Fusion of data-driven approach and physical metallurgy
- S. Noguchi and J. Inoue, “Stochastic characterization and reconstruction of material microstructures for establishment of process-structure-property linkage using the deep generative model”, Physical Review E, 104 (2021) 025302.
- S. Noguchi, H. Wang, J. Inoue, "Identification of microstructures critically affecting material properties using machine learning framework based on metallurgists' thinking process", Scientific Reports, https://doi.org/10.1038/s41598-022-17614-0
Recrystallization and evolution of a texture is the complex phenomenon affected by various kinds of factors, and the problem which is the main dominating factor of recrystallization has not been resolved. In this study, application of Data-driven method for recrystallization model was done and the dislocation density contained in the subgrain was estimated quantitatively. For the model of recrystallization mechanism, a multi phase-field model was adopted and the recrystallization has been assumed to be a subgrain growth affected by the grain boundary energy and mobility depending on misorientation, and driving force caused by dislocation density. As observation data, microstructure obtained by Electron Back Scattering Diffraction analysis was used. By repeating procedure that is consisted of annealing and analysis several times, the recrystallization process in the same view point was observed. Then the dislocation density was estimated by assimilating simulation data with observation data. By comparing estimated value with experimental value the validity of model can be discussed quantitatively.
- S. Ito, H. Nagao, T. Kurokawa, T. Kasuya, and J. Inoue, “Bayesian inference of grain growth prediction via multi-phase-field models”, Physical Review Materials, 3 (2019) 053404.
- S. Ito, H. Nagao, T. Kasuya, and J. Inoue, “Grain growth prediction based on data assimilation by implementing 4DVar on multi-phase-field model”, Science and Technology of Advanced Materials, 18 (2017) 857-868.
- S. Ito, H. Nagao, A. Yamanaka, Y. Tsukada, T. Koyama, M. Kano, and J. Inoue, “Data assimilation for massive autonomous systems based on a second-order adjoint method”, Physical Review E, 94 (2016) 043307.
Depending on alloy composition and process control, the microstructure of steels may consist of a range of different phases. If the microstructure consists of more than one phase, the properties of the material strongly depend on the type and distribution of the respective phases. Therefore, it is crucial to determine the type and amount of the different phases in order to assess the underlying structure-property relationship. In this study, an efficient deep learning method is presented for distinguishing microstructures of a low- carbon steel. There have been numerous endeavors to reproduce the human capability of perceptually classifying different textures using machine learning methods, but this is still very challenging owing to the need for a vast labeled image dataset. Therefore, we introduce an unsupervised machine learning technique based on convolutional neural networks and a superpixel algorithm for the segmentation of a low-carbon steel microstructure without the need for labeled images. The effectiveness of the method is demonstrated with optical microscopy images of steel microstructures having different patterns taken at different resolutions. In addition, several evaluation criteria for unsupervised segmentation results are investigated along with the hyperparameter optimization.
- H. Kim, J. Inoue, T. Kasuya. "Unsupervised microstructure segmentation by mimicking metallurgists' approach to pattern recognition." Scientific Reports , https://doi.org:/10.1038/s41598-020-74935-8.
- H. Kim, Y. Arisato, J. Inoue, "Unsupervised segmentation of microstructural images of steel using data mining methods.", Computational Materials Science 210 (2022) 110855.
It is well-known that the key of almost everything in materials science relates to process-structure-property-performance (PSPP) relationships, which are far from being well-understood. When establishing PSPP relationships of a material using data driven techniques, two modeling routes can be adopted; forward modeling for prediction and inverse modeling for materials discovery. In general, the former is usually not difficult because its relationship is many to one. On the other hand, the latter whose relationship is one to many requires much more effort for at least two reasons: (i) the model parameters may have different values or not consistent with the data, and (ii) discovering the model parameters usually requires the exploration of a huge parameter space. In this study, we aim to solve inverse problems in materials research especially in case of various properties of metallic materials by applying sparse modeing.
There have been various numerical models to explain phase transformation of steels suggested by researchers. The transformation process can be identified by fitting model parameters to experimentally obtained dilatometric curves. However, several issues still remain to be resolved. The first issue is related to the uncertainty in the kinetic models. It is widely accepted that models are imperfect since real phenomena are composed of complex physics taking place across different lengths and time scales. Even if the correct values of the model inputs are used in a simulation, the output of the model will differ owing to the incomplete understanding of the model parameters and insufficient knowledge of the underlying physics. The second issue is related to the uncertainty arising from the choice of a particular model class. In this study, a Bayesian approach is presented for clarifying the best kinetic model explaining the transformation kinetics of a low-carbon steel under different continuous cooling conditions only form dilatometric curves. To estimate kinetic parameters as well as the model plausibility of candidate kinetic models, the exchange Markov chain Monte Carlo method was used. The effectiveness of the proposed method was demonstrated by metallographic investigations of the ferrite formation in a Fe-0.15C-1.5Mn alloy. It is shown that the method is successfully applied for clarifying ferrite transformation kinetics, such as transformation start temperatures, formation mechanisms, and fractions of microstructures.
Deformation and phase transformation kinetics of structural materials
When steel austenite is continuously cooled from Ae3 temperature, plate-like or lath-like ferrite products usually form, which play important roles in determining the mechanical properties of low-carbon steels. For instance, coarse-grained WF or BF may form fracture initiation sites, reducing the fracture toughness of steels. In order to control the microstructures and mechanical properties of low-carbon steels, it is important to reveal the transformation mechanism of these microstructures. Examples of our in-situ observations of the transformation behavior can be found here.
- S. Komine, K. Sekido, and J. Inoue. "In-situ measurement of surface relief induced by Widmanstätten and bainitic ferrites in low carbon steel by digital holographic microscopy." Scripta Materialia 162 (2019) 241-245.
- J. Inoue, S. Komine, R. Misaki, and K. Sekido. "Development of digital holographic microscope for in-situ surface relief measurement of low-carbon steel." Materials Transactions 1 (2019) 42-48.
- S. Nambu, M. Ojima, J. Inoue, T. Koseki, and HKDH Bhadeshia, “In situ observations and crystallographic analysis of martensitic transformation in steel”, Acta Materialia, 61 (2013) 4831-4839
- Y. Mishiro, S. Nambu, J. Inoue, and T. Koseki, “Effect of Stress on Variant Selection in Lath Martensite in Low-carbon Steel”,ISIJ International, 53 (2013) 1453-1461
- 奥信明・朝倉健太郎・井上純哉・小関敏彦, 「低炭素鋼の連続冷却過程におけるフェライトプレート形成その場観察」, 鉄と鋼, 94 (2008) 363-368
Lath martensite has long been used as the primary phase for tool materials due to its exceptional combination of hardness and toughness, while recently it has been increasingly applied as one of the primary phases to enhance the strength of advanced high-strength steel (AHSS). This new interest in lath martensite has led to the need for better understanding of its plastic deformation behaviors, and a number of papers have reported its plastic deformation under different loading conditions. In our lab, various deformation behaviors of structural materials, not only steel but also Mg and Al alloys under different loading conditions has been analyzed through in-situ observation. Examples of such observation can be found here.
- J. Inoue, A. Sadeghi, and T. Koseki. "Slip band formation at free surface of lath martensite in low carbon steel." Acta Materialia 165 (2019) 129-141.
- A. Sadeghi, J. Inoue, N. Kyokuta, and T. Koseki, “In situ deformation analysis of Mg in multilayer Mg-steel structures”, Materials & Design, 119 (2017) 326-337
- “Effects of Solute Carbon on the Work Hardening Behavior of Lath Martensite in Low-Carbon Steel”, T. Niino, J. Inoue, M. Ojima, S. Nambu, and T. Koseki, ISIJ International, 57 (2017) 181-188.
- H. Na, S. Nambu, M. Ojima, J. Inoue, and T. Koseki. "Strain localization behavior in low-carbon martensitic steel during tensile deformation." Scripta Materialia 69 (2013) 793-796.
- H. Na, S. Nambu, M. Ojima, J. Inoue, and T. Koseki. "Crystallographic and Microstructural Studies of Lath Martensitic Steel During Tensile Deformation." Metallurgical and Materials Transactions A 45 (2014) 5029-5043.
- S. Nambu, M. Michiuchi, Y. Ishimoto, J. Inoue, and T. Koseki, “Transition in Deformation Behavior of Martensitic Steel during Large Deformation under Uniaxial Tensile Loading”, Scripta Materialia, 60 (2009) 221-224
- M. Michiuchi, S. Nambu, J. Inoue, and T. Koseki, “Relationship between Local Deformation Behavior and Crystallographic Features of As-quenched Lath Martensite during Uniaxial Tensile Deformation”, Acta Materialia, 57 (2009) 5283
Development of multilayered metallic composite
Multilayered steels have been developed to provide a novel route to achieving higher-performance steels by employing a high-strength steel and a high-ductility steel independently in the layer structure. It has been clarified that multilayered steels exhibit exceptional combinations of strength and ductility compared with existing monolithic steels and also excellent deformation behaviors under high-strain-rate deformation as well as good formability. Those improved performances of multilayered steel are achieved by increased interfacial toughness between the layers and decreased thickness of the brittle steel layers according to the fracture toughness of the brittle steel and the strength of the ductile steel.
- T. Koseki, J. Inoue, and S. Nambu. "Development of Multilayer Steels for Improved Combinations of High Strength and High Ductility." Materials Transactions 55 (2014) 227-237.
- J. Taendl, S. Nambu, J. Inoue, N. Enzinger, and T. Koseki, “Friction stir welding of multilayered steel”, Science and Technology of Welding and Joining, 17 (2012) 244-253
- P. Lhuissier, J. Inoue, and T. Koseki, “Strain field in a brittle/ductile multilayered steel composite”, Scripta Materialia, 63 (2011) 970-973
- S. Nambu, M. Michiuchi, J. Inoue, and T. Koseki, “Effect of Interfacial Bonding Strength on Tensile Ductility of Multi-layered Steel Composite”, Composites Science and Technology, 69 (2009) 1936–1941
- J. Inoue, S. Nambu, Y. Ishimoto, and T. Koseki, “Fracture Elongation of Brittle/Ductile Multilayered Steel Composites with a Strong Interface”, Scripta Materialia, 59 (2008) 1055-1058
The concept of multilayered steels has been extended to Mg/steel multilayered composite. For the development of the Mg/steel multilayer, new bonding technique between Mg and steel was first developed, which can be found in this page. With the help of the new bonding technique, the excellent mechanical properties of Mg/steel multilayered was demonstrated. The improved strength of the multilayer samples was clarified due to the combined effect of surface crack prevention by the steel layer and the higher work-hardening rate caused by the possible increased activity of non-basal systems.
- J. Inoue, A. Sadeghi, N. Kyokuta, T. Ohmori, and T. Koseki. "Multilayer Mg-stainless steel sheets, microstructure, and mechanical Properties." Metallurgical and Materials Transactions A 48 (2017) 2483-2495.
- A. Sadeghi, J. Inoue, N. Kyokuta, and T. Koseki. "In situ deformation analysis of Mg in multilayer Mg-steel structures." Materials and Design 119 (2017) 326-337.
- A. Sadeghi, N. Kyokuta, J. Inoue, and T. Koseki, “Effect of initial texture and microstructure of Mg on mechanical properties of Mg - Stainless steel laminated metal composites”, Materials Characterization, 127 (2017) 171-178
- A. Cetin, J. Krebs, A. Durussel, A. Rossoll, J. Inoue, T. Koseki, and A. Mortensen, “Laminated Metal Composites by Infiltration”, Metallurgical and Materials Transactions A, 42A, 3509-3520 (2012)
Stress partition measurement using high energy beams
Stress partitioning in multilayered steels consisting of martensitic and austenitic layers was measured during tensile deformation by in situ neutron diffraction measurements to investigate the mechanism of the improved strength–elongation balance. The deformation mode can be classified into three stages, and the results indicate that the applied stress is effectively transferred to the martensitic phase, because no stress concentration sites exist, owing to the multilayered structure. Hence, even as-quenched martensite can deform uniformly, resulting in improved strength–elongation balance in multilayered steels.
- P.-G. Xu, S. Harjo, M. Ojima, H. Suzuki, T. Ito, W. Gong, S.C. Vogel, J. Inoue, Y. Tomota, K. Aizawa, and K. Akita, “High stereographic resolution texture and residual stress evaluation using time-of-flight neutron diffraction”, Journal of Applied Crystallography, 51 (2018) https://doi.org/10.1107/S1600576718004004.
- 小島真由美・城鮎美・鈴木裕士・井上 純哉・菖蒲敬久・徐平光・秋田貢一・南部 将一・小関敏彦，「放射光X線回折法を用いた積層型高強度鋼板におけるマルテンサイト層の局所変形挙動評価」，材料，66（2017）420-426
- R. Cao, X. Xu, Z. Feng, M. Ojima, J. Inoue, and T. Koseki, “Effect of Annealing Temperature and Time on Microstructure and Mechanical Properties of Multilayered Steel Composite Sheets”, Metallurgical and Materials Transactions A, 47A (2016) 6042-6055
- RI. Barabash, OM. Barabash, M. Ojima, ZZ. Yu, J. Inoue, T. Koseki, and ZL. Feng, “Interphase Strain Gradients in Multilayered Steel Composite from Microdiffraction”, Metallurgical and Materials Transactions A, 45A (2014) 98-108
- M. Ojima, J. Inoue, S. Nambu, P. Xu, K. Akita, H. Suzuki, and T. Koseki. "Stress partitioning behavior of multilayered steels during tensile deformation measured by in situ neutron diffraction." Scripta Materialia 66 (2014) 139-142.
Mechanical properties of thin films
New technique to evaluate the fracture toughness of a brittle thin film on a elastoplastic substrate was developed. In this technique, the fracture toughness can be evaluated simply from the thickness of the brittle layer and the crack interval in the layer after applying uniaxial tensile deformation. The technique was applied to various kinds of Intermetallic compound layer developed on steel substrates to reveal the fracture behavior of brittle thin films.
- 坪田大・井上純哉，「Fe-Zn系金属間化合物複相皮膜の破壊機構」，鉄と鋼，102 (2016) 714-721
- N. Kyokuta, M. Koba, T. Araki, S. Nambu, J. Inoue, and T. Koseki. "Fracture toughness evaluation of thin Fe-Al intermetallic compound layer at reactive interface between dissimilar metals." Materials Transactions 54 (2013) 994-1000.
- J. Inoue, Y. Fujii, and T. Koseki, “Void Formation in Nanocrystalline Cu Film during Uniaxial Relaxation Test”, Acta Materialia, 56 (2008) 4921-4931
Formation mechanism of bonding interface between dissimilar metals
Heterogeneous bonding has been of constant interest in recent years, because combining the properties of two base materials by forming a strong and ductile bond has a wide range of applications in industry. The formation kinetics of microstructure at bonding interface is the key for developing new bonding techniques.
- 井上純哉・三輪哲嗣・小関敏彦，「純亜鉛融液／鋼界面におけるFe-Zn系金属間化合物形成に及ぼす鋼中Siの影響」, 鉄と鋼，19（2014）390-396
- M. Koba, T. Araki, S. Nambu, J. Inoue, and T. Koseki, “Bonding Interface Formation between Mg Alloy and Steel by Liquid-phase Bonding using the Ag Interlayer”,Metallurgical and Materials Transactions A, 43A (2012) 592-597
- G. Reboul, S. Nambu, J. Inoue, and T. Koseki, “Phase Evolution During the Liquid-Phase Bonding of Zirconium and Austenitic Stainless Steel with Zinc Insertion”, Metallurgical and Materials Transactions A, 43A (2012) 2366-2377
- C. Schneider, T. Weinberger, J. Inoue, T. Koseki, and N. Enzinger, “Characterization of interface of steel/magnesium FSW”, Science and Technology of Welding and Joining, 16 (2011) 100-106
- T. Araki, M. Koba, S. Nambu, J. Inoue, and T. Koseki, “Reactive Transient Liquid Phase Bonding AZ31 Magnesium Alloy and Low Carbon Steel”, Materials Transactions, 52 (2011) 568-571