Maraging 300 (18Ni300M) steel is a ferrous alloy renowned for its good combination of mechanical strength and ductility, making it ideal for aerospace and defense applications. A previous study demonstrated that the atomization process has a significant influence on the monotonic mechanical properties and microstructure of as-built components produced by powder bed fusion with a laser beam (PBF-LB) technique. In Part II, the tensile and high-cycle fatigue behavior of 18Ni300M steel aged at 480 ºC for 3 h was investigated across two processing routes: conventional vacuum induction melting followed by vacuum arc remelting (VIM/VAR), and PBF-LB using gas-atomized (GA) and water-atomized (WA) powders. The research included tensile and rotary bending fatigue tests, transmission electron microscopy (TEM) for nanoparticle analysis, and electron backscatter diffraction (EBSD) for identifying secondary microcrack paths. The results showed that aging increased the mechanical strength of both GA and VIM/VAR samples, albeit with a reduction in ductility. In contrast, the WA condition exhibited compromised plasticity, as oxide inclusions acted as critical-size defects. The VIM/VAR specimens demonstrated the highest fatigue resistance, followed by the GA condition, which was limited by nano-oxide formation and process-induced defects. The WA specimens displayed the lowest fatigue performance due to a greater number of defects exceeding the critical defect size predicted by Murakami’s model. These findings highlight the influence of powder characteristics, processing routes, and microstructural features on the mechanical properties of an ultra-high-strength steel intended for structural applications.

The aim of this chapter is to provide the reader with an outline of the methods most commonly used to characterize samples, taken from studies involving physical metallurgy, using techniques allied with transmission electron microscopy. In the main, rather than provide full and comprehensive details on all methods including various imaging techniques, diffraction methods, and analytical spectroscopies, it is the attempt of the coauthors to outline techniques, and then provide ways in which difficulties in interpretation may be avoided.

Al6Mn is an important precipitate phase in many Al-alloys that contain Mn. However, the three-dimensional (3D) shapes of the Al6Mn precipitates are still unclear because drastically different geometries have been shown in TEM images. In order to understand the equilibrium shapes of Al6Mn precipitates as a function of their sizes, we first derive possible lattice site correspondences (LCs) between the Al6Mn and Al-matrix phases from experimentally observed orientation relationships between and crystal structures of the two phases, which are then further discriminated by crystallographic analysis and transformation strain calculations. We then formulate a phase-field model to simulate the growth process, equilibrium shapes, and habit planes of the precipitates in 3D as a function of size under the chosen LC. Precipitate shapes of all variants at various 2D cross-sections are presented, which could be used to make direct comparisons to TEM images to facilitate the confirmation of the derived LC and to develop a better understanding of precipitate shapes in 3D in specific alloys.

Polymer blends and composites play a vital role in various engineering fields such as medicine, electronics, biotechnology, and energy storage; in part, due to the cost and effectiveness of tailoring specific blends to meet desired mechanical properties.Mechanical properties for polymer blends are controlled by homogeneity, size, shape and morphology of dispersed phases, often these phases are below 100nm [1].For impactful correlation of microstructure/property relationships in polymeric blends and composites, one must first image and identify various polymer phases correctly.Current state of the art for this analysis is available through a limited number of synchrotrons capable of acquiring near edge x-ray absorption fine structure (NEXAFS) with spatial resolution of ∼100nm.By contrast, modern scanning transmission electron microscopes (STEM) achieve a nanometer scale probe routinely and have spectrometers capable of resolving electronic near edge structure [2].Electron energy loss spectroscopy (EELS) is a powerful tool for probing materials' chemistry with high spatial resolution.Polymers, even at low spatial resolutions, have proven difficult to characterize stemming in part from electron beam induced damage; consequently, core-loss EELS has yielded inconsistent results when compared with x-ray absorption spectra that should yield analogous results, theoretically.Polymers are known to exhibit sensitivity to radiolysis from high energy electrons, limiting the potential spatial resolution achievable with EELS, optimistically, many of the classical shortcomings attributed to EELS should not still manifest as limiting factors with modern equipment.This study establishes that EELS can generate identifiable carbon K-edge spectra with features that match prior x-ray absorption spectra.EELS features broaden intuitively with energy resolution, and when beam-induced changes are unavoidable, they are readily differentiated with dose-dependent spectra.The results are used to estimate practical pixel sizes for spectrum imaging core-loss EELS with modern equipment and are demonstrated for spectrum images of a model polymer system [2,3].

The addition of Mn to 7xxx series Al-alloys helps improve tensile properties owed to the presence of a precipitates (Al(Mn,Fe)Si, simple cubic, 50-200 nm, non-shearable) in addition to the eta' precipitates (Mg2Zn5-xAl2+x, hexagonal, 4-6 nm, shearable) commonly observed in the 7xxx series Al-alloys. The coexistence of multiple alpha and eta' variants, 24 for alpha and 4 for eta.', coupled with their small size-scale, makes the experimental determination by x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) challenging. This work formulates a phase-field model to predict precipitate shapes in three-dimension (3D) using experimental characterization as inputs to create virtual precipitate cross-sections for use in morphological comparison with experimental 2D (S)TEM images. Based on the atomic structures and orientation relationships observed in the experiments, the lattice site correspondences between the matrix and the two precipitate phases are derived, which are required for the prediction of shapes of coherent precipitates. Systematic phase-field simulations are then carried out to document the 3D shapes for all possible variants, as well as the corresponding 2D cross-sectional shapes when observed parallel to low-index matrix planes. These 2D cross-sectional shapes are compared with high-angle annular dark-field STEM (HAADF-STEM) images, which demonstrates that the identification of Mn precipitate type is possible by such comparisons. This helps unravel some of the complications encountered when characterizing precipitate microstructures in Mn containing Al-alloys by STEM. Finally, the equilibrium shapes as a function of precipitate size and the effect of interfacial energy anisotropy are investigated.

Electron energy loss spectroscopy (EELS) is a proven tool for probing materials chemistry at high spatial resolution. Core-loss EELS fine structure should allow measurement of local polymer chemistry. For organic materials, sensitivity to radiolysis is expected to limit the resolution achievable with EELS: but core-loss EELS has proven difficult at any resolution, yielding inconsistent spectra that compare unfavorably with theoretically analogous x-ray absorption spectra. Many of the previously identified shortcomings should not be limiting factors on modern equipment. This study establishes that EELS can generate identifiable carbon K-edge spectra for a range of common polymer types and chemistry, and demonstrates fine structure features matching prior x-ray absorption spectra. EELS fine structure features broaden intuitively with the instrument's energy resolution, and beam-induced features are readily differentiated by collecting spectra at a series of doses. The results are demonstrated with spectrum images of a model polymer blend, and used to estimate practical pixel sizes that can be used for mapping core-loss EELS as a function of electron dose.

Microstructural parameters such as precipitate volume fraction, size, shape, and spatial distribution determine the relative effectiveness of precipitation hardening achieved for hardenable metallic alloys. The ability to accurately measure these microstructural parameters provides quantitative inputs for predictive models. For 7xxx series Al alloys, intermetallic precipitates may have a marked effect on mechanical properties, and depending on thermomechanical history, the effect may be positive or negative [1]. As Mn intermetallics are believed to play an important role in enhancing 7XXX series Al alloy’s strength, proper identification by STEM is critical for accurate microstructural characterization. Modern scanning transmission electron microscopy (STEM) instruments with x-ray energy dispersive spectroscopy silicon-drift-detectors (XEDS-SDD) provide researchers a potent tool for phase identification of the various precipitates observed in Mn containing Al-alloys by probing the crystal structure and composition. Modern systems also provide the ability to directly image the lattice and interface to compare to image simulation and further improve predictive models. While the microstructural evolution for intermetallic precipitate phases is thought to be well understood for the 7XXX series, when adding Mn to form Al-Zn-Mg-Mn alloys, unique identification of precipitates becomes challenging as two intermetallic precipitates are expected to grow with the addition of Mn; Al 57 Mn 12 and Al 6 Mn. Multiple researchers relationships for the Mn-containing precipitates by classical electron diffraction, however technological limitations restricted this to selected area diffraction without compositional data. This compositional data assumptions by the researchers that the precipitate being characterized was indeed a Mn intermetallic. phases from morphology difficult. Differentiating and uniquely identifying the small intermetallic precipitates is compounded due to difficulty in collecting quantifiable spectroscopy signals to confirm compositions. This work utilizes aberration corrected STEM, coupled with XEDS mapping, to provide unique identification of various intermetallic precipitates and correlates the observed atomic structure with image simulations to identify phase morphologies for distinct precipitates.

In selective laser melting (SLM) heat diffusing from the melt pool promotes the growth of surface oxide layers on powder particles surrounding the built part, and material ejected from the melt pool oxidises rapidly before landing on the powder bed, creating local variability in the oxygen content of any used powder. Although large particles are removed when recycling, smaller oxidised particles (the size of the specified powder for the machine) and oxide residue (<10 mu m) are not removed and become incorporated into subsequent builds on powder reuse. This paper considers the effect these oxidised particles may have on part integrity and how they affect mechanical failure. In this research, grade 23 Ti-6Al-4 V metal powder was artificially oxidised to produce a range of interference colours that correspond to specific oxide thicknesses. Powder characterisation established the oxygen wt% of each coloured powder. Yellow and blue powder were chosen for further investigation as in the context of this study, they represent low (0.4 wt%) and high (0.7 wt%) oxygen levels respectively. Tensile builds were produced using SLM with a known feedstock layer, part way up the build, formed of a blend of oxidised and virgin particles. Tensile tests were performed for each build to evaluate the failure modes. Microscopy techniques were used to examine the material near the fractured region, including chemical composition and semiquantification of the oxygen levels, allowing any microstructural and chemical changes to be investigated. It was shown that the region doped with oxidised particles negatively affected the mechanical properties of the final build, as they produce mechanical (oxide films/residue) and chemical flaws (interstitial elements). Unless these particles can be removed from recycled feedstock their effects will limit the reuse of powder, especially in safety critical industries, significantly increasing the costs of components produced by this route.

Intermetallic precipitates found in 7xxx series Al alloys, such as Al-Zn-Mg-Mn alloys, can have a marked effects on mechanical properties and depending on thermomechanical history, may have a positive or deleterious effect. Two intermetallic precipitate phases, Al57Mn12 and Al6Mn, are believed to play an important role in enhancing 7XXX series Al alloy’s strength. Microstructural parameters such as precipitate volume fraction, size, shape, and spatial distribution determine the relative effectiveness of precipitation hardening achieved, however characterization of these precipitates has proven challenging[1]. Identification of various Mn-containing precipitates has been performed by classical electron diffraction to determine orientation relationships, but this characterization technique does not allow for individual precipitate phase identification. Typically, intermetallic precipitates need to remain small to provide positive strengthening benefits and this makes uniquely identifying the small intermetallic precipitates through experimental characterization of three-dimensional precipitate morphology and shape difficult. To overcome this, concurrent imaging and phase identification of the various precipitate are required to correlate the observed two-dimensional cross section to the correct intermetallic precipitate. Inherent in TEM imaging are thin foils, and often intermetallic precipitates will have a dimension that extend past the TEM foil dimensions resulting in varied, observed two-dimensional cross sections; this discrepancy has resulted in conflicting results and researchers have speculated as to the actual three-dimensional shape to explain varied two-dimensional cross sections observed by TEM, with little consensus reached as multiple intermetallic precipitates are observed in a field of view. Currently, differentiating and uniquely identifying the small intermetallic precipitates is size precipitates dimensionally cross sectioned correlate predicted precipitate morphologies experimentally. Three-dimensional morphologies

In this article, we review some of the recent developments in instrumentation and methods that have led to the rise of cryo-electron microscopy (cryo-EM) in the life sciences community, and consider how researchers in the materials community might benefit from these advances. Transmission electron microscopy (TEM) is compared with scanning transmission electron microscopy (STEM) for cryogenic imaging in both biological and materials science applications. We discuss the developments in detector technologies that have in part powered the development of cryo-EM and anticipate exciting areas for productive overlap between life science and materials science cryo-EM applications.

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Using position averaged convergent beam electron diffraction (PACBED) the Jahn-Teller distortion in LaMnO_{3} is quantitatively measured using a straightforward pattern-matching approach. The fit between experimental patterns and PACBED patterns simulated using the quantum excitation of phonons model allows a three-dimensional measure of octahedral distortion and rotation information from the near transmitted disk region with picometer precision. The effects of plasmon and other inelastic components on quantification using this method are investigated and discussed. The results provide an avenue for accurate local studies of the crystal structure origins of emergent physics in parallel with high-resolution annular dark field scanning transmission electron microscopy imaging at interfaces and defects in quantum materials.

In this contribution experimental evidence of plasmonic edge modes and acoustic breathing modes in gold nanostars (AuNSs) is reported. AuNSs are synthesized by a surfactant-free, one-step wet-chemistry method. Optical extinction measurements of AuNSs confirm the presence of localized surface plasmon resonances (LSPRs), while electron energy-loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM) shows the spatial distribution of LSPRs and reveals the presence of acoustic breathing modes. Plasmonic hot-spots generated at the pinnacle of the sharp spikes, due to the optically active dipolar edge mode, allow significant intensity enhancement of local fields and hot-electron injection, and are thus useful for size detection of small protein molecules. The breathing modes observed away from the apices of the nanostars are identified as stimulated dark modes - they have an acoustic nature - and likely originate from the confinement of the surface plasmon by the geometrical boundaries of a nanostructure. The presence of both types of modes is verified by numerical simulations. Both these modes offer the possibility of designing nanoplasmonic antennas based on AuNSs, which can provide information on both mass and polarizability of biomolecules using a two-step molecular detection process.

A major goal in quantum science is to create a new generation of devices based on spin manipulation [1]. Through spin manipulation, magnetization can be induced in a nonmagnetic material due to close proximity with a ferromagnetic insulator. This is known as the magnetic proximity effect and has been shown to occur in platinum on cobalt ferrite [1]. CoFe2O4 is a ferromagnetic insulator with a spinel structure. Spinel oxides have diverse chemical, magnetic, and electric properties, which can be tuned by varying the cation species and coordination environment [2-4].

Transmission and scanning transmission electron microscopes, (S)TEMs are enabling groundbreaking discoveries in fields ranging from materials science to medicine.Scanning electron microscopes (SEMs) and dual-beam focused-ion-beam (FIB) instruments are multi-technique platforms that are being used for research ranging from in situ studies of mechanical properties to 3D reconstruction of biomaterials.Multimodal and multiscale correlative approaches are combining imaging and analytical modalities such as optical microscopy, scanning electron microscopy (SEM), and (S)TEM, and FIB with X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and X-ray micro-tomography (XMT), to yield complementary and unique insights beyond that achievable with a single method.