US3835007A - Process for bonding copper or iron to titanium or tantalum - Google Patents

Abstract

COPPER OR IRON ARE SECURELY BONDED TO TITANIUM OR TANTALUM SUBSTRATE METAL BY INITIALLY SUBJECTING THE SUBSTRATE METAL TO IONIC BOMBARDMENT IN WHICH THE SUBSTRATE METAL PERFORMS THE ROLE OF A CATHODE AND THEN TO CATHODE SPUTTERING IN WHICH THE SUBSTRATE METAL PERFORMS THE ROLE OF AN ANODE, AND THE COPPER OR IRON THE ROLE OF A CATHODE. THEREAFTER, THE BONDED COPPER OR IRON IS SUPPLEMENTED BY ADDITIONAL DEPOSITS BY CONVENTIONAL MEANS SUCH AS ELECTRODEPOSITION, ETC. SUPERIOR INDUSTRIAL PRODUCTS RESULTING FROM THE PROCESS ARE USEFUL AS ANODES IN ELECTROLYSIS CELLS AND AS HEAT EXCHANGERS.

Description

Sept. 10, 1974 RA EI'AL PROCESS FOR BONDING COPPER 0R 3,835,007 IRON T0 TITANIUM on TANTALUM Filed D80. .13. 1972 United States Patent PROCESS FOR BONDING COPPER OR IRON TO TITANIUM OR TANTALUM Alain Ferat, Robert Masotti, and Hubert Chavanel, Lyon, France, assignors to Rhone-Progil, Paris, France Filed Dec. 13, 1972, Ser. No. 314,858 Claims priority, application France, Dec. 24, 1971, 7147874 Int. Cl. C23c /80 US. Cl. 204-192 7 Claims ABSTRACT OF THE DISCLOSURE Copper or iron are securely bonded to titanium or tantalum substrate metal by initially subjecting the substrate metal to ionic bombardment in which the substrate metal performs the role of a cathode and then to cathode sputtering in which the substrate metal performs the role of an anode, and the copper or iron the role of a cathode. Thereafter, the bonded copper or iron is supplemented by additional deposits by conventional means such as electrodepositiou, etc. Superior industrial products resulting from the process are useful as anodes in electrolysis cells and as heat exchangers.

BACKGROUND OF THE INVENTION The present invention relates to a new process of bond ing copper or iron to titanium or tantalum and to the new industirial products resulting from it.

Bonding of these metals has been known for many years and has employed such processes as rolling, plating, hammering, co-drawing, classical or ultra-sonic soldering. Those techniques are intended to permit one to bring together as closely as possible sheets or plates of titanium or tantalum and of another metal. This prior art bonding has also been achieved by electro-deposition of a metal on a sheet or plate of titanium 'or tantalum.

The results obtained by utilization of all those interesting conventional prior art methods are, however, often insufiicient for the contemplated applications of the bonded product. Indeed, because of a lack of homogeneity and adherence between the surfaces of the two metals, the bonding lacked tenacity and tear resistance between the two metals was relatively low.

The present invention contemplates, by using the process according to invention, to provide an important solution of the problem of bonding titanium or tantalum to copper or iron.

It is, accordingly, an object of the invention to provide a superior bonding of copper or iron to titanium or tantalum.

It is another object of the present invention to provide an economical method of tenaciously bonding these metals.

It is also an object of the invention to provide a superior bonded product of these metals.

Other objects of the invention will be apparent to those skilled in the art from the present description, taken in conjunction with the appended drawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 'is a plan view of bonded sheets of copper (Cu) and titanium (Ti) in accordance with the invention, which are employed to conduct a conductivity test, to be described hereinbelow, showing one of the important advantages of the bonded products of the invention.

FIG. 2 is an elevation of the bonded sheets of FIG. 1.

GENERAL DESCRIPTION OF THE INVENTION In general the present invention comprises first depositing on titanium or tantalum, in accordance with certain conditions, a thin adhering layer of the contemplated metal, copper or iron, the layer having a very strong adherence or bond with the support metal, titanium or tantalum, then of increasing this adhering layer by adding additional copper or iron by any known means.

To obtain a good adherence or bonding of the adhering metal layer on the support metal, it is necessary that the support metal surface is perfectly clean and in the free metal state, on which the adhering metal layer is deposited under conditions of the invention which avoid the formation of brittle compounds. Cathodic pulverization of copper or iron on the metal support, in accordance with the conditions of the invention provides a satisfactory bond- 'ing of the adhering layer of copper or iron.

The present process, consists of in a first stage, depositing a thin adhering layer of copper or iron on the support metal, then in a second stage, adding by any known way additional amounts of deposited metal layer. This process is characterized in that the supporting metal (titanium or tantalum) is first subjected to a mechanical and/or chemical cleaning treatment, then to an ionic bombardment in a residual atmosphere of rare gas and receives afterwards a copper or iron deposit by cathodic sputtering of one of these metals in a residual atmosphere of rare gas at a temperature of less than 500 C., the resulting adhering layer of copper or iron being subsequently supplemented in any known way.

It is necessary to employ a temperature less than 500 C. since in the range of 500 C. and upward, intermetal diffusion is no longer negligible and leads to the compounds Ti (Me) or Ta (Me) which are highly brittle (Me being the deposited metal, x and y being integers). Cathodic sputtering of copper or iron on the support metal after ionic bombardment of the support metal, may be made on a cooled support metal as well as at high temperature resulting from the ionic bombardment. However, it is advantageous for the deposition of bonding metal to be made in a temperature range of about 300 to 400 C. Under these conditions, it is possible to deposit copper or iron bonding layer on the support metal, which layer has a thickness of between about 0.5 and 5 microns. This layer is then thickened or supplemented in any known way, such as electro-deposition, etc. There is then obtained a final layer having a thickness comprised between about 0.5 and 5 millimeters or more.

The techniques of cathodic sputtering are characterized by depositing a metal by electrical discharge in a low pressure of inert gas.

The apparatus for cathodic sputtering consists of a vacuum enclosure, a pumping system, a high voltage electrical feed and an inert gas introduction system.

The supporting metal (titanium or tantalum), before being introduced in the vacuum enclosure is subjected to a thermal and/or chemical treatment of sanding and/0r degreasing. This supporting metal and the metal to be pulverized are put in electrode position in enclosure containing a rare gas residual atmosphere (such as argon). In the first stage of ionic bombardment the supporting metal is positioned cat'hodically in applying negative high voltage. It becomes the cathode for some time and a small portion of the surface is pulverized. The other metal to be bonded is protected during this operation, by means of a moving mask, against becoming contaminated with particles eminating from the support metal. This ionic bombardment of the support has for its purpose to degas and scour the surface which is to receive the deposit of other metal, by removing oxide layers, traces of hydrocarbons, fats, etc. As a result, the surface of the support metal is converted as closely as possible to the pure metallic state.

The supporting metal is next disconnected from the high voltage source and placedin the anode position ready to receive the deposit resulting from sputtering of the metal to be bonded (copper or iron), which is placed in the cathode position. The copper or iron metal is cleared of its mask and then connected to the high voltage source. Cathode sputtering on the anode is then conducted in a residual atmosphere of pure rare gas, such as argon, radon, etc.

As a result of the foregoing conditions, the process of the invention provides a very strongly bonded layer or coating of copper or iron on titanium or tantalum. Finally, after supplementing the bonded layer of copper or iron by conventional means, there is obtained a product which has mechanical and electrical characteristics high- 1y desirable for the contemplated applications.

DETAILED DESCRIPTION OF THE INVENTION In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are given. It should be understood, however, that .this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims. In the examples which follow, and throughout the specification, the quantities of material are expressed in terms of parts by weight, unless otherwise specified.

I. EXAMPLES OF BONDING COPPER TO TITANIUM(EXAMPLES 1-6) Although the nature and texture of the bonding produced by the present invention are difiicult to define by the classical physico-chemical means, the mechanical and electrical performances of the bonding resulting from cathodic sputtering are readily ascertainable. Those characteristics will be readily appreciated by comparison with the performances obtained by depositions achieved by conventional means, such as electro-deposition, shoopage, etc.

Example I A square titanium plate of 100 mm. on each side and 8/ mm. thick was scoured by subjecting it to a fluonitric attack by immersion for 2 minutes in a mixture of nitric and hydrofluoric acids, washed with water, then with acetone and finally dried.

Next are cleansed plate was introduced in a vacuum enclosure, the pressure of which was decreased to 10" torr. First, high voltage was connected to a copper target situated in front of the titanium plate and submitted in this way to a presputtering to remove copper surface impurities which deposit on a moving mask placed between the copper target and titanium plate or support. Next, the titanium ionic bombardment phase was achieved by connecting the titanium plate to a high voltage source of continuous current of 3000 volts, under a partial pressure of pure argon, at approximately 40 10- torr. pressure for 30 minutes. The titanium plate temperature was stabilized at the end of this operation at about 400 C. During all of the operation, the freshly cleaned copper target was protected by the moving mask. Next the high voltage was connected to the copper target, and mask being removed, copper sputtering was made on the freshly scoured titanium, at a temperature near 350 C. This copper sputtering is made under the residual atmosphere of pure argon of 20X 10- torr. pressure, at 3000 volts, until obtaining a copper layer nearly 1 micron thick over portions of the titanium sheet (average deposit speed 300 angstroms per minute). The product obtained is illustrated by FIGS. 1 and 2 of the drawings. The titanium plate with its very tenaciously adhering thin copper layer is removed from the enclosure after cooling for about minutes.

The thickness of the thin copper coating is increased by electro-deposition of an additional copper layer of 1 mm. under the following conditions: The work iece was introduced as the cathode into an acid electrolysis bath of copper sulfate containing 250 grams per liter of cupric sulfate pentahydrate, 75 grams per liter of sulfuric acid (having a specific gravity of 1.66) in distilled Water. The electrolysis bath was stirred while at room temperature. The anode was of copper. The density of the electrolysis current was 3 amperes per square decimeter.

Example 2 Example 1 was repeated but the titanium plate was treated by sanding with Fontainebleau sand (40-80 microns) before the fluonitric attack.

Example 3 Example 1 was repeated, except that the copper deposition was made on a titanium plate freshly scoured and cooled for 30 minutes, at a greater speed, namely, 600 angstroms per minute.

Example 4 Example 1 was repeated, except that the titanium sheet was treated by sanding before the fiuonitric attack and the copper deposition was made on titanium while at room temperature at a speed of 600 angstroms per minute.

Example 5 Example 1 was repeated, except that the titanium plate was not subjected to any fluonitric attack.

Example 6 Example 1 was repeated, except that the titanium plate was not subjected to fluoronitric attack, but instead to a sanding with corundum having a granule size of about 250 microns.

II. EXAMPLE OF BONDING IRON TO TITANIUM Example 7 Example 1 was repeated, but copper was replaced by iron in producing the iron bonding on the titanium sheet and the iron coating was then coated with a copper deposit by electro-deposition under the following conditions. The workpiece was introduced as the cathode in an electrolysis bath containing 100 grams per liter of cupric sulfate pentahydrate, cc. per liter of diethylenetriamine and 10 cc. per liter of ammonium sulfate, all in distilled water. The deposition was conducted maintaining the bath at a temperature of about 60 C. with the electrolysis current density being about 4 amperes per square decimeter. The anode was of copper.

III. EXAMPLE OF BONDING COPPER TO TANTALUM Example 8 Example 1 was repeated, except that the titanium plate was replaced by one of tantalum of the same dimensions.

IV. EXAMPLE OF BONDING IRON TO TANTALUM Example 9 Example 7 was repeated, except that the titanium plate was replaced by one of tantalum of the same dimensions.

Various tests were made to compare the qualities of the bonding resulting from utilization of the process of the invention with bondings obtained with methods of the prior art.

ADHERENCE On the titanium sample sheet covered with a bonded copper or iron coating layer obtained by cathodic sputtering treatment of the several examples, surfaces of 2 mm. were delimited and protected with a silicone coating. The whole was then subjected to attack by nitric acid which dissolves copper or iron layer where it is not protected, by

silicone. Thus islets are obtained on titanium, presenting a copper or iron bonded layer which was then thickened with copper by electro-deposition until a thickness was obtained which was sufficient for achieving a tin brazing solder. After being brazed, a device was obtained allowing one to measure the tear resistance under the influence of a traction stress. Sheets of titanium bonded with copper by prior art methods were also subjected to the same treat ment. The comparative adhesion test results are shown in Table 1, below.

electro-deposition without any intermediary bonded layer 0.2 Copper layer deposited directly on titanium by shoopage without any intermediary bonded layer 0.2

MEASURE OF CONDUCTIVITY In a titanium sample covered with a copper bonded layer in accordance with the invention, thickened by electro-deposi-tion of additional copper, a current of 0.5 ampere was passed and the difference in potential between points about cm. apart was measured.

The sample geometry was that shown in accordance with the appended drawings. The difference in potential was measured at various points; 3 measures were made between points situated on titanium and copper, on copper alone, and on titanium alone. The following results were obtained, with a titanium thickness of 8/ 10 millimeter and a copper thickness of ll/ 10 millimeters:

Points position Difference in Potential Ti-Cu 0.85 X 10* volts Cu-Cu 0.65 10- volts Ti-Ti 0.85 X 10- volts The results obtained on a titanium plate of 8/10 millimeter without any copper deposition, was:

Ti-Ti 14.5 X 10 volts Calculating this value for 19/20 millimeters, which is the thickness of the plate covered with copper, the result obtained is:

Ti-Ti 6.1 10- volts It is well known that electrical current is always inclined to choose the path presenting the least resistance. The interpretation of results hereinabove permits one to determine that the electrical current in a titanium sample, covered with copper bonding by the process of the invention, is inclined to bypass copper through the achieved titanium-copper bonding, because the latter has a lower resistance. Therefore, there is a very good electrical bonding between titanium and copper.

FOLDING AT 90 C.

Folding tests at 90 C. have shown that copper-titanium bonding achieved in accordance with the invention did not become detached. A notable detachment is observed on a titanium sample covered directly with copper by electrodeposition without any intermediary bonded layer and on a titanium sample covered of copper by rolling.

The applications of the bonding process of the invention have shown themselves to be especially interesting in the case of titanium and tantalum utilisation for their characteristics of corrosion resistance, the achieved bonding being obliged to have at least one of the following properties:

(1) Adherence homogeneity on the whole of the common surface, without brittleness (2) Good electrical conductibility (application in anodes for electrolysis) (3) Good thermal conductibility (applications in heat exchangers) The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A process of bonding a substrate metal selected from the class consisting of titanium and tantalum with a coating metal selected from the class consisting of iron and copper, comprising, in a first stage, depositing a thin bond ing layer of coating metal on said substrate metal, and, in a second stage, of thickening the deposited layer in any known method with additional metal, characterized in that said substrate metal is first subjected to a preliminary cleaning treatment, then to an ionic bombardment in a residual atmosphere of rare gas and afterwards a bonded layer of said coating metal is deposited by cathodic sputtering on said substrate metal in residual atmosphere of rare gas at a temperature lower than 500 C, said bonded layer of said coating metal being thickened by addition of more metal.

2. A process according to Claim 1, wherein said cleaning treatment consists of a mechanical treatment.

3. A process according to Claim 1, wherein said cleaning treatment of said substrate metal is a sanding with a material selected from the class consisting of fine sand and corundum.

4. A process according to Claim 1, wherein said cleaning of said substrate metal is made by scouring with a mixture of nitric and hydrofluoric acids.

5. A process according to Claim 1, wherein said substrate metal, after cleaning treatment, is connected in a cathodic sputtering device, first in the form of a target cathode, which sputters, under ionic bombardment, then in the form of an anode which receives a deposit of coating metal which is coupled as a cathode and which sputters.

6. A process according to Claim 1, wherein the thickness of the bonding layer of coating metal deposited by cathodic sputtering is increased by electrodeposition.

7. A process according to Claim 1, wherein said cleaning treatment consists of a chemical treatment.

References Cited UNITED STATES PATENTS 3,393,446 7/1968 Hughes et al 204192 X 3,479,269 11/1969 Byrnes Jr. et al 204192 3,507,248 4/1970 Seeley et al. 204298 X 3,649,503 3/1972 Terry 204192 3,723,276 3/1973 Lane et al. 204192 JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner

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