US2491866A - Alloy of high density - Google Patents

Description

Patented Dec. 20, 1949 UNITED T1 S ALLOY OF HIGH DENSITY Jacob Kurtz, Teaneck, and Harold G. Williams, Ramsey, N. J., assignors to Callite'Tungsten Corporation, Union City, N. J., a. corporationof Delaware No Drawing. Application September 30, 1942, Serial No. 460,226

1 Claim.

'1 The present invention relates to alloys of refractory metals such as tungsten, molybdenum, rhenium, and tantalum. More particularly, it

, relates to alloys of such metals that are of high density and free from the usual porosity and intergranular voids that are characteristic of alloys time that the article is strong enough to be handled for further treatment. Further treating and sintering at temperaures equal to approximately 90% of the fusing current for the particular rod or ingot, further shrinks and strengthens the rod or ingot. The treated ingot, however, is still quite porous and has many intergranular voids, the density at this stage being approximately 17-18 grams per cubic centimeter in the cast of tungsten.

The rod or ingot must then be hot swaged until it is further compacted whereby the density increases rapidly from the values of 17-18 to a value approximately 19.3 for fully swaged rods, having a reduction in area of 80-90%. This density is generally referred to as the theoretical density.

According to the method of the present invention, purified refractory metal powder, such as tungsten or molybdenum, having a particle size of approximately from 1 to .25 microns, is combined with a small but effective amount of powdered metals that result in the alloying, bonding and densifying of the rod or ingot without the necessity of swaging. These alloying metals are formed from an appropriate selection of a first group of metals that are more properly described as alloying metals, and a second group that perform the function of refining the grain structure so as to permit control of grain growth, and a third group consisting of the noble metals. In the first group are manganese, iron, cobalt and nickel; the second group consists of beryllium, zirconium, chromium, vanadium, titanium and uranium; and the third group consists of platinum, palladium, gold, osmium, iridium, ruthenium and rhodium.

This alloying, bonding and densifying metal consists of a mixture of finely divided'metal'powders approximately one-half by weight of base metal and the balance noble metal. After these two constituents are thoroughly mixed they are added to the refractory metal powder in the proportion of approximately .25%-4% by weight, thoroughly ball-milled and mixed to assure uniform distribution of the densifying metal throughout the refractory metal. The mixture is then ready for pressing into formed pieces, discs, and the like, and subsequent heat treatment at a temperature of 1500-2000 C. in a hydrogen or neutral atmosphere or even in a high frequency vacuum furnace, using a molybdenum or tung sten tube or elongated crucible.

Where the term refractory metal is used in this specification it is intended to denote metals not easily fusible and Whichhave melting points as high as, or'higher than, 2500 C., and more particularly, the metals tungsten, molybdenum and tantalum.

The following'two examples are given, the first being without a metal of the second group, and the second containing such a metal:

Example I First, the alloying, bonding and densifying metal mixture is prepared. Approximately equal portions by weight of pure finely divided nickel powder, and pure finely divided platinum powder are thoroughly mixed and ball-milled. Platinized nickel powder (containing approximately 50% by weight of'platinum) made by shaking nickel powof tungsten powder.

This mixture is then ready for pressing in a suitable mold either in a tablet machine, or in a conventional hydraulic press, depending on the size and shaped the desired finished piece. After pressing, the formed pieces are then heat treated in an electric furnace at a temperature of 1500-1850 C. in a dry hydrogen atmosphere for about one hour, the time depending, of course, on the size, shape and number of pieces inserted into the hot zone, and the characteristics of the furnace.

After this heat treatment, the pieces have been fully sintered and shrunk in volume in a uniform .in the same manner as in Example 1.

manner maintaining in a characteristic way all the sharp contours of the pieces. The volume shrinkage will vary from about 15-25% of the original volume depending on pressures and sintering temperatures used. With 4% Ni and /4% Pt 99.5% tungsten, densities are obtained without swaging as high as 19.35 grams per cubic centimeter, comparable to the density of a piece of hot swaged tungsten rod of 19.3.

This high density is an indication of a fully sintered body exceptionally free from porosity and intergranular voids. The micro-structure confirms this, and shows a well ordered, well developed, fairly large grained crystal structure.

Example II The alloying, bonding and densifying metal mixture is prepared. Approximately equal proportions by weight of finely divided nickel beryllium powder and pure finely divided platinum powder are thoroughly mixed and ball-milled. Then approximately 1% by weight of this prepared mixture is added to finely divided tungsten powder of a particle size of 1-25 microns, and is thoroughly mixed. It may be ball-milled for a period of several hours or at least long enough to insure the uniform distribution of the small amount of alloying powders throughout the mass of tungsten powder.

This mixture is then pressed in a mold and heat treated in an electric furnace at a temperature of 1500-1800 C. in a dry hydrogen atmosphere In this method the grain size and structure may be controlled by ng the proportions of the alloyfr" ing, bonding and densifying metal between 25% to 4% by weight. Somewhat more than 4% may be added but little if any advan age is secured thereby. As in Example I, densities are obtained without swaging higher than 19.35 grams per cubic centimeter, comparable to the density of a piece of hot fully swaged tungsten rod of 19.3. The grain structure may vary from quite small grains to very large grains in accordance with the amount of the alloying metals that have been added.

An alternate method of adding the nickel and platinum in Example I may be employed with equally satisfactory results. Standard stock solutions of the soluble salts or compounds, or the metals to be added, are made up. The salts chosen belong to the class which when completely dehydrated are easily decomposable to their metallic states When heated in a reducing atmosphere. rides, and nitrates of iron, cobalt, nickel and manganese; chlorplatinic acid, ammonium chlorplatinate, gold chloride, and similar compounds of the other metals used. A measured amount of the solution of the base metal and the noble metal is added to the oxide of the refractory metal, thoroughly dried in a manner to assure uniform distribution of the salts, and subsequent ly this mixture is reduced in the usual manner to metal powder. Or the solutions may be added to the refractory metal powder forming a slurry, care being taken to mix and stir the powder thoroughly to get uniform distribution of the metallic Examples of such are the acetates, chlo- 4 salts added. The slurry is carefully dried with constant stirring, and, when dry, it is sieved to break up any lumpy formation, put into a nickel coat and run through a reduction furnace to insure complete reduction to their metallic states.

"The powders are then sieved through 200 mesh and are now ready for pressing into any desired form or shape.

The examples given above illustrate an alloying of tungsten with nickel and platinum and tungsten with nickel, beryllium and platinum. However, excellent results may be obtained by substituting for all or part of the nickel, a nickelous alloy of zirconium, chromium, vanadium, titanium or uranium. These nickelous alloys can be made to contain from 10-50% of the grain refining metals, beryllium, zirconium, chromium,

vanadium, titanium, uranium. Therefore, the

percentages of these metals can be adjusted to give any desired amount up to 50% of the nickel content.

Additions of beryllium, zirconium, etc., increase the hardness of the refractory metal alloy. Heating at approximately 600-1000 C. for periods of about l-lO hours will cause precipitation hardening whenever'desired. They also perform the function of grain refining and of effecting a uniform grain structure in the finished alloy, thus affording a ready means of controlling the grain growth.

While the examples given above illustrate the method of making the dense alloy of the invention with tungsten as the refractory metal, it will be understood that a similar method of alloying molybdenum, rhenium and tantalum also comes within the scope of the invention. In the case of molybdenum, however, about 1% of the alloying, bonding and densifying metals should be added.

The alloys of the invention are extraordinarily suitable for making the face plates of contact points and may be used for making large shaped objects such as crucibles and cylinders, both solid and hollow. They may, in fact, be used wherever hard, strong, dense metal capable of withstanding high temperatures is desired.

Having thus described our invention, what we claim is:

Sintered alloy of high density comprising 99% tungsten, 0.25% nickel, 0.25% beryllium, and 0.50% platinum and having a density approximating 19.3 grams per cubic centimeter.

JACOB KURTZ. HAROLD G. WILLIAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,418,081 Laise May 30, 1922 1,932,678 Ruben Oct. 31, 1933 2,074,474 Jedele Mar. 23, 1937 2,157,935 Hensel et a1 May 9, 1939 2,183,359 smithels Dec. 12, 1939 2,200,088 Kelly May 7, 1940 2,227,446 Driggs Jan. 7, 1941