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Jan 1, 1969

By J. L. Perry

FOR many years, you and your fellow members of the American Institute of Mining and Metallurgical Engineers have devotedly and ably applied yourselves to the art of making iron and steel. having foremost in your minds the conservation of raw materials, suitable and efficient facilities, economical processes, and improved quality of product. For the past three strenuous years you have contributed wholeheartedly to meeting the problems of increased production. You have conducted scientific and technical investigations and research, recommended experiments. and gathered all the available and valuable information possible to gain the desired objectives. You have had many obstacles and difficulties to overcome. In the early days of your organization, there was some lack of co-operation from the industry itself-perhaps, for example, some failure to recognize the mutual advantages of free exchange of experiences and information. But regardless of any hindrances, you have made many and valuable contribution which have tended to make iron and steel manufacture leas of an art and more of a science.

Jan 1, 1944

By Gerard Matthes

ONLY in recent years has any practical headway been made in the application of aerial photography to geological problems, and up to the present time its principal value to the geologist and mining engineer has been in "areal geology;" i. e., the study of formations as revealed at the surface. The object of this paper is to set forth briefly the principal advantages that may be derived from aerial photographic data in geological work and to serve in a measure as a guide to those who may be con-templating its use. Geophysical prospecting has for object the locating of mineral under the surface. Inasmuch as the geologist's chief complaint in life is a dual one-inability to see under the surface and inability to visualize comprehensively what he does see on top of the ground-geophysical prospecting coupled with aerial photography should do much to lessen his burdens. To what extent aerial photography can be made a useful adjunct to geophysical prospecting remains to be proved, but the inference drawn here is that it holds many alluring possibilities. To avoid disappointments, it should be stated at the outset that to the :geologist or mining engineer an aerial photograph or mosaic is only a tool, the effecient use of which he must set out to master. Upon his skill and ingenuity in applying it to particular problems will depend largely the value of the results that he will obtain. Under the most favorable conditions an aerial mosaic or even a few loose photographs, because of the exceptionally comprehensive oversight which they afford of field data, such as dips and strike observations at isolated outcrops, local indications of faulting, mineral and fossil finds, greatly facilitate study and correlation, save much tedious foot work, and may repay their cost many times. Even so, types of country may be found where the most, skillful use of the best of pictures will produce results so meager as to render the cost of aerial photography entirely unwarranted.

Jan 1, 1928

By T. Carl Shelton

The coal industry of the United States in 1967 had reasons to be both exuberant and concerned about its present and future role in the economy of the country. Continuing a momentum that began in the early 1960's, the industry has moved ahead in providing competitive customized products to strengthen its long-term domestic and foreign commitments, and has maintained with steady progress its position as a major supplier of energy. On the other hand, the industry must overcome air- water pollution and conservation-reclamation problems that have been identified by 1967 legislation. Throughout the year, the industry was characterized as "progressive," "healthy" and "dynamic." To have been termed a "growth industry" in 1967, is an accolade the coal industry can accept with pride. Culminating its efforts throughout the decade, the industry has emerged with a competitive image that is representative of its future strength.

Jan 2, 1968

By R. M. Kuralt

CONCESSION from the Chilean government granting the company use of the Rio Salado water stipulates that a minimum of 35,000 metric tons of such salty water must be diverted from the Salado daily, and be disposed of in a manner not to contaminate the Rio Loa to the east of its confluence with the Rio San Salvador at Chacance, Fig. 1. Consequently, the selection of a suitable site for the sulphide plant tailing disposal had the additional problem of the disposal of excess brackish waters. Studies of the terrain in the area directly to the south of the plant indicated that construction of tailing ponds would be costly, and generally unsatisfactory due to excessive slope of the ground, lack of flanking hills, danger of raising the groundwater level thus causing springs along the Antofagasta-Bolivia railroad; and the possibility of creating a dust nuisance at the plant site or at Calama due to blowing sands. Further to the southwest the San Salvador river canyon offered some possibilities and surveys were made at sites A to D, inclusive, Fig. 1. Here again costly dams would have been necessary to impound the tremendous quantity of tailing produced by the new plant, and provision would have to be made to handle a considerable flow of water through the disposal area to the west of the Rio Opache. Additional surveys were made in the area to the southeast of the plant which brought to light the existence of a natural basin of about 14 1/2 square miles, flanked by low-lying hills, and requiring only the most rudimentary dams to close the outlets at the western end. It has been estimated that the Salar de Talabre, as this basin is called, has the ultimate storage capacity of 1 billion tons of tailing with dam heights of only 60 ft. Pipe Line Layout After the decision had been reached to use the Salar de Talabre for the main disposal area various methods were considered for transporting the tailing from the 300 ft diam thickeners to the disposal site, 17.7 miles away. The first plan was to construct a. concrete launder on a 11 pct grade but a survey of this grade line indicated it would not lead directly into the Salar but would terminate somewhat to the north, and from that point on the slope would be considerably less than 1 pct along a natural watercourse. A slope of 2 pct or even 2 ¼ pct in such a rough watercourse or ditch is the ideal, judging from the success of operations at Cananea. Since a simple ditch is the most economical vehicle for the transportation of tailing, it was decided to use one with a 2 ¼ pct grade for as much of the distance as was possible with the existing terrain and to construct a concrete headbox, or forebay, at the terminus of the ditch to supply a steel pipe line leading the rest of the way into the Salar. Referring to the maps of the Chuquicamata area outlining the tailing disposal system, Figs. 1 and 2, one can trace the flow of the tailing from the thickeners to the Salar as follows: The 8-in. spigot pipes from the thickeners (1) discharge into a concrete sump feeding a concrete launder with a 2 pct slope. The launder carries the tailing into a concrete junction box (2) located south of the sulphide plant. The purpose of the junction box is to provide emergency facilities for diverting the tailing flow from the main disposal area to the emergency area. It also provides a junction point for the launder from the sulphide plant's future east extension. The box is fitted with a pair of radial gates controlling flow into the main tailing ditch (6) or the emergency ditch (3) which terminates on the pampa. All ditches are of the same cross section, namely 4 ft wide at the bottom with 1 : 1 side slopes and with a minimum depth of 21/2 ft. Where the nature of the ground demands it, the ditches are lined with stone rubble. The overflow from the plant's 10 million gal reservoir (4) is led into the main tailing ditch by way of a spillway ditch (5). The main ditch terminates in a trashscreen fitted, concrete forebay (7) which serves as a headbox for a 24 in. O.D. x 3/8 in. wall, Dresser coupled, steel pipe (10) and a 12 in. x 8-gage spiral welded, wedge-lock coupled, steel pipe (8). The forebay is fitted with two compartments, one for each pipe, and flow into each is controlled by radial gates. Each compartment is fitted with a 6-in. drain pipe controlled by a rubber pinch valve. To protect the forebay from the abrasive effects of the tailing, the sides of the compartments will be lined with old

Jan 1, 1952

CYRIL STANLEY SMITH, Chairman CARL E. SWARTZ, Past-Chairman ARTHUR PHILLIPS, Vice-Chairman E. E. SCHUMACHER, Vice-Chairman H. A. MALONEY, Treasurer FRANK. T. SISCO, Secretary 9 West 39th Street, New York, N. 1. Executive Committee 1944 1945 WILLIAM C. ELLIS C. S. BARRETT ALAN MORRIS T. A. WRIGHT KENT R. VAN HORN L. L. WYMAN

Jan 1, 1943

The pellet plant, built by Dravo Corp, in Groveland, Mich., for the Hanna Mining Co., is now in full operation. Although using jasper, a type of iron ore with low iron content (approximately 28% Fe), the plant has a rated capacity of 1,250,000 tans of pellets per year. In its four years of existence, the nearby concentrating plant has seen its capacity increase from 700,000 tons to 1,500,000 tons a year as part of a major expansion program at Groveland. Utilizing the Dravo-Lurgi continuous grate process, the pellet plant produces %a-in. pellets of more than 60% iron content. The fully-hooded pelletizing grate, largest in the U.S., is 9 ft. 10% in. wide and 223 ft. 1% in. tong over 34 windboxes, with an effective hearth area of 2195 sq. ft. Drying, firing, and cooling functions are all carried out on this single piece of equipment.

Jan 4, 1964

By W. A. Backofen, D. Lee

Tlze condition of superplasticity or neck-resistanl flow that results front high strain-rate sensitivity has been observed in isothermal tension tests on several titanium alloys and one of zirconium hi general, il was associated with reasonably fine-grain micro-structures being stvained in the transformation range at rates below i - 10 -3 sec-&apos;. The metallographic mean-free path, L, was measured at room temperature after rapid cooling from the temperature of test-ing. The flow stress of Ti-GAL-4V at 950°C was proportional to La at different constanl <; the value of a decreased with increasing. E but at E< 1.5 x 10-4 sec-1 it varied only from 0.9 to 1.25. The findings were interpreted to mean that viscous boundary shear is the rate-controlling process of deformation at high levels of strain rate sensitivity in these materials. Elongation of over 1000 pet could be obtained, but a1 temperatures so high and rates so low that any practical application of the full effect would probably be difficult. As the transformation range was narrowed, by turning from Ti-6AL-4V to Ti-5Al-2.5sn to nomznally pure titanium, the allowable temperature varialion was correspondingly reduced. Superplasticily was not found in Armco iron, presumably because the transformation range was too narrow to allow the developtnenl of a reasonably stable microstructure for isolhermal lesting. THE work represented by this paper grew out of a recent study of texture hardening in a(hcp) titanium and zirconium-alloy sheet,&apos; of which part has now been published.2 It was found that, with heating, the tensile plastic-anisotropy index, R,* was decreased from well above 1 towards 1 as the temperature range for the a(hcp) -ß(bcc) phase change was entered. The clearest example of that trend is illustrated with previously unpublished data in Fig. 1. It might have been thought that such a development resulted simply from introduction of the cubic and therefore plastically less anisotropic phase. However, the accompanying change in the index of tensile strain-rate sensitivity, m = a log a/a log E, was rapidly upwards, to a high of 0.85 in some cases (also illustrated in Fig. 1). At the same time, the total tensile elongation rose to a maximum and the flow strength dropped away as R (and m) approached 1. Taken together, the observations cannot be understood as resulting from the presence of cubic phase, per se. It has been concluded instead that they reflect the largely noncrystallographic deformation which characterizes superplasticity. As demonstrated in other recent work? a necessary condition for super-plasticity is strain-rate sensitivity of flow stress sufficiently high that m is above a lower limit of -0.3. The origin of large m has been traced, in turn, to grain size so small that a substantial amount of viscous deformation is introduced by such processes as Nabarro-Herring diffusional flow4 and/or grain boundary shear.5,6 Because of problems in the processing of titanium and zirconium alloys—problems of high strength, limited ductility, and excessive springback, originating largely in slip resistance-it was natural to wonder if something useful might be done with superplasticity in those materials. Therefore experiments were made for more closely identifying and generally bounding the phenomenon with temperature and strain-rate limits, before attempting to decide about its exploitation. The results are being reported here. EXPERIMENTAL Materials. The two of primary interest were the titanium alloys of nominal composition (in wt pct) 5A1-2.5Sn and 6A1-4V. Others were a 4A1-1/4O2 titanium alloy, titanium of commercial purity (RC-70), Zircaloy-4. and Armco iron. All were received as annealed 3/16 in. thick sheet, except RC-70 which was & in. thick, and tested in that condition. Details of transformation temperature and grain size are given in Table I. The results of dilatometry for the measurement of transformation temperatures were unsatisfactory. Data were finally obtained by metallographic examination of each specimen after test, to determine from the amount of transformed 4 where the specimen had been heated in relation to the critical temperatures. Results were in reasonable agreement with information from the supplier. Strip tensile specimens were of full sheet thickness and taken along the rolling direction, except for those

Jan 1, 1968

By Larry Kaufman, Martin Schatz

The effect of pressure on the extension of the ? loop in the FeSi system has been determined by means of metallogvaphic studies and hardness measurements performed on a series of high-purity Fe-Si alloys containing 7.5, 11.0, and 13.9 at. pct Si, respectively. These mensurements, performed at 42 kbar and temperatures up to 1200oC, indicate that the ? loop is expanded to about 10 at. pct Si at 42 kbar as opposed to a maximum extension of 4 at. pct Si at 1 atm. Comparison of the experimental results with thermodynamic predictions of the pressure shifts yields satisfnctory results. DURING the past few years, several studies have been performed in our laboratory1-&apos; in order to determine the effect of high pressure on phase equilibrium in pure iron and iron-base alloys. The purpose of these studies has been to elucidate the effects of high pressure experimentally and to compare the observed results with predicted pressure effects derived on the basis of known thermody-namic and volumetric data at 1 atm. These studies have included work on pure iron2,5,7 as well as Fe-Ni,1,5 Fe-cr,l,5 and Fe-c4-6 alloys. In addition, Tanner and Kulin3 have reported results of pressure studies on two Fe-Si alloys containing 2.0 and 6.25 at. pct Si. At the time of this latter study, no detailed information was available concerning the difference in volume between the a (bcc) and ? (fcc) phases in the Fe-Si system as a function of silicon content. In order to compare their observations with calculated pressure shifts, Tanner and Kulin were forced to assume that silicon had no effect on the difference in volume between a and ? iron. The resulting discrepancy between their calculation of the a/? phase boundary at 42 kbar and the observed results led them to the conclusion that silicon additions probably decrease the difference in volume between a and ? iron. Recently: Cockett and Davis8,9 have reported de- tailed studies of the lattice parameters of a series of Fe-Si alloys at temperatures ranging from 20" to 1150°C. These measurements, performed on alloys in the bcc and fcc range, show that silicon does indeed decrease the difference in volume between a and ? iron. By correcting the calculations of Tanner and Kulin in line with the observed effect of silicon they were able to show improved agreement between computed and observed pressure shifts.&apos; The present measurements were undertaken to provide additional corroboration of this effect, by extending the range of composition, in addition to exploring a situation where large extensions of a ? loop could result in impingement of the ? field with an ordered bcc phase (based on Feo.75Sio.25). I) EXPERIMENTAL PROCEDURES AND RESULTS The alloys investigated were obtained from Dr. F. Kayser of M.I.T. They were prepared at the Ford Scientific Laboratory by vacuum melting electrolytic iron and high-purity silicon. The melts were poured under an argon atmosphere into hot-topped steel molds. Subsequently the ingots were hot-worked down to 1/2-in.-diam rods. Three alloys containing 7.5, 11.0, and 13.9 pct Si were studied. Carbon, regarded as the principal impurity, analyzed at, or below, 0.001 wt pct for all of the alloys. Prior to pressure-temperature treatment, the rod was annealed for 24 hr in vacuum at 1000°C, water-quenched, and subsequently machined into 0.100-in.-diam by 0.100-in.-long specimens. Subsequent to machining, the specimens were again annealed and then examined metallographically. They were found to exhibit a clear coarse-grained ferrite similar to Figs. 10 and 110 of Ref. 1 and Fig. 2 of Ref. 3. Subsequently, specimens of each alloy were equilibrated at 42 kbar at various temperatures in supported piston apparatus.1,3,4,6 Three specimens, one of each alloy, were wrapped in platinum and exposed simultaneously. The pressure-temperature cycle consisted of increasing the pressure from ambient to 42 kbar at 25oC, heating rapidly to the desired temperature, holding for 15 min, and quenching to 100°C, followed by slower cooling to 25°C and pressure release. The temperature was measured with a Pt/Pt-13 pct Rh thermocouple which was not corrected for pressure effects. Subsequently, specimens were examined metallographically and by

Jan 1, 1964

By John G. Hall

The pumping operations at the Chief mine have been unique in the respect that for many years the entire flow of water into the mine has been disposed of by pumping into natural underground " caverns" or "sinks." Volumes up to 4000 gpm have been pumped into these caverns with no apparent tendency for the caverns to fill with water, and it has never been proven that any of the water returns to the mine workings. Major pumping operations have been carried on during two periods, the first from 1918 to 1927, and the second from 1942 to the present time.

Jan 1, 1949

By M. K. Seguin

The study described in this paper is first centered on the determination of the physical properties (gravimetric, magnetic, electrical, and electromagnetic) o f metamorphosed iron ores of the Carol Lake-Labrador City District. Different geophysical surveys available in the Carol Lake-Wabush area were interpreted quantitatively and the dimensions, attitude, and tonnage of the ore bodies investigated were determined. A geophysical-statistical study was undertaken which permitted the determination of the grade of iron, magnetite, and, subsequently, specularite in the ore bodies. A discussion of the theory and logical progression of the study and the application of the results to actual geophysical data is presented. The conclusions, which are of real significance from the economic standpoint, may be predicted from the data obtained from geophysical surveys before any diamond drilling is undertaken. An integrated interpretation of this type is useful in planning future exploration work and selecting the most favorable geological structures. It also serves as a guide to minimize and determine tonnage drilling patterns. The general conclusion that a restricted range of residual gravity and magnetic anomalies are a key to exploration is valid. Indeed large depths to the top of deposits are absent since all the ore bodies are overturned synclinal structures with tops located close to the surface. Certain irregular geometries do occur but they are not common and the alignment of the iron ore bodies is sub parallel so that magnetic anomalies are evenly reduced in the earth&apos;s magnetic field vector.

Jan 1, 1975

By A. M. Gaudin

This year the American Institute of Mining, Metallurgical and Petroleum Engineers has chosen to give me its Robert H. Richards Award, a distinction which is widely regarded as the highest honor in the field of mineral engineering. I am deeply moved by this tribute, which suggests not only regard for my service to the profession but also the affectionate esteem of my fellow mineral engineers. You have made me happy at the prospect of the permanent association of my name with that of Robert Hallowell Richards and of the distinguished recipients of the award, Arthur Fay Taggart, Frank R. Milliken, John F. Myers, Edward William Englemann, C. Harry Benedict, Edward W. Davis and Arthur W. Fahrenwald. I wish to thank you all for an honor so generously bestowed. Professor Richards is known to us all as a legendary figure, and we can read about him in the Richards Memorial Volume of our Transactions. Some of us have even had the good fortune of knowing him. I count myself among those lucky few. In its intangible attributes the Award recalls those things for which Professor Richards stood: for Science in Art, for thoroughness, for meticulous accuracy, for bold imaginativeness, most of all for professional integrity. Now, as in his day, these attributes are central to an engineer&apos;s creed. They are appropriately needed in a formulation of a definition of the mineral engineering profession.

Jan 6, 1957

By Carle R. Hayward

LEAD ore smelting plants have been operating in general at reduced capacities and secondary lead has assumed relatively more importance during the last year. Present smelting practice results in a large amount of dross, often over 25 per -cent, from blast-furnace lead. This is usually treated at a fairly high temperature in a reverberatory furnace to remove part of the lead and produce a matte-speiss product which is shipped to a copper plant. Few smelters are satisfied with this &apos;treatment. The fume losses are high and the matte-speiss contains considerable lead. It would seem that a fruitful field for research was open here.

Jan 1, 1934

By H. L. Teicliman, E. M. Sipprelle

ENACTMENT of Public Law 290 by the 78th Congress authorized the U. S. Department of the Interior, Bureau of Mines, to conduct an experimental program to develop the technology for obtaining oil from oil shale. In adopting and later extending this legislation, the Congress recognized the impending necessity of supplementing ground petroleum reserves with synthetic fuels. Under the provisions of this legislation, the Bureau of Mines, among other things, was charged with the responsibility of developing mining techniques, methods, and equipment for mining the oil shales of the Green River formation of Colorado, Utah, and Wyoming.

Jan 1, 1950

By H. Foster Bain

Jan 1, 1910

By Paul M. Tyler

DOES mining pay? Inasmuch as the whining of minerals from Nature is one of the world&apos;s principal sources of new wealth, this question is of general economic interest but it is obviously of even more vital concern to investors and those engaged in mining. In a previous article on "Wage Costs in the Mineral Industries,&apos; published in the November issue, I attempted to show that wages paid workers on the job accounted for, roughly, 50 per cent of the mine dollar. Salaries normally range over 5 per cent - lower for large metal mines but higher in stone quarries and minor nonmetallic min. in, industries. Purchases of supplies, materials. fuel, and power generally aggregate within the range of 15 to 25 per cent of total receipts, with the average well under 20 per cent. The total of all such specified expenditures which may he loosely described as

Jan 1, 1934

By E. R. Darby

When bronze is melted in open-flame furnaces a considerable amount of slag is formed during the melting operation. This slag may be incidental to the melting practice or it may be formed intentionally by slag-forming constituents added to the furnace charge to provide a covering for the melted metal When this slag is removed from the furnace, it contains, in addition to the free metal carried with it by the skimming operation, a considerable amount of metal as oxide either combined or mechanically mixed with it. By the usual crushing and washing methods this metallic oxide generally goes to the tailings pile, so diluted by other foundry waste that its recovery is economically impossible. If this furnace slag is not inixed with other foundry waste, practically all of the metal oxide as well as the free metal may be recovered by some form of smelting operation. The first side of the problem to be considered is the amount of slag produced. It may not be true that the majority of foundries have no record of the amount of slag made, but it is certainly true that a very great many either have no record or pay little attention to it. Usually the collection of furnace slag for one normal week&apos;s run will be sufficient to determine the advisability of its being handled in a different manner from the crushing and concentrating generally employed. If a large representative sample of the accumulation is crushed and concentrated and the recovery compared with the results of a careful assay, it will be found that a large percentage of the total metal content was lost in the washing process. The percentage of loss will be greater than the metallic oxide content, as some free metal in extremely fine particles always is carried away in grains of slag. From such a comparison, it may be determined whether or not the slag should be melted, sold or treated as before. An example of an actual test of this kind is given below. In a foundry melting 50,000 to 80,000 Ib. of bronze per day, a week&apos;s accumulation of furnace slag and ladle skimmings amounted to 16,500 1b.—over three times as much as the foundry superintendent estimated before the accumulation was made. Two tons of this material was taken as representative of the lot. This was ground through a thoroughly cleaned ball-mill and concentrated over a Wilfley table. The

By N. Tiner

The mechanical properties of magnesium-alloy castings are greatly improved by grain refinement, and at present considerable attention is being paid to methods of obtaining fine-grained castings. One method of achieving this end is the use of proper melting and superheating techniques. These have been employed com-rnercially to a great extent, but no comprehensive study of the subject appears to have been published at present. Numerous investigations found in the literature include some reference to superheating techniques,1"4 and Achenbach, Nippcr and Piwowarsky,% ased principally on thermal analysis, ascribe the grain-refilling action of superheating to the influence of solid foreign particles or dissolved gases present in the melt upon the course of crystallization. The primary purpose of this paper is to present the principal facts concerning the cffect of superheating on grain size of magilesium alloys. .ittempts are also made to explain the experimental results in terms of a general hypothesis. The investigations are limited chiefly to common commercial casting alloys. In order to carry on this work, it was necessary to determine the factors influencing grain size and to develop a proper technique for the preparation of samples. Thc preliminary tests made by the author indicated that the grain size of magnesium alloys resulting from the solidification of a melt is determined by alloy composition, presence of impurities, rate of cooling during solidification, thermal history of the melt and to some extent the structure of the charge used. The rate of cooling is in turn dependent upon the mass of the melt, pouring temperature, and dimensions, properties and temperature of the mold into which the melt is poured. The final grain size of the alloys is still further modified by heat-treatment subsequent to casting. It is not within the scope of the present paper to discuss all of these factors, and it would suffice to note here that when equal amounts of magnesium alloys are prepared from the same alloying materials, melted in graphite crucibles under the same thermal conditions, then cast into graphite molds at a constant temperature, the resultant solids have the same grain size. By maintaining all other factors constant, it is thus possible to vary thermal conditions of a melt and to examine the grain size of resultant castings. Preparation of Samples and Grain-size TestiNg The alloys investigated in this paper were taken from ingots made by Permanente the Or or prepared by the author with pure carbothermic magnesium and necessary alloying elements. Melting was carried out under a flux in a graphite crucible heated uniformly by an

Jan 1, 1946

By N. Tiner

The mechanical properties of magnesium-alloy castings are greatly improved by grain refinement, and at present considerable attention is being paid to methods of obtaining fine-grained castings. One method of achieving this end is the use of proper melting and superheating techniques. These have been employed com-rnercially to a great extent, but no comprehensive study of the subject appears to have been published at present. Numerous investigations found in the literature include some reference to superheating techniques,1"4 and Achenbach, Nippcr and Piwowarsky,% ased principally on thermal analysis, ascribe the grain-refilling action of superheating to the influence of solid foreign particles or dissolved gases present in the melt upon the course of crystallization. The primary purpose of this paper is to present the principal facts concerning the cffect of superheating on grain size of magilesium alloys. .ittempts are also made to explain the experimental results in terms of a general hypothesis. The investigations are limited chiefly to common commercial casting alloys. In order to carry on this work, it was necessary to determine the factors influencing grain size and to develop a proper technique for the preparation of samples. Thc preliminary tests made by the author indicated that the grain size of magnesium alloys resulting from the solidification of a melt is determined by alloy composition, presence of impurities, rate of cooling during solidification, thermal history of the melt and to some extent the structure of the charge used. The rate of cooling is in turn dependent upon the mass of the melt, pouring temperature, and dimensions, properties and temperature of the mold into which the melt is poured. The final grain size of the alloys is still further modified by heat-treatment subsequent to casting. It is not within the scope of the present paper to discuss all of these factors, and it would suffice to note here that when equal amounts of magnesium alloys are prepared from the same alloying materials, melted in graphite crucibles under the same thermal conditions, then cast into graphite molds at a constant temperature, the resultant solids have the same grain size. By maintaining all other factors constant, it is thus possible to vary thermal conditions of a melt and to examine the grain size of resultant castings. Preparation of Samples and Grain-size TestiNg The alloys investigated in this paper were taken from ingots made by Permanente the Or or prepared by the author with pure carbothermic magnesium and necessary alloying elements. Melting was carried out under a flux in a graphite crucible heated uniformly by an

Jan 1, 1946

By R. G. Treuting, W. C. Ellis

The twinned state is characterized by a lattice of coincidence sites. Imperfections are required at stable lateral twin interfaces. Twinned regions can occur with relative ease in the diamond cubic IN recent contributions1,2 on the origin and growth of cubic annealing twins, attention has been directed to the orientation relations between such twinned components and their parent matrix. There are some aspects of twinning which may be illuminated by a more detailed consideration of the twinned state" alone. As an extreme example, the dense twinning in cast ingots of germanium,&apos; as contrasted with the rarity of twins in cast face-centered cubic metals, is yet to be accounted for. It has been this that has led us to the present work, which, it will be noted, uses methods and constructions in many respects similar to those of Kronberg and Wilson.&apos; In the cubic systems, a 70" 32&apos; rotation about a <110> axis is angularly equivalent, as to twinning, to the more usually considered 180" rotation about a <111> axis. Figs. 1 and 2 show a (110) projection of a twinned face-centered cubic lattice and a twinned diamond cubic lattice. In both figures, the two adjacent planes A and B, shown by the larger and smaller circles, are sufficient to represent the entire array. In each case a section of lattice, the original atom sites of which are shown by open circles, has been rotated as indicated through 70" 32&apos; to bring an original. [112] direction into coincidence with the [112] diiection. The latter is the intercept on the (110) projection of the (ill) plane normal thereto, the twinning plane. In the face-centered cubic case the rotation can be performed about an axis passing through an atom-site; the mirror plane then is also a composition plane containing atoms common to both twinned and untwinned lattices. The diamond cubic lattice may be construed as two interpenetrated face-centered lattices. Its (111) planes recur in a sequence of alternately short and long interspacings. Consequently a mirror plane for twinning cannot be a composition plane, but must be the bisector of one of the spacings. When the longer spacing is selected, the closest distance of approach across the mirror plane in the [ill] direc- tion is identical with that in the untwinned structure. In each case periodically recurring (ill) planes (parallel with the twinning plane) are found, on which there is coincidence of atom sites of the pre-twinned and twinned orientations; these are indicated by the cross-hatched circles. In the face-centered lattice there is such coincidence every third (ill) plane; in the diamond cubic lattice, on two adjacent planes in every six. At the twinning interface in the latter, there is on each side of the mirror plane a (ill) plane of atoms common to both twin components. Conceivably, there is little influence on a plane of atoms about to be adhered to such a pair of coincidence planes, whether it be laid down in a normal or in a twinned position with respect to the previously formed structure. Slawson% as attributed the high incidence of twinning in diamond to this boundary state. Further examination shows that the motion of intermediate planes can consist of various pairs of equal and opposite translations, for example of (ill) planes in the [l&apos;;i2) direction, the familiar twinning shear, indicated in the small schematics in the figures. Since the translations form a system of shears of alternating sign between coincidence planes, twinning could take place by such a mechanism over an extended region without extensive shear; in fact, in this case any atom moves but the distance in the [1i2] direction. One alternative construction for the face-centered cubic lattice leading to the same end result is illustrated in Fig. 3. The plane (711) with respect to the pretwinning orientation (the twinning plane of Fig. 1) is given, the twinned region arbitrarily bounded by <110> and <112> directions. The coupled shear is identical to that of Fig. 1. The "rotational" movement about coincidence sites generating the same twinned position could consist as shown of the translation a,/d% for each atom of a group of three in the B layer in a different one of the three <112> directions, and a similar translation of the underlying three atoms in the C layer in either the same or the opposite sense. This is not dissimilar to Kronberg and Wilson&apos;s construction for their 22" rotation of three adjacent (111) planes.

Jan 1, 1952