Materials and Man's Needs Materials Science and Engineering (1974) / Chapter Skim
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Opportunities in Material Research
Opportunities in Material Research
Pages 97-153
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From page 97... ...
the priority that should be given to applied research and engineering in a given materials specialty (out of a list of 463 to assure progress toward a national objective (nine Areas of Impact and S2 Subareas)
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From page 98... ...
Respondents were asked also, in connection with each materials specialty, to assign priorities to basic research problems not necessarily identified with any particular area of impact. The results differed somewhat in emphasis from those for applied research, but the two overlapped considerably; problems described under the basic research heading were often the same as those described by others under the applied research heading.
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From page 102... ...
Process;es Testing: nondestructive testing; characterization; analysis; interaction with optical, acoustical, and other forms of radiation. Joining: adhesives; welding.
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From page 103... ...
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From page 105... ...
· Materials: ceramics; composites; glass and amorphous; plastics; prosthetic. · Processes: testing and nondestructive testing.
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From page 106... ...
felt that basic research in this field might be expected to yield diminishing returns today, perhaps because of extensive research in the past. Materials like concrete, asphalt, and wood, in contrast, have not been subjected to comparable basic research, so that the corresponding fundamental understanding may not yet be advanced to the point where research opportunities are recognizable, even by experts in the field.
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From page 107... ...
The mechanism of stress corrosion probably differs in detail from system to system. Problems pertinent to many systems include the role of mechanical fracture; the effect of stress on the rate of anodic dissolution; continuous versus discontinuous cracking; the relevancy of continuum mechanics as opposed to atomistic analyses of crack propagation; the effect of defect structure and of chemical composition and distribution at the macro and micro levels in the metal; and the role of hydrogen generated at the crack tip.
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From page 108... ...
More specifically, the following must be examined: the crystallography of surface films and the factors that determine crystal size and transitions between the crystalline and amorphous state; the defect structures; the conductivity of, and diffusivities within, the films and their effects on filmgrowth kinetics; the mechanical properties of corrosion films; and the thermodynamics and kinetics of the transformation from one corrosion product to another during the high-temperature gaseous corrosion of complex alloys. Such studies could lead to new alloys with better corrosion properties, or to less costly compositions.
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From page 109... ...
The success of empirical efforts to devise better fire retardants for flammable materials has apparently peaked. Recent progress has mainly involved optimizing the forms and amounts of antimony, halogen,
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From page 110... ...
At this interface between the animate and inanimate worlds, many questions must be answered at a most basic level. Among typical research topics in the field is the surface architecture of biomaterials, including surface energy and changes that can result from contact with body fluids.
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From page 111... ...
Glass ceramics based on the calcium phosphate glasses are potentially useful in areas that include degradable orthopedic devices. Only a small research effort is under way on these materials, however, and more seems warranted.
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From page 112... ...
Another significant field is membranes for kidney dialysis, The big problem here is cost, since membranes currently exist that maintain life. As the emphasis shifts toward full rehabilitation of patients, however, there will be a need for a totally implantable artificial kidney of superior diffusion and surface properties as well as acceptable cost.
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From page 113... ...
Fundamental understanding of fracture mechanisms is important to the design of safer, more reliable engineering structures. Relatively sophisticated theories of fracture, which take into account polycrystallinity or microstructure, have led lately to better testing procedures and tougher materials.
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From page 114... ...
Another active area is the use of computers to average individual dislocation reactions into macroscopic plastic deformation. Dislocation theory is now being applied through analytical models relating the dynamic behavior of dislocations and point defects to mechanical behavior, including such practical applications as creep and hot pressing of crystalline solids.
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From page 115... ...
Indeed, difficulty in large-scale processing is a major obstacle to widespread use of other superconductors having relatively high transition temperatures, such as niobium-tin. Stoichiometry and atomic order are critical material parameters, so that basic research in phase equilibria and kinetics of phase transformations is a necessary prelude to new or improved processing techniques.
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From page 116... ...
Fiber-resin composites usually consist of glass fibers in an epoxy or polyester resin. Many metal-matrix composites have been studied, including steel or boron fibers in aluminum, aluminum oxide fibers in iron, and tungsten fibers in copper or stainless steel.
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From page 117... ...
Structural analysis of these complex materials is still in its infancy. Other advances to be sought include better joining methods, higher resistance to erosion by rain and dust, greater toughness, and the development of structural-property data banks.
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From page 118... ...
Fibers now wider development, including glass, have potential for easy, low-cost manufacturing. Glass-coated aluminum oxide fiber, for example, could have four times the specific modulus of conventional glass fibers and be made by a relatively inexpensive process.
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From page 119... ...
The physicochemical properties of these materials in relation to the other constituents of concrete require thorough investigation. Reinforcing materials such as steel rods and fibers increase the tensile strength and toughness of concrete.
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From page 120... ...
Major questions to be answered in the development of protective coatings include the influence of alloying additions on the diffusivity of the constituents; on the thermodynamics and kinetics of formation of competing oxide films; on competition between internal and external oxidation; and on vacancy behavior and its possible role in spelling. Processing offers many possibilities for enhancing the properties and performance of superalloys.
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From page 121... ...
The general approach is to develop new compositions and processing techniques that permit superior properties to be achieved through close control of composition, density, and grain structure. Thus, increasing emphasis will be placed on the relationships among composition, microstructure, and material properties.
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From page 122... ...
Recent studies have indicated that improved high-temperature properties may be possible in complex systems such as solid solutions of nitrides and oxides of silicon or aluminum; here, high density can be achieved by sintering at relatively low temperatures. Accordingly, ceramics based on silicon-aluminum-oxygen-nitrogen and related systems are promising candidates for structural materials Composite materials containing ceramic fibers represent a way to combine a high-strength fiber with a ductile matrix, but the interface-bonding problem inhibits full realization of their potential.
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From page 123... ...
Investigations of brittle fracture, ultimate strength, notch sensitivity, and static fatigue have led to more efficient use of the intrinsic strength of glass products. The fundamental limits on the mechanical properties of the material, however, remain unknown.
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From page 124... ...
This discovery has produced intense activity in preparing glass fibers of precise dimensions that are extremely pure and free of light-scattering and light-absorbing defects. The work has underscored the need for improved ultrapurification processes for glasses and chemical compounds.
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From page 125... ...
A host of polymers are glassy at ordinary temperatures and many of them, like the inorganic glasses, have valuable optical properties. Fundamental work with monomers or combinations of monomers to yield polymers with desired properties, such as a particular optical absorption or refractive index, has been highly productive and can be expected to be so in the future.
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From page 126... ...
Most new processing techniques are developed for specific materials and applications, but basic research in this connection should spawn new approaches.
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From page 127... ...
Another new technique, rheocasting, involves casting metal that is partially solidified; high fluidity is maintained by vigorous mechanical stirring. The lower pouring temperature reduces mold erosion, centerline shrinkage, and freezing time.
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From page 128... ...
The results should lead to more economical utilization of materials. In joining methods like diffusion bonding, which is used to fabricate metal-matrix composites, progress requires further knowledge of adhesion as influenced by solid-state reactions under conditions that include heat, pressure, and surface films.
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From page 129... ...
The equilibrium form of Nb3Ge, a compound of niobium and germanium, for example, becomes superconducting at 7 K; splat cooling yields a metastable form of the compound whose transition temperature is 17 K Splat cooling also produces metallic glass alloys that, mechanically, are among the strongest of the nonferrous materials.
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From page 130... ...
The high creep rates of this class of materials currently exclude them from many applications, but commercial rubbers could result from proper choice of monomers and the development of the necessary polymerization techniques. Cold forming of both amorphous and crystalline polymers is an active field at present.
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From page 131... ...
Testing is required for quality control; for establishing standards to ensure in-service durability, reliability, and safety; for sensing in production processes and automation; and to avoid environmental degradation. In a 1967 reports Characterization of Materials, the Materials Advisory Board stated, "Attempts to provide the superior materials that are critically needed in defense and industry are usually empirical and often wasteful of efforts and funds.
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From page 132... ...
Other well-known examples are x-ray diffraction, the optical and electron microscopes, and spectrochemucal analysis. The realization that the composition of the surface of a solid usually cannot be inferred from measurements of the bulk material has stimulated the development of new spectrometric instruments for surface analysis.
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From page 133... ...
Nondestructive testing is among the areas of materials technology requiring urgent attention. In the past, nondestructive testing generally meant testing only for geometric size, defects, and some mechanical properties, but it should be interpreted much more broadly -- testing for composition, microstructure, and the full range of physical properties.
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From page 134... ...
This progress has come largely because the single-crystal state of matter lends itself to theoretical analysis, particularly of electronic properties. Only recently have basic scientists begun to turn to the more complex forms of matter, the glassy, polycrystalline, and polymeric states found in most practical materials, particularly those employed structurally.
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From page 135... ...
But such calculations, improved by the relatively large computers that were appearing then, have led to strikingly detailed insights into the electronic and optical properties of semiconductors. The calculations were steadily refined, particularly for semiconductors, and extended to other crystalline materials.
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From page 136... ...
But stating the problem this way makes us realize just how primitive is our quantitative knowledge of such basic matters as interatomic forces, chemical bonding, and configurational interactions. Besides the need for theoretical progress, we shall continue to depend on sensitive experimental determinations of such basic descriptions of the solid as the band structure, the phonon spectra, and the Fermi surface with which to test the soundness of theoretical calculations.
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From page 137... ...
If we understood melting properly, we would have much more insight into the roles of interatomic forces, cooperative interactions, and related phenomena in determining the structure and stability of solids. The microscopic mechanisms that bring about phase transitions are an object of intense research at present, and part of the deep atraction of this study lies in the remarkable universality of certain general phenomena in the vicinity of higher-order phase transitions, regardless of the type of material or even of the type of phase transition -- the liquid-gas (at the critical point)
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From page 138... ...
Less is known about the glassy or amorphous state of matter than about crystalline matter. But the possibility that the completely disordered state offers the next most tractable model after the perfectly ordered or crystalline state is attracting widespread theoretical and experimental attention.
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From page 139... ...
In addition to continuing debate over the detailed changes occurring in bond structures on passing from the crystalline to the glassy state, there are questions concerning possible electronic phase transitions and high electric-field transport effects in semiconducting glasses. The correct interpretation of optical-absorption and photoconductivity spectra in terms of electronenergy states is by no means clear; nor are the mechanisms of the converse radiative recombination transitions that give rise to luminescence.
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From page 140... ...
Despite the enormous amount of work that has been done on impurity effects in semiconductors, for example, we lack a general theory of the effects of impurities on material properties at the microscopic level. The dilute limit, while theoretically simplest, is experimentally difficult, while the converse is true for high concentrations of impurities.
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From page 141... ...
Optical studies have suggested the presence of excitonic molecules and have stimulated speculation on the possibility of creating, within a crystal, a fluid or perhaps even a solid phase composed entirely of electron-hole pairs. Another continuing controversy concerns the role of interstitial impurities in increasing the low-temperature yield strength (thereby enhancing brittleness)
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From page 142... ...
Surface properties are related also to the properties of the underlying bulk material, but in ways that are not often clear. And though bulk properties, by-and-large, are understood in principle, if not always in detail, this is not true of many of the surface properties, where the broad outlines of the phenomenology are only now being drawn.
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From page 143... ...
It has been shown recently that various surface states on semiconductors correlate with various surface structures as revealed by low-energy electron diffraction. Surface nucleation, vapor deposition, adsorption, and surface contamination, topics with clear practical significance are currently being investigated in detail for a variety of systems, with emphasis on the simpler systems.
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From page 144... ...
Infrared reflection spectroscopy gives information about chemical bonding, and insights concerning deep electronic levels can be obtained from the analysis of Auger spectra. The techniques developed for surface research, such as ion mass analysis and Auger spectroscopy, are providing the best, and often the only, methods for investigating materials problems associated with thin films, grain boundary segregation, interdiffusion phenomena, and trace analysis.
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From page 145... ...
The elucidation of catalytic processes is not detailed in most cases. Considerable (ualitative insight is available, but the roles of surface structure, surface defects, surface geometry, surface electronic properties, and even the bulk properties of catalysts have not been clarified in detail.
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From page 146... ...
There is much ignorance regarding the effects of surface stress, defect structure, and nonequilibrium conditions on the reactivity of metal surfaces, and these effects are of major importance in the performance of materials One- and Two-Dimensional Systems. Until recently, calculations of physical phenomena in one- or two-dimensional systems were considered to be mainly of academic interest.
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From page 147... ...
Particularly intriguing is the effect of a microscopic upper limit to the interaction distance in certain directions on the critical properties near phase transitions in lower dimensional systems. While some magnetic transitions have been studied in this context, virtually nothing has been done on structural, order-disorder, or
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From page 148... ...
The fabrication of structures that extend only a few tens of angstroms in one or two directions has made clear the opportunity for more careful experiments and sophisticated interpretations in the physics of such structures. Two indicative examples are the observation of a nearly fivefold increase in the superconducting transition temperature in thin films of aluminum and the increased sound-attenuation coefficient of small-diameter glass fibers.
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From page 149... ...
In view of the primitive state of theoretical concepts and analytical procedures for dealing with ordinary glasses, it is not surprising that we are a very long way from being able to go the whole distance of determining from first principles the fundamental properties of the polymeric molecules themselves and then the physical properties of the macroscopic plastic materials. Collective Behavior.
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From page 150... ...
Since a single elementary excitation involves the participation of all the atoms in the system, the concept is quite powerful in elucidating the cooperative behavior among large numbers of particles that results in a particular phenomenon or property. As was indicated briefly in the discussion of phase transitions, the collective-mode concept has been fruitful in describing even anomalous material properties.
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From page 151... ...
Similar mathematical techniques have been employed to describe elementary excitations in the paramagnetic (disordered) phase of a spin system.
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From page 152... ...
Lasers and negativeresistance semiconductor devices are familiar examples of nonequilibriwn physics in action. Recent progress in clarifying the transient and threshold behavior has illuminated analogies with equilibrium higherorder phase transitions.
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From page 153... ...
153 fores te of what might be in store is the use of these fast laser pulses to study short-lived excited states of radicals and molecules, with consequent insights into the detailed sequence of atomic or molecular events taking place in chemical reactions .
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