The mechanical properties of amorphous olivine (a-olivine) deformed at room temperature are investigated in situ in a TEM under uniaxial tension using a Push-to-Pull (PTP) device. Thin films of a-olivine were produced by pulsed laser deposition (PLD). With or without electron irradiation, a-olivine films deform plastically, with a gradual transition that makes impossible the determination of a precise threshold. The strength attains values up to 2.5 GPa. The increasing strain-rate in load control results in an apparent softening with stress drop. The fracture strain reaches values close to 30 % without e-beam irradiation. Under electron illumination at 200 kV, the strength is lower, around 1.7 GPa, while higher elongations close to 36 % are obtained. Alternating beam-off and beam-on sequences lead to exceptionally large fracture strains equal to 68 % at 200 kV and 139 % at 80 kV. EELS measurements were performed to characterize the interaction between the electron beam and a-olivine. At a voltage of 80 kV, radiolysis accompanied by oxygen release dominates whereas at high voltage (300 kV) the interaction is dominated by knock-on type defects. Radiolysis is also the main interaction mechanism at 200 kV with low exposition which corresponds to most of our in situ TEM deformation experiments. To interpret the mechanical data, a simple 1D model has been developed to rationalize the load transfer between the PTP device and the specimen. The strain-rate sensitivity is 6 to 10 times higher when a-olivine is deformed under electron irradiation.

Focused ion beam-scanning electron microscopy (FIB-SEM) is a microscopy technique that can be used to investigate the quality and structural properties of industrial materials such as polyolefins. An understudied aspect and possible drawback of the technique could be the implantation of the impinging ions under the sample surface and damage to the molecular structure, hindering its use as a sample preparation tool for surface-sensitive techniques. We systematically investigated the damaging effects of gallium liquid metal focused ion beam under grazing incident beam angle and various accelerating voltages on polyethylene. Changes in molecular structure and ion implantation depth were analyzed with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiling and optical profilometry. Our results show that the gallium ion beam causes significant damage to the polyolefin structure, which is especially observed as dehydrogenation of the molecular structure of the (sub)surface. These molecular products are concentrated in distinct sub-surface zones, where damage is coupled to the presence of implanted gallium from the FIB etching.

The effect of Cu on the evolution of the Al3 Zr phase in an Al-Cu-Zr cast alloy during solution treatment at 500 degrees C has been thoroughly studied by combining atomic resolution high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and first-principles calculations. The heat treatment initially produces a pure L12 -Al3 Zr microstructure, allowing for about 13 % Cu to be incorporated in the dispersoid. Cu incorporation increases the energy barrier for anti-phase boundary (APB) activation, thus stabilizing the L12 structure. Additional heating leads to a Cu-induced "branched" path for the L12 structural transformation, with the latter process accelerated once the first APB has been created. Cu atoms may either (i) be repelled by the APBs, promoting the transformation to a Cu-poor D023 phase, or (ii) they may segregate at one Al-Zr layer adjacent to the APB, promoting a transformation to a new thermodynamically favored phase, Al4 CuZr, formed when these segregation layers are periodically arranged. Theoretical studies suggest that the branching of the L12 transformation path is linked to the speed at which an APB is created, with Cu attraction triggered by a comparatively slow process. This unexpected transformation behavior of the L12 -Al3 Zr phase opens a new path to understanding, and potentially regulating the Al3 Zr dispersoid evolution for high temperature applications. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The annealing of irradiation defects in tungsten was investigated under in-situ observations conducted using transmission electron microscopy (TEM). ITER-specification tungsten was exposed to heavy-ion irradiation by 10 MeV Au+ ions to 0.5 and 1 dpa at room temperature to generate defects. Subsequently, the thermal stability and recovery mechanisms of the generated defects are investigated by in-situ TEM at 600 °C, 800 °C, 900 °C and 1000 °C. The obtained TEM data are used to visualize and quantify the defect characteristics such as loops and voids as well as for observing the evolution of the microstructure and defect diffusion/recovery mechanisms. Focus is made on specific spatial phenomena such as loop-loop interaction, loop-dislocation and loop-grain boundary decoration, loop pinning, entanglement, formation of raft and transformation of loops into a dislocation network. The obtained results are in line with earlier obtained data for pure recrystallized tungsten, still, present results provide important information such as radiation-induced defect characteristics and recovery mechanisms under high temperature for the ITER-specification tungsten.

Thin film metallic glasses (TFMG) provide rich information on plastic phenomena owing to a more ductile behaviour than bulk counterparts. However, correlation between the macroscopic and the atomic strain for sub-micron scale specimens remains a challenge which is essential towards unravelling the origin of the mechanical properties. Here, complementary results were obtained combining high-resolution X-ray synchrotron scattering and in situ annealing transmission electron microscopy measurements on ZrNi thin freestanding films showing remarkable strength/ductility balance. The evolution of the structure factor shows the occurrence of spatially homogeneous and isotropic atomic dilatancy without shear banding upon tensile loading at room temperature. The in situ TEM results reveal that such dilatancy is also triggered during thermal annealing but only in undeformed samples. The discussion aims at linking this behaviour to the specific microstructure of the films, which involves nanoscale chemical/density heterogeneities inherited from the deposition process, and to the mechanical properties.

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.

Ultrafine faulty C14-MgZn2 Laves phase precipitates containing quasicrystalline clusters and demonstrating the formation of binary quasicrystalline precipitates with Penrose-like random-tiling were observed in the over-aged FCC matrix of a commercial 7N01 Al-Zn-Mg alloy, using high angle annular dark field scanning transmission electron microscopy. The evolution from C14-Laves phase to quasicrystalline clusters is illustrated, and five-fold symmetry can be found in both real and reciprocal spaces. Our findings reveal the possibility of quasicrystalline formation from Laves phase in a highly plastic metal matrix like Al and demonstrate the structural relationship between Laves phase and quasicrystals.

Although largely studied, contradictory results on nickel oxide (NiO) properties can be found in the literature. We herein propose a comprehensive study that aims at leveling contradictions related to NiO materials with a focus on its conductivity, surface properties, and the intrinsic charge defects compensation mechanism with regards to the conditions preparation. The experiments were performed by in situ photo-electron spectroscopy, electron energy loss spectroscopy, and optical as well as electrical measurements on polycrystalline NiO thin films prepared under various preparation conditions by reactive sputtering. The results show that surface and bulk properties were strongly related to the deposition temperature with in particular the observation of Fermi level pinning, high work function, and unstable oxygen-rich grain boundaries for the thin films produced at room temperature but not at high temperature (>200 degrees C). Finally, this study provides substantial information about surface and bulk NiO properties enabling to unveil the origin of the high electrical conductivity of room temperature NiO thin films and also for supporting a general electronic charge compensation mechanism of intrinsic defects according to the deposition temperature.

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/ )

The microstructural features of intergranular irradiation-assisted stress corrosion crack tips from a redeemed neutron-irradiated flux thimble tube (60 dpa) have been investigated using focused-ion beam analysis and (scanning) transmission electron microscopy. The current work presents a close examination of the deformation field and oxide assembly associated with intergranular cracking, in addition to the analysis of radiation-induced segregation at leading grain boundaries. Evidence of stress induced martensitic transformation extending from the crack tips is presented. Intergranular crack arrest is demonstrated on the account of the external tensile stress orientation, and as a consequence of MnS inclusion particles segregating close to the fractured grain boundary. Exclusive observations of grain boundary oxidation prior to the cracking are presented, which is in full-agreement with the internal oxidation model.(c) 2022 Elsevier B.V. All rights reserved.

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.

This study reports the properties of irradiation assisted stress corrosion crack tips extracted by means of focused-ion beam from 60 to 80 dpa neutron-irradiated O-ring specimens tested under straining conditions under a pressurized-water reactor environment. Various crack tip morphologies and surrounding deformation features were analyzed as a function of applied stress, surface oxidation state and loading form - constant versus cyclic. All investigated cracks exhibit grain boundary oxidation in front of the crack tip, with the extent of oxidation being proportional to applied stress. These findings clearly demonstrate that, under the subcritical crack propagation regime, the grain boundary oxide grows faster than the crack. On the other hand, crack tips appertaining to specimens with removed oxide layer at the outer surface show comparatively less oxidation at the crack tip, which could indicate towards crack initiation from regions that exemplify lower stress, such as the O-ring inner surface. Cyclic loading is found to have a more pronounced effect on the crack tip microstructure, demonstrating increased deformation twinning and α′-martensitic transformation, which signifies towards an increased susceptibility to intergranular failure. Still, the extent of crack tip grain boundary oxidation in this case agrees well with expected values for maximum stress applied during cyclic loading. All results are interpreted based on the probabilistic subcritical crack propagation mechanism and provide strong support to a stress-driven internal oxidation model.

The interaction between dislocations and nano-precipitates during deformation directly influences hardening response of precipitation-strengthening metals such as Al-Mg-Si alloys. However, how coherent and semi-coherent nano-precipitates accommodate external deformation applied to an Al alloy remains to be elucidated. In-situ tensile experiments in a transmission electron microscope (TEM) were conducted to study the dynamic process of dislocations cutting through coherent needle-like beta '' precipitates with diameters of 3 similar to 8 nm. Comprehensive investigations using in-situ, ex-situ TEM and atom probe tomography uncovered that beta '' precipitates were firstly sheared into small fragments, and then the rotation of the fragments, via sliding along precipitate/matrix interfaces, destroyed their initially coherent interface with the Al matrix. In contrast, semi-coherent beta' precipitates with sizes similar to beta '' were more difficult to be fragmented and accumulation of dislocations at the interface increased interface misfit between beta' and the Al matrix. Consequently, beta' precipitates could basically maintain their needle-like shape after the tensile deformation. This research gains new insights into the interaction between nano-precipitates and dislocations. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tailoring heat treatments for Laser Powder Bed Fusion (LPBF) processed materials is critical to ensure superior and repeatable material properties for high-end applications. This tailoring requires in-depth understanding of the LPBF-processed material. Therefore, the current study aims at unravelling the threefold interrelationship between the process (LPBF and heat treatment), the microstructure at different scales (macro-, meso-, micro-, and nano-scale), and the macroscopic material properties of AlSi10Mg. A similar solidification trajectory applies at different length scales when comparing the solidification of AlSi10Mg, ranging from mould-casting to rapid solidification (LPBF). The similarity in solidification trajectories triggers the reason why the Brody-Flemings cellular microsegregation solidification model could predict the cellular morphology of the LPBF as-printed microstructure. Where rapid solidification occurs at a much finer scale, the LPBF microstructure exhibits a significant grain refinement and a high degree of silicon (Si) supersaturation. This study has identified the grain refinement and Si supersaturation as critical assets of the as-printed microstructure, playing a vital role in achieving superior mechanical and thermal properties during heat treatment. Next, an electrical conductivity model could accurately predict the Si solute concentration in LPBF-processed and heat-treated AlSi10Mg and allows understanding the microstructural evolution during heat treatment. The LPBF-processed and heat-treated AlSi10Mg conditions (as-built (AB), direct-aged (DA), stress-relieved (SR), preheated (PH)) show an interesting range of superior mechanical properties (tensile strength: 300–450 MPa, elongation: 4–13%) compared to the mould-cast T6 reference condition.

In the present work two different cold working and annealing schemes were utilized, and the asymmetric superelastic response of thermomechanically processed materials were then assessed through cyclic tensile and compressive modes of deformation. The values of transformation stress, transformation strain, and pseudoelastic strain were measured for each treated and solutionized specimens and the asymmetric response was compared. In the solution annealed state, the difference of these parameters at different deformation modes was negligible due to the weak texture of the material, while for thermomechanically treated ones, development of specific deformation and recrystallization texture components was identified to be one of the underlying reasons of intensified asymmetry. The evolved substructure during the thermomechanical processing also played a substantial role in determining the asymmetric response. The presence of fine grains and dense dislocation substructure could hinder the movement of the transformation front, thus limiting the range of transformation. In tensile mode, the transformation stress was lower, but higher transformation strain was achieved, which was discussed relying on the slip activity in specified oriented grains. The lower transformation strain in compression mode led to lower pseudoelastic strain due to the narrow transformation range which finally degraded superelastic response of the material. (C) 2021 Elsevier B.V. All rights reserved.

Stable emissive carbon nanodots were generated in zeolite crystals using near infrared photon irradiation gradually converting the occluded organic template, originally used to synthesize the zeolite crystals, into discrete luminescent species consisting of nano-sized carbogenic fluorophores, as ascertained using Raman microscopy, and steady-state and time-resolved spectroscopic techniques. Photoactivation in a confocal laser fluorescence microscope allows 3D resolved writing of luminescent carbon nanodot patterns inside zeolites providing a cost-effective and non-toxic alternative to previously reported metal-based nanoclusters confined in zeolites, and opens up opportunities in bio-labelling and sensing applications.

This work addresses the early stages (<= 1000 h) of the dissolution corrosion behavior of 316L and DIN 1.4970 austenitic stainless steels in contact with oxygen-poor (C-O < 10(-8) mass%), static liquid lead-bismuth eutectic (LBE) at 500 degrees C for 600-1000 h. The objective of this study was to determine the relative early-stage resistance of the uncoated steels to dissolution corrosion and to assess the protectiveness of select candidate coatings (Cr2AlC, Al2O3, V2AlxCy). The simultaneous exposure of steels with intended differences in microstructure and thermomechanical state showed the effects of steel grain size, density of annealing/deformation twins, and secondary precipitates on the steel dissolution corrosion behavior. The findings of this study provide recommendations on steel manufacturing with the aim of using the steels to construct Gen-IV lead-cooled fast reactors.

Time evolution of precipitates related to age-hardening in Ti–2.3 wt pct Cu alloys was investigated by electron microscopy. In isothermal aging at 723 K, the hardness increases continuously owing to precipitation strengthening, whereas in two-step aging where the aging temperature is switched from 673 K to 873 K after 100 hours, the hardness is found to drastically drop after the aging temperature switches. In isothermal aging, metastable and stable precipitates are independently nucleated, whereas characteristic V-shaped clusters of precipitates are observed during the two-step aging. It is revealed by atomic-scale observations that the V-shaped clusters are composed of metastable and stable precipitates and each type of precipitate has a different orientation relationship with the α phase: $$(10\bar3)$$ //(0001)α and $$[0\bar10]$$ // $$[11\bar20]_\alpha$$ for the metastable, and (201)// $$(1\bar103)_\alpha$$ and $$[0\bar10]$$ // $$[11\bar20]_\alpha$$ for the stable precipitates, respectively. The drop in hardness during two-step aging can be explained by a synergistic effect of decreased precipitation strengthening and solid solution strengthening.

In this work, we report an anomalous phenomenon on superelastic cycling of NiTi shape memory alloys when deforming at the temperature close to the border of superelastic window. New unexpected effects are found—(i) critical stress for inducing martensite transformation during the second loading cycle is higher than that of the first cycle; (ii) the plateau stress of the second cycle decreases to the original level when the strain overcomes the limit of the first cycle; (iii) transition from good superelasticity in the first cycle to fully irreversible strain in the second. We propose that defects generated during the first superelastic cycle close to the border of superelastic window impede following stress-induced martensitic transformations, leading to the increase of critical stress beyond yield stress of the B2 matrix, and thus functional fatigue of NiTi alloys.