FR2659581A1 - PROCESS FOR FORMING AN ARTICLE HAVING A VARIABLE ALLOY COMPOSITION - Google Patents

Abstract

A method of forming a structure having multiple alloy properties is disclosed. The process involves spray forming and employs a single alloy system which is subject to change by the addition of modifying elements. An initial preform (26) is made of the alloy in the absence of modifying elements. These are added to mix and dissolve in the alloy in a distribution crucible (12) for spray forming. The latter parts of the preform have a changed alloy content and exhibit properties which are changed based on the change in the alloy content. Application to the manufacture of structures which must have different properties between one part and the other, for example to jet engine discs.

Description

The present invention relates to the formation of structural

  with a variable alloy composition.

  firstly, it relates to a process in which structures having an inner part having a certain composition and an outer part of another composition can be formed. The invention is related to patent pending applications of the United States of America having serial number 487 094

and 487,095.

  Superalloys, including nickel and iron-based superalloys, are known to have been the subject of

  intensive use in applications requiring resistance

  high mechanical strength at high temperatures The design of jet engines was largely determined by the properties of the superalloys used.

  as a material for manufacturing engine components.

  Improving the properties of the alloys also allows that of the design of a jet engine, and obtaining higher ratios between thrust and weight. In general, the high temperature operation results in a better use of the fuel for fuel. decette engines

  nature and purpose of using operating temperatures

  and superalloys capable of operating at such temperatures is a permanent criterion for the manufacture of increasingly efficient 2-cycle engines. The need for superalloys having a high mechanical strength when used at high temperatures is always present as efforts are made to continue improving the performance of jet engines. A great deal of progress has been made in metallurgy with the aim of improving high mechanical strength superalloys. One of these is the increase of the volume fraction of the precipitate for the gamma prime precipitating agent of these alloys. In addition, improvements have been made through powder metallurgy and the use of isothermal forging. In this way, the improvement in temperature stability of superalloys has been achieved. the components of a jet engine are not subject to the same operating conditions and different metallurgical compositions can be employed in the various engine components to better meet the needs of a component. There are parts for which there are compromises in terms of characteristics because the part is large enough that the operating conditions of the engine are not the same in all its extent. In other words, some large parts mounted in a are subject to different temperatures and requirements for properties and service between one part of the part and the other Therefore, for large components of this type, it is necessary to sacrifice a property in a location. of the component so as to obtain an acceptable property in another place Such different properties are necessary, for example, in the motor discs rotating at high speeds of 12000 rpm and more, which causes the application of important constraints. in their

outer portions.

  In order to compensate for the different property requirements of the various parts of the discs, arrangements and methods have been developed to impart desirable combinations of properties to the inner and outer portions of the discs. United States of America 4,820,358 relates to a method in which a disc made of a single alloy may have different properties at its inner portion in contrast to its outer portion. Obtaining different properties in the various parts of the disc. is a

  realization of great interest.

  Other efforts have been devoted to the formation of the inner part of a disc with a certain alloy and its outer part with another alloy. However, there are problems when trying to join the two alloys Si oxide layers are present at the limit, it is difficult to be assured that a previous welding operation triumphed over the presence of the oxide and did not leave an area of weakness in the disc. detection of straws in such welds between an inner portion and an outer portion of a disk is

a difficult operation.

  The object of the present invention is to modify the composition of an alloy during a spray treatment so that a part of the deposit obtained by projection, with the properties thus conferred on this part, has a first composition and than another part of the depot, with its different set of properties for

  the alloy, has a second composition.

  Accordingly, the present invention provides a method for forming a composite structure having two or more different compositions at various portions thereof. Another object of the invention is a structure in which portions of alloy are joined without any clear cut.

demarcation between them.

  The present invention further relates to a method for forming a preform of a disc having at least two

  different metallic compositions.

  The subject of the invention is also an alloy structure in which two different alloys are present in

different portions.

  In one of its broader aspects, the present invention relates to a projection forming device in which a first metal flows in the form of a current between a distribution crucible and an atomization zone. metal is atomized in said zone and deposited by spraying on a receiving surface so as to form a first layer of a preform on the surface; projection of the first metal to form a preform on the surface is carried out continuously; If a large portion of the first metal is present in the crucible, a small portion of an additional metal is added to the crucible so as to mix the first and second metals and obtain a modification of the first composition. The deposit is continued by spraying the metal onto the preform. from the dispensing crucible in order to enlarge the preform but there is no addition of metal in the dispensing crucible It results producing a preform in which the first metal is deposited on the receiving surface and the modified metal is bonded to the

  first metal to form its outer portions.

  The following description refers to the figures

  annexed which respectively represent: FIG. 1, a schematic illustration of the arrangement

  a mandrel, a preform, and a dispensing crucible

  tion; FIG. 2, a schematic illustration similar to that of FIG. 1, but showing the addition of alloying agents to the distribution crucible, and FIG. 3 a graph of experimental results representing the variation of the concentration of an element.

  alloy depending on the depth of a preform.

  There are alloy systems that are significantly modified depending on the additives present in the alloy.

  admits, for example, that some elements of addition increase

  the strength of an alloying system so that an alloy having a smaller amount of the reinforcing additives has a lower mechanical strength while the same alloy with the reinforcing additives in higher concentrations has a lower value. great

of its mechanical resistance.

  In a similar way, there are

  which adversely affect the ductility of an alloy system so that an alloy with lower concentrations of the ductilization additive has a smaller ductility and the same alloy with a higher concentration of

  the ductilization additive has a greater ductility.

  The present invention takes advantage of the systems of

  binding which are subject to such alteration of the properties

  desired according to the quantity of the modifying

  the properties of the alloy such as reinforcing agents or ductilization agents or other characteristics modifying agents.

  nature is indicated in the context of the present invention.

  In particular, it has been found that the

  high resistance of superalloys and improves it by increasing

  both the volume fraction of the precipitate for the super-

  bindings reinforced by gamma prime precipitate In others

  terms, it has been found that by the specific addition of

  forming a precipitate for the purpose of causing an increase in the volume content of the gamma prime precipitate,

  the reinforcement of the alloy itself is obtained.

  According to the present invention, an alloying projection process is commenced employing a modifier-free alloy composition or having a lower value of a modifier of the elements present and the process is continued after incorporating a modifier. in the composition of the alloy so that the last part of the formation is carried out with the modified alloy instead of the unmodified alloy which was used at the beginning of the projection. Unique advantages of the alloy are obtained. use of a single-alloy base in two different parts of a projection-formed article, where different properties are required in two

different portions of the article.

  For example, in the case of a disk, it is known that a higher mechanical strength is required in the periphery of the disk than in its central portion. Therefore, an appropriate use of the present invention is to project by forming a preform of disc in which its central portion has a base alloy content which has a

  lower concentration for certain additives or modifications

  and its outer part has the higher concentration of additive or modifier, where this modifier

  or this additive confers additional mechanical strength

  silence the outer portion of the disc finally made

from the preform.

  The results of the test carried out with the present invention will now be described with reference to FIG. 3, which is a graph of the values obtained using the present invention, in conjunction with FIGS. 1 and 2. invention on a system

particular alloy.

  FIG. 1 is a schematic elevation, partly in section, of a projection-forming operation such as that used in connection with the present invention. In this respect, a crucible 10, 12 is used as a distribution crucible. crucible to contain a certain quantity of liquid metal and to distribute it under 7 -

  form of current to an atomization zone lying

  The crucible is preferably segmented, that is to say made up of a number of water-cooled metal segments which are mounted on the crucible.

  around and form its walls like a barrel moat.

  Each segment is electrically isolated from the contiguous segments and is individually cooled by water. An advantage of water cooling is to allow the formation of a molten metal pocket bottom on the inside of the crucible so However, the melt is maintained at its operating temperature under the effect of a set of induction coils 14 The segmented nature of such a crucible 12 allows the flow electric to penetrate it in order to act on its liquid metal content

  this way, we avoid some of the disadvantages of including

  of ceramic particles as discussed in

  the background of the present invention.

  The stream 18 of liquid metal which is discharged through the lower nozzle 20 of the crucible 12 enters an atomization zone 21 in which it is subjected to the effect of one or more jets of atomizing gas supplied by a

  source, not shown, at the nozzle 20.

  The result of the atomization of the liquid stream 18 by the gas in the atomization zone 21 is the production of a cone 24 of liquid metal droplets. The formation of the cone is normal practice in the conventional projection formation technique. droplets fall on a receiving surface 26 consisting of an annular band formed on a hollow mandrel 28 The mandrel 28 is subjected by a drive means, not shown, to a rotation and to a movement back and forth indicated by the arrows These movements cause the formation of an even layer on the receiving surface The first part, and in the illustrated illustration, the inner part of the preform 26 is made of an alloy which is subjected to a modification by the addition of a modifier such as an agent

  reinforcement or ductilization or other type of agent.

  The second part of the preform, and in the illustration

  shown, the outer part of it, consists of an alloy which has been modified.

  many ways to perform the modification of the alloy.

  Essentially, the modification is effected by the addition of a modifier to the liquid remaining in the crucible of

distribution.

  Now in a more specific connection with FIG. 2, the device of FIG. 1 is represented again with the deposited preform 26 half completed. In addition, about half of the liquid metal 16 has been removed from the crucible 10. a charge of a modifier 32 with a convenient means such as a scoop or a probe. The modifier may be added in liquid form or as a solid powder or in any other form that will dissolve readily in the liquid body. The heating coil 14 acts on the liquid inside the crucible not only to heat it but also to stir it so that there is a continuous action of agitation and that the added modifier 32 is rapidly stirred, mixed and dissolved in the metal

  liquid 16 inside the crucible 10.

  Referring now to FIG. 3 FIG. 3 is a graph of the results obtained in an experiment made using an alloy that could be modified by the addition of aluminum in a percentage by weight

relatively small.

  The experiment was carried out by first forming the first or inner half of the preform 26 by employing an alloy having a small volume in percent of a gamma prime microstructure. At a determined time of the atomization, it was plunged a known amount of aluminum in the rest of the molten metal bath Within seconds, the bath composition changed from a low gamma prime 9-alloy to an alloy having a high gamma prime The curve in figure 3 shows the variation of the aluminum concentration of the alloy as a function of the thickness of the preform indicated on the abscissa As shown in the figure, the initial weight concentration of the aluminum was of about 2.2 and this concentration was present in the preform to a thickness of about 38 mm. At this stage, aluminum was added and, as it appears in the curve, this addition resulted in by a significant increase in the aluminum content of the alloy to a thickness of about 43 mm For the alloy at a depth or thickness of about 50 mm, the aluminum content was about 4% By weight The concentration of aluminum in the alloy was maintained at about 4% by weight during the

rest of the test.

  Two tests are shown in Figure 3, which are

  respectively indicated by references 1 and 2.

  Although in the illustrative example, aluminum was added to a melt so as to vary the gamma prime content of the preform during atomization, it should be noted that it is also possible to add other elements of modification to an alloy system in order to change the properties of a deposit by projection in one part with respect to another For example, it is envisaged to dissolve other elements such as tantalum or alloys masters in a dispensing crucible while

  the atomization continues so as to provide a micros-

  desired structure and obtain a particular set of

  properties at different parts of the preform.

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Claims (4)

  Process for forming a preform (26) having different properties in various parts thereof, characterized in that it comprises the steps of: providing a dispensing crucible (10, 12) so as to contain a mass melted (16) a metal to be projected; supplying a lower nozzle (20) into the crucible to deliver a liquid metal stream (18) to an atomization zone (21) below the crucible, supplying the area with a certain amount of atomizing gas in order to atomizing the liquid metal stream delivered from the crucible to form a cone of fine droplets (24), providing a receiving surface (28) to be coated with the fine droplets of the cone, adding (30) a modifying metal ( 32) to the melt in the dispensing crucible so as to change the properties of the metal that is in the molten state, mix the modifying metal with the melt, and continue the projection so as to deposit the mass modified fondue on the preform.   Process according to claim 1, characterized in that the metal melt is a nickel-based superalloy. Process according to Claim 1, characterized in that the metal melt is a superalloy and the metal   modifier is a reinforcement modifier.   Process according to Claim 1, characterized in that the metal melt is a superalloy and the metal   modification is a prime gamma-forming metal.   Process according to Claim 1, characterized in that the metal melt is a superalloy and the metal of modification is aluminum.