Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0433—Nickel- or cobalt-based alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/09—Mixtures of metallic powders

Definitions

• the subject of the present invention is a method for manufacturing alloy parts by powder metallurgy, and more particularly a method for manufacturing superalloy parts based on nickel or on iron, having the form of discs or blades of turbines for rotating machines.
• the manufacturing methods by casting and by forging have certain drawbacks, in particular for the production of alloy parts very loaded with additives because the operations of casting and transformation by forging become more and more complex due to the difficulties due mainly the appearance of segregations which increase the brittleness of the alloys.
• the powder metallurgy manufacturing methods make it possible to avoid the aforementioned drawback because by dividing the alloy into micro-ingots which are then combined by sintering, it is possible to produce highly alloyed preforms having a minimum of segregation.
• the methods using liquid phase sintering require the use of a sintering aid such as phosphorous nickel to lower the temperature and the pressure for shaping the powder, and the addition of a foreign element, even at very low contents, risk of profoundly altering the mechanical properties of the alloy
• the present invention specifically relates to a method of manufacturing alloy parts by powder metallurgy which overcomes the aforementioned drawbacks because it allows sintering in the liquid phase without requiring the addition of a foreign element and without implementing high pressures.
• the method according to the invention is characterized in that it consists in preparing from the constituents of said alloy an powder or a mixture of two powders each comprising all the constituents of said alloy, said powder or the mixture of said powders comprising a solid phase fuse at a temperature T 1 lower than the theoretical burning temperature T of said alloy, then sintering under load said powder or the mixture of said powders at a temperature at least equal to T 1 , said temperature being such that only one of the phases of the powder is liquid.
• said alloy is preferably chosen from the group comprising nickel-based alloys and iron-based alloys.
• the method as characterized above advantageously takes advantage of the fact that, starting from a powder or a mixture of powders having the property of forming a liquid phase at a temperature below what is agreed to call the theoretical temperature of "burning" of the alloy, that is to say the temperature which corresponds to the melting of a phase of an alloy in which several phases are in equilibrium, phase sintering can be carried out liquid of the powder at a lower temperature, in addition in certain cases avoiding that the whole of the powder forms a liquid phase.
• said powder is prepared by rapidly cooling liquid droplets of said alloy to obtain by solidification of said droplets powder particles comprising a solid phase whose composition does not correspond to equilibrium, said solid phase being fusible at a temperature T 1 lower than the theoretical burning temperature of the alloy.
• the liquid droplets can for example be formed from a cylindrical ingot of said alloy by bringing to a melting temperature the end surface of said ingot rotated about its axis so that the molten alloy is ejected from the surface end of the ingot, under the action of centrifugal force, in the form of liquid droplets.
• the liquid present at the solidification interface rapidly reaches the eutectic composition while the solidified part of the alloy does not have the composition corresponding to the solubility limit.
• This mode of formation of a more fusible phase in the powder particles can be applied to alloys other than nickel alloys and in particular to all alloys which can be reduced to binary alloys, for example steels in which the interdendritic spaces consist of ferrite.
• said powder is prepared by homogeneously mixing a powder of an alloy A 1 and a powder of a alloy A 2 , said alloys A 1 and A 2 comprising all the constituents of said alloy but having a different content in at least two of said constituents so that the alloy A 1 forms a liquid phase at a temperature T 1 lower than the temperature T 2 at which the alloy A 2 forms a liquid phase, and said mixture of powders is sintered under load at a temperature between T 1 and T 2 .
• the concentration of the main constituents of the alloys A 1 and A 2 is identical and only the contents of certain addition elements present at minor concentrations vary, in particular, the contents of certain addition elements such as carbon , boron and zirconium.
• This second embodiment of the process of the invention proves to be particularly advantageous since the use of two types of powder makes it possible to form a liquid phase only in a single type of powder without requiring the addition of an element. foreign and by modifying only very little the content of one of the powders in one of the constituents of the alloy.
• the mixture of powders is, for example, constituted by equal volumes of powder of alloy A 1 and of powder of alloy A 2 whose particle sizes are substantially identical for example of the order of 50 to 300p.
• variable volumes of powder of alloy A 1 and of powder of alloy A 2 provided, however, that in the mixture homogeneous powders, each less fusible particle of alloy A- is in contact with a more fusible particle of alloy A 1 .
• variable particle sizes can be used for each of the powders of alloy A and alloy A 2 , for example in order to obtain a more compact stacking of powder particles.
• the duration and the pressure of sintering are chosen according to the nature of the alloy.
• the sintering pressure is advantageously of the order of 100 bars and the duration of sixty minutes.
• the powder or the mixture of powders For the operation of sintering the powder or the mixture of powders, it is preferable to bring the powder or the mixture of powders to the sintering temperature as quickly as possible, for example by heating so as to increase the temperature of the powder or mixture of powders from 1,000 to 10,000 ° C per hour. By operating in this way, large diffusion and homogenization during heating of the powder are avoided, which would be detrimental to obtaining good sintering kinetics.
• the powder or powder mixture when the powder or powder mixture is at the sintering temperature, it is important to keep the powder or the powder mixture at this sintering temperature only for a relatively short time to avoid diffusion and magnification. grains and thus obtain a dense structure, well sintered and generally homogeneous.
• the powder or mixture of powders is maintained at the sintering temperature for a period of at most one hour.
• An example relates to the manufacture of a piece of nickel alloy, according to the second embodiment of the method of the invention, that is to say by sintering of a mixture of powders of two alloys having a similar composition, the other relating to a sintering of an iron-based alloy according to the first embodiment.
• the first powder of alloy A 1 contains 12% chromium, 18% cobalt, 3% molybdenum, 4% titanium, 5% aluminum, 0.011% boron, 0.05% zirconium and 0.2 % carbon, the rest being nickel
• the second powder of alloy A 2 contains 12% chromium, 18% cobalt, 3% molybdenum, 4% titanium, 5% aluminum, 0.011% boron, 0.05% zirconium and 0.003% carbon, the rest being nickel.
• the powders of alloy A 1 and of alloy A 2 each have a particle size between 50 and 300 ⁇ .
• the mold is then placed inside a heating device, by inserting between the walls of the mold and the device a refractory metal powder having a low sinterability, at the temperature chosen for sintering the powder mixture.
• the mold containing the powder mixture is then brought to a temperature of approximately 1,290 ° C., heating the mold filled with powders very quickly, by example by increasing its temperature by 1000 ° C per hour.
• the mold is then kept at the chosen temperature of 1290 ° C., under a uniaxial pressure of 50 to 100 bars, for a period of approximately sixty minutes to ensure the sintering of the powder mixture.
• the compression of the powder during sintering is carried out by means of a piston of refractory material which takes place at the top of the mold and can slide in the cylindrical counterweight in order to load inside the mold the additional quantity of powder initially placed in this feeder, thus helping to eliminate the porosity in the sintered part.
• the parts After demolding, the parts have a perfect surface condition with grains with an average size of 50 ⁇ .
• This powder obtained by centrifugation of a bar, reveals by metallography a ferritic structure 6 with excess eutectic liquid coming from the non-equilibrium during solidification.
• This powder whose grain diameter is between 100 and 600 ⁇ , is sintered at 1,200-1,220 ° C for three minutes under 300 bars.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)

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Citations (7)

• 1978
  • 1978-05-16 FR FR7814432A patent/FR2425906A1/fr active Granted
• 1979
  • 1979-05-14 DE DE7979400302T patent/DE2967309D1/de not_active Expired
  • 1979-05-14 EP EP79400302A patent/EP0005668B1/de not_active Expired
  • 1979-05-15 JP JP5872079A patent/JPS54150309A/ja active Granted

Patent Citations (7)

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