At higher levels of structure, researchers are beginning to understand, and build, structures with crystals or “grains” that contain only small groupings of atoms, in which as many atoms lie in the grain boundaries as in the grains themselves. Researchers are also finding new properties in “nanocomposites” —composites on the scale of nanometers. Element sizes in electronic chips are rapidly decreasing and are approaching the size of small groups of atoms.
The level of microstructure and macrostructure above the nanometer scale continues to have rich promise for research. Developments at this level include modern composites, directionally solidified high-temperature turbine blades, and flaw-tolerant ceramics. Development and application of modern fracture mechanics and design have also been important. Much of the innovation and development in modern processing is concerned with controlling structure at this level as well as at finer levels. Examples include new strip casting processes and near-net-shape forming. Major opportunities exist for computer modeling to aid development of new processes and more rapid introduction of new designs and novel production processes.
The following sections describe selected research opportunities for structural, electronic, magnetic, photonic, and superconducting materials and for biomaterials. The list is by no means intended to be complete, but rather to illustrate the vitality and rich promise of the field. The emphasis on function underscores the use of materials; it makes explicit the link between fundamental research and the applications of research; it highlights the opportunities for research to contribute to areas of societal need.
The properties of structural materials—toughness, strength, hardness, stiffness, and weight, for example—are determined by the interaction of atoms by their arrangement as manifested in molecules, crystalline and non-crystalline arrays, and defects, and by higher levels of structure including flaws and other microscopic heterogeneities. Consequently, the ability to predict and control materials structure at all levels, from the lattice dimensions to the macroscopic level, is central to developing structural materials that achieve the level of performance needed to accomplish the nation’s technological, economic, and military goals.
Two examples bring this relationship into focus. Without major advances in propulsion technology, reducing the structural weight of launch vehicles is the only means of lowering the prohibitive cost of transporting heavy commercial, scientific, and military payloads into orbit. Reducing structural weight will require new materials with very high strength-to-weight ratios and the capacity to withstand high temperatures. Currently, the materials