We use in situ synchrotron X-ray diffraction during friction stir processing (FSP) of a binary Al - 4 at.% Si model alloy to understand its dynamic microstructural evolution as a function of a comprehensive matrix of experiments. We position the synchrotron beam within the stir zone and study the microstructural evolution via two approaches: static (fixed region of interest) and trailing (constant 0.16 mm distance behind the FSP tool). In static configuration, we study the stir zone microstructure during cooling as the FSP tool moves away from the region of interest. In trailing configuration, we study the microstructural changes developing along the processing length. Complementary postmortem microstructural characterization via energy dispersive spectroscopy, electron backscatter diffraction, transmission electron microscopy, and atom probe tomography are provided, relating in situ observations to the final microstructures. Our results provide valuable insights on the relationship between lattice expansion/contraction of Al and Si under different combinations of tool rotation speeds and processing speeds. We calculate the evolution of the processing temperatures along the processing length based on the linear expansion coefficients of Al and Si. The non-deformable brittle nature of the Si phase, alongside its limited solubility in Al, allows Si to serve as a crystallographic thermocouple. The occurrence of dynamic recrystallization is studied through the evolution of the full width at half maximum (FWHM) of the Al peaks. Our results demonstrate the practicality of in situ synchrotron X-ray diffraction as a tool to expand the current understanding of dynamic recovery and recrystallization during FSP.

In pressurized water reactors (PWR), intergranular oxidation of structural materials in the primary‑coolant circuit is accelerated by plastic deformation concentrating along random high‑angle grain boundaries (RHAGBs), providing a precursor state for intergranular stress corrosion cracking (IGSCC). However, because IGSCC initiation is inherently stochastic, conventional macroscopic strain descriptors are ineffective at identifying which oxidized RHAGBs will eventually crack. This limitation motivates a focused search for mechanistic signatures that distinguish vulnerable boundaries from benign ones. Here, we evaluate RHAGB oxidation morphology as a potential mechanistic signature by comparing solution‑annealed (SA) and cold‑tensile‑strained (CTS) Fe–18Cr–14Ni exposed to simulated PWR primary‑water environments. Electron microscopy reveals a deformation-driven transition in RHAGB oxidation morphology, from continuous oxides in SA to complex non-planar morphologies in CTS comprising Cr-enriched filaments advancing ahead of the oxidation front. We propose a “Leading Filament” mechanism to explain this transition, where short-circuit transport enables high-aspect-ratio, stress-concentrating filaments. While macroscopic strain controls oxidation depth, boundary-specific strain heterogeneity likely governs filament morphology, offering a mechanistic descriptor relevant to the boundary-to-boundary variability in IGSCC initiation.

Atom probe tomography (APT) fills a crucial need in the characterization workflow of materials by its ability to inform the three-dimensional local composition at the nanoscale. As with any characterization technique, APT has strengths and limitations that inform the interpretation of the data. Therefore, a challenge for the materials characterization community, and the APT community in particular, is the need to establish repeatable and reproducible workflows around the APT data acquisition, reconstruction, analysis, and sharing, in order to inform interpretation. Data interpretation also requires the continued development of our understanding of the physical processes responsible for field evaporation. We review recent developments in the experimental analysis of field evaporation and in the modeling of field evaporation, leading to a new understanding of common artifacts observed in reconstructed data. We then discuss current challenges with data analysis, translation of results, and data interpretation in the absence of community-agreed standards, and therefore, the crucial need for standardization at every stage of APT research, from data collection all the way to data reporting. This perspective is a summary of the invited presentations and discussions that took place during a workshop (August 4-5, 2024, Alexandria, Virginia).

Despite their versatility and easy manufacturability, polymer-bonded magnets find limited application due to their lower mechanical properties and temperature resistance. In this study, we fabricated aluminum-bonded SmCo5 magnets by utilizing a low-temperature, shear-assisted friction consolidation technique. The resulting bonded-magnets showed effective consolidation with nanocrystalline microstructures. Magnetic properties were found to be tunable through variations in binder phase content, with coercivity reaching values up to 15.3 kOe (1217.5 kA/m) and maximum magnetic energy product up to 3.3 MGOe (similar to 26.3 kJ/m(3)), which are comparable to other isotropic bonded Sm-Co magnets. Electrical resistivities were lower than the polymer-bonded magnets, but comparable to the sintered ones. We observed an average flexural strength of 223 MPa for 60 vol% SmCo5/Al sample, which is nearly two times higher than the reported values of sintered and bonded Sm-Co magnets. Our research demonstrated an effective approach to fabricate metal-bonded permanent magnets with superior mechanical properties potentially suitable for demanding applications.

Hydrogen-induced degradation is a critical lifetime-limiting mechanism for Mo/Si multilayer mirrors used in extreme ultraviolet (EUV) and future Beyond-EUV (BEUV) lithography systems. In this work, we employ a hydrogen plasma focused ion beam (H-FIB) as a highly controlled, localized irradiation tool to investigate the nucleation and growth of hydrogen blisters in Mo/Si multilayer stacks[1]. The H-FIB enables precise spatial and dose control of hydrogen ion implantation, allowing us to systematically vary irradiation conditions (energy, flux, and fluence) and directly correlate them with the onset of subsurface bubble formation, blister nucleation, and subsequent blister coalescence and growth. Through a combination of in situ and ex situ characterization, including surface morphology, cross-sectional imaging, and multilayer structural analysis by transmission electron microscopy and compositional analysis by atom probe tomography, we track the evolution of damage from the earliest stages of hydrogen accumulation to advanced blistering and delamination of the multilayer mirrors[2], [3]. These in situ experiments are also coupled with an agentic AI approach (Sci-LM) to quantitatively analyze the results from microscopy images. The resulting mechanistic insight clarifies the critical thresholds and pathways by which hydrogen plasma degrades optical performance and structural integrity in multilayer mirrors. This knowledge directly supports the development of more robust mirror designs and operating conditions, including optimized multilayer architectures, barrier or capping layers, and hydrogen management strategies. Ultimately, our findings contribute to extending the operational lifetime, reliability, and cost-effectiveness of mirrors in EUV and BEUV lithography tools, enabling more stable high-volume manufacturing at advanced technology nodes.

Electrochemical conversion of iron oxide to iron metal can enable low-cost batteries for long duration energy storage and zero-emissions ironmaking for steel. Iron oxides, such as hematite, can be electrochemically reduced to metallic iron in concentrated alkaline electrolytes at modest temperatures, but the relative influences of solid-state and dissolved intermediates at practical reaction rates remains unclear. Here we prepare a homologous set of well-defined hematite particles to measure how the nanoscale morphology of oxides controls both their reactivity and apparent reduction mechanism in concentrated hydroxide. Correlated electron microscopy and rotating-ring-disk-electrode measurements revealed that nanoporous hematite and solid intermediates formed iron via a dissolution-redeposition pathway. In contrast, dense hematite particles directly formed iron metal via reactive fracture. While previous studies on iron electrowinning have primarily emphasized the role of particle diameter at the micron scale, these results demonstrate the importance of the dissolution-redeposition pathway to support rapid reaction rates and suggest that nanoscale porosity controls iron oxide reactivity at temperatures <100 °C. Therefore, iron-oxide-to-metal electrolyzers and fast-charging iron-air batteries supported by curtailed electricity can increase the rate of metal formation by accelerating fracture and dissolution in reactant oxides.

Vacancy engineering, the intentional control of atomic-scale vacancies in metals and alloys, is emerging as a powerful yet underexplored strategy for tailoring microstructures and optimizing performance across diverse applications. By enabling excess vacancy populations through quenching, severe deformation, thermomechanical treatments, or additive manufacturing, new microstructures can be obtained that achieve unique combinations of strength, ductility, fatigue life, corrosion resistance, and conductivity. Vacancies are distinct among lattice defects: they are non-conserved entities essential for solute diffusion, yet variably coupled to solutes, dislocations, and phase boundaries. They can accelerate transformations such as nucleation and precipitation or retard kinetics when trapped in clusters, and their transient trapping and release can drive microstructural evolution across time and length scales. This Review synthesizes recent advances in generating, modeling, and characterizing vacancies, highlighting their role in diffusion, precipitation, and phase stability. Case studies in lightweight, high-temperature, fatigue-resistant, electrical, and biomedical materials demonstrate the broad potential of vacancy control. We conclude by emphasizing the opportunity for the metallurgical community to fully exploit excess vacancies as controllable, design-relevant defects that enable new pathways for microstructure and property optimization in next-generation alloys.

Lightweight materials are essential for applications in harsh environments, such as space explorations, where materials must exhibit exceptional durability and resistance to radiation damage for both humans and equipment. Boron nitride nanoplatelets (BNNPs) serve as a reinforcement in metals offering superior radiation shielding along with excellent thermal and mechanical properties for extreme environments. In this work fully dense Al-BNNP composites are fabricated by solid-state friction stir welding (FSW). The neutron mass absorption coefficient of the FSW Al-BNNP composite was measured at 0.136 cm2/g, significantly higher than the 0.06 cm2/g of its counterpart FSW aluminum. This remarkable neutron shielding effectiveness is attributed to the transmutation of the 10B isotope of BNNP to Li and He. This neutron capture mechanism was experimentally investigated at the atomic scale by atom probe tomography (APT). Notably, Al-BNNP composites demonstrate great potential as multi-functional materials for future space explorations, from spacecraft assemblies to rocket fuel tanks, benefiting from their high strength, low weight, and superior radiation shielding.

Understanding how composition affects deformation mechanisms in austenitic stainless steels is essential for developing accurate predictive models of stress-induced failures and stress corrosion cracking. Nickel (Ni), an element classified as a critical element, plays a crucial role in these processes. It is important to examine how Ni concentration influences stacking fault energy (SFE) and, consequently, the deformation mechanisms of austenitic stainless steels. However, in commercial stainless steels, the effects of other alloying elements and impurities can obscure Ni's role, complicating efforts to isolate its impact. In this study, we use two high-purity Fe-Cr-Ni alloys to investigate how Ni concentration and SFE interact to alter deformation mechanisms and induce martensitic transformation. By combining in situ synchrotron X-ray diffraction (XRD) tensile testing and postmortem electron microscopy with density functional theory simulations, we gain precise insights into these phenomena. We find that the Fe18Cr10Ni (wt%) alloy, with its low SFE, exhibits higher stacking fault probability, deformation-induced martensitic transformation, and a lesser increase in dislocation density with plastic strain. In contrast, the Fe18Cr14Ni (wt%) alloy, with its higher SFE, shows enhanced deformation twinning and greater dislocation density with increasing strain. These findings from high-purity ternary alloys provide valuable insights that can guide the search for alternative elements to replace Ni while achieving similar effects on phase stability and deformation behavior.

Magnesium (Mg) alloys are ideal candidates for automotive applications due to their high strength to weight ratio, castability, recyclability etc., however, they lack corrosion and oxidation resistance. Solid-state deposition techniques, such as cold spray, have been demonstrated to enhance their corrosion resistance as it relies on the severe plastic deformation of powder particles upon impact with the substrate to form a metallurgical bond with the substrate and within the coating. At cold sprayed interfaces, a heterogeneous microstructure is formed that includes some porosity, oxides and intermetallics which can significantly affect coating performance. Thus, establishing a direct correlation between the interface microstructure and its properties can aid in designing optimal cold spray parameters. In this study, we investigated the microstructure and mechanical properties of a zinc (Zn) coating deposited on a high pressure die cast (HPDC) AZ91 Mg substrate via high resolution scanning transmission electron microscopy, in situ micro-tensile testing, and finite element method (FEM) modeling. Micro-tensile pillars fabricated using the plasma focused ion beam (PFIB) successfully isolates the coating-substrate interface within the gauge length. The average bond strength of Zn-Mg interface was determined to be ∼140 MPa with failure occurring partially at the interface and mostly into the coatings. A detailed microstructural characterization revealed evidence of a strong metallurgical bonding at the Zn-Mg interface and formation of the C14 MgZn2 laves phase interlayer resulting in a mixed mode of fracture during the micro-tensile experiments. FEM modeling reveals the stress distribution along the interfaces and suggests that a MgZn2 layer thickness between 200–400 nm is optimum to increase the bond strength and minimize the triaxiality. Such a site-specific interfacial analysis with correlative computational modeling provides crucial insight into the overall performance of cold spray interfaces.

Understanding the deformation mechanisms behind microstructural evolution during shear loading has been a long-standing area of interest. However, establishing a connection between microstructure, mechanical properties, and the extent of shear deformation is challenging and requires refined experimental approaches. Microshear testing offers a controlled method to introduce shear into small volumes of material, allowing for detailed site-specific microstructural characterization. In this work, we investigated the shear deformation behavior and properties of copper (Cu) matrix and at copper-niobium (Cu-Nb) interfaces using micro-shear testing. The yielding under shear loading is dependent on the orientation of the interfaces. Intuitively, when the interface is along the shear direction, the flow stresses are lower compared to when it is across. Transmission electron microscopy examination shows stacking faults and high dislocation density dominating the deformation on the Cu side while limited dislocation activity in the neighboring Nb crystal. Moreover, an amorphous layer was observed at the Cu-Nb interface which likely formed after shear deformation. In summary, our study provides an understanding of the shear deformation behavior of phase-interfaces in an immiscible system at a micro-scale. The focus of the paper is demonstrating the applicability of the S-shaped pillar geometry for local shear measurements and deformation of specifically oriented interface boundaries.

We introduce a fully unsupervised clustering method we call Compositional Community Detection (CCD) to identify chemical motifs in atom probe tomography (APT) reconstructions. In the CCD approach, APT point clouds are broken into overlapping spherical neighborhoods, and repeated k-means clustering coupled with Louvain community detection is used to group neighborhoods based on their ion composition. Kolmogorov-Smirnov statistics for present ion types provide interpretable descriptors of each community that indicate the relative level of enrichment or depletion of ions within a community. We demonstrate our technique on a set of APT reconstructions of irradiated 316 stainless steel. Our method detected chromium carbide and Ni-Si-rich precipitates and located a grain boundary based on Ni and Si enrichment. Spatial correlations between communities indicated that chromium carbide precipitates were flanked by regions of Fe depletion. Our results highlight the potential of CCD in the analysis of chemical segregation in broader classes of materials, in terms of both varying synthesis methods and exposure to extreme environments.

In this study, a multi-length-scale strengthening approach was used to tailor the microstructure and the mechanical properties of a NiCoCr-based multi-principal element alloy (MPEA). Grain size refinement, severe lattice distortion, and stacking fault energy (SFE) reduction with Mo addition (up to 10 at.%) enhance yield strength by 85 % with only 10 % reduction in ductility in as-annealed MPEAs. A pronounced increase in the strain hardening rate was observed with the addition of Mo, which is ascribed to the promotion of complex stacking fault (SF) interaction and intersection, accompanied by Lomer-Cottrell (L-C) and Hirth locks inhibiting dislocation motion and substantial increase in the accumulation of back stress. To push the limit of the yield strength further, the Suzuki segregation phenomenon was manipulated by a careful control of SF density by pre-straining and a subsequent 500 degrees C heat treatment. The stress-strain responses of the pre-strained and heat treated MPEAs showed an obvious SF density and Mo concentration dependence. The yield strength of the pre-strained Mo-added MPEAs with subsequent heat treatment was increased up to true stress of 2.3 GPa with a corresponding fracture elongation of 12 % true strain. SFs formed during pre-straining served as Cr segregation sites during subsequent heat treatment, which substantially varies the local SFE within the SF, presenting a roughened landscape and frustrating the dislocation dynamics. Beyond conventional strengthening strategies, incorporation of refractory elements along with the manipulation of Suzuki segregation process provide a promising route in tailoring desired mechanical properties of MPEAs.

Understanding hydrogen embrittlement mechanisms requires insights into nanoscale hydrogen isotope segregation in materials. Cryogenic-transfer atom probe tomography (APT) can provide this insight, if the sample exposure is precisely controlled. Therefore, we quantified the nanoscale changes of in austenitic FeCrNi alloy during ultrahigh vacuum transfer using a LEAP 6000 XR APT system with UV laser-assisted and voltage-pulsed modes. We introduced a quasi-in situ method to study deuterium out-diffusion kinetics from electrochemically charged FeCrNi needles, which involved analyzing a deuterium-charged sample using APT, pausing for controlled thermal treatments at room temperature and 150°C, followed by reanalysis. Comparison of experimental results with a heat transfer–hydrogen diffusion model showed that slow deuterium out-diffusion was due to an oxide layer acting as a permeation barrier. These findings highlight the importance of managing sample exposure during cryogenic-transfer APT and demonstrate this quasi-in situ method’s potential for studying hydrogen isotope diffusion in metallic alloys.

The flash phenomenon, first discovered in the context of sintering, has grown broadly into many areas of science and technology. It enables the synthesis of materials that are far from equilibrium. Flash is characterized by massive generation of defects, up to 25 mol% within the crystal lattice, astronomical rates of solid-state diffusion, electronic conductivity in nominally insulating ceramics, solid-state plasmas, and electroluminescence. In this work, we show that ordinary carbon deposited on the surface of a copper wire permeates throughout it, while at the same time, transforming into a network of graphene. Graphene is confirmed by Raman spectroscopy. Networks of carbon are imaged by atom probe tomography and scanning transmission electron microscopy. The network suppresses creep at high temperature (900 degrees C). The graphene network forces the wire to retain its shape when its temperature is raised above the melting point of copper. The benchmark for copper conductivity is 58.1 MS m(-1) or 100% international annealed copper standard (IACS). The conductivity of this graphene-infused copper is 105%-110% IACS, greatly exceeding the 102% IACS first reported by Scherer who introduced graphene into molten copper containing carbon by passing current. The flash experiment is carried out in the solid state by injecting current into copper and increasing it at a constant rate (without a furnace). The transformation is completed in a few seconds. Thermodynamically, carbon is barely miscible in copper (approximately 9 ppm). Here, mole fractions of 0.11% are achieved. Therefore, these results demonstrate the far-from-equilibrium nature of the process. The question of the electronic structure of the high-conductivity graphene-copper interface is highlighted.

This research investigates the feasibility of hybrid aluminum metal matrix composites (MMC) incorporating TiB2 particles for brake rotor applications. The composites were produced by incorporating both in-situ, submicronsized TiB2 particles and regular micron-sized TiB2 powders via stir and squeeze casting techniques into A206 aluminum alloy matrix. Systematic adjustments in the fractions of in-situ and ex-situ TiB2 particles were conducted to evaluate their impact on wear behavior and mechanisms. Combination of both particle types allowed composites with up to 10 vol% of reinforcements. Composites with higher proportions of ex-situ particles demonstrated increased wear resistance compared to those solely composed of in-situ particles, control specimens without TiB2, and conventional cast iron counterparts. The lowest wear rate for the hybrid composites sliding against phenolic brake pads was 1.1 x 10-5 mm3/Nm, signifying a 3-fold reduction relative to cast iron sliding against the same pads. Wear analysis elucidated distinctive mechanisms within the hybrid composites, characterized by mild fragmented abrasive wear, adhesive wear, and plastic deformation, accompanied by the formation of an intermixed tribo-oxide layer.

In alignment with the Materials Genome Initiative and as the product of a workshop sponsored by the US National Science Foundation, we define a vision for materials laboratories of the future in alloys, amorphous materials, and composite materials; chart a roadmap for realizing this vision; identify technical bottlenecks and barriers to access; and propose pathways to equitable and democratic access to integrated toolsets in a manner that addresses urgent societal needs, accelerates technological innovation, and enhances manufacturing competitiveness. Spanning three important materials classes, this article summarizes the areas of alignment and unifying themes, distinctive needs of different materials research communities, key science drivers that cannot be accomplished within the capabilities of current materials laboratories, and open questions that need further community input. Here, we provide a broader context for the workshop, synopsize the salient findings, outline a shared vision for democratizing access and accelerating materials discovery, highlight some case studies across the three different materials classes, and identify significant issues that need further discussion.

Application of atom probe tomography to electrically non-conductive materials is typically enabled by pulsing a laser onto a sample under strong electric fields to induce field evaporation. The measured composition depends on the laser-material interaction, necessitating systematic optimization experiments. This is particularly important for hydroxyapatite (Ca10(PO4)6(OH)2), a biologically and geologically relevant mineral for which subtle compositional changes can have significant implications. Therefore, we performed a series of experiments on synthetic hydroxyapatite to systematically assess how the laser pulse energy, definition of ranges in the mass-to-charge state spectrum, and calcium charge state ratio have an impact on the measured calcium-to-phosphorous ratio and mechanism of field evaporation on separate atom probe systems equipped with ultraviolet (355 nm wavelength) and deep ultraviolet (257.5 nm) lasers. We also evaluated the stoichiometric accuracy of the simultaneous voltage pulsing mode on the deep ultraviolet system, which both reduces the background and introduces artifacts into the mass-to-charge state spectrum. Correlations between the calcium-to-phosphorus ratio and the charge state ratio and fraction of ions ranged were identified. In turn, these analyses provide guidance for improving measurement accuracy of hydroxyapatite and other insulating materials using atom probe tomography.

Zirconium (Zr) alloys are widely used as fuel cladding in nuclear power reactors due to their thermal stability, mechanical durability, corrosion resistance, and low neutron absorption cross-section. However, their performance is challenged by oxidation in reactor environments, making the study of Zr alloy corrosion behavior crucial for ensuring the safety, longevity, and economic viability of nuclear power systems. While the oxidation behavior of Zr-based cladding materials has been extensively studied since the 1950s, a mechanistic understanding into the relationship between structure evolution, solute element redistribution, and properties remains elusive. Valuable insights may be obtained through advanced experimental methods, such as in-situ and high resolution microscopy techniques. In this study, the oxidation behavior of Zircaloy-4 at 500 degrees C in O2 is characterized using a multimodal advanced characterization approach. Using in-situ X-ray diffraction, the phase evolution from metastable to stable oxides is tracked in real time. Complementary high-resolution techniques, including electron microscopy and atom probe tomography, reveal nanoscale insights into the microstructural changes and solute redistribution across the oxide/metal interface. Nanohardness mapping across the oxide/metal interface highlights localized mechanical property variations that may be linked to changes in microstructure and crystal structure within the oxide layer. These findings offer valuable insights into the microstructure and property evolution of Zircaloy-4 during oxidation, contributing to a better understanding of microstructural changes in Zr-based alloys under oxidative environments.