US3372024A

US3372024A - Zone refinement of liquid-phase sintered tungsten alloys

Info

Publication number: US3372024A
Application number: US594317A
Authority: US
Inventors: Niranjan M Parikh
Original assignee: Army Usa
Current assignee: US Department of Army
Priority date: 1966-11-10
Filing date: 1966-11-10
Publication date: 1968-03-05
Anticipated expiration: 1985-03-05

Description

United States Patent 3,372,024 ZONE REFHNEMENT F LIQUID-PHASE SINTERED TUNGSTEN ALLGYS Niranjan M. Parilch, Chicago, Ill., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army No Drawing. Filed Nov. 10, 1966, Ser. No. 594,317 4 Claims. (Cl. 75-84) ABSTRACT OF THE DISCLOSURE This process is a treatment of a sintered tungsten alloy for a matrix which utilizes zone refining for the removal of the low melting matrix while depositing therefrom the contained tungsten on the sintered tungsten for the production of practically pure tungsten.

The invention described herein may be manufactured and used by or for the Government, for governmental purposes, without the payment to me of any royalty there on.

This invention relates to the refinement of tungsten alloys in an improved manner thereby circumventing the difiicult, wasteful and expensive operations presently employed in current industrial operations.

The treatment of this process is based on the techniques of powder metallurgy and it is therefore the object of this invention to produce pure sheets or bars of tungsten in this manner.

It is a further object of this invention to utilize zone refining for the removal of the liquid phase of a sintered tungsten alloy for the production of practically pure tungsten in which the microstructure indicates that the tungsten grain boundaries are clean and the grains are characteristically equiaxed.

This process employs liquid phase sintering of high tungsten alloys using a nickel-iron alloy for a matrix and subsequently removing the low melting nickel-iron alloy This treatment consists in forming compacts from powders of compositions ranging from 9099% by weight of tungsten and the balance nickel and iron in a ratio of 5.5 to 8.2, respectively. These compacts in the form of long bars are sintered at temperatures above 1475 C. in a protective atmosphere such as hydrogen, vacuum or argon. Densifiication takes place first by liquification of the low melting nickel-iron alloy with an increasing temperature and subsequently decreasing the temperature for the solution and reprecipitation of tungsten in this liquid.

The tungsten-nickel-iron bars prepared in this way are then moved through a narrow hot zone at a controlled rate of speed, for example one inch per hour in a protective atmosphere. Maintaining this hot zone above the nickel-iron matrix causes the liquid to migrate out of the sintered bar and reprecipitates all the excess tungsten on the tungsten grains.

Tests were made in which a 98% tungsten-2% (6Niz4Fe) alloy was sintered at 1560 C. in an atmosphere of hydrogen and microstructures of this sintered alloy showed tungsten grains embedded in a semi-continuous matrix of nickel-iron rich alloys; this sintered alloy was passed through the hot zone at a temperature of 1550 C. at a nominal rate of motion of one inch per hour, for the zone refinement of the liquid phase. Microstructures of the refined alloy showed that the liquid phase of the matrix had been removed and that the tungsten boundaries were clean and the grains characteristically equiaxed.

A further test was made employing an alloy having an 3,372,024 Patented Man 5, 1 968 initial sintered composition of 95% tungsten and 5% (6Niz4Fe) and when zone refined at 153 0 C. in a vacuum the microstructures showed the same results.

Thus, this treatment employing zone refining of liquid phase of sintered tungsten alloys as a means of producing pure tungsten without the difiicult high temperature operations normally employed and with the achievement of claim boundaries between tungsten grains and the equiaxed grain structure is indicative of a very desirable degree of grain refinement.

What is claimed is: 1. A process for the production of pure tungsten from a sintered iron-nickel-tungsten alloy comprising,

maintaining the sintered material above the melting point of the iron-nickel matrix by zone refining so as to release the tungsten held in the matrix not in pure form and thereby depositing the tungsten freed from the matrix on the pure tungsten grains by draining the molten matrix metal, whereby practically pure tungsten is produced having a microstructure indicating clean boundaries and characteristically equiaxed. 2. A process for the production of bars of pure tungsten comprising,

forming compacts of long bars prepared from powdered -99% tungsten alloys using a powdered ironnickel alloy as a matrix, sintering said bars at a temperature above 1475 C. in

a protective atmosphere, maintaining the sintered material above the melting point of the iron-nickel matrix by zone refining so as to release the tungsten held in the matrix not in pure form and thereby depositing the tungsten freed from the matrix on the pure tungsten grains by draining the molten matrix metal, whereby the zone refining of the liquid phase of a sintered alloy removes the impurities of the matrix to produce practically pure tungsten. 3. A process for the production of bars of pure tungsten comprising,

forming compacts of long bars prepared from powdered 90-99% tungsten alloys using a powdered iron nickel alloy as a matrix, sintering said bars at a temperature above 1475 C.

in a protective atmosphere, densifying the sintered material by increasing the temperature above the melting point of the iron-nickel alloy to free the tungsten in the matrix, and subsequently decreasing the temperature for the solution and precipitation of tugnsten in this liquid and zone refining the densified material by passing the densified material slowly through a hot zone at 15 50 C. in a protective atmosphere to permit the removal of the molten iron-nickel matrix, whereby the zone refining of the liquid phase of a sintered alloy removes the impurities of the matrix to produce practically pure tungsten. 4. A process for the production of bars of pure tungsten comprising,

forming compacts of long bars from a powdered tungsten alloy containing -99% tungsten, 15% of a nickel-iron alloy having a ratio of 6Niz4Fe using the nickel iron alloy as a matrix, sintering said bars at a temperature above 147 5 C. in

a hydrogen atmosphere, zone refining the sintered material by passing the sintered material through a hot zone at approximately 1530 C. in a vacuum at a rate of approximately one inch an hour for refining by freeing the tungsten 4 combined in the matrix for deposit on the free tung- References Cited r 2il 1 6 3i1t6n matrix metal while in the hot UNITED STATES PATENTS in Zone, g 3,218,154 11/1965 Sell et a1 75 10 whereby practically pure tungsten is obtained as a product of the zone refining of the liquid phase of 5 DEWAYNE RUTLEDGE "nary Exammer the sintered alloy. M. I SCOLNICK, Assistant Examiner.