Yusuke Onuki

• D. Eng.
• Associate Professor at Tokyo Denki University

Additive manufacturing (AM) involves an unprecedented thermal history during solidification and post-melt high-temperature exposure, leading to unique microstructural evolution. In this study, we employed neutron-diffraction-based microstructural analysis to better understand the microstructural evolution and mechanical behavior of AM alloys, with...

50 days' free access: https://authors.elsevier.com/c/1j82O3jWfF9iyZ

In this study, we investigate the influence of dislocation strengthening in the metastable parent phase on the deformation-induced martensitic transformation behavior of a face-centered cubic (fcc) Co20Cr20Fe34Mn20Ni6 high-entropy alloy. Annealed and hot-swaged specimens were prepared. In-situ neutron diffraction experiments captured an accelerated...

Medium manganese steels, containing 3~10 mass% of Mn, are considered promising as the 3rd generation high strength steel. In this study, in situ neutron diffraction experiments were conducted during uniaxial tensile deformation for Fe-4.91Mn-0.092C (mass%). The primary aim was to investigate the change of austenite texture accompanied with the defo...

The reverse transformation behavior during heating in Fe-10%Mn-0.1%C (mass%) martensitic alloy consisting of α’-martensite, ε-martensite and retained austenite was investigated using the in-situ neutron diffraction. When the temperature was elevated with a heating rate of 10 K/s, the ε→γ reverse transformation occurred first at the temperature rang...

The reverse transformation behavior during heating in Fe-10%Mn-0.1%C (mass%) martensitic alloy consisting of α'-martensite, ε-martensite and retained austenite was investigated using the in-situ neutron diffraction. When the temperature was elevated with a heating rate of 10 K/s, the ε→γ reverse transformation occurred first at the temperature rang...

A newly developed single BCC phase 30Nb5Ta30Ti15V20Zr refractory high entropy alloy (RHEA) has been designed for low density, high mechanical properties, and superior fretting wear resistance. In this study, we focus on the study of the fretting wear resistance in a comparison with Ti6Al4V alloy. The 30Nb5Ta30Ti15V20Zr demonstrated the better frett...

We reveal the mixed-mode mechanism of elastocaloric effect in the course of slim-hysteresis superelasticity in a severely deformed NiTi shape memory alloy with tailored (negative/zero/positive) thermal expansion anisotropy. It is shown that in addition to the latent heat of phase transformation, the reversible heat from elastic deformation (known a...

Herein, in situ temperature‐dependent neutron experiments investigate the microstructural evolution of additively and conventionally manufactured CoCrFeNi high‐entropy alloys, as‐received, and after grain refinement through high‐pressure torsion. The evolution of texture after grain refinement and during heating is consistent with typical fcc metal...

Ti–6Al–4V alloys undergo a multiple phase transformation sequence during electron beam powder bed fusion (EB-PBF) additive manufacturing, forming unique dislocation substructures. Thus, determining the dislocation density is crucial for comprehensively understanding the strengthening mechanisms and deformation behavior. This study performed time-of...

Copper and copper alloys exhibit wide varieties of deformation textures depending on the chemical compositions and production process. Precise analysis and modeling of texture evolutions are important for developing the various copper alloys efficiently. In this study, we conducted in–situ neutron diffraction experiments during tensile tests of pur...

In this study, a microstructure of moderately deformed 1 %C-doped CoCrFeNi complex concentrated alloys (CCA) was investigated in a correlation with microstructure evolution at different annealing temperature for 1 h. After 60 % thickness reduction of cold rolling, the dislocation density accumulated as large as 19 × 10¹⁵ m⁻². The interstitial carbo...

It is well known that variations of alloy and microstructural parameters i.e., alloy composition and grain size are favorable ways to improve the mechanical properties in non-heat-treatable aluminum alloys including Al–Mg alloys. It leads to a change in stress-strain curve behaviors. The flow stress is mainly correlated with dislocation interaction...

Metallic materials inherently possess small coefficients of thermal expansion (CTE). Engineering the CTEs of metals to large values is demanded in many applications but has proved challenging. Here, we propose a strategy to achieve large tailored CTEs in ferroelastically-transformable alloys through uniaxial stress state control by utilizing their...

This study demonstrates transformation-induced plasticity (TRIP) in conjunction with twinning-induced plasticity (TWIP) in α $ + $ + β titanium alloys by introducing metastable retained β-phase. By annealing at 850 °C followed by water quenching, metastable retained β-phase (∼25%) was obtained in Ti–6Al–4V alloy. Stress-induced phase transformation...

Strengthening of biomedical Co–Cr–Mo alloys has been explored via thermomechanical processing for enhancing the durability of their biomedical applications. However, the effects of cold and hot deformation on the cellular activity continue to be unclear. In this study, we prepared Co–Cr–Mo alloy rods via cold swaging and hot-caliber rolling and stu...

Retained austenite is a key feature used to realize the transformation-induced plasticity in bainitic high strength steels. In this study, the authors focused on the formation of metastable austenite in Fe-0.61C-1.9Si-0.98Mn (mass%) during isothermal heating processes using in situ neutron diffraction techniques. Quantitative discussion of carbon p...

A series of tensile tests of polycrystalline high purity iron were carried out in order to trace microscopic orientations in different grains during plastic deformation. Crystal rotations were classified into two stages: one was the initial stage to the maximum strength or onset of necking, and the other was the subsequent stage from necking to fra...

Ti–6Al–4V alloys prepared via electron beam powder bed fusion (EB-PBF) generally exhibit a hierarchical microstructure consisting of columnar β-grains, an acicular α-matrix, and nanoscale β-precipitates at α-lath interfaces. In this study, we performed time-of-flight neutron diffraction measurements to investigate the texture and volume fraction of...

This report demonstrates, for the first time, structural evolution during nano structuring by severe plastic deformation and comprehensive structural relaxation upon heating in an additive‐manufactured 316L stainless steel by applying the characterization techniques of X‐ray diffraction and in‐situ neutron diffraction analyses. This study by Megumi...

A multifunctional NiTi alloy with Invar (dimension-invariant), Elinvar (elastic modulus-invariant) and Rinvar (resistivity-invariant) properties over the temperature range from 125 K to 375 K is fabricated through cold rolling of 60% thickness reduction. The underlying microstructure of such multifunctional NiTi alloy mainly consists of B2 and B19′...

The relationship between the mechanism of high temperature deformation and the evolution behavior of microstructure and the texture during deformation, which has been found in various solid solution alloys, is clarified. It is shown that the preferential dynamic grain growth (PDGG) mechanism proposed by the authors can explain the behavior of micro...

The transformation and stabilization behaviors of the austenite (γ) phase during bainite transformation in the early stages of austempering treatment of low-alloy transformation-induced plasticity-aided bainitic ferrite (TBF) steel were investigated by in-situ neutron diffraction measurement and microstructure observation. Neutron diffraction peak...

Middle-carbon martensite steels are vital materials for mechanical components and their mechanical properties have attracted significant interest. However, the decrease in the elastic limit of the as-quenched materials is one of the remaining puzzles. Herein, we quantitatively characterized the dislocation density and its structure in the as-quench...

Herein, lab‐scale X‐ray diffraction and in situ heating neutron diffraction analyses for evaluating the structural changes at postprinting nanostructuring and structural relaxation upon heating, respectively, in an additive‐manufactured (AM) 316L stainless steel are conducted. The nanostructured AM steel after nanostructuring by high‐pressure torsi...

Texture memory is a phenomenon in which retention of initial textures occurs after a complete cycle of forward and backward transformations, and it occurs in various phase-transforming materials including cubic and hexagonal metals such as steels and Ti and Zr alloys. Texture memory is known to be caused by the phenomena called variant selection, i...

The CoCrFeMnNi high entropy alloys (HEAs) performs large work strengthening with excellent deformability. The work strengthening and deformation mechanism are facilitated by dislocation activities and dislocation accumulation. In this study, the dislocation density and microstructure of the CoCrFeMnNi HEA were characterized by the neutron line prof...

Cu-doped martensitic steels (Fe-(13, 16)Cr-3W-2Cu-1C) (mass%) with multiple carbide precipitates were prepared at different quenching temperatures, and their corrosion behaviours were examined by measuring the weight loss during immersion in a 0.5 M H 2 SO 4 solution. Lower weight losses and corrosion rates were obtained for the alloy samples prepa...

Manipulating macroscopic thermal expansion (TE) through microstructure engineering is emerging as a new research topic of shape memory alloys (SMAs). Here, we perform a modelling-and-experiment combined study to design and tune the coefficient of TE (CTE) of polycrystalline martensitic SMAs based on reorientation deformation. Using Landau thermodyn...

Many established, but also potential future applications of NiTi-based shape memory alloys (SMA) in biomedical devices and solid-state refrigeration require long fatigue life with 107–109 duty cycles1,2. However, improving the fatigue resistance of NiTi often compromises other mechanical and functional properties3,4. Existing efforts to improve the...

[in Japanese] Fullsize Image

Precipitation-hardened ferritic stainless steels are used for soft magnetic actuators of engines, as these steels exhibit high strength and soft magnetic properties. These ferritic stainless steels are hardened by nanoscale precipitates formed during an aging process after solution treatment. Furthermore, texture control of these steels is required...

Shear deformation is imposed on materials by several advanced techniques for microstructural and textural control. Shear texture evolved during deformation tends to remain after subsequent annealing. Texture evolutions with shear deformation and subsequent annealing in aluminum and Al-3mass%Mg alloy rolled sheets have been investigated by neutron d...

Texture memory of Si-Mn and ODS steels has been explored via in situ neutron time-of-flight and synchrotron high-energy X-ray diffractions as well as texture prediction by the double Kurdjumov-Sachs relation. The two steels exhibited very different behaviors of the texture memory. Three behaviors were observed: (1) for Si-Mn steel, the moderate ini...

Herein, the texture developments of γ austenite, ε martensite, and α’ martensite during the tensile deformation of SUS 304 stainless steel were observed by using the in situ neutron diffraction technique. Combined with the microstructure and local orientations measured by electron backscattered diffraction (EBSD), the mechanisms involved in the def...

Shape memory alloy (SMA) sheets processed via unidirectional rolling (UniR) exhibit macroscopic low thermal expansion (TE) over a wide temperature span but only along a certain direction. Here, we use controlled cross rolling (CroR) to achieve in-plane low coefficients of TE (CTEs) of polycrystalline NiTi sheets. It is shown that the in-plane CTEs...

The authors have developed the in situ neutron diffraction technique focusing on bainite transformation during austempering. Thanks to the features of time-of-flight type neutron diffraction, textures, phase fractions and lattice parameters can be simultaneously measured at high temperature. In this paper, the design of experimental equipment and a...

Relationship between dislocation multiplication and work hardening of tensile-deformed Cu-Zn alloys with different grain sizes was investigated. X-ray diffraction line-profile analysis was employed to evaluate dislocation parameters. It was confirmed that dislocation multiplication was enhanced with a decrease in the grain sizes. This was mainly ca...

Work hardening of solid–solution copper alloys is enhanced by dislocation multiplication during plastic deformation, and work hardening coefficients depend on alloying elements. To understand the effects of alloying elements of solid–solution copper alloys on work hardening, we investigated the dislocation evolution of Cu–2 at％ MS （MS＝Mg, Sn, Si） d...

Multiplication and rearrangement of dislocations in face-centered cubic (FCC) metals during tensile deformation are affected by grain size, stacking fault energy (SFE), and solute elements. X-ray diffraction (XRD) line-profile analysis can evaluate the dislocation density (ρ) and dislocation arrangement (M) from the strength of the interaction betw...

We tailor the temperature dependence of elastic modulus (TDEM) of polycrystalline NiTi plates by cold rolling up to 60% thickness reduction. In-plane Elinvar property is obtained with a low elastic modulus temperature coefficient of 6.0 × 10⁻⁵ K⁻¹ over a temperature range of 192 K. The microstructure mainly consists of approximately equal volume fr...

304 stainless steel is one of the most common stainless steels due to its excellent corrosion resistance and mechanical properties. Typically, a good balance between ductility and strength derives from deformation-induced martensite transformation (DIMT), but this mechanism has not been fully explained. In this study, we conducted in situ neutron d...

Surface effect-induced phase transformation heat treatment is performed on cold-rolled commercial pure titanium sheet to change and control the transformation texture. The results show that the type of final transformation texture changes from the texture memory effect type texture of TD-split basal to the surface effect type texture of 〈11−20〉//ND...

By using a steel with standardized chemical composition and conventional manufacturing processes for flat-rolled steel strip, a 1500 MPa class stainless steel sheet, whose product of yield strength (YS) and total elongation (El) exceeds 30000 MPa%, was developed and its mass production was established. Besides the excellent YS–El balance, the devel...

The demand for a reliable and quantitative method to determine phase fractions has been increasing due to the developments of multi-phase materials, such as TRIP steels. The authors conducted a mutual verification between the two methods for phase fraction analysis, the saturation magnetization measurement and the newly developed neutron diffractio...

In order to reveal the behaviors of two kinds of martensites (ε-M and α′-M) transformation during TRIP and reversion process and to separate transformation textures from rolling textures during the TRIP process, the phase transformation and texture evolution during cold rolling and the subsequent heating in high manganese TRIP steel were investigat...

By using a steel with standardized chemical composition and conventional manufacturing processes for flat-rolled steel strip, a 1,500 MPa class stainless steel sheet whose product of yield strength (YS) and total elongation (El) exceeds 30,000 MPa% was developed and its mass production has been established.Besides the excellent YS-El balance, the d...

Relationship between phase transformation and dislocation evolution of Fe-Mn-Si-Cr shape memory alloy upon tensile deformation and subsequent annealing treatment was investigated. Neutron diffraction and electron backscatter diffraction (EBSD) measurements were carried out to evaluate dislocation density and phase transformation. Reasonable phase f...

An in situ neutron diffraction experiment during austempering of low-alloyed transformation-induced plasticity steel, Fe-1.48Si-1.52Mn-0.15C, in wt pct was conducted. In this study, time-of-flight neutron diffractometer with a large detector coverage, iMATERIA at J-PARC MLF, was employed. The phase fraction and carbon concentration in austenite cou...

In order to study the plastic deformation mechanism of AZ31 magnesium alloy, in situ texture measurement during uniaxial tensile deformation is conducted by using neutron diffraction. The specimen is prepared from a rolled sheet so that the deformation axis is parallel to the rolling direction. By increasing strain, the alignment of <10-10> along t...

The overview of the recent works by the author at iMATERIA, BL20 of J-PARC MLF is introduced. From the viewpoint of microstructural control, the author and coworkers have expanded the availability of iMATERIA to metallurgical studies. The authors have established the measurement/analysis scheme for crystallographic textures and phase fractions in m...

鉄鋼材料に代表される金属のミクロ組織に対し，放射光，中性子線の量子ビームを用いた 新たなアプローチが可能になる．放射光の高輝度特性を活かしたマイクロ領域測定や高温そ の場測定により，構造材内部の転位の分布，転位の回復現象の追跡が可能となる．また，中 性子線はバルク平均情報の特徴を活かすことで，複相鋼の強化機構メカニズムが詳細に考察 できる．これら解析事例を原理とともに紹介する．

The authors have developed the simultaneous measurement scheme for texture and phase fraction by using the Time-Of-Flight (TOF) neutron diffractometer, iMATERIA at J-PARC MLF, Japan. The Rietveld texture analysis (RTA) was applied for the data analysis method, which has been developed mainly at HIPPO diffractometer at LANSCE, USA. Because of the di...

Co–Cr alloys have been used in biomedical purposes such as stents and artificial hip joints. However, the difficulty of plastic deformation limits the application of the alloys. During the deformation, Co–Cr alloys often exhibit strain-induced martensitic transformation (SIMT), which is a possible reason for the low formability. The distinct increa...

To investigate the characteristics of dislocation evolution in ferritic and austenitic stainless steels under tensile deformation, neutron diffraction line-profile analysis was carried out. The austenitic steel exhibited higher work hardening than the ferritic steel. The difference in the work hardening ability between the two steels was explained...

We carried out in situ tri-axial magnetostriction analysis for cube-oriented Fe-18%Ga single crystal by X-ray diffraction measurement under magnetic field. Periodic change in tri-axial magnetostriction with applied magnetic field direction was clearly observed. However, those values in [100] and [010] directions were not equivalent. Theoretical cal...

The accuracy of the phase fraction determined by time-of-flight neutron diffraction measurement at iMATERIA was verified by preparing model samples consisting of laminations of ferritic and austenitic stainless-steel sheets. Rietveld texture analysis, based on 132 diffractograms, was employed as the analysis method. The analyzed volume fractions of...

Fe-Ga alloys show large magnetostriction, which strongly depends on crystal orientation. This phenomenon is associated to some degree with large elastic anisotropy. In this study, white X-ray diffraction with micro-beam synchrotron radiation was used to evaluate the microscopic stresses evolved in a polycrystalline Fe-Ga alloy under tensile loading...

Texture is an important property especially for metallic materials having hexagonal close-packed crystal structure. In order to understand the overall property or change in the microstructure of materials, neutron diffraction is a powerful tool of investigation. In this study, we attempt to measure the textures of Ti­–6Al–­4V (mass%) alloy by using...

The texture control of Fe–Ga solid solution alloy is examined by high temperature deformation, based on the previously suggested mechanism of high temperature deformation texture formation, “preferential dynamic grain growth (PDGG)”. As the result of uniaxial compression deformation of Fe-15 mol% Ga alloy at 1173 K, sharp alignment of <001> along t...

We investigated the effect of the relationship between the scattering vector of neutron diffraction and the sample direction processed by cold-rolling on line-profile analysis. It was revealed that dislocation parameters became unstable when using a diffraction profile at the scattering vector parallel to the rolling direction. This is probably due...

The authors measured texture change during uniaxial tensile deformation of extruded bar of AZ31 magnesium alloy by time-of-flight neutron diffraction and EBSD (electron backscatter diffraction). Texture measurement by neutron diffraction revealed the transition of tensile axis distribution in overall gauge volume during the deformation. The concent...

We carried out in situ x-ray diffraction measurements of magnetostriction in an Fe-18at%Ga alloy single crystal under magnetic fields. The sample studied here was a Goss-oriented square plate (dimensions: 10 mm × 10 mm × 1 mm height) cutting from as-grown single crystal ingot produced by the Czochralski method. In-plain magnetic fields were applied...

The authors have developed the texture measurement system at iMATERIA, which is the neutron diffractometers built in Materials and Life Science Experimental Facility (MLF) at J-PARC, Japan. The high flux of the incident beam and Time-Of-Flight method enabled the complete texture measurement within several minutes in case of steels. Since the neutro...

A rapid texture measurement system has been developed on the time-of-flight neutron diffractometer iMATERIA (beamline BL20, MLF/J-PARC, Japan). Quantitative Rietveld texture analysis with a neutron beam exposure of several minutes without sample rotation was investigated using a duplex stainless steel, and the minimum number of diffraction spectra...

A newly developed, austenitic lightweight steel, containing a low-density element, Al, exhibits tensile elongation up to 50% as well as high ultimate-tensile stress (tensile fracture at 1800 MPa) without necking behavior. Electron backscatter diffraction analysis is carried out to investigate the orientation dependence of the martensitic transforma...

The local stress state developed during the elastic deformation of polycrystalline Fe-17mol%Ga was measured by synchrotron white X-ray radiation, and the heterogeneity of the elastic deformation resulting from the pronounced elastic anisotropy of the FeeGa alloy system was examined. Tensile loading generated local stresses perpendicular to the tens...

We have investigated anisotropy behavior of coercivity and scaling law for nano-scale ferromagnetic phases embedded in a paramagnetic matrix of an austenitic stainless steel. Small ferromagnetic martensites are induced by uniaxial tensile deformation. A scaling-law relationship between the hysteresis loss and remanence, with a power law exponent of...

X-ray diffraction (XRD) and electron microprobe microanalysis (EPMA) were used for characterizing the structure and composition of surface layers formed on austenitic Fe-Mn-Si shape memory alloys under vacuum. The XRD results demonstrated that during annealing, face centered cubic austenite is transformed to hexagonal close packed martensite on the...

High speed rolling is recognized as the process that can produce sheets of magnesium alloys having RD-split basal texture without or with minimum preheating. However, the mechanism of the texture formation during high speed rolling has not been fully clarified yet. In this study, conventional AZ31 and a rare earth - yttrium added alloy, WE43 were r...

A single crystal of the Fe-6 at% Co-15 at% Ga ternary alloy was successfully grown by the Czochralski method. The as-grown ingot with the <100> orientation parallel to the pull-up direction was about 17 mm in maximum diameter and about 55 mm in length. The magnetostriction constant in the <100> orientation λ100 of the single crystal specimen was ab...

抄録 We have performed high-sensitivity magnetic measurements for tensile-deformed SUS304-type austenitic stainless steel to elucidate a relationship between morphology of martensite particles and structure-sensitive magnetic hysteresis properties. A monotonic increase of the volume fraction of martensite phase up to 14.3% through strain-induced mart...

It is known that magnesium alloys can be rolled up to a large thickness reduction and develop a unique texture when the rolling speed is high (>1000 m/min). In order to understand the texture formation mechanism during high-strain-rate deformation, high-speed rolling of AZ31 magnesium alloy samples having different initial textures was conducted. T...

In order to clarify the effect of solutes on texture formation during high-temperature deformation of BCC solid solution alloys, the texture and microstructure formations in Fe-3.1mass%Si (Fe-Si) and Fe-3.2mass%Si-0.12mass%P (Fe-Si-P) during high-temperature uniaxial compression deformation are studied. The analysis of true stress-true strain curve...

A new mechanism of texture evolution, named “preferential dynamic grain growth mechanism”, is examined experimentally by high-temperature plane-strain compression deformation of Fe–3.0 mass% Si alloy. The proposed mechanism is based on preferential growth of the orientations having low Taylor factors and stability against deformation. According to...

Synopsis: High temperature uniaxial compression tests are conducted in order to clarify the effect of test conditions to the evolution of microstructures and textures. Fiber texture with {001} and {111} (compression plane) is formed as major and minor component, respectively. In contrast to the deformation at room temperature, axis density at <001>...

Texture formation during uniaxial compression at elevated temperatures in Fe-3mass%Si and 430 stainless steel is studied. The behavior is analyzed in relating to the understanding on the texture development in Al-Mg solid solution alloy at high temperatures. It is found that the fraction of {001} (compression plane) is much higher than that of {111...

Texture formation during high temperature uniaxial compression on Fe-3mass%Si solid solution alloy with BCC structure is investigated. It is found that the strong (001) fiber texture develops at high temperature uniaxial compression deformation. Microstructure observation suggests that (001) fiber texture in Fe-3%Si alloy is also derived from the p...