Although fatigue is closely related to microstructural changes, current fatigue criteria for shape memory alloys (SMAs) fail to account for this information due to the lack of research on quantifying microstructural defects associated with fatigue. In this study, we introduce local stored energy as a quantifiable parameter that reflects microstructural evolution and demonstrate its effectiveness as a reliable fatigue indicator. Ex-situ synchrotron X-ray diffraction tests were conducted on a series of NiTi specimens subjected to cyclic loading and stopped at different fatigue stages. The results revealed inhomogeneous microstructures along the gauge section, characterized by residual R-phase accumulation, defect density, and residual stress in active zones. These microstructural changes, resulting from localized deformation, were quantified by local stored energy at the microscale via X-ray peak analysis. Consistent with these inhomogeneous microstructures, the distribution of local stored energy was uneven, with maximum values in active zones where fatigue cracks preferentially occur. As fatigue progressed, local stored energy in these zones increased, eventually stabilizing at a steady state. This steady state exhibited a negative correlation with fatigue lifetimes, where higher loading frequencies resulted in increased stored energy and shorter lifetimes. These findings validate local stored energy as a crucial fatigue indicator, paving the way for development of a physically-grounded fatigue criterion based on this quantity.

Visible–near-infrared (Vis–NIR) organic photodetectors (OPDs) are promising for advanced optoelectronic sensing. However, their performance is often limited by instability arising from the oxygen and moisture sensitivity of small-bandgap organic semiconductors required for NIR absorption. Here, we report PM6:Y12 (BTP-4F-12) based Vis–NIR broadband OPDs and investigate ambient stability using three encapulation strategies: (i) low-temperature atomic layer deposition (ALD) of Al2O3 (~45 nm) at 95℃, (ii) chemical vapor deposition (CVD) deposition of parylene C (~1 µm) at room temperature (RT), and (iii) a hybrid encapsulation combining both. The hybrid-encapsulated OPDs (0.25 cm²) exhibit superior stability with low dark current density of 5.4 × 10⁻8 A/cm² and open-circuit voltage (VOC) ~0.5 V. Under monochromatic illumination (100 µW/cm2) across the 400–1000 nm range, the OPD exhibits peak responsivity of 0.59 A/W at 730 nm, corresponding to a detectivity of 8.9 × 1012 Jones. At 850 nm a responsivity of 0.45 A/W is achieved, with 93% responsivity retention and a stable linear dynamic range (LDR) of 83 dB after 50 days storage in ambient conditions (20 ℃ and 45% RH). A maximum external quantum efficiency (EQE) of 152% is observed at 455 nm indicating internal photoconductive gain. Structural and compositional analyses confirm a dense (2.7 g/cm3), amorphous and uniform Al2O3 barrier with a growth rate ~0.9 Å/cycle with <2% residual carbon. These results establish a clear stability-performance relationship and demonstrate hybrid encapsulation as an effective engineering strategy for achieving durable and high-performance Vis–NIR OPDs.

The European Hydrogen Backbone initiative plans to develop a large hydrogen transport grid, mainly from repurposing of existing Natural Gas infrastructures The mechanical integrity of such infrastructure still relies on a better and quantified knowledge of the effect of hydrogen on the steel properties. This paper discusses the hydrogen embrittlement mechanisms of ferrite-pearlite low alloy pipeline steel (L485MB steel) subjected to monotonic tensile loading in a pressurised hydrogen environment. Although the main mechanisms involved are now well described in the literature, uncertainties remain regarding their respective quantified implications, in particular concerning the effect of hydrogen on enhanced or reduced local plastic activity. Thus, tensile tests on smooth specimens were performed at room temperature up to 30 MPa H2 gas with initial strain rates of 10-6 s-1 and 10-4s-1. The results under hydrogen display a strong plastic localisation at the macroscale in very active shear bands oriented at 45 degrees of the tensile axis. Such hydrogen induced localisation leads to a transition from diffuse necking under air to localised necking under hydrogen pressure. Although softening was not observed at a macroscopic level on tensile curves, this strain localisation is attributed to a softening effect of hydrogen. This assumption is supported by dislocation density measurements. Moreover, the observation of the gage length of the smooth specimen shows that during tensile testing under hydrogen, microcracks formed in mode 1 in pearlite bands and served as initiation sites for shear bands. Based on these observations, a complete failure scenario is proposed.

A combination of the modified Warren–Averbach (mWA) and modified Williamson–Hall (mWH) methods was applied to characterize the local dislocation structure at the micrometre scale of a laser-shock-peened Ni specimen. Peak profiles obtained by energy scanning of Laue microdiffraction peaks were analyzed in terms of dislocation density, stored energy and interaction between dislocations. The applied methods, exploiting the asymptotic form of the Fourier transform of the peak (mWA method) and the long-range screening described by the full width at half-maximum (mWH), are complementary and offer for the first time the possibility of checking the adequacy of an assumed dislocation model. The combined method is applicable to a dilute dislocation structure, when the mWH plot should be linear. The results for the dislocation density are in reasonable agreement with previous literature data obtained by transmission electron microscopy.

The effect of femtosecond laser shock peening on a model Al-0.3Mn alloy was investigated experimentally and numerically by molecular dynamics. Micro-diffraction experiments performed at synchrotron source revealed depth profiles of the residual stress and the stored energy of dislocations, a measure of local plasticity. The depth of the maximum compressive stress did not coincide with that of the maximum dislocation energy, which was found at the surface. The interaction between the laser and the metal was simulated with LAMMPS using a two temperature molecular dynamics package. The model accurately described the equation of state of aluminum and showed nearly equal resolved shear stresses on all slip systems at the wavefront. The dislocation density at depth of 1 mu m, predicted by the Meyers' model [1], was higher than the experimental data, suggesting possible recovery due to the increased temperature of the sample after repeated shock loading.

The microstructure evolution associated with the cold forming sequence of an Fe-14Cr-1W-0.3Ti-0.3Y2O3 grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material, initially hot extruded at 1100 °C and then shaped into cladding tube geometry via HPTR cold pilgering, shows a high microstructure stability that affects stress release heat treatment efficiency. Each step of the process was analyzed to better understand the microstructure stability of the material. Despite high levels of stored energy, heat treatments, up to 1350 °C, do not allow for recrystallization of the material. The Vickers hardness shows significant variations along the manufacturing steps. Thanks to a combination of EBSD and X-ray diffraction measurements, this study gives a new insight into the contribution of statistically stored dislocation (SSD) recovery on the hardness evolution during an ODS steel cold forming sequence. SSD density, close to 4.1015 m−2 after cold rolling, drops by only an order of magnitude during heat treatment, while geometrically necessary dislocation (GND) density, close to 1.1015 m−2, remains stable. Hardness decrease during heat treatments appears to be controlled only by the evolution of SSD.

Fatigue behavior is intrinsically linked to microstructural alterations induced by cyclic loading. However, the quantification of microstructural defects associated with fatigue damage of NiTi shape memory alloys (SMAs) is lacking, which hinders the development of a physically based fatigue criterion. To this end, a multi-scale experimental analysis was conducted on cyclically deformed NiTi SMAs, which evidenced a strong correlation between microstructural inhomogeneity and localized deformation behavior. The microstructural change associated with fatigue was quantified in terms of stored strain–energy, with the highest values observed in the regions where fatigue cracks initiate. Consequently, stored energy is deemed as an effective fatigue indicator, offering valuable insights for future work in the design and optimization of SMAs’ structures against fatigue.

Conventional tungsten carbide (WC) cermet parts containing a cobalt matrix phase are generally produced via powder sintering. In this study it is shown that cermet parts can also be produced by laser powder bed fusion from WC-17Co powder precursor. Optimal process parameters were found for manufacturing without preheated building plate. Micro-structural analysis revealed noteworthy porosity fraction (1.41%) as well as the presence of small-scale cracks in the as-built specimens. It is further shown that most of these defects can be eliminated by heat treatment at ambient pressure or by hot isostatic pressing. Heat treatment also led to the dissolution of the fragile W 2 C phase. Hardness test results indicate that the performance of the AM parts was comparable to that of a reference produced via powder sintering. The work is a successful demonstration of manufacturing of cermet parts using laser powder bed fusion.

Friction stir processing (FSP) is applied for the post-treatment of an Al-Cu-Ni cold spray metal composite in order to produce an alloy coating. The results are compared with laser remelting of the same material. It was shown that both post-treatment procedures form an alloy containing new intermetallic phases AlNi and Al2Cu initially absent in the as-sprayed material. The integrity of the coating treated by FSP was significantly higher than the laser-treated one due to the absence of material melting, which can introduce significant porosity. Thus, FSP could be considered an efficient post-treatment process of cold sprayed composite coatings leading to the improvement of the coating uniformity and modification of the phase composition.

Two X-ray methods are applied to estimate the strain energy of crystals containing dislocations, a simpler method based on the full width at half-maximum (FWHM) of the diffraction peaks, and asymptotic line profile analysis (LPA), which exploits the functional form of the Fourier transform corresponding to small Fourier parameters. It is shown analytically that, in the single-defect approximation, the modified Williamson–Hall (mWH) plot of the FWHMs is linear and the slope of the line is directly related to the strain energy of the dislocation system. Evaluation of the numerically generated peaks for randomly arranged edge dislocation dipoles shows that the method based on the mWH plot gives accurate strain energy, while asymptotic LPA overestimates it by about 50%. The accurate result given by the mWH plot is explained by the long correlation distance associated with the FWHM, which better captures the dislocation arrangement over large distances. By contrast, asymptotic LPA is related to atomic correlations over distances smaller than the mean dislocation–dislocation spacing, where the displacement gradient is mainly determined by the field of single dislocations. Therefore, asymptotic LPA leads to a very accurate dislocation density (with error less than 1%) and the result is independent of the dislocation arrangement. However, these short-range correlations overestimate the outer cut-off radius by one order of magnitude.

Constitutive laws underlie most physical processes in nature. However, learning such equations in heterogeneous solids (e.g., due to phase separation) is challenging. One such relationship is between composition and eigenstrain, which governs the chemo-mechanical expansion in solids. In this work, we developed a generalizable, physically-constrained image-learning framework to algorithmically learn the chemo-mechanical constitutive law at the nanoscale from correlative four-dimensional scanning transmission electron microscopy and X-ray spectro-ptychography images. We demonstrated this approach on Li$_X$FePO$_4$, a technologically-relevant battery positive electrode material. We uncovered the functional form of composition-eigenstrain relation in this two-phase binary solid across the entire composition range (0 $\leq$ X $\leq$ 1), including inside the thermodynamically-unstable miscibility gap. The learned relation directly validates Vegard's law of linear response at the nanoscale. Our physics-constrained data-driven approach directly visualizes the residual strain field (by removing the compositional and coherency strain), which is otherwise impossible to quantify. Heterogeneities in the residual strain arise from misfit dislocations and were independently verified by X-ray diffraction line profile analysis. Our work provides the means to simultaneously quantify chemical expansion, coherency strain and dislocations in battery electrodes, which has implications on rate capabilities and lifetime. Broadly, this work also highlights the potential of integrating correlative microscopy and image learning for extracting material properties and physics.

Cermets are composite materials consisting of a ceramic reinforcement and a metal matrix. Laser Powder Bed Fusion (L-PBF) is an Additive Manufacturing (AM) technology. The present paper deals with the feasibility study of AM of cermet parts by L-PBF using WC-17Co powder. The results showed that parametric optimization of the L-PBF process allowed the production of solid WC-17Co part. Structural analysis revealed the presence of significant porosity (1.41%) and small-scale cracks in the as-built samples. Post-processing by HIP (Hot Isostatic Pressure) significantly improved the structure of manufactured parts. The porosity became very low (0.01%) and XRD phase analysis revealed the absence of the fragile W2C phase. Abrasive wear and hardness tests showed that performances of additively manufactured parts were comparable to a reference part produced by powder sintering. The study successfully demonstrated the possibility of manufacturing wear-resistant cermet parts by L-PBF.

Using a 1042 nm laser, we control the conductivity of PEDOT:PSS over 3 orders of magnitude. We show that the cause of this change in conductivity is the agglomeration of the PEDOT cores, and use this process to fabricated OECTs.

Diffraction peak profiles were calculated numerically for dislocation ensembles with different spatial arrange-ments and correlations between the Burgers vector signs. The latter property determines the stored elastic energy in the crystal and the width of the diffraction peaks. It is shown that within the approximation of the asymptotic line-profile theory the relationship between peak breadth and the magnitude of the diffraction vector in the modified Williamson-Hall (mWH) plot is linear. The slope of the line is proportional to the arrangement parameter M0.3 and to the square root of the dislocation density. The only rigorous way for determining M is the asymptotic Fourier method. Therefore, the evaluation of the dislocation density from the mWH-plot alone is impossible and should be avoided. The mWH plot however, is very useful in practice. Its linearity indicates a consistent asymptotic line-profile analysis.

Precipitation hardening is the most effective strategy to enhance the mechanical properties of metals. Dislocation mechanisms to control strengthening during precipitation have been demonstrated extensively. However, owing to the complexity of different precipitates in alloys, variations in ductility caused by precipitation are complex and have not been clarified so far. In this study, the effects of precipitation on ductility in precipitation hardening aluminium alloys are investigated based on a modified dislocation-based approach and experimental characterisation. The AlMgScZr alloy with spherical Al3(Sc, Zr) precipitates is used as a model alloy system to understand the effects of precipitation on ductility. Via heat treatment, shearable and nonshearable Al3(Sc, Zr) precipitates are introduced in the AlMg matrix. The results show that the ductility of AlMgScZr alloy decreases when shearable precipitates occur, while it increases with shearable precipitates being replaced by nonshearable precipitates. The variation in ductility of AlMgScZr alloy is mainly controlled by the dynamic recovery rate of the dislocations. Finally, by analysing the different precipitate–dislocation interactions and evaluating the dislocation density evolution during deformation, the dislocation mechanisms of ductility during precipitation for AlMgScZr alloy are demonstrated. This study reveals the dislocation mechanism for controlling ductility during precipitation for AlMgScZr alloy which can provide a theoretical foundation for the design of high-performance structural materials.

Ultrafast laser was recently used to modify the surface integrity and peen the surface region of aluminum based alloy 2024-T351 without a sacrificial layer prior to the process. We show that controllable laser parameters such as fluence and pulse duration have a significant influence on peening qualities, such as the compressive residual stress, hardness, and surface roughness of peened parts. The residual stress profile was analyzed by x-ray diffraction. By controlling the laser fluence and pulse duration, it was possible to obtain 200 MPa of compressive residual stresses close to the surface and 100 MPa of compressive residual stresses at 50 μm depth. Moreover, micro-hardness was increased from 2.1 to 2.5 GPa in the near-surface region. In addition, the dislocation densities were evaluated from high-resolution x-ray diffraction peaks. The increase of the dislocation density indicates that plastic deformation occurred, which generated compressive residual stresses and hardness enhancement. Plastic deformation is considered to be created by an ultrafast laser-induced pressure wave. The correlation between laser parameters and modified surface properties is interpreted by the complex interplay between laser excitation, material relaxation, and pressure waves. A pulse duration in the picosecond range and a relatively low fluence is possibly the optimal condition for a best peening quality with small surface roughness, which could potentially be used to reduce surface cracking and associated failures of additively manufactured parts.

The well-known mechanisms of interaction between precipitates and dislocations are shearing (for shearable precipitates) and bypassing mechanisms (for nonshearable precipitates). The transition from shearable to nonshearable precipitates in precipitation hardening alloys leads to changes of dislocation motion mode and dislocation multiplication behavior, which inevitably causes different PLC behaviors. In this study, we systematically investigate the influence of shearable and nonshearable Al3(Sc, Zr) precipitates on PLC behaviors by experimental characterization for precipitation hardening AlMgScZr alloys. We analyze the onset strain, critical strain-rate range, serration amplitude, and propagation behavior of PLC bands in detail for AlMgScZr alloys with shearable and nonshearable precipitates, respectively. We find that the transition from shearable to nonshearable precipitates changes the PLC band propagation behavior, decreases the magnitude of serration amplitude, expands the strain-rate range as well as decreases the critical strain rate between normal behavior (the critical strain increases with the increase of strain rate) and inverse behavior (the critical strain decreases with the increase of strain rate) regimes due to the different dislocation-precipitate interactions. Besides, the transition from shearable to nonshearable precipitates increases the onset strain at normal behavior while decreases the onset strain at inverse behavior depending on the different roles of precipitates in the solute-dislocation interaction. Finally, we reveal the nature of influence of different dislocation-precipitate interactions on PLC behavior considering different strengthening mechanisms based on quantitative characterization on precipitates and dislocation density.

During the past 20 years, third-generation high-energy synchrotron sources have made possible the development of several diffraction-imaging methods, which have led to meaningful physical insights into the real structure and dynamics of bulk polycrystalline materials. A not exhaustive list could include work on stress corrosion cracking (King et al., 2008), predictions of crystal plasticity (Pokharel et al., 2014), stress variation in copper through-Si vias (Levine et al., 2015), martensitic transformation (Sedmák et al., 2016) and long-range symmetry breaking in embedded ferroelectrics (Simons et al., 2018). The pioneering work of Poulsen (2004) paved the way for the majority of the techniques using monochromatic radiation, commonly called three-dimensional X-ray diffraction (3DXRD) or high-energy diffraction microscopy (HEDM) (Suter et al., 2006). Since then, a wide variety of techniques have been developed, which are mostly classified on the basis of the distance between the detector and the specimen as (a) far-field or (b) near-field techniques. However, from the point of view of the final reconstruction describing the spatial distribution of the crystallographic orientation (implicitly the grain shape) and strain/stress, a classification based on their spatial and angular resolutions seems to be more appropriate. According to this ‘two-resolution criterion’, all existing techniques can be included in one of the following three categories: (a) High-spatialand low-angular-resolution methods use a near-field setup with a highresolution detector (effective pixel size of about 1 mm), closely placed downstream of the specimen at a distance of a few millimetres. Their angular resolution is relatively low ( 0.1 ), but they can resolve the structure at micrometre/sub-micrometre length scales over millimetre sample sizes. Grain and intragrain orientations are obtained via scans done with either a broad (Ludwig et al., 2008) or a planar beam (Li & Suter, 2013), the beam size being usually adapted to the grain size to avoid peak overlap. (b) Low-spatialand high-angular-resolution methods involve a low-resolution detector with a pixel size of about 50–200 mm placed in the far field ( 0.2–1 m as a function of the pixel size and beam energy). Since diffraction peak positions can be determined with sub-pixel accuracy (Borbely et al., 2014), this setup has high angular resolution (<0.01 ) that allows the elastic strain to be determined. However, the grain shape remains unknown. Measurements are usually performed with a broad beam. (c) Finally, high-spatialand high-angular-resolution methods enable characterization of both the crystallographic orientation and the strain inside single grains at submicrometre length scales, even for deformed materials. It is expected that these ‘holy grail’ methods will provide the missing local experimental evidence for understanding unsolved problems in materials science such as polycrystal plasticity, recrystallization and damage initiation. There are already two methods achieving high spatial and high angular resolution: differential-aperture X-ray microscopy (DAXM; Larson et al., 2002) and dark-field X-ray microscopy (DFXM; Simons et al., 2015). The first uses a polychromatic pencil beam with sub-micrometre cross section for identifying the local orientation from the resulting Laue pattern and an additional energy scan (Chung & Ice, 1999) for strain determination. DFXM uses monochromatic radiation and compound refractive lenses in the diffracted beam, which magnify a small diffractive volume of the analyzed grain/ subgrain. To improve the spatial resolution of the low-spatialand high-angular-resolution methods, Hayashi et al. (2015) proposed a ‘scanning 3DXRD’ approach, using a monochromatic pencil beam, where the spatial resolution could be controlled by the beam size. Combining a lateral scanning of the sample and a tomographic approach (rotation ISSN 1600-5767

Precipitation hardening is the most effective strategy to enhance the mechanical properties of metals. Dislocation mechanisms to control strengthening during precipitation have been demonstrated extensively. However, owing to the complexity of different precipitates in alloys, variations in ductility caused by precipitation are very complex and have not been clarified so far. In this study, the effects of precipitation on ductility in precipitation hardening aluminium alloys are investigated based on a modified dislocation-based approach and experimental characterisation. The AlMgScZr alloy with spherical Al3(Sc, Zr) precipitates is used as a model alloy system to understand the effects of precipitation on ductility. Via heat treatment, shearable and non-shearable Al3(Sc, Zr) precipitates are introduced in the AlMg matrix. The results show that the ductility of AlMgScZr alloy decreases when shearable precipitates occur, while it increases during the shearable–non-shearable transition. The variation in ductility is mainly controlled by the dynamic recovery rate of the dislocations. This dislocation mechanism is supported by analysing the different precipitation–dislocation interactions and evaluating the dislocation density evolution during deformation. This study reveals the dislocation mechanism for controlling ductility during precipitation, which can provide a theoretical foundation for the design of high-performance structural materials.

Damage evolution during tensile straining of an AlSi12Ni alloy has been analyzed in situ at synchrotron source using microtomography and in the scanning electron microscope by surface imaging. It is shown that damage development in the analyzed alloy presenting an interconnected network of intermetallic phases is completely different from damage progression previously observed in materials with disperse distribution of particles. In the present material, which is typical for most eutectic structures, damage is dominated by the rupture of the brittle intermetallic phase while void growth is limited by a shielding effect of the intermetallic particles encasing the void. Primary voids exhibit a size close to the thickness of branches of the intermetallic phase. Final failure occurs by void coalescence, but without the formation of secondary voids. Damage analysis from tomographic scans was only possible by applying 3D image correlation to successive reconstructions, which thanks to its sub-voxel resolution, could satisfactorily detect the volume fraction of small-voids inaccessible by conventional thresholding. The presence of many small voids issued from the breakage of the intermetallic phase also was confirmed by scanning electron microscopy imaging performed at higher resolution.