US3167428A

US3167428A - Titanium powder metallurgy

Info

Publication number: US3167428A
Application number: US158986A
Authority: US
Inventors: Alfred R Globus
Original assignee: Consolidated Astronautics Inc
Current assignee: Consolidated Astronautics Inc
Priority date: 1961-12-13
Filing date: 1961-12-13
Publication date: 1965-01-26
Anticipated expiration: 1982-01-26

Description

Jan. 26, 1965 A. R. GLOBUS TITANIUM POWDER METALLURGY Filed Dec. 15. 196 1 INVENTOR l l a W United States Patent 3,167,428 TETANTUM PUWDER METALLURGY Alfred R. Giobus, Forest Hiiis, N.Y., assignor to Consolidated Astronautics inc, Long lsiaud City, N.Y., a corporation of Delaware Filed Dec. 113, 1961, Ser. No. 158,986 7 Claims. (Ci. 75-2tl-i) This invention relates to new and useful improvements in titanium powder metallurgy.

The invention more particularly relates to an improved process for producing sintered titanium articles, an improved titanium powder material for use in the process and to the articles produced with the material and by the process.

Articles are conventionally produced using powder metallurgy technology by compacting a metal powder or metal powder mixture into the form of the article and thereafter sintering the compact.

The compacting is generally effected by pouring metal powder into a die corresponding to the shape of the article and subjecting it to the action of one or more punches or plungers operated by a hydraulic or mechanical press. The compacting which may also be effected by extrusion or centrifugal force results in the formation of a green compact which must have sufiicient coherence to permit subsequent handiing in the process such as transferring to the sintering furnace and sintering.

After the compacting the green compact is removed from the press and may, if desired, prior to the sintering be pre-sintered in order to increase its mechanical strength and adherence and/or be touched up to correct imperfections.

The sintering of the compact is effected in a sintering furnace at a temperature below the melting point of the powder as for example at a temperature of /3 the melting point (degrees K.) to just below the melting point of the metal powder. The sintering results in the conversion Of the compact without complete melting into a strong, coherent mass in which recrystallization and grain growth has taken place across the former boundaries between the particles. In the case of metal mixtures and alloys, the sintering may also result in a homogenization.

in producing titanium articles by product metallurgy, difiiculties were encountered in that the titanium powder was not readily workable in the compacting, and it was difiicult to obtain a uniform satisfactory green compact.

Furthermore, the hard titanium powder would often tend to score and scratch the dies used in the compacting and a lubricant, as for example a calcium stearate, was required in order to render the titanium powder workable into the compact and to minimize damage to the die. The use of the lubricant, however, required special control of the subsequent sintering operation and would often detrimentally afiect characteristics of the end sintered product.

One object of this invention is a titanium powder for the production of sintered articles which is much more workable into the form of green compacts than the prior known titanium powder used in powder metallurgy, which results in the formation of a green compact which can be much more readily and easily handled and further finished and which, upon sintering, produces a much harder and more resistant article.

A further object of this invention is a process for producing sintered articles of titanium without the prior art difiiculties. A still further object of this invention is the end product as produced by the above-mentioned powder and process.

These and still further objects will become apparent from the following description read in conjunction with the drawing in which:

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FIG. 1, shown on an enlarged scale, is a grain of the novel powder in accordance with the invention, and

FIG. 2 diagrammatically shows the compacting of the powder.

In accordance with the invention, a commercial titanium powder utilizable in powder metallurgy, as for example titanium powder having a particle size between about and 200 and preferably between about 30 and 100 mesh US. Standard Screen size, and preferably having a Brinell hardness of 175 or less is intimately blended together with very fine graphite having a particle size below about 325 mesh and preferably below 10 microns as for example as formed by micronizing, until the graphite powder ceases to exist as a separate entity and a product is formed which consists of the titanium powder having the graphite intimately dispersed on its surface and penetrating its pores.

An amount of graphite should be used which is below the stoichiometric quantity required to form the titanium carbide and should preferably be between about 5-18% and most preferably about 12% by weight based on the titanium.

The blending is preferably effected by mixing the titaniurn powder and the graphite together in a ball mill utilizing balls of a softer material than the titanium as for example soft iron. The blending, however, can be also effected in any known or conventional blending device which will distribute the graphite on the surface of the titanium powder particles and force the same into at least may be effected by filling the powder into the mold cavity 2 of the die 3 provided with the lower punch 4 and upper punch 5. The punches may be actuated in a hydraulic or mechanical press to come together at a pressure between about 2050 tons per square inch forming the green compact 6.

The titanium powder with the intimately surface-bound graphite is much more readily workable in the compacting than conventional titanium powder and higher quality green compacts with a much lesser percentage of rejects may be produced with much less wear on the compacting equipment.

The titanium powder product in accordance with the invention shows self-lubricating qualities so that the compounding may be etfected without the use of additional or special lubricants, and the tendency to scratch and injure the compacting equipment is greatly reduced.

Though the lubricants are not required, it is, of course, possible to use the conventional lubricants.

The green compact is then removed from the die and can be much more readily handled without fear of breakage and injury and may be much more readily worked up if desired or necessary prior to the sintering.

The green compact is then further treated in the conventional manner, including a sintering operation, at a temperature between 1800-2200 degrees R, which is preferably effected in a vacuum or under an inert gas such as argon.

Prior to the sintering, the green compact may be subject to any conventional or known finishing or treating operation as for example a pre-sintering. The end sintered product is much harder and much more resistant than the conventional sintered titanium articles and may, for example, have a Rockwell hardness (A) exceeding 85. This end product may be characterized as a sintered body of titanium having discrete areas of titanium carbide distributed therethroughout and having a carbon content of of between about and 18% by weight.

The invention may be used for the production of any known or sintered titanium articles as for example nozzles for rockets, or jets, sliding or wear-resistant members, dies, and the like.

The titanium powder produced in accordance with the invention with the intimately bound graphite may also be used in place of conventional titanium powder for other purposes and thus, for example, may be admixed with other powders when making mixed sintered articles containing titanium.

The following examples are given by way of illustration and not limitation:

Example 1 Commercial titanium powder having a particle size between about 30-100 mesh U.S. Standard Screen size and a Brinell hardness of about 175 is blended together with about 12% by weight of very fine graphite powder having a particle size below microns in a ball mill. The blending is continued until the graphite ceases to exist as a separate entity, and there results a product consisting of the titanium particles, having the graphite intimately dispersed on its surface and penetrating its pores. A die having a cylindrically shaped 1" diameter internal cavity, /2" in thickness is filled with this powder and the powder is pressed in the die from opposite sides with cylindrical punches corresponding to the die shape in a hydraulic press at a pressure of about 50 tons per square inch. The green compact consisting of the cylindrical slug is then removed from the die and sintered in a conventional vacuum sintering furnace at a temperature of about 2,000 degrees F. for 20 minutes.

The sintered slug thus produced is extremely hard and resistant and is characterized by titanium carbide domains distributed throughout its mass and corresponding to a carbon content of about 10%. The slug makes an excellent wear-resistant insert.

While the invention has been described with reference to certain specific embodiments, various changes and modifications which fall within the spirit of the invention and scope of the appended claims will become apparent to the skilled artisan. The invention is, therefore, only intended to be limited by the appended claims or their equivalents wherein I have endeavored to claim all inherent novelty.

I claim:

1. In the method of producing articles by powder metallurgy, the improvement which comprises compacting and sintering titanium powder of a particle size between about 20-200 mesh having about 5-12% by weight of graphite intimately dispersed upon its surface and penetrating its pores.

2. Improvement according to claim 1 in which said titanium powder has a particle size between about 30-100 mesh.

3. In the method of producing articles by powder metallurgy, the improvement which comprises blending titanium powder having a particle size between about 20-200 mesh with about 5-12% by weight of graphite having a particle size below about 325 mesh to intimately disperse the graphite on the surface of the titanium, and thereafter compacting and sintering the said powder.

4. Improvement according to claim 3 in which said titanium powder is a particle size between about 30-100 mesh.

5. Improvement according to claim 4 in which said graphite has a particle size below about 10 microns.

6. Method for producing titanium powder suitable for compacting and sintering which comprises blending titanium powder having a particle size between about 20-200 mesh with about 512% by weight of graphite having a particle size below about 325 mesh to intimately disperse the graphite on the surface of the titanium and cause the graphite to penetrate into the pores of the titanium.

7. Method according to claim 6 in which said titanium powder has a particle size between about 30-100 mesh and said graphite has a particle size of less than 10 microns.

References Cited by the Examiner UNITED STATES PATENTS 2,895,822 7/59 Peras 29-182.8 2,944,893 7/60 Koenig -204 2,998,641 9/61 Atkinson 29182.8 3,000,087 9/61 Dyer 29.182.8 3,054,166 9/62 Spendelow et a1 29-1828 OTHER REFERENCES CARL D. QUARFORTH, Primary Examiner.

OSCAR R. VERTIZ, Examiner..

Claims

1. IN THE METHOD OF PRODUCING ARTICLES BY POWDER METALLURGY, THE IMPROVEMENT WHICH COMPRISES COMPACTING AND SINTERING TITANIUM POWDER OF A PARTICLE SIZE BETWEEN ABOUT 20-200 MESH HAVING ABOUT 5-12% BY WEIGHTD OF GRAPHITE INTIMATELY DISPERSED UPON ITS SURFACE AND PENETRATING ITS PORES.