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X-ray microcomputed tomography was conducted on an AA7075-T651 sample immersed in a 3.5 wt% NaCl solution to provide time-resolved measurements of localized corrosion. A nondestructive, volumetric analysis of pitting sites and local microstructural features followed, and quantitative results were combined with 2D and 3D visualizations. During alternating immersion periods, pitting was initiated at cathodic intermetallic inclusions and continued throughout the study. Rates of pit growth varied as a response to the decoupling of inclusions from the matrix, resulting in a start-and-stop trend that was observed in a significant number of examined sites. When a sample with a higher extent of cold rolling was examined with the same procedure, a finer and more homogeneous distribution of inclusions correlated with an increase in the maximum and mean pit depth. This change was attributed to the more frequent exposure of subsurface inclusions by localized corrosion, a phenomenon that mitigated the passivating effect of decoupling. Additionally, the effects of continuous immersion vs. alternate immersion were examined for metallurgically identical samples. Intermittent drying during the alternate immersion period destabilized the passive layer, increasing mean pit depth, while continuous immersion for 20 d produced a uniform and protective layer of corrosion product.

With miniaturization and heterogeneous integration in packaging, there has been a drive toward developing lower temperature solders. Sn-58Bi eutectic solder provides an attractive alternative with its meting point at 138°C. Due to the lower melting temperature of Sn-Bi solder, Bi coarsening may occur even at room temperature. In this paper, the microstructural evolution in Sn-58Bi joints was observed during room temperature storage. Room temperature aging induced the dissolution and coarsening of Bi phases in the solder matrix, especially in the primary Sn phases and Sn-Bi dendrites. The mechanical properties of individual Sn-rich and Bi-rich phases were measured by nanoindentation. The results showed that the Sn-rich phases had higher Young’s modulus and hardness than Bi-rich phases in aged solder joints due to solution strengthening. Bi phases were more compliant and had lower hardness than Sn.

Four state-of-the-art Deep Learning-based Convolutional Neural Networks (DCNN) were applied to automate the semantic segmentation of a 3D Transmission x-ray Microscopy (TXM) nanotomography image data. The standard U-Net architecture as baseline along with UNet++, PSPNet, and DeepLab v3+ networks were trained to segment the microstructural features of an AA7075 micropillar. A workflow was established to evaluate and compare the DCNN prediction dataset with the manually segmented features using the Intersection of Union (IoU) scores, time of training, confusion matrix, and visual assessment. Comparing all model segmentation accuracy metrics, it was found that using pre-trained models as a backbone along with appropriate training encoder–decoder architecture of the Unet++ can robustly handle large volumes of x-ray radiographic images in a reasonable amount of time. This opens a new window for handling accurate and efficient image segmentation of in situ time-dependent 4D x-ray microscopy experimental datasets.

Biodiversity provides a massive library of ideas for bio-inspired design, but the sheer number of species to consider can be daunting. Current approaches for sifting through biodiversity to identify relevant biological models include searching for champion adapters that are particularly adept at solving a specific design challenge. While the champion adapter approach has benefits, it tends to focus on a narrow set of popular models while neglecting the majority of species. An alternative approach to bio-inspired design is the comparative method, which leverages biodiversity by drawing inspiration across a broad range of species. This approach uses methods in phylogenetics to map traits across evolutionary trees and compare trait variation to infer structure–function relationships. Although comparative methods have not been widely used in bio-inspired design, they have led to breakthroughs in studies on gecko-inspired adhesives and multifunctionality of butterfly wing scales. Here we outline how comparative methods can be used to complement existing approaches to bio-inspired design, and we provide an example focused on bio-inspired lattices, including honeycomb, and glass sponges. We demonstrate how comparative methods can lead to breakthroughs in bio-inspired applications as well as answer major questions in biology, which can strengthen collaborations with biologists and produce deeper insights into biological function.

In situ X-ray microtomography was used to characterize the changes in internal structure of an expanded thermoplastic polyurethane (eTPU) bead foam used in footwear midsole during compression. Quantitative data on cell size and volume changes based on conventional segmentation were computed. Image correlation on the 4D datasets, i.e. a 3D tomogram collected at various points during deformation, was performed to map the strain fields to aid in analysis of observed deformation. Morphological and structural characterization revealed the gradient porosity and ligament thickness and its influence on the global mechanical behaviour of individual bead foam. The correlation of changes in void size and shape, identified areas of potentially weak regions. Strain maps derived by using voids as markers were adequate to capture the instabilities in local cell collapse. The smaller cells at the surface densified more readily providing more resistance to deformation. In addition, the thicker ligaments in the centre of the bead also aided resistance to deformation. Finally, our results showed the initiation of failure in cell structure was influenced by the heterogeneities around the immediate neighbours in a cluster of voids.

Recently In has been considered as an additional alloying element in Sn-rich solders primarily due to its abilities to decrease the solder melting temperature and to modify mechanical properties and microstructure. While In is an attractive candidate for addition to solder, its effect on solder microstructure is not well understood. In order to study the effect of minor In additions on Sn-rich solder alloys, solder joints were prepared using Sn-0.7 wt.% Cu and Sn-0.7 wt.% Cu

Understanding mechanical failure, crack propagation, and compressive behavior at the micrometer scale is essential for tailoring material properties for structural performance in cellular materials. Typically, modeling of traditional polymer foam materials is clouded by the lack of control in material morphology and its inherent stochastic structure. Additive manufacturing with sub-micrometer resolution provides a direct path for experimenters to specifically tailor structures needed by modelers to explicitly probe mechanical performance. Using laboratory-based 3D X-ray computed tomographic imaging (CT), the examination of deformation and damage provides a critical path to understand how these soft materials behave. Additionally, synchrotron CT yields realistic information at higher strain rates to directly validate the robustness of our finite element modeling. For this study, nanolithographic printing was employed to generate a series of engineered lattices with increasing levels of defects through the random removal of ligaments. These structures were mechanically tested and imaged with laboratory-based microCT. Additionally, synchrotron experiments were conducted in which the structures were imaged in 3D at 14 Hz during compression at a 0.4 s−1 strain rate. These 3D images show the changes in the structure as the ligaments bend, buckle and fracture in real time. This technique provides a robust framework for developing our methodologies and future exploration of engineered structures.

Electromigration (EM) causes intermetallic and void growth that decreases the reliability and lifetime of solder joints. As a diffusion-controlled process, EM is highly dependent on the fastest diffusion pathways in a structure. In anisotropic β-tetragonal Sn those pathways are along high angle grain boundaries and along the c-axis of the Sn grains. A bicrystal sample with two major grain orientations and two major grain boundary types was EM tested for 100 h. EM was interrupted at intervals for x-ray microtomography to reveal the 3D evolution of intermetallic compounds (IMCs) and voids within the joint. Quantitative IMC growth along high angle grain boundaries and twins was captured for the first time and related to the effective Cu diffusivity of multiple grains. Using a correlative approach that combined scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) mapping, IMC growth and morphology were linked to the evolution of the Sn grain structure. Unusual void shrinkage and void splitting behavior were connected to uneven cathode interface consumption and thermal compression.

The ongoing interest in colloidal nanocrystal solids for electronic and photonic devices necessitates that their thermal-transport properties be well understood because heat dissipation frequently limits performance in these devices. Unfortunately, colloidal nanocrystal solids generally possess very low thermal conductivities. This very low thermal conductivity primarily results from the weak van der Waals interaction between the ligands of adjacent nanocrystals. We overcome this thermal-transport bottleneck by crosslinking the ligands to exchange a weak van der Waals interaction with a strong covalent bond. We obtain thermal conductivities of up to 1.7 Wm-1 K-1 that exceed prior reported values by a factor of 4. This improvement is significant because the entire range of prior reported values themselves only span a factor of 4 (i.e., 0.1-0.4 Wm-1 K-1 ). We complement our thermal-conductivity measurements with mechanical nanoindentation measurements that demonstrate ligand crosslinking increases Young's modulus and sound velocity. This increase in sound velocity is a key bridge between mechanical and thermal properties because sound velocity and thermal conductivity are linearly proportional according to kinetic theory. Control experiments with non-crosslinkable ligands, as well as transport modeling, further confirm that ligand crosslinking boosts thermal transport.

Single drop granule formation on a static powder bed of pharmaceutical mixtures was studied to investigate the effects of hydrophobicity and primary particle size distribution on the powder bed packing structure and the content homogeneity of active pharmaceutical ingredient (API) in granules formed. The granule formation mechanisms, drop penetration time, granule morphology and internal structure have been previously investigated in a mixture of coarse microcrystalline cellulose (MCC) and fine acetaminophen (APAP). When the APAP amount increased (decreasing particle size and increasing hydrophobicity), drop penetration time increased, formation mechanisms transitioned from Spreading to Tunneling, the granules became smaller in size, and the internal porosity of the granules decreased (Gao et al., 2018). In the current study, single drop granulation on mixtures of MCC and APAP with different particle sizes were investigated for formation mechanisms and granule morphology. Additionally, the powder bed packing structure was characterized by X-ray micro-CT and the API content uniformity was measured by UV–vis spectrometry. It was found that in the mixture made from coarse MCC and fine APAP, the internal structure became heterogeneous and there were dense aggregate regions in both the powder bed and granules from 25% APAP proportion, where the transition from Spreading to Tunneling occurs. The content uniformities of granules from fine powder beds are much more compromised (indicating a discrepancy between the actual value and theoretical value) than those from coarse powder beds. This content discrepancy becomes much larger when the APAP proportion in the powder bed is higher (above 50%). This was previously observed by other researchers (Nguyen et al., 2010) and was attributed to the preferential wetting of the ingredients. It is believed that the primary particle size of the powder bed is more significant than the hydrophobicity in affecting the formation mechanism, granule internal structure, and content uniformity.

Solder joints can experience fatigue cracking at the interface between the solder and substrate during thermal cycling due to the difference in thermal expansion between joined components. In order to strengthen the interfacial region and prevent cracking, two Cu pad surface treatments were studied on Sn-3Ag-0.5Cu solder, and on matte Sn plate and Ni plate coatings. The resulting intermetallic microstructures were characterized using scanning electron microscopy and energy-dispersive spectroscopy. Mechanical testing was performed using nano-indentation on the solder joints. The matte Sn plate on Cu sample formed an uneven distribution of Ag3Sn particles and a planar Cu6Sn5 interfacial intermetallic. The Ni-plated sample formed a needle-like Ni-rich interfacial intermetallic and uniform dispersion of Ag3Sn particles. The rough intermetallic compound (IMC)/solder interface and even IMC particle distribution cause the Ni-plated sample to experience reduced damage under board-level thermomechanical cycling because the interfacial structure reduces the Sn matrix recrystallization that contributes to fatigue cracking. In contrast, the matte Sn-plated sample exhibited an Ag3Sn particle-free zone adjacent to a planar Cu6Sn5 IMC layer which allows for rapid Sn recrystallization and fatigue crack propagation.

Anisotropic polymer/nanoparticle composites display unique mechanical, thermal, electrical, and optical properties depending on confirmation and configuration control of the composing elements. Processes, such as vapor deposition, ice-templating, nanoparticle self-assembly, additive manufacturing, or layer-by-layer casting, are explored to design and control nanoparticle microstructures with desired anisotropy or isotropy. However, limited attempts are made toward nanoparticle patterning during continuous fiber spinning due to the thin-diameter cross section and 1D features. Thus, this research focuses on a new patterning technique to form ordered nanoparticle assembly in layered composite fibers. As a result, distinct layers can be retained with innovative tool design, unique material combinations, and precise rheology control during fiber spinning. The layer multiplying-enabled nanoparticle patterning is demonstrated in a few material systems, including polyvinyl alcohol (PVA)-boron nitride (BN)/PVA, polyacrylonitrile (PAN)-aluminum (Al)/PAN, and PVA-BN/graphene nanoplatelet (GNP)/PVA systems. This approach demonstrates an unprecedentedly reported fiber manufacturing platform for well-managed layer dimensions and nanoparticle manipulations with directional thermal and electrical properties that can be utilized in broad applications, including structural supports, heat exchangers, electrical conductors, sensors, actuators, and soft robotics. W.X. and R.F. contributed equally to this work. This work was funded by the Global Sports Institute (GSI) at Arizona State University and the U.S. National Science Foundation (NSF, EAGER 1902172). Scopus

In situ three-dimensional X-ray synchrotron tomography was used to visualize and quantify the fatigue crack initiation and growth from corrosion pits in high strength aluminum alloys. Corrosion pitted Al 7075 and Al 7475 samples of peak-aged, over-aged, and highly over-aged conditions were prepared by soaking in 3.5 wt pct NaCl solution for fifteen days. These samples were fatigue tested in situ in 3.5 wt pct NaCl solution using synchrotron X-ray tomography to analyze the fatigue crack initiation and growth characteristics (4D). Increases in maximum pit depth and fatigue crack growth rate variability were found with increased aging. A detailed analysis of crack morphology and deflection, as a function of aging, was carried out and it discussed.

Effective and accurate characterization and quantification of complex microstructure of a heterogeneous material and its evolution under external stimuli are very challenging, yet crucial to achieving reliable material performance prediction, processing optimization and advanced material design. Here, we address this challenge by developing a set of hierarchical statistical microstructural descriptors, which we call the “n-point polytope functions” Pn, for quantitative characterization, representation and modeling of complex material microstructure and its evolution. These polytope functions successively include higher-order n-point statistics of the features of interest in the microstructure in a concise, expressive, explainable, and universal manner; and can be directly computed from multi-modal imaging data. We develop highly efficient computational tools to directly extract the Pn functions up to n = 8 from multi-modal imaging data. Using simple model microstructures, we show that these statistical descriptors effectively “decompose” the structural features of interest into a set of “polytope basis”, allowing one to easily detect any underlying symmetry or emerging features during the structural evolution. We apply the Pn functions to quantify and model a variety of heterogeneous material systems, including particle-reinforced composites, metal-ceramic composites, concretes, porous materials; as well as the microstructural evolution in an aged lead-tin alloy. Our results indicate that the Pn functions can offer a practical set of basis for quantitative microstructure representation (QMR), for both static 3D complex microstructure and 4D microstructural evolution of a wide spectrum of heterogeneous material systems.

Even after nearly a century of extensive use of aluminum alloys in structural applications, our understanding of such precipitation-strengthened materials is far from complete. With the advent of next generation advanced characterization techniques, our ability to probe materials in unique ways and at different length scales has established a new paradigm for devising new pathways to alloy design by engineering materials and tailoring specific properties at the nanoscale. Here, we perform in situ nanomechanical testing in conjunction with synchrotron-based hard X-ray nanotomography to capture initiation and evolution of damage in 3D in Al–Cu alloys. Precipitates in these alloys are seen to exhibit unprecedented localized deformation in compression, which is attributed to novel observations of kinking in these brittle second-phase particles, accompanied with the generation of a fine polycrystalline texture in the adjacent matrix. We observe a size-dependent transition in precipitate deformation behavior that has been thoroughly investigated using a comprehensive correlative approach.

X-ray tomography was used to monitor damage evolution in nano-silver sintered joints during thermal cycling. Samples consisted of a silicon die joined to a direct bond copper substrate by sintering nano-silver paste. The amount of observable damage was significantly affected by the amount of allowable warping during the thermal cycling tests. By fully constraining the sample from flexing during thermal cycling, all observable damage was eliminated.

Laboratory diffraction contrast tomography (LabDCT) is a laboratory-scale x-ray microtomography technique that can be used to non-destructively map grains and grain boundaries in 3D. The fidelity of grain mapping significantly depends on the quality of grain reflections obtained from the illuminated volume of the specimen. In this article, we report the application of a novel forward modeling approach to improve the reliability of grain mapping. Through this approach, a comparison between the obtained grain reflections and simulated grain reflections can be used to perform a self-fitting operation. This can be used to optimize instrumental parameters and iteratively improve the quality of reconstruction. To demonstrate the effectiveness of the forward modeling approach, LabDCT was used to map the grains in a polycrystalline specimen of the magnesium alloy AZ91E and iteratively improve reconstruction quality significantly.

In situ studies using X-ray tomography have gained immense popularity in the recent past owing to their non-destructive nature and ability to capture the microstructure of a wide range of materials in 3D. In this work, we have conducted in situ micropillar compression and studied damage evolution in Al/SiC nanolaminates using a laboratory-based nanoscale X-ray microscope. Nanoscale defects present in the microstructure were characterized in 3D. The effect of these nanopores on damage initiation was quantified and is discussed. Additionally, the effect of Ga+ ion milling on micropillar fabrication was characterized by performing a comparative experiment on pillars fabricated using Ga+ and Ne+ ion source based focused ion beams.

Cast duplex stainless steels (CDSS) is being extensively used in many industries. The morphology and distribution of ferrite phase present, as well as the micropores defect, significantly influences the hot cracking susceptibility and corrosion resistance of CDSS. In this work, the microstructure and the micropores of the inner wall and outer wall position of a primary coolant pipe used in the pressurized water reactor (PWR) were characterized and compared using a lab scale X-ray microtomography approach. During centrifugal casting process, the local ferrite grains tend to grow in the same direction. Although the ferrite phases seem separated from each other in a two-dimensional (2D) image, most of them are connected in a three-dimensional (3D) view. Solution treatment can result in homogeneous distribution in both fraction and morphology of ferrite phase. Micropores always form along the ferrite/austenite interface and the inner wall position is more prone to porosity.