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The deformation behavior of materials that exhibit a ductile-to-brittle transition have traditionally been characterized ex-situ and limited to bulk samples. Here, we use a unique experimental setup to perform in-situ cryogenic mechanical testing of Sn 96 solder alloy in a clamped beam configuration at − 142 °C, well below the alloy’s DBTT. Electron backscattered diffraction analysis before and after the in-situ experiments showed how deformation ahead of the crack tip is accommodated by the Sn matrix or intermetallic phase particles. Similar to behavior observed in pure Sn, within the Sn matrix of the Sn 96 alloy deformation twinning is the primary deformation mechanism below the DBTT. Similar to the twins previously observed in pure Sn, twinning behavior in the Sn matrix is consistent with the formation of the {301} and {101} twins in Sn. Within the intermetallic phase in Sn96, slip steps were observed that were not observed prior to bending.

The influence of dispersoids and grain boundary characteristics on the crack propagation behavior in AA3xxx during deep drawing has been investigated using scanning transmission electron microscopy, energy-dispersive spectroscopy, and the dictionary indexing method applied to transmission Kikuchi diffraction (TKD) patterns. Observations showed that cracks formed on the surface of the material at the earliest stages of deformation and lengthened with increasing deformation. Subsurface analysis showed that the cracks propagated from the surface and bifurcated as they extended deeper into the material, forming branches. All of the observed cracks followed intergranular paths with bifurcations correlating with triple junction locations, but no strong trends were found relating grain boundary characteristics to the crack propagation pathway. Dispersoids located at the grain boundaries were found where cracks terminated, suggesting that dispersoids arrest crack propagation and divert crack growth pathways. This paper demonstrates the first practical application of combining the dictionary indexing method with TKD analysis.

A micro-electromechanical system (MEMS) based technique is demonstrated for in situ transmission electron microscopy (TEM) measurements of stress relaxation with simultaneous observation of the underlying plastic deformation processes. True activation volumes are determined from repeated stress relaxation transients and thus provide a signature parameter of the governing mechanisms of plastic deformation. The technique is demonstrated with 100 nm-thick ultrafine-grained gold microspecimens under uniaxial tension. True activation volumes of approximately 3-5b3 (where b is the Burgers vector length) are obtained for tensile stresses ranging from 200-450 MPa. Grain boundary-dislocation interactions are observed via in situ TEM during stress relaxation measurements. The miniaturization of stress relaxation tests inside the TEM provides unique opportunities to characterize the plastic kinetics and underlying mechanisms in ultrafine-grained and nanocrystalline materials.

In this study, a multiscale electron microscopy-based approach is applied to understanding how different aspects of the microstructure in a notched AA6061-T6, including grain boundaries, triple junctions, and intermetallic particles, promote localized dislocation accumulation as a function of applied tensile strain and depth from the sample surface. Experimental measurements and crystal plasticity simulations of dislocation distributions as a function of distance from specified microstructural features both showed preferential dislocation accumulation near intermetallic particles relative to grain boundaries and triple junctions. High resolution electron backscatter diffraction and site-specific transmission electron microscopy characterization showed that high levels of dislocation accumulation near intermetallic particles led to the development of an ultrafine sub-grain microstructure, indicative of a much higher level of local plasticity than predicted from the coarser measurements and simulations. In addition, high resolution measurements in front of a crack tip suggested a compounding influence of intermetallic particles and grain boundaries in dictating crack propagation pathways.

Using electron backscatter diffraction, over 1000 grain boundary/twin interactions were investigated in pure Re after uniaxial compression. Crystallographic factors such as grain boundary disorientation angle, displacement gradient tensor accommodation, and twin plane and shear vector alignment were taken into account as well as the macroscopic Schmid factor. It was found that the crystallographic relationship between coincident twin pairs at grain boundaries fall into two categories. In the first category, the twin pairs satisfied two criteria: the twin plane alignment was maximized across the boundary and the twin variant was kept constant across the boundary. In the second category, comprising approximately 5% of the characterized interactions, twin variant selection appeared to be driven by the macroscopically applied stress state, as resolved by the Schmid factor. In comparison to published results on twin/grain boundary interactions in Mg and Zr, it was found that twins transmit across grain boundaries in Re far more readily, regardless of the grain boundary disorientation angle. This is likely to be a function of the anomalously low twin boundary energy in Re as well as the difference in magnitude of the twinning-induced deformation that must be accommodated at the boundary, with the {11 2 ¯ 1} 26 ¯ > system being dominant in Re and the {10 1 ¯ 2} 11 ¯ > being dominant in Mg and Zr.

A hexagonal close-packed (HCP) to face-centered cubic (FCC) phase transition has been observed in freestanding alpha-titanium (α-Ti) thin foils under two separate conditions: (1) after focused ion beam (FIB) irradiation, and (2) during in situ heating in a transmission electron microscope (TEM). The FCC phase is not found on the Ti single-component equilibrium phase diagram, however, both FCC structures were found to be stable after formation under these conditions. Here, we combine analytical TEM and Atom Probe Tomography (APT) investigations into the chemical nature of these anomalous FCC Ti-X phases. Both occurrences of the FCC phase were observed in thin films containing (initial) prismatic HCP surface plane texturing and appear to be facilitated by hydrogen and oxygen impurities. Our results suggest that the FIB-induced FCC Ti-X is a form of titanium hydride (δ-TiH2 and/or γ-TiH), while the thermally-induced FCC Ti-X appears to be tied to the incorporation of oxygen.

Titanium alloys, produced via additive manufacturing techniques, offer tremendous benefits over conventional manufacturing processes. However, there is inherent uncertainty associated with their properties, often stemming from the variability in the manufacturing process itself along with the presence of residual stresses in the material, which prevents their use as critical components. This work investigates Ti-6Al-4 V produced via selective laser melting by carrying out crystal plasticity finite element (CPFE) simulations and high-resolution digital image correlation (HR-DIC) on samples subject to cyclic loading. This is preceded by detailed material characterization using electron backscatter diffraction, back-scattered electron imaging and transmission electron microscopy, whose results are utilized to inform the CPFE model. A method to incorporate the effect of grain-level residual stresses via geometrically necessary dislocations is developed and implemented within the CPFE framework. Using this approach, grain level information about residual stresses obtained spatially over the region of interest, directly from the experimental material characterization, is utilized as an input to the model. Simulation results match well with HR-DIC and indicate that prior β boundaries play an important role in strain localization. In addition, possible sites for damage nucleation are identified, which correspond to regions of high plastic strain accumulation.

Plastic deformation induced pyramidal ⟨c + a⟩ dislocations in a Zr-2.5Nb alloy have been investigated by electron tomography in the transmission electron microscope. The 10 1 − 1 1st order pyramidal planes were determined to be the primary slip plane, with the 11 2 − 2 2nd order pyramidal planes acting as a secondary slip system. The slip behavior showed asymmetrical response with loading direction, characterized by restricted planar slip in ⟨c⟩ axis compressive loaded grains and frequent cross slip in ⟨c⟩ axis tensile loaded grains.

Using ex-situ transmission electron microscopy and the recently developed nanoprobe diffraction (NPD) technique, we characterize a nanoindented solution treated gum metal. Lattice rotations are resolved at a 1.2 nm length-scale and shown to be continuous within the nanoindentation pit; further, it is shown that these can be accommodated by a reasonable number of geometrically necessary dislocations at a density of ∼1015/m2. We additionally provide direct evidence that dislocations within the nanoindent, rather than secondary phase nanoparticles, can serve as potent barriers to dislocation motion. We also demonstrate that plasticity in these alloys under nanoindentation can be accommodated solely by dislocation nucleation and propagation, with no competing deformation mechanisms present. Conventional transmission electron microscopy and “g•b” analysis reveal the presence of dislocations on 〈 1 ¯ 11 〉 {110} slip systems and highly localized plastic deformation in the form of shear bands on { 1 ¯ 1 ¯ 2 } slip systems, similar to previously observed “giant faults”.

The microstructure and fatigue behavior of additive manufactured Inconel 718 (IN718) were studied using digital image correlation (DIC), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The samples were produced with selective laser melting and underwent two different heat treatments (stress relieved and fully post-processed) that produced different microstructures. The solidification process led to the formation of dendrites where misorientation between each branch was accommodated with dislocations, producing subgranular cell structures. EDS observations revealed that Ti and Nb segregate to the cell and grain boundaries, forming carbides. The stress relieved sample retained the cell boundaries, which acted as barriers for dislocation propagation, thereby distributing strain evenly throughout the microstructure. In contrast, the post-processed sample contained no cell boundaries, and strain was localized at the grain boundaries. Mechanical tests showed that the precipitates and the annealing twins in the post-processed sample were much more effective at improving the strength than small grain size and cell boundaries found in the stress relieved sample.

Pure Ti traditionally exhibits the hexagonal closed packed (HCP) crystallographic structure under ambient conditions and the body centered cubic (BCC) structure at elevated temperatures. In addition to these typical structures for Ti alloys, the presence of a face centered cubic (FCC) phase associated with thin films, interfaces, or high levels of plastic deformation has occasionally been reported. Here we show that small FCC precipitates form in freestanding thin foils during in situ transmission electron microscope (TEM) heating and we discuss the potential origins of the FCC phase in light of the in situ observations. This FCC phase was found to be stable upon cooling and under ambient conditions, which allowed us to explore its mechanical properties and stability via nanomechanical in situ TEM testing. It was found that FCC platelets within the HCP matrix phase were stable under mechanical deformation and exhibited similar mechanical deformation behavior as the parent HCP phase.

The mechanical response of modern alloys results from a complex interplay between existing microstructure and its evolution with time under stress. To unravel these processes, in situ approaches intrinsically have a critical advantage to explore the basic mechanisms involving dislocations, grain boundaries (GBs), and their interactions in real time. In this article, we discuss recent findings using in situ nanomechanical testing techniques and refined crystallographic analysis tools. Advancements in in situ nanomechanics not only include multiaxial loading conditions, which bring us closer to real-world applications, but also high strain-rate testing, which is critical to compare experiments and simulations. In particular, unraveling the details of GB-based mechanisms and related microstructural changes will facilitate significant breakthroughs in our understanding of the behavior of materials on macroscopic length scales.

A rapid image segmentation and correlation-based approach to investigating the local microstructural effects on pitting corrosion susceptibility is introduced. The impact of four different microstructural features, consisting of grain orientation, proximity to grain boundaries, proximity to intermetallic particles, and local geometrically necessary dislocation (GND) density, on pitting initiation in the 5083 aluminum alloy was directly investigated using automated pit detection processing in combination with electron microscopy-based characterization. Three different thermomechanical treatments were used to vary the system microstructure and samples were immersed in 3.5 wt% NaCl aqueous solution for 24 h to induce pitting. GND density and proximity to intermetallic particle both showed positive correlations, while grain orientation and proximity to grain boundary showed no correlation with pit initiation sites.

Nanocrystalline Al thin films have been strained in situ in a transmission electron microscope using two separate nanomechanical techniques involving a push-to-pull device and a microelectromechanical system (MEMS) device. Deformation-induced grain growth was observed to occur via stress-assisted grain boundary migration with extensive grain growth occurring in the necked region, indicating that the increase in local stress drives the boundary migration. Under applied tensile stresses close to the ultimate tensile strength of 450 MPa for a nanocrystalline Al specimen, measured boundary migration speeds are 0.2 – 0.7 nm s−1 for grains outside necked region and increases to 2.5 nm s−1 for grains within the necked region where the local estimated tensile stresses are elevated to around 630 MPa. By tracking grain boundary motion over time, molecular dynamics simulations showed qualitative agreement in terms of pronounced grain boundary migration with the experimental observations. The combined in situ observation and molecular dynamics simulation results underscore the important role of stress-driven grain growth in plastically deforming nanocrystalline metals, leading to intergranular fracture through predominant grain boundary sliding in regions with large localized deformation.

Nanocrystalline Ni thin films with different as-deposited textures were synthesized by varying the substrate temperature during pulsed-laser deposition. The influence of initial texture variations on the thermal stability and annealing behavior of the thin films was studied via in situ transmission electron microscopy annealing and transmission Kikuchi diffraction analysis. It was found that, as the substrate temperature during deposition was increased, the initial microstructure varied from a random distribution of grains to one almost entirely composed of (001) – oriented grains, with the volume fraction of (001) – oriented grains increasing with increasing substrate temperature. The (001) – oriented grains increased thermal stability and constrained grain growth during annealing, resulting in a bimodal grain size distribution in the annealed films. Despite different surface orientations after annealing, the misorientation distribution functions for the films were similar, suggesting that the boundary state is a primary factor in dictating equilibrium.

In situ straining in the transmission electron microscope and diffraction-contrast electron tomography has been applied to investigate dislocation interactions in α-Ti. Dislocation debris, in the form of small loops, was seen to form from sequential cross-slip events. Electron tomography provided direct three-dimensional visualisation of the dislocation structures, allowing accurate identification of slip planes, dislocation line directions and spatial relations between dislocations.

High resolution electron backscatter diffraction (HREBSD), an SEM-based diffraction technique, may be used to measure the lattice distortion of a crystalline material and to infer the geometrically necessary dislocation content. Uncertainty in the image correlation process used to compare diffraction patterns leads to an uneven distribution of measurement noise in terms of the lattice distortion, which results in erroneous identification of dislocation type and density. This work presents a method of reducing noise in HREBSD dislocation measurements by removing the effect of the most problematic components of the measured distortion. The method is then validated by comparing with TEM analysis of dislocation pile-ups near a twin boundary in austenitic stainless steel and with ECCI analysis near a nano-indentation on a tantalum oligocrystal. The HREBSD dislocation microscopy technique is able to resolve individual dislocations visible in TEM and ECCI and correctly identify their Burgers vectors.

Domains and domain walls are critical in determining the response of ferroelectrics, and the ability to controllably create, annihilate, or move domains is essential to enable a range of next-generation devices. Whereas electric-field control has been demonstrated for ferroelectric 180° domain walls, similar control of ferroelastic domains has not been achieved. Here, using controlled composition and strain gradients, we demonstrate deterministic control of ferroelastic domains that are rendered highly mobile in a controlled and reversible manner. Through a combination of thin-film growth, transmission-electron-microscopy-based nanobeam diffraction and nanoscale band-excitation switching spectroscopy, we show that strain gradients in compositionally graded PbZr1-xTixO3 heterostructures stabilize needle-like ferroelastic domains that terminate inside the film. These needle-like domains are highly labile in the out-of-plane direction under applied electric fields, producing a locally enhanced piezoresponse. This work demonstrates the efficacy of novel modes of epitaxy in providing new modalities of domain engineering and potential for as-yet-unrealized nanoscale functional devices.

Automated image recognition and analysis techniques were combined with liquid cell transmission electron microscopy to explore the oxidation kinetics of nanocrystalline Fe thin films in a water vapor environment. From in situ microscopy experiments, localized oxidation was observed to initiate in the film then propagate in an unsteady fashion, alternatingly arresting and progressing. The oxidation front propagation occurred via new oxidation sites initiating 10s of nm ahead of the existing front rather than through a continuous expansion mechanism. The oxidation rate was seen to be highly dependent on electron dose rate, with increasing electron dose rate accelerating the oxidation front propagation and increasing the density of oxidation initiation sites. The in situ experiments were also performed in diffraction space where it was seen that Fe2O3 was formed during oxidation. Coupling in situ microscopy with automated image analysis creates new opportunities for studying the early stages of localized corrosion by providing direct observation of oxidation propagation as well as quantification of the oxidation rates and rapid identification of byproducts.

Detailed defect structure of dendrite formation was studied in order to connect the mesoscopic with the atomistic structure. It was demonstrated that twinning and stacking fault formation play a central role in the growth of electrodeposited Ag dendrites. The broad faces of Ag dendrites and the main trunk growth direction were found to be ((1) over bar 11) and [(1) over bar1 (2) over bar], respectively. Dendrite branches also formed and grew from the main trunk parallel to the [12 (1) over bar] and [(211) over bar] crystallographic directions. Twins and stacking faults were found to reside on the {111} crystallographic planes, as expected for a face centered cubic (FCC) Ag crystal. Using electron back scattered diffraction (EBSD) we found two variants of in-plane 60 degrees rotational twin domains in the ((1) over bar 11) broad dendrite surface plane. The intersections of twins and stacking faults with dendrite arm surfaces are perpendicular to the (112) arm growth directions. However, occasionally twins on the {111} planes parallel to the (112) arm growth directions were also observed. Although defect assisted dendrite growth is facilitated by twinning and stacking fault formation on {111} planes, the growth directions of the trunk and branches are not of the (111) type, but rather close to (112). The (112) growth directions are maintained by breaking dendrite facets into thermodynamically stable 111 and 200 steps and structural ledges of different length.

Decorating 1D nanostructures (e.g., wires and tubes) with metal nanoparticles serves as a hierarchical approach to integrate the functionalities of metal oxides, semiconductors, and metals. This paper examines a simple and low-temperature approach to self-assembling gold nanoparticles (Au-np)—a common catalytic material—onto silicon nanowires (SiNWs). A conformal ultra-thin film (i.e.

The mobility of defects such as dislocations controls the mechanical properties of metals. This mobility is determined both by the characteristics of the defect and the material, as well as the local stress and strain applied to the defect. Therefore, the knowledge of the stress and strain during deformation at the scale of defects is important for understanding fundamental deformation mechanisms. Here, we demonstrate a method of measuring local stresses and strains during continuous in situ deformation with a resolution of a few nanometers using nanodiffraction strain mapping. Our results demonstrate how large multidimensional data sets captured with high speed electron detectors can be analyzed in multiple ways after an in situ TEM experiment, opening the door for true multimodal analysis from a single electron scattering experiment.