Abstract: The ultrahigh-strength steels used in aerospace applications are primarily alloys developed 25 or more years ago, which would seem to illustrate the conservatism of alloy producers. However, the now widespread use of AF1410, which was developed in the mid-1970s, suggests that new alloys will be adopted for aerospace applications if their mechanical properties are markedly superior to incumbent alloys. Given the excellent properties of the secondary hardening steels such as AF1410, it would appear that the greatest need is for alloys with yield strengths of 1,725 MPa and higher, which have improved fracture toughness and resistance to stress-corrosion cracking. Control of sulfide-type inclusions, coupled with low sulfur levels, may be a means of achieving quite reasonable toughness at high strength levels. Improving resistance to stress-corrosion cracking appears to be a more difficult problem, but it is hoped that a general solution for the case of intergranular fracture by stress-corrosion cracking will arise from ongoing fundamental studies of the effects of segregating impurities and alloying additions on grain boundary cohesion.

Abstract: Despite years of effort, researchers have been unable to develop a high-temperature niobium-base alloy with the ability to form a protective oxide scale. Although some of the alloys tested have potentially useful properties, the alloying elements usually act to the detriment of at least one property. Currently, niobium-base alloys are protected from high-temperature oxidation with a highly reliable silicide coating. This article reviews the efforts to develop oxidation-resistant alloys and summarizes the results of recent research on oxidation-resistant niobium-base intermetallics.

Abstract: The development of composite coating technology has progressed such that applications can now be found in general consumer products, and more applications are on the horizon. This advancement is driven not only by the unique characteristics of the composite coatings, but because their longer lifetimes and increased mean times between failures make the replacement of classical coatings cost-effective. Models have been developed that yield a quantitative description of the process under well-formulated experimental conditions. The complete picture of the codeposition process and the exact nature of the particle-cathode interactions are still under debate, but hopes are high that they can be uncovered in the near future.

Abstract: Sodium jarosite is readily converted into hematite by hydrothermal reaction at temperatures greater than 220°C. Although the initial acid and ferric ion concentrations must be kept low to avoid the unwanted formation of Fe(SO4)(OH), the conversion reaction is unaffected by modest concentrations of ZnSO4, FeSO4 or Na2SO4. Hematite seeding is desirable to promote the reaction and to stabilize the reaction system. The hematite conversion product will likely contain ∼0.5% Zn and ∼2% SO4; most of the arsenic in the jarosite will remain with the hematite.

Abstract: Low-cycle fatigue life of turbine engine disk alloys is determined by the initiation and propagation of fatigue cracks. Performance improvements can be achieved through the combination of clean melting technology, to reduce the defect size, and a new generation of high-strength superalloys with fatigue cracking resistance. Metallurgical control of fatigue crack propagation in high-strength superalloys becomes feasible only through a clear understanding of the fatigue cracking mechanism, as well as the micro-structure/property relationships. Many metallurgical parameters have been identified to control the fatigue cracking resistance at high temperatures. One of the most effective methods, applicable to all high γ′ content superalloys, is to modify the grain boundary structure by means of a controlled cooling from a supersolvus solutioning. The precipitation reaction occurring on the grain boundaries during cooling generates a serrated structure that exhibits a good stress oxidation resistance for fatigue cracking.

Abstract: As the performance requirements of structures and devices increase, new and improved materials and processes are required. One such technique is thermochemical processing, which involves the use of hydrogen as a temporary alloying element. Thermochemical processing significantly enhances both the fabricability and mechanical behavior of titanium alloys.

Abstract: The impurities in copper anodes occur both in solid solution in the copper metal matrix and in discrete inclusions at the copper grain boundaries. During electrorefining, all the impurities undergo extensive chemical and/or morphological changes. These changes impact significantly on anode passivation, cathode quality, electrolyte purification and, of course, the subsequent recovery of by-products from the anode slimes. Recently, mineralogical studies have been undertaken to characterize the various impurities and elucidate their transformations during copper electrorefining.

Abstract: The two most widely industrialized techniques for aluminum refining are the three-layer electrolytic refining process and the segregation process. The three-layer process uses molten salt electrolysis to produce aluminum of greater than 99.99% purity. The segregation process produces aluminum of 99.98–99.99% purity. Although aluminum refined by the segregation process has a somewhat lower purity than that produced by the other methods, the segregation process has become increasing common since it consumes less energy. Ultrahigh-purity aluminum (99.9999%), which has uranium and thorium impurities reduced to less than 1 ppb, can also be produced.

Abstract: There are numerous viable approaches to the treatment of anode slimes from electrolytic copper refining. Of particular interest in the treatment of slimes are the behavior and recovery of selenium. The understanding of the process chemistry involved in the treatment of anode slimes should be aided considerably by recent work on the formation and characterization of slimes. Most promising is a direct furnace treatment of decopperized and detellurized slimes, in which selenium is volatilized as the dioxide, impurities such as lead are slagged off, and a high-quality dore metal is obtained.

Abstract: This book covers the following topics: metals and materials processing, ironmaking and steelmaking. The paper presented include: Processing and oxidation protection of carbon/carbon composites and Coal-based ironmaking via melt circulation.

Abstract: In the lost-foam casting process, liquid metal is poured directly onto a refractory-coated, foamed polymer pattern which is buried in loose sand. The polymer pattern undergoes thermal degradation and is gradually replaced by the molten metal, which solidifies and produces the casting. The inherent operating advantages of this innovative technique have generated considerable interest among casting manufacturers. Currently, the process is being utilized to manufacture a wide variety of ferrous and nonferrous components catering primarily to the automotive industry. Because the process is relatively new, there is a compelling need to quantify the influence of process parameters on microstructure and mechanical properties. Furthermore, the interaction of the thermal degradation products with the solidifying metal may produce several unique defects in the casting.

Abstract: A program to implement real-time sensing and control of spray-formed preform conditions is underway at the David Taylor Research Center. The objective of the program is to develop sensor and control technologies that can be used to monitor critical process conditions and modify operational parameters during the spray forming of components. This task has been divided into two phases. The first entails developing sensors and controls to monitor and correct simulated process conditions. In the second phase, the selected sensors and controls will be combined with actuators, thereby integrating research center equipment and enabling the production of nonsymmetric preforms.

Abstract: Experimental and mathematical consideration of microstructural coarsening during liquid-phase sintering has resulted in kinetic laws which define grain size to the third power as being proportional to the isothermal sintering time. Despite thoseprior efforts, the situations typical to liquid-phase sintering are poorly treated by the current models because the models assume a structure consisting of widely separated spherical grains (zero contiguity). No experiment had been completed to quantify the effect of contiguity on the growth kinetics. In order to do this, the contiguity and growth rates of tungsten grains in a liquid matrix at 1,750K were measured in sintered heavy alloys of 78,83, 88,93 and 98 wt.% Wbalanced with 70Ni-30Fe. The observed grain growth rates were compared with the theoretical predictions of the LSW theory and volume fraction modified theories. By modifying the volume fraction effect with a contiguity term, a model was produced that closely followed the experimental results.

Abstract: Recent advances in the ion implantation process have shed light on the underlying mechanisms for improved surface properties of titanium alloys. Ion implantation of reactive species such as carbon or nitrogen creates hard-phase carbide or nitride precipitates which impart surface hardness to titanium alloys. Concurrently, the ion implantation process creates disorder in the surface of titanium and destroys the grain boundaries, and is responsible for lower friction of the surface. The ion implantation process duplicates shot peening on a microscopic scale and imparts compressive stress to the surface of the titanium, thereby improving high-cycle fatigue life of titanium components. Ion implantation also improves the resistance to corrosion and chemical etching of titanium surfaces.

Abstract: The Second International Conference on Semi-Solid Processing of Alloys and Composites will be held on June 10–12, 1992, at MIT in Cambridge, Massachusetts.

Abstract: Biotechnology is an alternative process for the extraction of metals, the beneficiation of ores, and the recovery of metals from aqueous systems. Currently, microbial-based processes are used for leaching copper and uranium, enhancing the recovery of gold from refractory ores, and treating industrial wastewater to recover metal values. Future developments, emanating from fundamental and applied research and advances through genetic engineering, are expected to increase the use and efficiency of these biotechnological processes.

Abstract: Nb, the lowest-density refractory metal, is of great interest for aircraft propulsion applications whose service temperatures are of the order of 1100-1150 C; the major impediment to such applications has thus far been the difficulty of fostering inherent, rather than coating-imparted oxidation resistance in Nb-base alloys. An additional impetus for Nb alloy development is the need for structural materials applicable to space nuclear power reactors, such as the SP-100 that is currently under development. Significant development has recently occurred in the use of Nb alloys as matrices reinforced by TiC particles or by W fibers.

Abstract: An evaluation is made of the development status and prospective performance advantages and cost reductions obtainable through the application of state-of-the-art Al-Li alloys to naval aircraft airframes and ultrahigh strength Ni-Co alloy steels to their landing gears. Structural weight fractions are expected to be reduced by 8-10 percent through substitution of high-stiffness Al-Li for conventional Al alloys. Ni-Co alloy steels enhance landing gear damage tolerance and resistance to environmental degradation, without associated weight penalty, when supplanting conventional low-alloy steels. Both materials are judged ready for immediate application to existing and next-generation U.S. Navy aircraft. 8 refs.

Abstract: In the operation of a typical mini-mill, about 1 to 2% of each charge to the electric furnace is converted to dust, which is collected as particulate matter in the baghouse system. The dust is considered hazardous because it contains lead and cadmium. However, it also contains large, recoverable quantities of zinc and iron. To make the dust environmentally acceptable and to recover the valuable content, pyrometallurgical processing was studied on a laboratory scale. The experimental results show that successful removal of zinc, lead and cadmium and considerable upgrading of iron from the electric furnace dust have been accomplished, and that a nonhazardous inert slag have been formed by pyrometallurgical processing at two temperatures.

Abstract: In recent years there has been renewed interest in the development of tungsten alloys for space power and advanced aerospace propulsion systems. Tungsten alloys have great potential for ultrahigh-temperature applications because of their thermal capabilities and exceptional high-temperature mechanical properties. Recent investigations of second-phase particle-strengthened W-Re alloys show that fine HfC and ThO2 particles significantly improve the high-temperature tensile and creep properties of tungsten alloys. The superior high-temperature strengths of these alloys above 2,000K are attributed to the strong interaction between these second-phase particles and dislocations as well as excellent stability of these particles.

Abstract: In many fracture situations, the quantification of fractography may be useful in linking idealized fracture mechanics models of cracks with experimental studies of fracture. The specific applications demonstrated herein derive their mathematical basis from an earlier theory of stereology of fracture derived by the author and consisting of twelve basic theorems dealing with areal, lineal, volumetric, and feature count analyses of fractures. Correlations are established between some basic measures of fracture resistance under either monotonic or cyclic loading for five areas of practical interest. The basic postulate made here is that the micromechanisms of fracture affect the measures of fracture resistance, leaving characteristic information to be derived from the fracture topography, the plastic zone, acoustic emissions and heat. Such information, if adequately collected and correctly interpreted, may be useful in failure interpretation and prevention. In combination with probabilistic fracture mechanics, this information will pave the way toward predictive quantitative fractography.

Abstract: This article briefly describes the classical processes of dore furnacing and refining and identifies the major problems and costs associated with these methods. The process chemistry of the wet chlorination of slimes is then described, followed by an examination of the various unit processes employed to recover the metal values from slimes. Finally, a conceptual treatment of slimes is presented and compared to conventional processes.

Abstract: Currently, most high-technology materials are inspected for quality after processing, with very low yields, great variability and high costs. Intelligent process control potentially enables much greater yields of high-quality materials, which will reduce the designers’ inhibitions about consideration of new, emerging materials in the design of new products, and enable their earlier intro-duction into systems and their components. Development of concurrent engineering tools and systems, with the development of intel-ligent processing of materials technology as a cornerstone to concurrent engineering, will then lead to long-term changes in the way that organizations conduct product development. Potential benefits include a large reduction in the time required to develop new products, increased quality and reduced life-cycle costs.

Abstract: Extensive batch and continuous testing has been completed using a high-temperature, nitric acid pressure leach (Redox) process for oxidizing the refractory gold-containing arsenopyrite tailings presently stockpiled at Snow Lake, Manitoba. This process has achieved up to 99% oxidation of the arsenopyrite compound and precipitated more than 90% arsenic into a stable iron-arsenic compound (resembling ferric arsenate) in less than eight minutes of overall retention time at temperatures of 195–210°C and an oxygen overpressure of 345 kPa. The oxidation step then exposes the contained gold, allowing a recovery of 91.5% in a standard carbon-in-leach circuit. The main advantages of this process are fast reaction rates, the high proportion of arsenic precipitated, and the stability of the precipitate.

Abstract: A variety of feed materials may be subjected to pressure oxidation of their sulfide content to liberate gold contained therein for later recovery by cyanidation. Energy is required to pump the feed slurry into the pressurized reaction vessel, to heat the slurry to the reaction temperature, to supply oxygen, and to agitate the slurry and disperse the oxygen. At a certain grade of sulfide, depending on the mineralogy, the process becomes autothermal, obviating the need for heating during normal operation. The sulfide level required for autothermal operation can be reduced by providing one or more stages of heat recovery, wherein steam is flashed from the product and used to heat the feed. The production of oxygen required for the reaction is power intensive, and any steps improving oxygen utilization are beneficial.

Abstract: Metal-matrix composites may offer better damping properties than unreinforced alloys. Because damping properties (and metal-matrix composites) are becoming important in airframe design, the damping capabilities of a number of aluminum-matrix composites were measured over a wide range of frequencies at low strain amplitudes, using a new laser vibrometer technique. Silicon carbide and alumina reinforcements resulted in a material with damping properties similar to that of unreinforced aluminum 6061-T6, but unidirectional and planar-random graphite continuous-fiber reinforcements increased the damping by 5 and 14 times, respectively. The increased damping of the continuous fiber composites is attributed to the absence of interfacial reaction resulting from the high-pressure infiltration method used for their manufacture.