US3779717A - Nickel-tantalum addition agent for incorporating tantalum in molten nickel systems - Google Patents

Abstract

A physical admixture of nickel powder and scrap tantalum powder is made to dissolve in molten nickel as rapidly as a conventional true master alloy of comparable proportions of these metals in pure form by pressing the admixture of the two metal powders under a pressure of at least 10,000 pounds per square inch.

Description

United States Patent [1 1 Gustison A NICKEL-TANTALUM ADDITION AGENT FOR INCORPORATING TANTALUM IN MOLTEN NICKEL SYSTEMS Robert A. Gustison, Reading, Pa.

Kawecki Berylco Industries, Inc., New York, N.Y.

Filed: July 12, 1972 Appl. No.: 271,114

Inventor:

Assignee:

US. Cl. 29/192 R, '75/0.5 R, 75/170, 264/11 1 Int. Cl. B221 3/02, B22f 3/04 Field of Search 75/0.5 R, 170, 171; 29/192 R, 420; 264/111 References Cited UNITED STATES PATENTS 8/1960 Thielman 75/171 51 Dec. 18, 1973 3.161426 l/l965 Freche et a1 75/171 OTHER PUBLICATIONS Goetzel, C. 6.; Treatise on Powder Metallurgy; Interscience Publishers, Inc.; 1950 Vol. II; page 634.

Primary ExaminerW. W. Stallard Att0rneyDean S. Edmonds et al.

[5 7] ABSTRACT A physical admixture of nickel powder and scrap tantalum powder is made to dissolve in molten nickel as rapidly as a conventional true master alloy of comparable proportions of these metals in pure form by pressing the admixture of the two metal powders under a pressure of at least 10,000 pounds per square inch.

4 Claims, No Drawings NlCKEL-TANTALUM ADDITION AGENT FOR INCORPORATING TANTALUM IN MOLTEN NICKEL SYSTEMS This invention relates to master alloys and, more particularly, to nickel-tantalum master alloys for addition to molten nickel.

in the production of high temperature oxidationresistant alloys such as nickel base alloys containing tantalum, the high melting point of tantalum has made it difficult to dissolve tantalum metal directly into molten nickel either in producing the desired alloy directly or in producing a high tantalum-content nickel base master alloy for addition to molten nickel. ,7 I,

It has been proposed heretofore to produce master alloys by briquetting the individual powders of the metals of the master alloy (Goetzels Treatise on Powder Metallurgy, lnterscience Publishers, Inc., N. Y. 1950, Vol. IL, pages 569-570) but this technique has generally been limited to powder components of metals of low to moderate melting points. Where master alloys have been made of components including high temperature melting point metals such as tantalum, it has been the practice to produce the desired master alloy by the aluminothermic reduction of tantalum oxide in the presence of nickel powder and often with the addition of a heat-producing supplemental oxidizer such as sodium chlorate or barium peroxide (Ibid., page 634). The latter approach has the following disadvantages when applied to the production of a nickel-tantalum master alloy:

1. Poor recovery of tantalum (generally between 80 to 90 percent);

2. Variable concentration of tantalum in the master alloy;

3. Residual amounts of the reducing agent (aluminum) in the final alloy;

4. Use of high-priced virgin starting material (tantalum oxide);

5. Variability of alloy particle size because the smelted alloy must be crushed;

6. Narrow range of acceptable tantalum compositions which is based on the lower melting point ranges of the nickel-tantalum phase diagram.

1 have now found that ideal nickel-tantalum addition agents for incorporating tantalum in molten nickel systems can be produced by pressing an intimate mixture of powders of these metals. The resulting product, consisting of an intimate physical admixture of tantalum metal powder and nickel metal powder compressed under a pressure of 10,000 to 100,000 pounds per square inch, and not subsequently sintered, dissolves in molten nickel or nickel-base alloy at least as fast as a true master alloy of comparable proportions of nickel and tantalum.

The high rate of solution of the nickel-tantalum addition agent of the invention is attributable to the uniform intimate contact between its components with resulting promotion of uniform exothermic reaction between these components. When a finely divided mixture of nickel and tantalum powders compacted pursuant to the invention is introduced into a molten nickel bath, the following sequence of steps can be visualized for the process of dissolution of the addition agent in the molten nickel:

l. The compact is rapidly and uniformly heated to the temperature of the molten bath;

2. The nickel component of the compact starts to melt;

3. The molten nickel component of the compact reacts with the high surface area tantalum powder, forming an intermetallic compound such as TaNi and Ta Ni and 4. The nickel-tantalum reaction evolves heat which assists in the solution of the resulting nickel-tantalum intermetallic compound in the molten nickel.

The range of nickel to tantalum proportions can vary from 1 to 99 percent by weight of either component, the balance being essentially the other component. A proportion of about 35 percent nickel and 65 percent tantalum, carried over from the conventional nickeltantalum master alloy art, can be used with particular advantage.

Both nickel and tantalum metal powders are readily available in high purity form for use in practicing the invention. Nickel powder is generally obtained by the decomposition of nickel carbonyl gas into nickel powder and carbon monoxide, and this form of nickel powder is presently preferred for use in practicing the invention. Tantalum powder is generally obtained from either of two sources, and it is a particular advantage of the present invention that it can use a high purity tantalum powder whose cost is reduced by being classed as, or being derived from, scrap tantalum. One of these sources comprises tantalum metal as normally produced in powder form. Such powder as does not meet the requirements for tantalum capacitor grade powder is generally considered scrap by such standards, but is nevertheless of high purity and is wholly suitable for use in producing the compacts of this invention. The other source of tantalum powder for use in practicing the invention is from metallurgical tantalum scrap, such as mill ends, sheet or plate croppings, ingot butts and the like, which can be hydrided, ground and dehydrided to produce a high purity tantalum metal powder. Inasmuch as both of these tantalum sources can be considered as scrap sources, the prac' tice of the present invention can be considered a means of converting tantalum scrap into a useful product.

The particle size of the nickel and tantalum powders is not critical, although the powders are advantageously of minus 60 mesh Tyler standard, and preferably minus 100 mesh, for optimum intimacy of the particles of the two metals in the mixture. This intimacy of contact is further enhanced by thorough mixing of the two powders for, in general, at least 10 minutes in a conventional tumbler-type blender.

By pressing the nickel-tantalum powder mixture at pressures of at least about l0,000 psi, and up to about 100,000 psi, and advantageously under isostatic conditions, the particles of nickel and of tantalum are brought into a uniform degree of contact in all directions and with a degree of intimacy conducive to prompt reaction of the tantalum with the nickel when the nickel particles have been heated to the molten state. This intimate and unifonn contact between the nickel and the tantalum throughout the mass of the compacted powder also insures uniform and rapid transfer of heat to the interior of the compact from the molten mass of nickel in which it is immersed during the tantalum innoculation or addition operation.

The practice of the present invention is illustrated by the following example:

A mixture of 350 pounds of lnco Type 128 carbonylnickel powder, with an average particle size of 7-9 microns, and 650 pounds of minus 100 mesh Tyler standard tantalum powder prepared by hydriding tantalum scrap, grinding to minus 100 mesh in a ball mill and dehydriding the resulting powder under vacuum at 950 C., was blended for 15 minutes in a conventional twinshell blender. Polyethylene bags encased in perforated copper retaining molds 1-% inches square by about 30 inches long were filled with the blended powder mixture, were sealed and were then introduced into an isostatic press wherein a pressure of 60,000 pounds per square inch was applied. The powder mixture was thus converted into strong bars l-% inches square by about 30 inches long which were sheared into 1 to l-Vz inch lengths. The density of the powder metal compacts was about 85-90 percent of the theoretical density of its components. To compare the solution rates in molten nickel of the compact of the invention versus a conventional nickel-tantalum master alloy, three samples were prepared:

1. A piece of nickel-tantalum compact, produced as described in the foregoing example and weighing 100 grams;

2. A 100 gram piece of the aforementioned compact which had been sintered under vacuum at l,000 C. for 60 minutes; and

3. A 100 gram piece of a conventional 35 percent Ni-65 percent Ta alloy prepared by aluminothermic reduction of Ta O in the presence of nickel powder.

The solution rate of each of the three samples in the form of a rod was measured in a molten bath of pounds of nickel held at 1,600 C. The results were:

Sample No. Solution Rate, grams/second l 5.6 2 5.7 3 5.2

TABLE I Purity of Ni-Ta Compact Vs. Ni-Ta Alloy Element Ni-Ta Compact Ni-Ta Alloy Ni 35 i 0.2 35-36 Carbon 0.02 0.02 Hydrogen 0.005 0.00] Iron 0.005 0.!

Oxygen 0.l 0.03 Nitrogen 0.005 0.006 Sulfur 0.005 0.007 Phosphorous 0.005 0.0! Silicon 0.15 0.07 Manganese 0.005 0.002 Aluminum 0.005 0.50

The nickel-tantalum compacts of the invention have the following advantages over standard aluminothermically produced nickel-tantalum master alloys as addition agents for introducing tantalum into molten nickel systems:

1. Exact composition for exact dosage of added tantalum;

2. Uniform composition;

3. A solution rate in molten nickel at least as fast as that of the master alloy;

4. High recovery of contained tantalum;

5. Can utilize low-cost tantalum scrap;

6. No cleaning of the alloy is required, as is the case with an aluminothermic master alloy;

7. No residual amounts of reducing agent in the product;

8. Higher purity in most respects;

9. Uniform shape of addition agent as produced; and

10. Infinite range of compositions possible.

1 Claim:

1. A compacted powder metal nickel-tantalum addition agent for incorporating tantalum in molten nickel systems which comprises an unsintered intimate physical admixture of nickel metal powder and tantalum metal powder compressed under a pressure of at least about 10,000 pounds per square inch.

2. An addition agent according to claim 1 having a density of about to percent of maximum theoretical density.

3. An addition agent according to claim 1 in which the metal powders are of minus 60 mesh particle size.

4. A product in accordance with claim 1 wherein the blended mixture is compacted isostatically at a pressure of 10,000 to 100,000 pounds per square inch.

Claims (3)

1. 2. An addition agent according to claim 1 having a density of about 75 to 95 percent of maximum theoretical density.
2. 3. An addition agent according to claim 1 in which the metal powders are of minus 60 mesh particle size.
3. 4. A product in accordance with claim 1 wherein the blended mixture is compacted isostatically at a pressure of 10,000 to 100,000 pounds per square inch.