US3801309A - Production of eutectic bodies by unidirectional solidification - Google Patents

Abstract

Eutectic bodies with controlled morphology are produced by establishing a thin liquid film of a eutectic composition on a hot supporting surface, growing a body of said composition from said film by unidirectional solidification, pulling the body away from the film at a rate consistent with the rate of solidification, and replenishing the film so as to sustain continuous growth.

Description

United States Patent Mlavsky Apr. 2, 1974 1 PRODUCTION OF EUTECTIC BODIES BY 3,434,892 3/1969 Heimke 148/].6 x UNIDRECTIONAL SOLIDIFICATION 3,591,348 7/1971 La Belle 23/301 SP 3,694,193 9/1972 Carpay et al. 75/129 [75] Inventor: Abraham 1. Mlavsky, Lincoln, Mass.

[73] Assignee: Tyco Laboratories, Inc., Waltham, Primary EXami"erHYland Bizot Mass Assistant Examiner-E. L. Weise Attorney, Agent, or FirmSchiller & Pandiscio 22 F1led: Nov. 8, 1971 [21] Appl. No.: 196,448 [57] ABSTRACT Eutectic bodies with controlled morphology are pro- [52] U5. Cl 75/135, 23/301 SP duccd y hing a hin liq i film f a eu ec ic [51] Int. Cl. C22c 1/02 composition on a hot pp g surface, g g a [58] Field of Search 75/135; 23/301 SP; body of said composition from said film by unidirec- 148/1,6 tional solidification, pulling the body away from the film at a rate consistent with the rate of solidification, [56] Referen e Cited and replenishing the film so as to sustain continuous UNITED STATES PATENTS growth- 3,124,452 3/1964 Kraft 75 135 13 Claims, 6 Drawing Figures l6 57 ER Il 8 I 8 X N PATENTEDAPR 21914" 31801309,

SHEET 2 UF 2 F G 0 6 INVENTQR ABRAHAM I. MLAVSKY BY 9 pana iuib AT TORN E YS PRODUCTION OF EUTECTIC BODIES BY UNIDIRECTIONAL SOLIDIFICATION This invention relates to production of eutectic materials and more particularly to production of eutectic compositions by controlled directional solidification.

It is recognized in the art that unidirectional solidification of various eutectic compositions may have the effect of providing products having unique crystallographic and mechanical properties. In this connection see F. D. Lamkey et al., The Microstructure, Crystallography, and Mechanical Behavior of Unidirectionally Solidified Al-Al Ni Eutectic, Transactions of the Met allurgical Society of AIME, Vol. 233, pp. 334-341, Feb., 1965; and R. W. I-Iertzberg et al., Mechanical Behavior of Lamella (Al-CuAl and Whisker Type (Al-Al Ni) Unidirectionally Solidified Eutectic A]- loys", Transactions of the Metallurigcal Society of AIME, Vol 233, pp. 342-354, Feb., 1965. It has been demonstrated that if l) a planar liquid-solid interface is established in a binary eutectic alloy by proper control of heat flow during the solidification process and (2) the interface is moved unidirectionally, it is possible to produce a eutectic crystal structure consisting of an essentially parallel array of discrete phases. Thus it has been possible to produce two dominant phase microstructures: (a) one comprising parallel alternating rods of one phase embedded in a continuous matrix of the second phase. The directional solidification technique usually used for this purpose essentially consists of melting a mixture of the refined constituents of the desired eutectic, maintaining the melt long enough to insure complete mixing, and cooling the melt to form ingots. Then these ingots are remelted in a crucible and unidirectionally solidified by unidirectionally withdrawing the crucible from the heat source (or vice versa) at as uniform a rate as possible with the object of producing a constant rate of growth and maintaining a constant thermal gradient in the liquid ahead of the liquid-solid interface.

While this prior art technique has produced eutectic materials having unique properties, e.g. an alloy of highly anisotropic mechanical properties comprising single crystal whiskers of Al Ni in an aluminum metal matrix, it has a number of limitations. For one thing, the center of the melt tends to cool at a slower rate (particularly in a large diameter crucible) and hence the crystallographic structure tends to vary along planes parallel to the liquid-solid interface. A further limitation is the inability to grow such eutectic compositions in indefinite lengths. Further problems are phase discontinuities and difficulty in (a) maintaining a planar liquid-solid interface, (b) controlling the temperature gradient at that interface within close limits, and (c) holding the rate of growth constant.

Accordingly, the primary object of this invention is to provide a new and improved method of unidirectionally solidifying eutectic compositions so as to produce bodies that are characterized by unique crystallographic relationships between the constituent phases thereof.

Another important object of this invention is to provide a method of producing binary eutectic compositions as duplex single crystals.

Still another important object is to provide a method of producing binary eutectic compositions having microstructures that consist of substantially parallel alternating lamellae of each phase or long thin parallel rods of one phase embedded in a continuous matrix of the other phase.

A further object is to provide eutectic compositions having unique microstructures.

The foregoing objects are achieved by establishing a relatively thin molten film of the eutectic composition and growing and pulling a crystalline body from the thin film while simultaneously replenishing the film by feeding thereto additional melt under the influence of surface tension. The process may be conducted on a continuous basis so as to produce bodies of indefinite length and the body may be grown to a predetermined arbitrary cross-sectional configuration. v

Other features and advantages of the process and the nature of the products produced thereby are set forth in or rendered obvious by the following detailed description of the invention which is to be considered together with the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of one form of crucible and die arrangement for practicing the invention;

FIG. 2 is a fragmentary view of the apparatus of FIG. 1 showing a film of melt and a seed for effecting solidification and growth of a eutectic body;

FIG. 3 is a vertical sectional view of a second crucible and die arrangement;

FIG. 4 is a view similar to FIG. 1 showing a die assem bly for growing a hollow eutectic body;

FIG. 5 is a photomicrograph of a transverse section of a eutectic body comprising UP and NaCl grown according to this invention; and

FIG. 6 is a photomicrograph of a transverse section of a eutectic body comprising LiF and CaF grown according to this invention.

The present inventions utilizes the so-called EFG process previously known for growing monocrystalline bodies of materials such as alumina. The term EFG stand for edge-defined, filmfed growth and designates a process for growing crystalline bodies from a melt. The essential features of the EFG process are described in US. Pat. No. 3,591,348, issued July 6, 1971 to Harold E. LaBelle, Jr. for METHOD OF GROWING CRYSTALLINE MATERIALS.

In the EFG process the shape of the crystalline body that is produced is determined by the external or edge configuration of a horizontal end surface of a forming member which for want of a better name is called a die, although it does not function in the same manner as a die. By this process a variety of complex shapes can be produced commencing with the simplest of seed geometries, namely, a round small diameter seed crystal. The process involves growth on a seed from a liquid film or film material sandwiched between the growing body and the end surface of the die, with the liquid in the film being continuously replenished from a suitable reservoir of melt via one or more capillaries in the die member. By appropriately controlling the pulling speed of the growing body and the temperature of the liquid film, the film can be made to spread (under the influence of the surface tension at its periphery) across the full expanse of the end surface of the die until it reaches the perimeter or perimeters thereof formed by intersection of that surface with the side surface or surfaces of the die. The angle of intersection of the aforesaid surfaces of the die is such relative to the contact angle of the liquid film that the liquid s surface tension will prevent it from overrunning the edge or edges of the dies end surface. Preferably the angle of intersection is a right angle which is simplest to achieve and thus most practical to have. The growing body grows to the shape of the film which conforms to the edge configuration of the dies end surface. Thus it is possible to grow a substantially monocrystalline body with any one of a variety of predetermined cross-sectional configurations, e.g. bodies with circular, square or rectangular crosssection. Furthermore, since the liquid film has no way of discriminating between an outside or inside edge of the dies end surface, it is possible to grow a monocrystalline body with a continuous hole by providing in that end surface a blind hole, i.e. a cavity of the same shape as the hole desired in the growing body, provided, however, that any such blind hole is made large enough so that surface tension will not cause melt film around the hole to fill in over the hole. From the foregoing brief description it is believed clear that the term edgedefined, film-fed growth denotes the essential feature of the EFG process the shape of the growing crystalline body is defined by the edge configuration of the die and growth takes place from a film of liquid which is constantly replenished.

It has been determined that essential factors contributing to the essential monocrystalline character of the bodies that are grown by the EFG process are the relatively shallow depth of the melt film supported by the die, the fact that the film-supporting surface of the die functions as a substantially isothermal heater (i.e. the film-supporting surface has a substantially flat temperature profile along its entire expanse), and the fact that melt film is not affected by perturbations in the melt reservoir and can be maintained at an average temperature lower than the average temperature of the melt in the reservoir. The thin melt film has a sharp vertical temperature gradient and a relatively small horizontal temperature gradient. It has been found that because of these factors, coupled with the additional fact that the thickness, i.e. depth, of the melt film can be maintained substantially constant by adjusting the rate of heating and the pulling speed, it is possible to utilize the EFG technique to unidirectionally solidify eutectic compositions so as to produce coherent eutectic bodies of indefinite length and controlled cross-sectional configurations. As used herein, the term coherent eutectic denotes a eutectic composition having a high order of regularity of dispersal of one phase in another. Eutectic compositions produced in accordance with this invention are characterized by crystallographic properties that are substantially more uniform than eutectic bodies of the same chemical composition produced by prior art unidirectional solidification techniques. Depending upon their chemical constituents, eutectic compositions produced as herein described may be used, for example, as structural materials for jet engines and to produce components for electrical and electronic devices and systems.

THe present invention may be used to unidirectionally solidify a wide variety of eutectic compositions, including, for example, Al-Al Ni, Al-CuAl Pb-Sn, Zn- Sn, Cd-Zn, Mg-Mg Al NiSb-lnSb, and Cu-Cr eutectic alloys, nickel-base super alloys (such as those commercially designated as PWA Nos. 101 1A, 655, 659 and 689), LiF-NaCl, and LiF-CaF Although the following detailed description of the invention includes specific examples of producing bodies of only a few of the foregoing eutectic compositions, persons skilled in the art will appreciate that the invention is applicable to directionally solidifying all of the foregoing corn positions and also many other compositions, including, but

not limited to, those specified by G. A. Chadwick, Eu-

tectic Alloy solidification Progress In Materials Science, Vol. 12, No. 2, Pergamon Press, Oxford, 1963.

In the following description like reference characters on the drawings refer to like elements in the several figures.

Turning now to FIG. 1, the illustrated apparatus comprises a crucible 2 for holding a reservoir supply of a melt 4 of a eutectic composition which is to be directionally solidified in accordance with this invention. The crucible is made of a material that will withstand the operating temperatures and will not react with the die assembly hereinafter described and will not react with or dissolve in the melt 4. The crucible is mounted within a susceptor 6 by means of a plurality of short rods 8. The susceptor is made of a material that will not evolve substances that will react with the crucible and preferably is spaced from the crucible if it is madeof a material that will react with the crucible or die assembly at the operating temperatures. The top end of the susceptor is open but its bottom end is closed off by an end wall 10.

Mounted within the crucible is a die assembly 14 that comprises a disc 16 that is locked to the crucible by a removable collar 17. The disc 16 functions as a heat shield to reduce radiative heat loss from the melt and also supports a die member in the form of a cylindrical, vertically-extending solid non-porous rod 18 which is securedly mounted within a centrally located hole in the disc. Rod 18 extends a short distance above the disc and its bottom end terminates short of the bottom of the crucible. Rod 18 has a flat, substantially horizontal top end surface 20 and several through holes in the form of axially-extending bores 22 that are uniformly spaced about the axis of the rod and are sized to function as capillaries for the melt 4. Disc 16 and rod 18 are made of a material that will not react with the crucible and will not react or dissolve in the melt. Additionally, the rod 18 is made of a material that is wetted by the melt and the diameters of capillaries 22 are such as to cause melt to rise up and fully fill them so long as the bottom end of the rod is trapped by, i.e. submersed in, the melt.

The apparatus of FIG. 2 is mounted in a suitable induction heating furnace (not shown) that is adapted to envelope the crucible and the growing eutectic body in an inert atmosphere and includes a pulling mechanism that is adapted to position a seed crystal as hereinafter described and to pull the seed at a controlled rate as melt solidifies on the seed. One form of furnace that may be used in the practice of this invention is illustrated and described in U.S. Pat. No. 3,591,348 and also U.S. Pat. No. 3,471,266, issued 10/7/69 to Harold E. LaBelle, Jr. for GROWTH OF INORGANIC FILA- MENTS. The susceptor 6 is mounted within the furnace by attaching it to the upper end of a support rod 24 that is mounted in the furnace. Rod 24 may be mounted to the base 2 of the furnace shown in U.S. Pat. No. 3,471,266.

Production of a solid eutectic body is initiated by using a seed of any desired cross-sectional configuration. Thus the seed may be a round filament, a flat ribbon or a crystalline body of other suitable shape. The seed crystal serves as a nucleating medium for the melt and may also be used to establish a film of melt in the upper surface 20 of the die assembly. The seed may be a single crystal of one of the components of the eutectic composition or may be a previously solidified body of substantially the same composition as the melt. The essential requirement of the seed is that it be wetted by the melt.

The method of the present invention will now be described with reference to the apparatus of FIG. 1. Assume for ease of description that the crucible 2 and the susceptor 6 are mounted in an induction furance of the type described in U.S. Pat. No. 3,471,266, with the crucible and the capillaries of the die assembly filled with a melt of a selected binary eutectic composition and an inert gas atmosphere being continuously circulated through the furnace. Assume also that a seed 26 in the form of a monocrystal of one of the constituents of the eutectic or a single crystal of the eutectic composition is supported by the crystal pulling mechanism associated with the furnace in coaxial alignment with rod 18. With the upper surface 20 of rod 18 at a temperature of about -40C higher than the eutectic point temperature of the melt composition in the crucible, the seed is lowered into contact with surface 20 and held there long enough for its end to melt and form a liquid film 32 that connects with the melt in the capillaries 22 (see FIG. 2). It is to be noted that the capillaries are shown empty in FlGS. l-2 in order to render them more distinct to the reader and that before the end of the seed is melted to form film 32 the melt in each capillary has a concave meniscus with the edge of the meniscus being substantially flush with the surface 20. It is to be noted also that the temperature gradient along the length of the seed is one factor influencing how much of the seed melts and forms film 32. The seed 26 functions as a heat sink so that its temperature is lower at successively higher points therein. However, the thermal gradients along the seed and vertically across the film 32 are affected by the power input to the induction heating coil of the furnace and the height and distance of the heating coil and susceptor 6 relative to the seed and the die assembly. In practice these parameters are adjusted so that the film 32 is maintained at a thickness in the order of 0.2 mm during growth of desired eutectic solid. After the film 32 has connected with the melt in the capillaries, the pulling mechanism is actuated so as to pull the seed vertically away from the surface 20. The initial pulling speed is set so that surface tension will cause the film 32 to adhere to the seed long enough for solidification to occur due to a drop in temperature at the seed-liquid film interface. This drop in temperature occurs because of movement of the seed away from surface 20, i.e., because the solid-liquid interface advances vertically to a relatively cooler region. It is to be noted that radiative and conductive heat losses from the seed cause it to exhibit a decrease in temperature with an increase in distance from the surface 20. If it is desired that the eutectic solid have a constant cross-section conforming in shape and area to surface 20, it is necessary to have the film 32 fully cover surface 20. Accordingly, if the film initially established by melting the seed does not fully cover surface 20, the pulling speed must be set so that surface tension will cause the film to spread radially out to the edge of surface 20 as solidification progresses.

Preferably enough of the seed is melted for the film 32 to fully cover the end surface of the die assembly, in which case the initial pulling speed is set at the level at which solidification will occur on the seed across the full expanse of the film. If the initial film covers less than all of the surface 20, a pulling speed is used at the beginning of the solidification process which will cause the film to spread radially, and once the surface 20 is fully covered, the pulling speed is increased to a level at which the film is maintained at a suitable thickness and solidification will occur on the seed along the full expanse of the film. It is to be noted that the pulling speed and the temperature of the film control the film thickness which also controls the rate of film spreading. Increasing the temperature of surface 20 (and hence the average temperature of film 32) and increasing the pulling speed (but short of the speed at which the seed and the growth occurring thereon will pull clear of the film) each have the effect of increasing the film thickness.

As the seed is pulled away from surface 20, liquid from film 32 will solidify on the seed at all points along the full horizontal expanse of the film, with the result that additional accretions of solid will form a longer and longer solid eutectic body. The liquid consumed by solidification at the interface of the growing solid and the film 32 is replaced by additional melt which is supplied to surface 20 via capillaries 22 under the influence of surface tension. The rate at which fresh melt is supplied to the surface 20 is determined by the number and size of the capillaries and, within limits, is always enough to maintain the film 32. The process may be continued until the solid extension on the seed has grown to a desired length or until the supply of melt in the crucible has been depleted to the point where the bottom end of the capillaries are no longer trapped, whichever event occurs first. Furthermore, the growth process may be terminated at any time by increasing the pulling speed enough to cause the growing body to pull free of the melt film. Once growth has been terminated, the furnace is shut down and the seed with its newly acquired eutectic extension is removed for inspection and use.

Because of the sharp temperature gradient that is attainable across the melt film and because the average temperature of the melt film can be maintained constant at a level near to but below the temperature of the melt in the crucible, it is possible to achieve a constant thermal gradient in the film below the solid-liquid interface and to maintain a planar solid-liquid interface, with the result that by preferably adjusting the pulling speed and hence the solidification rate, it is possible to achieve a predetermined and uniform micromorphology. This is particularly important for eutectics that have been shown to exhibit a tendency to undergo a change in morphology, e.g. a transition from rod-like to lamella structure, or a change in inter-rod or interlamella spacing, with increasing growth rate. Furthermore, since the film thickness is relatively small and the film is remote from the crucible, the solidification process is relatively free of perturbations of the type that produce localized depletions of one phase in the other. Such areas of localized phase depletions are known to be sources of premature failure under stress.

FIG. 3 relates to a preferred modification of apparatus used in practicing the invention. In this case the die assembly 14A consists of the disc 16 and a rod 18A which is secured within a centrally located hole in the disc. Like rod 18, rod 18A extends a short distance above the disc. The bottom end of rod 18A extends close to and may even engage the bottom of the crucible. Rod 18A has a flat substantially horizontal top surface 20 which functions to support a film of melt 32. However, rod 18A differs from rod 18 in that it is a po rous member characterized by a myriad of small interconnected open cells sized to function as capillaries whereby melt will rise in the rod by capillary action. Preferably the cells are sized so that melt will rise to the top surface 20 by capillary action so long as the level of the melt in the crucible is high enough to trap the bottom end of the rod. As with rod 18, rod 18A is made of a material that is wetted by the melt but will not react with the melt or the crucible at the operating temperatures.

Growth of eutectic bodies with the apparatus of FIG. 3 is accomplished in the same manner as with the apparatus of FIGS. 1 and 2, except that (l the melt rises in rod 18A via the open interconnected cells rather than through discrete bores as shown at 22, and (2) because the capillary action occurs across the full cross-section of rod 18A, infeeding of melt to the film 32 involves little or no horizontal flow of melt along surface 20 as may occur with rod 18. This substantial elimination of flow of fresh melt laterally along surface 20 minimizes perturbations. Furthermore, with the film being replenished with fresh melt at a large number of points instead of at a limited number of points as is the case when using capillary bores 22, it is easier to maintain an even melt thickness.

it is recognized that the choice of seed, crucible, susceptor and die assembly materials and the determination of satisfactory operating temperatures and pulling speeds will vary in accordance with the eutectic to be solidified, and also that such choice is well within the skill of the art. Accordingly, the following specific examples, which are provided to assure a full and accurate understanding of the invention, should be considered to merely illustrate and not to limit the invention.

EXAMPLE I A crucible having the general appearance of the crucible 2 ofFlG. 2 and made of nickel is mounted on rods 8 in a susceptor 6 that is mounted in a furnace in the manner shown in HO. 1 of US. Pat. No. 3,471,266.

- The rod 8 is made of alumina and the susceptor 6 is made of molybdenum. Disposed in the crucible is a die assembly constructed generally as shown in FIG. 1. The

rod 18 is made of nickel and has four capillaries 22 of about 0.040 inch diameter spaced uniformly about its center axis. The crucible has an internal diameter of about 1 inch and an internal depth of about 1.5 inches. The rod 18 has an outside diameter of about Va inch and a rod length such that its upper end projects about 1/16 inch above the crucible. The crucible is filled with a solid composition comprising 23% UP and 77% NaCl by weight. An elongate seed crystal 26 consisting of UP is mounted in the seed holder of the crystal pulling mechanism associated with the furnace so that it is aligned with rod 18. The seed crystal is supported in axial alignment with rod 18.

With the crucible mounted in the furnace, the induction heating coil of the furnace is located so that its upper end is approximately even with the middle of the susceptor and its lower end at least even and preferably a little below the susceptor. Then the furnace enclosure is evacuated and filled with argon gas to a pressure of about one atmosphere which is maintained during the growth period, and the induction heating coil is energized and operated so that the charge in the crucible is brought to a fully molten condition and the surface 20 is brought to a temperature of about 700C. As the charge in the crucible is converted to the melt 4. columns of melt will rise in and till the capillaries 22. Each column of melt rises until its meniscus is substantially flush with the top surface 20 of rod 18. After affording time for temperature equilibrium to be established, the pulling mechanism is activated and operated so that the seed 26 is moved down into contact with the upper surface 20 and allowed to rest in that position long enough (e.g. about one minute) for the bottom end of the seed to melt and form a film 32 which fully covers surface 20 and connects with the melt in the capillaries. Then the seed is withdrawn vertically at a rate of about 0.1 inch per minute. As the seed is withdrawn, surface tension causes film material to adhere to the seed and also cause additional melt to flow out of the capillaries and add to the total volume of film. The liquid film material adhering to the seed experiences a temperature drop due to its movement away from the relatively hotter surface 20 and the fact that the seed functions as a heat sink. As a consequence of this temperature drop, the liquid that is in contact with the seed undergoes directional solidification and growth of solid occurs on the seed. Concurrently with the consumption of film by growth of solid on the seed, surface tension causes additional melt to flow up out of the capillaries onto surface 20 to replenish the film. The pulling speed and temperature are maintained constant and growth of solid on the seed continues to propagate vertically throughout the entire horizontal expanse of the film 32, with the result that successive accretions of solid form an elongate extension on the seed having substantially the cross-sectional shape and area of surface 20 (the openings of capillary 20 may be disregarded in considering what is the configuration of surface 20 since they are filled with melt). Growth is continued until the growth on the seed has reached a length about 6inches. Thereafter the pulling speed is increased rapidly to about 10 inches per minute, with the result that the grown body pulls free of the film 22. Then the furnace is cooled and the seed retrieved for sectioning and ex amination of the grown body.

FlG. 5 is a photomicrograph of a transverse microspecimen, magnified by a factor of 940, of a eutectic body produced by practicing the invention according to the procedure of the foregoing example. The eutectic body was found to be of uniform morphology throughout its entire volume. As is apparent from FIG. 5, the eutectic body consists of substantially uniformly sized rods spaced substantially uniformly throughout a matrix phase. The rod diameters are in the order of 0.0001 inches and the spacing between rods is in the order of 0.00015 inches. The rods extend parallel to the direction of solidification. The rods have been found to be of indefinite length, with the result that the body is characterized by a high aspect ratio, (i.e., the ratio of rod length to rod diameter).

EXAMPLE I] A eutectic body consisting of 56% UP and 44% CaF is produced by using the same apparatus and following the same procedures as in Example I, except that the crucible is initially charged with UP and CaF in the above proportions, the furnace is operated so as to hold the top surface 20 of the die assembly at a temperature of about 775C, and the pulling speed of the crystal is maintained at about 0.1 inch per minute.

FIG. 6 is a photomicrograph similar to FIG. 5 ofa microspecimen, magnified by a factor of 940, of a LiF-CaF eutectic body produced in accordance with the procedure of Example II. As is evident, the product is a lamellar or plate-type eutectic, the LiF phase being in the form of plates of indefinite length dispersed through a CaF matrix. As with the LiF-NaCl eutectic, it has a coherent microstructure, the two phases having an exceptionally high degree of regularity with the parallel alternate lamellae extending parallel to the direction of solidification.

EXAMPLE III A crucible having the general appearance of the crucible 2 of FIG. 2 and made of alumina is mounted on rods 8 in a susceptor 6 that is mounted in a furnace of the type shown in FIG. 1 of U.S. Pat. No. 3,471,266, except that the pulling mechanism is constructed in accordance with the teachings of U.S. Pat. No. 3,552,931, issued Jan. 5, 1971 to Paul R. Doherty et al., for APPARATUS FOR IMPARTING TRANSLA- TIONAL AND ROTATIONAL MOTION, so that the seed crystal (and the growth that occurs thereon) will undergo rotational motion as it is being withdrawn. The rods 8 are made of alumina and the susceptor 6 is made of molybdenum. Disposed in the crucible is a die assembly constructed as shown in FIG. 2A and made of an alumina foam or sponge which consists of a myriad of small interconnected open cells having an average diameter in the order of 0.0002 inch. The diameter and length of rod 18A and the depth and internal diameter of the crucible are the same as specified in Example I. Into the crucible is placed an aluminum-nickel ingot comprising 6.2 weight per cent nickel. The ingot is prepared by inductively melting substantially pure aluminum and nickel in an argon atmosphere at 900C for 1 hour to assure complete mixing, and then cooling the melt. An elongate aluminum seed crystal is mounted in the seed holder of the crystal pulling mechanism associated with the furnace. Then with the induction heating coil located as described in Example I, the furnace enclosure is evacuated and filled with argon to a pressure of about one atmosphere and the heating coil is energized. The furnace temperature is raised high enough to melt the ingot and then adjusted so as to hold the temperature of the upper surface of rod 18A at about 675C. The molten liquid in the crucible infiltrates the cells of rod 18A and rises up to its top surface by action of capillary rise. After the cells of rod 18A are filled with melt, the crystal pulling mechanism is operated to move the aluminum seed down into contact with the upper surface of rod 18A and held there long enough for its bottom end to melt and form a thin film that extends along surface 20. Then the pulling mechanism is operated to withdraw the seed vertically at a rate of about 2 centimeters per hour while the temperature of surface 20A is held steady at about 675C. As the seed is withdrawn, liquid film material solidifies on the seed and surface tension causes additional melt to flow up rod 18A to the film on surface 20A to replace the material lost by solidification. About 10 minutes after solidification is evident on the seed, the pulling mechanism is caused to rotate the seed at a rate of about 10 degrees per hour at the same time that it is being pulled. The pulling and rotational speeds are held constant and growth of solid continues to propagate vertically on the seed to a cross-sectional configuration corresponding to the shape of surface 20. Growth is terminated when the supply of melt in the crucible is substantially exhausted. Thereafter the furnace is cooled and the seed retrieved from the pulling mechanism for sectioning and examination of the grown body. An Al-Al Ni body grown according to this example has a eutectic microstructure consisting of a lamellar micromorphology. The body has substantially parallel alternating lamellae of each phase with all of the lamellae extending spirally about the bodys longitudinal axis. The lamellae are coextensive and substantially free of discontinuities. It also is possible to produce a rod-like eutectic microstructure, i.e., a micromorphology consisting of thin parallel rods of Al Ni embedded in a continuous matrix of Al, by increasing the pulling speed (and hence the solidification rate) to about 8-10 centimeters per hour. If the seed is rotated at an appropriate speed, the parallel rods of Al Ni will also extend spirally about the growth axis. If the seed is not rotated, the lamellae and rods will extend parallel to the growth axis.

Other eutectic alloys also may be grown with a twisted structure using a pulling procedure like that of Example III. It also is possible by solidification of the film-supporting surface of the die, e. g. by providing one or more blind holes or cavities 38 as shown in FIG. 4 that are too large in diameter to function as a capillary, to grow eutectic bodies having one or more through holes extending parallel to the axis of growth. In this case it is preferred to use a seed crystal in the form of a hollow tube 40 as shown or a solid body that has a cross section with a substantially smaller area than the upper surface 20 of the rod of the die assembly 14B. In the latter case the initial film that is formed may cover less than all of the surface 20 and must be made to spread out around the cavity 38 so as to fully cover the surface 20; hence the initial growth of solid will not conform to the desired shape but will grow to that shape as the film spreads out over surface 20.

It also is to be understood that the eutectic compositions may include trace amounts of impurities or minor amounts of selected elements introduced for reasons obvious to persons skilled in the art without departing from the present invention. Accordingly, the term essentially consisting of as used herein with respect to the eutectic composition is intended to allow for such additional impurities or selected elements.

Eutectic bodies produced according to this invention offer a number of advantages. The most important advantage is a high degree of regularity of the phases with the phases being substantially free of discontinuities. Thus, for example, in a eutectic body having a rod-like morphology, the individual rods will extend for substantially the full length of the body. The ability to produce a body with one or more holes avoids the problem of irregular phase termination and particle breakout such as occurs when a hole is drilled in an alloy body. Growing a body so that the phases are curved about the bodys longitudinal axis is advantageous when it is desired to machine a curved part. By properly controlling the speed at which the body is rotated as it is being grown, it is possible to have the phases oriented so that machining transverse to the direction of the phases can be avoided when the body is being machined into a finished part of predetermined size and shape. Furthermore, since the pulling rate is consistent with the rate of growth along the pulling axis (which in turn depends upon the temperature gradient across the film from which growth occurs), it is possible by controlling the rate of heat input and the rate of heat loss by radiation and conduction to control the rate of growth within close limits and to maintain the film thickness substantially constant. Also since the film is supported by the end surface of the die and its position with respect to the height of the heater coil is held fixed, the solidliquid interface is substantially planar at all times while a eutectic body is being grown. Another important advantage is that it is possible to grow eutectic bodies with any one of a variety of arbitrary cross-sectional configurations, e.g., a body having the general crosssectional shape of an air-foil with one or more holes extending lengthwise of the body. Still other advantages, in addition to those noted above, will be obvious to persons skilled in the art.

What is claimed is:

1. Method of producing polyphase eutectic bodies of uniform morphology comprising:

establishing a thin liquid film of a eutectic composition on a substantially flat supporting surface and controlling the temperature of said film so that it has (1) a sharp temperature gradient along its depth with the film being hottest at said surface, (2) a substantially flat temperature profile along its length and breadth, and (3) an average temperature approximately equal to the eutectic point temperature of said composition; solidifying and pulling a mass of said composition from the cooler side of said film at a selected rate; and simultaneously supplying an additional quantity of said mixture in liquid form to said surface to replace the liquid consumed in producing said eutectic mass. 2. Method according to claim 1 wherein said eutectic composition is a binary composition.

3. Method according to claim 1 wherein said eutectic composition is an alloy.

4. Method according to claim 3 wherein said alloy essentially comprises nickel and aluminum.

5. Method according to claim 4 wherein said alloy essentially comprises nickel, indium and antimony.

6. Method according to claim 1 wherein said mass is turned about its pulling axis as it is pulled from said film.

7. Method according to claim 1 wherein said flat supporting surface is porous.

8. Method according to claim 7 wherein said porous surface is part of a member consisting of a myriad of interconnected open cells, and further wherein said additional quantity of said mixture is supplied to said surface via said cells.

9. Method of producing a polyphase eutectic body having a coherent microstructure comprising:

establishing a thin liquid film of a selected eutecticcomposition on a substantially horizontal and planar end surface of a heat conducting member, and controlling the temperature of said film so that it has (1) a sharp vertical temperature gradient, (2) a substantially flat horizontal temperature profile, and (3) an average temperature approximately equal to the eutectic point temperature of said composition;

growing and vertically withdrawing a coherent polyphase solid body from said film at a selected rate; and

supplying additional quantities of said composition in liquid form to said end surface via a passageway in said member as said solid body is being grown to replace the liquid consumed in producing said body.

10. Method according to claim 9 wherein the thickness of said film is held substantially constant during growth and withdrawal of said body.

11. Method according to claim 9 wherein growth of said body is initiated by use of a crystalline seed.

12. Method according to claim 9 further including the step of rotating said body as it is withdrawn from said film.

13. Method according to claim 9 wherein said member is supported in a heated crucible containing a reservoir supply of said selected composition in liquid form,

and said film is replenished from said reservoir supply.

Claims (12)

1. 2. Method according to claim 1 wherein said eutectic composition is a binary composition.
2. 3. Method according to claim 1 wherein said eutectic composition is an alloy.
3. 4. Method according to claim 3 wherein said alloy essentially comprises nickel and aluminum.
4. 5. Method according to claim 4 wherein said alloy essentially comprises nickel, indium and antimony.
5. 6. Method according to claim 1 wherein said mass is turned about its pulling axis as it is pulled from said film.
6. 7. Method according to claim 1 wherein said flat supporting surface is porous.
7. 8. Method according to claim 7 wherein said porous surface is part of a member consisting of a myriad of interconnected open cells, and further wherein said additional quantity of said mixture is supplied to said surface via said cells.
8. 9. Method of producing a polyphase eutectic body having a coherent microstructure comprising: establishing a thin liquid film of a selected eutecticcomposition on a substantially horizontAl and planar end surface of a heat conducting member, and controlling the temperature of said film so that it has (1) a sharp vertical temperature gradient, (2) a substantially flat horizontal temperature profile, and (3) an average temperature approximately equal to the eutectic point temperature of said composition; growing and vertically withdrawing a coherent polyphase solid body from said film at a selected rate; and supplying additional quantities of said composition in liquid form to said end surface via a passageway in said member as said solid body is being grown to replace the liquid consumed in producing said body.
9. 10. Method according to claim 9 wherein the thickness of said film is held substantially constant during growth and withdrawal of said body.
10. 11. Method according to claim 9 wherein growth of said body is initiated by use of a crystalline seed.
11. 12. Method according to claim 9 further including the step of rotating said body as it is withdrawn from said film.
12. 13. Method according to claim 9 wherein said member is supported in a heated crucible containing a reservoir supply of said selected composition in liquid form, and said film is replenished from said reservoir supply.

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