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“Tomographic spectroscopic imaging, an experimental proof of concept”. van den Broek W, Verbeeck J, Schryvers D, de Backer S, Scheunders P, Ultramicroscopy 109, 296 (2009). http://doi.org/10.1016/j.ultramic.2008.11.022
Abstract: Recording the electron energy loss spectroscopy data cube with a series of energy filtered images is a dose inefficient process because the energy slit blocks most of the electrons. When recording the data cube by scanning an electron probe over the sample, perfect dose efficiency is attained; but due to the low current in nanoprobes, this often is slower, with a smaller field of view. In W. Van den Broek et al. [Ultramicroscopy, 106 (2006) 269], we proposed a new method to record the data cube, which is more dose efficient than an energy filtered series. It produces a set of projections of the data cube and then tomographically reconstructs it. In this article, we demonstrate these projections in practice, we present a simple geometrical model that allows for quantification of the projection angles and we present the first successful experimental reconstruction, all on a standard post-column instrument.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 1
DOI: 10.1016/j.ultramic.2008.11.022
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“TEM investigation of the formation mechanism of deformation twins in Fe-Mn-Si-Al TWIP steels”. Idrissi H, Renard K, Schryvers D, Jacques PJ, Philosophical magazine 93, 4378 (2013). http://doi.org/10.1080/14786435.2013.832837
Abstract: The microstructure of a Fe-Mn-Si-Al twinning-induced plasticity (TWIP) steel exhibiting remarkable work hardening rate under uniaxial tensile deformation was investigated using transmission electron microscopy to uncover the mechanism(s) controlling the nucleation and growth of the mechanically induced twins. The results show that the stair-rod cross-slip deviation mechanism is necessary for the formation of the twins, while large extrinsic stacking faults homogenously distributed within the grains could act as preferential sources for the activation of the deviation process. The influence of such features on the thickness and strength of the twins and the resulting mechanical behaviour is discussed and compared to similar works recently performed on Fe-Mn-C TWIP steels.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 1.505
Times cited: 15
DOI: 10.1080/14786435.2013.832837
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“Optimization of Automated Crystal Orientation and Phase Mapping in TEM Applied to Ni-Ti All Round Shape Memory Alloy”. Yao X, Li Y, Cao S, Ma X, Zhang X-ping, Schryvers D, MATEC web of conferences
T2 –, Proceedings of ESOMAT 2015 10th European Symposium on Martensitic Transformations, September 14-18, 2015, Antwerp, Belgium 33, 03022 (2015). http://doi.org/10.1051/matecconf/20153303022
Abstract: A new application which focuses on an artificial sphincter fabricated by Ni-Ti SMAs for human implantation is under investigation by applying the all-round shape memory effect with precise control of the phase transformation temperatures. In this study, a Ni51at.%-Ti alloy was fabricated by arc melting with fast solidification, followed by a proper strained aging which induces the two way shape memory effect needed for this particular application. Differential scanning calorimetry was used to investigate the thermal behavior and transmission electron microscopy was used for studying the microstructure of the alloys. With the latter the novel technique of automated crystal orientation microscopy is used and optimized to obtain phase and orientation mapping of the various structures.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT)
Times cited: 1
DOI: 10.1051/matecconf/20153303022
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“Cross-section transmission electron microscopy characterization of the near-surface structure of medical Nitinol superelastic tubing”. Potapov PL, Tirry W, Schryvers D, Sivel VGM, Wu M-Y, Aslanidis D, Zandbergen H, Journal of materials science: materials in medicine 18, 483 (2007). http://doi.org/10.1007/s10856-007-2008-y
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.325
Times cited: 14
DOI: 10.1007/s10856-007-2008-y
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“Electron energy-loss spectroscopy and first-principles calculation studies on a Ni-Ti shape memory alloy”. Yang Z, Tirry W, Lamoen D, Kulkova S, Schryvers D, Acta materialia 56, 395 (2008). http://doi.org/10.1016/j.actamat.2007.10.001
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 20
DOI: 10.1016/j.actamat.2007.10.001
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“ALPHABETA: a dedicated open-source tool for calculating TEM stage tilt angles”. Cautaerts N, Delville R, Schryvers D, Journal of microscopy 273, 189 (2019). http://doi.org/10.1111/jmi.12774
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.692
Times cited: 2
DOI: 10.1111/jmi.12774
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“In Situ Quantitative Tensile Testing of Antigorite in a Transmission Electron Microscope”. Idrissi H, Samaee V, Lumbeeck G, Werf T, Pardoen T, Schryvers D, Cordier P, Journal Of Geophysical Research-Solid Earth 125 (2020). http://doi.org/10.1029/2019JB018383
Abstract: The determination of the mechanical properties of serpentinites is essential toward the understanding of the mechanics of faulting and subduction. Here we present the first in situ tensile tests on antigorite in a transmission electron microscope. A push‐to‐pull deformation device is used to perform quantitative tensile tests, during which force and displacement are measured, while the evolving microstructure is imaged with the microscope. The experiments have been performed at room temperature on 2 × 1 × 0.2 μm3 beams prepared by focused ion beam. The specimens are not single crystals despite their small sizes. Orientation mapping indicated that several grains were well oriented for plastic slip. However, no dislocation activity has been observed even though the engineering tensile stress went up to 700 MPa. We show also that antigorite does not exhibit a purely elastic‐brittle behavior since, despite the presence of defects, the specimens accumulate permanent deformation and did not fail within the elastic regime. Instead, we observe that strain localizes at grain boundaries. All observations concur to show that under these experimental conditions, grain boundary sliding is the dominant deformation mechanism. This study sheds a new light on the mechanical properties of antigorite and calls for further studies on the structure and properties of grain boundaries in antigorite and more generally in phyllosilicates.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.9
DOI: 10.1029/2019JB018383
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“Datasets for the analysis of dislocations at grain boundaries and during vein formation in cyclically deformed Ni micropillars”. Sandfeld S, Samaee V, Idrissi H, Groten J, Pardoen T, Schwaiger R, Schryvers D, Data in Brief 27, 104724 (2019). http://doi.org/10.1016/J.DIB.2019.104724
Abstract: The dataset together with the corresponding Python scripts and Jupyter notebooks presented in this article are supplementary data for the work presented in Samaee et al., 2019 [1]. The data itself consists of two parts: the simulation data that was used in [1] to analyze the effect of a particular grain boundary on curved dislocations and the precession electron diffraction (PED) strain maps together with post-processed data for analyzing details of the observed dislocation vein structures. Additionally, the complete stress tensor components, which are not shown in [1], have also been included. The data sets are accompanied by Python code explaining the file formats and showing how to post-process the data. (c) 2019 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
DOI: 10.1016/J.DIB.2019.104724
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“Internal architecture of coffin-shaped ZSM-5 zeolite crystals with hourglass contrast unravelled by focused ion beam-assisted transmission electron microscopy: INTERNAL ARCHITECTURE OF COFFIN-SHAPED”. Lu J, Bartholomeeusen E, Sels BF, Schryvers D, Journal of microscopy 265, 27 (2017). http://doi.org/10.1111/jmi.12459
Abstract: Optical microscopy, focused ion beam and transmission electron microscopy are combined to study the internal architecture in a coffin-shaped ZSM-5 crystal showing an hourglass contrast in optical microscopy. Based on parallel lamellas from different positions in the crystal, the orientation relationships between the intergrowth components of the crystal are studied and the internal architecture and growth mechanism are illustrated. The crystal is found to contain two pyramid-like components aside from a central component. Both pyramid-like components are rotated by 90 degrees along the common c-axis and with respect to the central component while the interfaces between the components show local zig-zag feature, the latter indicating variations in relative growth velocity of the two components. The pyramid-like intergrowth components are larger and come closer to one another in the middle of the crystal than at the edges, but they do not connect. A model of multisite nucleation and growth of 90 degrees intergrowth components is proposed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.692
Times cited: 4
DOI: 10.1111/jmi.12459
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“TEM and AES investigations of the natural surface nano-oxide layer of an AISI 316L stainless steel microfibre”. Ramachandran D, Egoavil R, Crabbe A, Hauffman T, Abakumov A, Verbeeck J, Vandendael I, Terryn H, Schryvers D, Journal of microscopy 264, 207 (2016). http://doi.org/10.1111/jmi.12434
Abstract: The chemical composition, nanostructure and electronic structure of nanosized oxide scales naturally formed on the surface of AISI 316L stainless steel microfibres used for strengthening of composite materials have been characterised using a combination of scanning and transmission electron microscopy with energy-dispersive X-ray, electron energy loss and Auger spectroscopy. The analysis reveals the presence of three sublayers within the total surface oxide scale of 5.0-6.7 nm thick: an outer oxide layer rich in a mixture of FeO.Fe2 O3 , an intermediate layer rich in Cr2 O3 with a mixture of FeO.Fe2 O3 and an inner oxide layer rich in nickel.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.692
Times cited: 12
DOI: 10.1111/jmi.12434
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“Influence of stress aging process on variants of nano-N4Ti3precipitates and martensitic transformation temperatures in NiTi shape memory alloy”. Radi A, Khalil-Allafi J, Etminanfar MR, Pourbabak S, Schryvers D, Amin-Ahmadi B, Materials &, design 262, 74 (2018). http://doi.org/10.1016/J.ELECTACTA.2018.01.024
Abstract: In this study, the effect of a stress aging process on the microstructure and martensitic phase transformation of NiTi shape memory alloy has been investigated. NiTi samples were aged at 450 degrees C for 1 h and 5 h under different levels of external tensile stress of 15, 60 and 150 MPa. Transmission electron microscopy (TEM) was used to characterize different variants and morphology of precipitates. The results show that application of all stress levels restricts the formation of precipitates variants in the microstructure after I h stress aging process. However, all variants can be detected by prolonging aging time to 5 h at 15 MPa stress level and the variants formation is again restricted by increasing the stress level. Moreover, the stress aging process resulted in changing the shape of precipitates in comparison with that of the stress-free aged samples. Coffee-bean shaped morphologies were detected for precipitates in all stress levels. According to the Differential Scanning Calorimetry (DSC) results, the martensite start temperature (M-s) on cooling shifts to higher temperatures with increasing the tensile stress during the aging process. This can be related to the change ofaustenite to martensite interface energy due to the different volume fractions and variants of precipitates. (c) 2018 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.364
DOI: 10.1016/J.ELECTACTA.2018.01.024
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“Direct Observation of Ferroelectric Domain Walls in LiNbO3: Wall-Meanders, Kinks, and Local Electric Charges”. Gonnissen J, Batuk D, Nataf GF, Jones L, Abakumov AM, Van Aert S, Schryvers D, Salje EKH, Advanced functional materials 26, 7599 (2016). http://doi.org/10.1002/adfm.201603489
Abstract: Direct observations of the ferroelectric domain boundaries in LiNbO3 are performed using high-resolution high-angle annular dark field scanning transmission electron microscopy imaging, revealing a very narrow width of the domain wall between the 180° domains. The domain walls demonstrate local side-way meandering, which results in inclinations even when the overall wall orientation follows the ferroelectric polarization. These local meanders contain kinks with “head-to-head” and “tail-to-tail” dipolar configurations and are therefore locally charged. The charged meanders are confined to a few cation layers along the polarization direction and are separated by longer stretches of straight domain walls.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
Times cited: 23
DOI: 10.1002/adfm.201603489
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“Quantitative Landau potentials for the martensitic transformation in Ni-Al”. Salje EKH, Zhang H, Schryvers D, Bartova B, Applied physics letters 90, 221903 (2007). http://doi.org/10.1063/1.2743927
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.411
Times cited: 9
DOI: 10.1063/1.2743927
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“Melamine–Formaldehyde Microcapsules: Micro- and Nanostructural Characterization with Electron Microscopy”. Heidari H, Rivero G, Idrissi H, Ramachandran D, Cakir S, Egoavil R, Kurttepeli M, Crabbé, AC, Hauffman T, Terryn H, Du Prez F, Schryvers D, Microscopy and microanalysis 22, 1222 (2016). http://doi.org/10.1017/S1431927616012484
Abstract: A systematic study has been carried out to compare the surface morphology, shell thickness, mechanical properties, and binding behavior of melamine–formaldehyde microcapsules of 5–30 μm diameter size with various amounts of core content by using scanning and transmission electron microscopy including electron tomography, in situ nanomechanical tensile testing, and electron energy-loss spectroscopy. It is found that porosities are present on the outside surface of the capsule shell, but not on the inner surface of the shell. Nanomechanical tensile tests on the capsule shells reveal that Young’s modulus of the shell material is higher than that of bulk melamine–formaldehyde and that the shells exhibit a larger fracture strain compared with the bulk. Core-loss elemental analysis of microcapsules embedded in epoxy indicates that during the curing process, the microcapsule-matrix interface remains uniform and the epoxy matrix penetrates into the surface micro-porosities of the capsule shells.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.891
Times cited: 2
DOI: 10.1017/S1431927616012484
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“Effect of hydriding induced defects on the small-scale plasticity mechanisms in nanocrystalline palladium thin films”. Lumbeeck G, Idrissi H, Amin-Ahmadi B, Favache A, Delmelle R, Samaee V, Proost J, Pardoen T, Schryvers D, Journal Of Applied Physics 124, 225105 (2018). http://doi.org/10.1063/1.5055274
Abstract: Nanoindentation tests performed on nanocrystalline palladium films subjected to hydriding/dehydriding cycles demonstrate a significant softening when compared to the as-received material. The origin of this softening is unraveled by combining in situ TEM nanomechanical testing with automated crystal orientation mapping in TEM and high resolution TEM. The softening is attributed to the presence of a high density of stacking faults and of Shockley partial dislocations after hydrogen loading. The hydrogen induced defects affect the elementary plasticity mechanisms and the mechanical response by acting as preferential sites for twinning/detwinning during deformation. These results are analyzed and compared to previous experimental and simulation works in the literature. This study provides new insights into the effect of hydrogen on the atomistic deformation and cracking mechanisms as well as on the mechanical properties of nanocrystalline thin films and membranes.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 2.068
Times cited: 2
DOI: 10.1063/1.5055274
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“Demonstration of lanthanum in liver cells by energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and high-resolution transmission electron microscopy”. Yang Z, Schryvers D, Roels F, d' Haese PC, de Broe ME, Journal of microscopy 223, 133 (2006). http://doi.org/10.1111/j.1365-2818.2006.01601.x
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Pathophysiology
Impact Factor: 1.692
Times cited: 29
DOI: 10.1111/j.1365-2818.2006.01601.x
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“Electron-diffraction evidence for ordering of interstitial silver ions in silver bromide microcrystals”. Goessens C, Schryvers D, van Dyck D, van Landuyt J, de Keyzer R, Physica status solidi: A 143, 277 (1994). http://doi.org/10.1002/pssa.2211430211
Abstract: The occurrence and origin of diffuse intensity contours in electron micrographs of AgBr crystals are investigated. The observations are interpreted in terms of a model, which attributes diffuse scattering to the presence of predominant atom or vacancy clusters of a particular polyhedral type. It is shown that irrespective of the crystal morphology, interstitial Ag ions order in AgBr material in clusters of finite size along 001 type planes. A different geometry of the diffuse intensity locus observed for triangular and hexagonal tabular grains is explained in terms of the different twin plane morphology of these grains.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Times cited: 7
DOI: 10.1002/pssa.2211430211
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“Fabrication and characterization of functionally graded Ni-Ti multilayer thin films”. Tian H, Schryvers D, Mohanchandra KP, Carman GP, van Humbeeck J, Functional materials letters 2, 61 (2009). http://doi.org/10.1142/S1793604709000570
Abstract: A functionally graded multilayer NiTi thin film was deposited on a SiO2/Si substrate by d.c. sputtering using a ramped heated NiTi alloy target. The stand-alone films were crystallized at 500°C in vacuum better than 10-7 Torr. Transmission electron microscopy micrographs taken along the film cross section show two distinct regions, thin and thick, with weak R and B2 phases, respectively. The film compositions along the thickness were measured and quantified using the standard-less EELSMODEL method. The film deposited during the initial thermal ramp (thin regions) displays an average of 54 at.% Ni while the film deposited at a more elevated target temperature (thick regions) shows about 51 at.% Ni.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.234
Times cited: 9
DOI: 10.1142/S1793604709000570
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“High-quality sample preparation by low kV FIB thinning for analytical TEM measurements”. Bals S, Tirry W, Geurts R, Yang Z, Schryvers D, Microscopy and microanalysis 13, 80 (2007). http://doi.org/10.1017/S1431927607070018
Abstract: Focused ion beam specimen preparation has been used for NiTi samples and SrTiO(3)/SrRuO(3) multilayers with prevention of surface amorphization and Ga implantation by a 2-kV cleaning procedure. Transmission electron microscopy techniques show that the samples are of high quality with a controlled thickness over large scales. Furthermore, preferential thinning effects in multicompounds are avoided, which is important when analytical transmission electron microscopy measurements need to be interpreted in a quantitative manner. The results are compared to similar measurements acquired for samples obtained using conventional preparation techniques such as electropolishing for alloys and ion milling for oxides.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.891
Times cited: 82
DOI: 10.1017/S1431927607070018
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“The influence of crystal thickness on the image tone”. van Renterghem W, Schryvers D, van Landuyt J, van Roost C, de Keyzer R, Journal of imaging science 47, 133 (2003)
Abstract: It is known that the neutral image tone of a developed photographic film becomes brownish when the thickness of the original silver halide tabular crystals is reduced. We investigate by electron microscopy to what extent the silver filament structure has changed and how it induces the shift in image tone. Therefore, two samples of AgBr {111} tabular crystals with average thicknesses of 160 nm and 90 nm respectively, are compared. It is shown that the dimensions and defect structure of the filaments are comparable, but that the 90 nm crystals result in a more widely spaced structure, which explains the shift in image tone on a qualitative level. The influence of the addition of an image toner, i.e., phenylmercaptotetrazole, on the filament structure is also investigated. An even more open filament structure of longer, but smaller filaments was observed.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 0.348
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“Internal calibration technique for HREM studies of nanoscale particles”. Schryvers D, Goessens C, Safran G, Toth L, Microscopy research and technique
T2 –, JOINT MEETING OF DUTCH SOC FOR ELECTRON MICROSCOPY / BELGIAN SOC FOR, ELECTRON MICROSCOPY / BELGIAN SOC FOR CELL BIOLOGY, DEC 10-11, 1992, ANTWERP, BELGIUM 25, 185 (1993). http://doi.org/10.1002/jemt.1070250216
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.154
Times cited: 1
DOI: 10.1002/jemt.1070250216
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“Microstructural mechanism of development in photothermographic materials”. Potapov PL, Schryvers D, Strijckers H, van Roost C, The journal of imaging science and technology 47, 115 (2003)
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 0.348
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“Microstructure and functional property changes in thin Ni-Ti wires heat teated by electric current: high energy X-ray and TEM investigations”. Malard B, Pilch J, Sittner P, Gartnerova V, Delville R, Schryvers D, Curfs C, Functional materials letters 2, 45 (2009). http://doi.org/10.1142/S1793604709000557
Abstract: High energy synchrotron X-ray diffraction, transmission electron microscopy and mechanical testing were employed to investigate the evolution of microstructure, texture and functional superelastic properties of 0.1 mm thin as drawn NiTi wires subjected to a nonconventional heat treatment by controlled electric current (FTMT-EC method). As drawn NiTi wires were prestrained in tension and exposed to a sequence of short DC power pulses in the millisecond range. The annealing time in the FTMT-EC processing can be very short but the temperature and force could be very high compared to the conventional heat treatment of SMAs. It is shown that the heavily strained, partially amorphous microstructure of the as drawn NiTi wire transforms under the effect of the DC pulse and tensile stress into a wide range of annealed nanosized microstructures depending on the pulse time. The functional superelastic properties and microstructures of the FTMT-EC treated NiTi wire are comparable to those observed in straight annealed wires.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.234
Times cited: 21
DOI: 10.1142/S1793604709000557
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“Stability of Ni in nitinol oxide surfaces”. Tian H, Schryvers D, Liu D, Jiang Q, van Humbeeck J, Acta biomaterialia 7, 892 (2011). http://doi.org/10.1016/j.actbio.2010.09.009
Abstract: The stability of Ni in titanium oxide surface layers on nitinol wires known to release certain amounts of Ni was investigated by first principles density functional theory and transmission electron microscopy. The oxides were identified as a combination of TiO and TiO2 depending on the thickness of the layer. The calculations indicate that free Ni atoms can exist in TiO at ambient temperature while Ni particles form in TiO2, which was confirmed by the transmission electron microscopy observations. The results are discussed with respect to surface stability and Ni release due to free Ni atoms and Ni particles.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.319
Times cited: 39
DOI: 10.1016/j.actbio.2010.09.009
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“Structural characterization of nanostructured Ni3Al processed by inert gas condensation”. Yandouzi M, Pauwels B, Schryvers D, Van Swygenhoven H, Van Tendeloo G, Diffusion and defect data : solid state data : part A : defect and diffusion forum 213, 19 (2003)
Abstract: High-resolution transmission electron microscopy was performed on compacted Ni(3)Al nanostructured material prepared by the inert gas condensation technique. From electron diffraction data an incomplete L1(2) ordering of the crystallites is observed in the free particles as well as in the room temperature compacted samples. However, a completely ordered L1(2) structure with much bigger and well-defined crystallites exhibiting several defects is observed in material compacted and annealed at 773 K. Sharp crystallite boundaries as well as amorphous material and voids are observed in between crystallites in all samples, the former being dominant in the annealed material, the latter in the as-prepared one.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
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“Transmission electron microscopy investigation of dislocation slip during superelastic cycling of NiTi wires”. Delville R, Malard B, Pilch J, Sittner P, Schryvers D, International journal of plasticity 27, 282 (2011). http://doi.org/10.1016/j.ijplas.2010.05.005
Abstract: Superelastic deformation of thin NiTi wires containing various nanograined microstructures was investigated by tensile cyclic loading with in situ evaluation of electric resistivity. Defects created by the superelastic cycling in these wires were analyzed by transmission electron microscopy. The role of dislocation slip in superelastic deformation is discussed. NiTi wires having finest microstructures (grain diameter <100 nm) are highly resistant against dislocation slip, while those with fully recrystallized microstructure and grain size exceeding 200 nm are prone to dislocation slip. The density of the observed dislocation defects increases significantly with increasing grain size. The upper plateau stress of the superelastic stressstrain curves is largely grain size independent from 10 up to 1000 nm. It is hence claimed that the HallPetch relationship fails for the stress-induced martensitic transformation in this grain size range. It is proposed that dislocation slip taking place during superelastic cycling is responsible for the accumulated irreversible strains, cyclic instability and degradation of functional properties. No residual martensite phase was found in the microstructures of superelastically cycled wires by TEM and results of the in situ electric resistance measurements during straining also indirectly suggest that none or very little martensite phase remains in the studied cycled superelastic wires after unloading. The accumulation of dislocation defects, however, does not prevent the superelasticity. It only affects the shape of the stressstrain response, makes it unstable upon cycling and changes the deformation mode from localized to homogeneous. The activity of dislocation slip during superelastic deformation of NiTi increases with increasing test temperature and ultimately destroys the superelasticity as the plateau stress approaches the yield stress for slip. Deformation twins in the austenite phase ({1 1 4} compound twins) were frequently found in cycled wires having largest grain size. It is proposed that they formed in the highly deformed B19′ martensite phase during forward loading and are retained in austenite after unloading. Such twinning would represent an additional deformation mechanism of NiTi yielding residual irrecoverable strains.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.702
Times cited: 157
DOI: 10.1016/j.ijplas.2010.05.005
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“Microstructural Characterization and Transformation Behavior of Porous Ni50.8Ti49.2”. Yao X, Cao S, Zhang XP, Schryvers D, Materials Today: Proceedings 2, S833 (2015). http://doi.org/10.1016/j.matpr.2015.07.411
Abstract: Porous Ni50.8Ti49.2 bulk material was prepared by powder metallurgy sintering. Solid solution and aging treatments were applied to improve the phase homogeneity and phase transformation behavior. Scanning and transmission electron microscopy, aided by energy dispersive X-ray analysis, were used to study the microstructure and chemical phase content of the alloys. In-situ cooling was carried out to observe the phase transformation behavior. As-received material contains dispersed Ni2Ti4O particles while Ni4Ti3 precipitates appear after aging. Close to pore edges, the latter have a preferential orientation due to the induced stress fields in the matrix.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT)
DOI: 10.1016/j.matpr.2015.07.411
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“Low-temperature plasticity of olivine revisited with in situ TEM nanomechanical testing”. Idrissi H, Bollinger C, Boioli F, Schryvers D, Cordier P, Science Advances 2, e1501671 (2016). http://doi.org/10.1126/sciadv.1501671
Abstract: The rheology of the lithospheric mantle is fundamental to understanding how mantle convection couples with plate tectonics. However, olivine rheology at lithospheric conditions is still poorly understood because experiments are difficult in this temperature range where rocks and mineral become very brittle. We combine techniques of quantitative in situ tensile testing in a transmission electron microscope and numerical modeling of dislocation dynamics to constrain the low-temperature rheology of olivine. We find that the intrinsic ductility of olivine at low temperature is significantly lower than previously reported values, which were obtained under strain-hardened conditions. Using this method, we can anchor rheological laws determined at higher temperature and can provide a better constraint on intermediate temperatures relevant for the lithosphere. More generally, we demonstrate the possibility of characterizing the mechanical properties of specimens, which can be available in the form of submillimeter-sized particles only.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Times cited: 32
DOI: 10.1126/sciadv.1501671
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“Optimization of Automated Crystal Orientation Mapping in a TEM for Ni4Ti3 Precipitation in All-Round SMA”. Yao X, Amin-Ahmadi B, Li Y, Cao S, Ma X, Zhang X-P, Schryvers D, Shape memory and superelasticity 2, 286 (2016). http://doi.org/10.1007/s40830-016-0082-z
Abstract: Automated crystal orientation and phase mapping in TEM are applied to the quantification of Ni4Ti3 precipitates in Ni–Ti shape memory alloys which will be used for the implantation of artificial sphincters operating using the all-round shape memory effect. This paper focuses on the optimization process of the technique to obtain best values for all major parameters in the acquisition of electron diffraction patterns as well as template generation. With the obtained settings, vast statistical data on nano- and microstructures essential to the operation of these shape memory devices become available.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 2
DOI: 10.1007/s40830-016-0082-z
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“In-Situ TEM Stress Induced Martensitic Transformation in Ni50.8Ti49.2 Microwires”. Pourbabak S, Orekhov A, Samaee V, Verlinden B, Van Humbeeck J, Schryvers D, Shape memory and superelasticity 5, 154 (2019). http://doi.org/10.1007/s40830-019-00217-6
Abstract: In-situ transmission electron microscopy tensile straining is used to study the stress induced martensitic transformation in Ni50.8Ti49.2. Two microwire samples with different heat treatment are investigated from which one single crystal and three polycrystalline TEM specimens, the latter with micro- and nano-size grains, have been produced. The measured Young’s modulus for all TEM specimens is around 70 GPa, considerably higher than the averaged 55 GPa of the original microwire sample. The height of the superelastic stress plateau shows an inverse relationship with the specimen thickness for the polycrystalline specimens. Martensite starts nucleating within the elastic region of the stress–strain curve and on the edges of the specimens while also grain boundaries act as nucleation sites in the polycrystalline specimens. When a martensite plate reaches a grain boundary in the polycrystalline specimen, it initiates the transformation in the neighboring grain at the other side of the grain boundary. In later stages martensite plates coalesce at higher loads in the stress plateau. In highly strained specimens, residual martensite remains after release.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1007/s40830-019-00217-6
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