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By E. S. Greiner

STUDY of the plasticity of germanium or other semiconductor crystals affords unusual opportunities to extend our knowledge of deformation mechanisms. Crystals are available having extraordinary perfection and very high purity. They deform by slip on the systems {111} <110>,1-3 as do crystals of the simple face-centered-cubic structure. Dislocations generated in them during slip are easily revealed in the form of etch pits on either (111) or (100) surfaces.4,5 This fact alone makes possible more detailed studies of mechanisms than is usually the case with metals but, even further, the effect of deformation on their electrical conductivity is very large compared with metals. This comes about not only because the mobility of the charge carriers is reduced, as in deformed metals, but also because the number of these carriers is greatly altered. This latter effect seems closely related to the formation of both line and point imperfections during deformation and thus provides a needed tool for the study of the kinds and distributions of these imperfections. Other investigators have deformed germanium at elevated temperatures by bending,1, 6-8 compres-sion,6, 0,10 tension,2,3,6,11,12 torsion,23 and indentation." Wang and Alexander" have also reported successful indentation at room temperature. Dislocation etch pits consequent to deformation have been observed and studied.7,8,10,18,14,20 The experiments to be de- scribed here include principally the compression and the subsequent annealing of germanium with concomitant studies of etch pits, microstructures, and electrical properties. Both single crystals and heavily twinned specimens were used. Some indentation studies are included. Experimental Methods Plastic compression was effected in the apparatus shown schematically in Fig. 1. It consists of two tantalum platens contained in a helium atmosphere and so arranged that pressure can be applied by a hydraulic press. The specimen between the platens is heated by the surrounding furnace. The specimen is usually a small crystal cube about 0.30 in. on an edge. A control specimen is always inserted so, that it is subject to the same thermal cycle as the one being deformed. This serves to detect any impurity contamination that might accompany the thermal treatment. For high temperature work, where such impurity contamination often occurs, the specimens were first plated with gold whenever subsequent electrical properties were to be determined. This method" is effective in preventing significant contamination of germanium up to temperatures at least as high as 750°C, as evidenced by the constancy of the electrical conductivities of control specimens subjected to the same heat treatments. The total range of temperature used for deformation was from 375°C, the lowest at which significant flow was observed, up to 900°C. Microscopic examination was made after mechanical and chemical polishing and etching. Dislocation pits were revealed with CP-4 etchant by the tech-

Jan 1, 1958

By A. C. Losekamp, R. M. Fincel, J. B. Conway

TANTALUM like several other metals exhibits a great affinity for or reactivity with certain gases. Tested in atmospheres which are not completely pure this metal becomes contaminated by certain impurities (notably nitrogen, oxygen, and hydrogen) with a resultant change in various properties. Well-known are the drastic changes in hardness, ductility, and electrical resistivity. Also previously recorded are the distortions of the lattice1,2 accompanying the increased content of oxygen and nitrogen in tantalum. This pronounced affinity for certain gases along with the significant property variations thereby produced makes it necessary to observe additional experimental precautions in making various property determinations with tantalum. Some recent measurements of the linear thermal-expansion characteristics of tantalum have made this point quite emphatically. Failure to observe the greatest precautions in reducing the contaminating influence has led to some extremely distorted results. Not only does such operation lead to different heating and cooling curves during the thermal-expansion measurements, but upon cooling to room temperature the sample is found to have suffered a permanent (actually semipermanent since the specimen can be returned to its original length by a 3-hr degassing treatment in vacuum at 2300°C) elongation. In addition, subsequent heatings will not follow the initial heating curve unless the expansion measurements are based on the actual specimen length at the beginning of the heating cycle. These thermal-expansion measurements were made by positioning the specimen horizontally at the longitudinal midpoint of a 20-in.-long, 4-in.-diam resistively heated tungsten tube furnace. The specimens were in the form of 20-mil sheet formed into a sharp U-shape about 0.3 in. in width and 0.3 in. in depth. Fiducial marks in the form of 0.010-in. holes drilled at either end of the 2.5-in.-long sheet specimens were viewed by a paired filar micrometer telescope system mounted on an Invar bar on the top of the furnace. Tests were made in helium with temperatures measured by a Pt/Pt-lORh thermocouple to 1000°C; above 1000°C temperature was measured by means of an optical pyrometer sighted into a black-body hole drilled into the specimen-holding fixture in the vicinity of the specimen. Previous tests with black-body holes drilled in a 0.25-in.-diam rod specimen had confirmed the temperature uniformity between specimens and specimen-holding fixture in this furnace. A typical thermal-expansion curve for arc-cast tantalum in helium is shown in Fig. 1 for the case where no attempt is made to remove all the impurities from the cover-gas atmosphere. The initial heating curve appears smooth and has a shape characteristic of all metals. However, it is known that the sample begins absorbing impurities at temperatures above 1000°C which are sufficient to distort the lattice and lead to specimen lengths which are somewhat larger than would be obtained in the absence of contamination. During the cooling cycle the expansion curve is seen to be significantly different from the heating curve. This is due to the impurity content causing a semipermanent (i.e., permanent until the impurities are removed by vacuum degassing) deformation which will not allow the speci-

Jan 1, 1965

By J. H. Wernick

IN temperature-gradient zone-melting1 a molten zone is moved through a solid or across a solid surface by the establishment of a temperature gradient. This technique has both practical and fundamental aspects. One practical application is to make p-n junctions for semiconductive devices, particularly for devices in which the junctions are desired within the semiconductor. From a fundamental point of view, the technique is being investigated as a method for determining diffusivities in liquid alloys, and preliminary diffusivity results have been reported by the writer." In this paper, the effects of crystal orientation, temperature, and molten zone thickness in temperature-gradient zone-melting, and the bearing of these effects on diffusivity measurements and n-p-n junction formation are discussed. Experimental Procedure An effect of crystal orientation was noted in early experiments. To facilitate its study, movements of wire zones across a surface, rather than through the body of a single crystal, were observed for various surface planes and travel directions. The experirr-entai setup is illustrated in Fig. 1. The graphite end-section for the high temperature heater has an apron about 1/16 in. above the upper surface of the crystal. This apron insures that the surface temperature of the block is equal to or greater than the temperature within the block at every point, Thus, the zone does not penetrate the block and convection in the liquid is minimized. The experi-through a block is shown in Fig. 2,

Jan 1, 1958

By Michael B. Bever, Barton Roessler

The effects of deformation by wire drawing at 78OK on initially ordered and initially disordered specimens of the alloy Cu3Au were investigated. The resistivity, stored energy, drawing force, and microhardness were measured as functions of strain; microstructural changes were observed. The results are interpreted in terms of the structural imperfections and the changes in atomic configuration resulting from deformation. A few experiments on the effects of room-temperature annealing after deformation at 78°K were made; they suggest vacancy-promoted ordering in disordered alloys. BARTON ROESSLER, Junior Member AIME, formerly Graduate Student and Alcoa Fellow, Department of Metallurgy, Massachusetts Institute of Technology, Cambridge, Mass., is with Westinghouse Research Laboratories, Pittsburgh, Penn. MICHAEL B. BEVER, Member AIME, is Professor of Metallurgy, Massachusetts Institute of Technology. Based in part on o thesis by B. ROESSLER submitted in October, 1959 to the Massachusetts Institute of Technology in partial fulfillment of the requirements for the degree of Doctor of Science. Manuscript submitted April 6, 1961. IMD AN investigation of the effects of deformation at room temperature on the alloy Cu3 Au was reported in a recent paper,&apos; which included a review of the literature on the deformation of order-disorder alloys. In general, plastic deformation of ordered alloys reduces the degree of long-range order and causes corresponding changes in their properties. Deformation of disordered alloys changes their properties in a manner characteristic of solid solution alloys; these changes can in part be attributed to the destruction of short-range order. The effects of deformation on solid solution alloys are of two kinds: 1) generation of structural imperfections, which occurs as a result of deformation in any metallic system including pure metals, and 2) changes of atomic configuration, which are characteristic of solid solutions and particularly of order -disorder systems. These two types of effect are not independent of each other and the state of a deformed solid solution alloy is determined in a complex manner by the way in which the structural imperfections cause changes in atomic configuration both during and after deformation.

Jan 1, 1962

By A. S. Appleton, M. B. Bever, G. E. Dieter

A gold-silver alloy was deformed by explosive loading at shock pressures up to 510 kbars. The stored energy and hardness increased over the whole range of pressures; the largest rates of increase were observed between 120 and 150 kbars. In this range, markings rkavacteristic of defornation twins first appeared; higher pressures produced markings in all grains. These effects are compared with those of conventional deformation processes and are discussed in relation to probable structural changes. In recent years, increasing efforts have been devoted to the investigation of the effects produced in metals by the passage of high-intensity shock waves of explosive origin. By properly utilizing the energy released by the detonation of a high explosive, it is possible to generate pressure pulses of the order of 500 kbars and higher. (One kbar equals l0 9 dynes per sq cm or approximately 1000 atm.) The passage of a shock wave through a metal occurs at pressures which are very much greater than the yield strength. As the shock front passes a point in the metal, the pressure rises almost instantaneously, and continues to act at the point for a few microseconds. Thus, metals subjected to explosive shock loading experience a nearly instantaneous increase in pressure, and a subsequent release of pressure, which is almost as rapid. Under these conditions mechanical twinning and shear transformations occur readily. smith1 has investigated the metallurgical changes in copper and iron resulting from exposure to explosive shock waves. He found an appreciable increase in hardness in both metals. In copper, a hardness greater than that resulting from 95 pct reduction in thickness by rolling was obtained, yet in the explosive deformation, the thickness of the specimen decreased only a few percent. After explosive loading, the micro-structure of copper showed markings characteristic of mechanical twins. The amount of stored energy resulting from explosive loading is of interest. Measurements of the stored energy of cold work as a function of strain, temperature, strain rate, and composition have been made with gold-silyer alloys deforyed by rolling, orthogonal cutting,3 drilling,4 filing, wire drawing, and torsion. The investigation reported here was also carried out with a gold-silver alloy and its results can be compared with those for the deformation of this alloy by more conventional methods. EXPERIMENTAL PROCEDURES An alloy containing 82.6 wt pct Au and 17.4 pct Ag was purchased in several batches from Handy and Harman Co., New York, as annealed rod 1/4 in. dim. The rod was cold-rolled to a sheet approximately

Jan 1, 1962

By W. A. Backofen, R. L. Fleischer

Single crystal, bicrystal, and polycrystal tensile tests of aluminum at 4.2°K, 77°K, and 300°K have been used to examine the role of grain boundaries in the deformation process. Results indicate that a grain boundary may affect the extent and slope of easy glide. The stage II hardening rate, on the other hand, is independent of the presence or absence of grain boundaries. This conclusion allows the size of the region of multiple slip caused by an incompatible grain boundary to be determined. For the size of bicyystal sample used in this study, multiple slip occurs in about half of the cross section. PREVIOUS studies of the stress-strain characteristics of bicrystals of face-centered-cubic metals have been limited to aluminuml-5 at room temperature. Recent results, however, indicate that the stress-strain curves of single crystals of such metals may be separated into at least three stages6 in which different deformation processes are occurring7 provided testing is done at sufficiently low temperatures.&apos; Since for aluminum a well-defined stage II develops only below room temperature, previous studies have not been able to relate effects of grain boundaries to all of the three stages of deformation. It is therefore to be expected that low-temperature deformation of aluminum single crystals and bicrystals should clarify the effects of grain boundaries on the different processes of deformation. EXPERIMENTAL PROCEDURE Single crystals and bicrystals were grown from the melt by the standard techniqueg with aluminum reported by Alcoa to be 99.993 pct pure. Ridges in the boat were used to guide the grain boundary during growth, assuring that the boundary would bisect the sample.10 The rate of furnace motion during growth was 1.0 cm per hr. During growth zone purification resulted, as evidenced by the ability of the first material to freeze to recrystallize at room temperature following severe deformation. Samples were approximately 4.4 X 6.6 mm in cross section and 103.5 mm in length between grips. Samples were annealed at 635" i 5°C for 40 hr and furnace cooled over a 7-hr period. They were then electropolished in a solution of 5 parts methanol to 1 part perchloric acid at a current density of 15 amp per sq dm for about 30 min at temperatures below 0°C. Tensile testing was performed at 295" (room temperature), 77" (sample in liquid nitrogen), and 4.2"K (sample in liquid helium) on the hard-type machine indicated schematically in Fig. 1. The machine con- sists basically of a tube surrounding a rod; one end of the sample is attached to each member, and the rod is pulled up the tube to extend the sample. The rod is rigidly mounted and is moved vertically by a system described by asinski." The pulling force is measured continuously by an electrical strain gage load cell, and the relative displacement of the tube and rod is also recorded continuously by a soft cantilever beam with electrical strain gages. Maximum stress and strain sensitivities were ±2g per sq mm and * 3-10-5. In all tests the strain rate was approximately 5.10-5 per sec. The thin wires in the tensile apparatus introduce softness, which may be corrected for, however, by measuring load vs displacement with the sample replaced by an elastic member. For loads greater than 15 kg the spring constant is 1.875.106 g per cm. The flexible wires also served to reduce substantially the large shearing forces which may arise in the case of grips having horizontal rigidity.&apos;&apos; As in any gripping system, however, bending moments will arise in the course of deformation by single slip. Engineering stress, s = (load)/(original cross-sectional area), and strain, E = (increase in length)/ (original length), are used for stress-strain curves unless otherwise indicated. Tables list resolved shear stress, T=mo and shear strain ? = dm, where m is the usual Schmid resolved shear stress factor for the primary slip system at the start of deformation. The first group of samples to be described forms an isoaxial set, all of the crystals making up the single crystals or bicrystals having the same tensile axis, the orientation of which is indicated by the cross in Fig. 2. For this orientation the primary slip plane and slip direction make angles of 45 deg with the tensile axis and the Schmid factor m has its maximum possible value of 0.5. Rotations about the tensile axis are indexed by means of an angle 0 between the small-area surface of the samples and the projection of the primary slip direction onto the cross section, as defined in Fig. 3. In single crystals, values of 0 were 0 and 90 deg, while in bicrystals 0 values were (0 deg, 180 deg), (90 deg, 270 deg), and (0 deg, 90 deg) as indicated in Fig. 4.

Jan 1, 1961

By H. I. Aaronson, S. Toney

When the component grains of .ferritic hicrystals of an Fe-1.55 pct Si alloy are disoriented through an angle "6 " about a conzmon [ll0] axis, the tendency for preferential growth of austenite crystals along the grain boundary during transformation at elevated temperatures is small when 11 deg, but increases rapidly at larger angles. This type of orientation-dependence indicates that grain boundary diffdsion promotes preferential growth along large-angle boundaries. Morphological differences between austenite crystals formed at small-angle [1101 and [loo] boundaries suggest that precipitate morphology can be dependent on the dislocation structure of the boundary. ThE morphology of precipitate crystals nucleated at a grain boundary can be significantly affected by the structure of the boundary.&apos; The limited amount of experimental evidence available in the literature indicates that the morphological effects of boundaries made up of arrays of dislocations, such as subbound-aries and small-angle grain boundaries, are different from those of boundaries having essentially disordered structures, i.e., large-angle grain boundaries. On the basis of indirect evidence, it has been concluded that large-angle grain boundaries give rise to the formation of grain boundary allotriomorphs (crystals which nucleate at grain boundaries, and grow preferentially and more or less smoothly along them)2 in the proeutectoid ferrite and the proeutec-toid cementite reactions in plain-carbon steels, and apparently also in many non-ferrous alloys.&apos; At small-angle grain boundaries in a plain carbon steel, on the other hand, ferrite crystals were found to take the form of primary side plates. Similarly, Guinie, loys. Primary sideplates formed at a subboundary with a constant orientation tend to be parallel to only one, or occasionally two matrix habit planes, and a marked change in the orientation of the boundary is accompanied by a change in the habit plane. Previous studies on the morphological effects of grain boundary structure were performed on poly-crystalline aggregates. Information on the disorien-tation of the pairs of grains forming the boundaries at which the various morphologies appeared in these specimens was largely either qualitative or semi-quantitative. Precipitate morphologies accordingly could not be accurately and systematically correlated with grain boundary structure, and thus theories which have been proposed for the various morphological effects could not be satisfactorily tested. This investigation was undertaken in an attempt to remedy these deficiencies by studying the morphological effects of grain boundary structure with a method in which the boundaries are formed by matrix grains whose disorientations are known and controlled with reasonable accuracy. EXPERIMENTAL PROCEDURE The crystallographic requirements of this study were fulfilled by means of oriented bicrystals of silicon-iron. Disorientation of the component ferrite crystals was carried out about common, major crystallographic axes through angles ranging from 1/2 to 44 deg. The silicon content was low enough SO that the bicrystals could be partially transformed to austenite by heating to elevated temperatures. The silicon-iron used had the following initial composition: 1.55 pct Si, 0.04 pct C, 0.0031 pct N, 0.17 pct Mn, 0.020 pct S, and 0.002 pct P. The alloy was obtained in the form of 0.036-in. sheet. The procedures employed to prepare seed crystals in strips of this sheet, to reorient the seeds, and to grow them into bicrystals are essentially those described by Dunn and Nonken and aynes." The characteristics of the bicrystals are given in Table I. The "bicrystal type" indicates the crystallographic plane parallel to the broad faces of the strip in both grains and the crystallographic direction which was parallel to the long edges of the strip in both grains prior to disorientation. The angular disorientation of the grains, 8, which was performed about the direction normal to the plane of the broad faces of the strip, was measured between the [ 00l] directions. Orientation of the grain boundary, , was taken as the angle between the plane of the grain boundary and a plane containing the axis of disorienta-

Jan 1, 1962

By William D. Klopp

A study was conducted of the tensile and creep properties of are-melted and electron-beam-melted tungsten over the temperature range 2250° to 4140°F. The tensile and creep strengths vary with pain size, the finer -grained materials being stronger. The activation energy for transient creep at 2250° to 3500°F is 95,000 cal per (g)(mole), while that for steady creep at 3300o to 4000°F is 141,000 cal per (g)(mole). At 2875o to 3300°F the apparent activation energy for steady creep decreased with decreasing temperature. It is suggested that cross slip is rate controlling during transient creep, while dislocation climb is rate controlling during steady creep above 3300° F. ALTHOUGH considerable data have been generated on the high-temperature tensile properties of powder-metallurgy tungsten,1 relative few data have been published on the properties of are-melted2 or electron-beam melted tungsten.3 Furthermore, the available data show a fairly large amount of scatter at high temperatures. The effects of structure and purity have not yet been defined, aside from observations that high-purity electron-beam (EB)-melted tungsten3 and single-crystal-plasma-flame tungsten4 are weaker than less pure powder-metallurgy tungsten. The creep behavior of powder-metallurgy tungsten has been studied, but no data are available on the creep behavior of tungsten consolidated by melting. Green5 found that powder-metallurgy tungsten exhibited linear creep at 4082° to 5072°F with an activation energy of 160,000 cal per (g) (mole). The similarity of this activation energy to that of 153,000 cal per (g)(mole) for volume self-diffusion6 suggests that recovery of strain hardening by dislocation climb is rate controlling in this temperature range. In studies at 4800°F, Sutherland and Klopp7 concluded that grain size significantly affected the creep behavior of commercial powder-metallurgy materials. This grain-size effect was suggested by sherby,8 although the opposite relation had been reported for aluminum.&apos; The purpose of the present study was twofold: first, to provide baseline data on high-temperature tensile and creep properties of are-melted and EB-melted tungsten for concurrent tungsten alloy studies, and, second, to determine the phenomenolo-gical effects of structural and purity variables on the high - temperature mechanical properties of tungsten. EXPERIMENTAL The are-melted tungsten materials were prepared by melting sintered 1-1/4-in.-diam electrodes into 2-1/2-in.-diam by 5-in.-long ingots. The are-melting facility has been described previously.&apos; Eight ingots were melted, machined, and hot-extruded at

Jan 1, 1965

By A. A. Burr, D. G. Ebeling

The effects of casting texture, grain orientation and grain size upon the performance of Alnico permanent magnets is described. Single-crystal specimens were produced by special sintering and grain coarsening techniques to study the effect of crystal orientation. In addition to texture and orientation effects, an analysis of the results indicates that the permanent magnet performance is impaired by a refinement of the grain size. AN excellent historical review of the development of Alnico permanent magnets has been prepared by Bozorth.1 The desirable permanent magnet characteristics of Fe-Ni-A1 alloys were discovered in 1932 by Mishima.2,3 The work of Ruder&apos; showed that the alloys were age-hardenable, and Betteridge5 defined the best composition and heat treatment for the magnetically isotropic alloy known as "Alnico 3." Horsburgh and Tetley0 increased the energy product by the addition of cobalt and copper, "Alnico 2," and Oliver and Sheddon7 demonstrated that cooling in a magnetic field improved the residual induction of this alloy. Jonas8,9 then disclosed the great practical benefits of heat treating an alloy of higher cobalt content in a magnetic field and the resulting alloy, "Alnico 5," has become the standard of the industry. This paper describes the fundamental aspects of a procedure which can be used to further improve the properties of these anisotropic permanent magnet alloys. A study of the casting techniques used in the production of anisotropic Alnico permanent magnets indicated that the magnetic quality was affected by the as-cast macrostructure. Improved performance was observed in magnets containing a high percentage of columnar grains whose long axes were parallel to the magnetic axis of the casting. McCaig10 studied the effect of such columnar grain structures upon the magnetostriction characteristics of similar alloys, however no data was presented showing the effects on other magnetic properties. The following paragraphs describe two experiments which were conducted to determine the effect of various grain orientations upon the energy product. Special composite molds were prepared of highly conductive and highly refractive components to remove the heat of solidification from the casting in a controlled manner. Representative macrostructures produced by these techniques are shown in Fig. 1, along with the relative volumes of favorably oriented columnar grains. The alloy, Alnico 5, has the highest permanent magnet performance of any commercial magnet material. It has the nominal weight composition of 8 pct Al, 14 pct Ni, 24 pct Co, 3 pct Cu, and 51 pct Fe. A heat of this material was cast into molds producing the type A and B grain structures shown in Fig. 1 and pairs of the resulting magnets were placed in heat-treating boats so as to eliminate any biasing effects of boat position. After a standard heat treatment the type A magnets, with 16 pct of the volume composed of favorably aligned grains, had a maximum energy value of 3,940,000 gauss-oersteds, while the type B magnets with 73 pct aligned grains averaged 5,090,000. This large im-

Jan 1, 1954

By W. R. Hansen, F. W. Boulger

Twenty-nine laboratory steels were studied to determine the effects of composition and ferrite grain size on drop-weight and Charpy V-notch transition temperatures. The experimental steels covered the following ranges in composition.. 0.10 to 0.32 pct C, 0.30 to 1.31 pct Mn, 0.02 to 0.43 pct Si, md nil to 0.136 pct acid-soluble Al. Although most of the data were obtained on hot-rolled samples, some plates were heat-treated in order to cover a wider range in ferrite grain size. The experimental data were used for a multiple-correlation analysis conducted with the aid of an electronic computer. The study showed that carbon raises and that manganese, silicon, aluminum, and finer ferrite grains lower both drop-weight and Charpy transition temperatures. Quantitatively, variations in composition and grain size have a more marked effect on V15 Charpy transition temperatures than on the drop-weight transition temperature. Useful correlations were found between transition temperatures in drop-weight tests and those defined by seven different criteria for Charpy tests. Evidence was accumulated that the conditions ordinarily used for drop-weight tests are more severe for 1-1/4-in. -thick plate than for 5/8- to 1-in. -thickplate. PROJECT SR-151, to study quantitatively the effects of metallurgical variables on performance in the drop-weight test, was established by the Ship Structure Committee late in 1958 on recommendation of the National Academy of Sciences, National Research Council. This project was initiated as a result of the increasing use of the drop-weight (nil-ductility) test in predicting the ductile-to-brittle behavior of steel. Qualitative data indicated the drop-weight was not as sensitive to metallurgical variables as the Charpy V-notch test. Furthermore, the available information indicated that the drop-weight test did not show the superiority of killed steels over semikilled steels reflected by Charpy tests. This difference in sensitivity to brittle fracture is considered important because the drop-weight transition temperature has been reported1 to correlate better with service-temperature failures than the V-notch test does at a constant energy level. Therefore, this project was concerned with establishing quantitatively the effects of metallurgical variables in the drop-weight test. For comparison, Charpy V-notch data were obtained for the steels investigated. This paper summarizes the results of the investigation. Most of the steels used for the study were made and processed in the laboratory. However, some tests were also made on commercial killed steels available from Project SR-139 (SSC-141). During the course of the investigation, data were obtained on the effects of carbon, silicon, manganese, and aluminum on transition temperatures of drop-weight and Charpy specimens. In addition, the effects of heat treatment which changed the ferrite grain size and the transition temperatures were also investigated. Finally a few exploratory studies were made on commercial killed steels to evaluate the effects of plate thickness, grain size, and heat treatment on the performance of drop-weight specimens. EXPERIMENTAL PROCEDURES Preparation of Materials. A total of twenty-nine 500-lb induction-furnace heats were made and processed in the laboratory for the investigation. Carbon, manganese, silicon, and aluminum contents were systematically varied. Melting and rolling techniques proven satisfactory in a previous project2 were used as a guide for the current investigation. Composition. The composition of the twenty-nine laboratory heats made for this project are given in Table I. The steels are divided into three groups. The first group consists of ten aluminum-killed steels similar in composition to Class C ship-plate steel. The second group consists of ten semikilled or Class B type steels. In both of these groups the carbon and manganese contents were intentionally varied over a wide range. This wide range in composition was helpful in obtaining quantitative data from a limited number of steels. The primary purposes of these two groups of steels was to determine the effects of carbon, manganese, and deoxidation practice. In addition, one steel in each group (Steels 2-2 and 9-2) were made about 1 year after the start of the program in order to check consistency of melting practice. The third group of nine steels listed in Table I was intended for studies on the effects of silicon and aluminum. In eight of these steels carbon and manganese were held relatively constant at levels of about 0.2 and 0.8 pct, respectively, while silicon and

Jan 1, 1963

By G. W. P. Rengstorff, L. E. Olds

High purity molybdenum ingots containing controlled amounts of a single impurity element (oxygen, nitrogen, or carbon) were prepared. These ingots were tested for ductility by bending test specimens at various temperatures. The relationship between the plastic behavior of the ingots and their chemical composition has been determined. MANY proposed applications for molybdenum require ductility at or near room temperature. At the present time, it is possible to obtain wrought molybdenum with considerable ductility only if special fabrication techniques are used to control the grain structure. Starting with are-cast or powder metallurgy ingots, the usual methods for obtaining ductility rely on fabrication procedures that result in fibered microstructures in the finished product. Recently, it has been found that the ductility of either powder metallurgy or are-cast molybdenum can be improved by uniform recrystallization of the metal to a very fine equiaxed grain structure.&apos; The need for a fibered or a fine grained structure may limit the practical usefulness of molybdenum. For example, welding. which may be used in fabricating the metal, generally produces coarse grained structures that lead to brittleness. This applies, certainly, to currently available commercial molybdenum. Although commercial molybdenum is brittle when the grains are coarse, it has been shown experimentally that fine grained structures are not always essential for ductility. For instance, as-cast molybdenum with a coarse columnar grain structure is ductile if it is sufficiently pure.&apos; Because high purity cast molybdenum has good ductility even when coarse grained, it is probable that the brittleness in coarse grained commercial molybdenum is caused by the impurity content of the metal. Although the general effects of impurities on the cold ductility of molybdenum have been known in a qualitative manner for some time, no quantitative evaluation of these effects has been available. The present investigation was made in order to determine more accurately the effects of oxygen, nitrogen, and carbon on the cold ductility of cast molybdenum. Oxygen has long been known to be detrimental to ductility, although the minimum amount which will embrittle molybdenum has been open to speculation. Parke and Ham" showed that ingots with oxygen contents above 0.003 pct could not be forged. Maringer and Schwope have described the embrittle-ment of molybdenum wire by oxygen. A discussion on the effects of heat treatment on the distribution of oxygen in molybdenum has been given by Perry, Spacil, and Wulff." Although nitrogen would also be expected to have harmful effects on ductility, no extensive work has been done previously to determine whether this is so. However, Tury and Krausz" found that wires presumably with less than 0.007 pct N were brittle. Carbon is added to commercial cast molybdenum for deoxidation. Parke and Ham" have shown that molybdenum containing as much as 0.06 pct C could be forged if the oxygen was kept below 0.003 pct. Also, Bruckart and others&apos; found that the room temperature ductility of sintered molybdenum improved with carbon contents up to 0.84 pct. However, Rengstorff and Fischer&apos; found that residual carbide particles in cast molybdenum apparently had an unfavorable effect on room temperature ductility.

Jan 1, 1957

By S. I. Liu

THE effects of strain histories, consisting of several prestrains in opposite directions, on the flow and fracturing characteristics of metals determined in a final test have been investigated previously.&apos;" Such strain histories vary from a single prestrain in tension or compression to the number of strain cycles leading to fatigue failure.&apos; Between these two limits, various strain histories could be visualized and some can be attained readily. One such example is a strain history consisting of a first prestrain in tension of various magnitudes and a second prestrain in compression also of various mag-nitude. In this investigation the strain history was extended to the combination of these two limits, i.e., a single prestrain in tension or compression followed by balanced strain cycles of a selected magnitude e, = k0.12. It was found in this case that only compressive initial prestrains could be investigated with sufficient accuracy.* Such strain histories can be considered also as (low cycle) fatigue tests of a metal subjected to various amounts of cold working. It appears from previous publications that cold working within a wide range of reductions usually raises the un-notched fatigue strength of many metals.&apos;-&apos; This effect, however, has been found to be inconsistent and sometimes reversed for other metals?.7 Furthermore, Ludwik reports that the yield strength of cold-worked specimens may be reduced by cyclic strains, while that of materials without cold work is generally increased in the initial cycles." " In addition to the above tests, a study was made of the effect of intermediate re-solution heat treatment on low cycle fatigue behavior. Such anneals should eliminate the strain hardening induced by the cyclic strains. As far as their effect on the fracture characteristics is concerned, a few previous tests seemed to indicate that the damage resulting from cyclic strains is retained only partially after heat treatment." A further investigation was made in which one specimen was subjected to repeated unbalanced tension cycles in which the strain interval was approximately $ 0.013. This repetition of plastic tension damages the material slightly. This result appears to confirm Ludwik&apos;s observations." " Commercial 3/4-in. rod of the aluminum alloy 24ST4 was selected for this investigation. The material was subjected to the following treatments before machining: 1—Re-solution treatment at 920" ± 10°F for 45 min, 2—water quench at room temperature, and 3—aging for four days at room tem-perature.? The treated material then was machined to desired specimen contour and tested. A coolant was used during machining to minimize any artificial aging effects of heating during machining. In some cases the 24ST4 specimens were reheat treated after having been strained. In these cases, the heat treatment was the same as the re-solution heat treatment described above. Procedure As shown in Fig. 1, threaded end specimens with a minimum diameter of 0.266 in. and a contour radius of 2 in. were used for prestraining to an axial compressive strain ranging from 6, = —0.10 to E, = —0.48. For large prestrains, two consecutive corn-

Jan 1, 1952

By D. W. Lillie

Property changes produced by irradiation of Al-0.4 wt pet Li alloys at 270°C to a burnup of 0.155 pct of all atoms are described. Metallographic evidence of the formation of internal pores and the concentration of gases at grain boundaries is shown. Some conclusions are drawn concerning desirable property characteristics for resistance to radiation swelling. RADIATION induced gases are of great practical significance in nuclear engineering since they affect the behavior of fissionable fuels and control rod materials. In fuels the gases xenon and krypton are the major offenders, producing serious em-brittlement at low irradiation temperatures and gross swelling at high irradiation temperatures. In control rod materials containing boron, the production of helium from the B 10 (n, 0) Li7 reaction produces similar reactions. Since the trend in reactor design is for operation at increasingly high temperatures, the phenomenon of high-temperature swelling by these induced gases has been the subject of considerable recent study. The objectives of such work have been to obtain engineering information and quantitative data on the effects in specific fuels and control rods and to obtain further understanding of the mechanism of gas damage so that more intelligent corrective steps can be made. Analogue systems are often useful for the latter objective and in this case alloys containing Li are suitable in view of the reaction Li6 + n - He4 + He 4. Both products are gases and no serious radiation problem is produced to complicate post irradiation handling. Considerable caution is, of course, necessary in any operations in which tritium release is possible. The present program was initiated to provide a detailed study of the effects of He + H3 generated by irradiation in Li-bearing alloys. The results on Mg-Li solid solution alloys have been reported elsewhere.&apos; This paper presents information on irradiation of an A1-0.4 pct Li alloy in which the lithium was present as highly enriched Li6 in order to maximize the radiation burnup. PROCEDURE The original intent in the selection of the alloy content was to have Li in solid solution at all temperatures. It became apparent, however, that the solubility of Li in A1 was substantially lower than that reported in the original reference consulted.&apos; This was substantiated by the work of Nowak3 who reported solubility of less than 0.01 pct Li at 100°C. The alloy used (0.4 pct Li) was therefore two phase at room temperature. The irradiation temperature was estimated to be about 270° C, and at that temperature all or almost all of the Li would be soluble under equilibrium conditions. The precise state of the alloy under irradiation is not known. Aluminum used was 99.996 pct purity (max. impurities Si 0.002 pct, Mg 0.001 pct, Fe 0.0005 pct, and Cu 0.0005 pct). The lithium was obtained from Oak Ridge National Laboratory; 96.1 + 0.1 pct of the lithium was ~i~, but chemical impurities were 0.25 pct Ca, 0.05 pct Fe, 0.02 pct Na, 0.02 pct Cu, 0.01 pct Sr, and 0.01 pct Ba. The two metals were melted in an alumina crucible in a resistance heated furnace in an atmosphere of helium. A l-in. ingot was cast in an iron mold, machined to %-in. round, hot swaged (350°C) to 0.080-in. round, cold swaged to 0.060-in. round, and finally cold drawn to 0.040-in. round. Four-inch wire lengths were then cut and annealed at 250°C for 4 hr in helium. Irradiations were carried out in a VT hole in the Argonne CP-5 reactor. The wires were held in an aluminum jig, sixteen wires per capsule, and were maintained in a helium atmosphere for maximum heat transfer. Eight wires of pure aluminum and eight of Al-Li alloy were placed in each capsule. Argome Laboratory statements were accepted as establishing flux and exposure levels. These were based on previous experience and flux map-

Jan 1, 1961

By G. W. Form, W. A. Spitzig

The effects of hydrogen and vacuum shtering treatments on the physical and mechanical properties of arc plasma-sprayed tungsten were inuestigated. Temperatures examined ranged from 3000" to 4000°F in vacuum and 2000" to 3000°F in hydrogen for both single and duplex sintering cycles. Densities of 92 pct of theoretical density were obtained when a long-time hydrogen treatment at 2000°Fpreceded sintering in vacuum at 4000°F for 4 hr. This cycle also produced the highest ualues for modulus of rupture and bend angle. The results of this investigation point out the desirability of using a low-temperature long-time hydrogen treatment prior to a high-temperature vacuum sinter for arc plasma-sprayed tungsten. ADVANCES in the development of arc plasma-generating equipment have provided a high-temperature heat source that makes the fabrication of tungsten shapes possible by a metallizing process. Tungsten in the as-sprayed condition is very brittle. It has a density between 80 and 85 pct of theoretical density, a lamellar structure with elongated pores, and a high interstitial impurity content. To improve these properties, sintering treatments can be applied to the as-sprayed material, similar to those used for the densification of compacted tungsten powder. However, in view of the differences in the density and microstructure of as-sprayed tungsten as compared with compacted tungsten, responses to sintering were expected to be different. EXPERIMENTAL PROCEDURES The tungsten powder used in this investigation had a particle size varying from 3 to 13 p with an average diameter of 8p. The impurity level was less than 0.1 pct. The arc plasma spraying was done with an F-40 Thermal Dynamics Corp. plasma jet. Spraying was performed in air and thus required cooling of the substrate by an air blast in order to minimize oxidation. The spraying parameters employed in the fabrication of all specimens are listed below: Power input, kw 12 Arc-gas flow, cfh 95N2 + 5H2 Powder feed rate, g per min 33 Powder carrier gas flow, cfh ION, Spray distance, in. 3 Traverse rate, in. per min 30 Mandrel speed, rpm 100 Nozzle orifice, in. 7/32 These values of the spraying parameters correspond to optimum conditions ascertained in a previous study. Sintering was conducted at 3000°, 3500, and 4000°F in vacuum (< 0.1 Hg), and at 2000 and 3000°F in hydrogen. Duplex sintering treatments investigated are listed in Table I together with the designations that will be used for reference throughout this paper. The samples were fabricated by spraying onto a copper mandrel which was removed prior to sintering. The specimens used for the sintering analyses had the shape of small hollow truncated cones 1 in. high with an inside diameter varying from 0.500 to 0.125 in. and a wall thickness of 1/8 in. Specimens for bend testing were taken from hollow hexagonal prisms 1-1/2 in. high with a 1-in. diam across the flats and a wall thickness of 1/8 in. The bend-test specimens were ground to the dimensions 0.085 by 0.350 by 1-1/2 in. Prior to bend testing 0.0025 in. of stock was removed from each surface by electro-polishing. Density measurements were made by the water-displacement method. In addition, a porosimeter was used to determine the amount of interconnected porosity for representative samples. Strength and ductility were determined from recorded values in transverse bending using a cross head speed of 0.020 in. per min. The load was applied at the midpoint of a 1-in. span. The deflection data reported herein refer only to the plastic portion of the total deflection. RESULTS AND DISCUSSION The as-sprayed samples had a density corresponding to 83 pct (l pct) of the theoretical density of tungsten. Fig. 1 shows a representative as-sprayed tungsten structure.

Jan 1, 1964

By Nicholas J. Grant, Gordon D. Gemmell

CREEP rupture characteristics of high purity Al-Mg solid solution alloys were studied by Mul-lendore and Grant&apos; to investigate solid solution strengthening of pure aluminum and the accompany- ing effects on deformation and fracture characteristics. This paper presents the results of an extension of that work to A1-Cu and Al-Zn alloys to permit a comparison of the relative effects of the three solute elements on the high temperature strength and on the deformation and fracture characteristics. Experimental Procedure A total of nine alloys was studied. They were all made of ultra high purity aluminum alloyed with high purity copper, zinc and magnesium. The corn-

Jan 1, 1958

By J. P. Hammond, C. J. McHargue, S. E. Adair

Cold-rolled sheet textures have been determined for binary solid solutions of aluminum, columbium, tantalum, and zirconium in titanium. An alloy containing 3.8 pct Al had a (0002) [10101 texture, whereas alloys with the other elements had rotated (0002) [10101 textures similar to that of iodide titanium. THERE have been relatively few studies of the effect of alloying on deformation textures. A second element may be present in the base metal in solid solution and/or as a second phase. The literature offers no satisfactory explanation for the effects of solid solution alloying on textures noted thus far. For example, there is no satisfactory explanation of the difference in the textures of copper and a brass. The most complete study of the effects of solid solution alloying on deformation textures has been that of Brick, Martin, and Angier.¹ These investigators reported that the copper texture was retained by alloys of copper with up to 30 pct Ni, less than 5 pct Zn, less than 2 pct A1 or Co up to the limit of solubility. Copper containing more than 5 pct Zn, more than 2 pct Al, or the maximum soluble concentration of tin, silicon, or manganese showed the deformation texture of a brass. Bakarian² reported that additions of 0.20 pct Ca to 99.98 pct Mg or 2.0 pct Mn plus 0.15 pct Ca to magnesium resulted in entirely different textures than for the pure magnesium. The texture obtained for high-purity magnesium sheet showed the basal plane to be concentrated parallel to the rolling plane. The texture obtained for the alloy containing 0.20 pct Ca had the basal planes concentrated in elliptical areas whose centers were tilted 15" from the center of the pole figure toward the rolling direction. This split basal orientation was even more pronounced in the alloy containing 2.0 pct Mn and 0.15 pct Ca. Fuller and Edmunds" studied the rolled sheet textures in a zinc alloy containing 1 pct Cu and 0.01 pct Mn. The basal pole figure of this alloy contained a region of strong concentration not found in the pole figure for pure zinc.&apos; In the above cases, results were discussed in terms of possible changes in slip and/or twinning systems and critical shear stresses. However, there were no experimental data to relate these speculations with the observed textures. It has been suggested that the deformation textures of titanium, zirconium, and beryllium could be directly ascribed to their low c/a ratios. The complex deformation mechanisms of titanium" also have been suggested to be characteristic of hexagonal close-packed metals with low c/a ratios. The purpose of this investigation was to study the cold-rolled sheet textures in binary titanium-base a alloys in which the c/a ratios were greater than, less than, and about the same as the c/a for iodide titanium. The annealed textures of these alloys will be reported in a subsequent article. Materials and Methods The chemical analyses of the metals used in this investigation are given in Table I. The alloys were prepared as 15 g buttons on a water-cooled copper block in a vacuum arc-furnace. The furnace was evacuated to pressures of the order of 10.&apos; mm Hg, flushed with 99.98 pct pure argon, and melting was carried out in 0.2 atm pressure argon. Each button was remelted until radiographs and chemical analyses indicated complete solution of the solute elements. All buttons were forged and homogenized 72 hr at 500°C. The buttons to be rolled were ground and etched to sizes and shapes suitable for the rolling

Jan 1, 1954

By Y. Nakada, U. F. Kocks, B. Chalmers

The stress-strain behavior of the gold single crystals in easy glide was found to be affected by the specimen dimension which is parallel to the projection of the Burgers vector of the primary-slip system. The larger this dimension is, the larger is the slope of easy glide. Previously severa1 investigators attributed the size effects to either the existence of surface films or the grip constraints. However, in this experiment both of these possible causes were not present. It is proposed that the length of slip path (defined as the crystal dimension parallel to the Burgers vector of the primary system) is the controlling factor in the size effect observed in gold. THERE are many possible effects of the specimen dimension on the work-hardening behavior of single crystals: grip effects which prevent end regions of the crystal from deformation or rotation; effects of a surface film, for example a coherent oxide; effects of a subsurface layer of accidental or intentional

Jan 1, 1964

By R. J. Arsenault

The yield drop that occurs in tantalum, Cu-AZ. and Ag-Al was investigated as a function of strain rate and at several temperatures. From the strain-rate dependence of the yield drop an activation volume was calculated and found to agree with that obtained from differential strain-mte tests. The temperature dependence of the yield drop can he explained in terms of the parameter temperature divided by activation volume. The yield drop is attributed to the rapid multiplication of dislocations during their motion. THE yield-point or yield-drop (upper yield stress minus the lower yield stress) phenomenon has been the subject of numerous investigations1-9 in both bcc and fcc metals. Also, there is no dearth of theoretical explanations10-20 to account for the yield-point phenomenon. The present explanations can be divided into two categories: the concept of dislocation locking and subsequent unlocking and the concept of multiplication of dislocations due to their motion. The Vottrell10,11mechanism of locking and unlocking, as applied to bcc metals, is the best known of the three proposed locking mechanisms. The two additional mechanisms, short-range order (SRO)7,16,17 and Suzuki-type locking,14,15 have been employed to account for the existence of yield points in fcc metals. The experimental evidence supporting the locking of dislocations, especially in bcc metals, is well-established. The dependence of the yield point on interstitial concentrations,&apos; the kinetics of strain aging,2 and the observations by electron-transmission microscopy18 are some of these experimental results. The number of experimental observations supporting dislocation locking in fcc metals is not as extensive as in bcc metals. The unlocking of dislocations, which actually is supposed to account for the yield drop, is by no means well-established by experimental results for either bcc or fcc metals. The similar temperature dependence6 of the yielding and plastic flow is one of the experimental factors that cannot be explained in terms of the unlocking of dislocations. The mechanism based on the rapid multiplication of dislocations has been proposed by several investigators. 18-20 Johnston and Gilman19 have proposed a detailed model of yielding, which was later employed by Hahn21 to predict quantitatively the yield drop in iron. This mechanism was discussed in a previous paper22 and several limitations were pointed out. In the same paper it was shown that an activation volume could be obtained from the strain-rate dependence of the yield drop and that a correlation existed between the activation volumes obtained from the yield-drop tests and from differen-

Jan 1, 1964

By Y. Nakada, B. Chalmers

The work-hardening behavior of surface layers of aluminum and gold single crystals was investigated by alternately deforming and then removing a thin surface layer by electropolishing or by etching. Aluminum crystals exhibited lower flow stresses after the surface removal; gold crystals did not. Abrasion of surface eliminated easy glide in both gold and aluminum crystals. By alternately deforming and removing the surface layer, it was shown that the abraded crystals work-harden preferentially under the abraded layer. It is suggested that this phenomenon is caused by the difficulty of propagating dislocations through the abraded layer. It has been demonstrated in numerous cases&apos;-3 that the plastic behavior of metals in either single-crystal or polycrystal form is sensitive to the environment and to the condition of the surface; it has also been reported4-6 that single crystals of some metals, when deformed in tension, exhibit more work hardening near the surface than in the interior. A third type of effect that has been attributed to the special part played by the surface in plastic deformation is the influence of the dimensions of the specimen on the various parameters that define its plastic-deformation characteris- tics.?-&apos;&apos; Many of these experiments were made on aluminum, on which an oxide film is always present under available experimental conditions; many of the effects have been attributed to the oxide film, either in terms of its higher elastic moduli, which would cause local stress redistribution, or its higher strength, which would oppose the escape of dislocations at the surface of the metal. On the other hand, it has been suggested II,12 that the mere presence of a surface should be sufficient to produce the observed results. A rigorous examination of this question could, in principle, be carried out by comparing the behavior of aluminum with its oxide film with that of the same material without oxide. This experiment would present great difficulties. The most practical alternative is to compare aluminum with gold, which has no crystalline surface film at room temperature, and to study the effects of various surface treatments on gold. The experiments described in this paper fall into two groups, the objectives of which were to determine 1) whether single crystals of gold shared the property of aluminum that the removal of a surface layer after some plastic deformation reduced the flow stress for further deformation and, since the result of this was negative, 2) whether a surface treatment could be found that caused gold to behave in this way. I) EXPERIMENTS AND RESULTS All the tests described below were carried out on single crystals of about 6 by 6 mm cross section and of sufficient length to provide a gage length of about 10 cm.

Jan 1, 1964

By C. S. Barrett

Measurements of impact hardness of ß-brass are reported for a wide range of temperatures. Abrupt softening is observed when temperatures are raised above 425ºC, accompanied by abrupt widening of deformation bands in the deformed samples. Current theories of these effects, and of the lack of twinning, are discussed. HARDNESS1 and flow stress2 of a sample of ß-brass at room temperature depend upon the temperature from which the sample is quenched. It is believed that the state of order in the superlattice is responsible for this dependence—not the order within individual domains, which reaches near-perfection during the quench from any temperature, but the size of the domains which is presumed to be a minimum in the hardest samples, those quenched from temperatures near the critical disordering temperature of 468°C. Measurements of impact hardness made over a range of temperatures and microstructural studies of samples deformed both rapidly and slowly over a range of temperatures, reported herein, should be of aid in reaching a more complete understanding of the underlying factors controlling the properties of the disordered body-centered-cubic material and the ordered material. It appears that such data have not

Jan 1, 1955