We employed solid state dewetting to fabricate faceted single crystalline Pt nanoparticles on sapphire substrates. The as-fabricated particles exhibited (111) out-of-plane orientations. The particles were compressed by a flat diamond wafer to various plastic strains and annealed at temperatures between 900 °C and 1000 °C. Plastic deformation caused a systematic drift of the out-of-plane orientation away from (111) toward (112) and (101) orientations. The grains with original (111) orientations re-appeared after annealing, and the microstructural evidence pointed at the nucleation of recrystallized grains at the center of deformed particles. Particles subjected to the highest strains developed multiple holes to the substrate near their edge after recrystallization. We discussed the nucleation of both recrystallized grains and annealing-induced holes in a unified framework that attributes these phenomena to non-equilibrium state of grain boundaries and the Pt-sapphire interface generated by plastic deformation and subsequent thermal annealing.

Solid state dewetting of polycrystalline (PX) thin films typically yields disordered patterns due to the lack of longrange orientation alignment. In contrast, single-crystalline (SX) films exhibit highly ordered, symmetry-driven dewetting morphologies governed by anisotropic surface energies and epitaxial orientation relationships (ORs). Here, we introduce a phase transformation assisted strategy that overcomes this intrinsic limitation in PX Fe-C-Fe tri-layer films (25 nm Fe/1.3 nm C/25 nm Fe) on c-oriented sapphire substrates. Carbon redistribution during annealing at 1050 degrees C induces partial BCC to FCC phase transformation, establishing two distinct dewetting pathways: carbon-lean domains remain ferritic (alpha-phase), while carbon-rich domains transiently form austenite (gamma-phase). This dual-pathway mechanism gives rise to three remarkable phenomena: (i) formation of straight, long PX nanowires, which can only be observed in heteroepitaxial SX systems; (ii) coexistence of threefold (star-like) and four-fold (dendrite-like) symmetry patterns within a single film, defying the substrateimposed symmetry constraints; and (iii) localized high dislocation density segments within nanowires, in contrast to the defect annihilation typically accompanying dewetting. The ferritic domains stabilize three-fold patterns via heteroepitaxial variant selection, while the gamma-phase domains yield four-fold symmetry through high temperature anisotropy and subsequent gamma to alpha reversion obeying the Bain OR. These findings demonstrates that phase transformation can be harnessed to modulate dewetting symmetry, opening new opportunities for designing ordered nanostructures from polycrystalline films.

We show that chemical etching markedly alters the mechanical response of gold nanoparticles produced by solid-state dewetting. Both pristine and etched particles exhibit similar microcompression behavior: an initially elastic-like regime followed by an abrupt displacement burst, with pre-burst stresses in the gigapascal range characteristic of nucleation-controlled plasticity. However, etched particles display anomalously high pre-burst strains, reaching up to 45%. We demonstrate that etching introduces a high density of nanopores and stacking fault tetrahedra, which act as exhaustible dislocation sources. Their progressive annihilation during loading produces an elastic-like response, explaining the unusually large pre-burst deformations observed in etched nanoparticles.

Understanding phase transformations (PT) under bending is essential for designing ductile refractory nano-materials. Here, we systematically investigate deformation mechanisms in single-crystalline molybdenum (Mo) nanowires through molecular dynamics simulations and microcantilever bending experiments. Under monodirectional bending, we uncover a sequential bcc1 -> quasi-stable fcc -> bcc2 transformation, with fcc Mo acting as a lubricating layer that facilitates lattice rotation and relative motion. This quasi-stable fcc phase, maintained under high stress but disappearing upon unloading, reveals a stress-stabilized intermediate structure in bcc systems. Geometrically necessary dislocation calculations further confirm that dislocations alone cannot account for the observed bcc reorientation, establishing PT as the dominant deformation mechanism. Next, in bidirectional bending simulations, we discover {112} penta-twin formation in both the tensile and compressive regions of the Mo nanowire-behavior often seen in fcc systems. Unloading simulations further demonstrate the persistence of these twins under stress-free conditions. Our simulations and experiments bridge nanoscale and microscale observations, highlighting how bending-driven PT can be harnessed to enhance strength and ductility. These insights open pathways toward designing ductile, flexible refractory nanomaterials through controlled-PT engineering.

Understanding stress accommodation at the atomic scale in nanocrystals is essential for operation in extreme environments. We use high-pressure Bragg Coherent Diffraction Imaging (BCDI) in a diamond anvil cell (DAC) to track three-dimensional strain and defects in individual platinum nanoparticles. The particle hosts an interfacial Shockley partial dislocation up to 2.7 GPa, followed at 5.0 GPa by nucleation of a dense dislocation network accompanied by anisotropic Bragg peak broadening, which later relaxes, indicating plasticity. Upon partial unloading, the interfacial partial reappears and transforms into a perfect dislocation that propagates into the crystal via cross-slip; additional glide events occur, while at 6.7 GPa anisotropic broadening re-emerges. Elastic finite-element modeling predicts shear stress concentrations near the particle-substrate interface, whereas nucleation is observed near the particle top surface. These results show that high-pressure BCDI captures dislocation activity and links reciprocal- and real-space signatures of plasticity in nanocrystals.

The production of fibrous oxides, particularly V2O5, by intensive stirring in water is examined through the framework of driven systems, an approach developed in the 1980s by Georges Martin et al. for systems under irradiation or severe plastic deformation. Instead of ballistic diffusion, the model introduces ballistic detachments of atoms from the oxide surface under stirring. A simplified Monte Carlo scheme is proposed for crystal evolution within the terrace-ledge-kink (TLK) model. This scheme accounts for anisotropy and additional athermal detachment probabilities. An individual cluster within a limited volume becomes elongated in a steady state or dissolves. For an ensemble of clusters, the total number decreases (similar to common ripening), but the mean length of the fibers grows. This leads to an increase in the total surface energy, which is contrary to the behavior observed in common ripening.

Upon annealing thin gold line gratings supported by a sapphire substrate, the line gratings were often seen to break up into linear sections, each containing roughly similar size undulating shaped grains along with occasional larger "abacus" grains and sometimes larger grains at the end of a continuous section of line grating, as well as some spherical grains which had broken away. We find that many of the features of the line grating structures which were seen in our experiments can be mimicked by composite axisymmetric steady states whose exterior surfaces are spherical or unduloidal and which may contain internal catenoidal or planar grain boundaries. To the best of our knowledge, these composite steady states have not been previously discussed in either the materials science or the mathematical literature, and they should be relevant in studying polycrystalline metallic nanowires as well as line gratings.

Bragg coherent diffraction imaging (BCDI) is a lens-less technique capable of imaging the strain in a particle in the size range from 20 nm up to several micrometres. This indirect measurement technique, used in X-ray synchrotrons or free-electron lasers all over the world, requires an inversion step using iterative algorithms in order to recover the real-space complex object encoding the particle shape and deformation field. However, artefacts such as scattering peaks called `aliens' from nearby particles can affect the accuracy of the final reconstruction and require meticulous and time-consuming manual masking of the raw data. This becomes problematic for BCDI reconstructions during an experiment and/or for large volumes of data. Here, we explore the potential of machine learning, and specifically clustering techniques, to speed up this procedure while keeping the maximum spatial resolution of the object reconstruction. We also provide a user-friendly Python Jupyter notebook program available on Github.

A key challenge in additive manufacturing (AM) of metallic alloys is the absence of concurrent deformation processes during fabrication, which are crucial for optimizing microstructure and achieving properties comparable to those of wrought or thermomechanically processed materials. In this study, an approach to enhance the thermomechanical behavior of printed metals by mechanically preconditioning the feedstock powder is presented. Specifically, high-energy ball milling (HEBM) is applied to a Ni-Ti shape memory alloy (SMA) spherical powder prior to processing via the solid-state MoldJet AM technique. Our results show that HEBM lowers the sintering temperature and increases the sintered density, all while preserving the alloy’s thermal and superelastic mechanical properties. At the same time, the highly deformed morphology of the ball-milled powder is not evident in the sintered samples, which was attributed to the grain boundary migration and grain growth during sintering. These findings demonstrate the potential of HEBM as a beneficial pretreatment not only for SMAs but also for a broader class of metals processed through sinter-based AM, paving the way for further research into powder conditioning strategies in additive manufacturing.

A comparative study of the microstructure and properties of a Ni43.9Co22.4Fe8.8Al10.7Ti11.7B2.5 [at%] alloy processed via two routes is presented: (i) arc melting followed by high-pressure torsion, and (ii) sintering of blended elemental powders followed by high-pressure torsion. In both cases, part of the material samples were subjected to short annealing treatments at 750 and 850 °C after severe plastic deformation. The powder-sintered samples exhibit consistently higher hardness compared to their cast counterparts under all processing conditions. An exceptionally high hardness exceeding 10 GPa was achieved in the powder-derived alloy after HPT and subsequent annealing at 750 °C, surpassing previously reported values by more than 1 GPa. The physical mechanisms responsible for this ultrahigh hardness are analysed and discussed.

It has been observed that formation of nanoscale interfacial disordered layers adjacent to grain boundaries of highly ordered grains leads to ultrahigh yield strength accompanied by large tensile ductility of the alloy. We propose a theoretical description and formulate criteria of existence of such layers and present strategies of alloy design based on the proposed theory.

Small-scale bicrystal creep experiments were performed on contacts formed via in situ high-temperature diffusion bonding of metal-oxide interfaces including Ag-ZrO2, Pd-ZrO2, Pt-ZrO2, and Ag-high entropy oxide. This work characterizes deformation and failure at metal-oxide interfaces during mechanical loading. Interfacial sliding can be activated easily, while tensile interfacial creep was not observed at any condition of stress or temperature measured. Plastic strain, instead, localizes within the metal under tensile loading. A variety of mechanisms for plastic strain occur in the metal including lattice dislocation-mediated plasticity, twinning, low-angle grain boundary formation, and low-angle grain boundary creep. Surface and low-angle grain boundary diffusion occur under conditions where no metal-oxide tensile creep is observed, highlighting the significant differences in their interfacial mechanical response. High-temperature interfacial failure occurs when the mean curvature at the contact neck is approximately zero and the applied stresses comparable to brittle fracture stresses. The brittle fracture stresses were measured to be 6f = 180 +/- 90 MPa at the Ag-ZrO2 interface at 225 degrees C, 6f = 460 +/- 160 MPa at the Pd-ZrO2 interface at 680 degrees C, and 6f = 640 +/- 440MPa at the Pt-ZrO2 interface at 1010 degrees C.

The intergranular penetration of liquid metal involved in the grain boundary (GB) embrittlement phenomenon has been studied for decades. However, strategies with high adaptability to bulk workpieces that could effectively suppress the penetration of liquid metal along the GB network have rarely been proposed. Herein, we observed abnormally shallow penetration depth (<10 m) of liquid Bi into severely deformed Cu disks after annealing at 600 degrees C for 60 min. By conducting scanning transmission electron microscopy and transmission Kikuchi diffraction characterization, we surmised that the dramatic suppression of the liquid Bi intergranular penetration was due to the continuous GB migration during annealing enabled by nanosized nitrogen-filled bubbles in the sub-surface layer of the Cu disk. This study sheds light on the microstructure design and possible methods for the suppression of intergranular penetration and GB embrittlement in polycrystals.

Additive Manufacturing (AM) of Shape Memory Alloys (SMA), and specifically Ni–Ti alloys, is an evolving field with significant potential to applications in actuation, energy harvesting, and refrigeration. Sinter-based AM technologies show promise in tailoring and controlling the microstructure and properties of Ni–Ti, because the metal particles remain in the solid-state throughout the process. Here, we report on the manufacturing and characterization of Ni–Ti produced using a novel sinter-based MoldJet method: a wax-based mold is deposited layer-by-layer using jet-printing, and its cavities are simultaneously filled with metallic paste. This additive process produces a green body that is sintered to form a dense metal part. The low content of organic binder in the metallic paste results in reduced carbon and oxygen contamination compared to other sinter-based AM methods. Consequently, the reduced formation of carbides and oxides enhances the thermomechanical properties. Here, we show that Ni–Ti produced via MoldJet exhibits a superelastic response with a substantial recoverable strain of 5.6

We employed magnetron co-sputtering to fabricate homogeneous Mo-Cu thin films on a heated sapphire substrate. Partial dewetting at 750-1000 degrees C led to the formation of Mo-Cu bicontinuous film and Cu particles. The Mo self-diffusion coefficient along the Mo-Cu interface at 750 degrees C was estimated at 1.8 x 10-14 m2/s from bicontinuous structure coarsening kinetics. After full dewetting at 900 degrees C for 12 h, isolated, closely spaced Mo nanoparticles and large Cu particles decorated with Mo nanoparticles were observed. Two orientation relationships between the Mo and Cu particles were identified, and the energies of the respective interfaces were estimated using atomistic molecular dynamics simulations. Selective etching of Cu exposed numerous Mo nanoparticles beneath each large Cu particle, while Cu evaporation at 1000 degrees C revealed fewer but larger Mo nanoparticles, indicating coalescence of Mo nanoparticles during Cu evaporation. We developed a semi- quantitative kinetic model describing the migration of Mo nanoparticles at the edge of a large evaporating Cu particle in terms of Mo self-diffusion on the exposed Mo surface and along the Mo-Cu interface. The driving force for Mo nanoparticles migration was estimated with the aid of atomistic simulations. Mo nanoparticles, dragged by shrinking Cu particles, increased in size by absorbing their smaller stationary counterparts beneath the Cu particle. The model-based estimate of effective Mo diffusion coefficient was in good agreement with the literature value of surface self-diffusion coefficient of Mo. Our findings provide new insights into the mechanisms of solid-state dewetting in binary immiscible thin films with vastly different component diffusivities.

In this experimental-computational study, we propose a novel method to study the inhomogeneous deformation of nanoporous Au structures and quantifying locally their deformation. By combining the dewetting method and dealloying of Ag-Au alloys, we fabricated sub-micrometer scale hemispherical nanoporous Au nanoparticles (NPG-NPs). The formed nanoparticles have an average ligament diameter of 13 nm and diameter ranging between 200 and 800 nm. A few grain boundaries, mostly of twin type, were found within the NPG-NPs. Under compression with a flat diamond punch, the load-displacement curves exhibited linear increase, up to a certain compression depth, above which a significant rise in the slope was identified. Molecular dynamics (MD) simulations of NPG-NPs with various sizes, porosities, and ligament diameters were conducted. The simulated load-displacement curves closely matched the experimental ones. With the help of the MD simulations, we identified the dependencies of the NPG-NP mechanical properties on their geometry. To better understand how to quantify these dependencies, we analyzed the densification profiles during the deformation. We found that the densification is inhomogeneous and localized beneath the compressing punch. In combination with the dislocation density profiles, we correlated the densification region with the mean-free path of dislocations and their depletion due to the high surface-to-volume ratio. We showed that the slope increase in the load-displacement curves is attributed to the interaction between the densified region (dislocation structure) and the substrate. Finally, we propose a model for the inhomogeneous deformation, enabling to determine the contact stresses in the experiments.

In this study, we fabricated thermodynamically stable nanoparticles containing face centered cubic Au-based, and body centered cubic Fe-based phases employing a solid-state dewetting of thin Fe/Au bilayers deposited on sapphire substrate. We found that the size distribution and morphology of the two-phase nanoparticles can be varied by changing the overall composition, the deposition order of individual sub-layers, and the parameters of dewetting and subsequent heat treatments. The presence of Fe precipitates in the Au\Fe nanoparticles results in formation of Janus-like structure, as well as in other complex microstructures with unusual shapes and topographies. It was found that coherent twin boundaries are formed in the Au(Fe) phase, and that Au(Fe) and Fe phases share a coherent interface with orientation relationship of Bain type: [001](Fe)vertical bar vertical bar[011](Au) and (010)(Fe) vertical bar vertical bar similar to 4 degrees to (100)(Au). Additionally, Au segregation on Fe precipitate facets was detected; it was found that the Au-rich segregation layer on the (110) facet of Fe contains 16 +/- 4 at.% Au. A thermodynamic possibility of extraparticle precipitation of the Fe-rich phase during particles annealing in the two-phase area of the Fe-Au phase diagram was demonstrated by considering the balance of surface energy and driving force for transformation. Also, a simple geometrical model was employed to demonstrate how the Janus-like nanoparticles can approach their equilibrium shape by formation and migration of coherent twin boundaries.

The tensile performance of a boron-containing Ni43.9Co22.4Fe8.8Al10.7Ti11.7B2.5 multi-principal element alloy was studied through tensile tests after electrochemical hydrogen pre-charging. Hydrogen pre-charging notably reduced both the elongation and strength of the alloys. Brittle cracking regions and an increased number of cracks appeared at the hydrogen pre-charged alloys after tensile deformation. Tensile cracks in the hydrogen pre-charged samples propagated in the mixed intergranular and transgranular cracking modes. Grain boundaries containing the hexagonal close-packed phases were susceptible to crack propagation. The cracking behavior of the hydrogen pre-charged alloys was attributed to the combined hydrogen-enhanced localized plasticity and hydrogen-enhanced decohesion mechanisms.

Nanoparticles obtained by solid-state dewetting are known to exhibit an extraordinarily high mechanical strength under uniaxial compression. While most of such particles are single-crystalline, some may contain a coherent twin boundary (CTB) parallel to the substrate. The role of the CTB in the mechanical properties of such particles remained unknown. This work combines nano-mechanical testing, advanced characterization methods, and atomistic computer simulations to investigate the CTB effect of the mechanical behavior of Ni-Co nanoparticles produced by solid-state dewetting on a sapphire substrate. The results indicate that the CTB does not make any significant impact on the particle strength, toughness, solute softening, or strain hardening. These properties remain virtually the same as those of single-crystalline particles of the same alloy. The mechanisms of dislocation nucleation and the dislocation-CTB interactions are investigated in detail. The work lends additional confidence to the previous results for the mechanical behavior of nanoparticles produced by solid-state dewetting, some of which could have contained twin boundaries.