発率から、100Gyの線が変異誘発に最適であると考えられた。M2世代で選抜された雄性不稔変異体には4つのタイプ、すなわち、(1)稔性は無いが酢酸カーミンで花粉が染色される個体、(2)酢酸カーミンで花粉が染色されない個体、(3)花粉が形成されない個体、及び(4)花粉量が著しく少ない個体、が見られた。本研究で得られた雄性不稔変異体は、生殖や果実形成を制限することによって、葉の収量の増加につながると期待される。

超重元素原子科学研究に向けたEBGP(Electron-Beam-Generated-Plasma)イオン源の開発

青木 涼太; 佐藤 哲也; 内馬場 優太; 宮地 優太*; Gong, G.; 名取 日菜*; 伊藤 由太; 浅井 雅人; 塚田 和明; 永目 諭一郎*

no journal, , 

原子番号が100を超える超重元素のイオンビームを物理・化学研究に応用するため、短寿命単一原子に適用可能な新しいイオン源としてEBGP(Electron Beam Generated Plasma)イオン源を構築した。本EBGPイオン源を、オンライン同位体分離器(Isotope Separator On-Line: ISOL)用に装着し、各種貴ガスを用いて、イオンビーム生成条件の探索を行った結果、イオン源が安定して動作することを確認するとともに、イオンビームが生成できることを確かめた。

反跳相関崩壊分光に向けたRaイオンのin-trap崩壊測定

内馬場 優太; 伊藤 由太; 佐藤 哲也; 青木 涼太; 浅井 雅人; Gong, G.; 塚田 和明; 名取 日菜; 宮地 優太; 永目 諭一郎*

no journal, , 

イオントラップされたRIイオンの崩壊分光による核種同定や崩壊相関を組み合わせた精密質量測定を目的として、大立体角での放射線及び崩壊反跳イオン検出が可能な特殊な電極構造を持つポールトラップを開発した。トラップ内に保持した不安定核イオンの崩壊に伴う放射線と反跳イオンの相関測定に向け、高周波電極至近における半導体検出器の動作試験とRaイオンを用いたin-trap崩壊測定の実証を行った。

High stereographic resolution texture and residual stress evaluation using time-of-flight neutron diffraction

徐 平光; Harjo, S.; 小島 真由美*; 伊藤 崇芳*; Gong, W.*; 鈴木 裕士; 秋田 貢一; 井上 純哉*; 友田 陽*; 相澤 一也

no journal, , 

The neutron diffraction technical environment for high stereographic resolution texture and residual stress combined evaluation was established at TAKUMI engineering materials diffractometer through proper neutron detector panel-region division. The pole figure evaluation of an limestone standard sample with a trigonal structure suggested that the texture measurement precision is comparable with that of the established neutron beamlines utilized for texture measurement, such as the HIPPO diffractometer at LANL and the D20 angle-dispersive neutron diffractometer at ILL. The martensite-austenite multilayered steel sheets were employed to further examine the reliability of simultaneous Rietveld analysis of the multiphase textures and the macro stress tensors. By using the BulkPathGEO micro-mechanical model, the macroscopic stress tensor analysis with a plane stress assumption confirmed a RD-TD in-plane compressive stress distribution in martensite layers and a RD-TD in-plane tensile stress distribution in austenite layers at a stress balance within 20 MPa. The phase stress partitioning at a stress level of 300 MPa was ascribed mainly to the additive effect of the volume expansion during martensite transformation and the linear contraction misfit between austenite layers and newly transformed martensite layers during the water quenching process.

Effect of hydrogen charging on anisotropic tensile deformation behavior of high strength steel plate

徐 平光; 石島 暖大; Qiu, H.*; 諸岡 聡; Gong, W.*; Harjo, S.

no journal, , 

Hydrogen-induced ductility loss or hydrogen embrittlement is related to the diffusional entrance of environmental hydrogen into ultrahigh strength steel materials. Neutron diffraction as a powerful nondestructive method has been developed well for monitoring the elastoplastic deformation and the crystallographic texture evolution. However, considering the tiny amount of diffusive hydrogen on crystal structure of steel materials, the monitoring using neutron diffraction is thought as a challenging research. Neutron diffraction during tensile deformation of cylinder samples prepared from a 12mm-thick high strength steel plate with and without hydrogen charging was carried out in situ, and the grain orientation rotations were discussed through the relative change of normalized integration intensity of individual diffraction peaks. The anisotropy of elastoplastic deformation behaviors of high strength steel plate and the effect of hydrogen charging on total elongation and reduction in the area has been confirmed. 110-fiber preferred orientation becomes stronger during uniaxial tensile deformation of samples with and without hydrogen charging; the complex multiaxial stress field during local necking deformation induces more evident weakening of final 110-fiber preferred orientation in the non-hydrogen steel than the hydrogen charged steel, suggesting that neutron diffraction is suitable for monitoring the plastic deformation of hydrogen-charged high strength steel.