Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Post sintering operation
Patent
1986-10-16
1987-11-17
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Post sintering operation
419 26, 419 29, 419 31, 419 33, 419 38, 419 42, 419 53, 419 54, 419 68, 420590, B22F 324
Patent
active
047073322
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process for the manufacture of structural parts of complicated shapes from powder of intermetallic phases capable of being sintered. Intermetallic phases, especially TiAl, TiAl.sub.3, NiAl, NiAl.sub.3 have a low specific weight and high melting point. Materials on this basis are therefore interesting for the use in thermally and mechanically highly loaded structural parts, especially in aircraft propulsion units.
STATE OF THE ART
The problem of these materials reside in their brittleness. Processes are known for some time to increase the ductility of the intermetallic phases. This takes place by additionally alloying a further element, for example, B in NiAl or Nb in TiAl.sub.3.
The materials are made heretofore by melting metallurgical techniques or by reaction of the elements, i.e., for example, Al powder is mixed with Ti powder and Nb powder and is heated in a ram press. Heat results during the chemical reaction which sets in and the desired alloy is formed. It has not been possible heretofore with this process to manufacture in a simple manner structural parts of complex shape.
DESCRIPTION OF INVENTION
It is the task of the invention to indicate a process which permits to manufacture in a simple manner structural parts from intermetallic phases which are of complicated shape. This is solved by the features of claim 1.
BEST MODE TO CARRY OUT THE INVENTION
One starts with a pre-alloy of the intermetallic phase which, apart from unavoidable impurities, only contains the same, for example, Ni.sub.3 Al, NiAl, TiAl, TiAl.sub.3. This pre-alloy is obtained by melting.
By reason of the brittleness of the intermetallic phases, the pre-alloy can be ground in a manner known as such into a fine powder by any conventional means (impact mill, ball mill, air-jet mill) or can be atomized (as known as such, for example, from the DE-AS No. 22 22 830).
Granular size range:
0.5 .mu.m to 50 .mu.m, specific surface of 1 m.sup.2 /g to 25 m.sup.2 /g. Preferred: 3 to 5 m.sup.2 /g (BET-surface).
This powder is now mixed with a powder of one or several further elements. It is thereby desirable that the powders of the further elements are finer than that of the intermetallic phase.
As further elements are used those which effect an increase of the ductility of the intermetallic phase (for example, B for NiAl, Nb for TiAl.sub.3 with a proportion of 0.5 to 10% by weight.
The prepared powder mixture can now be brought to its final shape, apart from a shrinkage of 10 to 20% (by volume), by any known methods:
(a) Providing with a binding agent, cold-isostatically pressing (CIP) in green condition. Binding Agents: Waxes, thermoplastics and/or duroplastics (CIP) see, for example, DE 33 28 954. Machining by grinding and polishing to the final dimensions.
(b) Preparing an injection-moldable mass with the aid of lubricants and binding agents, injection molding technologies as used with plastic materials. Expellable binding agents as in (a) Lubricant such as stearine. Injection molding by machines customary for plastics (for example, with heatable feed worm and mouthpiece, respectively, nozzles at the tip thereof), also by injection molding presses, extrusion presses and extruding.
The lubricant and binding agents are thereby removed by a heat treatment in a manner known as such (heat treatment in a vacuum or inert gas up to 600.degree. C.). The sintering takes place in the same atmosphere as the aforementioned heat treatment and under conditions known as such, especially at temperatures above 900.degree. C. but smaller than 95% of the melting temperature. This sintering can also take place in several stages.
The elements which were added for the increase of the ductility act at the same time as sintering assist so that at a temperature of 70 to 95% of the absolute melting point of the intermetallic phase, a sintering can be carried out successfully. Densities of 95 to 99% of the theoretical density are attained thereby within 0.1 to 24 hours.
Subsequently, the parts can be hot isostatical
REFERENCES:
patent: 3953205 (1976-04-01), Cox et al.
patent: 4347076 (1982-08-01), Ray et al.
patent: 4624705 (1986-11-01), Jatkar et al.
Lechert Jr. Stephen J.
MTU Moroten-und Turbinen-Union Muenchen GmbH
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