US3475227A - Copper base alloys and process for preparing same - Google Patents

Description

United States Patent 3,475,227 COPPER BASE ALLOYS AND PROCESS FOR PREPARING SAME Elmer J. Caule, New Haven, Michael J. Pryor, Hamden, and Philip R. Sperry, North Haven, Conn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Oct. 4, 1966, Ser. No. 584,097 Int. Cl. C23c 7/06; C22c 9/10 U.S. Cl. 148-6.31 7 Claims ABSTRACT OF THE DISCLOSURE Oxidation resistant copper base alloys and process for preparing same, with the alloys containing from 0.01 to 0.50% by weight of a Group V element and from 2.0 to 25.0% by weight of at least two additional elements, with the ratio of the first to the second of said elements being from 0.03:1 to 10:1, the first of said elements being either aluminum, gallium, indium or beryllium and the second of said elements being either silicon, germanium, tin or beryllium. When beryllium is the second element, aluminum is the first element.

The present invention relates to new and improved copper base alloys having substantially improved resistance to oxidation and tarnishing in moist and contaminated atmospheres.

Copper base alloys have found wide and varied uses in industry and commerce in general; however, the many useful physical properties of these alloys are almost invariably negated to some degree by their extremely low resistance to oxidation and to tarnishing, especially in moist and contaminated atmospheres. This poor oxidation and/or tarnishing resistance has limited the utility of copper base alloys and has resulted in long and continuing eiforts to overcome this disadvantage.

It has long been the object of the copper industry to develop new copper base alloys which overcome these disadvantages and are characterized by good oxidation and/or tarnishing resistance. The copper industry has aimed to develop new copper base alloys whose resistance to oxidation and tarnishing is at least as good as austenitic stainless steels. The previous approach to this problem has been the investigation of the oxidation and tarnishing characteristics of binary copper alloys where the binary alloying addition is strongly reducing in nature and which, by itself, grows highly protective oxidation films, for example, aluminum. This approach has been unsuccessful in attaining stainless properties which are self-healing in everyday environments.

There has been some limited success where the binary alloys were processed in such a manner as to completely prevent the oxidation of the copper matrix while still permitting oxidation of the alloying addition, see, for example, Journal of the Institute of Metals, 63, 21 (1938), by L. E. Price and G. T. Thomas. This result has been usually attained by selective oxidation whereby the binary alloys are subjected to high temperature treatment in atmospheres, such as moist hydrogen, which will oxidize the reducing alloying ingredient but which maintain the copper, with its lower free energy of oxidation, in the reduced condition. This type of treatment often produces protective, invisible, oxide films of the alloying addition. These films protect the copper matrix as long as they are not mechanically damaged. When the films are mechanically damaged, as they are in even mild forming operations, such as straightening sheet, involving less than 1 percent plastic deformation, they do not repair themselves spontaneously with protective films free of ICC copper oxide at normal temperatures or in the absence of special atmospheres.

In U.S. Patent 3,259,491, by Michael]. Pryor, patented July 5, 1966, an oxidation resistant copper base alloy is formed by bulk alloying with copper at least two alloying ingredients in concentration ratios to form certain complex oxides on the surface of the alloy, i.e., the alloying ingredients are added in concentration ratios so that they diffuse to the surface of the alloy in proportion to the concentration of the individual alloying ingredient in the complex oxide. The above patent provides an alloy representing a considerable advance in the art and atfording a high degree of oxidation resistance. The alloys therein are particularly advantageous at elevated temperatures and provide extensive oxidation resistance at, for example, 800 C. However, it is a disadvantage of these alloys that less protection is afforded over a wide range of temperatures.

Co-pending application Ser. No. 436,746, now U.S. Patent 3,341,369, by Elmer J. Caule, Michael I. Pryor, and Philip R. Sperry, filed Mar. 3, 1965, represents an improvement over the above U.S. Patent 3,259,491. The above co-pending application attains an alloy with extensive oxidation resistance over a wide range of temperatures.

In accordance with the teaching of said co-pending application, from 2 to 25% by weight of two elements are alloyed with copper and the material heated in an oxidizing environment for at least one minute at a temperature of from 400 C. to the solidus temperature of the alloy. The first of said two elements is selected from the group consisting of: aluminum; gallium; indium; and beryllium, the second of said two elements is selected from the group consisting of: silicon; germanium; tin; and beryllium, provided that when beryllium is the second element, aluminum is the first element. Further, the ratio of the first to the second of said elements is from 0.03:1 to 10:1.

In accordance with said co-pending application this forms a first outside layer of copper oxides and oxides of the alloying additions 25 to 5000 angstroms in depth and a second oxidation resistant layer of a thickness of at least 50 angstroms immediately beneath said first layer containing a discrete dispersion of a complex oxide ineluding at least one of the alloying additions.

It is a finding of the above co-pending application that the first layer may be bright and shiny and oxidation resistant; however, this first layer could be and often is mottled or darkened in appearance. The first layer may, therefore, be removed to bare the second highly ennobled oxidation resistant layer which affords considerable protection to the alloy.

The present invention is related in concept to the aforementioned co-pending application and represents an improvement over said co-pending application. In accordance with the present invention the oxidation and tarnish resistance of both the first and second layer is greatly improved. This is particularly surprising in view of the already extensive protection afforded in accordance with the above co-pending application.

In accordance with the present invention it has now been found that the first layer actually contains two strata, with the first or outermost stratum being rich in copper oxides and the second or innermost stratum 'being rich in oxides of one of the alloying elements. In accordance with the present invention certain additional alloying elements are provided which greatly enhance the oxidation and tarnish resistance of the second or innermost stratum. Furthermore, the additional alloying elements of the present invention enhance the oxidation and tarnish resistance of the second highly oxidation resistant layer.

Accordingly, it is a principal object of the present invention to provide a process for the preparation of new and improved copper base alloys which are capable of substantial resistance to oxidation under a wide variety of conditions.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily obtained and new and improved copper base alloys capable of substantial resistance to oxidation may be prepared.

The novel alloys of the invention may be prepared by (A) providing a copper base alloy containing from 0.01 to 0.50% by weight of a Group V element selected from the group consisting of phosphorus, arsenic, antimony, bismuth and mixtures thereof, and from 2.0 to 25.0 percent by weight of two elements, with the ratio of the first to the second of said elements being from 0.03:1 to 10:1, the first of said elements being selected from the group consisting of: aluminum; gallium; indium; and beryllium, the second of said elements being selected from the group consisting of: silicon; germanium; tin; and beryllium, provided that when beryllium is the second element, aluminum is the first element; and

(B) heating said alloy in an oxidizing environment for at least one minute at a temperature of from 180 to 850 C. to form (1) a first outside layer 25 to 5000 angstroms in depth, said first layer containing (a) a first outermost stratum rich in copper oxides, and (b) a second innermost stratum rich in oxides of said first element, and (2) a second oxidation resistant layer immediately beneath said first layer containing a discrete dispersion of a complex oxide including at least one of said two elements, said second layer being of a thickness of at least 50 angstroms and preferably substantially greater; and (C) preferably removing the first stratum.

In the preferred embodiment an additional alloying element is provided. This may be either cobalt, cerium or iron or mixtures thereof with the total of these materials being provided in an amount from 0.05 to 5.0%, preferably 0.2 to 0.8%. These materials provide still greater improvement in properties in the present alloy.

As indicated hereinabove, from 2.0 to 25% by weight of two elements are alloyed with copper. The preferred combined amount is from 2 to 7% by weight. The relative ratio of the first to the second of said elements must be maintained with the following ratio, from 0.03:1 to 10:1. That is, the ratio of the first to the second of said elements must be maintained within the foregoing ratio. Naturally, the ratio which is chosen for a particular system will vary widely within the foregoing broad ratio depending upon the particular system and the relative atomic weights of the elements which are added. For example, when the two elements are aluminum and silicon, which is preferred, the following ratio of aluminum to silicon should be employed, from 2.5 :1 to 0.5 :1. Similarly, for elements which have lower or higher atomic weights than aluminum, the ratio should be adjusted, for example, the beryllium-silicon system utilizes the following ratio of beryllium to silicon, 2.021 to 0.15:1. The indium-silicon system utilizes the following ratio of indium to silicon, 10:1 to 02:1. The gallium-silicon system utilizes the following ratio of gallium to silicon, 10:1 to 0.2:1. The aluminum-germanium system utilizes the following ratio of aluminum to germanium, :1 to 02:1 and the aluminum-tin system utilizes the following ratio of aluminum to tin, 3:1 to 0.03:1. Similarly, the following ratios apply to the following systems: aluminum to beryllium, 10:1 to 0.5 :1; gallium to germanium, 5:1 to 0.1:1; gallium to tin, 3:1 to 01:1; indium to germanium, 10:1 to 02:1; and indium to tin, 5.021 to 01:1.

It should be noted that the exact proportion of the first of said elements to the second of said elements will be affected by the atomic weights of the respective elements, the specific complex oxides to be formed, and also the diffusion and chemical characteristics of the particular elements.

In addition, the alloy of the present invention also contains from 0.01 to 0.50% by weight of a Group V element selected from the group consisting of phosphorus, arsenic, antimony, bismuth and mixtures thereof, and preferably from 0.05 to 0.20% by weight. The preferred Group V element is phosphorus.

In addition to the foregoing, it is preferred that a total from 0.05 to 5% by weight of either cobalt, cerium or iron or mixtures thereof be employed, preferably from 0.2 to 0.8% by weight, with cobalt being the preferred additive.

Naturally, the present invention contemplates within its scope the use of other materials in combination with copper and the foregoing ingredients in order to achieve particularly desired results or to provide a particular alloy. For example, still greater oxidation resistance may be obtained by adding the following in addition to the two principal alloying ingredients: boron; manganese; zinc; cadmium; and beryllium where beryllium is not one of the alloying ingredients. Also, particularly desired properties may be enhanced by the addition of other alloying ingredients while retaining oxidation resistance.

In accordance with the present invention, the particular method of alloying copper with the chosen alloying additions is not particularly important and conventional methods may be readily employed provided that the molten copper to which the alloying elements are added is initially oxygen free so that the alloying elements are not present in the alloy as oxides prior to solidification. As is conventional, the elements may be added as master alloys or in elemental form.

It is a critical aspect of the present invention, however, that after the alloying additions have been added to copper, the alloy solidified and if desired brought into a suitable or desired product form, the resultant alloy is heated in an oxidizing environment for at least one minute, and preferably at least five minutes, at a temperature of from C. to 850 C., and preferably from 400 C. to 850 C. Temperatures from 180-400 C. are insufiicient to form the second layer, forming only the first layer containing the first and second strata. Temperatures in excess of 400 C. form both the first and second layers.

In the preferred embodiment, the alloy is heated in an I oxidizing atmosphere, such as air, to desired temperatures at a rate of at least 5 C. per hour. Naturally, the particular temperature of treatment will vary depending upon the particular system and the particular results desired. However, in the preferred embodiment a temperature range of from 500 C. to 800 C. is employed. The time of holding the alloy at these elevated temperatures should for practical purposes be less than 2 days, although longer heating times may be utilized if desired. The optimum heating time is from one (1) hour to 10 hours.

It is critical that the alloy be heated in an oxidizing environment. Any oxidizing environment may be readily employed, for example, preferably air or oxygen and also molten oxidizing salt baths may be employed, such as those containing sodium nitrate.

After the alloy has been held under the above conditions the alloy is cooled to room temperature.

The foregoing process results in an alloy having a first outside layer and a second highly oxidation resistant layer. The first outside layer is 25 to 5000 angstroms in depth and contains a first outermost stratum rich in copper oxides and a second innermost stratum rich in oxides of said first element, i.e., either aluminum, gallium, indium or beryllium. The second highly oxidation resistant layer is immediately beneath the first layer, is at least 50 angstroms in depth and contains a discrete dispersion of a complex oxide including at least one of said two elements.

In accordance with the present invention the first layer consists of two strata. The first or outermost stratum is predominantly copper oxides. This stratum is generally colored and provides little or no oxidation or tarnish resistance, therefore, is preferably removed. The thickness of this stratum will vary depending on the temperature of formation.

The second or innermost stratum of the first layer is predominantly oxides of the first element, i.e., predominately oxides of aluminum, gallium, indium or beryllium. In accordance with the present invention this stratum provides considerable oxidation and tarnish resistance. This stratum is transparent, thus retaining the original luster and color of the substrate alloy. In accordance with Ser. No. 43 6,746, referred to above, in 1-2 months spots of discoloration appear on the second stratum in sufficient number to destroy the decorative utility of a fabricated article. In accordance with the present invention, however, very few fine spots of discoloration appear on the second stratum after a prolonged time, e.g., industrial exposures in excess of one year did not destroy the decorative utility of the article and the article was still bright and shiny. This is due to the addition of the Group V elementswhich have a marked effect on the second stratum, although they are not present in a discrete form in the second stratum. Accordingly, for practical purposes, the second stratum will provide adequate oxidation and tarnish resistance.

The copper oxides of the first stratum can be readily removed, for example, by dissolving them away with dilute sulfuric acid solution leaving the improved second stratum of the present invention. As pointed out above, the second stratum itself provides a high degree of resistance to further oxidation and to outdoor tarnishing. However, if it becomes necessary to remove the second stratum, as by pickling, bufling, etching or some mechanical forming operation, or if the second stratum is mechanically damaged, then continued protection is alforded by the improved second layer, which is oxidation and tarnish resistant. The Group V element effects an improvement in the second layer, although a less marked improvement than is effected in the second stratum. As with the second stratum, the Group V element is not present in discrete form in the second layer.

The depth of the second layer will vary widely depending upon the particular treatment conditions, with in all cases the thickness being at least 50 angstroms. In general, in order to provide reasonable oxidation protection, the second layer should be a minimum of 50 angstroms in depth and preferably at least 200 angstroms. The maximum depth of the second layer is completely dependent upon the treatment conditions and the particular system utilized, that is, longer holding times and higher temperatures will provide a thicker second layer. Normally,

however, a second layer of around 2 mils is the preferred value, although for some uses it may be preferable to get a thicker second layer or even if desired obtain a second layer which comprises all of the rest of the alloy.

The second layer or highly oxidation resistant layer is characterized by containing a discrete dispersion of complex oxides including at least one of said two elements. The discrete dispersion is present in the metal matrix.

In accordance with the present invention the second layer is bright and shiny in appearance and provides extensive oxidation and tarnish resistance over a wide temperature range at or below the formation temperature range. In other words, oxidation and tarnish resistance is provided in a bright and shiny alloy having characteristics desired in alloys of this type over a wide temperature range up to the temperature of the heat treatment step. This second layer behaves chemically as if it were a more noble metal than copper, i.e., it resists chemical attack by strong chemical reagents which are normally used for pickling copper.

Beneath the second layer is normally the copper base alloy itself. This base would normally have only the original oxidation resistance in the absence of the oxidation resistant layer of the present invention, but would not have the enhanced resistance.

It is particularly surprising in accordance with the present invention that the addition of a group V element greatly enhances the oxidation and tarnish resistance of the second stratum, especially the tarnish resistance. Furthermore, the oxidation and tarnish resistance of the second layer is also improved, especially the oxidation resistance.

The cobalt, cerium or iron additions provide still further improvement. Oxidation at elevated temperature causes grain growth. The cobalt, cerium or iron additions form a fine dispersion of the additive and/or intermetallic compounds formed with them which inhibits grain growth. Thus, the alloy of the present invention contains a fine dispersion rich in cobalt, cerium or iron.

The present invention and improvements resulting therefrom will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE I A series of copper base alloys were prepared utilizing high purity copper and high purity alloying additions. The alloys were prepared by tilt mold casting into 1% x 1% x 4 inch shape, heating to 1600 F. (871 C.), hot rolling in a number of passes to 0.190 inch, and cold rolling and annealing into 10 mil sheet. The resultant alloys had the compositions indicated in the Table I below where amounts of ingredients are percentages by weight. In all the alloys, the balance was essentially copper.

Alloys A, B, and C, prepared in Example I, in 10 mil sheet, cold rolled form, were carefully cleaned and heated in air for two hours at various temperatures from 350 to 800 C. The weight gain in micrograms per square centimeter is shown in Table II below.

TABLE II Weight Gain in Micrograms Per Square Centimeter 350 C. 450 C. 600 C. 800 C.

It is apparent that with alloys B and C film growth has virtually stopped at a lower oxygen uptake at temperatures of 600 C. or less, i.e., those alloys with phosphorus or phosphorus and cobalt present.

EXAMPLE III spotted; alloys B and Cthere were no mottling or spotting on any of the samples and all samples were bright and shiny. Those alloy B and C samples treated at 500 C., and 450 C. showed a slight haze but were still shiny.

EXAMPLE IV The following example demonstrates the unique character of the second stratum of the alloys of the present invention. Alloys A and B after the treatments of Example lI oxidized at 600 C., were dipped in dilute H 80 to remove the first stratum and to bare the second stratum. The parallel resistance of a fixed area of film was measured by means of an AC capacitance bridge. At a frequency of one kilocycle, alloy B attained a peak resistance of 80,000 ohms for a one square centimeter area compared to only 20,000 ohms for alloy A. This demonstrates that alloy B with the phosphorus addition has four times the electrical resistance as alloy A and is four times as good an electrical insulator.

EXAMPLE V The following example demonstrates that the alloy of the present invention has improved oxidation resistance in the second layer. Alloys A and B were oxidized as in Example II for two hours at 800 C. The first layer of both samples was removed, including both the first and second stratum, by strong acid etching, removing about 5000 micrograms per square centimeter for each sample. Each sample was then reoxidized for two hours at 450 C. Alloy B registered no weight gain within the limits of detectability of the microbalance (approximately 0.5 microgram per square centimeter), while alloy A registered a weight gain of 2 micrograms per square centimeter.

EXAMPLE VI The following example demonstrates the unique character of the second stratum in alloy C. Alloy C after the treatment of Example II oxidized at 650 C., was treated as in Example IV and the parallel resistance measured as in Exmple IV. At a frequency of one kilocycle, alloy C attained a peak resistance of 103,000 ohms for a one square centimeter area.

EXAMPLE VH In the following example alloy C was oxidized as in Example II for two hours at 650 C. The first stratum was removed by sulfuric acid pickling and the second stratum was removed by means of a gas propelled abrasive unit. The sample was exposed for several months on a rooftop in an industrial atmosphere and retained its original golden luster, with no mottling and no haze.

EXAMPLE VIII Alloys D and E, prepared in Example I, in mil sheet, cold rolled form were treated as in Example H for two hours at 800 C. The samples were dipped in dilute H 80, to remove the first stratum and to bare the second stratum. The resultant samples were bright and shiny. The samples were exposed for several months as in Example VII and retained their original golden luster, with no mottling and no haze.

What is claimed is:

1. A process for the preparation of a copper base alloy capable of substantial resistance to oxidation which comprises:

(A) providing a copper base alloy containing from 0.01 to 0.50% by weight of a Group V element selected from the group consisting of phosphorus, arsenic, antimony, bismuth and mixtures thereof, and from 2.0 to 25.0 percent by weight of two elements, with the ratio of the first to the second of said elements being from 0.03:1 to 10:1, the first of said elements being selected from the group consisting of: aluminum; gallium; indium; and beryllium, the second of said elements being selected from the group con- 8 sisting of: silicon; germanium; tin; and beryllium, provided that when beryllium is the second element, aluminum is the first element; and

(B) heating said alloy in an oxidizing environment for at least one minute at a temperature of from to 850 C. to form (1) a first outside layer 25 to 5000 angstroms in depth, said first layer containing (a) a first outermost stratum rich in copper oxides, and (b) a second innermost stratum rich in oxides of said first element, and (2) a second oxidation resistant layer immediately beneath said first layer containing a discrete dispersion of a complex oxide including at least one of said two elements, said second layer being of a thickness of at least 50 angstroms.

2. A process for the preparation of a copper base alloy capable of substantial resistance to oxidation which comprises:

(A) providing a copper base alloy containing from 0.01 to 0.50% by weight of a Group V element selected from the group consisting of phosphorus, arsenic, antimony, bismuth and mixtures thereof, and from 2.0 to 25.0 percent by weight of two elements, with the ratio of the first to the second of said elements being from 0.03:1 to 10:1, the first of said elements being selected from the group consisting of: aluminum; gallium; indium; and beryllium, the second of said elements being selected from the group consisting of: silicon; germanium; tin; and beryllium, pro vided that when beryllium is the second element, aluminum is the first element; and

(B) heating said alloy in an oxidizing environment for at least one minute at a temperature of from 400 to 850 C. to form (1) a first outside layer 25 to 5000 angstroms in depth, said first layer containing (a) a first outermost stratum rich in copper oxides, and (b) a second innermost stratum rich in oxides of said first element, and (2) a second oxidation resistant layer immediately beneath said first layer containing a discrete dispersion of a complex oxide including at least one of said two elements, said second layer being of a thickness of at least 50 angstroms.

3. A process according to claim 2 wherein said first stratum is removed.

4. A process according to claim 2 wherein said alloy (A) contains from 0.05 to 5.0% by weight of a material selected from the group consisting of cobalt, cerium, iron and mixtures thereof.

5. A copper base alloy capable of substantial resistance to oxidation comprising:

(A) from 0.01 to 0.50% by weight of a Group V element selected from the group consisting of phosphorus, arsenic, antimony, bismuth and mixtures thereof, and from 2.0 to 25.0 percent by weight of two elements, with the ratio of the first to the second of said elements being from 0.03:1 to 10: 1, the first of said elements being selected from the group consisting of: aluminum; gallium; indium; and beryllium, the second of said elements being selected from the group consisting of: silicon; germanium; tin; and beryllium, provided that when beryllium is the second element, aluminum is the first element; and

(B) said alloy having an inner oxidation resistant layer of a thickness of at least 50 angstroms containing a discrete dispersion of a complex oxide including at least one of said alloying additions; and

(C) said alloy having an outer stratum less than 5000 angstroms in depth rich in oxides of said first alloying addition.

6. An alloy according to claim 5 wherein said alloy has an outermost stratum rich in copper oxides.

9 10 7. An alloy according to claim 5 including from 0.05 to 3,341,369 9/1967 Caule et a1 1483 5.0% by weight of a material selected from the group con- 3,347,717 10/ 1967 Eichelman et a1. 75162 X sisting of cobalt, cerium, iron and mixtures thereof. 3,366,477 1/ 1968 Eichelman et a1. 75153 X References Cited 5 CHARLES N. LOVELL, Primary Examiner UNITED STATES PATENTS U.S.Cl. X.R.

3,259,491 7/1966 Pryor 75162 75-153; l482, 11.5, 31.5