Advanced Mg alloys require a stable microstructure that maintains good mechanical properties when exposed to high temperatures. On the basis of this demand, the search for new Mg alloys has stimulated the imagination of material scientists. This review`s discussion ranges from modifications of commercial Mg-Al- and Mg-Zn-based alloys by Ca and rare earth (RE) elements to the investigations of new families of Mg alloys based on Mg-Sn and Mg-Gd. It reports the fundamental findings of these efforts, including microstructure, mechanical properties, and strengthening mechanisms.

Advanced fission and future fusion energy will require new high-performance structural alloys with outstanding properties that are sustained under long-term service in ultrasevere environments, including neutron damage producing up to 200 atomic displacements per atom and, for fusion, 2000 appm of He. Following a brief description of irradiation damage and damage resistance, we focus on an emerging class of nanostructured ferritic alloys (NFAs) that show promise for meeting these challenges. NFAs contain an ultrahigh density of Y-Ti-O-enriched dispersion-strengthening nanofeatures (NFs) that, along with fine grains and high dislocation densities, provide remarkably high tensile, creep, and fatigue strength. The NFs are stable under irradiation up to 800°C and trap He in fine-scale bubbles, suppressing void swelling and fast fracture embrittlement at lower temperatures and creep rupture embrittlement at high temperatures. The current state of the development and understanding of NFAs is described, along with some significant outstanding challenges.

Electron energy loss fine structure near the threshold of inner-shell edges can potentially give valuable information on bonding on an atomic scale. To use near-edge structure it is essential to understand what factors influence both the occupied and unoccupied local density of states in the material of interest. Different techniques of electronic structure theory are suitable for metals, semiconductors, and ionic materials, although some methods can be applied to a wide range of systems. To extract quantitative information on bonding it is important to avoid those edges that are strongly affected by the presence of the core hole such as cations in ionic materials.

The unique geometry of multilayer thin films, with layer thicknesses on the nanoscale, gives rise to a wide range of novel properties and behavior that are not observed in the bulk. The novel behavior is critically dependent on the microstructure of the films. This paper reviews the use of a range of transmission electron microscopy (TEM) techniques to elucidate the structure, chemistry, and properties of multilayer thin films. The paper includes a brief introduction to the technological applications to which multilayer thin films are suited, followed by a description of the various TEM techniques. The final section of the paper presents the application of these techniques to various multilayer thin film systems.

This article reviews data on wetting and the work of adhesion in metal/oxide systems at high temperatures in terms of proposed mutual adsorption models. Favorable adsorption energies can induce changes, especially near the high- and low-p(O2) limits of the coexistence range that often mimic bulk oxidation or reduction reactions. However, in some systems, an intermediate range of p(O2) exists wherein all the interfaces are stoichiometric and the contact angle and work of adhesion are independent of p(O2). A revision of existing data for several pure metal/Al2O3 systems affirms predicted trends and reveals that the contact angle is 110°–130° at the plateau and drops to or below 90° at the high- and low-p(O2) limits. This article also compares the data with recent advances in the characterization and modeling of metal-ceramic interfaces at the atomic level.

The widespread enthusiasm for research on bulk metallic glasses is driven by both a fundamental interest in the structure and properties of disordered materials and their unique promise for structural and functional applications. Unlike the case for crystalline materials, the disordered and nonequilibrium nature of metallic glasses causes their underlying deformation mechanisms to be poorly known. A definite correlation between mechanical behavior and the atomic/electronic structures of metallic glasses has not been established. In this article, I focus on the micromechanisms of mechanical behavior of metallic glasses and present a brief overview of the current understanding of their strength, ductility, and plasticity at the microscopic and atomic scales. The important factors that control the mechanical behavior of metallic glasses are outlined on the basis of recent theoretical and experimental findings. The outstanding issues highlighted in this review are expected to be important for future research on the mechanical properties of metallic glasses.

A new paradigm for ceramic composite structural components enables functionality in heat exchange, transpiration, detailed shape, and thermal strain management that significantly exceeds the prior art. The paradigm is based on the use of three-dimensional fiber reinforcement that is tailored to the specific shape, stress, and thermal requirements of a structural application and therefore generally requires innovative textile methods for each realization. Key features include the attainment of thin skins (less than 1 mm) that are nevertheless structurally robust, transpiration holes formed without cutting fibers, double curvature, compliant integral attachment to other structures that avoids thermal stress buildup, and microcomposite ceramic matrices that minimize spalling and allow the formation of smooth surfaces. All these features can be combined into structures of very varied gross shape and function, using a wide range of materials such as all-oxide systems and SiC and carbon fibers in SiC matrices. Illustrations are drawn from rocket nozzles, thermal protection systems, and gas turbine engines. The new design challenges that arise for such material/structure systems are being met by specialized computational modeling that departs significantly in the representation of materials behavior from that used in conventional finite element methods.

This article summarizes the general structural features and important properties of quasicrystals, a relatively new class of materials belonging to solid-state substances. Quasicrystals, which have a long-range quasiperiodic order but no three-dimensional translational periodicity, are structurally different from both conventional crystals and glassy solids. Although applications are still highly limited, quasicrystals are attracting significant attention as a structual constituent of mixed-phase materials exhibiting high strength together with certain ductility and can be applied as structural materials.

The crystal chemistry of complex perovskite dielectric oxides is reviewed, with an emphasis on structures derived from ordering of the cations on the octahedral B-sites. New classes of perovskites, designed to exhibit 1:2 or 1:3 B-site order for application as low-dielectric-loss microwave ceramics, are identified, and their synthesis, structure, and properties are described. Through the use of B-site chemistries based on Li, Nb, Ta, Ti, and W, members of four new families with 1:2 order, A(βI 1/3βII 2/3)O3, and three new families with 1:3 order, A(βI 1/4βII 3/4)O3, were successfully prepared. The formation and stability of the new and previously prepared ordered perovskites are rationalized through the use of familiar crystal chemical tools such as cation size and charge difference, bond valence, tolerance factor, and new concepts related to the local charge imbalance on the A- and B-sublattices. These tools can be successfully applied to develop stability field maps for each structure and to predict other new ordered systems.

Patterning ferroelectric domains to engineer devices is a relatively recent phenomenon. It is practiced on nonlinear optical materials to make micrometer-sized devices and on perovskite-based thin crystals to progress toward memory devices. Such patterning forms the basis of lithographic processing of heterogeneous nanostructures on thin-film oxides and polymers. The fundamental aspects of polarization switching relevant to patterning are summarized, after which the most common methods of patterning ferroelectric compounds are reviewed, with an emphasis on poling mechanisms for each case. Issues related to the stability of domain patterns and limitations on the smallest domain size are discussed. Finally, lithography based on ferroelectric patterning is demonstrated for a number of complex systems.