JP2008545064A - Metal body bonding method by sintering - Google Patents

Abstract

A hollow metal sphere is heated in the presence of an organic substance in a high vacuum at a temperature at least as high as the melting point of the eutectic mixture between the carbon and metal components of the sphere.
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Description

  The present invention relates to a method of bonding metal bodies used in hot parts of an aircraft together by sintering.

  The sound wave emission from a commercial aircraft may reach 155 dB at takeoff, and the value exceeding the auditory pain threshold is estimated to be 130 dB. It is therefore desirable to reduce the emission of this level of sound waves.

  One way to try to solve this problem is to absorb one of the points of emission, i.e. the noise in the engine. In the “cold” part of the engine, solutions have already been developed, but at the present time the “hot” part is not subject to any acoustical treatment. It is therefore desirable to develop a sound absorbing material designed for the hot parts of aircraft engines. To do this, the development of nozzles with the ability to absorb some noise generated inside the engine is considered.

  Furthermore, manufacturing a system that has the ability to absorb large amounts of kinetic energy and at the same time has a very low weight is clearly beneficial to both people and assets.

  One system that can satisfy these various specifications requires the use of a sphere-based cellular material.

  However, at present, only nickel-based spheres and ceramic or organic spheres are commercially available. The association of these components by sintering does not allow the desired combination to achieve the above objectives. Furthermore, the temperature capability is very limited in all respects of the mechanical strength, oxidation resistance and corrosive environment required for aircraft engines.

  Powder metal can be sintered to reproduce alloy lumps, especially nickel-based aircraft superalloys. Reproduction methods by sintering include a number of densification methods such as dynamic molding, isostatic pressing, compression, and the like. These methods are applied at high temperatures, that is, about two-thirds of the melting point.

  In contrast, in the case of densification by normal sintering at the same temperature, that is, when there is no external pressure other than the earth's gravitational field, other porous alloys are produced.

  The present invention is to solve these difficulties.

In order to solve the difficulties of using these cellular materials based on spheres, we decided to study new materials with the following advantages.
-It can be constructed from a superalloy derived from powder metal and based on nickel, and the densification of the alloy can be carried out without using external pressure,
The possibility of having the expected performance characteristics in the specification derived from modeling,
-The possibility of being made from the best material for the specification,
-The possibility of having a dense wall in one operation-and the possibility of having many functions.

The present invention relates to a method of bonding metal bodies that are eutectic-reactive with carbon under vacuum in the presence of an organic substance that initially acts as a binder and that are initially bonded to each other by sintering under vacuum. The organic material of the metal body and the organic material at a degree of vacuum that is better than 10 ⁻³ Pa so that carbon produced by the decomposition of the organic material reduces the metal body To obtain local melting at a temperature equal to or slightly higher than the temperature of the eutectic mixture between the carbon resulting from the decomposition of the metal and the metal constituents of the metal body.

  By maintaining the temperature at the same temperature as or slightly higher than that of the eutectic mixture, the liquid phase is involved only in the region of the metal body in contact with the carbon, and the strength of the metal body during sintering with the metal body remaining in the solid phase. Can be assumed.

  This solid phase needs to be preserved particularly in the production of a hollow body made of superalloy powder. Actually, the diameter of the hollow body is usually about 10 to 100 times the thickness of the wall surface of the hollow body, and the thickness of the wall surface is usually about 2 to 100 times the average particle diameter of the particles constituting the wall surface.

In any feature of the invention, either additional or alternative will be given as follows.
-The degree of vacuum is better than ^10-4 Pa.
-Sintering in the absence of mechanical stress.
The metal body is a powder.
-A metal powder and an organic binder are included, and if necessary, the solvent mixture is heated at the temperature under the vacuum.
-To obtain a variety of hollow metal bodies having substantially the shape and dimensions of the starting nucleus, a variety of solids made of organic materials, each covered with a mixture of metal powder and organic adhesive. The core is heated at the temperature under the vacuum and the metal bodies are bonded together by sintering.
-Various hollow metal bodies bonded to each other using an organic adhesive are heated at the temperature under the vacuum, and the bond due to bonding is replaced with the bond due to sintering.
-A decarburization process is performed following sintering.
The metal body is made of nickel and / or cobalt, or alloys of these metals, in particular nickel-based and / or cobalt-based superalloys.

  According to one embodiment of the present invention, the final object is obtained from a mold or preform into which the metal powder is introduced, the metal powder being a piece, paste or any other thixotropic agent that is easy to inject ( It is prepared to form a thixotropic mixture.

  According to another aspect of the invention, metal powder is deposited on the surface of a body such as a ball. To do so, the desired alloy powder as a shell is bonded onto the surface of the sphere.

Therefore, the present invention may include the following steps.
-The production of an alloy powder / organic precursor mixture to obtain a thixotropic mixture that can be injected into a mold or preform;
Application to form hollow spheres, and optionally protection of the material by aluminum plating.

  When manufacturing hollow spheres, it is possible to use loose stacking technology without resorting to the teachings of French Patent No. 2585445A.

  The present invention relies on the following findings.

1. When an organism, i.e. composed of molecules based on the chemical nature of carbon, is subjected to high vacuum (P <10 ⁻³ Pa) and high temperature (T> 150 ° C.), it directly vaporizes or sublimates, or The transition from a solid (or liquid) to a gas, either by breaking into one or more units that may themselves turn into a gas. In order to properly select the organic material, more than 90% of the material exposed to such high temperature vacuum will be vaporized. However, particularly when decomposition occurs, since the reactivity with oxygen is high, a trace amount of elemental carbon may remain on the surface of the organic material container.

2. Oxidized metal element slightly, i.e. oxygen and in contact at room temperature to an atmosphere rich in water vapor, and better than 10 -4 ^Pa at a temperature exceeding 500 ° C. (under 10 -4 ^Pa) elemental carbon in vacuum In contact with the material, the naturally occurring oxide layer derived from this material is spontaneously reduced by the following reaction. This is the first action of carbon.

M _x O _y + yC → xM + yCO ↑
M _x O _y + yCO → xM + yCO ₂ ↑
3. When the metal element is reduced in step 2, the metal element is in direct contact with carbon. At this time, it is possible to obtain a eutectic melt by raising the temperature and using carbon as a flux. This is the second effect of carbon. The next form is in particular a eutectic reaction with carbon.

Co (T _m = 1320 ° C.), Cr (T _m = 1534 ° C.), Fe (T _m = 1153 ° C.), Ni (T _m = 1326 ° C.) and Pd (T _m = 1504 ° C.).

  Thus, sintering with any alloy powder, in particular either nickel-based or cobalt-based, ie in this case local melting, is possible sufficiently from a temperature several degrees higher than the temperature of the corresponding eutectic mixture . At such a temperature, the eutectic mixture does not melt because the metal element is not reduced.

  All that is necessary to do this is to reduce to the desired alloy powder type (advantageous, but not essential, the center of the particle size is 40 μm) and to use t To make a piece to which a binder is added.

  Here, the binder is, for example, an epoxy adhesive diluted with ethyl alcohol, polymethyl methacrylate diluted with acetone, or methyl cellulose diluted with water.

In order to remove the solvent (ethyl alcohol, acetone, water, any other polar solvent), the mixture thus formed is dried in an oven (T> 80 ° C.). It is then placed in a chamber with a vacuum better than 10 ⁻³ Pa and annealed at a temperature above the melting point of the metal / carbon eutectic mixture. What is obtained at the end of the experiment is a regenerated starting alloy, and the chemical analysis performed on the resulting molded ingot shows that carbon contamination remains within acceptable limits.

  The invention is illustrated below by non-limiting examples.

  In order to reproduce the early superalloy, the astroloy powder was sintered. Here, astroloy means the following weight percentage: Cr 15, Co 17, Mo 5.3, Al 4.0, Ti 3.5, C 0.06, B 0.03, and the balance is Ni, with a composition of 100. A nickel-based superalloy having The temperature of the eutectic mixture of astroloy with carbon is 1250 ° C.

In order to perform the sintering, the above Astroy powder was mixed with polyvinyl alcohol as a solvent and water. The resulting pieces contained 60% by volume of metal powder. To remove water, for 16 hours at 80 ° C., after heating in an ^oven, it was placed the assembly to ¹⁰ -3 better than Pa ^(less than ¹⁰ -3 Pa) of vacuum in the chamber. The assembly was gradually heated (about 1 ° C. per minute) until the decomposition temperature of the organic binder (about 450 ° C.) was reached.

  After holding the temperature for about two hours, the assembly was heated to 1250 ° C. at a rate of 100 ° C. per minute. After holding for a while, the assembly was quenched to room temperature.

What was obtained from the oven was a solid material with no holes at all. Steel quality tests revealed a conventional structure of the starting superalloy, ie a γ-nickel matrix in which Ni ₃ (Al, Ti) γ′-precipitates are dispersed. The chemical composition was consistent with that of the initial material.

  If excess carbon was detected, the content of this element could be reduced by decarburization treatment, for example heat treatment in wet hydrogen well known to those skilled in the art.

  The technology that exists in superalloy powders that are directly bonded to the surface of the ball by bonding was utilized.

  Compared to composite electroplating, bonding technology by adhesion makes it possible to obtain spheres with a composition very close to that of the superalloy. In fact, a myriad of chemical compositions can be realized depending on the nature of the powder used.

The powder was directly bonded to the surface of the spherical polystyrene support using the following procedure.
-In order to obtain the optimum mixture recommended by the manufacturer, about 90 cm ³ of astroloy powder (D ₅₀ of about 10 μm) was mixed with ARALDITE 2011 brand 10 cm ³ of epoxy adhesive on a watch glass. The amount of adhesive and curing agent was mixed using an applicator gun capable of measuring.
-Then in the second stage, about a hundred polystyrene balls were added thereto.
-The ball was then spun in a powder / epoxy adhesive mixture using a second watch glass. And—just after the entire surface of the support was covered, the balls covered in this way were placed on a perforated tray and dried in an oven at 60 ° C.

  The thickness of the obtained powder / epoxy adhesive was about 0.1 mm.

A new type of heat treatment has been developed to maintain a sufficient degree of mechanical strength of the spheres that will become hollow by removing the support. This involves placing the ball on a V-shaped support to obtain a suitably shaped support, eg a compact (compact) stack, depending on the final structure obtained, and then evacuating the vacuum oven. And placing it in an alumina container provided with a lid with an opening for the purpose of holding the position of the ball. Once a degree of vacuum better than 10 ⁻³ Pa (less than 10 ⁻³ Pa) was obtained, the following heat treatment was applied.
-Heating at 0.5 ° C per minute to a temperature of 450 ° C,
-Heat retention 120 minutes,
-Heating at 100 ° C per minute to a temperature of 1250 ° C,
-Keeping warm for 20 minutes,
-Rapid cooling (decreasing from 1250 ° C to 600 ° C over about 20 minutes).

  This approach was chosen because it is easy to process and minimizes the number of steps for the purpose of more easily industrializing the specified application. During vacuum annealing, polystyrene and epoxy adhesives enrich each other's powder surface with a small amount of elemental carbon. Once this carbon is formed, each powder undergoes a deoxygenation reaction.

  Finally, when the melting point of the eutectic mixture formed by carbon and Ni and other superalloy constituents, that is, 1250 ° C., each powder surface partially melts. In addition, due to the presence of a layer of liquid, the balls bond to each other during processing.

  This technique makes it possible to obtain sufficiently satisfactory structures formed from various nickel-based superalloy balls.

  The purpose of this example was to perform a simple eutectic mixture brazing by incorporating carbon into a pure nickel target. More specifically, the aim was to attach together the hollow spheres of pure nickel supplied by the French company Ateca.

The balls were bonded with an epoxy-based adhesive ARALDITE 2011 diluted with alcohol. The purpose of this dilution is to increase the time to handle the balls before curing. After an oven treatment in air at a temperature of 80 ° C. for 2 hours, the set of balls was placed in a chamber with a better vacuum than 10 ⁻³ Pa.

  The entire assembly was then subjected to the following heating program. A temperature of 1350 ° C., ie a temperature increase of 100 ° C. per minute to a temperature 25 ° C. higher than the temperature of the Ni—C eutectic mixture, a temperature maintained for 10 minutes, and a rapid cooling (from 1350 ° C. to 600 ° C. over about 25 minutes) .

  After cooling, it was found that the balls were brazed together as indicated by the meniscus formed at these contacts. It was impossible to separate the balls.

  For comparison, spheres selected from the same batch were carefully defatted and subjected to the same vacuum heat treatment. At the end of the experiment, no meniscus was formed at the contacts. Although a small amount of interdiffusion was observed at the same contact, the balls were easily separated.

  Of course, the present invention can be applied to metal materials other than the above-described examples, and particularly applicable to all nickel-based and cobalt-based superalloys.

  The present invention can be applied to the production of a hollow sphere made of a superalloy.

Claims (8)

A method in which a metal body capable of eutectic reaction with carbon and initially bonded to an organic substance is bonded to each other by sintering under vacuum, the metal body and the organic substance being decomposed into the organic substance. The carbon produced by the decomposition of the organic material of the metal body and the metal components of the metal body at a degree of vacuum that is better than 10 ⁻³ Pa so that the carbon produced by the reduction of the metal body A method of bonding metal bodies by sintering, characterized by heating to obtain local melting at a temperature equal to or slightly higher than the temperature of the eutectic mixture. The metal body bonding method by sintering according to claim 1, wherein the degree of vacuum is better than 10 ⁻⁴ Pa.   3. The method for bonding metal bodies by sintering according to claim 1 or 2, wherein the sintering is performed in the absence of mechanical stress.   The metal body bonding method by sintering according to any one of claims 1 to 3, wherein the metal body is a powder.   5. The method for bonding metal bodies by sintering according to claim 4, wherein each of the metal powders and the organic adhesive is bonded to obtain various hollow metal bodies having substantially the shape and dimensions of the starting nucleus. A sintered metal body characterized in that various solid nuclei made of an organic material covered with a mixture with an agent are heated at the above temperature at the above-mentioned vacuum degree, and these metal bodies are bonded together by sintering. Join method.   The metal body bonding method by sintering according to any one of claims 1 to 3, wherein various hollow metal bodies bonded to each other using an organic adhesive are heated at the temperature at the degree of vacuum. A method for bonding metal bodies by sintering, characterized in that the bonding by bonding is replaced by bonding by sintering.   The metal body bonding method by sintering according to any one of claims 1 to 6, wherein a decarburization treatment is performed following the sintering.   8. A metal body bonding method by sintering according to any one of claims 1 to 7, wherein the metal body is made of nickel and / or cobalt or an alloy of these metals, the alloy being a nickel base and A method for bonding metal bodies by sintering, characterized in that the metal body is a cobalt-based superalloy.