Transmission electron microscopy is a powerful technique for the analysis of solid samples, but it can also be used to image in liquid environments, gaining a unique view of processes and structures in liquids. Here, we describe recent developments in electron microscopy of liquids and discuss applications in several areas. We first describe closed-liquid-cell microscopy with its opportunities for visualizing electrochemical processes. We then discuss imaging of low-vapor-pressure liquids relevant to the operation of rechargeable batteries. Finally, we describe imaging of thick biological materials to obtain information on membrane proteins in intact mammalian cells that cannot be observed classically under dry or frozen conditions. Electron microscopy in liquid environments is developing rapidly and has the potential to solve key problems in materials science, physics, chemistry, and biology.

NiTi alloys are well known not only due to their exceptional shape-memory ability to recover their primary shape, but also because they show high ductility, excellent corrosion and wear resistance, and good biological compatibility. They have received significant attention especially in the field of laser additive manufacturing (AM). Among laser AM techniques, selective laser melting and laser metal deposition are utilized to exploit the unique properties of NiTi for fabricating complex shapes. This article reviews the properties of bulk and porous laser-made NiTi alloys as influenced by both process and material parameters. The effects of processing parameters on density, shape-memory response, microstructure, mechanical properties, surface corrosion, and biological properties are discussed. The article also describes potential opportunities where laser AM processes can be applied to fabricate dedicated NiTi components for medical applications.

There is increasing interest in the use of additive manufacturing (AM) for Ni-based superalloys due to their various applications in the aerospace and power-generation sectors. Ni-based superalloys are known to have a complex chemistry, with over a dozen alloying elements in most alloys, enabling them to achieve outstanding high-temperature mechanical performance as well as oxidation resistance when processed using conventional routes (e.g., casting and forging). Nonetheless, this complex chemistry results in the formation of various phases that could affect their processability using AM, resulting in cracking. Furthermore, due to the directional solidification and rapid cooling associated with AM processes, the alloys experience significant anisotropy due to the epitaxially grown microstructure, as well as the residual stresses that can sometimes be difficult to mitigate using thermal postprocessing techniques. This article highlights the outstanding issues in Ni-based superalloys AM processing, with special emphasis on defect formation mechanisms, process optimization, and residual stress development.

Conducting polymers are difficult to process, since unlike conventional polymers, they generally do not dissolve in common solvents or melt. By synthesizing nanostructured forms of the conjugated polymer polyaniline, simple methods for making conducting polymer inks become possible. By using either interfacial polymerization or a rapid-mixing technique, nanostructured polyaniline has been synthesized in a readily scalable process. Polyaniline nanofibers make excellent sensors for acids and bases. When decorated with metal nanoparticles, they can be used for molecular memory devices and catalysis. Using a flash from a camera, polyaniline nanofibers can be melted and patterned to make sensors, actuators, and asymmetric membranes. Single crystals of tetraaniline can be grown that exhibit conductivities approaching that of the bulk polymer.

This article overviews electron-beam melting (EBM), including process optimization issues. Examples of EBM-fabricated components described include hexagonal close-packed Ti-6Al-4V, face-centered-cubic René 142 (a Ni-based superalloy), and body-centered-cubic pure iron, corresponding to a melt temperature range from 1375°C to 1630°C. Residual microstructures observed for these fabricated components by optical microscopy, scanning electron microscopy, and transmission electron microscopy include equilibrium as well as nonequilibrium features, which illustrate prospects for novel structure–property manipulation in the EBM process. The EBM process relies on available pre-alloyed, precursor powders that are selectively melted layer by layer by a computer-aided design scanned electron beam to form relatively small, but often complex, products or components. Direct metal deposition innovations capable of truly three-dimensional metal printing are described, especially high-temperature metals and alloys for future additive manufacturing technologies.

Aluminum alloys are in high demand for additive manufacturing (AM) processing. However, the physical properties of Al alloys are less favorable for the production of repeatable and reliable parts, with factors such as surface oxide scales, high thermal conductivity, and large solidification shrinkage. Despite these characteristics, processing strategies have been developed to overcome these hurdles. The objective of this article is to highlight the different microstructure–processing–properties characteristics for the three main families of aluminum alloys: pure, casting, and wrought chemistries. The article focuses on AM processes involving solidification, including powder bed and direct energy deposition for both powder and wire feedstock.

This paper presents the results of an experimental study of the effects of pressure on polymer chain alignments in poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) blends that are used in bulk heterojunction organic photovoltaic cells (OPVs). The P3HT:PCBM blends on glass were subjected to pressure and annealing at 140 °C. The surface morphologies, nano-/micro-structures and the chain alignments were analyzed using atomic force microscopy techniques and grazing incidence x-ray scattering. The current–voltage characteristics of the resulting devices are also shown to change significantly with changes in the nano-/micro-structures. The polymer chains were aligned in the direction of the applied pressure (edge-on), which reduced the lamellae spacing between the polymer units and increased the degree of crystallinity. The increased crystallinity plays significant role in the current–voltage enhancements. The implications of the study are discussed for the design and control of the nano/microstructures of bulk heterojunction organic solar cells.