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By W. C. Ellis, M. E. Fine

INTRODUCTION IN the iron-cobalt system there are several property-composition relationships of theoretical importance. The alloys are ferromagnetic exhibiting a maximum saturation at approximately 33 at. pct cobalt;1 the interatomic distances at room temperature show large positive deviations from Vegard's rule;2 and in the region of 50 at. pct cobalt there is an order-disorder transition which has a large effect on other properties. The thermal expansion data for the system have been reported3,4.5,6 only from room temperature to 100°C, and for this temperature range a minimum in coefficient in the region of 50 at. pct cobalt is well established. 3,4,6 This paper reports the expansion properties in the iron-cobalt system for temperatures from 30 to 850°C, shows the correlation with other physical properties, and proposes an explanation for the interrelation. EXPERIMENTAL PROCEDURE The thermal expansivities of iron-cobalt alloys in 10 pct steps in composition were determined from 30 to about 850°C. The major series of alloys was prepared by induction melting from Armco iron and cobalt rondelles with the addition of about 0.6 wt pct manganese. This series was supplemented by three compositions: high purity electrolytic iron, high purity electrolytic cobalt, and an alloy of 52.1 wt pct cobalt prepared from the high purity electrolytic iron and electrolytic cobalt by vacuum-melting. The compositions of both series of alloys are given in Table I. The specimens for measurement were prepared from the cast ingots by first hot-swaging followed in most instances by cold-swaging to 0.180-in. diam rod. Some alloys in the region of 50 pct cobalt, because of inherent cold-brittleness, were swaged hot to the final diameter. The expansion specimens were approximately 2 ½ in. long with flat-ground and polished ends. Before measurement they were annealed in hydrogen for r hr at 900°C. In the apparatus used for the thermal expansivity measurements (Fig I), a modification of that designed by Hidnert and Sweeney,7 the differential expansion between the specimen and vitreous silica was measured by a dial micrometer reading to 0.001 mm. An invar fixture supported the dial gauge, and this fixture, in turn, was connected to a split invar collar which supported the outer silica tube. A pyrex "T" was placed over the outer silica tube and was sealed to the invar collar by Apiezon Q sealing compound. A movable hollow vitreous silica rod which rested on top of the test specimen slid through a flexible rubber diaphragm cemented to the top of the pyrex "T." The specimen rested on a vitreous silica pedestal fused into the outer tube and was kept centered by a silica sleeve. A non-oxidizing atmosphere was obtained by admitting hydrogen into the

Jan 1, 1948

By AIME AIME

AS a new departure the annual business meeting was held at 4 p. m. on Tuesday, Feb. 16, instead of in the morning, as previously. The retiring President, Robert E. Tally, called the meeting to order and briefly spoke of the large measure of success that had been attained in balancing the budget of the Institute in 1931, so that, although receipts had declined over $26,000 compared to the previous year, expenditures had come within $3,000 of income. He referred in complimentary ,terms to the work of the committees on Membership, Admissions, Papers and Publications, and MINING AND METALLURGY, from which more would be heard late:. He also announced that a large and important committee on economics has been under consideration, and will be announced later. As an evidence of growth it was noted that a new Division, Mineral Industry Education, had been organized just an hour previously.

Jan 1, 1932

By T. B. Nolan, R. N. Hunt

In terms of present metal prices, analysis of extant records of the Eureka district indicate past production of the magnitude of $200,000,000 in recovered silver, lead, and gold. Production to date has been thoroughly oxidized ore from massive replacements, fissures, manta, and pipe-like bodies-in large part from the massive Eldorado (middle Cambrian) and Hamburg (middle to late Cambrian) dolomite horizons. In the productive area of about 6 square miles carbonate rocks comprise 80 per cent of the section, which includes early Cambrian to late Ordovician horizons. Four-fifths or more of the district's production came from a block of Eldorado dolomite in Ruby Hill that was moved in over younger horizons on strands of a regional thrust fault. The lower 500 to 600 feet of the block was much fractured and brecciated and became host to the ores. The Ruby Hill fault, a late normal fault, limits the Ruby Hill block of dolomite on the north for its entire length of nearly a mile and terminates the downward extent and exploitation of its ores. It introduced an hiatus of some 40 years in the district's development. Drilling of the past 20-odd years, followed by underground work, has now exposed the down-faulted extension of the Ruby Hill block of Eldorado dolomite and its contained ores, dropped 1800 feet in a dip shift to depths beneath the surface of 2000 to 3000 feet. The ores at depth are the sulfide counterpart of those mined in early years on the footwall side of the fault. The ores of the district may be attributed to the same source as the intrusive quartz diorite outcropping in a limited way south of Ruby Hill but found at depth elsewhere in drill holes. The long north-south axis of the district, its anticlinal structure, its major faults, and the distribution of the intrusives and, in their relation to the surface, the ores themselves, all suggest that erosion has not cut deep enough to expose the extent of intrusives and the ores consequent upon them.

Jan 1, 1968

By Brahm Prakash, R. Schuhmann

Chemical conditions for flotation and nonflotation of cassiterite and fluorite with oleic acid as collector and with alizarin dyes as modifying agents were studied by means of small-scale, vacuum-flotation tests. Artificial cassiterite was prepared for these tests by high-temperature methods, especially by crystallization from borax melts.

Jan 1, 1950

By A. T. Shurick

THE NRA Administrator's casual reference to the coal code as the next "pineapple" to be fixed was a conservative estimate of his job. This thorny and adamantine morsel now looms as a critical test of NRA. A failure in coal supplies would have the gravest potentialities in the Administration's program at this time. And the loss of prestige from a breakdown of the enforcement machinery in this initial large-scale test of strength would accentuate the incipient indications of insurrection in other directions. General Johnson has had a difficult task. It involves problems festering for a quarter of a century. A succes¬sion of Presidents have been glad to tide over their respective regimens with inconclusive expedients; they have been baffled by the complexities of the technical angles and hopelessly irreconcilable concepts of powerful conflicting interests with large issues at stake.

Jan 1, 1933

NEW MEMBERS The following list comprises the names of those persons who became members during the period Dec. 10, 1916 to Dec. 31, 1916. BOWMAN, Joseph V., Chem., Andes Copper Mining Co., Chanaral, Chile, South America. CALDER, NORMAN L., Min. Geol., Cia. Minera y de Fomento, Watkins, Fomento Prov. de Santa Clara., Cuba. CONRADS, RALPH A., Met. Engr., Magna Plant, Utah Copper Co., Garfield, Utah. FARR, T. H. POWERS, JR. Asst. Assayer, Argonaut Mining Coy Jackson, Cal HAURY, PETER S., Min. Engr ...Alta Loma, Cal. HOULE, ARTHUR, Supt., Shattuck-Arizona Copper Co., Box 2009, Bisbee, Ariz. LEIB, VICTOR E?, Min. Engr 4204 Ave. D, Austin, Tex. LINDSLEY, THAYER, Min. Engr 82 Beaver St.,. New York, N. Y. POTTER, OCHA Supt., Superior Copper Co., Houghton, Mich. ROCCA, BERNARD T.; Engr., Bluebell Mine, Cons. Arizona Smelting Co., Mayer, Ariz. SAFFOLD, RAY P P.'0. Box 436, Douglas, Ariz. THOMS, JAMES EZRA, Asst. Chief, Milling, -Roasting, Acid Depts., Mineral Point Zinc. Co., Depue, Ill. TOMITA, HARUYOSHI, Met. Engr., Mitsubishi Co., Osaruzawa Mine, Akita-ken, Japan.

Jan 2, 1917

By AIME AIME

Gentlemen, we have ten questions on our list and a number of us here probably have other questions to ask. Therefore, we arc going to allocate the time to these different questions so that we will try to be finished by 4:30; from then until 5 o'clock, if any of you have any questions on subjects not related, you will be free to ask them. Mr. Morton and I have changed the order of the questions. Instead of what is now first, we have put No. 3 first, progress on basic-roof construction, inasmuch as we feel that it is quite important. At this time, H. S. Robertson, of Harbison-Walker, is going to give you a short talk, with slides, on what has been done to date on this subject.

Jan 1, 1940

By G. L. F. Powell

TURNBULL and Cech1 reported undercooling small droplets (approximately 50 mp in diam) of a large number of metals by approximately 0.18 TE (TEoK = the equilibrium freezing point). This was considered to be the undercooling for homogeneous nucleation in

Jan 1, 1968

[Year of Election 1944. WALTER HULL ALDRIDGE New York, N. Y. 1946. PETER M. ANDERSON Johannesburg, South Africa 1946. CHARLES CAMSELL Ottawa, Ont., Canada 1946. CHARLES AUGUSTUS CARLOW Fife, Scotland 1946. CECIL DESCH London, England 1946. WILLIAM FRASER London, England 1922. FEDERICO GIOLITTI Torino, Italy]

Jan 1, 1946

NEW MEMBERS The following list comprises the names of those persons who became members during the period of May 10, 1918, to June 10, 1918. ABEEL, GEORGE H., JR., Cons. Min. Engr., .4111 Lafayette Ave., St. Louis, Mo. ALLEN, CARL A Metal Min. Engr., U. S. Bureau of Mines, Butte, Mont. BECKER P. FRANK Engr., Lightner Min. Co., 35 Nassau St., New York, N. Y. BOCK, JAMES H., Steam Shovel Foreman, Chino Copper Co., Santa Rita, N. M. CARRON, FRANK X., Civ. and Min. Engr Rock Springs, Wyo. CROWE, THOMAS B., Mill Supt., Portland Mill, Portland Gold Min. Co., Victor, Colo. DOBSON, PERCY GRENSIDE, Min. Engr. and Geol., Crow's Nest Pass Coal Co., Fernie B. C., Canada. ESTABROOK, W. H., Capt., 3d Bat. 20th Engineers, A. E. F., Care postmaster, N.Y. FRASER, 0. B. J., Engr., International Nickel Co. of Canada, Ltd., Port Colborne, Ont., Canada. GARRIDO,. MANUEL F., Min. Engr 109 W. Myrtle St., San Antonio, Tex. GRODSKY, VLADIMIR ALEXANDROVITCH, Cons. Engr., Motor Products Corpn., Detroit, Mich.

Jan 7, 1918

By David J. Mack, Chin Bea Kim

The decomposition of the Ni-Zn eutectoid at 56 wt pct Zn was studied by isothermal transformation. Its progress was followed by metallographic, hardness, and X-ray diffraction methods. Three transformation products were found: lamellar pearlite at high temperatures; an intermediate temperature structure; and martensite at the lower temperaCures. No transition structu,ves were found. THE decomposition of the Ni-Zn eutectoid at 56 wt pct Zn was stuadied as part of a long-range program of study on the eutectoid transformation in alloy systems which do not have one or more components which exhibit allotropy. Available information on the Ni-Zn eutectoid transformation is limited to that presented in connection with the determination of the phase dilagram. No systematic studies of the eutectoid were found in the literature, alkhough the microstructures of the Ni-Zn eutectoid were reported by Tamuru.3 X-ray diffraction data exist for the ß, ß1, y , and y1 phases.' EXPERIMENTAL PROCEDURE The eutectoid alloy was prepared from "A" nickel shot and Bunker Hill super-purity zinc (99.998 pct).

Jan 1, 1962

By W. R. Barclay

IN MY general contact with industry I have become more and more impressed with the need for the closest possible co-operation between engineers and metallurgists, and particularly with the need for appreciation of the work that each group is doing to assist the other. Also, I am convinced that from time to time it. is vitally important to a true perspective of human progress in all its branches, and certainly a salutary corrective of undue optimism and pessimism to endeavor to carry the mind hack over certain periods in the advance of technical knowledge, and form some kind of broad estimate of what has been accomplished in the application of science to industry in the fields with which we, as individuals or groups, may for the time being be concerned. We cannot without some appreciable mental effort realize what our forerunners have dine For us. If the young engineer or metallurgist entering industry today could be suddenly transported to a quarter of a century ago, and be compelled to work with the materials then available and within the limitations of knowledge then attained, he would, on his return to present-day life, have a much greater appreciation of what has been accomplished before lie arrived on the scene, and, what is even more important, a far more acute sense of its inherent value to his profession. I propose here merely to indulge in a general summary of the subject of improved engineering metals and alloys rather than in details, and to deal exclusively with developments within my own experience.

Jan 1, 1938

By M. G. Corson

THE iron-silicon alloy series has always been one of the most puzzling among the binary alloys. Examining the well known mechanical properties of the iron-rich alloys only we meet the following situation: The ultimate strength and yield point of alloys worked and annealed under the usual conditions represent nearly a straight line function of the silicon content up to 4.5 per cent. silicon (Fig. 1). Starting at the ultimate strength of 35,000 lb. and at a yield point of 16,000 lb. for pure electrolytic iron, one reaches a maximum strength of 93,000 lb. and a maximum yield point of 74,000 lb. at 4.5 per cent. silicon. This corresponds to an increase in ultimate strength by 13,000 lb. per each per cent. of silicon added and nearly the same rate applies to the yield point. The data mentioned are taken from the investigation by T. D. Yensen,1 and while they do not exactly corroborate the results obtained by earlier investigators, they seem to be the most correct. Plastic properties of the alloys are controlled by a much more complicated relationship. Up to 2.5 per cent. Si, the elongation stays close to 50 per cent. (in 2 in.) and the area reduction amounts to 85 per cent;, a situation that forms the usual feature of all alloys representing strictly solid solutions. The plasticity of the latter is always nearly equal to that of their base metal. Beyond 2.5 per cent. silicon, the situation becomes much more complicated. Yensen observed an enormous drop in elongation and area reduction at about 2.65 per cent. silicon, where the first hardly reaches 10 per cent. and the second is still lower; he found, however, a considerable recovery in plasticity at about 2.8 per cent. Si and up to 4.5 per cent. Si it is represented by 20 per cent. for the elongation and 30 per cent. for area reduction.

Jan 1, 1928

By Carle R. Hayward

WHEN lead production began to recede from the peak productions of 1929 many plants took advantage of the curtailed operations to make necessary improvements and repairs about the plant. There followed a period of adjustment to synchronize production and demand, which merged in the present period of marking time. The lead smelting and refining industry has produced little that is new during the past year except in what might be called makeshifts, which have been introduced to make operation at fractional capacity profitable. This is more particularly true in refineries than in smelters. The Parkes process had become standardized during the period of normal production, with softening, desilverizing, and dezink-

Jan 1, 1935

By T. E. Evans, C. T. Baroch

ZrB2 was produced in batches of 4 to 6 Ib by interaction of ZrO2, B4C, B203, and carbon at around 2000°C in a simple graphite resistance furnace. Techniques of production are discussed and the final design of a suitable furnace is described in detail. Several other borides were made by the same technique and the process appears to have possibilities for commercial production. N seeking out new hard and refractory com- pounds, many researchers have turned to the investigation of the borides and excellent papers have been published on the properties of these compounds. Few papers, however, have appeared on the techniques and problems concerned with the production of these high temperature substances. This report describes progress made in developing a method for preparing zirconium diboride, ZrB2, on a pilot plant scale. The literature of the borides and other refractory hard metals recently has been reviewed, annotated, and classified so completely' that it is needless to attempt such an outline here. It is enough to say that three borides of zirconium have been reported: ZrB, ZrB2, and ZrB12.2 ZrB2 is the most stable of these and is especially stable in the presence of carbon up to and including its melting point of around 3000°C. Like most borides, it can be prepared in several ways. It can be prepared by synthesis of the elements, but these are expensive and difficult to produce in a high state of purity. Obviously, production directly from the oxides would have decided economic advantages. In electrolytic production such as that of calcium boride,:' the product is recovered as a sludge mixed with electrolyte; and separation of product from adhering electrolyte and regeneration of the electrolyte is an involved and difficult process. The work on borides was started on a small scale in 1948. Late in 1949, Naval Ordnance expressed a specific interest in ZrB2 and the project then centered on this compound. After the usual experimental work necessary in a new field, ZrB2 of good quality was produced by heating mixtures of B4C, ZrO2, B2O3, and carbon to a temperature of about 2000 °C in a resistance-type electric furnace. Over 100 lb was made for experimental use tests, and the method of production probably could be expanded into a commercial operation. A similar process has been described by Kieffer and coworkers.' The main chemical problems were the development of proper charges to insure complete reduction of the elements, determination of the proper temperature range at which these reductions took place, and adoption of techniques necessary to pre- vent inclusion of such impurities as carbon and nitrides. The mechanical problems consisted of developing a simple practical furnace that would attain the high temperatures required and permit use of a controlled atmosphere when necessary and determining of suitable refractories. Both problems were solved by designing a crucible resistance furnace. Crucible Resistance Electric Furnace Attempts were first made to produce ZrB2 in an electric arc furnace, but such a furnace would not provide the degree of carbon control required for producing clean graphite-free borides, so it was decided to try working in a crucible. Obviously, the furnace would have to be constructed of graphite, as the temperatures required are too high for other refractories or heating elements. Crucibles were made by hollowing out segments of graphite electrodes, which were fitted with a cover and clamped between two electrodes so that the current passing through the thin wall of the crucible would generate heat, using the principle of the Helberger crucible furnace."? Preliminary tests with this type of furnace were encouraging and led to the furnace design shown in Fig. 1. The essential components were a thin-walled graphite crucible resting on a graphite block, which formed the lower electrode assembly, and a top electrode assembly swung from a pipe column making contact with the top of the crucible. The space around the crucible was filled with graphite prepared from waste electrodes crushed to about ¼ in. This packing had excellent insulating properties, both electrically and thermally, and could be removed easily and quickly from around the crucible by means of an industrial vacuum cleaner. The largest resistor crucibles were machined from 8 in. electrode stock and were 26 in. long, with a side wall Yi in. thick and a 1 in. bottom. Temperatures were determined optically by sighting down a 1 in. hole drilled longitudinally through the top electrode and the crucible cover. Sealing this hole at the top was a water-cooled brass sight-glass assembly, shown in Fig. 2. An opening was provided for a light flow of helium to keep the sight opening clear of smoke, and a glass prism above the sight glass changed the line of sight to the horizontal for easier reading. More recently, the prism and optical pyrometer were replaced by a photoelectric recording pyrometer. At first the charges were placed directly in the resistor crucible but this meant that everything had to be withdrawn from the furnace every time the charge was emptied. Later, smaller crucibles were made up that could be placed inside the resistor

Jan 1, 1956

By Henry E. Wood

Cleveland Meeting, October, 1912.) IN my opinion, the concentration of minerals by flotation is the most interesting problem in ore-dressing, and will command eventually far more consideration than it has at present. For many ores it furnishes a complete method of concentration absolutely independent of specific gravity, and thus simplifies the milling of many difficult combinations. Not having to recognize the influence of specific gravity, we are also able to dispense with some of the complications resulting from classifying-conditions. Where flotation cannot be used for a complete separation of the minerals from the gangue, it will be found, in nearly all cases, to save those portions which are generally lost by reason of their fine state of division. For this reason, it should be looked upon mainly as an aid to general concentration, although there are many ores so well adapted to flotation that more than 90 per cent. of the valuable metals can be recovered from them in one operation by this process. In presenting the results of my investigations in. flotation, I have endeavored to theorize as little as possible. That side of the subject has been extensively discussed by others. My earliest work with flotation was done in 1895, when I used various oils, grease, soap, etc., with results that were remarkable. I did not realize then that with water alone equally good separations could be made. Up to 1906, my endeavors were confined to attempts to keep the concentrates on the tables well wetted and away from exposure to the air. In common with others, I observed that when there was any obstruction in. the wash-water on the table of sufficient size to divert the water to either side, the concentrates collected, and, on exposure to the air, would promptly float away. This convinced me that the sulphides were all good " swimmers," and that if,

Nov 1, 1912

By F. R. Koeberlin

ABOUT thirty miles south of the port of Coquimbo, Chile, nestling in one of the western outliers of the main Andes range, lies the little mining town of Andacollo, a place whose history and traditions make up one of the most romantic pages in the life story of this southern republic. The beginning of Andacollo is shrouded in the penumbra of the pre-Columbian era, but its first mining activity probably dates from about the years 1440 to 1460. It was in the middle of the fifteenth century that the Inca Tupac-Yupanqui, grandfather of Atahualpa, conquered this part of Chile. His domain extended even as far south as the present site of Santiago, and perhaps farther, but was maintained with increasing difficulty against the fiercely independent and indomitable tribes of Araucanian Indians of the South.

Jan 1, 1938

By David P. Shoemaker, Clara Brink Shoemaker

The I phase was discovered by Bardos, Malik, Spiegel, and Beck1 in the V-Ni-Si system at 1100°C and in the Mn-Co-Si and Mn-Ni-Si systems at 1000°C. Kuzma and Hladyshevskii2 and Kuzma, Hladyshevskii, and cherkashin3 have reported a new phase, which they named the S phase, in the Mn-Co-Si and the Mn-Ni-Si systems at 800°C at approximately the I phase compositions. The powder diffraction diagrams of the I and S phases, compared by Bardos el al.,1 are related but show distinct differences in relative intensities. Professor Paul A. Beck kindly sent us a specimen of the (v-Ni-Si) I phase for single-crystal study. Precession and Weissenberg diagrams taken with a tiny single-crystal fragment showed that the structure is monoclinic with a large unit cell. The cell dimensions were refined from a powder diffraction diagram taken with CrKa radiation in a 57.3-mm camera with our computer program LSCELP4 using only the indices of those reflections that were observed on Weissenberg diagrams (hnl, with n = 0 through 9 and n = 12) and precession diagrams (Okl, lkl, Izk0, hkl, hk2). Table I shows the agreement obtained between the l/d values calculated with the final values for the cell dimensions and the l/d values observed by Bardos et al .1 for I(V42Ni33Si25), by US for I(V41Ni36Si23), and by Kuzma and Hladyshevskii2 for S(MnpCoSi). The powder patterns contain many broad and diffuse lines. In fact practically all powder lines observed are near-superpositions of several reflections. The refinement program is not set up to handle several reflections contributing to one observed line: the position of each line is refined with the aid of one set of indices only. The final values for the cell dimensions were obtained from the lines of strong or medium intensity with the indices indicated by asterisks in Table I: a0 = 13.403(6), bo = 23.336(15), co = 9.129(6)A ß = 99.11(6) deg The standard deviations (given in parentheses) are those calculated by the refinement program from least-squares theory and do not take into account that the lines included in the refinement may not have been correctly indexed in every case or that the position of a line may also be partly determined by the overlapping reflections. The agreement between the calculated and observed I phase patterns is fairly good, although some discrepancies occur. Not all observed lines could be indexed with the incomplete set of sin-

Jan 1, 1968

By J. Chipman, T. P. Floridis

The equilibrium of gaseous H2O-H2, mixtures with liquid iron is used to establish the activity coefficient of dissolved oxygen as log f o = — 0.20 [%O]. Discrepancies in earlier work are explained or eliminated. Additions of cobalt, molybdenum, tungsten, and platinum increase the activity coefficient of oxygen whereas copper and gold decrease it. THE importance of dissolved oxygen as a refining agent in liquid steel has led to a number of studies of its thermodynamic properties. It is the purpose of this paper to examine the effects of a number of alloying elements on the activity of oxygen in the steel bath. As a preliminary to the study of the effects of alloying elements, it seemed desirable to examine certain minor discrepancies in the published data on the properties of oxygen in simple iron-oxygen solutions. The activity and free energy of oxygen in liquid iron were studied by chipman1 in 1933 by means of the reaction h2(g)+-o = H2O (g);K; = PH2O/PH2[% O] [1] The data were in fairly good agreement with calculations from results on the similar reaction CO (g) + O- = CO2 (g); K2 =P CO2/P CO [% O] [2] which had been obtained by Vacher and Hamilton2 as an incidental part of their study of the reaction of carbon with oxygen dissolved in the melt. It was found that the equilibrium ratio k1 was not a true constant but varied with the oxygen concentration in the manner shown in Fig. 1, which is copied from the original paper. This early observation has been refuted in subsequent work but is confirmed in the present paper, and an explanation of the discrepancy can now be presented. In Fig. 1, the two points on the extreme right were disregarded in drawing the

Jan 1, 1959

By T. J. Koppenaal, M. E. Fine

The critical resolved shear stress of aCu-A1 single crystals has been investigated as a function of composition, testing temperature, and strain rate. The strength, and its temperature and strain rate dependency increase markedly with aluminum content. The solid solution strengthening at 4.2°K is much larger than at room temperature. The activation energy for the low temperature dislocation cutting process increases from about 0.17 ev for a 0.5 at. pct A1 alloy to about 0.50 ev for a 14 at. pct A1 alloy. This result is attributed to an increase in the width of extended dislocations due to the known decrease in the stacking fault energy. In addition, the activation volumes at 4.2 and 77°K decrease with aluminum additions. Concerning the solid solution strengthening in the 296° to 373°K range, no definite conclusions are reached, but it is suggested that subgrains and cutting of subgrains are important. In a previous paper,' the authors reported that adding aluminum to copper produces two types of strengthening: a yield point effect and an increase in the lower yield stress. This behavior is illustrated in Fig. 1 by shear stress-shear strain curves of furnace-cooled single crystals of pure copper and Cu-14 at. pct A1. The yield point effect, At, was thoroughly studied previously1 and shown to be associated with short-range order. The present paper reports an investigation of the lower-yield stress in aCu-A1 single crystals as a function of composition, testing temperature, and strain rate. EXPERIMENTAL PROCEDURE Single cryski1 tensile specimens were prepared in the same manner as previously described.l Briefly,

Jan 1, 1962