Abstract:
An article is coated with a multilayer coating comprising a nickel-tungsten-boron alloy layer deposited on the surface of the article, a refractory metal, preferably zirconium, strike layer deposited on the nickel-tungsten-boron alloy layer, and a refractory metal compound, preferably zirconium nitride, deposited on the refractory metal strike layer. The coating provides the color of polished brass to the article and also provides abrasion protection.

Description:
FIELD OF THE INVENTION 
     This invention relates to substrates, in particular brass substrates, coated with a decorative and protective coating simulating brass. 
     BACKGROUND OF THE INVENTION 
     It is currently the practice with various brass articles such as lamps, trivets, candlesticks, 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. While this system is generally quite satisfactory it 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, particularly in outdoor applications where the articles are exposed to the elements and ultraviolet radiation. It would, therefore, be quite advantageous if brass articles, or indeed other metallic articles, could be provided with a coating which gave the article the appearance of polished brass and also provided wear resistance and corrosion protection. The present invention provides such a coating. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a metallic substrate having a multi-layer coating disposed or deposited on its surface. More particularly, it is directed to a metallic substrate, particularly brass, 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 wear and abrasion resistance. The coating provides the appearance of polished brass. Thus, an article surface having the coating thereon simulates a polished brass surface. 
     A first layer deposited directly on the surface of the substrate is comprised of nickel-tungsten-boron alloy. Over the nickel-tungsten-boron alloy layer is a layer comprised of a non-precious refractory metal such as zirconium, titanium, hafnium or tantalum, preferably zirconium or titanium. A top layer comprised of a nonprecious refractory metal compound, preferably a zirconium compound, titanium compound, hafnium compound or tantalum compound, more preferably a titanium compound or a zirconium compound such as zirconium nitride, is disposed over the refractory metal layer, preferably zirconium layer. 
     The nickel-tungsten-boron alloy layer is applied by electroplating. The refractory metal such as zirconium and refractory metal compound such as zirconium compound layers are applied by vapor deposition such as sputter ion deposition and reactive sputter ion deposition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a portion of the substrate having the multi-layer coating deposited on its surface. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The substrate 12 can be any platable metal or metallic alloy substrate such as copper, steel, brass, tungsten, nickel alloys, and the like. In a preferred embodiment the substrate is brass. 
     Disposed on the surface of the substrate 12 is a layer 20 comprised of nickel-tungsten-boron alloy. More specifically, layer 20 is comprised of a substantially amorphous composite alloy of nickel, tungsten and boron. Layer 20 is deposited on the substrate surface by conventional electroplating processes. The nickel-tungsten-boron alloy plating bath is normally operated at a temperature of about 115° to 125° F. and a preferred pH range of about 8.2 to about 8.6. The well known soluble, preferably water soluble, salts of nickel, tungsten and boron are utilized in the plating bath or solution to provide concentrations of nickel, tungsten and boron. 
     The nickel-tungsten-boron alloy layer generally contains at least about 50, preferably at least about 55, and more preferably at least about 57.5 weight percent nickel, at least about 30, preferably at least about 35, and more preferably at least about 37.5 weight percent tungsten, and at least about 0.05, preferably at least about 0.5, and more preferably at least about 0.75 weight percent boron. Generally the amount of nickel does not exceed about 70, preferably about 65, and more preferably about 62.5 weight percent, the amount of tungsten does not exceed about 50, preferably about 45, and more preferably about 42.5 weight percent, and the amount of boron does not exceed about 2.5, preferably about 2, and more preferably about 1.25 weight percent. The plating bath contains sufficient amounts of the salts, preferably soluble salts, of nickel, tungsten and boron to provide a nickel-tungsten-boron alloy of the afore-described composition. 
     A nickel-tungsten-boron plating bath effective to provide a nickel-tungsten-boron alloy of which a composition is commercially available, such as the Amplate™ system from Amorphous Technologies International of Laguna Niguel, Calif. A typical nickel-tungsten-boron alloy contains about 59.5 weight percent nickel, about 39.5 weight percent tungsten, and about 1% boron. The nickel-tungsten-boron alloy is an amorphous/nano-crystalline composite alloy. Such an alloy layer is deposited by the AMPLATE plating process marketed by Amorphous Technologies International. 
     The thickness of the nickel-tungsten-boron alloy layer 20 is generally at least about 20 millionths (0.00002) of an inch, preferably at least about 50 millionths (0.00005) of an inch, and more preferably at least about 100 millionths (0.0001) of an inch. The upper thickness range is not critical and is generally dependent on economic considerations. Generally, a thickness of about 2,500 millionths (0.0025) of an inch, preferably about 2,000 millionths (0.002), and more preferably about 1,000 millionths (0.001) of an inch should not be exceeded. 
     Disposed over the nickel-tungsten-boron alloy layer 20 is a layer 22 comprised of a non-precious refractory metal such as hafnium, tantalum, zirconium or titanium, preferably zirconium or titanium, and more preferably zirconium. 
     Layer 22 serves, inter alia, to improve or enhance the adhesion of layer 24 to layer 20. Layer 22 is deposited on layer 20 by conventional and well known techniques such as vacuum coating, physical vapor deposition such as ion sputtering, and the like. Ion sputtering techniques and equipment are disclosed, inter alia, in T. Van Vorous, &#34;Planar Magnetron Sputtering; A New Industrial Coating Technique&#34;, Solid State Technology, Dec. 1976, pp 62-66; U. Kapacz and S. Schulz, &#34;Industrial Application of Decorative Coatings--Principle and Advantages of the Sputter Ion Plating Process&#34;, Soc. Vac. Coat., Proc. 34th Arn. Techn. Conf., Philadelphia, U.S.A., 1991, 48-61; and U.S. Pat. Nos. 4,162,954, and 4,591,418, all of which are incorporated herein by reference. 
     Briefly, in the sputter ion deposition process the 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. 
     Layer 22 has a thickness which is at least effective to improve the adhesion of layer 24 to layer 20. Generally, this thickness is 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 or zirconium, preferably zirconium, and is deposited by sputter ion plating. 
     Layer 24 is preferably deposited on layer 22 by reactive ion sputter deposition. Reactive ion sputter deposition is generally similar to ion sputter deposition except that a reactive gas which reacts with the dislodged target material is introduced into the chamber. Thus, in the case where zirconium nitride is the top layer 24, the target is comprised of zirconium and nitrogen gas 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 made to be similar to that of brass of various hues. 
     Layer 24 is comprised of a hafnium compound, a tantalum compound, a titanium compound or a zirconium compound, preferably a titanium 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 24 provides wear and abrasion resistance and the desired color or appearance, such as for example, polished brass. Layer 24 is deposited on layer 22 by any of the well known and conventional plating or deposition processes such as vacuum coating, reactive sputter ion plating, and the like. The preferred method is reactive ion sputter plating. 
     Layer 24 has a thickness at least effective to provide abrasion resistance. Generally, this thickness is at least 2 millionths (0.000002) of an inch, preferably at least 4 millionths (0.000004) of an inch, and more preferably at least 6 millionths (0.000006) of an inch. The upper thickness range is generally not critical and is dependent upon 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 the preferred coating material as it most closely provides the appearance of polished brass. 
     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. 
     EXAMPLE 1 
     Brass door escutcheons 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 180°-200° F. for 30 minutes. The brass escutcheons are then placed for six minutes 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° F., and contains the conventional and well known soaps, detergents, defloculants and the like. After the ultrasonic cleaning the escutcheons are rinsed and placed in a conventional alkaline electro cleaner bath for about two minutes. The electro cleaner bath contains an insoluble submerged steel anode, is maintained at a temperature of about 140°-180° F., a pH of about 10.5-11.5, and contains standard and conventional detergents. The escutcheons are then rinsed twice and placed in a conventional acid activator bath for about one minute. 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 escutcheons are then rinsed twice and placed for about forty minutes in a nickel-tungsten-boron plating bath available from Amorphous Technologies International of California as the AMPLATE bath. The bath utilizes insoluble platinized titanium anode, is maintained at a temperature of about 115°-125° F. and a pH of about 8.2-8.6. A nickel-tungsten-boron layer of an average thickness of about 400 millionths (0.0004) of an inch is deposited on the surface of the substrate. The nickel-tungsten-boron plated escutcheons are then rinsed twice. 
     The nickel-tungsten-boron alloy plated escutcheons are placed in a sputter ion plating vessel. This vessel is a stainless steel vacuum vessel marketed by Leybold A.G. of Germany. 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, two sources of nitrogen gas are connected to the chamber by an adjustable valve for varying the rate of flow of nitrogen into the chamber. 
     Two pairs of magnetron-type target assemblies are mounted in a spaced apart relationship in the chamber and connected to negative outputs of variable D.C. power supplies. The targets constitute cathodes and the chamber wall is an anode common to the target cathodes. The target material comprises zirconium. 
     A substrate carrier which carries the substrates, i.e., escutcheons, is provided, e.g., it may be suspended from the top of the chamber, and is rotated by a variable speed motor to carry the substrates between each pair of magnetron target assemblies. The carrier is conductive and is electrically connected to the negative output of a variable D.C. power supply. 
     The plated escutcheons are mounted onto the substrate carrier in the sputter ion plating vessel. The vacuum chamber is evacuated to a pressure of about 5×10 -3  millibar and is heated to about 400° C. via a radiative electric resistance heater. The target material is sputter cleaned to remove contaminants from its surface. Sputter cleaning is carried out for about one half minute by applying power to the cathodes sufficient to achieve a current flow of about 18 amps and introducing argon gas at the rate of about 200 standard cubic centimeters per minute. A pressure of about 3×10 -3  millibars is maintained during sputter cleaning. 
     The escutcheons are then cleaned by a low pressure etch process. The low pressure etch process is carried on for about five minutes and involves applying a negative D.C. potential which increases over a one minute period from about 1200 to about 1400 volts to the escutcheons and applying D.C. power to the cathodes to achieve a current flow of about 3.6 amps. Argon gas is introduced at a rate which increases over a one minute period from about 800 to about 1000 standard cubic centimeters per minute, and the pressure is maintained at about 1.1×10 -2  millibars. The escutcheons are rotated between the magnetron target assemblies at a rate of one revolution per minute. The escutcheons are then subjected to a high pressure etch cleaning process for about 15 minutes. In the high pressure etch process argon gas is introduced into the vacuum chamber at a rate which increases over a 10 minute period from about 500 to 650 standard cubic centimeters per minute (i.e., at the beginning the flow rate is 500 sccm and after ten minutes the flow rate is 650 sccm and remains 650 sccm during the remainder of the high pressure etch process), the pressure is maintained at about 2×10 -1  millibars, and a negative potential which increases over a ten minute period from about 1400 to 2000 volts is applied to the escutcheons. The escutcheons are rotated between the magnetron target assemblies at about one revolution per minute. The pressure in the vessel is maintained at about 2×10 -1  millibar. 
     The escutcheons are then subjected to another low pressure etch cleaning process for about five minutes. During this low pressure etch cleaning process a negative potential of about 1400 volts is applied to the escutcheons, D.C. power is applied to the cathodes to achieve a current flow of about 2.6 amps, and argon gas is introduced into the vacuum chamber at a rate which increases over a five minute period from about 800 sccm (standard cubic centimeters per minute) to about 1000 sccm. The pressure is maintained at about 1.1×10 -2  millibar and the escutcheons are rotated at about one rpm. 
     The target material is again sputter cleaned for about one minute by applying power to the cathodes sufficient to achieve a current flow of about 18 amps, introducing argon gas at a rate of about 150 sccm, and maintaining a pressure of about 3×10 -3  millibars. 
     During the cleaning process shields are interposed between the escutcheons and the magnetron target assemblies to prevent deposition of the target material onto the escutcheons. 
     The shields are removed and a layer of zirconium having an average thickness of about 3 millionths (0.000003) of an inch is deposited on the nickel/tungsten/boron layer of the escutcheons during a four minute period. This sputter deposition process comprises applying D.C. power to the cathodes to achieve a current flow of about 18 amps, introducing argon gas into the vessel at about 450 sccm, maintaining the pressure in the vessel at about 6×10 -3  millibar, and rotating the escutcheons at about 0.7 revolutions per minute. 
     After the zirconium layer is deposited a zirconium nitride layer having an average thickness of about 14 millionths (0.000014) of an inch is deposited on the zirconium layer by reactive ion sputtering over a 14 minute period. A negative potential of about 200 volts D.C. is applied to the escutcheons while D.C. power is applied to the cathodes to achieve a current flow of about 18 amps. Argon gas is introduced at a flow rate of about 500 sccm. Nitrogen gas is introduced into the vessel from two sources. One source introduces nitrogen at a generally steady flow rate of about 40 sccm. The other source is variable and is regulated so as to maintain a partial ion current of 6.3×10 -11  amps, with the variable flow of nitrogen being increased or decreased as necessary to maintain the partial ion current at this predetermined value. 
     The pressure in the vessel is maintained at about 7.5×10 -3  millibar. 
     The zirconium-nitride coated escutcheons are then subjected to low pressure cool down, where the heating is discontinued, pressure is increased from about 1.1×10 -2  millibar to about 2×10 -1  millibar, and argon gas is introduced at a rate of 950 sccm. 
     This invention may be further developed within the scope of the following claims. Accordingly, the above specification is to be interpreted as illustrative of only a single operative embodiment of the present invention, rather than in a strictly limited sense.