In the GaAs/Inx(Al,Ga)1-xAs core/shell nanowire (CSNW) geometry, narrow cores exhibit significant bandgap reduction and enhanced electron mobility because of their ability to sustain extreme tensile elastic strain. In such an elastic state, the coherency limits and the resulting physical properties of the nanowires are governed by the strain field distribution and plastic relaxation mechanisms. Using atomic-resolution transmission electron microscopy, we determined the three-dimensional strain field, critical misfit, and plastic relaxation relative to the indium content of the shell, while maintaining constant core-shell dimensions. The strain was mapped experimentally in both coherent and plastically relaxed nanowires with a core radius of 10 nm and thick shells and was compared to atomistic and continuum calculations. Our findings reveal that, while axial strains remain uniform, elastic relaxation induces radial and tangential strain gradients. This is attributed to the strain concentration at the sharp interfaces, which persisted even after plastic relaxation. For the pertinent growth conditions, the maximum sustained elastic strain in the cores was observed for the GaAs/In0.5Al0.5As nanowires. The plastic relaxation of nanowires with shells of high indium content involved Frank partials delimiting horizontal intrinsic stacking faults (SFs), misfit dislocations gliding on inclined close-packed planes, and stair-rod dislocations along SF junction lines attributed to nanowire bending.Ab initiocalculations showed that the heterojunction remained type I even for the highest elastic strain, despite the existence of strain gradients at the core-shell interface. Our results elucidate the elastoplastic behaviour of CSNWs with narrow cores, offering new perspectives on growth strategies to further push their coherency limits.

Engineering the structure of grain boundaries (GBs) by solute segregation is a promising strategy to tailor the properties of polycrystalline materials. Solute segregation triggering phase transitions at GBs has been suggested theoretically to offer different pathways to design interfaces, but an understanding of their intrinsic atomistic nature is missing. We combined atomic resolution electron microscopy and atomistic simulations to discover that iron segregation to GBs in titanium stabilizes icosahedral units (“cages”) that form robust building blocks of distinct GB phases. Owing to their five-fold symmetry, the iron cages cluster and assemble into hierarchical GB phases characterized by a different number and arrangement of the constituent icosahedral units. Our advanced GB structure prediction algorithms and atomistic simulations validate the stability of these observed phases and the high excess of iron at the GB that is accommodated by the phase transitions.

Nanoparticle reinforced metallic composites manufactured using laser powder bed fusion (LPBF) provide an economically viable avenue to obtain high strength near-net shaped critical components in automotive and aviation industry. In this study, the equiatomic compositionally complex alloy (CCA) CoCrFeNi is manufactured by LPBF with two types of reinforcing particles, titanium nitride (TiN) and titanium oxide (TiO2). The reinforcing particles are introduced with varying size and volume concentration to the CCA powder fulfilling two purposes – improving the flowability of the feedstock and to cause nanoparticle strengthening, as demonstrated here using nanoindentation. We focus on the microstructure and texture evolution of all the alloys, and the phase transitioning of the particles. TiN nanoparticles of all sizes dissolve in the melt pool and uniformly precipitate as TiO2. We observed distinctive core-shell nanoparticle formation with higher TiN content that also resulted in 45 % higher tensile strength. The successful integration of homogenously distributed nanoparticles without inducing cracks or defects and with superior mechanical properties signifies a leap forward in the fabrication of high-performance metal matrix composites like the commercial oxide dispersion strengthened (ODS) alloys.

This study highlights the successful manufacturing of a crack-free, dense, hybrid ex-situ/in-situ particle reinforced (Ti+B4C)/Al-Cu-Mg composite, fabricated by laser powder bed fusion and exhibiting exceptional mechanical performance. In its as-built (AB) state, the composite displays a unique microstructure characterized by equiaxed grains with an average grain size of 1.0 ± 0.3 μm, notable interdendritic microsegregation of Cu, Mg, Mn, and Fe, randomly distributed ex-situ added Ti and B4C particles featuring a surface interaction layer with the metal matrix, and in-situ formed reinforcing particles, such as TiB2 and TiC. After subjecting the material to hot isostatic pressing (HIP) and subsequent aging treatment, dissolution of interdendritically segregated elements occurs, and precipitation of Al2Cu, Al12Mg17, and Al-Fe-Cu-Mn phases is observed. Significantly enhanced fatigue performance is recorded, reaching to 107 cycles at 250 MPa in AB and 330 MPa in HIP state, marking a 32% improvement. The current study highlights the intricate relationship between the different microstructural features in AB and HIPed state, leading to fracture during tensile and fatigue loading conditions.

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Industrial implementation of heat-treated Laser Powder Bed Fusion (L-PBF) processed Ti-6Al-4 V components requires a thorough understanding of the plastic deformation mechanisms to predict the part performance in safety-critical environments. Here, we study the micro-mechanical deformation behavior of a heat-treated L-PBF processed Ti-6Al-4 V by in-situ uniaxial tensile loading, during which high-resolution strain fields were monitored by Scanning Electron Microscope (SEM) based Digital Image Correlation (DIC). SEM-DIC revealed: (i) the transformed beta phase accommodates higher strain than the primary alpha phase; (ii) strain accumulation in primary alpha occurs primarily at the interface regions where the Al content is lower; and (iii) needle-shaped secondary alpha precipitate in the transformed beta creates strain localization pathways that bridge the interfacial strain bands. Based on the in-situ deformation behavior, recommendations are made on microstructure tailoring and alloy design to prevent strain localization and enhance the quasi-static mechanical properties of l-PBF processed titanium alloy components.

Metal powders in laser-powder-bed-fusion (L-PBF) often exhibit cohesive flow resulting from interparticle adhesion. Nanoparticle dry-coating can improve powder flowability and promote powder layer densification. A Co25Cr25Fe25Ni25 metal powder (20–90 µm) is dry-coated with TiN particles with a diameter of 16 nm at low concentrations of up to 69 ppm. The dynamic angle of repose decreased and bulk powder density increased compared to the uncoated state from 49 ° and 4.67 g/cm3 to 29 ° and 4.81 g/cm3 with dry-coating of TiN, respectively. UV/Vis spectroscopy showed negligible alterations by TiN additions on the powder light absorption. The powder modifications strongly affected their corresponding processability in L-PBF and reduced the melt pool signatures of the in situ detected confocal single-color pyrometer signal as well as ex situ measured melt pool depth and width. With increasing flowability, a significant decrease in thermal emission and melt pool size was observed. The results demonstrate the impact of powder flowability and bulk powder density on the quality of L-PBF parts when particle interactions are actively modified.

The structure and chemistry of grain boundaries (GBs) are crucial in determining polycrystalline materials’ properties. Faceting and solute segregation to minimize the GB energy is a commonly observed phenomenon. In this paper, a deposition process to obtain pure tilt GBs in titanium (Ti) thin films is presented. By increasing the power density, a transition from polycrystalline film growth to a maze bicrystalline Ti film on SrTiO3 (001) substrate is triggered. All the GBs in the bicrystalline thin film are characterized to be Σ13 [0001] coincident site lattice (CSL) boundaries. The GB planes are seen to distinctly facet into symmetric {7̄520} and asymmetric {101̄0} // {112̄0} segments of 20-50 nm length. Additionally, EDS reveals preferential segregation of iron (Fe) in every alternate symmetric {7̄520} segment. Both the faceting and the segregation are explained by a difference in the CSL density between the facet planes. Furthermore, in the GB plane containing Fe segregation, atom probe tomography is used to experimentally determine the GB excess solute to be 1.25 atoms/nm2. In summary, the study reveals for the first time a methodology to obtain bicrystalline Ti thin films with strong faceting and an anisotropy in iron (Fe) segregation behaviour within the same family of planes.

The design of high performance structural materials is always pursuing combinations of excellent yet often mutually exclusive properties such as mechanical strength, ductility and thermal stability. Although crystal-glass composite alloys provide better ductility compared to fully amorphous alloys, their thermal stability is poor, due to heterogeneous nucleation at the crystal-glass interface. Here we present a new strategy to develop thermally stable, ultrastrong and deformable crystal-glass nanocomposites through a thermodynamically guided alloy design approach, which mimics the mutual stabilization principle known from symbiotic ecosystems. We realized this in form of a model Cr-Co-Ni (crystalline)/Ti-Zr-Nb-Hf-Cr-Co-Ni (amorphous) laminate composite alloy. The symbiotic alloy has an ultrahigh compressive yield strength of 3.6 GPa and large homogeneous deformation of-15% strain at ambient temperature, values which surpass those of conventional metallic glasses and nanolaminate alloys. Furthermore, the alloy exhibits similar to 200 K higher crystallization temperature (T-X > 973 K) compared to that of the original TiZrNbHf-based amorphous phase. The elemental partitioning among adjacent amorphous and crystalline phases leads to their mutual thermodynamic and mechanical stabilization, opening up a new symbiotic approach for stable, strong and ductile materials.

InGaN/GaN quantum wells (QWs) with sub-nanometer thickness can be employed in short-period superlattices for bandgap engineering of efficient optoelectronic devices, as well as for exploiting topological insulator behavior in III-nitride semiconductors. However, it had been argued that the highest indium content in such ultra-thin QWs is kinetically limited to a maximum of 33%, narrowing down the potential range of applications. Here, it is demonstrated that quasi two-dimensional (quasi-2D) QWs with thickness of one atomic monolayer can be deposited with indium contents far exceeding this limit, under certain growth conditions. Multi-QW heterostructures were grown by plasma-assisted molecular beam epitaxy, and their composition and strain were determined with monolayer-scale spatial resolution using quantitative scanning transmission electron microscopy in combination with atomistic calculations. Key findings such as the self-limited QW thickness and the non-monotonic dependence of the QW composition on the growth temperature under metal-rich growth conditions suggest the existence of a substitutional synthesis mechanism, involving the exchange between indium and gallium atoms at surface sites. The highest indium content in this work approached 50%, in agreement with photoluminescence measurements, surpassing by far the previously regarded compositional limit. The proposed synthesis mechanism can guide growth efforts towards binary InN/GaN quasi-2D QWs.

Titanium thin films were deposited on silicon nitride (SiNx) coated Si, NaCl, and sapphire substrates varying the deposition conditions using e-beam evaporation to investigate thin film growth modes. The microstructure and texture evolution in dependence of substrate, deposition rate, film thickness, and substrate temperature were studied using X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Thin films obtained on SiNx and NaCl substrates were nanocrystalline, while the films deposited on sapphire transformed from nanocrystalline to single crystalline at deposition temperatures above 200 degrees C. Predominantly, a surface plane orientation of (0002) was observed for the single crystalline films due to the minimization of surface energy. The orientation relationship of epitaxial single crystalline films grown on C-plane sapphire substrate is found to be (0002)Ti 0 (0006)Sapphire, (1120)Ti 0 (0330)Sapphire. In this orientation relationship, both the total surface and strain energy of the film are minimized. The results were complemented by resistivity measurements using the four-point probe method reporting an increase from ti 60 mu omega cm to ti 95 mu omega cm for single crystalline and nanocrystalline films, respectively.