DE2007638A1 - Process for sintering metal powders - Google Patents

Description

Dr. Ing. E. BERKENFELD · Dipl.-Ing. H. BERKENFELD, patent attorneys, Cologne

Homogeneous Metals, inc, ^Anl : ^ae ^ February 17, 197omy // * ^kten "^id; ^en _H 9 * 1/2

to enter the '*'"*» Name of the note ~

Process for sintering metal powders

The invention relates to methods for sintering metal powders and in particular a method of sintering metal powders without the use of lubricants, slip agents or the like.

The manufacture of parts from metal powders presents some special features Problems. One of the most troublesome of these problems is obtaining a perfectly dense product. Currently is no method of molding and sintering a dry, loose metal powder known in an economic process. Essentially all parts made from metal powders become one so-called raw pellet pressed, usually a lubricant mixed with the powder is used to achieve to support a greater strength of the pellet. Some parts are made by a process known as slide casting. In this process, the metal powder is mixed with a liquid medium and as a slurry in a poured porous shape. The liquid is then sucked off, leaving a raw powder compact, which is then sintered will. The sliding casting process is mainly used in conjunction used with powders that have poor compactability, such as spherical powders.

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When processing high alloy powders, often referred to as superalloy powders, which are strong containing reactive elements such as titanium, columbium, aluminum and so on, particular problems arise which make these known methods unsatisfactory. The surfaces of these reactive elements become almost instantaneous covered with a film of oxide which can be as thick as 1 or 2 molecules, but which is effective for each particle encapsulated. Because of the physical structure of the oxide film, there appears to be no diffusion of oxygen into the metal and the oxide remains as a stable particle on the surface of each particle, moreover the reactive one closes Type of metal powder consisting of the use of lubricants, the remains of which give a PiIm on the particle. These films that are formed do not necessarily prevent that the pores diffuse to the circumference of the metal mass during sintering. However, they act as a barrier to diffusion from metal to metal and therefore result in a solid metal mass, which has a relatively weak inner network, which is determined by the film surrounding the particles.

To eliminate these problems, it seems that the powder processed in the dry state and sintered in the absence of gases which react with the reactive elements, such as the oasis of oxygen and nitrogen, as well as water vapor. However, it has been found that the sintering carried out in the ordinary metal containers is undesirable porous material resulted.

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It has also been found that all of these problems are avoided can be processed when the metal powder in a dry state in a vacuum or in an inert atmosphere and in a Container are sintered, which has a ceramic lining or the like, with which the metal powder during of the sintering process does not connect. It has been found that by this method it is possible to use a starting material to use dry metal powder that is free of lubricant or liquid, and sintered compacts even made from superalloy powders to produce which is an essentially looffige | Have density (based on theoretical density calculations and metallographic testing). According to this procedure The pellets produced were free from continuous Network of the non-metallic or intermetallic fila that has so far characterized such pellets.

The invention thus relates to a method for sintering metal powders in the dry state to avoid the formation of the film network resulting from the presence of lubricants and gaseous reaction products results. The method is characterized according to the invention in that the dry Metal powder is placed in contact with a ceramic surface defining a container for the same, that the dry powder is in contact with the ceramic surface at an elevated temperature, preferably in a vacuum is changed in which the partial pressures of oxygen and nitrogen do not exceed 0.05 mm, and that the product is later cooled down.

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The invention will be further elucidated by reference to the following examples be easier to understand.

I. Example I « Astroloy is an alloy with the following composition: Carbon 0.03 - o _t lo Aluminum 4, o - 5, o

Mon M, 5 - 6.0

Ti 2.8-3.8

Cr 14, ο -17, o

Co 15 »o -19 * 00

Pe o, 5o maximum Sl o, 2o maximum Nn o, 15 maximum

Nl rest

B o, oo ^ -o, o33

Zr 0.06 maximum

Cu o, Io maximum S o, ol5 maximum

Astrology powder of high purity was after under high vacuum one of the usual powder metallurgy processes and transferred to a flask that is continuously flushed with argon became. The netall powder was then in. From the flask through a closed system using a tygon tube Transferring a (ceramic) crucible made of pure aluminum oxide, both the crucible and the flask being flushed with argon became. The crucible was then sealed under argon and placed in

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introduced a vacuum sintering furnace which had been purged with argon 1st. The oven was then sealed and opened for four hours under a reduced pressure of less than ο, οοΐ mm Heated 1,288 ° + 12 ° C. At the end of the four hours, the crucible and its contents were cooled and the part removed. The resulting portion was devoid of internal film network and was essentially loojfige in density.

Example II

The procedure of Example I was followed using a metal container repeated, with the periphery of the powder core fused to the container and the pores from the periphery into the interior of the Kerns diffused, which resulted in a large cavity inside. In some cases, the pores differed in that they were in a plane near the center.

Example «. III

The procedure described in Example I was repeated several times and delivered consistently satisfactory results.

The method according to the invention enables relatively coarse powder (with a particle size of less than 0.8 mm) to use in order to achieve the desired density, since the surface energy of the powder is high without the contaminating film.

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The invention is not limited to the exemplary embodiments described above limited the various amendments can experience without departing from the scope of the invention.

PATENT CLAIMS

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Claims (1)

Dr. Ing. E. BERKENFELD · Dtpl.-Ing. H. BERKEN fELD, patent attorneys, Cologne Anlogt ' ^utn B ^ab «of ^February 17, 197oray // ** - · ^Λ ^ Homogeneous Metale, Inc. H 94/2 PATENT CLAIMS 1. Process sum sintering of metal powders, thereby characterized in that the powder in the dry state is placed in contact with a ceramic surface which limits a container for the same, such as that the dry powder in contact with the ceramic Surface sintered at elevated temperature and later cooled will. 2. The method according to claim 1, characterized in that the powder in a ceramic container is arranged. 3. The method according to claim 1, characterized in that the powder in one with kemlschem Material lined container is placed. H. The method according to claim 1, characterized in that the powder is placed in a container coated with ceramic material. H 9I / 2 -1- 109808/1180 5. The method according to claim 1, characterized gekennsei ch net that the sintering process in one not reactive atmosphere. 6. The method according to claim 5, characterized in that the non-reactive atmosphere a faculty exists. 7. The method according to claim, characterized in, that the non-reactive atmosphere consists of an inert oasis. 8. The method according to claim 5 »characterized in that ά In the non-reactive atmosphere, but short of the partial pressures of oxygen and STlckstoff o, oo5 not mm. 109808/1180