Harjo, S.; 川崎 卓郎; 土田 紀之*; 諸岡 聡; Gong, W.
鉄と鋼, 107(10), p.887 - 896, 2021/10
In situ neutron diffraction measurements of two low-alloy TRIP steels and a 304-type stainless steel during tensile and creep tests were performed at room temperature. Changes in the diffraction pattern, the peak integrated intensities of austenite () and the peak positions of were analyzed and discussed to understand a relationship between intergranular stress in and the occurrence of martensitic transformation during deformation. From tensile loading, it was found that the susceptibility of martensitic transformation depended on -() grains, in which -(111) grains underwent martensitic transformation at the latest. The -() dependence in the susceptibility of martensitic transformation was found to be controlled by the shear stress levels in -() grains, which were affected by the intergranular stress partitioning during deformation.
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
Harjo, S.; 川崎 卓郎; 土田 紀之*; 諸岡 聡; Gong, W.*
ISIJ International, 61(2), p.648 - 656, 2021/02
neutron diffraction measurements of two low-alloy steels and a 304-type stainless steel during tensile and creep tests were performed at room temperature. Changes in the diffraction pattern, the integrated peak intensities of austenite (), and the peak positions of were analyzed and discussed to elucidate the relationship between intergranular stress in and the occurrence of martensitic transformation during deformation. Tensile loading experiments revealed that the susceptibility to martensitic transformation depended on the -(hkl) grains, where -(111) grains underwent martensitic transformation at the latest. The -hkl dependence of the susceptibility to martensitic transformation was found to be controlled by the shear stress levels in -(hkl) grains, which were affected by the intergranular stress partitioning during deformation.
Zhang, X. X.*; Andr, H.*; Harjo, S.; Gong, W.*; 川崎 卓郎; Lutz, A.*; Lahres, M.*
Materials & Design, 198, p.109339_1 - 109339_9, 2021/01
Here, in-situ neutron diffraction is employed to explore the residual strains, stresses, and dislocation density in the LPBF AlSi10Mg during loading-unloading-reloading deformation. It is found that the maximum residual stresses of the Al and Si phases in the loading direction reach up to about -115 (compressive) and 832 (tensile) MPa, respectively. A notable dislocation annihilation phenomenon is observed in the Al matrix: the dislocation density decreases significantly during unloading stages, and the amplitude of this reduction increases after experiencing a larger plastic deformation. At the macroscale, this dislocation annihilation phenomenon is associated with the reverse strain after unloading. At the microscale, the annihilation phenomenon is driven by the compressive residual stress in the Al matrix. Meanwhile, the annihilation of screw dislocations during unloading stages contributes to the reduction in total dislocation density.
Wang, Y.*; 友田 陽*; 大村 孝仁*; Gong, W.*; Harjo, S.; 田中 雅彦*
Acta Materialia, 196, p.565 - 575, 2020/09
The continuous and discontinuous yielding behaviors in ferrite-cementite steels were complementarily investigated via nano- and macroscale deformation examinations. The results obtained by electron microscopy, synchrotron X-ray, and neutron diffractions indicate that the ferrite-cementite interface of the heat-treated specimen is semi-coherent with a high internal stress field, whereas that of the recrystallized one is incoherent with a low internal stress field. Moreover, coherency strain, which depends on the total area of the ferrite-cementite interface, and thermal strain, which is governed by temperature, are the two factors that influence peak broadening. The nanoindentation tests revealed that the critical loads are significantly lower near the semi-coherent interface than those near the incoherent interface and the ferrite grain boundary; this suggests that dislocations are easily emitted from the semi-coherent interface.
Harjo, S.; 窪田 哲*; Gong, W.*; 川崎 卓郎; Gao, S.*
Acta Materialia, 196, p.584 - 594, 2020/09
To understand work hardening behavior during low-cycle loading, ductile cast iron containing spheroidal graphite, pearlite, and ferrite matrix was investigated in an in situ neutron diffraction study of up to four cycles of tensile-compressive loading with applied strains of 0.01. The amplitudes of applied stress, Bauschinger stress, and Bauschinger strain were found to increase with increasing cycle number, indicating work hardening as cyclic loading progressed. Absolute values of ferrite lattice strain at maximum and minimum applied strains increased with increasing cycle number, indicating an increase in ferrite strength. Consequently, the stress contribution to the strength from ferrite increased as cyclic loading progressed. The increase in ferrite strength, caused by dislocation accumulation in ferrite during cyclic loading, played an important role in the work hardening of the ductile cast iron.
友田 陽*; Wang, Y.*; 大村 孝仁*; 関戸 信彰*; Harjo, S.; 川崎 卓郎; Gong, W.*; 谷山 明*
鉄と鋼, 106(5), p.262 - 271, 2020/05
The phase transformation behavior from austenite upon cooling in a 1.5Mn-1.5Si-0.2C steel was monitored using dilatometry, X-ray and neutron diffractions. The starting temperature of ferrite transformation was in good agreement between dilatometry and neutron diffraction, whereas much higher in X-ray diffraction. Such a discrepancy in transformation temperature is attributed to the change in chemical composition near the surface of a specimen heated to elevated temperatures in a helium gas atmosphere for X-ray diffraction. neutron diffraction enables us to investigate the changes in lattice constants of ferrite and austenite, which are affected by not only thermal contraction but also transformation strains, thermal misfit strains and carbon enrichment in austenite. Pearlite transformation started after carbon enrichment in austenite reached approximately 0.7 mass% and contributed to diffraction line broadening.
Harjo, S.; 相澤 一也; Gong, W.*; 川崎 卓郎
Materials Transactions, 61(5), p.828 - 832, 2020/04
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.
Wang, Y.*; 友田 陽*; 大村 孝仁*; 諸岡 聡; Gong, W.*; Harjo, S.
Acta Materialia, 184, p.30 - 40, 2020/02
A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium-carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during quenching with and without the ausforming process. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. After ausforming, the data reveal that lattice parameters are larger in austenite whereas smaller in martensite compared with those in the non-ausformed case, which is ascribed to the introduced dislocations. The cutting-edge operant quantitative measurements with neutron diffraction for steel production is demonstrated.
Mthis, K.*; Drozdenko, D.*; Nmeth, 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
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 200C 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.
柴田 曉伸*; 竹田 泰成*; Park, N.*; Zhao, L.*; Harjo, S.; 川崎 卓郎; Gong, W.*; 辻 伸泰*
Scripta Materialia, 165, p.44 - 49, 2019/05
Nowadays, a new concept of process utilizing dynamic ferrite transformation, which can achieve ultrafine-grained structure with a mean grain size of approximately 1m, has been proposed. This paper reports transformation mode of dynamic ferrite transformation and formation mechanism of ultrafine-grained structure revealed by our novel technique of neutron diffraction analysis during thermomechanical processing. Dynamic ferrite transformation occurs in a diffusional manner, whose partitioning behavior changes from para- to ortho-equilibrium with the progress of transformation. Moreover, we propose that dynamic recrystallization of dynamically-transformed ferrite is the main mechanism for the formation of ultrafine-grained structure.
友田 陽*; 小嶋 真由美*; Harjo, S.; Gong, W.*; 佐藤 成男*; Ungr, T.*
Materials Science & Engineering A, 743, p.32 - 39, 2019/01
Heterogeneous plastic deformation behavior of oriented individual grains-family with respect to the tensile direction in austenitic steels was studied using electron back scatter diffraction (EBSD) and neutron diffraction (ND) measurements. The kernel averaged misorientation value determined by EBSD for a plastically deformed specimen was different in grain to grain, suggesting different dislocation densities. Such insights obtained from the surface observations with EBSD were quantitatively evaluated as bulk-averaged data using ND. The convolutional multiple whole profile fitting (CMWP) for ND profiles has revealed different dislocation densities in oriented grains-families, showing good coincidence with the EBSD results in trend.
川崎 卓郎; 中村 龍也; Gong, W.*; 及川 健一
Physica B; Condensed Matter, 551, p.460 - 463, 2018/12
Neutron diffraction is widely used for the investigation of lattice strain, texture and phase transformation in bulk materials. Although the distributions of these characteristics can be obtained by scanning the sample, the spatial resolution of the measurement is limited. Recently, Bragg-edge imaging technique is developed and adopted for the evaluations of lattice strain, crystal orientation and phase distributions in polycrystalline engineering materials such as steel. On the other hand, neutron diffraction imaging has a potential to be another technique for such purpose. Diffraction imaging at a pulsed neutron source requires a counting type two-dimensional position sensitive detector with high spatial resolution. We developed prototype imaging detector with wavelength-shifting fiber (WLSF) readout, and tried to observe sub grains in the b-Sn single crystal and grain distribution in the coarse-grained steel plate at NOBORU (BL10) of J-PARC MLF.
川崎 卓郎; 稲村 泰弘; 伊藤 崇芳*; 中谷 健; Harjo, S.; Gong, W.*; 相澤 一也
Journal of Applied Crystallography, 51(3), p.630 - 634, 2018/06
A time-resolved time-of-flight neutron diffraction technique to characterize the structural properties of materials during cyclic tests has been developed. By adopting the developed technique, the behaviors of the crystal lattice and domains of the piezoelectric material in a multilayer-type piezoelectric actuator driven by a cyclic electric field were evaluated. The variation in diffraction intensity during the application of a cyclic electric field was obtained successfully, and the hysteresis-like behaviors of both the lattice strain and the 90 domain switching were revealed.
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
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.
中村 良彦*; 柴田 曉伸*; Gong, W.*; Harjo, S.; 川崎 卓郎; 伊東 篤志*; 辻 伸泰*
Proceedings of International Conference on Martensitic Transformations: Chicago, p.155 - 158, 2018/04
The microstructure evolution of medium manganese steel (Fe-5Mn-2Si-0.1C (wt%)) during thermo-mechanical processing in ferrite + austenite two-phase region was investigated by in situ neutron diffraction analysis and microstructure observations. When the specimens were isothermally held at a temperature of 700C, the fraction of reversely transformed austenite increased gradually with an increase in the isothermal holding time. However, it did not reach the equilibrium fraction of austenite even after isothermal holding for 10 ks. On the other hand, the fraction of reversely transformed austenite increased rapidly after the compressive deformation at a strain rate of 1 s at 700C and reached the equilibrium state during subsequent isothermal holding for around 3 ks.
中島 健次; 川北 至信; 伊藤 晋一*; 阿部 淳*; 相澤 一也; 青木 裕之; 遠藤 仁*; 藤田 全基*; 舟越 賢一*; Gong, W.*; et al.
Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12
Harjo, S.; 土田 紀之*; 阿部 淳*; Gong, W.*
Scientific Reports (Internet), 7(1), p.15149_1 - 15149_11, 2017/11
Two TRIP-aided multiphase steels with different carbon contents were analyzed in situ during tensile deformation by time-of-flight neutron diffraction to clarify the deformation induced martensitic transformation behavior and its role on the strengthening mechanism. The difference in the carbon content affected mainly the difference in the phase fractions before deformation, where the higher carbon content increased the phase fraction of retained austenite (). However, the changes in the relative fraction of martensitic transformation with respect to the applied strain were found to be similar in both steels since the carbon concentrations in were similar. The stress contribution from martensite was observed increasing during plastic deformation while that from bainitic ferrite hardly changing and that from decreasing.
Harjo, S.; 川崎 卓郎; 友田 陽*; Gong, W.*; 相澤 一也; Tichy, G.*; Shi, Z.*; Ungr, T.*
Metallurgical and Materials Transactions A, 48(9), p.4080 - 4092, 2017/09
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 m 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.
Harjo, S.; 川崎 卓郎; 友田 陽*; Gong, W.
Materials Science Forum, 905, p.46 - 51, 2017/08
To understand the strengthening mechanism of a metallic material with high dislocation density, the plastic deformation behavior of lath martensite was studied by means of in situ neutron diffraction measurements during tensile deformations using a 22SiMn2TiB steel and a Fe-18Ni alloy. The characteristics of dislocation were analyzed and were discussed with the relation of stress-strain curves. The dislocation densities induced by martensitic transformation during heat-treatment in both materials were found to be originally as high as 10 m order, and subsequently to increase slightly by the tensile deformation. The parameter M value which displays the dislocation arrangement dropped drastically at the beginning of plastic deformation in both materials, indicating that the random arrangement became more like a dipole arrangement.