Materials Science and Engineering for the 1990s Maintaining Competitiveness in the Age of Materials (1989) / Chapter Skim
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3. Research Opportunities and Functional Roles of Materials
3. Research Opportunities and Functional Roles of Materials
Pages 74-109
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From page 74... ...
Materials researchers can now analyze and manipulate the properties of materials in ways that were hard to imagine just a few years ago. At the atomic level, instruments such as the scanning tunneling microscope and the atomic resolution transmission electron microscope can reveal, with atom-by-atom resolution, the structures of materials.
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From page 75... ...
STRUCTURAL MATERIALS 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 noncrystalline 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.
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From page 76... ...
The opportunity now exists, however, to fill important gaps in understanding and to develop theories that provide quantitative guidelines for the design of materials. With new instruments such as the scanning tunneling microscope and the atomic resolution transmission electron microscope, it is possible to view defects on an atomic scale.
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From page 77... ...
Metals The central role of processing in controlling and improving the performance of structural materials, first recognized in the late 1960s, has become a major focus in this area in the past decade. Processing is now viewed as complementary to the chemistry and physics of materials as a tool in controlling properties.
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From page 78... ...
Product improvements will play an important role in maintaining market share in the competition of metals with ceramics, polymers, and composite materials. There is an excellent opportunity for innovative product research that will enable accurate predic
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From page 79... ...
These are achievable through advanced processing techniques, such as rapid solidification processing, permitting the attainment of structural refinement and control of metastable and equilibrium-phase transformation. Such materials can have excellent combinations of strength, ductility, and corrosion resistance.
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From page 80... ...
Low-dislocation or dislocation-free single crystals are now commonly grown from the melt or are obtained through subsequent processing; much improvement in the quality of such crystals is needed and can be expected in the years ahead. The appeal of ceramics as structural materials is easy to understand.
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From page 81... ...
Attrition, melt atomization, and physical vapor deposition produce such particles without chemical change. Chemical precursors are involved in sol-gel and thermal degradation processes.
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From page 82... ...
All rights reserved.) crystalline diamond films by energetically assisted chemical vapor deposition processes at far lower temperatures and at low pressures.
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From page 83... ...
Progress to date is well illustrated by the remarkable strength-to-density ratio of aromatic polyamide polymers; development of other impressively strong polymers of lower cost can be expected. Polymer adhesives are already replacing rivets in many joining applications, and polymer-fiber composites are replacing metals in many FIGURE 3.3 Fracture surface of silicon carbide-reinforced alumina.
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From page 84... ...
Studies should address the physical and chemical dynamics of surfaces, interracial regions of polymer blends and alloys, polymer melts in confined geometries, and crystal-amorphous interfaces in semicrystalline polymers. These interfaces control adhesion, wetting, colloidal stabilization, and mechanical properties, and they are intimately involved in the failure and deformation of polymers.
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From page 85... ...
The result is a "molecular composite," akin to a fiber-reinforced composite with the individual rigid macromolecules acting as the "fiber." The uniform dispersion creates a polymer mixture of long-range molecular order and, thus, with no interfaces. Molecular composites are expected to have superior impact resistance, fracture toughness, and compressive strength, while offering opportunities for novel combinations of electrical and optical properties.
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From page 86... ...
The chemical dynamics of curing polymeric matrix composites is fairly well understood, at least in a qualitative sense, but very little is known about the reactions occurring during the production of metal matrix and ceramic matrix composites. Filling these serious gaps in understanding would advance efforts to develop fabrication methods to achieve the property improvements that are theoretically possible for a particular combination of materials.
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From page 87... ...
Ko, Fibrous Materials Research Center, Drexel University.) Unless manufacturing difficulties are overcome, many promising composites, especially ceramic and metal matrix composites, may never fulfill their commercial promise.
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From page 88... ...
Optimization or development of individual electronic materials must be accompanied by fundamental research into how materials interact with one another. For example, information processing and communication to the external world take place through metal lines connecting semiconductor chips, logic and memory circuits, ceramic or polymer chip-carrier modules, and polymer-fiber composite cards and boards.
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From page 89... ...
A wide range of technologies that use these features are being investigated, such as data transmission over optical fibers, holographic image transfer, and optical storage media on disks or tapes. One of the most important features of these materials is the number of permutations possible between elements in the group III and group V families.
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From page 90... ...
Figure 3.7 illustrates extremely small silicon structures prepared by lateral thermal oxidation processes.
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From page 91... ...
Panels a, b, and c show transmission electron microscope (TEM) images of isolated single-crystal silicon islands prepared by the lateral thermal oxidation of single-crystal silicon trench structures capped with silicon nitride.
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From page 92... ...
Polymer layers have intrinsically lower dielectric constants and preparation temperatures, can be applied onto a surface with controllable flatness, and are compatible with lithographic processing of metal transmission lines. Mechanical stability and heat dissipation are areas requiring further research, but hybrid ceramic-polymer layers are now being produced in which the polymer layers are processed on top of or adjacent to chips when metal lines of the highest density and highest perfor~ance are required.
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From page 93... ...
Research issues include the stability of the contacts made to the semiconductors; interdiffusion between, on the one hand, metal layers, contacts, and conductor lines, and, on the other hand, the structures on the chip and substrate; reliability at the high current densities resulting from finer lithography; structural and chemical compatibility with the insulating materials that separate the wiring layers; and the effects of environmental attack. New metal deposition processes using vapor transport and radiation enhancement are being developed to expand the list of candidate metals and diffusion barriers that can be implemented.
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From page 94... ...
(Courtesy IBM Corporation.) MAGNETIC MATERIALS Magnetic materials have received less public attention during recent decades than have semiconducting or superconducting materials.
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From page 95... ...
Control of magnetic surfaces and interfaces is also the basis for synthesis of new artificial magnetic materials multilayers and superlattices. Early experiments have already shown complex couplings between the different magnetic layers, which could be the basis for new properties not available in bulk materials.
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From page 96... ...
These and many other remarkable developments point to a remarkable richness of research opportunities and a large impact on applications in the field of magnetic materials. PHOTONIC MATERIALS Photonic materials are now where electronic materials were in the early 1950s at the very beginning of a steep growth curve.
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From page 97... ...
Substantial advances have been made in many other areas of photonics, such as optical phase conjugation, two-wave mixing and energy exchange, erasable optical memories, high-power optical materials, gradient-index coatings, phase transition materials, flat panel displays, and optical window materials. The development of suitable high-performance materials is the key to success in all these areas.
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From page 98... ...
If the speed advantage offered by photonics over electronics is ever to be matched at least by parity in the spatial domain, materials or structures must be found that permit optical modulation over micron rather that millimeter distances. Increasing the nonlinear optical response of photonic materials is thus a fundamental challenge to materials scientists and theoretical physicists.
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From page 99... ...
(Courtesy AT&T Bell Laboratories.) SUPERCONDUCTING MATERIALS The recent discovery of high-temperature superconductivity in ceramic oxides is one of the most dramatic breakthroughs in physics and materials science in recent decades.
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From page 100... ...
These superconducting materials, which so far have shown low to modest transition temperatures, have not captured the public or wider scientific imagination. However, their underlying physics and the materials issues associated with them are of great complexity and interest.
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From page 101... ...
The new superconductors have already been prepared in the form of wires, thin films, and single crystals, in addition to sintered granular material. Yet many challenges remain: the ceramic or polycrystalline material suffers from low critical current densities (the highest current the material can carry before losing its superconductivity)
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From page 102... ...
But basic information on high-quality single crystals has only begun to appear, and vital experiments such as neutron scattering still await the availability of large enough crystals. Although many theories have been proposed, most theorists agree that more experimental information is needed before a consensus will begin to emerge.
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From page 103... ...
The products that incorporate biomaterials are extremely varied and include artificial organs; biochemical sensors; vascular grafts; artificial hearts; disposable materials and commodities; drug-delivery systems; hybrid artificial organs; dental, plastic surgery, ear, and ophthalmological devices; orthopedic replacements; prostheses and repairs; wound management aids; and packaging materials for biomedical and hygienic uses. The success of already developed materials, notably of implants and joint replacements in older patients, has helped create an increased demand for these devices in all age groups.
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From page 104... ...
Some of the key issues for these materials are adsorbability and its measurement and definition, the effects of absorption on the tissue site, the effects of enzymes and other biologically active materials on the adsorbability of the polymers, the biological effects of degradation products, the effects of sterilization on functionality and degradability, the behavior of labile release agents incorporated into the polymer, and the effects of substances on wound healing.
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From page 105... ...
In addition, research will be required to enable understanding of the biological effects of degradation products of adhesives, the biological pathways that interact with degradation products and the effects of degradation products on those pathways, the effects of processing and sterilization on biodegradation, and the effects and control of wound healing. Metals, Ceramics, and Glass Metals and metal alloys are broadly used in biomedical applications, such as in orthopedic replacements, plastic surgery, and sutures.
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From page 106... ...
The biological effects of degradation, the effects of biological materials such as enzymes, and the effects of processing and sterilization on the behavior of synthetic biomaterials are also important issues. For bioabsorbable ceramics, which are projected for use in orthopedics, research should focus on the measurement of bioabsorption; the influence of particular tissue sites; the effects of the ceramics on calcification, bone formation, and wound healing; and the ramifications of incorporating labile release agents into the ceramics.
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From page 107... ...
Creation of surfaces with affinities for specific proteins will probably be a major focus for the development of new polymers. Long-Term Opportunities Related to Biomaterzals The incorporation of biochemical and pharmacological activity into medical devices is an area that is already undergoing rapid development.
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From page 108... ...
If such an instrument can indeed be applied to biological macromolecules, viruses, and cell surfaces, it will transform research and understanding in these areas. There has been considerable progress in adapting micron- and submicronscale processes commonly used in the electronics industry to biological materials.
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From page 109... ...
From strip casting of metals through the synthesizing of new nonlinear optical media in photonic materials to improving the critical current requirements of the new high-temperature superconductors, synthesis and processing are crucial for the continuing advancement of those technologies that depend on these functional properties. Numerical simulations, modeling, and calculation of properties from first principles are increasingly used by scientists and engineers as means to shorten the time to develop understanding and applications of materials.
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