FR2774612A1 - METHOD FOR MANUFACTURING AN INTERMETALLIC IRON-ALUMINUM ALLOY, AND INTERMETALLIC IRON-ALUMINUM ALLOY - Google Patents

Abstract

The present invention relates to a method for manufacturing an iron-aluminum intermetallic alloy, to an iron-aluminum intermetallic alloy obtainable by said method, and to an element made of such an alloy. comprises a step of preparing a powder of a mixture essentially comprising iron and aluminum, and a step of hot compression of the powder after degassing thereof. The process of the invention is particularly advantageous by example for the manufacture of parts or elements made of such an alloy, in substitution for steels or superalloys.

Description

METHOD FOR MANUFACTURING AN INTERMETALLIC ALLOY

  IRON-ALUMINUM, AND INTERMETALLIC ALLOY IRON-ALUMINUM

DESCRIPTION

  TECHNICAL FIELD OF THE INVENTION The invention relates to a process for manufacturing an iron-aluminum intermetallic alloy, to an iron-aluminum intermetallic alloy obtainable by said process, and to a component

of such an alloy.

  Iron-aluminum intermetallic alloys have special properties compared to other structural alloys which are

  low density and specific resistance, that is

  say a property related to the density of the material, high compared to steels and superalloys. They have for example a high specific rigidity compared to light alloys, steels and nickel alloys, a high ductility compared to that of other intermetallics such as TiAl or NiAl, a high mechanical resistance up to 700 C compared to alloys of aluminum and organic matrix composites, high dry corrosion resistance compared to most stainless steels and superalloys, and low cost of

basic materials.

  All of these properties make it possible to consider these alloys as possible substitutes for light alloys, steels or superalloys, for industrial applications exploiting their particular properties. Indeed, a density reduced by 25% compared to steels and nickel alloys, for properties and means of implementation comparable elsewhere, makes it possible to envisage a reduction in weight of aeronautical and space structural parts such as parts of hardware, landing gear, brake system parts, etc.

  The high specific resistance of these alloys also makes it possible to envisage applications in substitution for high resistance alloys such as steels and superalloys, used for the manufacture of critical moving parts of heat engines and of turbomachines, such as valves, axes and shafts, turbine blades. The reduction in mass of such components generally reduces the problems of inertia, friction and vibration, and therefore results in a possible reduction in mass of other components such as bearings, springs, fastening systems and cooling, intervening..DTD: in the movements of these critical parts.

  Specific stiffness is a particularly interesting property of these materials. It is in fact 10 to 20% higher than that of the structural alloys currently used such as light alloys, steels and superalloys, for the manufacture of parts having to work in vibratory regimes close to resonance limit, or even at- beyond, such as certain turbine power shafts or certain injection nozzles or pipes

of fluid.

  The corrosion resistance properties of these OJ alloys allow them to be used for the manufacture of furnace resistors or tubes

heat exchanger.

  State of the art In a composition range between 25 to

  % aluminum, an iron intermetallic alloy

  aluminum has an ordered crystalline phase of centered cubic structures of type B2. This ordered phase, also called the first phase, has excellent resistance in an oxidizing, sulfurizing or fuel environment, up to 1000 ° C., and good resistance to erosion. However, it has a great brittleness at room temperature and an elastic limit and a creep resistance, little

high at high temperature.

  Iron-aluminum intermetallic alloys are currently manufactured by extrusion processes, from powder mixtures essentially comprising

iron and aluminum.

  Numerous researches aimed at improving the strength and ductility of intermetallic iron-aluminum alloys obtained by extrusion have been carried out. This research mainly focused on the composition of the powders used for the manufacture of these alloys and on the particle size of these powders to obtain an alloy by extrusion.

  ductile and resistant iron-aluminum intermetallic.

  Thus, it has been shown that the ordered crystalline phase of this alloy supports the addition of various additional elements which reinforce the mechanical properties of the alloy. These additional elements can be for example nickel, cobalt, titanium, magnesium, zirconium, boron, chromium, cerium or a mixture of these elements, etc.

  varying proportions and combinations.

  It has also been shown that it is possible to reinforce such an alloy by introducing, in addition to the additional elements previously mentioned, dispersoids, that is to say particles said to be of second phase, very fine and well dispersed. oxides

  very stable such as for example A1203, Fe203, or Y203.

  The manufacture of these iron-aluminum intermetallic alloys by extrusion, however, has a number of drawbacks which are in particular a high cost, and a large reduction in cross section of the parts manufactured during extrusion, which considerably limits the diametrical dimensions of these rooms. Another disadvantage is that the intermetallic iron-aluminum alloys are difficult to machine, and when the shape of the parts to be manufactured moves away for example from a shape of cylinder, this one

  may require significant machining.

  SUMMARY OF THE INVENTION The object of the invention is precisely to provide a method of manufacturing an iron-aluminum intermetallic alloy having a cost of manufacturing the alloy significantly lower than that entrained by an extrusion process. In addition, the method of the invention makes it possible to manufacture an alloy having a high mechanical strength and sufficient ductility

for many applications.

  The process for manufacturing an iron-aluminum intermetallic alloy according to the invention comprises the following steps: - preparation of a powder of determined particle size from a mixture comprising iron and aluminum, - degassing of said powder, and - a hot compression of the degassed powder so as to obtain an iron-aluminum intermetallic alloy. According to the invention, the powder can also comprise an element chosen from nickel, cobalt, titanium, magnesium, zirconium, boron, chromium,

  cerium, or a mixture of these.

  According to the invention, the powder may for example comprise from 20 to 50% by weight of aluminum, and may also comprise from 0.05 to 0.5% by weight of zirconium, from 0.001 to 0.02% by weight boron, the rest

  being inevitable iron and impurities.

  According to the invention, the powder may comprise approximately 21 to 28% by weight of aluminum, and may also comprise approximately 0.08 to approximately 0.14% by weight of zirconium, approximately 0.012 to approximately 0.018% by weight of boron , the rest being iron and impurities

inevitable.

  According to the invention, the particle size of the powder can be in a range from 10 to 500 μm, preferably in a range ranging from 10 to μm. According to the invention, the method can also comprise a step of dispersing in the powder an oxide chosen from Y203, A1203, Fe203, or a mixture of these

  oxides, in the form of a nanometric powder.

  According to the invention, the method can also comprise a step of dispersing in the powder from approximately 0.5 to approximately 1.5% by weight of Y 2 O 3 in the form of a nanometric powder, preferably approximately 1% by weight.

from Y203.

  According to the invention, the powder can be prepared

  by dry grinding said mixture under a neutral gas.

  This dry grinding can be carried out for example in a

ball mill.

  According to the invention, the powder is then degassed

  for example by means of a vacuum pump.

  According to the invention, the hot compression of the degassed powder can be carried out at a temperature ranging from approximately 900 to approximately 1300 ° C., preferably at

  a temperature ranging from approximately 1000 to approximately 1200 C.

  According to the invention, the hot compression of the degassed powder can be carried out at a pressure ranging from about 50 to about 400 MPa, preferably at

a pressure of about 100 MPa.

  According to the invention, the compression of the powder can be carried out at variable pressure or at isostatic pressure. According to the invention, the compression can be carried out for a period ranging from approximately 0.5 to approximately 4 hours, preferably for a period

about 2 hours.

  The invention also relates to a feraluminium intermetallic alloy obtainable by the process of the invention, said alloy comprising iron, aluminum, zirconium, boron, and yttrium oxide, and having an elongation of approximately 1.5% and an elastic limit of approximately

960 MPa.

  The invention also relates to a feraluminium intermetallic alloy obtainable by the process of the invention, said alloy comprising iron, aluminum, zirconium, boron, and yttrium oxide and having a elongation from about 0.2 to about 0.8% and an elastic limit

about 1240 MPa.

  The invention therefore consists in particular in densifying a powder of determined particle size from a mixture comprising iron and aluminum, by means

hot pressing.

  Surprisingly, the dense alloy obtained by this process has quite surprising properties for many applications. This alloy has in particular a mechanical resistance which can reach or exceed 1000 MPa and a

ductility which can exceed 1%.

  In addition, the process of the invention does not have the aforementioned drawbacks of processes for the extrusion of

prior art.

  The present invention also makes it possible to manufacture elements of large-size iron-aluminum intermetallic alloy. Indeed, the compression of the degassed powder can be carried out in a container or mold which can go, for example, up to 1 meter in diameter and 2 meters in height, without these limits being absolute, in order to obtain an element of iron-intermetallic alloy. aluminum having substantially the

same dimensions as the container.

  In addition, the container or mold may have a complex shape for producing elements of intermetallic iron-aluminum alloy of complex formS 'without

  necessarily have to resort to machining.

  The method of the invention also makes it possible to

  manufacture elements of iron intermetallic alloy

  aluminum near the dimensions or at the dimensions, that is to say that the parts thus produced require little or no

subsequent machining.

B 12944.3 EE

  Consequently, there are numerous examples of application of the invention to manufacturing

  elements or parts made of iron intermetallic alloy

  aluminum. Among them, we can cite for example without being limiting: - the manufacture of automotive, aeronautical and space structural parts: bolts, landing gear, parts

braking systems, etc.

  - the manufacture of critical moving parts of heat engines and turbomachines, such as valves, shafts and shafts, crankshafts and pistons, turbine blades; - the manufacture of parts having to work in vibrational regimes close to resonance limits, or even beyond such as certain turbine power shafts or certain nozzles or pipes for injecting fluids; - the manufacture of furnace resistors or heat exchanger tubes or parts subjected to difficult conditions of

dry corrosion.

  The description of the invention is illustrated below by an embodiment given by way of nonlimiting example.

Example 1

  In a first step of the process of the invention, a powder of determined particle size is prepared from a mixture comprising 24% by weight of aluminum, 0.11% of zirconium, 0.0026% by weight of boron, the rest being iron and unavoidable impurities. This mixture is melted to be

cast in the form of ingots.

  These ingots are then atomized under argon so

  to obtain a fine and spherical pre-alloyed powder.

  This pre-alloyed powder is then dry ground under argon in a ball mill, adding to the

  start of grinding 1% by weight of Y203.

  A powder with a particle size between 50 and

300 is obtained.

  All the steps of this example are carried out under conditions making it possible to limit contamination by the atmosphere or by exogenous inclusions. The grinding operation introduces an amount of about 0.03% by weight of oxygen and about 0.01% by weight of carbon into the alloy. The carbon comes from the wear of the balls in the ball mill during grinding. The ground powder is put in a container and densified by hot isostatic compression at a temperature of 1100 C under a pressure of 100 MPa

during 2 hours.

  An intermetallic alloy part near the

odds or odds is obtained.

  The mechanical properties of the alloy obtained were determined under the least

  favorable to the ductility of such an alloy, that is to say

  say on an unpolished machined workpiece

  dehydrated and at a low traction speed.

  The advantages in terms of mechanical strength and ductility are very clear. In particular, this alloy has an elongation of 1.5% and a limit

  elastic of 960 MPa at room temperature.

Example 2

  From a powder identical to that prepared in Example 1, and under the same conditions, the ground powder is put in a container and densified by hot isostatic compression at a temperature of 1000 C and under an isostatic pressure of 100 MPa

during 2 hours.

  A piece of iron-aluminum intermetallic alloy

  near the odds or odds is obtained.

  This alloy has an elongation of 0.2 to 0.8%

  and an elastic limit of 1240 MPa.

Claims (19)

RESELL I CATIONS   1. A method of manufacturing an iron-aluminum intermetallic alloy comprising the following steps: - preparation of a powder of determined particle size from a mixture comprising iron and aluminum, - degassing of said powder, and a hot compression of the degassed powder so as to obtain the iron-aluminum intermetallic alloy. 2. The method of claim 1, wherein the powder further comprises an element selected from nickel, cobalt, titanium, magnesium, zirconium, boron, chromium, cerium or a mixture of these elements.   3. The method of claim 1, wherein the powder comprises from 20 to 50% by weight of aluminum, and further comprises from 0.05 to 0.5% by weight of zirconium, from 0.001 to 0.02% by weight weight of boron, the rest being iron and unavoidable impurities.   4. The method of claim 1, wherein the powder comprises about 21 to 28% by weight of aluminum and further comprises about 0.08 to about 0.14% by weight of zirconium, about 0.012 to about 0.018% by weight boron, the rest being iron and unavoidable impurities.   5. Method according to any one of   claims 1 to 4, wherein the particle size of   the powder is in a range from 10 to 500 Pm.   6. Method according to any one of   claims 1 to 5, further comprising a step of   dispersion in the powder of an oxide chosen from Y203, A1203, Fe203, or of a mixture of these oxides, in the form of a nanometric powder.   7. Method according to any one of   claims 1 to 5, further comprising a step of   powder dispersion from about 0.5 to about 1.5%   by weight of Y203 in the form of a nanometric powder.   8. Method according to any one of   claims 1 to 7, wherein the powder is   prepared by dry grinding said mixture under a gas neutral.   9. The method of claim 8, wherein   dry grinding is carried out in a ball mill.   10. Method according to any one of   previous claims, in which the   hot compression at a temperature of about 900 to around 1300 C.   11. Method according to any one of   previous claims, in which the   hot compression at a temperature of about 1000 to about 1200 C.   12. Method according to any one of   previous claims, in which the   compression at a pressure ranging from about 50 to about 400 MPa. 13. Method according to any one of   claims 1 to 11, in which the   compression at a pressure of about 100 MPa.   14. Method according to any one of   claims 1 to 13, in which the   compression under isostatic pressure.   15. Method according to any one of   claims 1 to 14, in which the   compression for a period ranging from about 0.5 to about 4 hours.   16. Method according to any one of   claims 1 to 14, in which the   compression for a period of 2 hours.   17. Iron-aluminum intermetallic alloy comprising iron, aluminum, zirconium, boron and yttrium oxide, said alloy having an elongation of approximately 1.5% and an elastic limit of approximately 960 MPa, said alloy being obtained by the   method according to claim 6 or 7.   18. Iron-aluminum intermetallic alloy comprising iron, aluminum, zirconium, boron, and yttrium oxide, said alloy having B 12944.3 EE   an elongation of about 0.2 to about 0.8% and an elastic limit of about 1240 MPa, said alloy being obtained by the process according to claim 6 or 7. 19. Element made of feraluminium intermetallic alloy obtained by a process according to any one of claims 1 to 16. B 12944.3 EE