ORCID Profile
0000-0003-0028-3007
Current Organisation
Oregon State University
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Publisher: Elsevier BV
Date: 2012
Publisher: Springer Science and Business Media LLC
Date: 27-03-2010
Publisher: Springer Science and Business Media LLC
Date: 17-04-2010
Publisher: AIP Publishing
Date: 03-12-2012
DOI: 10.1063/1.4769216
Abstract: We present evidence that the level of the applied stress plays a critical role in deformation twinning in face-centred cubic alloys. While conventional cold rolling of a face-centred cubic structure produces a microstructure with a high-density of extended dislocations, increasing the applied stress using high-pressure torsion gives a nano-twinned coarse-grained structure. This suggests the existence of a critical stress for deformation twinning which thereby delineates an approach for the production of nano-twinned microstructures in coarse-grained materials with superior mechanical properties.
Publisher: AIP Publishing
Date: 06-07-2015
DOI: 10.1063/1.4926370
Abstract: We report an atomic-scale investigation of interface-facilitated deformation twinning behaviour in Ag-Cu nanolamellar composites. Profuse twinning activities in Ag supply partial dislocations to directly transmit across the Ag-Cu lamellar interface that promotes deformation twinning in the neighbouring Cu lamellae although the interface is severely deformed. The trans-interface twin bands change the local structure at the interface. Our analysis suggests that the orientation relationship and interfacial structure between neighbouring Ag-Cu lamellae play a crucial role in such special interface-facilitated twinning behaviour.
Publisher: Wiley
Date: 05-02-2014
Publisher: Springer Science and Business Media LLC
Date: 20-11-2019
DOI: 10.1038/S41598-019-53614-3
Abstract: Nanostructuring of bulk metals is now well documented with the development of severe plastic deformation (SPD) for improving the physical and mechanical properties of engineering materials. Processing by high-pressure torsion (HPT), which was developed initially as a grain refinement technique, was extended recently to the mechanical bonding of dissimilar metals during nanostrcturing which generally involves significant microstructural heterogeneity. Here we introduce, for the first time, a bulk metastable Al-Mg supersaturated solid solution by the diffusion bonding of separate Al and Mg metal solids at room temperature using HPT. Exceptional hardness was achieved homogeneously throughout the metastable alloy with a record maximum supersaturated Mg content of ~38.5 at.% in the Al matrix having a grain size of ~35–40 nm. Our results demonstrate the synthesis of a bulk nanocrystalline metastable alloy with good microstructural stability at room temperature where such bulk solids are not yet reported for mechanical alloying by powder metallurgy.
Publisher: Wiley
Date: 17-11-2021
Abstract: 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 torsion reached crystallite sizes of 23–26 nm, a dislocation density of ≈45 × 10 14 m −2 and a microstrain of .008. A limited amount of deformation‐induced ε ‐martensite was observed at a local region in the nanostructured AM steel. The time‐resolved neutron diffraction experiment upon heating successfully visualizes the sequential structural relaxation and linear thermal lattice expansion in the nanostructured AM steel. In practice, by calculating the changes in crystallite sizes, microstrains, and dislocation densities, the relaxation behaviors of the nanocrystalline AM steel is observed: 1) recovery with slow stress relaxation with increasing hardness up to 873 K, 2) recrystallization with accelerated stress relaxation at 873–973 K and 3) grain growth above 973 K with (iii′) total stress relaxation in lattices up to 1023 K. In addition, this manuscript makes connections between the critical subjects in materials science of advanced manufacturing, metal processing and properties, and novel time‐resolved characterization techniques.
Publisher: Wiley
Date: 28-03-2017
Publisher: Elsevier BV
Date: 02-2014
Publisher: AIP Publishing
Date: 30-01-2023
DOI: 10.1063/5.0138040
Abstract: We present unconventional magnetization in a high-pressure torsion (HPT) CoCrFeNi nanostructured high-entropy alloy: (i) the temperature dependent magnetization protocol and DC susceptibility suggest effects of spin-clustering. Moreover, HPT-processing of the alloy produces a heterogeneous and metastable nanostructure, changing its supermagnetic character: turning superparamagnetic to superspin glass dynamics, (ii) the material shows an inverted magnetic hysteresis loop, an inversion of the central part of the loop where the remanent magnetization points in a direction opposite to the applied field. The exquisite tunability of this inverted magnetism as a function of field and temperature and its reproducibility in a quasi-equilibrium setting make this spin-clustering phenomenon unique. We account for this phenomenon in terms of a non-equilibrium population of oppositely polarized domains of an ordered ferromagnetic state, enabled through the nanostructured, highly distorted, and locally disordered crystalline medium.
Publisher: Wiley
Date: 06-09-2023
Abstract: The cold angular rolling process (CARP) is being developed as a continuous severe plastic deformation (SPD) technique, which can process metal sheets without any length limitations at room temperature. CARP contains cold rolling and equal‐channel angular process components. The sheet thickness is kept consistent before and after CARP, allowing multiple passes of the sheet. The desired microstructure and mechanical properties can be achieved in the processed metallic sheets. The current study is aimed to evaluate the capability of CARP by processing copper sheets with different sheet widths for repetitive passes. The CARP‐treated sheets are examined by lab‐scale X‐ray and high‐energy synchrotron X‐ray diffraction to investigate the evolution in dislocation density, texture, and strain anisotropy, and by tensile testing to identify the bulk mechanical properties. The digital image correlation (DIC) method is applied to tensile testing so that strain localization within the s le gauge was visualized and deformation behavior was evaluated after yielding till post‐necking by estimating the hardening exponent and strain hardening rate of the CARP‐treated sheet. Comparing the reported continuous and multiple‐step processes on Cu and its alloys, the present study confirms CARP is potentially a useful sheet process for strengthening ductile metals. This article is protected by copyright. All rights reserved.
Publisher: Wiley
Date: 04-2022
Publisher: Elsevier BV
Date: 06-2011
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier BV
Date: 04-2015
Publisher: Springer Science and Business Media LLC
Date: 14-09-2010
Publisher: Elsevier BV
Date: 08-2013
Publisher: Elsevier BV
Date: 2014
Publisher: Elsevier BV
Date: 2016
Publisher: Wiley
Date: 10-09-2019
Abstract: A ductile duplex stainless steel consisting of a ferrite phase and an austenitic phase is chosen as a model material to investigate the development of shear strain patterns under high‐pressure torsion. Systematic analysis on the macroscopic and microscopic heterogeneities of local shear strain reveals that complex shear patterns can be developed only above a high strain level where the grain sizes are already refined to a steady state. It is concluded that grain boundary‐mediated deformation mechanisms provide sufficient freedom for reshaping the austenite phase domains, and thus the intrinsic factor required for the formation of these complicated shear patterns is well‐developed ultrafine grains and/or nanograins.
No related grants have been discovered for Megumi Kawasaki.