Processes For The Production Of Alloys

Abstract

A process for producing bulk alloys as engineering materials is carried out in a vacuum vessel and includes evaporating the constituents and depositing them upon a collector in such a way that the deposit is laid down in successive layers. This is achieved by arranging that the collector and the source or sources from which the constituents are evaporated move relative to one another. Preferably the source or sources are stationary and the collector is moved relative thereto. In this way it is possible to achieve the high evaporation and deposition rates necessary to economical production of alloys by deposition of the constituents from the vapor phase and also faults in the deposit such as columnar growth and intercolumnar porosity may be substantially eliminated. Apparatus in which this process may be carried out is described.

Description

The present invention relates to processes for the production of alloys by deposition of the constituents of the alloys from the vapor phase and to apparatus for carrying out said deposition.

Copending patent application, Ser. No. 665,844 filed Sept. 6, 1967, now U.S. Pat. No. 3,554,735, describes vapor deposition processes for alloy production which under certain conditions produce alloys having columnar structures with the growth direction towards the evaporation source. In general the columns are substantially perpendicular to the collector surface. Some of these deposits have inter-columnar porosity and cracks. This is a serious disadvantage in metals which have a stable, high melting point oxide, for example aluminum, magnesium, and chromium since on removal of the deposit from the vacuum system used in the process, oxygen pentrates the inter-columnar pores and forms an internal oxide film which cannot readily be worked into the body of the deposit and thus detracts from the properties of the alloy.

Furthermore, because these processes rely on vapor phase mixing to produce homogeneous alloys they are suitable for low deposition rates only, if separate sources are used. In general when low deposition rates are used only low process efficiencies are attained.

It is an object of the present invention to provide a process for the vapor deposition of alloys by which inter-columnar porosity may be substantially eliminated and relatively high process efficiencies, and sufficiently intimate mixing of the constituents may be achieved at a high deposition rate.

In accordance with the present invention a bulk alloying process for the production of a multiphase alloy in the form of an engineering material is carried out within a controllable vacuum or low pressure system and comprises the evaporation of constituents of the alloy from controllably heated evaporative source means and deposition of the constituents upon a temperature controllable collector, the surface of the collector and the source means repeatedly passing one another at such a speed that the constituents of the alloys are deposited in successive layers and inhomogeneity of deposit from individual sources is substantially eliminated.

The aforementioned evaporative source means may constitute a single source or a plurality of individual sources adapted to evaporate more than one alloy constituent or it may constitute a plurality of individual sources adapted to evaporate single constituents of the alloy, or a combination thereof. In practice it is generally convenient that the source means remains stationary and the collector is moved relative thereto.

An engineering material is defined as a deposit having a thickness greater than 0.01 inch, useful as a coating, with or without further treatment, or capable of being removed from the collector and shaped or worked or both into useful forms. By multi-phase alloy is meant an alloy having two or more phases. The material, coating or otherwise, may be treated or heat treated before, during, or after working to produce desired properties.

The source means is essentially a pool of molten metal and the rate at which the metal evaporates is governed by the temperature of the metal. The metal atoms pass from the source to the collector in the form of a vapor. As is well known the deposit thickness decreases towards the edge of the deposit and therefore with a stationary collector the deposit would be inhomogeneous being of non-uniform thickness, being thicker at the centre and decreasing towards the edges.

In order to achieve acceptable process efficiencies it is necessary to have high evaporation and high deposition rates. These imply high vapor pressures and mean free paths short when compared with the separation of the collector and the sources.

If separate sources are used for separate constituents the frequent gas phase collisions occuring when the mean free path is relatively short will result in poor interpenetration of the vapor leading to compositional inhomogeneities in the deposit. Vapor phase mixing is feasible only at low evaporation and deposition rates.

In the present invention the source and collector are moved relative to one another in order to alleviate these problems. Conveniently the source is stationary and the collector is moved. As the collector is moved the deposit obtained from an individual source is extended in the direction of movement of the collector to give a layer. If the collector is reciprocated above a source, each transit will result in a layer of the particular constituent evaporated from that source. Likewise if the moving collector is rotating above the source then each revolution will result in a layer of deposit. Each individual source will provide one layer for each transit of the collector so that if individual sources evaporate different constituents then the successive layers thus laid down will be of different constituents. The thickness of the individual layers is governed by the speed of the collector relative to the source from which the constituent of the particular layer is evaporated and the rate of such evaporation. Ideally the layers should be as thick as is compatible with obtaining useful products and may be as much as several microns. Another factor in determining actual thickness is the proportion of a particular constituent sought to be included in the final alloy. This is determined relative to the thickness of the base constituent and may be as little as 2A. or even less so that the constituent does not in substance form a separate continuous layer if it is to be present in sufficiently small quantities.

It will be realized that the substantial elimination of inhomogeneity of deposit is on the line of movement of the collector and the edges parallel to the line of movement of the collector may show decrease of thickness and non-uniform composition and be unsuitable as engineering material.

In a preferred embodiment of the present invention the source means is stationary and the collector is arranged to move; the moving collector comprises a disc and is rotated about a substantially perpendicular axis above the source means. Advantageously the collector is rotated at a speed of the order of 50 to 1,500 revolutions per minute, although speeds outside this range may be used with suitable adjustment of the evaporation rate of constituents of the alloy.

In order to obtain the advantages of the present invention the collector and the source or sources from which the constituents of the alloy are being evaporated should be placed as close as possible together so that the highest proportion of constituents possible is collected leading to high process efficiencies.

Each separate constituent of the alloy to be deposited is generally evaporated from a separate source, thus permitting optimum evaporation conditions for each constituent. This is particularly important where the constituents have widely differing volatilities, for example aluminum and titanium. However some constituents of the alloy may be co-deposited from a common source.

The deposit produced in the first instance by the present invention consists of successive layers of metal or compounds of metals and by varying the speed of rotation of the collector and evaporation rates of the various constituents, the thickness of the layers of the different constituents may be controlled. Compounds of metals mentioned above include intermetallic compounds and simple compounds of metals, for example, oxides or carbides, such as are customarily encountered in metallurgical practice and such compounds may be evaporated as such, or may be formed on deposition on the collector.

If one of the metal constituents has a tendency towards columnar growth, this may be reduced or prevented by depositing alternate layers of that metal with relatively thin layers of a second metal. In this way each metal must nucleate and begin growth afresh with the deposition of each layer and by suitable control of the process variables it can be arranged that columnar growth does not take place. For example aluminum is susceptible to columnar growth but a deposit of alternate layers of aluminum and another metal as described in the present application can produce deposits free from inter-columnar porosity and the shape and the size of the aluminum crystals can be controlled.

In order to prevent columnar growth the metal deposited in alternate layers with the base metal of the alloy should have a lattice structure that does not match that of the base metal and should also be laid down in layers of adequate thickness. For example when aluminum is the base metal and nickel is the other metal if the nickel is deposited too thinly it reacts with the aluminum to from NiAl.sub.3 shrinking at the same time to expose the surface of the aluminum, thus permitting columnar growth. It has been found that nickel deposited in layers 20A thick serves to prevent intercolumnar porosity in aluminum 1,000A thick when deposited on a substrate maintained at 100.degree.C, while a layer of iron 10A thick is sufficient with the substrate at a temperature in the region 150.degree.C to 250.degree.C. In general for a specific pair of metals, the higher the substrate temperature, the greater the thickness of second metal required to prevent columnar growth.

As stated in co-pending application Ser. No. 665,844 filed Sept. 6, 1967, now U.S. Pat. No. 3,554,735 the temperature of the collector upon which the metal is deposited is important in controlling the structure of the deposit and also is important to the adhesion of the deposit to the collector, if no other method of controlling adhesion is suitable. For example, with aluminum the deposit is preferrably started with the collector at a temperature greater than about 300.degree.C in order to ensure adequate adhesion then continued with the collector at the temperature necessary to obtain the desired deposit structure. This is generally of the order of 150.degree.C to 250.degree.C.

Although the initial structure of the deposit is layered, working and/or heat treatment may change its state. For example if the second metal forms an intermetallic compound with the first metal the final deposit may be alternate layers of the first metal and of the intermetallic compound or the intermetallic compound may break up on heat treatment into particles producing a dispersion of the intermetallic compound in a matrix of the first metal. A similar result may be achieved by working. If the intermetallic compound has the desired properties this may lead to a dispersion hardened alloy of the first metal and the present process is particularly advantageous for producing these materials since the dispersed phase may be produced in fine particle sizes and with a wider range of dispersed phases and proportions of these phases than can be achieved in general by more conventional methods.

Although dispersion hardened alloys of the present invention have been described heretofore in terms of a binary intermetallic compound as the dispersed phase, the dispersed phase may consist of one metal or of more than one metal or may be a metal compound as hereinbefore defined and need not involve the matrix metal. The dispersed phase may constitute any phase which can be deposited directly or can be formed either directly in the deposition process or by suitable treatment either on the collector or after removal therefrom.

A further advantage to be gained from the present invention is that the collector may be placed close to the evaporation sources leading to high deposition efficiencies and high rates of evaporation may be used such as to preclude mixing in the vapor phase but the rotation of the collector tends to even out adequately the composition of the deposit which would be uneven otherwise because of inhomogeneities in the metal vapor stream. In suitable circumstances 85 percent or more of the metal evaporated may be collected.

Apparatus for carrying out processes in accordance with the present invention conveniently comprises a vacuum or low pressure vessel, a plurality of evaporative source means and a temperature controllable collector, the evaporative source means and the temperature controllable collector being arranged for relative movement so that in operation the source means and points on the surface of the collector repeatedly pass one another. In practice it is convenient for the source means to remain stationary while the collector moves.

Advantageously the apparatus comprises a vacuum or low pressure vessel, evaporative source means and a temperature controllable collector; the collector being a substantially horizontal disc arranged to be rotated about a substantially perpendicular axis and the source means being positioned thereunder. Where the rotating collector is used the evaporative source means may be arranged so that more than one constituent of the alloy may be evaporated from the same source, for example as hereinafter described, or individual sources may be provided for separate constituents of the alloy. Of course a combination of these methods may be used. Advantageously the individual sources may be troughs arrayed with their longitudinal axes disposed radially below the collector.

The apparatus may also include shutter means whereby in operation the alloy constituents can be prevented from impinging upon the collector until desired. It is convenient to provide individual sources with individual shutters.

The source means may be continuously replenished by any convenient means and advantageously a wire feeding device and a seal in the wall of the vessel is provided for each individual source so that in operation each individual source may be replenished by passage of wire of the appropriate material through the seal in the vacuum vessel wall.

The apparatus may also include means for monitoring the background gas pressure in the vacuum vessel, heat input to and temperature of the source means, evaporation and deposition rates and also the temperature of the collector.

Suitable apparatus for carrying out the processes of the present invention will now be described, and one aspect of the invention will be explained by way of example with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of the apparatus in partial cross-section,

FIGS. 2 and 2a show the temperature controllable, rotatable collector in cross-section,

FIG. 3 shows in cross-section a crucible for the evaporation of metal,

FIG. 4 shows schematically an alternative plan arrangement for the evaporative source means, and

FIG. 5 is a graph showing the effect of substrate temperature and layer thickness on the formation of intercolumnar porosity in binary aluminum based alloys with nickel.

FIG. 1 shows the apparatus comprising a vacuum vessel 10, capable of being evacuated by a standard oil diffusion pump system 11, within which the pressure is monitored by an ionization gauge 12. Contained within the pressure vessel 10, are two crucibles 13 and 14 provided with heaters 15 and 16. Electrical current for the heaters 15 and 16 is supplied by wires 17 and 18 entering through seals 19 and 20 in the vacuum vessel 10. The crucibles 13 and 14 are provided with individual shutters 21 and 22 operated by external handles 23 and 24 through seals 25 and 26.

A rotatable collector assembly 27 mounted upon a shaft 28 comprises a collector plate 29 mounted upon a tube 30. The shaft 28 is free to rotate in bearings 31 and 32 within a cap 33 removably attached to the vacuum vessel 10. In order to maintain the vacuum within this vacuum vessel 10, the cap 33 is provided with Gaco seals 34, 35 and 36 bearing upon the shaft 28 and the space 37 between the bearings 31 and 32 is exhausted by means of an auxiliary pump system 38.

The collector assembly 27 is rotated by a motor 39 operating on the shaft 28 through a belt and pulley.

A water housing 40 extends around the shaft 28 and is attached to a platform 41 through which the shaft 30 protrudes. Water enters the water housing 40 through inlet pipes 42 and 43, is introduced into the collector assembly 27 through appropriately placed holes in the shaft 28, leaves from the shaft 28 through other holes and then leaves the water housing 40 through outlet pipes 44 and 45. The circulation of water as the heat exchange medium is illustrated in detail in FIGS. 2 and 2a. A revolution counter and a tachometer 46 driven by a belt 47 from a pulley 48 are mounted on the platform 41 to monitor the rate of revolution of the collector assembly. Also mounted on the platform 41 is a control means for the collector assembly, not shown in FIG. 1, but see FIGS. 2 and 2a.

FIGS. 2 and 2a shows in section the collector assembly 27, the shaft 28, the mounting of the shaft 28 on it bearings 31 and 32 in the cap 33 of the vacuum vessel (not shown), and the water housing 40.

The collector assembly 27 consists of the collector plate 29 integral with a tube 51 the cross-section of which decreases stepwise away from the collector plate 29. At its upper end the tube 51 is bolted to an upper plate 52 integral with the shaft 28 and an O-ring seal 53 seals the interior of the collector assembly from the interior of the vacuum vessel (not shown). Within the bore of the tube 51 is positioned a piston assembly 54 mounted on an inner shaft assembly 55 extending upwards within the shaft 28.

The shaft 28 consists of a load bearing outer tube 56, which engages the bearings 31 and 32 and has mounted upon it a pulley 57 by which the assembly is rotated. The water housing 40 is divided into an upper exit chamber 58, an upper entry chamber 59, a lower entry chamber 60 and a lower exit chamber 61, by spacers 62 and Gaco seals 63 arranged to permit rotation of the shaft 28 but prevent intermingling of the contents of the various chambers 58, 59, 60 and 61.

Water as a heat exhange medium is circulated through the rotatable member for cooling and temperature control.

The main circulation is of deionized water and enters through the upper inlet pipe 42 into the upper entry chamber 59 in the water housing 40, passes through circumferentially disposed holes 64 in the cylinder 56 and down through an annular space 65 between the outer surface of the inner shaft assembly 55 and the inner surface of an inner tube 66 in the shaft 28 to a space 67 within the bore of the tube 51 on the side of the piston 54 remote from the collector plate 59. The piston 54 is provided with holes 68 disposed around the inner shaft assembly 55 and the interior of the piston 54 is designed so that water entering through the holes 68 is constrained to pass through upper slots 69 to contact the inner wall of the tube 51 before passing through lower slots 70 and up an annular space 71 within the inner shaft assembly 55.

The piston is provided with two O-ring seals 72 and 73 the lower of which 73 prevents leakage of water into the space 74 between the piston 54 and the collector plate 29.

The water passes up the annular space 71 through circumferentially disposed holes 75 into a further annular space 76 within the inner shaft assembly 55, thence through circumferentially disposed holes 77 in the inner shaft assembly 55 into the upper exit chamber 58, whence it is discharged through the upper exit pipe 44. This water is cooled and then recirculated.

The rotatable collector assembly 27 has a subsidiary water circulation by which the bearings 31 and 32 are colled. Water enters the lower entry chamber 60 through a pipe 43 and passes through circumferentially disposed holes 78 in the first shaft assembly into an annular space 79. The water passes down the annular space 79 through circumferentially disposed holes 80 into a further annular space 81 adjacent the inner wall of the outer tube 56 of the shaft 28. In passing up the annular space 81 the water cools the walls of the shaft 28 and thus the bearings 31 and 32 after which it leaves the shaft 28 through circumferentially disposed holes 82 into the lower exit chamber 61 from which it is discharged to waste through a pipe 45.

An externally threaded tube 83 is mounted on the platform 41 and these portions of the shaft 28 and the inner shaft assembly 55 which extend above the platform 41 protrude into the externally threaded tube 83.

FIG. 2a illustrates the means for controlling the position of the piston 54 within the tube 51. The top of the inner shaft assembly 55 protrudes beyond the end of the shaft 28 into the externally threaded tube 83 and has a circumferential notch 90 positively engaged by the lower rim of a head 91 having an upwardly facing flange 92 upon which a bearing 93 runs. The externally threaded tube 83 is engaged by two internally threaded rings 94 and 95 which locate between them an unthreaded loosely fitting ring 96 bolted securely through longitudinal slots (bolts and slots not shown) in the externally threaded tube 83 to a carrier 97 in which the bearing 93 is mounted.

As the internally threaded rings 94 and 95 are screwed up and down the externally threaded tube 83, the motion is transmitted to the piston 54 by way of the carrier 97, head 91, and the inner shaft assembly 55. In this manner the position of the piston 54 within the tube 51 may be controlled.

FIG. 2 also shows a thermocouple 84 by which the temperature of the collector plate 29 is monitored and the collector plate 29 is provided with a heater 85. A rigid narrow tube 86 extends from the plate 50 through a tubular space 87 within the inner shaft assembly 55 to the head 91 and carries electrical leads to the thermocouple 84 and the heater 85. The head 91, is provided with a slip ring assembly 98 through which electrical connection is made with the thermocouple 84 and the heater 85. The space 87 connects with the atmosphere by way of holes 99 in the head 91 and provides a safety vent if water leaks from the piston 54 when the collector plate 29 is hot enough to evaporate it.

In operation the temperature of the collector plate 29 may be controlled to within 5.degree.C even when it is exposed to the sudden surge of heat caused by exposure of the metal sources at the beginning of the deposition.

FIG. 3 shows in cross-section a typical evaporation source shown schematically in FIG. 1 in which a vitreous carbon crucible 13 is supported upon three hollow molybdenum legs 100 one of which contains a tungsten-iridium thermocouple 101 to give an indication of the source temperature. Heat is supplied by a tantalum sheet heater 15 inside molybdenum radiation screens 102. Such sources may be used one for each constituent as shown in FIG. 1 or another crucible, shown by the chain dotted line 103, may be placed within the first crucible 13 to provide a source for the simultaneous evaporation of two separate constituents. This method is efficient only if the two constituents have suitable evaporation characteristics. In determining whether two metals have suitable evaporation characteristics it is necessary to consider, their relative vapor pressures, the proportions of the metals sought to be introduced into the alloy, and the relative surface areas of metal provided by the particular pair of crucible used.

FIG. 4 shows a schematic plan view of an alternative source means in which the constituents are evaporated from three troughs 110 arrayed with their axes at angles of 120.degree. on a circular base plate 111. The meeting point of the axes is under the centre point of the collector plate 29 (shown in FIG. 1). The contents of the troughs 110 are heated by electron beams from the electron guns 112 and the temperature and rate of heating of each of the troughs may be controlled independently. It will be realised of course that fewer than or more than three troughs 110 may be used depending upon the number of constituents sought to be evaporated.

Advantages occuring from the use of electron beam heating are that only the surface of the molten metal is raised to the temperature required for evaporation enabling reactive refractory materials to be evaporated with a minimum of contamination by reaction of the metal with the evaporation container.

The distance between the collector plate and the metal sources must be sufficient to permit the electron beams to reach the evaporation sources without impinging on the collector plate.

In operation the material, or materials, sought to be evaporated are placed in the crucibles 13 and 14, the apparatus closed and evacuated. With the shutters 21 and 22 in place the rotatable collector assembly 27 is raised to its operating temperature by the heater 85 and rotated at the desired rate. The crucibles 13 and 14, still with the shutters 21 and 22 in position, are slowly raised almost to the temperature to be used during the evaporation and then the shutters 21 and 22 are removed and the crucibles rapidly raised to the final evaporation temperature and maintained there during the course of the deposition.

When the shutters are opened the internally threaded rings 94 and 95 are screwed down the externally threaded tube to advance the piston 54 towards the collector plate 29 to increase the rate of heat removal until thermal balance is attained and the temperature of the collector plate remains constant at the desired value.

After sufficient metal has been deposited the shutters 21 and 22 are replaced, the heaters 15 and 16 switched off and the whole apparatus allowed to cool while still under vacuum.

After cooling the vacuum is broken and the deposit removed from the collector plate 29 for further treatment.

The deposit may be heat treated before removal from the collector plate 29, or even before the breaking of the vacuum by use of the heater 85, and after removal may be subjected to any of the treatments known to the metal working art to achieve desired properties.

The above is a description of a typical deposition but the details may be varied, for example, after deposition and before removal from the vacuum the deposit may be subjected to a heat treatment by use of the heater 85, or the collector plate temperature may be varied during the deposit, or more than two metals or metal compounds may be deposited, or only one metal and a gas, for example, oxygen as disclosed in patent application Ser. No. 665,844 filed Sept. 6, 1967, now U.S. Pat. No. 3,554,735.

By way of example only there will now be described the deposition of metal from the vapour phase as hereinbefore disclosed.

Example 1

An aluminum nickel deposit was made in the following way.

The apparatus consisted of a stainless steel, cooled, bell jar on a cooled base. Two evaporation sources were positioned on the base plate. They consisted of crucibles containing the metal to be evaporated, heated by tantalum sheet radiant heaters inside molybdenum sheet radiation screen assemblies. The temperature in each furnace was measured with a thermocouple situated near the crucible, i.e. in the crucible support.

Each source was fitted with a shutter.

About 2 cm above the top rims of the crucibles an aluminum alloy collector was rotated about a vertical axis which was mid-way between the centres of the crucibles. The temperature of this collector was controlled and measured during rotation. The collector surface was 16 cm diameter.

The collecting surface was first polished. It was then washed with detergent, rinsed with water, and dried in an oven.

A piece weighing 205 grams of 99.99 percent aluminum ingot was similarly washed and dried and a piece of nickel rod weighing 56 grams also. The aluminum was placed in a vitreous carbon crucible 5.7 cm dia. in one of the radiation furnaces, and the nickel in an alumina crucible 3.1 cm dia. in the other.

The apparatus was closed, and the vessel was evacuated with a diffusion pump system to an indicated pressure of 3 .times. 10.sup.-.sup.5 torr.

The shutters were positioned above the crucibles. The collector was rotated, and it was raised to a temperature of 300.degree.C. The collector was rotated at 400 r.p.m. during the rest of the experiment.

The two evaporation sources were then heated gradually, over a period of 50 minutes, to temperatures about 200.degree.C below the final values and the shutters were opened, the one over the aluminium about 10 seconds before that over the nickel. During the next 4 minutes the evaporators were taken up to the final evaporation temperatures and maintained thus for the following 114 minutes. The indicated pressure fell during this time from 6 .times. 10.sup.-.sup.5 to 1 .times. 10.sup.-.sup.5 torr.

After this the shutters were closed, the electric supply to the evaporators and the collector was switched off, and the whole apparatus was left to cool under vacuum to near room temperature.

The deposit was split from the collector in one piece with a knife. It was found that 156 grams of aluminum and 8 grams of nickel had evaporated, and that the deposit on the collector weighed 139 grams and the nickel content was about 7 percent.

The deposit was cut into several pieces and was hot rolled, with intermediate anneals at 140.degree.C. For example a piece 1 inch by 31/8 inches was first ground approximately flat, to a thickness of 0.13 inches, and it was rolled with six passes, with an anneal between each pass, to a final thickness of 0.032 inches. The hardness in this state was 110 Kg/mm.sup.2, the tensile strength was 22 tons/in.sup.2 and the elongation 5.5 percent.

Example 2

A deposit of aluminum and iron, containing about 5 wt % iron was made in the apparatus described in Example 1 and in this foregoing text. This deposit and all others quoted in the examples was of variable thickness and composition. The deposit was thin at the edge and at the centre, and it had an annulus of thick material at approximately the radius of the crucible centres. It is this thick material which was used for working, heat treatment and mechanical testing. The chemical composition refers to this region.

______________________________________ Weight of aluminum ingot 205.1 g Weight of vitreous carbon crucible 25.6 g Diameter of carbon crucible 5.74 cm Weight of pre-melted iron button 54.0 g Weight of alumina crucible 56.0 g Diameter of alumina crucible 3.54 cm ______________________________________

The aluminum was 99.99 percent Al. The iron was Swedish iron, previously vacuum melted, the collector, ingots and crucibles were washed with detergent, rinsed with water and dried, the collector having first been polished. The aluminum was placed in the vitreous carbon crucible in one of the evaporation furnaces and the iron in the alumina one in the other. The shutters were placed over the crucibles; the apparatus was assembled and closed, and the vessel was pumped out to 1 .times. 10.sup.-.sup.5 torr.

The collector was heated by means of the internal heater 85 to an indicated temperature of 350.degree.C and was rotated at 85 r.p.m. The aluminum heater was turned on, and after about 1 hour the shutter over the aluminum source was opened. At about the same time the iron heater was turned on and the piston was lowered inside 51 to reduce the collector temperature. Ten minutes after opening the shutter over the aluminum, the collector thermocouple was indicating 150.degree.C, and the temperature of the collector was kept steady for the rest of the deposition period. After another 10 minutes the shutter over the iron was opened, and 6 minutes later both heaters were at their final settings and they were kept steady thereafter. One hundred and fifty minutes after opening the first shutter, both shutters were closed and the heaters were switched off. During this time the pressure indicated by the ionisation gauge rose to a maximum of 7.2 .times. 10.sup.-.sup.5 torr after which it fell gradually to 8.7 .times. 10.sup.-.sup.6 torr.

The weight of aluminum evaporated was 139.3 g, and that of iron evaporated was 7.1 g. The deposit was removed from the collector by spark erosion. It was crack-free. The iron content was 5.2 percent.

A piece of deposit was cut from the thick region. It was pressed at 320.degree.C in two steps upon a thickness of 0.120 inches to 0.062 inches. It was then rolled at 250.degree.C in four passes to 0.024 inches. A sheet tensile test specimen was machined and tested at room temperature with the following results:

Tensile strength 31.3 tons/in.sup.2 0.1% proof stress 22.0 tons/in.sup.2 Elongation % 8 Young's modulus 10.3 .times. 10.sup.6 p.s.i.

Example 3

An iron aluminum deposit was made as follows.

______________________________________ Weight of aluminum ingot 205.2 g Diameter of carbon crucible 5.7 cm Weight of iron button 36.7 g Diameter of alumina crucible 3.5 cm ______________________________________

The same quantity of aluminum and iron were used as in Example 2.

The contents of the apparatus and the collector, were prepared as described above. The vessel was closed and pumped to 1 .times. 10.sup.-.sup.5 torr. The collector heater was turned on. When the collector thermocouple was reading 380.degree.C the aluminum source heater was switch on, and the collector was rotated at 170 r.p.m. and kept at this speed subsequently. Fifty-five minutes later the shutter over the aluminum was opened, the iron source heater was switched on and the collector temperature was reduced. After a further 15 minutes the collector had reached 150.degree.C, at which temperature it was kept for the rest of the deposition. Seventeen minutes after opening the first shutter, the shutter over the iron was opened. Thirteen minutes later both sources were up to the desired temperatures and they were then kept steady. A hundred and fifty minutes after opening the first shutter both shutters were closed and the heaters were switched off. During the experiment the pressure indicated by the ionisation gauge rose to 1 .times. 10.sup.-.sup.4 torr, and it fell later to 2 .times. 10.sup.-.sup.5 torr.

______________________________________ Weight of aluminum evaporated 185.8 g Weight of iron evaporated 6.1 g ______________________________________

A specimen was cut from the thickest part of the deposit, after the latter had been spark eroded from the collector. It was pressed in two steps at 300.degree.C from 0.170 to 0.068 inch. It was then rolled in four passes at 300.degree.C from 0.068 to 0.026 inch. A sheet tensile test specimen was machined and was tested at room temperature with the following results.

______________________________________ Tensile strength 29.6 tons/in.sup.2 0.1% proof stress 22.8 tons/in.sup.2 Elongation % 4 Young's modulus 10.0 .times. 10.sup.6 p.s.i. ______________________________________

Microprobe analysis of a cross-section of the gauge length showed that the iron content was non-uniform and lay mainly in the range 1.0 to 3.4 percent.

Example 4

The titanium aluminum deposit was made as follows:

Weight of aluminum ingot 205.6 g Diameter of vitreous carbon crucible for the aluminum 5.72 cm Weight of arc melted titanium buttons 39.4 g Diameter of vitreous carbon crucible for the titanium 4.5 cm

The titanium was sponge material, vacuum melted, brinell hardness 90.

The deposition was started in the way described above, with the following changes:

a. Collector rotation rate 400 r.p.m.

b. Both sources were heated up together with the shutters closed.

c. With the collector at 380.degree.C the shutter over the titanium was opened ten seconds after that over the aluminum.

d. The collector was maintained at 380.degree.C throughout.

e. The deposition was stopped 77 minutes after opening the first shutter.

f. The deposit was removed from the collector in one piece using a knife to prise it off.

______________________________________ Weight of aluminum evaporated 130.4 g Weight of titanium evaporated 9.4 Weight of deposit 116 g Chemical analysis of the thick region gave titanium content 6.5% ______________________________________

Specimens were cut and worked as follows: press at 300.degree.C from 0.11 to 0.049 inches in two stages. Two sheet tensile test pieces were machined and tested at room temperature. Test piece A was tested in the pressed condition, and test piece B after heating for 1,000 hours at 200.degree.C, with the following results:

0.1% proof stress Tensile strength elongation Young's modulus tons/in tons/in.sup.2 % .times. 10.sup.6 p.s.i. __________________________________________________________________________ A 17.4 29.7 5 10.3 B 22.9 29.5 6 10.7 __________________________________________________________________________

Example 5

A chromium-aluminum deposit was made as follows:

Weight of Al ingot 205.0 g Diameter of carbon crucible 5.75 cm Weight of chromium flake (electrolytic) 40.3 g Diameter of carbon crucible for chromium 4.5 cm

Apparatus assembled and pumped to 1 .times. 10.sup.-.sup.5 torr.

Collector heated to 300.degree.C.

Both evaporation heaters then turned on with shutters in position. Collector rotated at 400 r.p.m. throughout, and maintained at 300.degree.C.

Forty minutes later, shutter over the Al source was opened, and 10 seconds later that over the Cr was opened. One hundred and one minutes after the shutter over the Al was opened, both shutters were closed and the heaters were switched off.

______________________________________ Weight of Al evaporated 144.5 g Weight of Cr evaporated 10.0 g ______________________________________

The deposit was split from the collector using a knife. The chromium content of the thickest part was about 51/2 percent.

A piece of the deposit (A) was pressed at 350.degree.C in two stages from 0.140 to 0.046 inches; it was then rolled at 305.degree.C in four passes from 0.046 to 0.026 inch and then heated for 1,000 hours at 200.degree.C. A second piece (B) was pressed at 340.degree.C from 0.146 to 0.057 inch only.

A sheet tensile test-piece was machined from each piece and tested at room temperature with the following results:

Test- 0.1% proof stress tensile strength elongation Young's modulus piece tons/in.sup.2 tons/in.sup.3 % .times. 10.sup.6 p.s.i. __________________________________________________________________________ A 21.9 23.2 4 11.4 B 19.9 26.8 4 11.2 __________________________________________________________________________

Example 6

A manganese-aluminum deposit was made as follows:

Weight of Al ingot 205.3 g Diameter of carbon crucible 5.72 cm Weight of manganese flake 56.1 g Diameter of alumina crucible for 3.12 cm

The apparatus was assembled and pumped out as usual. The collector was taken to 300.degree.C and kept there and it was rotated at 400 r.p.m. throughout.

The Al and these source heaters were switched on when the collector reached 300.degree.C. Forty-five minutes later the shutter over the aluminum was opened, and 15 seconds later that over the manganese was opened. Deposition was continued for 140 minutes, with the ionisation gauge indicating a pressure of background gas between 1.3 .times. 10.sup.-.sup.5 and 5 .times. 15.sup.-.sup.6 torr.

______________________________________ Weight of aluminum evaporated 158.7 g Weight of manganese evaporated 8.3 g Manganese content of thickest part of deposit by chemical analysis 5.0% Maximum thickness of deposit 0.16" ______________________________________

Example 7

A nickel-aluminum deposit was made as follows:

Weight of Al ingot 205.3 g Diameter of carbon crucible 5.7 cm Weight of nickel bar 44.0 g Diameter of alumina crucible for Ni 3.1 cm

The apparatus was assembled and pumped out to 1 .times. 10.sup.-.sup.4 torr.

The collector was heated to 310.degree.C and the two evaporation sources were switched on. The collector was rotated at 400 r.p.m. Fifty-seven minutes after turning on the source heaters, the shutter over the Al was opened followed by that over the nickel. The collector was then at 320.degree.C and the ionisation gauge reading was 1.2 .times. 10.sup.-.sup.4 torr. The collector temperature was reduced, until 23 minutes later it reached 177.degree.C, where it was kept for the rest of the deposition. At this time the rotation speed of the collector was increased to 1,000 r.p.m. and it was kept there for the remainder of the time. The background pressure remained at about 1 .times. 10.sup.-.sup.4 torr. One hundred and eleven minutes after opening the shutters, they were closed again and the power was switched off.

The deposit was split off the collector in one piece with a knife.

______________________________________ Weight of Al evaporated 113.6 g Weight of Ni evaporated 4.7 g Weight of deposit 120.0 g Maximum thickness of deposit 0.130" Nickel content of thick portion, by chemical analysis 4.3% ______________________________________

A piece of the deposit was pressed at 190.degree.C. from 0.125 to 0.100 inch. It was then rolled at 175.degree.C in four passes from 0.100 to 0.025 inch. A sheet entile test-piece was machined and it was tested at room temperature with the following results:

0.1% proof stress tensile strength elongation Young's Modulus tons/in.sup.2 tons/in.sup.2 % .times. 10.sup.6 p.s.i. __________________________________________________________________________ 23.6 32.7 6 10.2 __________________________________________________________________________

Example 8

Similar deposits were made of aluminum with silicon, magnesium, cobalt, antimony and copper.

A series of experiments were carried out as hereinbefore described in order to determine the effect of substrate temperature and nickel layer thickness on the formation of intercolumnar porosity in an aluminum nickel binary deposit. Broadly high substrate temperature favours intercolumnar porosity and thick nickel layers tends to prevent it. In FIG. 5 points marked thus, X, indicate the presence of intercolumnar porosity and those marked thus, , its absence. It will be seen that the line 105 divides the graph into two fields, namely occurrence of intercolumnar porosity. Although a line has been drawn it will be realized that there is a region within which the change from intercolumnar porosity to non-occurrence of intercolumnar porosity takes place and no sharp dividing line can be drawn .

Claims

1. A bulk alloying process for the production of an aluminum based multi-phase alloy in the form of an engineering material, said process being carried out within a controllable low pressure or vacuum system and the said process comprising the steps of

a. evaporating the constituents of the alloy from separately controllably heated evaporative sources,

b. depositing the constituents upon a temperature controllable disc collector which is rotated about a substantially perpendicular axis, the sources being arranged below the collector so that the constituents of the alloy are deposited in successive layers, wherein the base metal constituent of the alloy is aluminum and the alloying constituent is selected from the group consisting of iron and nickel to prevent columnar growth within the aluminum layers,

c. continuing the deposition of the constituents until the deposit is at least 0.01 inch thick, and

2. A bulk alloying process as claimed in claim 1 wherein the alloying constituent is nickel and is deposited in layers of about 20A thickness and the temperature controllable collector is maintained at a temperature

3. A bulk alloying process as claimed in claim 1 wherein the alloying constituent is iron and is deposited in layers of about 10A thickness and the temperature controllable collector is maintained at a temperature of about 150 to 250.degree.C.