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By A. M. Gaudin

CHANGES in industrial practice, in plant design, and in research methods which are so clearly to be seen on every hand, have affected the mineral industry as well as others. In particular, ore dressing has passed through a revolution in practice brought about by the introduction of flotation and other quasi-chemical methods, until it has ceased to be solely the mechanical preparation of ores. In fact, the term "ore dressing" itself is obsolescent, and "mineral dressing" has been growing in popularity. This assures adequate recognition of the fact that mineral substances other than ores, e.g. coals, clays, and cement rock, are treated by the same general methods. As a result of these industrial changes it was felt that a complete rearrangement of the curriculum and laboratories at the Massachusetts Institute of Technology would be ad-vantageous. Such a rearrangement would allow instruction and research to proceed in wider accord with industrial evolution and the needs of our times.

Jan 1, 1942

By C. L. Meyers, J. L. Lytton, T. E. Tietz

The recovery of tensile flow stress of 99.995-pct Al and Al-1 pct Mg alloy was investigated using a fractional recovery parameter. Tensile strainirg was conducted at room temperature, and recovery treatments were made in the range from 80° to 200°C. Equal values of fractional flow stress recovery were found to result in equivalent structural states. Identical recovery treatments were found to produce constant values of fractional flow stress re covery, independent of prestrain. The activation energy for recovery of the 99.995-pct A1 between 80" and 200°C was found to be 23,000 +2000 cal per mole, and the activation energy for the Al-1 pct Mg alloy was 27,500 cal per mole. 1 HE degree of recovery of a cold-worked metal may be studied by measuring the changes which take place in any of a number of properties. Some of the properties which have been used by past investigators include X-ray diffraction phenomena, electrical resistivity, hardness, creep strength, elastic limit, and flow stress. Despite the apparent preponderance of such studies, little is known concerning the effect of recovery on the strength of metals except as deduced from changes in various types of hardness measurements. Furthermore, little information is avail- able concerning the effects which specific solute atoms have on the recovery process. Limited studies have indicated that in some cases solid-solution additions greatly decrease the rate of recovery,' whereas in at least the case of magnesium additions to alluminum an increase in the rate has been reported.2 The purpose of this investigation was to determine the effect of a 1 pct Mg addition on the recovery of high-purity aluminum. Because of the particular interest in the effect of solute additions on the recovery behavior as related to mechanical properties, the degree of recovery was evaluated in terms of tensile flow stress. For the purposes of this study, a recovery process shall be defined as any process, short of recrystallization, whereby the properties, of work-hardened metals tend toward their values ill the unstrained state. EXPERIMENTAL PROCEDURE Test Materials. The materials used in this study were a 99.995-3 A1 and an Al-1 pct Mg alloy made from high-purity base metal. The high-purity aluminum contained the following wt pct impurities: 0.001 pct Cu, 0.002 pct Fe, 0.001 pct Si, and 0.0004 pct Mg. The Pil-1 pct Mg alloy contained 0.001 pct Cu, 0.002 pct Fe, 0.003 pct Si, and 0.99 pct Mg. Both materials were obtained in the form of as-rolled 0.125-in.-thick sheets, from the Alcoa Research Laboratories, New Kensington, Penn. Tensile specimens were cut from these sheets with the longitudinal axis in the rolling direction. Both materials were recrystallized in a molten salt bath; the high-purity aluminum at 450° C for 20 min and

Jan 1, 1962

By J. Marin, H. A. B. Wiseman

This paper presents results of an experimental study dealing with the plastic stress-strain relations of aluminum alloy 14s-T6 subjected to combined biaxial tension and compression stresses. Plastic stress-strain relations for both constant and various types of variable stress ratios were determined and a comparison made with the simple flow theory of plasticity. THIS investigation was undertaken for two main purposes: 1—to obtain plastic stress-strain relations for Alcoa 14s-T6 when subjected to various combinations of biaxial stresses, and 2—to determine the validity of the flow theory in predicting plastic stress-strain relations for combined stresses. The biaxial stresses used were tension combined with compression. These stresses were produced by subjecting a thin-walled tube to axial tension and torsion. Various types of combined stress conditions were investigated. To provide control test data and information on the influence of biaxial stresses on the strength, the usual constant stress ratio type tests were made. These tests showed that the biaxial yield strength agrees approximately with the distortion energy theory. However, the Prager semi-empirical theory agrees best with the test results. For these constant stress ratio tests the plastic stress-strain relations were found to agree approximately with the flow theory. (For constant stress ratio the flow and deformation type theories are identical.) In view of the fact that the constant stress ratio tests cannot distinguish between the flow and deformation theories, a number of variable and special biaxial stress tests were made. These tests showed that the flow theory is inadequate, since large differences exist between the experimental and theoretical results. Special tests were also conducted to check the validity of the isotropic yielding assumption. This assumption is made in the linear-type flow theory. In these tests specimens were loaded in tension to predetermined values beyond the proportional limit stress. The tension load was removed from the specimen and the specimen was subsequently loaded in torsion to fracture. Other tests were applied with the order of torque and tension loading reversed. The nominal stress-strain curves for these two tests approximately coincide indicating that the assumption of isotropic yielding is valid. In addition, these tests verified the requirement by the slip theory of plasticity that prestraining below 140 pct of the proportioned limit stress in either torsion or tension did not influence the subsequent plastic stress-strain relations in tension or torsion. Another type of test was conducted to check the assumption that the axes of principal stress and strain coincide during plastic flow and variable stress conditions. These tests were conducted by applying combinations of axial tension, internal pressure, and torsional loads such that the axes of maximum principal stress could be rotated through 90" during the loading path. The results of those tests showed that the angle between the axes of principal stress and strain varied greatly and that the assumption of coincidence between axes of principal stress and strain is not valid. Introduction In various metal processes including forming of sheets, rolling of bars, and extrusion of rods, metals are subjected to stresses beyond the yield strength of the material. Often these stresses are not simple stresses acting in one direction, but are combined stresses acting in more than one direction. Structural and machine members are often subjected to combined stresses. To adequately determine the factors of safety for these members, it is necessary to know the plastic stress-strain relations of the material used for various combined stress conditions. Various theories have been proposed for predicting the plastic stress-strain relations for combined stress in terms of the simple tension plastic stress-strain relation for the material. To determine which theory might be adequate, test results must be obtained for various combined stress conditions, in order to compare the actual with the assumed theoretical behavior. Although there is considerable test data available for combined stress conditions in which the principal stress ratios are constant, relatively little test information is available for vari-

Jan 1, 1954

By Oliver Bowles

GLASS razor blades, glass chairs, and marble window panes attest that creative genius was still active in 1935. Many less striking, though doubtless more important, developments are to be recorded for the nonmetallic mineral industries, and not the least of them is the establishment of an Industrial Minerals Division in the A.I.M.E. under the able leadership of Samuel H. Dolbear, Chairman. Thus the nonmetallics are rightly granted equal dignity with metals and fuels in the category of mineral industries. The brief review of progress that follows merely touches the fringe of important developments in this broad field.

Jan 1, 1936

By W. A. Wood, W. H. Reimann

A study is made of the creep that can be induced in armco iron at room temperature by superposing small amplitudes of alternating torsion on a tensile creep load. It is shown that the creep differs from that in comparable tests on copper in being trmsient only. At the same time, though transient, the creep can produce extensions of some 10 pct under creep loads less than the tensile yield stress of the material. The creep can be largely suppressed b$ applying cyclic strain of suitable amplitude before applying the creep load and the metal thereby stabilized. At room temperature, plastic flow in a metal under steady load is normally limited by strain-hardening processes. However, if a small cyclic stress is superposed on the steady load these processes may be more or less neutralized and, as shown in recent investigations,'-4 plastic flow may continue. In this way annealed copper, for example, can be induced to creep continuously to fracture under loads as small as 1 tsi. Dislocation mechanisms possibly responsible for this room-temperature creep have been usefully reviewed by Feltner.But discussion so far has been based mainly on creep as it is found in close-packed metals initially in the annealed state, and their behavior may not be general. In fact, recent work shows that the form of creep in annealed copper is different from that even in cold-worked copper;7 the creep thus depends on the dislocation pattern already in a metal as well as on the metal itself. This paper describes the creep in annealed armco iron, tested in the same way as the above-mentioned copper. One object was to see how creep in a typical bcc metal compared with that in the annealed close-packed metals. Another object was to utilize the fact that a bcc metal like iron has a more pronounced elastic range than close-packed metals like copper and to find to what extent the creep load or superposed cyclic stress had to exceed their re-

Jan 1, 1964

By C. B. Foster, S. I. Freedman, E. M. Jamgochian

Coal-oil mixture (COM) combustion technology is regarded by the US Department of Energy (DOE) as near term and Potentially applicable to existing utility and industrial steam generators and for injection into blast furnaces. From work done previously, it has been established that COM can be burned in existing boilers and blast furnaces. Therefore, the issues being addressed by the current DOE program are: (1) determination of best available technology to achieve environmentally acceptable long-term reliable operation and (2) determination of applications for which COM can be utilized economically. Some of the technological options have begun to be determined by projects already under way. However, many projects are still in the early stages of development.

Jan 1, 1980

By E. Sengier

At the Director's dinner of the A.I.M.E. on. April 22, Mr. Sengier of the Union Minière du Haut Katanga was a guest. Though a member of the Institute for sev-eral years this was the first occasion on which he had had opportunity to meet with it, and in response to an invitation from President DeGolyer, after expressing his pleasure at being present, he told informally of the present development of the Congo with which he has been so closely related. From his remarks the follow-ing has been prepared.-EDITOR. AS you know, the Belgian Congo, a fairly large colony compared with the territory of Belgium, is in the center of Africa. Natural waterways, railroads now built and new railroads under construc-tion, give increasing means of transportation and are helping toward development. The mining industry is by far the most important part of our colonial activity. Considering that we are all engineers, I will confine my figures to mining enterprise. First I will show you the relative importance of the mining industry com-pared with the total exports of the Belgian Congo. During 1925 there was exported 100,000 tons of cop-per, valued at about $25,000,000; 900,000 carats of diamonds, 8000 lb. of gold, 1700 tons of cassiterite, 300 .tons of cobalt, and 20 grams of radium, of a total value of about $35,000,000. Other products to a value of about $12,000,000 and consisting mainly of palm nuts, palm oil, cotton, ivory, copal, rubber, were also exported. From this you will see that mineral products account for about 72 per cent of the total exported value. Copper alone amounts to 52 per cent of the total and 72 per cent of the mineral exports. All minerals, with the exception of gold, which is mined by the government, belong practically toy two mining companies in which American and British capi-tal is interested with Belgian. These two companies (one called Forminière, interested in the diamond busi-ness, and the other called the Union Minière, interested in copper, cobalt, tin and radium) were formed twenty-five years ago. They started producing in 1911, but the war prevented normal operations, and active de-velopment could only be carried on after the Armistice.

Jan 5, 1927

By J. A. Retty

IN the Labrador iron fields two concessions, totaling nearly 24,000 square miles, have been staked out and commercial-grade deposits delineated. The Newfoundland-Labrador concession, owned by the Labrador Mining and Exploration Co. Ltd., is a 20,000-square-mile tract in the upper basins of the Hamilton and N askaupi Rivers which drain into Lake Melville. The New Quebec licensed area is 3900 square miles, owned by the Hollinger North Shore Exploration Co. Ltd., lying to the northwest of the northwestern part of the Labrador concession. It includes the upper basin of the Swampy Bay River and part of the upper basin of the Whale River, both of which drain into Ungava Bay. Both of the above-named companies are controlled by Hollinger Consolidated Gold Mines Ltd. with The M. A. Hanna Co., of Cleveland, holding a minority interest. When exploration was first undertaken in 1936, the only published map of the area was that prepared by A. P. Low in 1895. It showed only the main watercourses and gave only a rough, general idea of the geology. The numerous lakes of this vast area had to be first sketched and then mapped. Since then, extensive geological and topographical surveys have been conducted by the Labrador company, work which is normally done by Government branches. The object of the work was to examine the area and gradually eliminate unfavorable or less favorable prospecting ground. With this object in view, geological

Jan 1, 1948

By Jack C. Haptonstall

This paper describes the analytical characteristics of Western subbituminous coal and the manner in which these characteristics apply to their use in a utility-sized steam generator. It compares these characteristics with those of typical Midwestern coal and Eastern bituminous coal. The paper also reviews in detail the design considerations that must receive attention when various blends of these three coals, or any combinations thereof, are planned to be used. This research paper describes variations in analytical and utilization characteristics when coals from different origins are blended in order to achieve a predetermined sulfur content for the purpose of predicting sulfur oxides emissions as they affect environmental regulations and the resulting alterations in utilization characteristics such blending would cause, and how such blends of coal would affect a utility-sized steam generator.

Jan 1, 1979

By Joseph C. Buchen

IN principle, production of salt from sea water is a simple operation. Sea water is trapped in ponds, the sun and wind cause evaporation of the water, and what is left is principally salt. Commercial production of solar salt, however, requires a careful consideration of many factors. Obviously, sufficient evaporation must take place throughout the making season to produce an economically adequate crop. Other factors are density of soil, contour of ground, height of ground above sea level, minimum dilution from fresh-water streams, and distance from market. Unfortunately, in the United States the localities of greatest evaporation, allowing for the other factors, are not the most suitable for the manufacture of sea salt by solar evaporation. The south end of San Francisco Bay most

Jan 1, 1937

By T. C. Sandford

Thermal conductivity measurements of intact rock specimens do not reflect the effects of natural rock discontinuities, and large scale insitu tests are location specific and costly. To allow extrapolation of laboratory measurements to rock masses with discontinuities, the effects of discontinuities on rock thermal conductivity were measured using divided-bar techniques. The introduced discontinuities lowered the thermal conductivity in all cases, and conductivity decreased systematically with increasing roughness of the discontinuity. Conductivity increased with increasing pressure on the discontinuity.

Jan 1, 1984

By Clyde E. Williams

IN planning a postwar program for manufactured products, it is essential that the bases for the plans be wisely chosen. First we must make certain assumptions as to the war's ending. Let us assume: (1) complete victory by the United Nations, (2) peace terms that will ensure the direction of the economy of all nations of the world toward peaceful pursuits, and (3) an early ending of the war, that is, before the nations of the world, excluding the enemy, are near the point of physical and spiritual exhaustion. Thus, our manufacturing plants and transportation facilities will still be in good shape. The plants and transportation facilities, as well as the cities of a large part of Europe, however, will be badly crippled. The rich mineral and other raw material resources of the world, little of which was under control. of the Axis powers before the war or will be after the war, will not be used up. Control of these raw materials, or at least an important part of them, will remain in the hands of the strong peaceful nations.

Jan 1, 1943

By E. R. Buchanan, R. E. Reed-Hill

Cylindrical magnesium single crystals were deformed in torsion. The axis of torsion was the basal pole. Five crystals were deformed to different strains between 0.08 and 1.03 and then sectioned in order to determine their dislocation densities using the transmission electron microscope. The work hardening rate of all specimens was at least an order of magnitude higher than that normally associated with easy glide in a tension test and comparable to that obserzed in stage B of a tension test. The correspondence between stage B in a tension test and the initial stages of a torsion test is believed to result from the fact that in both cases deformation occurs in a structure containing roughly equivalent densities of the dislocations associated with the three basal slip vectors. THERE are three basic ways of changing the shape of a crystal using slip dislocations. The crystal can be sheared along a slip direction in a slip plane; it can be bent about an axis in the slip plane normal to the slip direction; and, if the slip plane contains multiple slip directions, it can be twisted or rotated about the slip plane normal. Of the three processes, generally known as translational, flexural, and rotational slip, only rotational slip has not been extensively investigated. The object of the present research was to obtain basic information about this phase of crystalline plasticity. This paper is concerned with some aspects of the stress-strain curves obtained by twisting magnesium crystals about their basal poles. Magnesium was selected for four reasons. One, its recovery rate at room temperature is relatively low. Two, single crystals may be easily grown. Three, at room temperature the critical resolved shear stress for basal slip is about two orders of magnitude lower than that for nonbasal slip, so that rotational slip might be expected to occur primarily by basal slip. Finally, relationships between flow stress, shear strain, and dislocation density have been determined for tensile deformation of magnesium crystals,' thereby providing a basis of comparison for the torsional results. EXPERIMENTAL PROCEDURES Crystals were grown from 0.5 in. diam extruded sublimed magnesium rod furnished by the Dow Chemical Co. who reported that it contained in weight percent less than 0.0003 Al, 0.01 Ca, 0.01 Cu, 0.0012 Fe, 0.001 Mn, 0.0005 Ni, 0.003 Pb, 0.001 Si, 0.01 Sn, and 0.02 Zn, with the balance magnesium. All crystals were grown in a dried argon atmosphere using Jill-son's2 modified Bridgman technique. Two different methods were used to obtain crystals with the basal plane normal to the specimen axis. These included direct growth from seeds of the proper orientation, and spark machining (trepanning) of 0.5 in. diam cylinders from larger (1.5 in. diam) randomly grown crystals. The crystals thus produced were polished in a 20 pct HC1 water solution and then etched in a 1 pct HC1 water solution to develop etch pits lying in rows parallel to the basal plane trace. The crystals were then revolved about their axes on the stage of a low-powered microscope. Torsion specimens were prepared only from those crystals whose axes were normal to the rows of etch pits. It is estimated that this simple orientation method was accurate to about 51 deg. 1.625 in. long cylinders were next cut from these selected crystals and then acid machined in a 20 pct HC1 water solution into torsion specimens with a 1 in. long by 0.30 in. diam reduced gage section. Following this, they were annealed in air at 400°C and furnace cooled to room temperature. The specimens were given a final polish in a 10 pct HC1 water solution, rinsed in ethanol, dried, and cemented into brass grips with an epoxy resin. In addition to the torsion specimens, several tensile specimens with their basal planes at 45 deg to the stress axis were also prepared with similar dimensions except that the gage sections were increased to 4 in. in length. The torsion specimens were tested in the apparatus

Jan 1, 1970

By J. J. Thomas

THIS investigation was undertaken to determine, if possible, the relation between static and dynamic tensile tests as measured by the work required to break test specimens slowly, in a tensile testing machine, and rapidly, by means of a falling weight. It was hoped that the investigation would throw some light on the role played by ductility under different rates of application of load. FIG. 1.-STRESS-STRAIN DIAGRAM. In problems of design, it is usually assumed that the moduli of elasticity of all steels are equal; viz., about 30,000,000. The stress-strain diagram within the elastic limit is a straight line, as shown in Fig. 1, where OA is the curve of a hard steel and OB that of a soft steel. If the modulus of elasticity is constant, as assumed, the slope of the line OC

Jan 2, 1921

By L. H. Robinson

Triaxial compression tests have been performed to determine the strength characteristics of limestone, sand-stone and shale rocks subjected to controlled stress conditions. This control tuns exercised by varying the liquid pressures within and around a plastic-encased rock specimen. The pressure in the pores of the rock was varied throughout the range from atmospheric to 15,000 psig; the external pressure was changed over the same range with various positive pressure differences between is and the intertnal pressure. The data show that the rock strength increased and the mode of failure changed as the pressuire. surrounding the rock became greater than the pressure in the pores of the rock. These observations and the resu1ts of microbit drilling experiments indicate that the increased rock strength under pressure may bc an important effect in reducing drilling rare, but that other factors are probably of even greater importance. INTRODUCTION A large part of the research conductcd to reducc thc cost of drilling is directed toward improving present drilling technology and dcveloping new drilling methods. In spite of the fact that drilling is essentiaIly the act of making rocks fail, many details of the mechanism of failure are not known. It seems probable, therefore, that continuing studies of the fundamentals of rock failure can lay a foundation for future improvements in drilling technology. One of the factors which affects rock failure is the stress applied to the rock. This effect has been known for many years.'.'.; As an example, stress studics have been published by engineers' concerned with the strength characteristics of concrete in large dams. More recently, a number of investigators4-12 have explored the effects of stress on the strength of geologic formations and the geologic implications of their findings. During the last few years some research'" on rock strengths has also been conductcd in an attempt to gain additional insight into the factors which affeet rock drillability. In detcrmining the strength characteristics of rocks under different stress conditions, investigators have conventionally used triaxial compression equipment. wherein a jacketed rock cylinder is uniformly loaded from all directions and then compressed longitudinally. The results of this work have demonstrated that the mode of failure (brittle or malleable) is dependent upon the loading pressure, and that the strength of the rock increases as the loading pressure increases. These results clearly manifest that the stress, which is determined by the loading pressure, affects rock strength, and this implies that rocks under stress should be stronger and hence harder to drill. During the drilling of a porous rock the stress conditions are determined not only by the pressure surrounding the portion of the rock undergoing failure (confining pressure) but also by the pressure of the interstitial fluids within the rock (pore pressure). The importancc of both these pressures on the drilling rate of rocks has already been demonstrated by a number of investigators. Murray and Cunningham" found in microbit drilling expcriments that at constant pore pressures the drilling ratc decreased as the hydrostatic pressure surrounding an unjacketed, impermeable rock increased. Later Eckel" found that for jacketed Iimestone specimens the differcnce between hydrostatic (wellbore) pressure and formation (pore) pressure had an important effect on drilling rate. These observations of the effect of pressure on drilling rate emphasize that for drilling studies triaxial compression tests should be conducted under conditions of confining and pore pressure which simulate conditions underground. In the past, triaxial tests have been made under conditions which do not reproduce those underground. In particular, most of the tests on porous materials have keen made at varying confining pressures but with atmospheric pore pressures. In only one group of tests' was any data on the effect of pore pressurc reported, and these few data were on materials not representiltive of those encountered in drilling earth formations. The research described herein was initiated to deter-mine the importance of both internal pore pressure and confining pressure on failure characteristics of limestone. sandstone and shales. Triaxial loading equipment was used to obtain strength data at pressures up to 15,000 psig. An additional objective of this research was to apply these results to drilling rate studies by comparing them with the previously published drilling data of Murray and Cunningham" and of Eckel12. The work reported here is but one step in determining and evaluating the fundamental mechanisms which control drilling rate. Additional research is needed to clarify other aspects of the drilling process. The better

By Chas. H. Behre

MINING geology, both theoretical and practical, continued to make noteworthy progress during 1938. Mining companies generally, stimulated especially by the improvement in economic conditions during the latter part of the year, extended their workings and developed new ore bodies. Federal and state surveys expanded their search for favorable localities and actual ore bodies, with corresponding enlargement of regional knowledge. Theoretical investigations covered geochemistry of ore deposition, structural control of mineralization, and mineralogy of the ores (chiefly aided by the microscope). More geochemical work is greatly needed: ore searching is still too purely empirical, based on features that have been recognized else- where. Thus, clearer understanding of the conditions essential to transportation of metal salts is needed. Jean Verhogen has suggested that solubilities

Jan 1, 1939

By A. B. Kinzel

ALTHOUGH calcium carbide and other compounds of calcium, as well as a number of calcium alloys, are well known and are the basis of important industries in the of United States, calcium metal has been thought of as something of a rarity and has received comparatively little attention from industrial metallurgists. The metal may he made in a number of ways, but the electrolytic deposition of calcium from a molten calcium chloride bath was the first process to be used for its commercial production and is still the standard procedure. Calcium metal has elicited little interest among nonferrous metal producers, as the demand has been relatively small and its production restricted to only a few plants, exclusively in France and Germany.

Jan 1, 1941

By M. J. Marcinkowski, A. Szirmae, R. M. Fisher

Room -temperature hardness measurements obtained from single and polycrystalline samples of a 47.8 at, pet Cr-Fe alloy which were aged for various times al 500°C show a two-fold increase over that of the unaged alloy after annealing for 1000 hr. A detailed examination of the deformation markings in the neighborhood of the hardness imbressions reveals that twinning becomes an increasingly more important mode of deformation as aging proceeds. this observation is shown to be inconsistent with the Proposals that the transformation is eve of order-disorder On the other hand, the results are in agreement with previous observations of Fisher et al. of a coherent chromium-rich precipitate which forms in an iron-rich matrix as a result of a miscibility gap in this alloy system as proposed by Williams . Using the coherent precipitate hypotlzesis as a model, a detailed analysis of the various possible strengthening contributions to both the slip mid twinning stresses is made. In the case of' slip, lattice friction within the chromium-rich phase and the chemical energy associated with the interface between the two phases contribute about 60pet to the total strength. The contributions from coherency strains and modulus differences are thought to contribute the remaining 40 pet of the strength but are difficult to evaluate because of uncertainties regarding the flexibility of the dislocation line. All of the factors have nearly the same or else a smaller effect on the twinning stress in the aged alloy. Twinning is never observed in the unaged alloy because the twinning stress is much higher- than that for slip. With increased aging times, the various contributions to the total stress for both twinning and slip increase, but most of those for slip increase much more rapidly, so that, in the fully aged alloy, it surpasses the stress for twin propagation. When a twin is nucleated by the chance occurrence of an internal stress concentration during a test, the subsequent twin burst results in a low hardness reading. FeRNTIC Fe-Cr alloys from about 15 to 80 at. pet Cr content show considerable change in properties such as hardness, electrical resistivity, saturation magnetization, and so forth, after aging in the vicinity of 500°C.* The most marked change is a large increase in hardness accompanied by a sharp decrease in ductility, so the phenomenon has often been referred to as the 475°C (885°F) em-brittlement problem. Changes in microstructure are rather subtle and most investigators have not been able to observe any X-ray diffraction or metal-lographic changes during aging. There is little doubt that the phenomenon is inherent to the Fe-Cr binary system and is not directly related to the formation of a phase. Two distinct schools of thought have developed during the past decade concerning this problem. Masumoto, Saito, and sugiharal have concluded, from their own specific-heat measurements, that atomic ordering occurs in this temperature range. Pomey and Bastien2 have also attributed the changes in physical properties with aging in the neighborhood of 500°C to atomic ordering. In addition, Takeda and Nagai3 claimed to have found X-ray verification for superlattices corresponding to the compositions FesCr, FeCr, and FeCr3. However, all known attempts to observe superlattices in Fe-Cr alloys using neutron diffraction, which should be much more sensitive, have been unsuccessful. These have been reported by Shull et al.4 for 25 at. pet Cr, williams5 for 75 at. pet Cr, and Tisinai and samans6 for a 28.5 at. pet Cr. steel. The second and more prevalent opinion ascribes the 475°C embrittlement phenomenon to the formation of a coherent precipitate due to the occurrence of a miscibility gap in the Fe-Cr system below about 550°C. This latter concept was first indicated by the results of Fisher, Dulis, and Carroll,7 who were able to extract fine particles about 200Å in diameter from samples of 28.5 at. pet Cr steels aged from 1 to 3 years at 475°C. The extracted material was found to be nonmagnetic, to have a bee structure with a lattice parameter between that of iron and chromium, and to contain about 80 at. pet Cr. Williams and paxton8 and williams5 confirmed these results and first explicitly proposed the existence of a miscibility gap below the a region in the equilibrium diagram. Alloys aged within this gap

Jan 1, 1964

By H. R. Peiffer

Hardening of soft metals can be accomplished by dispersing finely divided hard particles in them. The dispersing of finely divided alumina in silver in the presence of oxygen yields a high strength material which is unusual in that its mechanical properties above the melting point of the continuous Ag-O alloy matrix are similar to other solids. The tensile strength is studied for two of these alloys, one of which contains 15 pct by weight alumina and the other 20 pct by weight alumina. The average fracture strengths above 960°C of these alloys were found to be 0.4 x106 dynes per sq cm and 3.8x106 dynes per sq cm respectively. The strengths appenred to be independent of temperature above 960° C. The creep behavior of the 20 pct alumina material was studied above 960°C. The initial creep rate, 6 , of this material can be represented by where s is the applied stress and E the activation energy for the process. This energy is of the order of 1.7 to 2.1 ev. HARDENING of soft metals by the addition of finely divided, hard particles has resulted in the production of materials with excellent creep resistance and with inhibited recrystallization.' It has been demonstrated that such composites have useful strength up to temperatures very near the melting point of the soft metals, but one might expect that the strengthening by the dispersed particles ceases to be of importance above the melting point of the softer phase. This, however, is not so.2 In this paper the strengthening of a liquid Ag-O solution by the presence of dispersed alumina is discussed and experimental data concerning the mechanical properties of such a material at temperatures above 960°C presented. EXPERIMENTAL PROCEDURE Specimens were prepared using powder metallurgical techniques. Finely divided silver oxide was mixed in the appropriate proportions with "Linde B" alumina. For these experiments the specimens contained 15 or 20 wt pct alumina in pure silver.* These alloys were used in these experiments since they were the ones that could be handled readily enough to yield experimental data. Silver oxide was used in preference to silver because it is readily available in a very finely divided form and because the presence of excess oxygen in the silver is important to the properties2 of the material. The powders were mixed wet, using alcohol as the medium, in an ordinary food blender until a uniform mixture was obtained. They were then dried and heated to reduce the silver oxide to silver. Only a fraction of the finely divided silver remains unoxi-dized upon removal from the oven since the finest particles of silver oxidize immediately upon contact with air. The remaining fine silver served as a binder during pressing. The mixture was then pressed at 20 tons per sq in. into shoulder-grip (reduced section 1/4 in. by l/4 in. by 1 1/4 in.) and rectangular bar specimens (l/4 in. by 1/4 in. by 2 in.). The green specimens were heated very rapidly in a globar furnace to 1000°C, held at temperature untic they had reached theoretical density and then furnace cooled. The strength of the two compositions at temperatures above 960 °C was determined by pulling shoulder grip specimens inside a furnace mounted on a tensile machine. Specimens were gripped by means of wires wrapped around the shoulders of the specimen. Temperatures were measured by means of a chro-mel-alumel thermo-couple placed in the vicinity of the specimen. Control of temperature (within ±°15C) was accomplished by means of a Weston Recorder-Controller. Before loading, specimens were held at temperature for approximately 15 min in order to insure uniform specimen temperature. The low loads were measured by a special load cell designed by Baldwin Lima Hamilton. All testing was performed on a FGT testing machine of the same com-pany. Creep studies were performed in bending utilizing rectangular specimens of the 20 pct alumina alloy. Specimens supported at both ends by knife edges of inconel were placed in a globar furnace, heated quickly to temperature, and the deflection of the beam measured optically as a function of time. The weight and size of the specimen were predetermined and the maximum stress on the beam calculated from

Jan 1, 1962

By JOHN W., E. C. SARCENT

The South Texas area discussed herein represents districts 2 and 4 of the Texas Railroad Commission. It extends from Jackson, Lavaca and Gonzales Counties on the northeast to the Rio Grande River, and comprises a total of 26 counties.

Jan 1, 1946