Coated Article

This invention relates to articles, in particular brass or zinc articles, with a multi-layer decorative and protective coating thereon.

It is currently the practice with various brass or zinc articles such as faucets, faucet escutcheons, door knobs, door handles, door escutcheons and the like to first buff and polish the surface of the article to a high gloss and to then apply a protective organic coating, such as one comprised of acrylics, urethanes, epoxies, and the like, onto this polished surface. This system has the drawback that the buffing and polishing operation, particularly if the article is of a complex shape, is labor intensive. Also, the known organic coatings are not always as durable as desired, and are susceptible to attack by acids. It would, therefore, be quite advantageous if brass or zinc articles, or indeed other metallic articles, could be provided with a coating which gave the article the appearance of highly polished brass, provided wear resistance and corrosion protection, and also provided improved acid resistance. The present invention provides such a coating.

The present invention is directed to an article, such as a plastic, ceramic, or metallic article, preferably a metallic article, having a multi-layer coating on at least a portion of its surface. More particularly, it is directed to an article or substrate, particularly a metallic article such as stainless steel, aluminum, brass or zinc, having deposited on its surface multiple superposed metallic layers of certain specific types of metals or metal compounds. The coating is decorative and also provides corrosion resistance, wear resistance and improved resistance to acids. The coating provides the appearance of highly polished brass, i.e. has a brass color tone. Thus, an article surface having the coating thereon simulates a highly polished brass surface.

In one embodiment a first layer deposited directly on the surface of the substrate is comprised of copper. The copper layer may be only one layer or it may comprise a duplex copper layer, e.g., an alkaline copper layer and an acid copper layer. Over the copper layer is a layer comprised of nickel. The nickel layer may be monolithic or it may consist of two different nickel layers such as, for example, a semi-bright nickel layer deposited on the surface of the copper layer and a bright nickel layer superimposed over the semi-bright nickel layer. Disposed over the nickel layer is a layer comprised of chrome. Over the chrome layer is a layer comprised of a non-precious refractory metal or non-precious refractory metal alloy such as zirconium, titanium, hafnium, tantalum, or zirconium-titanium alloy, preferably zirconium, titanium, or zirconium-titanium alloy. Over the non-precious refractory metal or metal alloy layer is a sandwich layer comprised of a plurality of alternating layers of non-precious refractory metal compound or non-precious refractory metal alloy compound and non-precious refractory metal or metal alloy. A layer comprised of zirconium compound, titanium compound, hafnium compound, tantalum compound or zirconium-titanium alloy compound, preferably a titanium compound, a zirconium compound or a zirconium-titanium alloy compound such as zirconium nitride, is disposed over the sandwich layer. Over the layer comprised of zirconium compound, titanium compound or zirconium-titanium alloy compound is a top layer comprised of (i) zirconium oxide, titanium oxide or zirconium-titanium alloy oxide, or (ii) the reaction products of a non-precious refractory metal or metal alloy such as zirconium, titanium, zirconium-titanium alloy, hafnium, and the like, oxygen and nitrogen.

The copper, nickel and chrome layers are preferably applied by electroplating. The refractory metal such as zirconium, refractory metal compound such as zirconium compound, and zirconium oxide, titanium oxide, or zirconium-titanium alloy oxide layers are applied by vapor deposition such as physical vapor or chemical vapor deposition.

FIG. 1 is a cross-sectional view, not to scale, of a portion of the substrate having the multi-layer coating deposited on its surface; and

FIG. 2 is a view similar to FIG. 1 of another embodiment of the instant invention illustrating a duplex nickel layer.

The article or substrate 10 can be comprised of any platable material such as plastic, ceramic, metal or metallic alloy. In one embodiment it is a platable metal or metallic alloy such as copper, steel, brass, zinc, aluminum, nickel alloys, and the like. In a preferred embodiment the substrate is brass or zinc.

A copper layer or layers 11 are deposited on at least a portion of the article surface 10 by, for example, conventional and well known electroplating processes. Copper electroplating processes and copper electroplating baths are conventional and well known in the art. They include the electroplating of acid copper and alkaline copper. They are described, inter alia, in U.S. Pat. Nos. 3,725,220; 3,769,179; 3,923,613; 4,242,181 and 4,877,450, the disclosures of which are incorporated herein by reference.

The preferred copper layer 11 is selected from alkaline copper and acid copper. The copper layer may be monolithic and consist of one type of copper such as alkaline copper 11a or acid copper 11b, or it may comprise two different copper layers such as a layer comprised of alkaline copper 11a and a layer comprised of acid copper 11b.

The thickness of the copper layer is generally in the range of from at least about 100 millionths (0.0001) of an inch, preferably at least about 150 millionths (0.00015) of an inch to about 3,500 millionths (0.0035), preferably about 2,000 millionths (0.002) of an inch.

When a duplex copper layer is present comprised of, for example, an alkaline copper layer and an acid copper layer, the thickness of the alkaline copper layer is generally at least about 50 millionths (0.00005) of an inch, preferably at least about 75 millionths (0.000075) of an inch. The upper thickness limit is generally not critical. Generally, a thickness of about 1,500 millionths (0.0015) of an inch, preferably about 1,000 millionths (0.001) of an inch should not be exceeded. The thickness of the acid copper layer is generally at least about 50 millionths (0.0005) of an inch, preferably at least about 75 millionths (0.00075) of an inch. The upper thickness limit is generally not critical. Generally, a thickness of about 1,500 millionths (0.0015) of an inch, preferably about 1,000 millionths (0.001) of an inch should not be exceeded.

The nickel layer 13 may be deposited on the surface of the copper layer 11 by conventional and well-known electroplating processes. These processes include using a conventional electroplating bath such as, for example, a Watts bath as the plating solution. Typically such baths contain nickel sulfate, nickel chloride, and boric acid dissolved in water. All chloride, sulfamate and fluoroborate plating solutions can also be used. These baths can optionally include a number of well known and conventionally used compounds such as leveling agents, brighteners, and the like. To produce specularly bright nickel layer at least one brightener from class I and at least one brightener from class II is added to the plating solution. Class I brighteners are organic compounds which contain sulfur. Class II brighteners are organic compounds which do not contain sulfur. Class II brighteners can also cause leveling and, when added to the plating bath without the sulfur-containing class I brighteners, result in semi-bright nickel deposits. These class I brighteners include alkyl naphthalene and benzene sulfonic acids, the benzene and naphthalene di- and trisulfonic acids, benzene and naphthalene sulfonamides, and sulfonamides such as saccharin, vinyl and allyl sulfonamides and sulfonic acids. The class II brighteners generally are unsaturated organic materials such as, for example, acetylenic or ethylenic alcohols, ethoxylated and propoxylated acetylenic alcohols, coumarins, and aldehydes. These Class I and Class II brighteners are well known to those skilled in the art and are readily commercially available. They are described, inter alia, in U.S. Pat. No. 4,421,611 incorporated herein by reference.

The nickel layer can be comprised of a monolithic layer such as semi-bright nickel or bright nickel, or it can be a duplex layer containing two different nickel layers, for example, a layer comprised of semi-bright nickel and a layer comprised of bright nickel. The thickness of the nickel layer is generally in the range of from about 100 millionths (0.000100) of an inch, preferably about 150 millionths (0.000150) of an inch to about 3,500 millionths (0.0035) of an inch.

In one embodiment as illustrated in FIG. 2, the nickel layer 13 is a duplex nickel layer and is comprised of two different nickel layers 14 and 16. Layer 14 is comprised of semi-bright nickel while layer 16 is comprised of bright nickel. This duplex nickel deposit provides improved corrosion protection to the underlying substrate. The semi-bright, sulfur-free plate 14 is deposited by conventional electroplating processes directly on the surface of substrate 10. The substrate 10 containing the semi-bright nickel layer 14 is then placed in a bright nickel plating bath and the bright nickel layer 16 is deposited on the semi-bright nickel layer 14.

The thickness of the semi-bright nickel layer and the bright nickel layer is a thickness effective to provide improved corrosion protection. Generally, the thickness of the semi-bright nickel layer is at least about 50 millionths (0.00005) of an inch, preferably at least about 100 millionths (0.0001) of an inch, and more preferably at least about 150 millionths (0.00015) of an inch. The upper thickness limit is generally not critical and is governed by secondary considerations such as cost. Generally, however, a thickness of about 1,500 millionths (0.0015) of an inch, preferably about 1,000 millionths (0.001) of an inch, and more preferably about 750 millionths (0.00075) of an inch should not be exceeded. The bright nickel layer 16 generally has a thickness of at least about 50 millionths (0.00005) of an inch, preferably at least about 125 millionths (0.000125) of an inch, and more preferably at least about 250 millionths (0.00025) of an inch. The upper thickness range of the bright nickel layer is not critical and is generally controlled by secondary considerations such as cost. Generally, however, a thickness of about 2,500 millionths (0.0025) of an inch, preferably about 2,000 millionths (0.002) of an inch, and more preferably about 1,500 millionths (0.0015) of an inch should not be exceeded. The bright nickel layer 16 also functions as a leveling layer which tends to cover or fill in imperfections in the substrate.

Disposed over the nickel layer 13, preferably the bright nickel layer 16, is a layer 21 comprised of chrome. The chrome layer 21 may be deposited on layer 16 by conventional and well known chromium electroplating techniques. These techniques along with various chrome plating baths are disclosed in Brassard, "Decorative Electroplating--A Process in Transition", Metal Finishing, pp. 105-108, June 1988; Zaki, "Chromium Plating", PF Directory, pp. 146-160; and in U.S. Pat. Nos. 4,460,438, 4,234,396, and 4,093,522, all of which are incorporated herein by reference.

Chrome plating baths are well known and commercially available. A typical chrome plating bath contains chromic acid or salts thereof, and catalyst ion such as sulfate or fluoride. The catalyst ions can be provided by sulfuric acid or its salts and fluosilicic acid. The baths may be operated at a temperature of about 112.degree.-116.degree. F. Typically in chrome plating a current density of about 150 amps per square foot, at about 5 to 9 volts is utilized.

The chrome layer generally has a thickness of at least about 2 millionths (0.000002) of an inch, preferably at least about 5 millionths (0.000005) of an inch, and more preferably at least about 8 millionths (0.000008) of an inch. Generally, the upper range of thickness is not critical and is determined by secondary considerations such as cost. However, the thickness of the chrome layer should generally not exceed about 60 millionths (0.00006) of an inch, preferably about 50 millionths (0.00005) of an inch, and more preferably about 40 millionths (0.00004) of an inch.

Disposed over chrome layer 21 is a layer 22 comprised of a non-precious refractory metal or metal alloy such as hafnium, tantalum, zirconium, titanium or zirconium-titanium alloy, preferably zirconium, titanium or zirconium-titanium alloy, and more preferably zirconium.

Layer 22 is deposited on layer 21 by conventional and well known techniques including vapor deposition such as cathodic arc evaporation (CAE) or sputtering, and the like. Sputtering techniques and equipment are disclosed, inter alia, in J. Vossen and W. Kern "Thin Film Processes II", Academic Press, 1991; R. Boxman et al "Handbook of Vacuum Arc Science and Technology", Noyes Pub., 1995; and U.S. Pat. Nos. 4,162,954, and 4,591,418, all of which are incorporated herein by reference.

Briefly, in the sputtering deposition process a refractory metal (such as titanium or zirconium) target, which is the cathode, and the substrate are placed in a vacuum chamber. The air in the chamber is evacuated to produce vacuum conditions in the chamber. An inert gas, such as Argon, is introduced into the chamber. The gas particles are ionized and are accelerated to the target to dislodge titanium or zirconium atoms. The dislodged target material is then typically deposited as a coating film on the substrate.

In cathodic arc evaporation, an electric arc of typically several hundred amperes is struck on the surface of a metal cathode such as zirconium or titanium. The arc vaporizes the cathode material, which then condenses on the substrates forming a coating.

Layer 22 has a thickness which is generally at least about 0.25 millionths (0.00000025) of an inch, preferably at least about 0.5 millionths (0.0000005) of an inch, and more preferably at least about one millionth (0.000001) of an inch. The upper thickness range is not critical and is generally dependent upon considerations such as cost. Generally, however, layer 22 should not be thicker than about 50 millionths (0.00005) of an inch, preferably about 15 millionths (0.000015) of an inch, and more preferably about 10 millionths (0.000010) of an inch.

In a preferred embodiment of the present invention layer 22 is comprised of titanium, zirconium or zirconium-titanium alloy, preferably zirconium, and is deposited by vapor deposition such as physical vapor deposition, e.g., by sputtering or cathodic arc evaporation.

A sandwich layer 26 comprised of alternating layers of a non-precious refractory metal compound or non-precious refractory metal alloy compound 28 and a non-precious refractory metal or non-precious refractory metal alloy 30 is deposited over the refractory metal or refractory metal alloy layer 22 such as zirconium or zirconium-titanium alloy. Such a structure is illustrated in FIGS. 1 and 2 wherein 22 represents the refractory metal or refractory metal alloy layer, preferably zirconium or zirconium-titanium alloy, 26 represents the sandwich layer, 28 represents a non-precious refractory metal compound layer or non-precious refractory metal alloy compound layer, and 30 represents a non-precious refractory metal layer or non-precious refractory metal alloy layer.

The non-precious refractory metals and non-precious refractory metal alloys comprising layers 30 include hafnium, tantalum, titanium, zirconium, zirconium-titanium alloy, zirconium-hafnium alloy, and the like, preferably zirconium, titanium, or zirconium-titanium alloy, and more preferably zirconium.

The non-precious refractory metal compounds and non-precious refractory metal alloy compounds comprising layers 28 include hafnium compounds, tantalum compounds, titanium compounds, zirconium compounds, and zirconium-titanium alloy compounds, preferably titanium compounds, zirconium compounds, or zirconium-titanium alloy compounds, and more preferably zirconium compounds. These compounds are selected from nitrides, carbides and carbonitrides, with the nitrides being preferred. Thus, the titanium compound is selected from titanium nitride, titanium carbide and titanium carbonitride, with titanium nitride being preferred. The zirconium compound is selected from zirconium nitride, zirconium carbide and zirconium carbonitride, with zirconium nitride being preferred.

The sandwich layer 26 generally has an average thickness of from about two millionths (0.000002) of an inch to about 40 millionths (0.00004) of an inch, preferably from about four millionths (0.000004) of an inch to about 35 millionths (0.000035) of an inch, and more preferably from about six millionths (0.000006) of an inch to about 30 millionths (0.00003) of an inch.

Each of layers 28 and 30 generally has a thickness of at least about 0.01 millionths (0.00000001) of an inch, preferably at least about 0.25 millionths (0.00000025) of an inch, and more preferably at least about 0.5 millionths (0.000005) of an inch. Generally, layers 28 and 30 should not be thicker than about 15 millionths (0.000015) of an inch, preferably about 10 millionths (0.00001) of an inch, and more preferably about 5 millionths (0.000005) of an inch.

A method of forming the sandwich layer 26 is by utilizing ion sputtering or cathodic arc evaporation to deposit a layer 30 of non-precious refractory metal such as zirconium or titanium followed by reactive ion sputtering or reactive cathodic arc evaporation to deposit a layer 28 of non-precious refractory metal nitride such as zirconium nitride or titanium nitride.

Preferably the flow rate of nitrogen gas is varied (pulsed) during vapor deposition such as reactive sputtering between zero (no nitrogen gas or a reduced value is introduced) to the introduction of nitrogen at a desired value to form multiple alternating layers of metal 30 and metal nitride 28 in the sandwich layer 26.

The number of alternating layers of refractory metal 30 and refractory metal compound 28 in sandwich layer 26 is generally at least about 2, preferably at least about 4, and more preferably at least about 6. Generally, the number of alternating layers of refractory metal 30 and refractory metal compound 28 in sandwich layer 26 should not exceed about 50, preferably about 40, and more preferably about 30.

In one embodiment of the invention, as illustrated in FIGS. 1 and 2, vapor deposited over the sandwich layer 26 is a layer 32 comprised of a non-precious refractory metal compound or non-precious refractory metal alloy compound, preferably a nitride, carbide or carbonitride, and more preferably a nitride.

Layer 32 is comprised of a hafnium compound, a tantalum compound, a titanium compound, a zirconium-titanium alloy compound, or a zirconium compound, preferably a titanium compound, a zirconium-titanium alloy compound, or a zirconium compound, and more preferably a zirconium compound. The titanium compound is selected from titanium nitride, titanium carbide, and titanium carbonitride, with titanium nitride being preferred. The zirconium compound is selected from zirconium nitride, zirconium carbonitride, and zirconium carbide, with zirconium nitride being preferred.

Layer 32 provides wear and abrasion resistance and the desired color or appearance, such as for example, polished brass. Layer 32 is deposited on layer 26 by any of the well known and conventional vapor deposition techniques such as, for example, reactive sputtering and reactive cathodic arc evaporation.

Reactive cathodic arc evaporation and reactive sputtering are generally similar to ordinary sputtering and cathodic arc evaporation except that a reactive gas is introduced into the chamber which reacts with the dislodged target material. Thus, in the case where zirconium nitride is the layer 32, the cathode is comprised of zirconium and nitrogen is the reactive gas introduced into the chamber. By controlling the amount of nitrogen available to react with the zirconium, the color of the zirconium nitride can be adjusted to be similar to that of brass of various hues.

Layer 32 has a thickness at least effective to provide abrasion resistance. Generally, this thickness is at least 0.1 millionths (0.0000001) of an inch, preferably at least 1 millionth (0.000001) of an inch, and more preferably at least 2 millionths (0.000002) of an inch. The upper thickness range is generally not critical and is dependent upon secondary considerations such as cost. Generally a thickness of about 30 millionths (0.00003) of an inch, preferably about 25 millionths (0.000025) of an inch, and more preferably about 20 millionths (0.000020) of an inch should not be exceeded.

Zirconium nitride is a preferred coating material as it most closely provides the appearance of polished brass.

In one embodiment of the invention a layer 34 comprised of the reaction products of a non-precious refractory metal or metal alloy, an oxygen containing gas such as oxygen, and nitrogen is deposited onto layer 32. The metals that may be employed in the practice of this invention are those which are capable of forming both a metal oxide and a metal nitride under suitable conditions, for example, using a reactive gas comprised of oxygen and nitrogen. The metals may be, for example, tantalum, hafnium, zirconium, zirconium-titanium alloy, and titanium, preferably titanium, zirconium-titanium alloy and zirconium, and more preferably zirconium.

The reaction products of the metal or metal alloy, oxygen and nitrogen are generally comprised of the metal or metal alloy oxide, metal or metal alloy nitride and metal or metal alloy oxy-nitride. Thus, for example, the reaction products of zirconium, oxygen and nitrogen comprise zirconium oxide, zirconium nitride and zirconium oxy-nitride. These metal oxides and metal nitrides including zirconium oxide and zirconium nitride alloys and their preparation and deposition are conventional and well known, and are disclosed, inter alia, in U.S. Pat. No. 5,367,285, the disclosure of which is incorporated herein by reference.

The layer 34 can be deposited by well known and conventional vapor deposition techniques, including reactive sputtering and cathodic arc evaporation.

In another embodiment instead of layer 34 being comprised of the reaction products of a refractory metal or refractory metal alloy, oxygen and nitrogen, it is comprised of non-precious refractory metal oxide or non-precious refractory metal alloy oxide. The refractory metal oxides and refractory metal alloy oxides of which layer 34 is comprised include, but are not limited to, hafnium oxide, tantalum oxide, zirconium oxide, titanium oxide, and zirconium-titanium alloy oxide, preferably titanium oxide, zirconium oxide, and zirconium-titanium alloy oxide, and more preferably zirconium oxide. These oxides and their preparation are conventional and well known.

Layer 34 containing (i) the reactive products of non-precious refractory metal or non-precious refractory metal alloy, oxygen and nitrogen, or (ii) non-precious refractory metal oxide or non-precious refractory metal alloy oxide generally has a thickness at least effective to provide improved acid resistance. Generally this thickness is at least about five hundredths of a millionth (0.00000005) of an inch, preferably at least about one tenth of a millionth (0.0000001) of an inch, and more preferably at least about 0.15 of a millionth (0.00000015) of an inch. Generally, layer 34 should not be thicker than about five millionths (0.000005) of an inch, preferably about two millionths (0.000002) of an inch, and more preferably about one millionth (0.000001) of an inch.

In another embodiment of the instant invention the vapor deposited layers are applied onto at least one nickel layer which is disposed over at least one copper layer. This embodiment is similar to that described hereinafore in FIGS. 1 and 2 except that the chrome layer 21 is absent. Thus a monolithic or duplex copper layer is disposed over at least a portion of the substrate surface, a monolithic or duplex nickel layer is electroplated over the copper layer, a non-precious refractory metal or metal alloy layer is vapor deposited over the nickel layer, and a sandwich layer comprised of a plurality of alternating layers of non-precious refractory metal compound or non-precious refractory metal alloy compound and a non-precious refractory metal or metal alloy is vapor deposited over the non-precious refractory metal or metal alloy layer. Over the sandwich layer is disposed, by vapor deposition, a non-precious refractory metal compound or non-precious refractory metal alloy compound. Over this layer is vapor deposited a layer comprised of (i) non-precious refractory metal oxide or non-precious refractory metal alloy oxide, or (ii) reaction products of non-precious refractory metal or non-precious refractory metal alloy, oxygen and nitrogen.

In yet another embodiment of the instant invention the vapor deposited layers are applied onto at least one copper layer which is applied, such as by electroplating, directly onto a portion of the substrate's surface. The copper layer, as in the preceding embodiments, may be an alkaline copper, an acid copper, or it may be a duplex copper layer comprised of an alkaline copper layer and an acid copper layer. The vapor deposited layers are the same as in the preceding embodiments and comprise a non-precious refractory metal or metal alloy disposed over the copper layer and a sandwich layer comprised of alternating layers of a non-precious refractory metal compound or non-precious refractory metal alloy compound and non-precious refractory metal or metal alloy disposed over the non-precious refractory metal or alloy. Over the sandwich layer is vapor deposited a layer comprised of a non-precious refractory metal compound or non-precious refractory metal alloy compound. Over this layer is a layer comprised of (i) a non-precious refractory metal oxide or non-precious refractory metal alloy oxide, or (ii) a layer comprised of the reaction products of a non-precious refractory metal or metal alloy, oxygen and nitrogen.

In order that the invention may be more readily understood the following example is provided. The example is illustrative and does not limit the invention thereto.

Brass faucets are placed in a conventional soak cleaner bath containing the standard and well known soaps, detergents, defloculants and the like which is maintained at a pH of 8.9-9.2 and a temperature of about 145-200.degree. F. for 10 minutes. The brass faucets are then placed in a conventional ultrasonic alkaline cleaner bath. The ultrasonic cleaner bath has a pH of 8.9-9.2, is maintained at a temperature of about 160-180.degree. F., and contains the conventional and well known soaps, detergents, defloculants and the like. After the ultrasonic cleaning the faucets are rinsed and placed in a conventional alkaline electro cleaner bath for about 50 seconds. The electro cleaner bath is maintained at a temperature of about 140-180.degree. F., a pH of about 10.5-11.5, and contains standard and conventional detergents. The faucets are then rinsed and placed in a conventional acid activator bath for about 20 seconds. The acid activator bath has a pH of about 2.0-3.0, is at an ambient temperature, and contains a sodium fluoride based acid salt.

The faucets are then rinsed and placed in a conventional and standard acid copper plating bath for about 14 minutes. The acid copper plating bath contains copper sulfate, sulfuric acid, and trace amounts of chloride. The bath is maintained at about 80.degree. F. A copper layer of an average thickness of about 400 millionths (0.0004) of an inch is deposited on the faucets.

The faucets containing the layer of copper are then rinsed and placed in a bright nickel plating bath for about 12 minutes. The bright nickel bath is generally a conventional bath which is maintained at a temperature of about 130-150.degree. F., a pH of about 4.0-4.8, contains NiSO.sub.4, NiCL.sub.2, boric acid, and brighteners. A bright nickel layer of an average thickness of about 400 millionths (0.0004) of an inch is deposited on the copper layer. The copper and bright nickel plated faucets are rinsed three times and then placed in a conventional, commercially available hexavalent chromium plating bath using conventional chromium plating equipment for about seven minutes. The hexavalent chromium bath is a conventional and well known bath which contains about 32 ounces/gallon of chromic acid. The bath also contains the conventional and well known chromium plating additives. The bath is maintained at a temperature of about 112.degree.-116.degree. F., and utilizes a mixed sulfate/fluoride catalyst. The chromic acid to sulfate ratio is about 200:1. A chromium layer of about 10 millionths (0.00001) of an inch is deposited on the surface of the bright nickel layer. The faucets are thoroughly rinsed in deionized water and then dried. The chromium plated faucets are placed in a cathodic arc evaporation plating vessel. The vessel is generally a cylindrical enclosure containing a vacuum chamber which is adapted to be evacuated by means of pumps. A source of argon gas is connected to the chamber by an adjustable valve for varying the rate of flow of argon into the chamber. In addition, a source of nitrogen gas is connected to the chamber by an adjustable valve for varying the rate of flow of nitrogen into the chamber.

A cylindrical cathode is mounted in the center of the chamber and connected to negative outputs of a variable D.C. power supply. The positive side of the power supply is connected to the chamber wall. The cathode material comprises zirconium.

The plated faucets are mounted on spindles, 16 of which are mounted on a ring around the outside of the cathode. The entire ring rotates around the cathode while each spindle also rotates around its own axis, resulting in a so-called planetary motion which provides uniform exposure to the cathode for the multiple faucets mounted around each spindle. The ring typically rotates at several rpm, while each spindle makes several revolutions per ring revolution. The spindles are electrically isolated from the chamber and provided with rotatable contacts so that a bias voltage may be applied to the substrates during coating.

The vacuum chamber is evacuated to a pressure of about 5.times.10.sup.-3 millibar and heated to about 150.degree. C.

The electroplated faucets are then subjected to a high-bias arc plasma cleaning in which a (negative) bias voltage of about 500 volts is applied to the electroplated faucets while an arc of approximately 500 amperes is struck and sustained on the cathode. The duration of the cleaning is approximately five minutes.

Argon gas is introduced at a rate sufficient to maintain a pressure of about 3.times.10.sup.-2 millibars. A layer of zirconium having an average thickness of about 4 millionths (0.000004) of an inch is deposited on the chrome plated faucets during a three minute period. The cathodic arc deposition process comprises applying D.C. power to the cathode to achieve a current flow of about 500 amps, introducing argon gas into the vessel to maintain the pressure in the vessel at about 1.times.10.sup.-2 millibar, and rotating the faucets in a planetary fashion described above.

After the zirconium layer is deposited the sandwich layer is applied onto the zirconium layer. A flow of nitrogen is introduced into the vacuum chamber periodically while the arc discharge continues at approximately 500 amperes. The nitrogen flow rate is pulsed, i.e. changed periodically from a maximum flow rate, sufficient to fully react the zirconium atoms arriving at the substrate to form zirconium nitride, and a minimum flow rate equal to zero or some lower value not sufficient to fully react with all the zirconium. The period of the nitrogen flow pulsing is one to two minutes (30 seconds to one minute on, then off). The total time for pulsed deposition is about 15 minutes, resulting in a sandwich stack with 10 to 15 layers of thickness of about one to 1.5 millionths of an inch each. The deposited material in the sandwich layer alternates between fully reacted zirconium nitride and zirconium metal (or substoichiometric ZrN with much smaller nitrogen content).

After the sandwich layer is deposited, the nitrogen flow rate is left at its maximum value (sufficient to form fully reacted zirconium nitride) for a time of five to ten minutes to form a thicker "color layer" on top of the sandwich layer. After this zirconium nitride layer is deposited, an additional flow of oxygen of approximately 0.1 standard liters per minute is introduced for a time of thirty seconds to one minute, while maintaining nitrogen and argon flow rates at their previous values. A thin layer of mixed reaction products is formed (zirconium oxy-nitride), with thickness approximately 0.2 to 0.5 millionths of an inch. The arc is extinguished at the end of this last deposition period, the vacuum chamber is vented and the coated substrates removed.

While certain embodiments of the invention have been described for purposes of illustration, it is to be understood that there may be various embodiments and modifications within the general scope of the invention.