GB2344355A - Multi-layer coated article - Google Patents

Abstract

An article has a coating comprising at least one nickel layer, a chrome layer, a layer comprised of titanium or titanium alloy, a layer comprised of titanium compound or titanium alloy compound, and a zirconium compound or zirconium alloy compound layer.

Description

1 2344355 ARTICLE COATED W=-H MULTILAYER COATING This 4;.nvention relates

to decorative and protective coatings.

it is currently the aractice with various brass articles such as lamps, tzivet's, faucets, 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. T 1-4 -i s system has the drawback that the recuisite b u f f i -n a and p 0 1 _J s h in g oceration, particularly if the ar-_Jcle is of a complex shape, -is labor intensive. Also, the known organic coa!_-,4;.ngs are not as durable as desired and wear off.

These deficiencies are remedied by a coating containing a nickel basecoa: and a non-precious refractory metal comuound such as zi_rconiuni nitride, titanium nitride and zircon-Jum-titan-Jum alloy n-'trlde coat. However, it has been discovered that when titanium is present in the coating, for examDle as titanium nitride or zir--on-ium titanium alloy nitride, in corrosive environments the coating may experience galvanic corrosion. This calvanic' corrosion renders the coatinc virtualiv useless. T- has been surnr'.singlv discovered that the cresence of a laver comorised o" zi_,conium comnound, such as zi_-conium nitride, or a zi--conium alloy compound over the lavers c.-r.z:a-;'.;,JLng the titanium compound or t ita n -i um alloy compound significantly reduces or e!4;.m_4na-_es galvanic corrosicn.

The present invention is dLrected to a protective and decorative coating for a subszraze, particularly a metallic substrate. More pa.-zicularly, it is directed to a substrate, particularly a meta-l-lic substrate such as brass, having on at least a portion of its sur-face a coating comprised of multiple superposed layers of certain specific types of me,--als or metal compounds wherein az least one of the layers contains titanium or a titanl_um alloy. The coating is decorative and also provides corrosion, wear and chemical resistance. In one embodiment the coating ides the appearance of polished brass with a golden provi hue, i.e. has a golden-brass color tone. Thus, an article surface having the coating thereon simulates polished brass with a gold hue.

A first layer deposited directly on the surface of the substrate is comior-ised of nickel. The firs-c: laver mav be monolithic, _J.e., a s:Lngle ri-ickel layer, or it may consist of two dif-J.'arent nickel lavers such as a se.mi-bright nickel layer deposited directly on t'!-.e surface of the substrate and a bright nickel layer super';_mposed over the semi-bright nickel layer. Over the nick-3-1 layer is a layer comprised of chrome. Over the chrome layer is a strike layer comprised of titanium ar titanium alloy. Over the titanium or titanium alloy laver is a layer comprised of titanium commound or titanium allov comnound.

Over the titanium comr-ou"d or titanium alloy compound layer is a thin layer comprised of zirconium compound or zirconium alloy compound. Th-'s layer -Functions to reduce or elimLnate galvanic corrosion.

2 Fig. 1 is a cross -sect -iora'. view, not to scale, of the mult-i-layer coating on a substzat-e.

The substrate 12 can be any plastic, metal or metallic alloy. illustrative of metal and metal alloy substrates are copper, steel, brass, tuncsten, nickel alloys and the like. In one embodiment the substrate is brass.

A rickel layer 13 is deposited on the surface of the substrate 12 bv conventional and well k.-own electroplating processes. These processes include using a conventional electroplating bath such as, -or example, a Watts bath as the plating solution. Typically such baths contain nickel sulfate, nickel chloride, and boric acid dissolved in water. All chloride, sulfamaze, and fluoroborate plating solutions car. also be used. These baths can opt-Jonal-'y include a number of well known and convent ionally used comr)ounds 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 I! is added to the plating solution. Class I brighteners are organic compounds which contain sulfur. Class I! brighteners are organic compounds which do not contain sulfur. Class!I brighteners can also cause leveling and, when added to the plating bath without the sulfuz-cont-a-ining class I b-righteners, result in semibright nickel deposits. These class i brighteners include alkyl naphtnalene and benzene sul.,Eonic acid. The benzene and naphthalene d-;and -k=_JsuIfon.:'.c acids, benzene and naphthalene sulfonamidles, and sulfonamides suc"' as saccharin, vinyl and allyl sulfonam_'des and sulfonic acids. The class 77 brighteners generaLly are unsaturated orcanic 3 materials such as, for exam=-'--, acetyleri-ic or ethylenic alcohols, ez. hoxylated and proccxy-lated acetylenic alcohols, coumarins, and aldehydes. These class 1 and class 11 brighteners are well known to 7:"cse skilled In the art and are readily commercially ava-J-7--able. They are described, inter alia, in U.S. Patent No. 4,421,611 incornorated herein by reference.

The nickel layer 13 can be comprised-4 of a sJ;.ngle nickel layer such as, for exannn-le, bright nickel, or it can be comprised of two different n_Jckel layers such as a semibright nickel layer and a brigi'nt nickel layer. I n th a figure layer 14 is comprised ot" semi-bright nickel while 4 layer 16 is comprised of bric',-7: n.;.ckel. This dunlex nickel deposit provides imioroved corrosion protection to the underlying substzate. The sulfur free plate 14 is deposited by convenziora-1 electroplating processes directly or. the surface of su-'-szrate 12. The substrate 1-2 containing the semi-bright n,;..c"<e-' layer 14 Ls ther. plated in a bright nickel plating ba--'n and the bright nickel layer 16 is deposited on the sem-4-br-'c'nz nickel laver 14, also by conventional electroplating processes.

The thickness of the nlckel layer 13 is generally in the range of from about 100 minlionths (0.0001) of an inch, preferably f-rom about 150 millionths (0.00015) of ar inch to about 3,500 millionths (0.0033) o,"L: an inc-.

In the embodiment where a dur)lex nickel layer is used, the thickness of the semi-br;.(;-,t nickel layer and zhe bright nickel layer is a thickness effffeczLve to provide imr)roved corrosion protection. Generally, the thickness of the sem-i-bright nickel lave= Id is at least abouz: 50 millionths (0.00005) of an -i-c-, preferablv a-, least about 100 millionths (0.0001) of an Lnch, and more areferabiv at 4 least about 7-5-0 millionths (0-00015) of an inch. The upper thickness is generally rot critical and is gcverned by secondary considerations such as cost and appearance.

Generally, however, a thickness oil about 1,500 T m411ionths (0-0015) of an inch, preferably about 1,000 millionths (0.001) o -f an inch, a In d more preferably about 750 millionths (0.0075) of an - inch should not be exceeded. The bright nickel layer 16 generally has a thickness of at least abouz 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 nickell I is layer - not critical and is generally controlled by considerations such as cost. Generally, however, a thickness of about 2,500 millionzhs (0-0025) of an preferably about 2,000 millionths (0.002) of an -inch, and more preferably about 1,500 mil.1-ionths (0.0015) of an in ch should not be exceeded. The bright nickel layer 16 also functions as a leveling layer which tends to cover or f il 1 in imnerfect-ions in the substrate.

Disposed over the nickel layer 13, particular! y the bright nickel layer, -is a laver 22 comprised of chrome. The chrome layer 22 may be deposited on layer 13 by conventional and well known chromium electroplating techniques. These technicues along with various chrome plating b at h s are disclosed in Brassard, "Decorative Electroplating - A Process in Transition", Metal Finish-ina, pp. 105-108, June 1988; Z ak _4 "Chromi um PF Directory, pp. 146-160; and U.S. Patent Nos. 4,460,438, 4,234,396 and 4,093,522, a of whic'n are incorporated herein by reference.

Chrome plating baths are well known and commercially available. A typical crirome platLng bath contains chromic acid or sales thereof, and cazalyst ion suc,. as sulfate or fluoride. The catalyst ions car. be provided by L.

L sulfurJ c acid or its salts and fluos-i-I-Lcic acid. The baths may be operated at a temperature of about 112 - 110" F. Typically in chrome plating a current dens-4sy of about 150 amips per square foot, at about 5 to 9 volts is utilized.

The chrome layer 22 serves to prov-;..de structural integrity to the vapor deposited layers or reduce or eliminate plastic deformation of the coating. The nickel layer 13 _J s relatively so_-Ift- compared to the titanium compound or titan-Jum alloy compound layer 30. Thus, an object impinging on, sz:rikJ.nq or pressing or. layer 30 will not penetrate this relatively hard layer, but this force will be transferred to t,e relatively soft underlying nickel layer 13 causLng plastic deformation of this layer. Chrome layer 22, being relat-ILvely harder than the nicke-I layer, will generally resist the plastic deformation thai: the nickel layer 13 undergoes. - Chrome layer 22 has a thickness at least efJfective to provide structural integrity to and reduce plastic deformation of the coating. This thickness is at least about 2 millionths (0.000002) of an inch, preferably at least about 5 (0-000005) of an inch, and more preferably at least about 8 m-J-1-1-4onths (0.000008) of an inch. Generally, the upper range of thickness _Js not critical and is det-erm-ined bv secondarv cons -41derat-ions such as cost. However, the thickness of the chrome lave= should generally -,ot exceed about 60 m-411-ionths (0.00006) of an inch, prefe-rabiv about 50 -n.-L-1-liontns (0.00005) of an -i-ch, and more preferably about 40 millionths (0.00004) of an inch.

Disposed over chrome layer 22 is a strike layer 29 comor-ised of titanium or titanium alloy.

The strike layer 28 functions, inter alia, to improve the adhesion of layer 30, comcrised of titanium comnound or titanium all o y compound, t 0 the chrome laver 22. Generallv, this thickness is a". least about 0.25 millionths (0.000000251/ 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 and appearance. Generally, however, layer 29 should not be thicker than about 50 mi-1-1-ionths (0-00005) of an inch, preferably about 15 millionths (0. 000015) of an inch, and more preferably about 10 m-illionths (0.000010) of an inch.

Over the str-4ke layer 28 is layer 30 comprised of titanium comnound or titanium allov comiDound. Layer 30 provides wear and abrasion resistance and the desired color or appeara.-.ce, such as for example a brass color with a golden hue. Layer 30 has a thickness effective to provide abrasion and wear resistance and to provide the requisite color. The color depends on the composition of layer 30. Thus, t itan. -4um- zirconium nitride wi1-1 provide a brass color with a golden hue.

Generally layer 30 has a thickness of at least about 9 millionths (0. 000002) of an inch, preferably at least 4 millionths (0.000004) of an -;.. :lch, and more preferably at: least 6 millionths (0.000006) of an inch. The upper thickness range is generally not: critical and is dependent uoon considerations such as ccs7-. Generaliv a thickness o--16 7 about 100 millionths (0.0001) of an inch, preferably about 50 mill-iontas (0.00005) of an inch, and more preferably about 30 millionths (0.00003) of an inch should not be exceeded.

The metals that are alloyed-4 with the titanium to form the titanium alloy or titanium alloy compound are the nonprecious refractory metals. These include z-Lrconium, hafnium, tantalum, and tungszei- The titanium alloys generally comprise from about 1-0 to about 90 weight percent titanium and from about 90 to about 10 weight)ercent of another non- precious refract-ory metal, preferably from about 20 to about 80 weight percent titanium and from about 80 to about 20 weight percent of another refractory metal. The titanium, co=ounds or titan_um alloy compounds include the oxides, nitrides, carbides and carbon-it-r-ides.

In one embodiment layer 30 is comorised of titan_um zirconium alloy nit-ride and laver 28 is comprised of titan -ium- z -4--con -Jum alloy. In th-is embodiment the titanium zirconium allov nitride layer 'has a brass color with a golden hue. - A method of foming layers 29 and 30 is by utilizing well known and conventional vacor deposition techniques such as physical vapor depos. 'Ition or chemical vapor deposition. Physical vapor deposition processes include sputtering and cathodic arc evaporazion. In one process of the instant invention s-cuttering or cathodic arc evaporation is used to deposiz a laver 28 of titanium alloy or titanium, followed by reaczive szuttering or reac,:-ive cathodic arc evaporation to dencsiz_ a layer 30 of t-it-an-Jum alloy compound such as tJ_z_=n_ium-z_i_-con4;_um nitride or titanium comiDound such as titan-4,am nitride.

To form layer 30 wherein the titanium compound or the titanium a!-'oy compound are the nitrides, nitrogen gas is introduced during vapor deposition s u c 'h as reactive sputtering or reactive cathcd-4c arc evaporation at a desired value or flow rate to form titanium nitride or titanium alloy nitride.

Over layer 30 is layer 34. Layer 34 is comprised of a zirconium compound or a zirconium alloy compound. 7h e zirconium comvounds or zi-rconi,,_= alloy compounds are the oxides, nitrides, carbides and carbonitr.-;.des. The metals that are alloyed with zirconium to form the zirconium alloy comiocunds are the non-precious refractory metal compounds excluding titanium. The zirconium alloy comprises from about 30 to about 90 weighz percent zirconium, the remainder being non-precious refractory metal other than titanium; preferably from a-'-ouz 40 to about 90 weight percent zirconium, the remainder being non-precious refractory metal other than tizanium; and more preferably from about 30 to about 90 weigh-c percent zirconium, the rem metal other than . ainder being non-precious refractory titanium.

Layer 34 may be, for exammle, zirconium nitride when layer 30 is zirconium- ti t anium alloy nitride.

Layer 34 is very thin. it 4 s thn enough so that it is non-oioacue, translucent or transparent in order to allow the color of: layer 30 to be seen. it is, however, thick enouah to sign-i Alicantly reduce or eliminate aalvanic corrosion. Generally layer 34 has a thickness from about 0.07 milli'-onth to about 0.7 mi.1-1-ionth, Preferabiv -from about 0.2 millionth to about 0.3 mill-ionth o_-" an inch.

Layer 34 can be denos-'zed by well known and conventional vapor deposizicn techniques, including 9 physical vapor deposition and chemical vapor deposition such as, for example, reacti7e sputtering and reactive cathodic arc evaporation.

Sputtering techniques and equipment are disclosed, inter alia, in J. Vossen and W. Kern "Thin F-Llm Processes Il", Academic Press, 1991; R. Boxman et a!, "Handbook of Vacuum Arc Science and Technology", Noyes Pub., 1995; and U.S. patent Nos. 4,162,954 and 4,591,418, all of which are incormorated herein by reference.

Brief.Iv, in the sputtering deposition process a refractory metal (such as titan-Jum or zi-rcon-ium) target, which is the cathode, and the substrate are placed in a vacuum chammer. The air in the chamber -is evacuated to produce vacuum, conditions in t.h e c h amb e r. 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 zirconiurr, atoms. The dislodged target 4 materi.al is then typically deposited as a coating f-J-1m on the substrate.

in cathodic arc evaoo--ation, 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 formaing a coating.

Re aCt4 ve cathodic arc evarorat4on and reactive 4 sputte.6ng 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 laver 32, the cathode is comprised of zi-rconium and nitrogen is the reactive gas int--oduced into the chamber. By controll.-4ng the amount of -1-itrocen available to react io with the zJ;_zccn_Ju:m, the color of the zircon-Jum nitride can be adjusted to be similar to that of brass of various hues.

7n -er that the invention may be more readily or L. - understood the following example is provided. The examnle is illustrative and does not li.-nit the invention thereto.

EXAIMPLZ 1 Brass taucets are rlaced in a conventional soak cleaner bath. conta-iiing 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 - 200F for 10 minutes. The brass faucets are then placed in a conventional ultrasonic alkal.-Lne cleaner bath. The ultrasonic cleaner bath has a pH of 8.9 9.2, is maintained at a temperature of about 160 180'7-, and contains the conventional and well known scans, detergents, defloculants and the like. Afzer the ultrasonic cleaning the faucet-s are rinsed and placed in a conventional alkaline electro cleaner bath for about 50 seconds. The elect-ro cleaner bath is maintained at a temr)eratu--e of about 1400 - 180"F, a pH of abou: 10.5 - 11.5, and contai.n.s standard and conventional detergents. The -faucets are then rinsed and placed in a conventional acid act-Lvator bath for about 20 seconds. The acid activator bath has a pH of about 2.0 - 3.0, is at an ambient ternzerature, and contains a sodium --Fluoride based acid sal--.

The faucets are then placed in a conventional and standard b_right nickel plating bath for about 12 minutes. The bright nickel bath is generally a conventional bath which is ma_'itained at a temnerazure of about 130 1500F, a pH of about 4.0 - 4.8, conta-4ns N.44.S04, NL-LCL,, boric acid, and brighteners. A bright nickel layer of an average thickness of about 400 millionths (0.0004) of an inch is decosited on the faucets. The bright nickel olated faucets are rinsed three times and then placed in a convenzional, commercially available hexavalent ch r o m -i um plat- Lng bath us -J.-I g conventional- chromium plating equipment for about sever. minutes. The hexavalent chromium bath is a conventional and well known bath which contains about 32 ounces/gallon or chromic acid. The bath also contains the conventional and well known chromium plating add- i7:-ives. The bath is maintained at a temperature of about 1-120-11-6"F, and utjl,'zes a mixed sulf ate/ fluoride cat-alvsz. The chromic acid to sulfate ratio is about 200:1. A chromium layer of about 10 millionths of an inch is decos-ited on the surface of the bright-nickel layer. The faucets are thoroughly rinsed in de-ionized water thar, 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 cnamber, which is adaoted to be evacuated bv means of pumps. A source of argor. gas is connected to the chamber by an ad"uszable valve for varying the rate oaf flow of gas.

A CVI 4 -.4.ndrical zirconium-c-itanium, alloy 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 wal 1. The cathode material comcr-ises zirconium and titanium.

The clated faucets are mounted on spindles, 16 of which are mounted on a rinc around the outside of the cathode. The entire ring rota--es around t, -,e cathode wt,-ile each sm-i-d-le also rotates around it's owr axis, resulting in 12 a so-called planetary motion which prov-'.des uniform ex,zosure to the cathode for t.-.e multiple faucets mounted around eac!i 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 wit'- rotatable contacts so that a bias voltace may be applied to the substrates during coatina.

The vacuum chamber is evacuat-ed to a c:ressure of about 5 XIO-3 millibar and heated to about 130C.

The electroolated faucer-s are then sub-4ected to a high-bias arc plasma clean-Lng -in wiich a (negative) bias voltage of about 500 volts is amplied to the electroplated faucets while an arc of acnrax_.mat-ely 500 amperes is struck and sustained on the cathode. The duration of the cleaning is approx-i-mately five minutes. Argon gas is introduced at a rate sufficient to mainza-L-1 a Pressure of about 3x_I 0-2 milli-bars. A layer of zircon-Jum-titanium alloy having an average thlickness of about 4 millionths of an inch is deposited on the chrome p-7-ar-ed faucets during a three minute per-Lod. The cathodic arc decosition process comprises applying D.C. power to the cathode to achieve a current flow oil about 500 amcs, introducing argon gas into the vessel to maintain the pressure in the vessel at about 1xI0_2 milL_'bar, and rotatinc the faucets in a o-lanetary fashion described above.

A Af-er the zirconium-t4t-anzun, alloy layer is deposited a thicker zirconium-t1tan-Lum nizr_'de comr-ound "color layer" is deposized over it. A flow of nit_-ogen is introduced into the vacuum chamber while the arc discarge continues at aomrox__-nately 500 amceres. 7'he n:-ocen flow raze is 1-3 set sufficiently high to fully react the zirconium and titanium aLloy atoms arriving at the substrate to form zirconium-t_tanium nit r ide comcound. The total time 4'. o r denosition -4s about 30 m-inutes. The arc is extilnguished at the end of this deposition per.-Lod, the vacuum chamber is vented and tie coated substrates removed.

After the zirconium-titanium nitride compound laver is demosited a final thin non-opt-4cally dense flash layer of Zirconium nitride is deposited to provide increased corrosion resistance and to ach-'eve the desired final color. The coated substrate parts are placed into another chamber fitted with cylindrical cathode target composed primarily of zirconium. metal. The chamber -is evacuated to pressures previously described as well as the parts cleaned again by subjecting them to hLah-bias arc alasma as described earlier. After the c-Ieanina_ process -is complete the cathod-'c arc depos-Ltion process is repeated with nitrogen and argon gas flows sersufficiently high to provide ful-I or nearly full reaction of the z.4.6rconium metal to zi-rcon.",Lyn, nitride compound. This flash process is carried out -or a one to three m'Lnute per-iod. Finally the arc is extinguished the chamner vented and the coated substrates removed.

While certain embodiments of the invention have been described for purposes of illustration, it is to be understood th a t there may be various embodiments and modif-'cat-ions within the general scope of the invention.

i 4 I cla-im:

1. An art-4cle having on at -!---=st a portion of its surface a coating comprising: at least one layer comprised of nickel; layer comprised of chrome; layer comprised of titan-Jum or titanium alloy; layer comDrised of t-itar-J;.---,m, compound or titanium alloy compound; and layer comprised of zirconium compound or zirconium alloy compound.

2. The arzicle of claim I wherein said titanium comDound is titanium nitride and said titanium alloy compound is titanium-zLrconium alloy nitria4e.

3. The arzicle of claim 2 said titanium a-',Icy is t-itan-ium-zircon-ium alloy.

4. The arT--icle of claim 3 wherein said zirconium comcound is zirconium n-itride.

5. The ar---icle of claim 3 wherein said zirconium, alloy compound is zirconium alloy nitr-Lde.

6. The article of claim 1 wherein said at least one layer comr)r-ised of nickel is comprised of bright nickel.

7. An art-'cle havtng on at least a portion of its surface a coating ccmpris-ing:

layer camprised of sem-i-bright nickel; layer ccmprised of bright nickel; laver ccmiorised of chrome; layer comprised of titanium or titanium allay; layer ccmprised of titanium compound or titanium alloy cc=ound; and layer comprised of comround or zirconium alloy compound.

8. The ar-:-icle of claim 7 wherein said titanium comnound is titaniam aitride.

9. The ar--icle of claim 8 wherein said titanium alloy comiDound is T:4tan-iUM-ZIrcor-4Um alloy compounc.

10. The arzicle of claim 9 wherein said titanii=-zirconium allov ccmmound is t-itan-i=-z-i----on-4,jm allov nitride.

11. Th e a=7:-Jcle of claim 7-or 10 wherein said zirconium comnound is zlrconium n-itride.

12. The az-:-4cle oil claim 7 or 10 wherein said zirconium alloy comr)ound is zirconium allov nitride.