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Liss, K.-D.*; Han, J.-K.*; Blankenburg, M.*; Lienert, U.*; Harjo, S.; 川崎 卓郎; 徐 平光; 行武 栄太郎*; Kawasaki, M.*
Journal of Materials Science, 23 Pages, 2024/00
被引用回数：0 パーセンタイル：0.01(Materials Science, Multidisciplinary)The magnesium alloy AZ31, which has undergone high-pressure torsion processing, was subjected to in situ annealing micro-beam synchrotron high-energy X-ray diffraction and compared to the as-received rolled sheet material that was investigated through in situ neutron diffraction. While the latter only exhibits thermal expansion and minor recovery, the nanostructured specimen displays a complex evolution, including recovery, strong recrystallization, phase transformations, and various regimes of grain growth. Nanometer-scale grain sizes, determined using Williamson-Hall analysis, exhibit seamless growth, aligning with the transition to larger grains, as assessed through the occupancy of single grain reflections on the diffraction rings. The study uncovers strain anomalies resulting from thermal expansion, segregation of Al atoms, and the kinetics of vacancy creation and annihilation. Notably, a substantial number of excess vacancies were generated through high-pressure torsion, and maintained for driving the recrystallization and forming highly activated volumes for diffusion and phase precipitation during heating. The unsystematic scatter observed in the Williamson-Hall plot indicates high dislocation densities following severe plastic deformation, which significantly decreases during recrystallization. Subsequently, dislocations reappear during grain growth, likely in response to torque gradients in larger grains. It is worth noting that the characteristics of unsystematic scatter differ for dislocations created at high and low temperatures, underscoring the strong temperature dependence of slip system activation.
Liss, K.-D.*; 徐 平光; 城 鮎美*; Zhang, S. Y.*; 行武 栄太郎*; 菖蒲 敬久; 秋田 貢一*
Advanced Engineering Materials, 9 Pages, 2023/00
In polycrystals, grains with certain orientations grow at high temperatures at the expense of grains with other unfavorable orientations. Grain growth involves a variety of situations and mechanisms that make experimental study, modeling, and understanding extremely complex. Normal grain growth occurs in a self-similar manner, with curved grain boundaries serving as the driving force and a parabolic growth law that scales up the grain size by the square root of time. More complex growth forms include boundary pinning of precipitates and other boundaries, topological transitions that alter driving forces, grain coalescence and anomalous grain growth, but these are considered "erratic" and their initiation is an open question in modern research, without a simple experimental approach on how they should be studied. Here, we show that grain rotation upon coalescence is spontaneously activated between one grain and a favorable neighbor, through the necessary diffusive mass transport at further boundaries of the same grain leading to their activation and a competitive "erratic" reorientation in a zigzag way, while other grains in the matrix remain stable. After two grains have eventually coalesced, their surrounding boundaries are still activated leading to further rotation and growth, filling the missing puzzle stone in thermodynamic theory between normal and abnormal growth, the latter stating that abnormal growth only takes place when the size of the growing grain is already large. Prerequisites and postulates of abnormal grain growth are based on advantageous texture, grain boundary mobility, enhanced diffusion kinetics and coalescence, which can be well explained by our observations. Moreover, our observations have been enabled through a novel experimental approach using the white-beam X-ray Laue diffraction method in bulk transmission mode on a polycrystalline.
Liu, X. J.*; 徐 平光; 城 鮎美*; Zhang, S. Y.*; 菖蒲 敬久; 行武 栄太郎*; 秋田 貢一*; Zolotoyabko, E.*; Liss, K.-D.*
Journal of Materials Science, 57(46), p.21446 - 21459, 2022/12
被引用回数：3 パーセンタイル：41.53(Materials Science, Multidisciplinary)In situ time/temperature-resolved synchrotron high-energy X-ray diffraction is applied to study heat-mediated structural changes and phase transformations in rolled sheets of AZ91 and AZ31 magnesium alloys. Azimuthal diffraction intensities along the Debye-Scherrer rings (AT-plots) are used to obtain information on grain recovery and recrystallization temperatures as well as temperature-assisted grain rotations. The azimuthally integrated diffraction intensities, plotted as functions of the scattering vector (QT-plots), provide vital data on the temperature-dependent lattice parameters of the Mg/Al matrix and intermetallic precipitates, as well as on the evolution of the precipitates' volume fraction. It was found that in AZ31, the main precipitates are of the AlMn type, which is rather stable in the investigated temperature range (up to 773 K). In contrast, in AZ91, the major intermetallic precipitates, Al
Mg
, undergo complete dissolution above 600 K. It is caused by the enhanced diffusion of Al into the Mg/Al matrix, which according to the Al-Mg phase diagram, can adopt more Al at elevated temperatures. This diffusion is revealed by the proportional diminishing of the matrix lattice parameter (chemical strain), allowing us to quantify the Al content in the matrix. Fast temperature-dependent manipulation with intermetallic content in the Mg/Al alloy can, in principle, be used for controlling its mechanical properties.
城 鮎美*; 菖蒲 敬久; 萩原 幸司*; 渡邉 真史*
SPring-8/SACLA利用研究成果集(インターネット), 10(5), p.438 - 446, 2022/10
長周期積層型(LPSO)マグネシウム合金は、濃度と構造の変調が同期しており、軽量かつ高強度・高耐熱性という性質を併せ持った新規材料である。LPSO相の局所的な格子ひずみと構造変調の関係を調べるために、単相18R LPSO Mg-Zn-Y合金の圧縮下での
放射光X線回折測定を実施した。圧縮応力の増加に伴い、格子ひずみの増加が確認されるとともに、0 0 L回折面からの回折強度の大小が入れ替わる現象が発生した。解析の結果、回折強度の変化はイットリウム原子の特徴的な変位によるものであり、弾性変形から塑性変形への移行に大きな影響を与える可能性を明らかにした。
Zn
Y
during compression and tensionHarjo, S.; 相澤 一也; Gong, W.*; 川崎 卓郎
Materials Transactions, 61(5), p.828 - 832, 2020/04
被引用回数：6 パーセンタイル：37.38(Materials Science, Multidisciplinary)In situ neutron diffraction measurements during compressive and tensile tests of an as-cast MgZnY alloy consisting of 
phase (Mg) as the matrix and a long period stacking ordered phase (LPSO) of 25 vol%, were performed to understand deformation behavior of each phase and to monitor the occurrence of kinking during deformation. The LPSO grains yielded possibly via kinking during compressive deformation above the applied true stress of about 137 MPa. The stress partitioning among Mg grains was observed larger in the compressive deformation than in the tensile deformation, that might be due to the large load sharing of Mg grains as a result of the yielding of LPSO grains during compressive deformation.
investigation of the microstructure evolution in Long-Period-Stacking-Ordered (LPSO) magnesium alloys as a function of the temperatureM
this, K.*; Drozdenko, D.*; N
meth, G.*; Harjo, S.; Gong, W.*; 相澤 一也; 山崎 倫昭*; 河村 能人*
Frontiers in Materials (Internet), 6, p.270_1 - 270_9, 2019/11
被引用回数：7 パーセンタイル：31.21(Materials Science, Multidisciplinary)Deformation behavior of two Mg-Zn-Y magnesium alloys, having a different fraction of the long-period-stacking-ordered (LPSO) phase, has been investigated at room temperature and 200
C by a combination of neutron diffraction (ND) and acoustic emission (AE) measurements. The results indicate that the twinning in the magnesium matrix and the kinking in the LPSO phase strongly depend on the composition of the material and the testing temperature. Further, active deformation mechanisms and particularly the load transfer from the magnesium matrix to the LPSO phase define the mechanical properties of the investigated alloys.
諸岡 聡; Gong, W.; Harjo, S.; 相澤 一也
no journal, ,
本研究は動的な引張-圧縮間その場中性子回折を用いて濃度変調と構造変調を伴ったシンクロ型LPSOマグネシウム合金の可逆繰り返し硬化挙動を調査することを目的とする。最大引張応力と最大圧縮応力は繰返し数の増加に伴い上昇し、繰返し数200回時の最大引張応力と最大圧縮応力はそれぞれ+97.4 and -176.7MPaである。これは、最大圧縮応力が圧縮変形時に生じる双晶(キンク帯)の影響により最大引張応力よりも大きくなったと示唆しており、このキンク帯は、動的な引張-圧縮間の(
)結晶粒群の積分強度の変化から可逆的生成・消滅が生じている証拠が本実験手法により得られている。
諸岡 聡; Gong, W.*; 相澤 一也; 川崎 卓郎; Harjo, S.
no journal, ,
Recently, a series of magnesium alloys containing a 18R Long-Period Stacking Ordered (LPSO) structure, have attracted considerable attention because they exhibit excellent mechanical properties, including high strength and reasonable ductility. To determine the plastic deformation behaviour of LPSO structure and the origin of the deformation mechanism are important for further materials development. In this study, deformation-kinking behavior of a Mg
Zn
Y
alloy was investigated by in-situ neutron diffraction during cyclic deformation. In-situ TOF neutron diffraction experiments during tension-compression and compression-tension cyclic loading at room temperature were performed by TAKUMI at MLF of J-PARC. The peak stress in the compression is larger than that of the tension, suggesting that quasi-twinning accompanying with hardening was occurred in compression deformation. On the other hand, results of individual (hkl) lattice strains in the loading direction show that, the (60.0) family grains in the loading direction accommodated a greater portion of elastic strain than that of the (00.18) family grains in the loading direction start accommodated less portion. This indicated that the latter started to yield prior to that of the former, causing the former to carry more applied load, i.e., intergranular stress. The large intergranular stresses generated with the progress of deformation, were speculated to accelerate the backward plastic flow that resulting in an increase of the Bauschinger stress and Bauschinger strain.
Y合金引張変形の中性子回折モニタリングHarjo, S.; 相澤 一也; Gong, W.*; 川崎 卓郎
no journal, ,
MgZnY合金はMg相と長周期積層(LPSO)相からなるマグネシウム合金であり、LPSO相の相分率は約25%である。LPSO相を含有したマグネシウム合金は、熱間押出後従来のマグネシウム合金よりも高強度および高延性を示す。熱間押出中にLPSO相に導入されたキンク組織がLPSO相を含有したマグネシウム合金に強化を与えることが知られている。キンク強化されたマグネシウム合金の強化メカニズムを調べる目的で引張変形中の格子面の応答をより詳しく調べるために鋳造後及び熱間押出後のMgZnY合金の引張変形中の中性子回折実験を行った。
ZnY consisting of LPSO phase and Mg phaseHarjo, S.; 相澤 一也; Gong, W.*; 川崎 卓郎
no journal, ,
MgZnY alloy is a magnesium alloy with a duplex microstructure consisting of a long period stacking ordered (LPSO) phase and an Mg phase. Kink deformation was observed in an as-cast MgZnY alloy subjected to hot compression, and the refinement of LPSO via kinking was found to be the reason for strengthening of the material from microscopy analyses. However, direct evidences showing the increase in strength via kinking have not been observed so far. In the present work, in situ neutron diffraction was used to investigate the anisotropic deformation behavior of LPSO and Mg phases during uniaxial compression or tension in an as-cast MgZnY alloy and an extruded MgZnY alloy. The evolutions of phase stresses in both the LPSO and Mg phases were evaluated and discussed with the occurrences of twinning and kinking during compression or tension.
ZnY内のMgとLPSO間の応力分配と押出比の関係Harjo, S.; 相澤 一也; Gong, W.*; 川崎 卓郎; 山崎 倫昭*; 河村 能人*
no journal, ,
押出比が異なる高温押出したMgZnY合金を室温で引張変形させならその場中性子回折実験を行った。高温押出によるMgとLPSOの集合組織の変化及び変形中の両相間の相応力分配を調べて、強化機構を議論する。
Harjo, S.; 相澤 一也; 川崎 卓郎; Gong, W.; 山崎 倫昭*; 河村 能人*
no journal, ,
MgZn
Y
alloy is a magnesium alloy consisting an Mg phase as the matrix and a Long-Period Stacking Ordered (LPSO) phase with the volume fraction of about 25%. In situ neutron diffractions during compression at room temperature of MgZnY alloys in as-casted condition and hot-extruded conditions with the extrusion ratios of 5.0, 7.5 and 12.5 were conducted to elucidate the deformation mechanism after hot-extrusion. The evolutions of integrated intensities of diffraction peaks, lattice strains of individual constituent phases measured from neutron diffraction were plotted with the applied stress and strain, and twinning in Mg and kinking in LPSO phase were discussed.
Harjo, S.; Gong, W.; 相澤 一也; 川崎 卓郎; 山崎 倫昭*; 河村 能人*
no journal, ,
Interesting mechanical properties changes were found in MgZnY alloy containing about 25-vol% long-period stacking ordered phase (LPSO) in the HCP structured matrix (Mg), by hot-extrusion. In situ neutron diffraction measurements during tensile loading were conducted on three MgZnY alloys with different processes: as-casted, and after hot-extrusion at 623 K with extrusion ratios of 5.0 and 12.5, to elucidate the relation between the changes in microstructure by hot-extrusion with the changes in mechanical property. The yield strength of Mg increased by the hot-extrusion, but when the extrusion ratio increased the Mg yield strength ironically decreased. LPSO was found to be strengthened monotonically as the extrusion ratio increased.
Harjo, S.; 相澤 一也; Gong, W.; 川崎 卓郎; 山崎 倫昭*; 河村 能人*
no journal, ,
The MgZnY alloy, a magnesium alloy with a duplex microstructure consisting of an phase (Mg) and a long period stacking ordered phase (LPSO) of approximately 25 vol.%, showed high strength and high ductility after hot extrusion at 623 K. To understand tensile deformation behavior of each phase and effect of kinks to the strength of the alloy, we have performed in situ neutron diffraction measurements during tensile tests of the alloys in an as-cast condition and after extruded at 623 K with different extrusion ratios.
Harjo, S.; 相澤 一也; Gong, W.; 川崎 卓郎
no journal, ,
Mg相とLPSO相で構成される2相Mg合金は、熱間押出により強度と延性が両方とも増加した。その原因及び変形メカニズムを明らかにするために、引張変形中の中性子回折実験を行い構成相それぞれの応力変化を調べた。得られた回折パターンから、変形中の格子ひずみ、集合組織等の変化を求め、そしてMg相及びLPSO相の相応力を評価し、変形メカニズム議論を行った。Mg相は軟質相として振る舞っているが、LPSO相の相応力は押出比とほぼ比例して大きくなった。
ZnY内のMgとLPSO間の応力分配Harjo, S.; 相澤 一也; Gong, W.; 川崎 卓郎; 山崎 倫昭*
no journal, ,
MgZnY合金は、Mg相とLPSO相の相分率が約25%からなる二相組織を持つLPSO型マグネシウム合金である。高温押出したMgZnY合金の繰り返し引張圧縮変形中のその場中性子回折による観察を行い、圧縮変形でのLPSO相のキンク変形と強度への効果について調べてみた。負荷ひずみが+0.01-0.02のサイクル実験での引張の最大応力は、2サイクル目では1サイクル目に比べると大きくなり、その増加量は負荷ひずみが+0.01-0.01の条件に比べて大きかった。構成相のそれぞれの集合組織,格子ひずみ等より相応力等を評価して圧縮変形でのLPSO相のキンク変形と強度への効果について詳細検討を行う。
Harjo, S.; Gong, W.; 川崎 卓郎; 相澤 一也
no journal, ,
HCP構造のマグネシウム合金の場合、弾塑性変形を開始すると、外力に対して格子ひずみが増加するhkl結晶粒と減少するhkl結晶粒が現れる。そのため応力への換算には、複数のhkl格子ひずみの平均、リートベルト法やポーリ法で得られた格子定数は用いられず、特定のhkl格子ひずみの選定に関する報告もなかった。本研究では、マグネシウム合金のその場中性子回折実験を行い、得られた格子ひずみ及び結晶方位変化より応力評価方法を検討した。
Mg/LPSO dual phase alloy by hot-extrusion using in situ neutron diffraction during deformationHarjo, S.; 相澤 一也; Gong, W.; 川崎 卓郎; 山崎 倫昭*
no journal, ,
In this study, in situ neutron diffraction during deformation was performed using three kinds of samples of MgZnY alloy: an as-casted sample (As-Cast), hot extruded samples with the extrusion ratio (R) values of 5.0 (R=5.0) and 12.5 (R=12.5). Crystallographic evolutions of Mg and LPSO phases by hot-extrusion and deformation behavior of the individual phases were investigated, and the unique deformation mechanism by hot-extrusion in this alloy will be discussed based on the obtained results.
