“Towards ductilization of high strength 7XXX aluminium alloys via microstructural modifications obtained by friction stir processing and heat treatments”. Lezaack MB, Hannard F, Zhao L, Orekhov A, Adrien J, Miettinen A, Idrissi H, Simar A, Materialia 20, 101248 (2021). http://doi.org/10.1016/J.MTLA.2021.101248
Abstract: High strength 7XXX aluminium series reach exceptional strength, higher than all other industrial aluminium alloys. However, they suffer from a lack of ductility compared to softer series. This work presents a procedure to improve the ductility of 7475 Al alloy in high strength condition, reaching a true fracture strain of 70% at full 500 MPa T6 yield strength. Using friction stir processing (FSP) and post-FSP heat treatments, 100% of industrial rolled material T6 yield stress is maintained but a 180% increase in fracture strain is measured for the processed material. This ductility improvement is studied by in-situ synchrotron X-ray tomography and is explained by the reduction of intermetallic particles size and the homogenization of their spatial distribution. Furthermore, the microstructure after FSP shows equiaxed refined grains which favour crack deviation as opposed to large cracks parallel to the elongated coarse grains in rolled plate. These results are paving the way to better formability and crashworthiness of 7XXX alloys.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1016/J.MTLA.2021.101248
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“Shear banding-activated dynamic recrystallization and phase transformation during quasi-static loading of β-metastable Ti &ndash, 12 wt % Mo alloy”. Choisez L, Ding L, Marteleur M, Kashiwar A, Idrissi H, Jacques PJ, Acta materialia 235, 118088 (2022). http://doi.org/10.1016/J.ACTAMAT.2022.118088
Abstract: Dynamic recrystallization (DRX) within adiabatic shear bands forming during the fracture of TRIP-TWIP β−metastable Ti-12Mo (wt %) alloy was recently reported. The formation of 1-3 µm thick-adiabatic shear bands, and of dynamic recrystallization, was quite surprising as their occurrence generally requires high temperature and/or high strain rate loading while these samples were loaded in quasi-static conditions at room temperature. To better understand the fracture mechanism and associated microstructural evolution, thin foils representative of different stages of the fracture process were machined from the fracture surface by Focused Ion Beam (FIB) and analyzed by Transmission Electron Microscopy (TEM) and Automated Crystal Orientation mapping (ACOM-TEM). Complex microstructure transformations involving severe plastic deformed nano-structuration, crystalline rotation and local precipitation of the omega phase were identified. The spatial and temporal evolution of the microstructure during the propagation of the crack was explained through dynamic recovery and continuous dynamic recrystallization, and linked to the modelled distribution of temperature and strain level where TEM samples were extracted.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/J.ACTAMAT.2022.118088
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“On the formation of antiphase boundaries in Fe₄Al₁₃, intermetallics during a high temperature treatment”. Ding L, Sapanathan T, Schryvers D, Simar A, Idrissi H, Scripta materialia 215, 114726 (2022). http://doi.org/10.1016/J.SCRIPTAMAT.2022.114726
Abstract: In this paper, we report atomic scale observations and formation mechanisms of a high-density of antiphase boundaries (APBs) within an ultra-fine-grained Fe4Al13 intermetallic layer at an Al/steel interface after a heat treatment at 596 degrees C. The results reveal that the APBs are formed by nucleation and the glide of partial dislocations with Burgers vector of b/3[010] (b = 12.47 angstrom). The intensive activation of APBs locally transforms the Fe4Al13 structure from the quasicrystal approximant structure to a quasicrystal. Very few stacking faults and nanotwins are observed indicating that the formation of planar defects is mainly driven by this transformation. This new insight on the formation of high density of APBs could possibly lead to an improvement in toughness by increasing the strength/ductility balance of this intermetallic.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6
DOI: 10.1016/J.SCRIPTAMAT.2022.114726
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“A new healing strategy for metals : programmed damage and repair”. Arseenko M, Hannard F, Ding L, Zhao L, Maire E, Villanova J, Idrissi H, Simar A, Acta materialia 238, 118241 (2022). http://doi.org/10.1016/J.ACTAMAT.2022.118241
Abstract: Self-healing strategies aim at avoiding part repair or even replacement, which is time consuming, expen-sive and generates waste. However, strategies for metallic systems are still under-developed and solid-state solutions for room temperature service are limited to nano-scale damage repair. Here we propose a new healing strategy of micron-sized damage requiring only short and low temperature heating. This new strategy is based on damage localization particles, which can be healed by fast diffusing atoms of the matrix activated during heat treatment. The healing concept was successfully validated with a com-mercial aluminum alloy and manufactured by Friction Stir Processing (FSP). Damage was demonstrated to initiate on particles that were added to the matrix during material processing. In situ 2D and 3D nano -imaging confirmed healing of the damaged material and showed that heating this material for 10 min at 400 degrees C is sufficient to heal incipient damage with complete filling of 70% of all damage (and up to 90% when their initial size is below 0.2 mu m). Furthermore, strength is retained and the work of fracture of the alloy is improved by about 40% after healing. The proposed Programmed Damage and Repair healing strategy could be extended to other metal based systems presenting precipitation. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/J.ACTAMAT.2022.118241
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“On the formation mechanisms of intragranular shear bands in olivine by stress-induced amorphization”. Idrissi H, Béché, A, Gauquelin N, Ul-Haq I, Bollinger C, Demouchy S, Verbeeck J, Pardoen T, Schryvers D, Cordier P, Acta materialia 239, 118247 (2022). http://doi.org/10.1016/J.ACTAMAT.2022.118247
Abstract: Intragranular amorphization shear lamellae are found in deformed olivine aggregates. The detailed trans-mission electron microscopy analysis of intragranular lamella arrested in the core of a grain provides novel information on the amorphization mechanism. The deformation field is complex and heteroge-neous, corresponding to a shear crack type instability involving mode I, II and III loading components. The formation and propagation of the amorphous lamella is accompanied by the formation of crystal defects ahead of the tip. These defects are geometrically necessary [001] dislocations, characteristics of high-stress deformation in olivine, and rotational nanodomains which are tentatively interpreted as disclinations. We show that these defects play an important role in dictating the path followed by the amorphous lamella. Stress-induced amorphization in olivine would thus result from a direct crystal-to -amorphous transformation associated with a shear instability and not from a mechanical destabilization due to the accumulation of high number of defects from an intense preliminary deformation. The pref-erential alignment of some lamellae along (010) is a proof of the lower ultimate mechanical strength of these planes.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
Times cited: 5
DOI: 10.1016/J.ACTAMAT.2022.118247
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“Discovery of core-shell quasicrystalline particles”. Yang T, Kong Y, Du Y, Li K, Schryvers D, Scripta materialia 222, 115040 (2023). http://doi.org/10.1016/J.SCRIPTAMAT.2022.115040
Abstract: Submicron-sized quasicrystalline particles were obtained in an Al-Zn-Mg-Cu alloy produced by traditional melting. These particles consist of an Al-Fe-Ni core and a Mg-Cu-Zn shell and were found to be stable and embedded randomly in the Al matrix. The diffraction patterns of these core-shell particles reveal a decagonal core and an icosahedral shell with, respectively, ten- and five-fold axes aligned. High resolution scanning transmission electron microscopy of the Mg-Cu-Zn shell confirms the five-fold symmetry atomic arrangement and the icosahedral structure. It can therefore be concluded that Fe and Ni impurities play an important role in mediating the formation of such an unusual ternary core-shell quasicrystalline particle. These findings provide some novel insights in the formation of quasicrystals in traditional industrial Al alloys.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6
DOI: 10.1016/J.SCRIPTAMAT.2022.115040
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“The effect of microstructure and film composition on the mechanical properties of linear antenna CVD diamond thin films”. Mary Joy R, Pobedinskas P, Baule N, Bai S, Jannis D, Gauquelin N, Pinault-Thaury M-A, Jomard F, Sankaran KJ, Rouzbahani R, Lloret F, Desta D, D’Haen J, Verbeeck J, Becker MF, Haenen K, Acta materialia 264, 119548 (2024). http://doi.org/10.1016/j.actamat.2023.119548
Abstract: This study reports the impact of film microstructure and composition on the Young’s modulus and residual stress in nanocrystalline diamond (NCD) thin films ( thick) grown on silicon substrates using a linear antenna microwave plasma-enhanced chemical vapor deposition (CVD) system. Combining laser acoustic wave spectroscopy to determine the elastic properties with simple wafer curvature measurements, a straightforward method to determine the intrinsic stress in NCD films is presented. Two deposition parameters are varied: (1) the substrate temperature from 400 °C to 900 °C, and (2) the [P]/[C] ratio from 0 ppm to 8090 ppm in the H2/CH4/CO2/PH3 diamond CVD plasma. The introduction of PH3 induces a transition in the morphology of the diamond film, shifting from NCD with larger grains to ultra-NCD with a smaller grain size, concurrently resulting in a decrease in Young’s modulus. Results show that the highest Young’s modulus of (113050) GPa for the undoped NCD deposited at 800 °C is comparable to single crystal diamond, indicating that NCD with excellent mechanical properties is achievable with our process for thin diamond films. Based on the film stress results, we propose the origins of tensile intrinsic stress in the diamond films. In NCD, the tensile intrinsic stress is attributed to larger grain size, while in ultra-NCD films the tensile intrinsic stress is due to grain boundaries and impurities.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/j.actamat.2023.119548
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“On-chip very low strain rate rheology of amorphous olivine films”. Coulombier M, Baral P, Orekhov A, Dohmen R, Raskin JP, Pardoen T, Cordier P, Idrissi H, Acta materialia 266, 119693 (2024). http://doi.org/10.1016/J.ACTAMAT.2024.119693
Abstract: Recent observations made by the authors revealed the activation of stress induced amorphization and sliding at grain boundary in olivine [1], a mechanism which is expected to play a pivotal role in the viscosity drop at the lithosphere-asthenosphere boundary and the brittle -ductile transition in the lithospheric mantle. However, there is a lack of information in the literature regarding the intrinsic mechanical properties and the elementary deformation mechanisms of this material, especially at time scales relevant for geodynamics. In the present work, amorphous olivine films were obtained by pulsed laser deposition (PLD). The mechanical response including the rate dependent behavior are investigated using a tension -on -chip (TOC) method developed at UCLouvain allowing to perform creep/relaxation tests on thin films at extremely low strain rates. In the present work, strain rate down to 10-12 s- 1 was reached which is unique. High strain rate sensitivity of 0.054 is observed together with the activation of relaxation at the very early stage of deformation. Furthermore, digital image correlation (DIC), used for the first time on films deformed by TOC, reveals local strain heterogeneities. The relationship between such heterogeneities, the high strain rate sensitivity and the effect of the electron beam in the scanning electron microscope is discussed and compared to the literature.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/J.ACTAMAT.2024.119693
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“TEM investigation of the microstructure and defects of CuZr martensite: 1: morphology and twin systems”. Seo JW, Schryvers D, Acta materialia 46, 1165 (1998). http://doi.org/10.1016/S1359-6454(97)00333-9
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 46
DOI: 10.1016/S1359-6454(97)00333-9
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“TEM investigation of the microstructure and defects of CuZr martensite: 2: planar defects”. Seo JW, Schryvers D, Acta materialia 46, 1177 (1998). http://doi.org/10.1016/S1359-6454(97)00334-0
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 21
DOI: 10.1016/S1359-6454(97)00334-0
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“Nanoscale inhomogeneities in melt-spun Ni-Al”. Potapov PL, Ochin P, Pons J, Schryvers D, Acta materialia 48, 3833 (2000). http://doi.org/10.1016/S1359-6454(00)00188-9
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 28
DOI: 10.1016/S1359-6454(00)00188-9
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“GP-zones in Al-Zn-Mg alloys and their role in artificial aging”. Berg LK, Gjønnes J, Hansen V, Li XZ, Knutson-Wedel M, Waterloo G, Schryvers D, Wallenberg LR, Acta materialia 49, 3443 (2001). http://doi.org/10.1016/S1359-6454(01)00251-8
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 261
DOI: 10.1016/S1359-6454(01)00251-8
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“Nano-structures at martensite macrotwin interfaces in Ni65Al35”. Boullay P, Schryvers D, Ball JM, Acta materialia 51, 1421 (2003). http://doi.org/10.1016/S1359-6454(02)00536-0
Abstract: The atomic configurations at macrotwin interfaces between microtwinned martensite plates in Ni65Al35 material are investigated using transmission electron microscopy. The observed structures are interpreted in view of possible formation mechanisms for these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular {110} austenite planes, enclose a final angle larger or smaller than 90degrees. Two different configurations, a crossing and a step type are described. Depending on the actual case, tapering, bending and tip splitting of the smaller microtwinvariants are observed. The most reproducible deformations occur in a region of approximately 5-10 nm width around the interface while a variety of structural defects are observed further away from the interface. These structures and deformations are interpreted in terms of the coalescence of two separately nucleated microtwinned martensite plates and the need to accommodate remaining stresses. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 31
DOI: 10.1016/S1359-6454(02)00536-0
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“On the crystal structure of TiNi-Cu martensite”. Potapov P, Shelyakov A, Schryvers D, Scripta materialia 44, 1 (2001). http://doi.org/10.1016/S1359-6462(00)00555-8
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 36
DOI: 10.1016/S1359-6462(00)00555-8
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“Effect of amorphous-crystalline interfaces on the martensitic transformation in Ti50Ni25Cu25”. Santamarta R, Schryvers D, Scripta materialia 50, 1423 (2004). http://doi.org/10.1016/j.scriptamat.2004.03.013
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 29
DOI: 10.1016/j.scriptamat.2004.03.013
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“Quantitative determination of strain fields around Ni4Ti3 precipitates in NiTi”. Tirry W, Schryvers D, Acta materialia 53, 1041 (2005). http://doi.org/10.1016/j.actamat.2004.10.049
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 97
DOI: 10.1016/j.actamat.2004.10.049
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“Analytical TEM investigations on concentration gradients surrounding Ni4Ti3 precipitates in Ni-Ti shape memory material”. Yang Z, Tirry W, Schryvers D, Scripta materialia 52, 1129 (2005). http://doi.org/10.1016/j.scriptamat.2005.02.013
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 49
DOI: 10.1016/j.scriptamat.2005.02.013
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“Oxidation processes at the metal/oxide interface in CoFe2/CoFe2O4 bilayers deposited by pulsed laser deposition”. Viart N, Sayed Hassan R, Ulhaq-Bouillet C, Meny C, Panissod P, Loison JL, Versini G, Huber F, Pourroy G, Verbeeck J, Van Tendeloo G, Acta materialia 54, 191 (2006). http://doi.org/10.1016/j.actamat.2005.08.041
Abstract: CoFe2/CoFe2O4 bilayers were made by pulsed laser ablation of a CoFe2 target on Si(I 0 0) substrates. The metallic layer was deposited first, in vacuum. The oxide was then deposited in an oxidizing O-2:N-2 (20:80) atmosphere. Two different procedures were used for the introduction of the oxidizing atmosphere in the deposition chamber: the laser ablation of the target was either stopped (discontinuous deposition process) or maintained (continuous deposition process) during the 20 min necessary for the establishment of the desired O-2:N-2 pressure. In both cases, the different electronegativities of Fe and Co cause an important modification of the Fe/Co ratio at the metal/oxide interface, with a depletion of Fe in the metal region and of Co in the oxide region. In the continuous procedure, the combination of the kinetic energy given by the ablation process to the Fe and Co adatoms with the one they get from their different affinity towards oxidation allows the formation of a low roughness metal/oxide interface with a high (111) preferred orientation of the CoFe2O4 layer, an induced re-crystallisation of the metal layer underneath and an unusual antiferromagnetic metal/oxide magnetic coupling. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 5
DOI: 10.1016/j.actamat.2005.08.041
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“Microstructure and precipitates in as-cast Co38Ni33Al29 shape memory alloy”. Bartova B, Schryvers D, Yang Z, Ignacova S, Sittner P, Scripta materialia 57, 37 (2007). http://doi.org/10.1016/j.scriptamat.2007.03.007
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 22
DOI: 10.1016/j.scriptamat.2007.03.007
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“Microstructural study of equiatomic PtTi martensite and the discovery of a new long-period structure”. Rotaru G-M, Tirry W, Sittner P, van Humbeeck J, Schryvers D, Acta materialia 55, 4447 (2007). http://doi.org/10.1016/j.actamat.2007.04.010
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 7
DOI: 10.1016/j.actamat.2007.04.010
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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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“Microstructure of precipitates and magnetic domain structure in an annealed Co38Ni33Al29 shape memory alloy”. Bartova B, Wiese N, Schryvers D, Chapman JN, Ignacova S, Acta materialia 56, 4470 (2008). http://doi.org/10.1016/j.actamat.2008.05.006
Abstract: The microstructure of a Co38Ni33Al29 ferromagnetic shape memory alloy was determined by conventional transmission electron microscopy (TEM), electron diffraction studies together with advanced microscopy techniques and in situ Lorentz microscopy. Rod-like precipitates, 1060 nm long, of hexagonal close-packed -Co were confirmed to be present by high-resolution TEM. The orientation relationship between the precipitates and B2 matrix is described by the Burgers orientation relationship. The crystal structure of the martensite obtained after cooling is tetragonal L10 with a (111) twinning plane. The magnetic domain structure was determined during an in situ cooling experiment using the Fresnel mode of Lorentz microscopy. While transformation proceeds from B2 austenite to L10 martensite, new domains are nucleated, leading to a decrease in domain width, with the magnetization lying predominantly along a single direction. It was possible to completely describe the relationship between magnetic domains and crystallographic directions in the austenite phase though complications existed for the martensite phase.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 23
DOI: 10.1016/j.actamat.2008.05.006
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“Transmission electron microscopy investigation of microstructures in low-hysteresis alloys with special lattice parameters”. Delville R, Schryvers D, Zhang Z, James RD, Scripta materialia 60, 293 (2009). http://doi.org/10.1016/j.scriptamat.2008.10.025
Abstract: A sharp drop in hysteresis is observed for shape memory alloys satisfying the compatibility condition between austenite and martensite, i.e. ë2 = 1, where ë2 is the middle eigenvalue of the transformation strain matrix. The present work investigates the evolution of microstructure by transmission electron microscopy as the composition of the Ti50Ni50−xPdx system is systemically tuned to achieve the condition ë2 = 1. Changes in morphology, twinning density and twinning modes are reported along with twinless martensite and exact austenitemartensite interfaces.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 56
DOI: 10.1016/j.scriptamat.2008.10.025
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“Is there a relationship between the stacking fault character and the activated mode of plasticity of FeMn-based austenitic steels?”.Idrissi H, Ryelandt L, Veron M, Schryvers D, Jacques PJ, Scripta materialia 60, 941 (2009). http://doi.org/10.1016/j.scriptamat.2009.01.040
Abstract: By changing the testing temperature, an austenitic FeMnAlSi alloy presents either å-martensite transformation or mechanical twinning during straining. In order to understand the nucleation and growth mechanisms involved in both phenomena, defects and particularly stacking faults, were characterized by transmission electron microscopy. It is observed that the character of the stacking faults also changes (from extrinsic to intrinsic) together with the temperature and the activated mode of plasticity.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 84
DOI: 10.1016/j.scriptamat.2009.01.040
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“Focused ion beam/scanning electron microscopy tomography and conventional transmission electron microscopy assessment of Ni4Ti3 morphology in compression-aged Ni-rich Ni-Ti single crystals”. Cao S, Somsen C, Croitoru M, Schryvers D, Eggeler G, Scripta materialia 62, 399 (2010). http://doi.org/10.1016/j.scriptamat.2009.11.040
Abstract: The size, morphology and configuration of Ni4Ti3 precipitates in a single-crystal NiTi alloy have been investigated by two-dimensional transmission electron microscopy-based image analysis and three-dimensional reconstruction from slice-and-view images obtained in a focused ion beam/scanning electron microscopy (FIB/SEM) dual-beam system. Average distances between the precipitates measured along the compression direction correlate well between both techniques, while particle shape and configuration data is best obtained from FIB/SEM. Precipitates form pockets of B2 of 0.54 ìm in the compression direction and 1 ìm perpendicular to the compression direction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.747
Times cited: 16
DOI: 10.1016/j.scriptamat.2009.11.040
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“On the mechanism of twin formation in FeMnC TWIP steels”. Idrissi H, Renard K, Ryelandt L, Schryvers D, Jacques PJ, Acta materialia 58, 2464 (2010). http://doi.org/10.1016/j.actamat.2009.12.032
Abstract: Although it is well known that FeMnC TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability of the twins, but also the strength of these twins and their interactions with the gliding dislocations present in the matrix. This experimental evidence is discussed and compared to recent results in order to relate the defects analysis to the macroscopic behaviour of this category of material.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 244
DOI: 10.1016/j.actamat.2009.12.032
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“Microstructure changes during non-conventional heat treatment of thin NiTi wires by pulsed electric current studied by transmission electron microscopy”. Delville R, Malard B, Pilch J, Schryvers D, Acta materialia 58, 4503 (2010). http://doi.org/10.1016/j.actamat.2010.04.046
Abstract: Transmission electron microscopy, electrical resistivity measurements and mechanical testing were employed to investigate the evolution of microstructure and functional superelastic properties of 0.1 mm diameter as-drawn NiTi wires subjected to a non-conventional heat treatment by controlled electric pulse currents. This method enables a better control of the recovery and recrystallization processes taking place during the heat treatment and accordingly a better control on the final microstructure. Using a stepwise approach of millisecond pulse annealing, it is shown how the microstructure evolves from a severely deformed state with no functional properties to an optimal nanograined microstructure (2050 nm) that is partially recovered through polygonization and partially recrystallized and that has the best functional properties. Such a microstructure is highly resistant against dislocation slip upon cycling, while microstructures annealed for longer times and showing mostly recrystallized grains were prone to dislocation slip, particularly as the grain size exceeds 200 nm.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 110
DOI: 10.1016/j.actamat.2010.04.046
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“On the relationship between the twin internal structure and the work-hardening rate of TWIP steels”. Idrissi H, Renard K, Schryvers D, Jacques PJ, Scripta materialia 63, 961 (2010). http://doi.org/10.1016/j.scriptamat.2010.07.016
Abstract: FeMnC and FeMnSiAl TWIP steels deformed under the same conditions exhibit different work-hardening rates. The present study investigates the microstructure of plastically deformed FeMnC and FeMnSiAl samples, particularly the internal structure of the mechanically generated twins and their topology at the grain scale. Twins in the FeMnC steel are finer and full of sessile dislocations, rendering this material distinctly stronger with an improved work-hardening rate.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 145
DOI: 10.1016/j.scriptamat.2010.07.016
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“Quantitative three-dimensional analysis of Ni4Ti3 precipitate morphology and distribution in polycrystalline Ni-Ti”. Cao S, Nishida M, Schryvers D, Acta materialia 59, 1780 (2011). http://doi.org/10.1016/j.actamat.2010.11.044
Abstract: The three-dimensional size, morphology and distribution of Ni4Ti3 precipitates in a Ni50.8Ti49.2 polycrystalline shape memory alloy with a heterogeneous microstructure have been investigated using a focused ion beam/scanning electron microscopy slice-and-view procedure. The mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured and/or calculated. The morphology of the precipitates was quantified by determining the equivalent ellipsoids with the same moments of inertia and classified according to the Zingg scheme. Also, the pair distribution functions describing the three-dimensional distributions were obtained from the coordinates of the precipitate mass centres. Based on this new data it is suggested that the existence of the heterogeneous microstructure could be due to a very small concentration gradient in the grains of the homogenized material and that the resulting multistage martensitic transformation originates in strain effects related to the size of the precipitates and scale differences of the available B2 matrix in between the precipitates.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 34
DOI: 10.1016/j.actamat.2010.11.044
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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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