WO1998017423A1

WO1998017423A1 - Dispersion strengthened copper

Info

Publication number: WO1998017423A1
Application number: PCT/US1997/019443
Authority: WO
Inventors: Evgueni P. DANELIA
Original assignee: Danielia Evgueni P
Priority date: 1996-10-22
Filing date: 1997-10-22
Publication date: 1998-04-30
Also published as: AU5089998A

Abstract

A dispersion strengthened copper alloy and a method for producing the alloy are provided. The alloy preferably comprises beryllium or aluminum, as first alloying metals and zirconium, titanium and hafnium as second alloying elements that are internally oxidized under controlled conditions to produce a dispersion strengthened copper material having good hardness and high conductivity. The dispersion strengthened material can be useful in many applications, including welding electrodes and electrical contacts.

Description

DISPERSION STRENGTHENED COPPER CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of co-pending U.S. Patent Application S.N. 08/464,603, filed June 5, 1995 for Dispersion Strengthened Copper which application, in turn, is a divisional application of U.S. Patent Application S.N. 107,529, filed October 17, 1993 for Dispersion Strengthened Copper, now U.S. Patent No. 5,551,970, the disclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to copper metal alloy that is dispersion strengthened with stable dispersed oxides and also to a method for making dispersion strengthened copper alloys .

2. Description of Related Art:

In the above referred to co-pending application and issued patent there is disclosed a dispersion strengthened copper and a method for making it which is predicated upon the incorporation into the copper of an aluminum, titanium, and hafnium alloy, introduced as the oxides thereof, and with a specific mass ratio of aluminum to titanium to hafnium of about 4:1:1. While the process and product of the co-pending application and patent are extremely efficacious for their intended use, it is to be appreciated by those skilled in the art to which the present invention pertains that such a dispersion strengthened product has excellent hardness, strength and electrical conductivity. However, on the other hand, such material has shortcomings in its ductility and capacity to be cold and or hot worked. Thus, there is a limit on the properties imparted to the resulting metal matrix. Thus, it would be highly desirable to provide a dispersion strengthened copper material or product or material having improved properties or which can have its properties tailored to predetermined or selected mechanical properties, e.g., conductivity, hardness, etc.

As detailed hereinbelow, it is to this to which the present is directed.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a dispersion strengthened copper as well as a process of manufacture therefor.

The dispersion strengthened material hereof comprises a copper metal matrix having dispersed oxides incorporated therewithin. The dispersed oxides include at least one oxide selected from the group consisting of aluminum oxide or beryllium oxide and, optionally, a second oxide selected from the group consisting titanium oxide, hafnium oxide, zirconium oxide and mixtures thereof.

The oxides are introduced into the dispersion strengthened material by the internal oxidization thereof. The first oxide and second oxide are present in a mass ratio of greater than 4:1.

In accordance herewith and in another aspect of the present invention there is provided a method of forming the dispersion strengthened material which includes the steps of forming a copper alloy, the alloy comprising copper, at least one metal selected from the group consisting of aluminum or beryllium, forming the alloy into either powder or granulated particles, oxidizing the particles to form an oxide skin on the surface of the products, internally oxidizing the particles to form a copper matrix comprising oxides of aluminum or beryllium compacting the particles into a billet or other compact form and, thereafter, extruding the compacted particles using a drawing coefficient of at least about 12 to form a dispersion strengthened material. Specifically, the present process contemplates the formation of the alloy by melting the copper, preferably, as scrap in an induction heating furnace under reducing condition using a protecting flux at a temperature ranging from about 2240°F up to about 2260°F. Thereafter, and in a preferred embodiment hereof, the aluminum or beryllium is introduced into the melt in a proportion of from about 1.3 to about 1.7 times the amount required in the final alloy. Thereafter, an additional metal selected from the group consisting of titanium, hafnium or zirconium is admixed thereinto. Next, the melt is superheated and thereafter immediately cast into an ingot or gas atomized.

After the internal oxidation step, the resulting powder product can be further processed by cold isostatically pressing the powder into billets which can be emplaced in a fill can and, then, extruded into any desired product.

For a more complete understanding of the present invention, reference is made to the following detailed description and accompanying examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to a dispersion strengthened copper material and a method therefor that includes the steps of forming a copper alloy having alloying elements capable of being oxidized and oxidizing the alloy using particular oxidation parameters to provide a final product with disperse oxide particles that preferably have an average size of about 10 nm or less. The oxide particles are uniformly distributed in the bulk of the matrix metal, which give the metal improved mechanical and electrical properties over non-strengthened copper and over prior art dispersion strengthened materials.

According to the present invention, the copper alloy includes at least on preferably at least two, alloying elements capable of being oxidized to form oxide particles within the copper metal matrix. In the preferred embodiment, the copper alloy comprises at least one metal which is either aluminum or beryllium as alloying elements. Additional alloying elements which may be included therewith hafnium, titanium, zirconium or mixtures thereof.

According to this embodiment, the aluminum or beryllium is present in an amount from about 0.01 weight percent to about 0.8 weight percent and preferably, less than about 0.6 weight percent of the total weight alloy. Where used, the titanium is present in an amount from about 0.01 weight percent to about 0.80 weight percent and, preferably, is present in an amount less than about 0.15 weight percent of the total weight of the alloy. The hafnium as well as the zirconium are, likewise, present in an amount from about 0.01 weight percent to about 0.80 weight percent and, preferably, comprise less than about 0.15 weight percent of the alloy. The balance of the alloy is essentially copper. In a preferred embodiment hereof, the weight ratio of aluminum or beryllium to the other alloys is greater than 4:1 and the total concentration of the alloying elements, preferably, does not exceed about 0.9 weight percent in the final product.

As disclosed in the above noted parent application and patent the copper alloy can be melted and formed into an ingot. The ingot can then be dispersed into chips with a milling machine having a flake or platelet form. The chips have a thickness of about 100 micrometers or less and can have a width of, for example, up to about 1 millimeter. Alternatively, the copper alloy can be particulated by spraying molten droplets of the alloy in an inert gas to produce discrete granules. The granules are, preferably, separated, such as by using a sieve, so that the granules have an average particle size of about 300 micrometers or less.

In accordance herewith, the dispersion strengthened material hereof is prepared by a process which includes initially forming the alloy by melting a source of copper, such as copper scrap, by induction heating under reducing conditions using a protective flux. Typically, melting occurs at a temperature ranging from about 2240°F to about 2260°F. Thereafter, the first metal, i.e. aluminum or beryllium is introduced into the melt, preferably, as large pieces thereof. Generally, the aluminum or beryllium is introduced into the melt in an amount equal to about 1.3 to about 1.7 times the quantity desired in the final alloy. Upon introduction into the melt, the temperature is raised to about 2300°F for about three to four minutes. Immediately thereafter the additional metals, where used, are introduced into the melt as master alloys, i.e. either copper- titanium alloy, copper-hafnium alloy or copper-zirconium alloy. Typically, they are introduced, in the order of titanium, then, hafnium and/or zirconium. Upon introduction into the melt the melt is superheated up to about 1290°C for about 1 to 2 minutes and thereafter it is immediately cast into an ingot or atomized in the powders granules.

The flakes or granules (hereinafter collectively referred to as particles) of the alloy are then subjected to surface oxidation to form an oxide skin on the surface of each particle. Preferably, the particles are dispersed on a tray such as a stainless steel tray, to permit substantially free access of the oxidizing environment to the particles. The depth of the particle layer in the tray can be up to about 5 centimeters .

The surface oxidation of the particles takes place at a temperature in the range of from about 250°C to about 900°C, and, preferably, in the range of from about 300°C to about

500°C, in the presence of an oxygen containing environment.

For example, the particles can be exposed to air or any other atmosphere having a sufficient oxygen content. Alternatively, over pressures of oxygen may be useful. A film of copper oxide is thereby formed on the surface of substantially every particle, which serves as the oxidant for the subsequent internal oxidation of the alloying elements. Since copper oxide is formed on the surface of substantially every particle, a uniform distribution of the oxidant and thus the internal oxidation of the alloying elements can also be uniform.

The preferred thickness of the copper oxide film depends on the average shape and the dispersivity of the particles, as well as on the concentration of alloying elements in the alloy. The formula for the calculation of the optimum oxidation time, as well as the oxidation temperature, and other parameters as described in the aforementioned application and patent.

Preferably, the internal oxidation includes the step of heating the powder particles in an inert atmosphere at a temperature of from about 850°C to about 950°C. The inert atmosphere can include argon, nitrogen, or a mixture of carbon dioxide and carbon monoxide. The atmosphere used should include a relatively low partial pressure of oxygen such as about 10^-7 atmospheres. Typically, in lower purity gases, there is enough residual water vapor to maintain such a low partial pressure of oxygen. The low partial pressure of oxygen will maintain the proper oxygen stoichiometry on the outside of the oxide skin on the particles, while the particles internally oxidize from the interface of the particle and the oxide skin layer. That is, oxygen for the internal oxidation of the alloying elements comes from the particle/oxide layer interface and the oxide layer is consumed from the inside toward the outside. If the partial pressure of oxygen is too low, the film may dissociate at the outside and the maximum oxygen level at the metal/oxide interface cannot be maintained. Preferably, the partial pressure of oxygen is therefore from about 10^"6 to 10^~8 atmospheres.

The duration of the internal oxidation process depends on the shape and the size of the powder particles, on the type and concentration of the alloying elements in the alloy, as well as on the temperature. The preferred time, in seconds, can be calculated, also, as described in the aforementioned application and patent.

The particles so produced will thus comprise a copper matrix strengthened by a dispersion of fine oxides of either aluminum oxide or beryllium oxide, optionally, with one or more of titanium oxide, hafnium oxide, zirconium oxide and mixtures thereof. Preferably, the oxides will have a size of less than about 10 nra as measured by electron microscopy techniques .

In practicing the present process the master alloys are used to introduce the alloying elements such as titanium, hafnium or zirconium into the melt. Typically, the master alloys will have a copper to other metal (s) weight ratio of from about 70:30 to about 30:70, depending on the introduced alloying elements. It is, also, desirable that the composition of the master alloys be brittle so that they break up easily to form small pieces before introducing into the melt for uniform distribution of the alloying elements in the melt. Likewise, it is desirous that the adjuvants, i.e. the master alloys, introduced into the copper melt have a melting temperature close to that of copper to prevent the oxidization of the metal. Likewise, the casting of the superheated melt takes place in a rapid period of time to preclude the oxidization of the alloys. The products hereof will have an aluminum or beryllium to adjuvant other metal ratio of greater than 4:1.

According to the present invention it is possible to have the following exemplary dispersion strengthened materials.

Cu-Al

Cu-Al-Ti

Cu-Al-Hf

Cu-Al-Ti-Hf

Cu-Al-Zr

Cu-Al-Ti-Zr

Cu-Be

Cu-Be-Zr

Cu-Be-Ti-Zr

According to the present invention, the particles have an oxidized skin layer formed thereon, which particles are then heated in an inert atmosphere to dissociate oxygen from the copper oxide skin and drive the dissociated oxygen into the bulk of the particles to oxidize at least a portion of the alloying elements.

The dispersion strengthened particles are either briquetted (e.g., pressed) or compacted into a fill can which can then be further processed when briquetted, they are then subjected to hot extrusion. Typically, a briquette is pressed at a pressure of from about 5 to about 6 metric tons per square centimeter. Preferably, the density of the briquette after pressing is a least about 90% or greater.

The briquettes are then extruded, preferably, at a temperature of from about 850°C to about 950°C, during which consolidation and diffusion welding of the particles occurs.

Good diffusion welding can advantageously be achieved by extruding the briquette with a drawing coefficient of at least about 12, more preferably at least about 16. That is, the cross sectional area of the briquette is preferably reduced by at least about a factor of 12 during extrusion, as described in the aforementioned application.

According to an alternative embodiment of the present invention, a simplification of the process and subsequent reduction of the cost of the process can be achieved if the briquetting of the powder is carried out immediately after the surface oxidation of the particles. That is, the particles having an oxide skin are briquetted prior to the internal oxidation of the alloying elements. The internal oxidation is thus carried out when the particles are in briquette form, but prior to extrusion.

Alternatively, the powders can be pressed by an isostatic process to form small compact billets which can then be loaded into a fill can and surrounded with other powders. This fill can then be extruded.

Products produced according to the present invention are useful in applications where the high conductivity of copper is desirable along with good hardness and strength, ductility, etc. particularly at elevated temperatures. Applications include welding electrodes, electrical contacts, heat conductors, foils, and the like.

For a more complete understanding of the present invention reference is made to the following illustrative examples wherein all percentages are by weight, absent contrary indications:

EXAMPLE 1 Several alloys, as set forth in Table I, were prepared by melting copper, in an induction-heating furnace under reducing conditions using carbon flux. The copper was melted at 2250°F. Then aluminum and beryllium was added to the copper and melted in about three minutes at a temperature increasing up to 2300°F. Thereafter, a second metal was introduced, as a master alloy, and melted at the same temperature. Then, the melt was superheated for about 1.5 minutes at 2350°F and, then, gas atomized. Thereafter, the particles were surface oxidized and then internally oxidized, to form powders in accordance herewith.

TABLE 1

Alloy Al* Ti* HP Zr* Be* Cu

Ad⁾ 0.2% 0.05% 0.05% - balance

B 0.2% - - balance

C 0.2% 0.05% - balance

D 0.2% 0.05% 0.05% - balance

E 0.2% balance

F 0.05% 0.2% balance

* = mass percent d⁾ as described in the present application

The powder was then loaded into a rubber can using a vibration process with an apparent density in the range of 45% to 56% (45%-56% of the theoretical density) and subjected to pressing in a cold isostatic press to obtain compact billets with an apparent density of from about 75% to 85%. The billets were loaded into a copper can having an internal diameter about 160mm. Additional powder was added to the can to fill it. The loaded can was welded shut and extruded into bars at the temperature 1550°F (about 850°C) .

The properties of these materials were compared with properties of the same compositions produced by the method disclosed in the co-pending patent application and patent (Table II) .

TABLE II

AlloyWHardnessW Tensile^) YieldW Elongation^¹⁾ Electrical ^!

HR strength, stress, % conductivity

(MPa) (MPa)W % of IACSω

A 73/74 500/510 460/470 18/22 89/90

B 63/67 420/450 340/370 26/30 91/92

C 66/70 450/480 380/420 24/26 89/90

D 69/73 460/480 400/440 20/25 89/89

E 69/71 450/470 420/450 15/15 87/89

F 71/73 470/490 440/480 13/18 86/88

d compares prior patent process to process of present application

EXAMPLE 2

Alloys A, B, C below were prepared according to the described in Example 1. Final bars were cold drawn into wires of 0.05 mm diameter for alloys B and C and into a wire 0.2 mm diameter for alloy A. Alloy A could not be drawn to a diameter of less than 0.2 mm because of breakage, in comparison to alloys B and C. The properties of the alloy wires after cold drawing (CD) and after the following annealing at 1832°F (1000°C) for 1 hour (A) are presented in Table III.

TABLE HI

AlloyW and Tensile^⁾ Yields Elongation^) Electrica ¹⁾

condition strength stress % conductivity

(MPa)ω (MPa)W % of iACS

A, CD 750/770 730/750 1/1 86/87

A, A 550/570 520/530 3/3 87/88

B, CD 600/650 570/620 1/1 89/90

B, A 450/480 380/420 8/10 90/91

C, CD 690/730 670/700 1/2 88/88

C, A 510/550 460/500 4/6 89/89

W compares prior patent process to process of present application

EXAMPLE 3

Alloys A, E and F below were prepared according to the procedure described in Example 1 for alloys E and F and by the method according to the parent application for alloy A. The final bars were hot and then cold rolled to a strip of 0.2 mm thick. Their resulting properties were determined after cold rolling, and, also, after annealing at 1832°F (1000°C) for 1 hour. The results are set forth in Table IV. TABLE IV

Alloy Elastic limit (MPa)

After cold working after annealing

A 350 300

E 370 320

F 400 350

Comparing the properties for different alloys produced by the process of the original application with that of the present application (see Tables IX and X in original patent and Tables I-IV in the present description) shows that the main properties such as hardness, tensile strength, yield stress and electrical conductivity of the present compositions produced by the present process are within intervals of the properties of the material disclosed in the parent applications. But, additionally, there is obtained hereby materials that can be produced as very thin wire or foil and which is easily soldered with a higher elastic limit that is favorable for using the material as a spring.

Having thus described the invention, what is claimed is:

Claims

1. A dispersion strengthened material, comprising:

(a) a copper metal matrix, and

(b) a disperse first oxide of aluminum oxide or beryllium oxide dispersed throughout said copper metal matrix.

2. The dispersion strengthened material of Claim 1 which further comprises:

(a) a disperse second oxide selected from the group consisting of titanium oxide, hafnium oxide, zirconium oxide and mixtures thereof.

3. A dispersion strengthened material as recited in Claim 1, wherein said disperse oxides have an average particle size of about 10 nanometers or less.

4. A dispersion strengthened material as recited in Claim 1, wherein said disperse oxides comprise not more than about 1.6 weight percent in relation to said copper metal matrix.

5. A dispersion strengthened material as recited in Claim 1 wherein the mass ratio of the metal of the first oxide to the metal of the second oxide is greater than about 4:1.

6. A dispersion strengthened material as recited in Claim 1, wherein said material comprises from about 0.01 weight percent to about 0.8 weight percent of the elemental metal of the first oxide in relation to the copper metal matrix.

7. The material Claim 2, wherein the first metal oxide is aluminum oxide.

8. A material Claim 2, wherein the second metal oxide is selected from the group consisting of hafnium, titanium, zirconium, a mixture of titanium and hafnium or a mixture of titanium and zirconium.

9. The material Claim 2, wherein the first metal oxide is beryllium.

10. The material Claim 2, wherein the second metal oxide is zirconium oxide or a mixture of zirconium oxide and titanium oxide.

11. A method for producing a dispersion strengthened material, comprising the steps of:

(a) forming an alloy comprising a first metal selected from the group consisting of aluminum or beryllium, the balance being copper;

(b) forming said alloy into particles;

(c) oxidizing said particles to form an oxide skin on the surface of said particles;

(d) internally oxidizing said particles to form a copper matrix comprising oxides of aluminum or beryllium; and

(e) extruding said copper matrix using a drawing coefficient of at least about 12 to form a dispersion strengthened material.

12. The method of Claim 11 which further comprises:

(a) adding a second metal selected from the group consisting of titanium, hafnium, zirconium and mixtures thereof, the second metal being added as a master alloy of copper.

13. The method of Claim 11 wherein the first metal is present in an amount ranging from about 0.01 weight percent to about 0.8 weight percent.

14. The method as recited in Claim 12, wherein said alloy comprises from about 0.01 weight percent to about 0.8 of each of the first metal and second metals.

15. A method as recited in Claim 13, wherein said dispersion strengthened material comprises not more than about 1.6 weight percent of the oxides.

16. The method of Claim 11 which further comprises: forming said alloys into particles having an average size of less than 300 micrometers.

17. The method of Claim 11 which further comprises: forming the particles into a powder with a density of at least 45% of the theoretical density .

18. The method of Claim 16 further comprising: isostatically pressing the powder into a compact billet with a density of at least 75% of the theoretical density.

19. The method of Claim 18 which further comprises:

(a) forming a final preform comprising a copper can filled with said compact billet preform and an additional amount of a powder.