US2794241A - Fabrication of intricate shapes from beryllium - Google Patents

Description

FABRICATION F INTRICATE SHAPES FROM BERYLLIUM Harry W. Dodds, Bay Village, and Charles B. Sawyer,

Cleveland Heights, Ohio, assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application December 31, 1952, Serial No. 329,102

1 Claim. (Cl. 29-4205) This invention relates to a powder metallurgical process and more specifically to such a process for forming dense, intricate shapes of beryllium and other metals such as Ti, Th, U, Mo and Zr.

In view of the diificulty with which beryllium cast material may be machined, and in further view of the waste of beryllium encountered in machining intricate shapes therefrom, powder metallurgical methods have been resorted to in order to minimize the amount of machining necessary and the attendant waste of beryllium metal. However, if beryllium articles are made in a die from beryllium powder by well known methods of powder metallurgy, the density is less than that of cast beryllium and sharp projections and indentations are usually not well formed and projections are liable to be porous as beryllium powder does not fiow well in moulding. Furthermore, dimensions cannot be maintained very accu rately due to the irregular and usually unpredictable shrinkage in sintering.

Accordingly, the primary object of the instant invention is to provide a powder metallurgical process for fabricating intricate shapes from powdered beryllium which will be substantially of uniform and maximum density throughout, and also possessing excellent machinability.

Still another object of the present invention is to provide a process for forming compacts of beryllium of substantially maximum density without necessitating the use of high temperatures that are conducive to the formation of excessively coarse grain structure.

Yet another object of this invention is to provide a process for producing sintered blanks of beryllium which are sufficiently ductile and of substantially maximum density so that such blanks may be easily coined to more intricate shapes uniformly of maximum density throughout.

Still other features and objects of the present invention will become apparent upon reference to the hereinafter detailed description of the invention.

Broadly, the present invention comprises three principal steps, namely, first, forming a compact of the powderedberyllium by heating the same to a temperature in the neighborhood of from about 350 C. to about 475 C. and then subjecting the same to a compacting pressure of about 100 tons per square inch for a time (usually about 15 seconds) sufficient to give the compact a density of about 1.85 per cubic centimeter, which is substantially the theoretical density of commercial beryllium. Second, the beryllium compact formed by the first step is then sintered by subjecting the same to a temperature of about 1050 C. while under a pressure of 100 pounds per square inch under vacuum (35-100 microns) for about five hours. Third, the sintered blank produced by the second step is then coined to the desired final shape in a suitably contoured die, such coining step being conducted with the beryllium blank at a temperature in the neighborhood of about 350 C. to 47 5 C. and under a pressure of 100 tons per square inch. Any single modii is then in the form of a flat compact i atented June 4, 1957 fication of the above can also be used i. e. powder pressed at tons per square inch at 425 C. reaches full density with a tensile strength of 30,000 pounds per square inch without subsequent sintering.

Inasmuch as the manner in which the beryllium powder is prepared prior to treatment in accordance with the instant invention does not form a part of this invention, it will sufiice for the purposes of this description to state that beryllium powder prepared in accordance with our patent application S. N. 770,170, filed August 22, 1947, now abandoned, serves satisfactorily for the instant process.

Obviously, the principles of the present invention may be utilized in forming an almost endless variety of beryllium shapes; however, it is thought that a detailed description of the process for forming three entirely distinct beryllium shapes will afford a clear understanding of the actual practice of the invention. Accordingly, there is hereinafter described procedures for forming a grooved button, a toothed channel and a tubular body.

In fabricating a grooved button, beryllium powder is placed in a graphite lubricated die, and the whole is heated to a temperature of from 350 C. to 475 C., preferably in the temperature range of from about 390 C. to about 450 C., and after the beryllium has been heated to the desired temperature, the die is operated to apply a pressure of about 100 tons per square inch for about 15 seconds. It has been found that if the temperature of the metal is below 350 C. it flows only with great difliculty thereby requiring excessive pressures and frequently produces fissures in the beryllium. On the other hand, if the temperature is above 475 C., the beryllium becomes weaker without appreciable increase in ductility (less flow takes place) and the bursting strength of the tool steel die rapidly deteriorates.

The beryllium powder, after the foregoing procedure, or button which has a denstiy of from about 1.85 to 1.86 grams per cubic centimeter, which is approximately the density of commercial beryllium with 0.5-1.5% BeO. It is evident that no appreciable further shrinkage of the beryllium will occur during subsequent treatment.

The compact is removed from the die and placed in a steel tube which is closed at one end and a steel disc is placed upon the compact. A plurality of such compacts and steel discs are alternately placed in the steel tube so that a plurality of beryllium compacts may be simultaneously sintered. In order to avoid adherence of the steel discs and the beryllium compacts, or the contamination of the beryllium by the steel, it is preferable that the steel discs are either provided with an oxide coating on the surface by heating or painted with graphite before the placing thereof in the steel tube. The steel tube is then placed in an upright position with its closed end lowermost and a dead weight is placed on the uppermost steel disc sufficient to provide a pressure of about 100 pounds per square inch thereon, it being evident that such pressure acts throughout the entire height of the stacked alternate compacts and steel discs. The temperature of the steel tube and its contents is then raised to about 1050" C. for about five hours in a vacuum (35-100 microns), after which the tube and its contents are allowed to cool. The contents of the tube are forced out and the beryllium blanks or washers which have been formed are separated from the steel discs. It is desirable to grind the blanks lightly on both sides to remove any surface contamination they may have acquired from the steel discs and to insure uniform thickness.

The fabrication of a toothed channel is very similar to the fabrication of a button, the procedure in this instance comprising initially forming a flat rectangular compact by placing powdered beryllium in a hardened steel die lubricated with graphite, the die and its contents then being heated to a temperature of from about 425 C. to about 450 C. and after the same has been heated to such temperature the same of about 100 tons per square inch while maintaining the beryllium at the desired temperature for about 15sec onds. A plurality of rectangular compacts thus produced are alternately placed with rectangular surface treated (coated with graphite or provided with an oxide surface) steel spacers in a rectangular steel-tube having a closed end. As in the production of buttons, the alternately placed beryllium compacts are placed under a pressure of about 100 pounds per square inch which acts throughout the stack of compacts and steel spacers. The rectangular steel tube and its contents are then heated to a. temperature of about 1050" C. for'five hours in a vacuum (35-400 microns) after which the whole is allowed to cool and the contents of rectangular steel tube are then removed. The beryllium blanks or plates are separated from the spacers, and are lightly ground on the top and bottom to provide a good surface finish and uniform thickness. 7

After the beryllium plates have been cleaned, they are then placed individually in a die of l841 or comparable tool steel which has the upper and lower faces thereof machined to the desired contour, that is, to provide a finished product of channel shaped transverse cross section having indentations in the flanges thereof defining teeth. The whole die assembly is then heated to a temperature of about 450 C. to 475 C., and a pressure of 100 tons per square inch'applied to the beryllium in not less than 30 seconds to full load after the desired temperature has been reached for about lminute. When cooled, the beryllium product is removed from the die, after which any core marks left on the beryllium may be removed by lightly grinding the edges thereof.

As a final example of the versatility of the instant invention, tubular bodies may be fabricated by the following procedure; a hardened steel die is provided having an internal diameter a few thousandths of an inchgreater than that is of the desired tubular product; anda center core of unhardened steel drill rod somewhat longer than the desired beryllium product is inserted in the center of the die; an unhardened steel drill rodhaving-been found to be the best material for this core, as a mild steel becomes distorted by the powder, and if a hardened steel drill is used it causes cracks in the beryllium. Thedie and core are coated with graphite for lubrication and suitable amount of beryllium powder is placed in the .die and compacted by vibration. The die and its contents are then heated to a temperature of about 450'-.C. and a pressure of 100 tons per square inch is applied. After the beryllium powder has been compacted to substantially maximum density, the same together with the core therein are forced out of the die and placed in a steel cylinder. A pressure of 100 pounds per square inch is applied to the beryllium, and the beryllium together with is compacted under a pressure.

the core therein arev heated to a temperature of about 1050 C. in a vacuum (35+100 microns) for about five hours to sinter the beryllium. Thereafter, the beryllium together with the core are removed from the cylinder and placed in a steel die, heated to a temperature of about 450 C., and a pressure of tons per square inch is applied about 20 seconds.

Subsequently, the die and its contents are allowed to cool and the beryllium together with the core therein are removed therefrom. The-drill rod core is then removed from the beryllium body by applying tension to the core sufficient to cause rupture. Owing to the decrease in diameter of the drill rod core due to elongation under tension, the drill rod core partsslip readily out of the beryllium without damage to the latter. The hole left in the beryllium by the drill rod core is ground to a smooth finish and a uniform internal diameter. Inasmuch as the beryllium thus produced possesses excellent machinability, the product may be further treated by machining. For example, the hollow tubular member may be placed on a mandrel and flutes formed by milling the surface thereof.

While the salient features of the invention have been described in detail with respect to the fabrication of several beryllium shapes, it will, of course, be apparent that numerous modifications may be made within the spirit and scope of the invention, and it is, therefore, not desired to limit the invention to the exact details set forth except insofar as they may be defined in the appended claim.

We claim:

A powder metallurgical process for forming intricate shapes from powdered beryllium, comprising the steps of heating beryllium .powder to a temperature from about 350 C. to about 475 C., then compacting the powder while at such temperature under a pressure of about 100 tons per square inch for ra period suflicient to obtain a compact thereof having a density of about 1.85 grams per cubic centimeter, sintering the compact thus formed under a pressure of about 100 pounds per square inch at a temperature of about 1050 C. while under vacuum to produce a malleable blank, and thereafter coining the blank thus formed in a die under a pressure of about 100 tons per square inch and at a temperature of about 350 C. to about 475 C.

Seybolt et al.: A. E. C. Document No. 2679, A Process For Pressing-Beryllium Powder, declassified August 18, 1949.

Hausner et al.: American Society For Metals, Preprint N0. 38, October 1950, ,18 pages.