Title of Invention	"A COATING COMPOSITION CONTAINING NICKEL AND BORON AND METHOD FOR COATING THE SAME"
Abstract	A coating composition containing nickel and boron and method for coating the same using a coating bath that provides a hard, wear and corrosion resistant, ductile coating on a substrate, said bath having a pH of about 10 to 14 and comprising: (I) about 0,175 to about 2,10 moles per gallon of coating bath of nickel ions; (2) an effective amount of lead rungstate to stabilize the bath and to form a continuous coating free from blotches without any substantial deposition of lead tungstate in the coating; (3) an effective amount of metal ion complexfng agent in an amount sufficient to inhibit precipitation of said metal ions from the coating bath ; and (4) an effective amount of a borohydride reducing agent.

Title of Invention

"A COATING COMPOSITION CONTAINING NICKEL AND BORON AND METHOD FOR COATING THE SAME"

Abstract

A coating composition containing nickel and boron and method for coating the same using a coating bath that provides a hard, wear and corrosion resistant, ductile coating on a substrate, said bath having a pH of about 10 to 14 and comprising: (I) about 0,175 to about 2,10 moles per gallon of coating bath of nickel ions; (2) an effective amount of lead rungstate to stabilize the bath and to form a continuous coating free from blotches without any substantial deposition of lead tungstate in the coating; (3) an effective amount of metal ion complexfng agent in an amount sufficient to inhibit precipitation of said metal ions from the coating bath ; and (4) an effective amount of a borohydride reducing agent.

Full Text	This invention is a continuation, in part Of United State Patent Application Number 09/074,703 filed May 8, 1998: BACKGROUND OF THE INVENTION This invention relates to novel metal coatings, which exhibit exceptional hardness. More particularly this invention relates to metal coatings containing nickel and boron end to the reductive deposition of said coatings on the surfaces of substrate articles from aqieous solutions at an alkaline pH. The plating or deposition of metal alloys by chemical or electrochemical reduction of metal ions on the surface of an article to modify its surface characteristics for both decorative and functional purposes is tell known in the art. Of particular commercial significance is the deposition of metal/metal alloy coatings on both, metal and activated non-metal substrates to enhance surface hardness and resistance to corrosion and wear. Nickel-boron and cobalt-boron alloy coatings are recognized in the art for their hardness and associated wear-resistance. The patent literature reflects an. ongoing research and development effort in the area of nickel-boron coatings with the goal of producing still harder, more corrosion resistance coatings. For example, see, U.S. Pat. Nos. 5,019,1,63; 3,738,849; 3,674,447; 3,342,338; 3,378,400; 3,045,3342; and 726,710- The art has recognized that when borohydride is used in a nickel/boron plating bath a harder coating is achieved. However, borohyd::ide, is very unstable; in the bath. The solution to the stability problem has beer: to add stabilizers such as thallium sulfate or lead chloride. The addition of the Stabilizers had the effect of interfering with the formation of the nickel coating thereby negatively impacting the hardness of the coating. Because the stabilizer is not co-deposited in the coating in accordance with the present invention the nickel coating is remarkably more hard than those described in the prior art. To-date nickel/boron coatings have always included a stabilizer as a third element. The only exception is a dimethyl borane coating. This type of coating does not have the stabilizer present in the coating. This process has very limited application because the bath has a very slow deposit rate and the coating is very thin. The deposit rates are in the order of .00015 inches per hour. The thickness of the deposit is limited to about 0.0001-0.0002 inches. These deposits are too thin to be used for wear surfaces. It is therefore a general object of this invention is to provide an article of manufacture coated on at least a portion of its surface with a hard ductile, wear and corrosion resistant metal coating comprising both nickel and boron, by reducing the negative impact caused by co-deposition of a stabilizer. Yet another object of this invention is to provide coating baths from which a hard, ductile, wear and coirosion resistant coating can be deposited on at least a portion of the surface of a metal or activated non-metal substrate. SUMMRY OF THE INVENTION According to the present invention there is provided a novel metal coating Composition containing both nickel and boron and lead tungstate. The coating composition can contain other metal ions such as cobalt. The coating composition is particularly useful for deposition on a surface of an article of manufacture, which is subject to exposure to corrosive conditions or one subject to sliding or rubbing contact with another surface under unusual wearing and bearing pressures. The metal coating composition of the present invention comprises about 67.5 to about 97.0 weight percent nickel, about 0 to about 48.5 weight percent cobalt, about 2.5 to about 10 weight percent boron. Cobalt can be substituted for nickel up to about 50% of the nickel. Preferably the -2- substitution of cobalt for nickel is Less than 25% of the nickel. A preferred range for the nickel coating is 94-97 weight percent nickel and 3-6 weight percent boron. The coating is remarkably hard, yet ductile, and is highly corrosion and wear resistant. It has now been surprisingly dis covered that by using lead tungstate. to stabilize a nickel-horon plating bath it becomes possible to form a nickel/boron coating with even higher hardness that had previously been achieved. Stabilizers have been conventionally added to these plating baths to retard the precipitation of the reducing agent in the coating bath itself. These stabilizers are co-deposited with the nickel coating. This co-depos: tion prevented full formation of the nickel coating thereby limiting the hardness and wear resistance of the nickel poron coating. The discovery was that by substantially preventing co-deposition of the stabilizer the hardness of nickel/boron coating is increased. In accordance with the present invention, lead tungstate precipitates out as a particle in the plating bath rather than co-deposits in the coating. These particles can be removed by trapping the particles in a filtration' system. The present coating is preferably applied to a substrate electrolessly by contacting the substrate with a coating bath/containing nickel ions, lead tungstate ions, a metal, ion complexing agent, and a boroliydride reducing agent at a pF of about 10 to about 14 and at an elevated temperature of about 180 to about 210° F. The coating can be plated at lower temperatures after the plating has been initiated within a temperature range of about 180 to about 210° F DETAILED DESCRIPTION OF THE INVENTION Suitable substrates for electroless deposition are those with so-called catalytically active surfaces including those composed of nickel, cobalt, iron, steel, aluminum, zinc, palladium, platinum, copper, brass, chromium, tungsten, 3 titanium, tin, silver carbon, graphite and alloys thereof. Those materials function catalytically to cause a reduction of the metal ions in the plating bath by the borohydride and thereby results in the deposition of the metal alloy on the surface of the substrate in contact with the plating bath. The plating of aluminum usually requires a protective strike coat to prevent dissolution during plating. Non-metallic substrates such as glass, ceramics and plastics are in general, non-catalytic materials; however, such substances can be sensitized to be catalytically active by producing a film of one of the catalytic materials on its surface. This can be accomplished by a variety of techniques known to those skilled in the art. One preferred procedure involves dipping articles of glass, ceramic, or plastic in a solution of stannous chloride and then contacting the treated surface with a solution of palladium chloride. A thin layer of palladium is thereby reduced on the treated surface. The article can then be plated or coated with the metallic composition in accordance with this invention by contact with a coating bath as detailed below. It is to be noted that magnesium, tungsten carbide and some plastics have exhibited some resistance to deposition of the present coatings. A coating bath for deposition of the present coatings comprises: (1) Nickel ions, about 0.175 to about 2.10 moles per gallon. Calculations were based on a nickel chloride range of .05 to .6 pounds per gallon. A preferred range of nickel ions is about .35 to about 1.57 moles per gallon based on .1 to about .45 pound per gallon of nickel Chloride. (2) Cobalt ions, up to 1.05 moles per gallon but no greater than 50% of the nickel present in the bath; (3) An effective amount of a chemical agent (such as alkali metal hydroxides, particularly sodium and potassium hydroxide and ammonium hydroxide) for adjusting the pH of the bath to between about 10 and about l4 (4) about 2.26 to about, 6.795 Moles per gallon of metal ion complexing agent (which includes ethylenediamine, diethylene triamine, triethylene tetramine, the organic acids, oxalic acids, citric acid, tartaric acid and ethylene diamine terra acetic acid and the water soluble salts as herein described), preferably 3.3 to 3.8 moles per gallon -4- ($) about 0.01 to about; .8 moles per gallon of coating bath of a borohydride reducing agert based on sodium borohydride preferably .020 to .032 moles per gallon of bath. (6) an effective amount of lead tungstate as a stabilizer that can range from about .0143 per grams per gallon to about 0,30 grams per gallon, preferably about 0.0182 to about 0.08 grams per gallon. The borohydride reducing agent can be selected from among the known borohydrides having a good degree of watar solubility and stability in, aqueous solutions. Sodium borohydride is preferred. In addition, substituted borohydrides in which sot more than three of the hydrogen. atoms of the borohydride ion have been replaced can be utilized. Sodium trimethoxyborohydride [NaB(OCH3)3H] is illustrative of that type of compound. The coating bath is prepared to have a pH of about 12 to about 14., Best results have been observed when the pH of the bath is maintained during the coating process within that range and more preferably at about pH 13,5, adjustment of bath pH can be accomplished by addition of any of a wids variety of alkaline salts or solutions thereof. Preferred chemical agents for establishing and maintaining bath pH are the alkall metal hydroxides, particularly sodium and potassium hydroxide, and ammonlum hydroxide. Ammonium hydroxide offers an additional advantage in that the ammonium ion can function to assist metal ion complexing in the costing bath', Due to the high alkalinity of the coating bath, a metal ion cospiexing or sequestering agent is required in the bath to prevent precipitation of the metal icns such as nickel and other netal hydroxides or other basic salts. Importantly, too the metal ion complexlng agent functions to lower metal ion reactivity; the completed or sequestered metal ions have minimal reactivity with the borohydride ions in the bulk solution but do react at the catalytic turfaces of substrates in contact with the solution. The term catalytic surface 5 refers to the surface any article composed of the aforementioned catalytic materials or to the surface of a non-catalytic material which has been sensitized by application of a film of said catalytic materials on its surface. The complexing or sequestering agents suitable for use in this invention include ammonia and organic complex-forming agents containing one or more of the following functional groups primary amino, secondary amino, tertiary amino, immino, carboxy and hydroxy. Many metal ion complexing agents are known in the art. Preferred complexing agents are ethylenediamine, diethylene triamine, triethylene tetramine, the organic acids, oxalic acid, citric acid, tartaric acid and ethylene diamine tetra acetic acid, and the water-soluble salts thereof. The most preferred is ethylene diamine, About 2.26 to about 6.795 moles per gallon of complexing agent are used per gallon of coating bath. This calculation was based on .3 to about .9 pound per gallon of ethylenediamine. Best results have been obtained when about 3.39 to about 3.77 moles per gallon of coating bath. This calculation was based on about 0.45 to about 0,5 pound per gallon of ethylenediamine for each gallon of coating bath. The metal ions like nickel ions in the coating bath are provided by the addition to the bath of the respective water-soluble salts. Any salts of those metals having an anion component which is not antagonistic to the subject coating process is suitable. For example salts of oxidizing acid such as chlorate salts are not desirable since they will react with the borohydride reducing agent in the bath. Cobalt and nickel, chlorides, sulfates, formates, acetates, and other salts whose anions are substantially inert with respect to the other ingredients in the alkaline coating bath are satisfactory. Lead tungstate can be added to the plating bath from a concentrate containing a pH modifier and a complexing agent. The complexing agent can be selected from those mentioned above. The preferred complexing agent is ethylenediamine. -6- The concentrate contains about 2 to abot t 31 grams per gallon of lead tungstate. The preferred range of lead tungstate is about 7 to about 12 grams per gallon. The concentration range of the complexing agent is 100 to 7)0 milliliters. The preferred range of complexing agent is about 300 to about 400 milliliters. The pH of the mixture is above 8, preferably at 10.5. The pH modifier is selected from those bases such as sodium hydroxide/ that are not harmful to the plating bath. The concentrate is added to the bath so that upon dilution the concentration of lead tungstate in the bath can range between about .0143 to about 30 grams per gallon of plating bath. The preferred concentration range is than about .0182 to about .082 grams per gallon of plating bath. The coating bath is typically prepared by forming an aqueous solution of the appropriate amounts. of nickel and cobalt salts, adding the complexing agent (s) and stabilizer, adjusting the pH to about 12 to about 14, heating to about 195°F, filtering and finally, immediately before introducing the substrate into the bath, adding the required amounts of sodium borohydride (typically in aqueous alkaline solution), The article to be coated or plated using a bath in accordance with this invention is prepared by mechanical cleaning, degreasing, anode-alkaline cleaning, and finally pickling in an acid bath in accordance with the standard practice in the metal-plating art. 'The substrate can be masked. if necessary to allow deposition of the metal alloy coating only on selected surfaces. Although the present coatings in genera; exhibit excellent adhesion to properly prepared substrate surfaces, in instances where coating adhesion is critical or where some adhesion problems are experienced, coating-adhesion can often be enhanced by depositing a nickel strike electrochemically on the . substrate surface prior to applying the present coating. The cleaned or otherwise surface-prepared article is immersed in the hot (about 180 to about 210oF on selected 7 surfaces. Although the present coatings in general exhibit excellent adhesion to properly prepared substrate surfaces, in instances where coating adhesion is critical or . where some adhesion problems are experienced, coating-adhesion can often be enhanced by depositing a nickel strike electrochemically on the substrate surface prior to applying the present coating. The cleaned or otherwise surface-prepared article is immersed in the hot (about 180 to about 210°F.) coating bath to initiate the coating process. The process is continued until deposition of" the coating has progressed to the desired thickness or until the metal ions are depleted from solution. Deposition rates vary under the conditions of the present process from about 0.1 mil (1 mil-one one-thousandth of an inch) to about 1.5 mil per hour. The preferred range of the ingredients of the plating bath comprises about 35 to about 1, 57 moles per gallon nickel/ about 0.0182 to about .08 moles per gallon lead tungstate ions, about 0.017 to about 0.035 moles per gallon of borohydride. The ratio of nickel, ccbalt, boron and lead tungstate in the present coatings can 5; e adjusted by varying the relative amounts of the metal salt components and borohydride in the coating bath. In accordance with the present invention, under normal usage conditions of the coating, bath lead tungstate and the borohydride reducing agent are added to the coating bath hourly in . amount equivalent to their uage in preparation of the bath initially. The heed to replenish the present coating baths with lead tungstate and borohydride depends on the ratio of coating bath volume to the surface area being coated. Thus replenishment of lead tungstate and borohydride to the present coatinc bath would not usually be required when small surface areas are being treated. One gallon of bath prepared in accordance with the preferred embodiment of the present invention will coat approximately 144 square inches to a thickness of 1 mil. For this result to be achieved the bath is replenished with 'lead. 8 tungstate and borohydride in accordance with the above description as those components are depleted from solution. The pH of the coating, bath will t and to drop during the coating process and should be checked periodically to assure that it is within the preferred pH range of about 12 to about 14. It. has been found that any probles,s with pH maintenance throughout the use of a coating bath can be minimized simply by using a highly alkaline (concentrated sodium hydroxide) solution of borohydride to replenish the borohydride' content of the bath as required. The coating deposition rate from the present electroless coating bath is about 0,1 to about 1 mil per hour and is dependent on bath temperature/ pH, and metal ion concentration. The deposition rate on most metal substrates from freshly prepared coating baths at a preferred temperature of about 185 to about 195°F is approximately 1 mil per hour. The practical aspects carrying out electroless coating processes are well known in the art. Such processes are disclosed generally in U.S. Pat. Nos. 5,109,613 issued to McComas on Hay 28, 1991; 3,338,726 issued to Berzins on Aug. 19, 1961; 3,096,182 issued to Berzins on Jul. 2, 1963; 3,045,554 issued to Berzins on Oct. 1, 1958; 3,378,400 issued to Sickles on Apr. 16, 1968; and 2,C58.841 issued to Gutzeit and Krieg on Nov. 10, 1953; the disclosures of. which are, hereby incorporated by reference. The electroless nickel coatings of the present indention exhibit unprecedented hardness and concomitant wear resistance. They are highly ductile allowing the coating to flex with the substrate while maintainirg a strong bond to the coated material. The coatings are amorpnous, and nonporous. After the nickel coating ,is deposited on a substrate, the conventional step in the prior art is to heat, treat the coating to achieve maximum hardness. prior to heat treatment the prior art nickel/boron coatings had a Knoop hardness of approximately 925. After heat treatment, the prior art nickel/boron coatings had Knoop hardness below 1373. In 9 contrast by using lead tungstate as a stabilizer the Knoop Hardness of the nickel/boron coating before heat treatment is about 1000. After heat treatment, the Knoop hardness Of the nickel/boron coating is in excess of 137£. The heat treatment is accomplished at a temperature of about 375 to about; 750°F. for a period of about one to about 24 hours. Shorter times, about one to two hours, is preferred for the higher temperatures of between about 550-750°F. Longer heat treatment times have been shown to be advantageous at the lower temperature ranges of between about. 375 to about 4S0°F. The structure of the nickel/baron coating changes during heat treatment. Before heat treatment the nickel and boron appear to combine to form a alloy. After heat treatment nickel, boride is formed. The coating appears to be a nickel boride dispersion within the nickel/boron alloy. Any thickness of the coating can be achieved Coatings thickness greater than 0001 inch to .04 inch or greater can be produced. Conventional wear coatings having a thickness range from about .0005 inch to about -004 inch can be produced. The present coatings have a wide range of applications, which will be recognized by those skilled in the art. They have particular utility for coating surfaces of articles that under normal use are subjected to highly abrasive, rubbing, or sliding conditions under high temperatures/pressures. Such high wear conditions are found at many ;points in construction of tools, internal combustion engines including gas turbine engines,, transmissions and in a wide variety of heavy equipment construction applications. The following example provide details of bath compositions, process conditions, and coating compositions and properties representative of the present invention. The example is illustrative of the invention and are not in anyway to be taken as limiting the scope thereof. to EXAMPLE A one(l) gallon batch unit of coating bath was prepared as follows, " For the purposes of this example, four solutions: were prepared: A (the bath), B the reducer), C (the stabiliser), and D (the bath replenishes:) . Firsts one gallon batches of each solution were prepared. Solution A (the bath) consisted of deoionised water, 0.2 lb. nickel chloride, O.S lb. ethyenediamine, and 0.33 lb. of sodium hydroxide. Solution B {the reducer) consisted of deionized water, 2. 5 lbs. of= sodium hydroxide and .8 lbs, of sodium borbhydride Solution C (the stabilizer) consisted of deionized water, 100 grams of sodium hydroxide and 10 qrams of lead tungstate and 400 ml of ethylene diamine. Solution D (the bath replenished consisted of deionized water, .6 lb. oil nickel chloride, 1.5 lbs. Of ethylenediamine and 1.0 lb. of sodium hydroxide (solution D was the same as solution A, but with less water) . Solution A was heated to 192°F. Two ln x 11' panels of stainless steel were cleaned with detergent, so that the panels are free of oil and soil. The panels were fixed to a steel wire and placed in a solution of 30% HC1 and 20% H2S04 for SO seconds in order to activate the parts. Just before the panels were placed into the bath for plating, 10 mls of Solution B mixed with 10 mls of Soluticn c were added to the heated Solution A. For solution C, ?- 12 milliliters can be used. After. 30 minutes, Solution A was titrated for the presence and amount of sodium borbhydride. An additional 10 mls of Solution B and 10 mis of Solution C, mixed together, were added after every 30 minutes of plating. The plating continued for 3 hours. After 3 hours, the panels were removed from the bath, and measured for deposit thickness. The heat treatment was at 7S0°F for ninety minutes. The panels measured .0347 inches before plating and .040? inch after plating, showing a total thickness increase of .006 inch, or ,003 inch per side, or a deposition rate of .001 inch per hour. 11 The panels were continuous without any blotches, and free from porosity. The panels were then cut, mounted, cross-sectioned and checked for hardness in accordance to standard micro hardness test studies. The coating could then be examined in the profile showing the interface area between the coating and substrate. This area was free of voids and foreign matter. The hardness of the coated panels was measured, using a Knoop indentor with a 100-gram load. The hardness values before heat treatment was about 950 to about 1050. The hardness values after heat treatments vere as follows; 1545, 1685, 1610, 1785, 1660, 1710, 1690, 1820, 1730, and 1710. If the highest and lowest value were dismissed and the remaining values averaged to a final hardness value of 1697. This shows that the novel plating composition produces reproducible high hardness values. This is at least 25% harder than other nickel boron coatings in the prior art and, therefore, manifested as much as a 300% improvement in wear resistance. The remaining plated samples wers analyzed using XCp technology to find the quantitative composition of the coating. The ICP results (X-ray) showed a composition of 95.5% nickel and 4.5% boron and trace elements with a probable error of 5%. Before heat treatment: the coating was a nickel/boron alloy. After heat treatmant the coating had a dispersion of nickel boride in the nickel/boron alloy. Heat-treated coatings in accordance with the present invention have been found to have a Kroop hardness value of between about 1400 and to about 2200. These values are higher than the best hardness values previously reported for nickel boron electxoless coatings. The present invention of using lead tungstate was compared to prior art nickel-plating baths using thallium as the stabilizer. In Bellis, US Patent Number 3,574,447, example: 3 produced a coating of nickel 93%; boron 3.5%; thallium 3.5% with a knoop hardness of 900-l000. In Klein, US Patent Number 3,295,999, example 2 produced a coating of 12 nickel 93%, boron 4%, and thallium 3% with a knoop hardness of 1000-1100. In McComas, US Patent Number: 5,109,613 example 1, produced a coating of nickel 90% cobalt 4% boron 4%; thallium 2% with a knoop hardness of 1200-1300. The knoop hardness of the Bellis and McComas coatings before heat treatment was measured to be less than about 925. These comparisons show the unexpected results of using lead tungstate as the stabiliser by achieving Knoop hardness from 1335 to 2200 after heat treatment and 950- 1050 before heat treatment with a continuous- coating free from any blotches. The concentration of lead tungstate in the bath was varied producing the following results. In grams per gallon of lead tungstate in , the bath:, at 00115 grams the bath was unstabler at .003 grams a slight improviwnent was observed; at .008 grams the deposition rate was uncontrollable with mild drop out after 10 minutes; at .0104 grams the bath was unstable with severe seed out; at .013 grams the bath was unstable with severe seed out; at .0116 grams the bath was unstable with seed out; at .0182 grams the bath was initially unstable but corrected it self in time; at .0208 grams good results; at . 05 grams excellent results; at .56 grams good results; at .06 grams good results; at .365 grams good results but slow deposition rates; at .07 grams same results; at .09 grams slower deposition rate; at .1 grams. slower deposition rates of about .0004 mils per hour; at .2 grams slow deposition rates of about .0003 mil/hour; at .3 grams same; at .4 grams plating stops. At about .0104 grams to about .014 grams per gallon of lead tungstate a non uniform coating was observed. The coating covered the surface with blotches. The structure of the costing was irregular. When the Lead tungstate in the bath ancreased above about 0.0142 the coating become continuous and uniform The blotches disappeared. 13 These results show that the cpncentration of lead tungstate in the bath can range betweer. about .0142 to 0.30 grams per gallon of plating bath. The preferred concentration range is from about .0128 grams to about .2 grams. with respect to the above description then, it is to be realized that the optimum proportions, process steps, and ingredients of the invention, to include variations in size/ materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will ;:eadily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be :resorted to, falling within the scope of the invention-How that the invention has been described, 14 WE CLAIM: 1. A coaling composition containing nickel and boron comprising a nickel horide dispersed in a nickel/boron alloy wherein (ho nickel is 67.5 to 97.0 wt%, and the boron is 2.5 to 10 wt% and the coaling has a Knoop hardness greater than 1385 and wherein ihe coaling is continuous and free from blotches. 2. A coating composition containing nickel and horon as claimed in claim I. wherein said wear resisiani coaling comprises from 93 to 97 wt% nickel and 7 to 3 wt% horon. .V A coating composition containing nickel and horon as claimed in claim 2. wherein said wear resistant coaling has a Knoop hardness of at least ahoul 1400 lo about 2200. 4. A coating composition containing nickel and horon as claimed in claim I. wherein said wear resistant coating has a thickness from ahout .001 to .04 inch. 5. A coating composition containing nickel and horon as claimed in claim I. wherein cobalt is substituted for nickel up to ahoul 50% of the nickel. 6. A coaling hath for providing a hard, wear and corrosion resisiani. ductile coating on a substrate, said bath having a pH of 10 to 14 and comprising. (I )0. I 75 to 2.10 moles per gallon of coaling hath of nickel ions: (2) an effective amount of lead lungstate to stabilize the bath and to form a continuous coating free from blotches without any substantial deposition of lead lungsiate in the coaling: -15- (3) an effective amount: of metal ion complexing agent (which includes ethylenediamine. dicthylene triamine, tricrhylcne leiramine. the organic acids, oxalic acids, citric acid, tartaric acid and ethylene diamine tetra acetic acid'and the water soluble salts as herein described), in an amount sufficient to inhibit precipitation of said metal ions from the coating bath: (4) an effective amount of a borohydride (such as sodium horohydride & sodium triniethoxyborohydride) reducing agent; and (5 ) optionally up to I .05 moles per gallon of cobalt. 7. The coaling bath as claimed in claim 6, wherein the bath containing about 0.0156 to about 3 grams per gallon lead lungstate as a stabilizer. 8. The coaling bath as claimed in claim 6, wherein the metal ion complexing agent is selected from the group of ethylenediamine, diethylene triamine. triethvlene teiramine the organic acids, oxalic acids, citric acid, tartaric acid and ethylene diamine terra acetic acid and the water soluble salts as herein described and ammonia. 9. The coating bath as claimed in claim S, wherein the metal ion complexing agent is ethylenediamine. 10. The coaling bath as claimed in claim 7 wherein the borohydride reducing agent is selected from the group consisting of sodium borohydride. potassium borohydride. sodium trimethoxyborohydride. and potassium trimeihoxyborohydride. -16- 1 1. The coaling bath as claimed in claim 10 wherein the borohydride reducing agent is sodium borohydride. 1.2. The coaling hath as claimed in claim. UK wherein the borohydride concentration is about .01 7 to about .035 moles per gallon. 13. The coating bath as claimed in claim 6 wherein the concentration of metal ion complexing compound is from about 2.26 lo about 6.795 moles per gallon of coaling both. 14. The coaling bath as claimed in claim 7 wherein the nickel ion concentration is about 0.35 to about. 1.57 moles per gallon. 15. The coating bath as claimed in claim 6 wherein the lead tumgstate ion concentration is about. .0182 to about 0.25 grams per gallon. lb. A method for depositing a metal coating containing nickel, and boron on a substrate, said method composing: providing a plating bath according to claim 6; immersing said substrate to be coaled into said bath; and electrolessly depositing the coating on the substrate. 17. The method as claimed in claim 16, wherein the pH of said bath prior to coating is adjusted to between about 12 and 14. which can be accomplished by addition of any of a wide variety of alkaline salts of solutions thereof. Preferred chemical agents for establishing and maintaining bath pH are the alkali metal hydroxides, particularly sodium and potassium hydroxide, and ammonium hydroxide. -17- 18. The method as claimed in claim 16 wherein the metal ion completing agent comprises a compound selected from the group consising of ethylenediamine, water soluble sails of tartaric acid and ammonia 19. The method as claimed in claim 18 wherein the metal ions complexing agent is elhylenediamine. 20. The method as claimed in claim 16 wherein the borohydride reducing agent is seleeted from the group consisting, of sodium borohydride, potassium borohydride. sodium trimethoxyborohydride. and potassium trimethoxyborohydride. 21. The meihod as claimed in claim 20 wherein the borohydride is reducing agent is sodium borohydride. 22. The meihod as claimed in claim 16 where in the metal coaling is heat-treated. 23. A coaling bath lor providing a hard, wear and corrosion resistant, ductile coating on a substrate, said bath having a pH. of about 12 to about 14 and comprising: (I) about 0.35 to about 1.57 moles per gallon of coaling bath of nickel ions; (2 ) about 0.0208 to aboul .08 grams per gallon lead lungstate as a stabilizer: (3)about 3.3 to about 3.8 moles per gallon of metal ion complexing agent to inhibit precipitation of said metal ions from the coating, bath: (4) about .045 lo about .08 moles per gallon of a borohydride reducing agent; and -18- (5) optionally cobalt. 24. A coaling composition as claimed in any of the claims I to 5 wherein said coaling comprises 67.5 to 97 wt% nickel. 2.5 to 10 wt% boron, said coating having thiekness in excess 0.0003 inch and a Knoop hardness of at cast about 950-1050 and wherein said coating has not been heat treated and the coating is continuous, and blotch free. 25. The coating bath produced according to claim 6. wherein the bath is formed by combining the ingredicnts (1). (2). (3), (4) and optionally (5). 26. A coating composition as claimed in any of the claims 1 io 4, wherein the coaling has a ihiekness in excess of .00025 inch 27. A coaling bath for providing a hard, wear and corrosion resistant", ductile coating on a substrate as claimed in claim 23, wherein the substrate is a metal such as nickel, cobalt, iron, steel, aluminum, zinc palladium, platinum, copper, brass, chromium, tungsten, titanium, tin, silver carbon, graphite and their alloys thereof. 28. An article, having a continuous wear-resistant amorphous coaling free from blotches, consisting essentially of a nickel boride dispersed in a nickel/ boron alloy wherein the nickel is 67.5 to 97.0 wt%. and the boron is 02.5 to 10 wt% and the coating has a Knoop hardness greater than about 1385. Dated this 18th day of October 2000 -19- A coating composition containing nickel and boron and method for coating the same using a coating bath that provides a hard, wear and corrosion resistant, ductile coating on a substrate, said bath having a pH of about 10 to 14 and comprising: (I) about 0,175 to about 2,10 moles per gallon of coating bath of nickel ions; (2) an effective amount of lead rungstate to stabilize the bath and to form a continuous coating free from blotches without any substantial deposition of lead tungstate in the coating; (3) an effective amount of metal ion complexfng agent in an amount sufficient to inhibit precipitation of said metal ions from the coating bath ; and (4) an effective amount of a borohydride reducing agent.

Full Text

This invention is a continuation, in part Of United State Patent Application Number 09/074,703 filed May 8, 1998:
BACKGROUND OF THE INVENTION
This invention relates to novel metal coatings, which exhibit exceptional hardness. More particularly this invention relates to metal coatings containing nickel and boron end to the reductive deposition of said coatings on the surfaces of substrate articles from aqieous solutions at an alkaline pH.
The plating or deposition of metal alloys by chemical or electrochemical reduction of metal ions on the surface of an article to modify its surface characteristics for both decorative and functional purposes is tell known in the art. Of particular commercial significance is the deposition of metal/metal alloy coatings on both, metal and activated non-metal substrates to enhance surface hardness and resistance to corrosion and wear. Nickel-boron and cobalt-boron alloy coatings are recognized in the art for their hardness and associated wear-resistance. The patent literature reflects an. ongoing research and development effort in the area of nickel-boron coatings with the goal of producing still harder, more corrosion resistance coatings. For example, see, U.S. Pat. Nos. 5,019,1,63; 3,738,849; 3,674,447; 3,342,338; 3,378,400; 3,045,3342; and 726,710- The art has recognized that when borohydride is used in a nickel/boron plating bath a harder coating is achieved. However, borohyd::ide, is very unstable; in the bath. The solution to the stability problem has beer: to add stabilizers such as thallium sulfate or lead chloride. The addition of the Stabilizers had the effect of interfering with the formation of the nickel coating thereby negatively impacting the hardness of the coating. Because the stabilizer is not co-deposited in the coating in accordance with the

present invention the nickel coating is remarkably more hard than those described in the prior art.
To-date nickel/boron coatings have always included a stabilizer as a third element. The only exception is a dimethyl borane coating. This type of coating does not have the stabilizer present in the coating. This process has very limited application because the bath has a very slow deposit rate and the coating is very thin. The deposit rates are in the order of .00015 inches per hour. The thickness of the deposit is limited to about 0.0001-0.0002 inches. These deposits are too thin to be used for wear surfaces.
It is therefore a general object of this invention is to provide an article of manufacture coated on at least a portion of its surface with a hard ductile, wear and corrosion resistant metal coating comprising both nickel and boron, by reducing the negative impact caused by co-deposition of a stabilizer.
Yet another object of this invention is to provide coating baths from which a hard, ductile, wear and coirosion resistant coating can be deposited on at least a portion of the surface of a metal or activated non-metal substrate.
SUMMRY OF THE INVENTION
According to the present invention there is provided a novel metal coating Composition containing both nickel and boron and lead tungstate. The coating composition can contain other metal ions such as cobalt. The coating composition is particularly useful for deposition on a surface of an article of manufacture, which is subject to exposure to corrosive conditions or one subject to sliding or rubbing contact with another surface under unusual wearing and bearing pressures. The metal coating composition of the present invention comprises about 67.5 to about 97.0 weight percent nickel, about 0 to about 48.5 weight percent cobalt, about 2.5 to about 10 weight percent boron. Cobalt can be substituted for nickel up to about 50% of the nickel. Preferably the
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substitution of cobalt for nickel is Less than 25% of the nickel. A preferred range for the nickel coating is 94-97 weight percent nickel and 3-6 weight percent boron. The coating is remarkably hard, yet ductile, and is highly corrosion and wear resistant.
It has now been surprisingly dis covered that by using lead tungstate. to stabilize a nickel-horon plating bath it becomes possible to form a nickel/boron coating with even higher hardness that had previously been achieved. Stabilizers have been conventionally added to these plating baths to retard the precipitation of the reducing agent in the coating bath itself. These stabilizers are co-deposited with the nickel coating. This co-depos: tion prevented full formation of the nickel coating thereby limiting the hardness and wear resistance of the nickel poron coating. The discovery was that by substantially preventing co-deposition of the stabilizer the hardness of nickel/boron coating is increased. In accordance with the present invention, lead tungstate precipitates out as a particle in the plating bath rather than co-deposits in the coating. These particles can be removed by trapping the particles in a filtration' system.
The present coating is preferably applied to a substrate electrolessly by contacting the substrate with a coating bath/containing nickel ions, lead tungstate ions, a metal, ion complexing agent, and a boroliydride reducing agent at a pF of about 10 to about 14 and at an elevated temperature of about 180 to about 210° F. The coating can be plated at lower temperatures after the plating has been initiated within a temperature range of about 180 to about 210° F
DETAILED DESCRIPTION OF THE INVENTION
Suitable substrates for electroless deposition are
those with so-called catalytically active surfaces including
those composed of nickel, cobalt, iron, steel, aluminum, zinc,
palladium, platinum, copper, brass, chromium, tungsten,
3

titanium, tin, silver carbon, graphite and alloys thereof. Those materials function catalytically to cause a reduction of the metal ions in the plating bath by the borohydride and thereby results in the deposition of the metal alloy on the surface of the substrate in contact with the plating bath. The plating of aluminum usually requires a protective strike coat to prevent dissolution during plating. Non-metallic substrates such as glass, ceramics and plastics are in general, non-catalytic materials; however, such substances can be sensitized to be catalytically active by producing a film of one of the catalytic materials on its surface. This can be accomplished by a variety of techniques known to those skilled in the art. One preferred procedure involves dipping articles of glass, ceramic, or plastic in a solution of stannous chloride and then contacting the treated surface with a solution of palladium chloride. A thin layer of palladium is thereby reduced on the treated surface. The article can then be plated or coated with the metallic composition in accordance with this invention by contact with a coating bath as detailed below. It is to be noted that magnesium, tungsten carbide and some plastics have exhibited some resistance to deposition of the present coatings.
A coating bath for deposition of the present coatings comprises:
(1) Nickel ions, about 0.175 to about 2.10 moles per gallon. Calculations were
based on a nickel chloride range of .05 to .6 pounds per gallon. A preferred range of
nickel ions is about .35 to about 1.57 moles per gallon based on .1 to about .45 pound
per gallon of nickel Chloride.
(2) Cobalt ions, up to 1.05 moles per gallon but no greater than 50% of the nickel present in the bath;
(3) An effective amount of a chemical agent (such as alkali metal hydroxides, particularly sodium and potassium hydroxide and ammonium hydroxide) for adjusting the pH of the bath to between about 10 and about l4
(4) about 2.26 to about, 6.795 Moles per gallon of metal ion complexing agent (which includes ethylenediamine, diethylene triamine, triethylene tetramine, the organic acids, oxalic acids, citric acid, tartaric acid and ethylene diamine terra acetic acid and the water soluble salts as herein described), preferably 3.3 to 3.8 moles per gallon
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($) about 0.01 to about; .8 moles per gallon of coating bath of a borohydride reducing agert based on sodium borohydride preferably .020 to .032 moles per gallon of bath. (6) an effective amount of lead tungstate as a stabilizer that can range from about .0143 per grams per gallon to about 0,30 grams per gallon, preferably about 0.0182 to about 0.08 grams per gallon.
The borohydride reducing agent can be selected from among the known borohydrides having a good degree of watar solubility and stability in, aqueous solutions. Sodium borohydride is preferred. In addition, substituted borohydrides in which sot more than three of the hydrogen. atoms of the borohydride ion have been replaced can be utilized. Sodium trimethoxyborohydride [NaB(OCH3)3H] is illustrative of that type of compound.
The coating bath is prepared to have a pH of about 12 to about 14., Best results have been observed when the pH of the bath is maintained during the coating process within that range and more preferably at about pH 13,5, adjustment of bath pH can be accomplished by addition of any of a wids variety of alkaline salts or solutions thereof. Preferred chemical agents for establishing and maintaining bath pH are the alkall metal hydroxides, particularly sodium and potassium hydroxide, and ammonlum hydroxide. Ammonium hydroxide offers an additional advantage in that the ammonium ion can function to assist metal ion complexing in the costing bath',
Due to the high alkalinity of the coating bath, a metal ion cospiexing or sequestering agent is required in the bath to prevent precipitation of the metal icns such as nickel and other netal hydroxides or other basic salts. Importantly, too the metal ion complexlng agent functions to lower metal ion reactivity; the completed or sequestered metal ions have minimal reactivity with the borohydride ions in the bulk solution but do react at the catalytic turfaces of substrates in contact with the solution. The term catalytic surface
5

refers to the surface any article composed of the aforementioned catalytic materials or to the surface of a non-catalytic material which has been sensitized by application of a film of said catalytic materials on its surface.
The complexing or sequestering agents suitable for use in this invention include ammonia and organic complex-forming agents containing one or more of the following functional groups primary amino, secondary amino, tertiary amino, immino, carboxy and hydroxy. Many metal ion complexing agents are known in the art. Preferred complexing agents are ethylenediamine, diethylene triamine, triethylene tetramine, the organic acids, oxalic acid, citric acid, tartaric acid and ethylene diamine tetra acetic acid, and the water-soluble salts thereof. The most preferred is ethylene diamine,
About 2.26 to about 6.795 moles per gallon of complexing agent are used per gallon of coating bath. This calculation was based on .3 to about .9 pound per gallon of ethylenediamine. Best results have been obtained when about 3.39 to about 3.77 moles per gallon of coating bath. This calculation was based on about 0.45 to about 0,5 pound per gallon of ethylenediamine for each gallon of coating bath.
The metal ions like nickel ions in the coating bath are provided by the addition to the bath of the respective water-soluble salts. Any salts of those metals having an anion component which is not antagonistic to the subject coating process is suitable. For example salts of oxidizing acid such as chlorate salts are not desirable since they will react with the borohydride reducing agent in the bath. Cobalt and nickel, chlorides, sulfates, formates, acetates, and other salts whose anions are substantially inert with respect to the other ingredients in the alkaline coating bath are satisfactory.
Lead tungstate can be added to the plating bath from a concentrate containing a pH modifier and a complexing agent. The complexing agent can be selected from those mentioned above. The preferred complexing agent is ethylenediamine.
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The concentrate contains about 2 to abot t 31 grams per gallon of lead tungstate. The preferred range of lead tungstate is about 7 to about 12 grams per gallon. The concentration range of the complexing agent is 100 to 7)0 milliliters. The preferred range of complexing agent is about 300 to about 400 milliliters. The pH of the mixture is above 8, preferably at 10.5. The pH modifier is selected from those bases such as sodium hydroxide/ that are not harmful to the plating bath.
The concentrate is added to the bath so that upon dilution the concentration of lead tungstate in the bath can range between about .0143 to about 30 grams per gallon of plating bath. The preferred concentration range is than about .0182 to about .082 grams per gallon of plating bath.
The coating bath is typically prepared by forming an aqueous solution of the appropriate amounts. of nickel and cobalt salts, adding the complexing agent (s) and stabilizer, adjusting the pH to about 12 to about 14, heating to about
195°F, filtering and finally, immediately before introducing the substrate into the bath, adding the required amounts of sodium borohydride (typically in aqueous alkaline solution),
The article to be coated or plated using a bath in accordance with this invention is prepared by mechanical cleaning, degreasing, anode-alkaline cleaning, and finally pickling in an acid bath in accordance with the standard practice in the metal-plating art. 'The substrate can be masked. if necessary to allow deposition of the metal alloy coating only on selected surfaces. Although the present coatings in genera; exhibit excellent adhesion to properly prepared substrate surfaces, in instances where coating adhesion is critical or where some adhesion problems are experienced, coating-adhesion can often be enhanced by depositing a nickel strike electrochemically on the . substrate surface prior to applying the present coating.
The cleaned or otherwise surface-prepared article is immersed in the hot (about 180 to about 210oF on selected
7

surfaces. Although the present coatings in general exhibit excellent adhesion to properly prepared substrate surfaces, in instances where coating adhesion is critical or . where some adhesion problems are experienced, coating-adhesion can often be enhanced by depositing a nickel strike electrochemically on the substrate surface prior to applying the present coating.
The cleaned or otherwise surface-prepared article is
immersed in the hot (about 180 to about 210°F.) coating bath to initiate the coating process. The process is continued until deposition of" the coating has progressed to the desired thickness or until the metal ions are depleted from solution. Deposition rates vary under the conditions of the present process from about 0.1 mil (1 mil-one one-thousandth of an inch) to about 1.5 mil per hour.
The preferred range of the ingredients of the plating bath comprises about 35 to about 1, 57 moles per gallon nickel/ about 0.0182 to about .08 moles per gallon lead tungstate ions, about 0.017 to about 0.035 moles per gallon of borohydride. The ratio of nickel, ccbalt, boron and lead tungstate in the present coatings can 5; e adjusted by varying the relative amounts of the metal salt components and borohydride in the coating bath.
In accordance with the present invention, under normal usage conditions of the coating, bath lead tungstate and the borohydride reducing agent are added to the coating bath hourly in . amount equivalent to their uage in preparation of the bath initially. The heed to replenish the present coating baths with lead tungstate and borohydride depends on the ratio of coating bath volume to the surface area being coated. Thus replenishment of lead tungstate and borohydride to the present coatinc bath would not usually be required when small surface areas are being treated.
One gallon of bath prepared in accordance with the preferred embodiment of the present invention will coat approximately 144 square inches to a thickness of 1 mil. For this result to be achieved the bath is replenished with 'lead.
8

tungstate and borohydride in accordance with the above description as those components are depleted from solution.
The pH of the coating, bath will t and to drop during the coating process and should be checked periodically to assure that it is within the preferred pH range of about 12 to about 14. It. has been found that any probles,s with pH maintenance throughout the use of a coating bath can be minimized simply by using a highly alkaline (concentrated sodium hydroxide) solution of borohydride to replenish the borohydride' content of the bath as required. The coating deposition rate from the present electroless coating bath is about 0,1 to about 1 mil per hour and is dependent on bath temperature/ pH, and metal ion concentration. The deposition rate on most metal substrates from freshly prepared coating baths at a preferred temperature of
about 185 to about 195°F is approximately 1 mil per hour.
The practical aspects carrying out electroless coating processes are well known in the art. Such processes are disclosed generally in U.S. Pat. Nos. 5,109,613 issued to McComas on Hay 28, 1991; 3,338,726 issued to Berzins on Aug. 19, 1961; 3,096,182 issued to Berzins on Jul. 2, 1963; 3,045,554 issued to Berzins on Oct. 1, 1958; 3,378,400 issued to Sickles on Apr. 16, 1968; and 2,C58.841 issued to Gutzeit and Krieg on Nov. 10, 1953; the disclosures of. which are, hereby incorporated by reference.
The electroless nickel coatings of the present indention exhibit unprecedented hardness and concomitant wear resistance. They are highly ductile allowing the coating to flex with the substrate while maintainirg a strong bond to the coated material. The coatings are amorpnous, and nonporous.
After the nickel coating ,is deposited on a substrate, the conventional step in the prior art is to heat, treat the coating to achieve maximum hardness. prior to heat treatment the prior art nickel/boron coatings had a Knoop hardness of approximately 925. After heat treatment, the prior art nickel/boron coatings had Knoop hardness below 1373. In
9

contrast by using lead tungstate as a stabilizer the Knoop Hardness of the nickel/boron coating before heat treatment is about 1000. After heat treatment, the Knoop hardness Of the nickel/boron coating is in excess of 137£.
The heat treatment is accomplished at a temperature of
about 375 to about; 750°F. for a period of about one to about 24 hours. Shorter times, about one to two hours, is preferred for the higher temperatures of between about 550-750°F. Longer heat treatment times have been shown to be advantageous at the lower temperature ranges of between about. 375 to about 4S0°F.
The structure of the nickel/baron coating changes during heat treatment. Before heat treatment the nickel and boron appear to combine to form a alloy. After heat treatment nickel, boride is formed. The coating appears to be a nickel boride dispersion within the nickel/boron alloy. Any thickness of the coating can be achieved Coatings thickness greater than 0001 inch to .04 inch or greater can be produced. Conventional wear coatings having a thickness range from about .0005 inch to about -004 inch can be produced.
The present coatings have a wide range of applications, which will be recognized by those skilled in the art. They have particular utility for coating surfaces of articles that under normal use are subjected to highly abrasive, rubbing, or sliding conditions under high temperatures/pressures. Such high wear conditions are found at many ;points in construction of tools, internal combustion engines including gas turbine engines,, transmissions and in a wide variety of heavy equipment construction applications.
The following example provide details of bath compositions, process conditions, and coating compositions and properties representative of the present invention. The example is illustrative of the invention and are not in anyway to be taken as limiting the scope thereof.
to

EXAMPLE A one(l) gallon batch unit of coating bath was prepared as follows, " For the purposes of this example, four solutions: were prepared: A (the bath), B the reducer), C (the stabiliser), and D (the bath replenishes:) . Firsts one gallon batches of each solution were prepared. Solution A (the bath) consisted of deoionised water, 0.2 lb. nickel chloride, O.S lb. ethyenediamine, and 0.33 lb. of sodium hydroxide. Solution B {the reducer) consisted of deionized water, 2. 5 lbs. of= sodium hydroxide and .8 lbs, of sodium borbhydride Solution C (the stabilizer) consisted of deionized water, 100 grams of sodium hydroxide and 10 qrams of lead tungstate and 400 ml of ethylene diamine. Solution D (the bath replenished consisted of deionized water, .6 lb. oil nickel chloride, 1.5 lbs. Of ethylenediamine and 1.0 lb. of sodium hydroxide (solution D was the same as solution A, but with less water) .
Solution A was heated to 192°F. Two ln x 11' panels of
stainless steel were cleaned with detergent, so that the panels are free of oil and soil. The panels were fixed to a steel wire and placed in a solution of 30% HC1 and 20% H2S04 for SO seconds in order to activate the parts. Just before the panels were placed into the bath for plating, 10 mls of Solution B mixed with 10 mls of Soluticn c were added to the heated Solution A. For solution C, ?- 12 milliliters can be used.
After. 30 minutes, Solution A was titrated for the presence and amount of sodium borbhydride. An additional 10 mls of Solution B and 10 mis of Solution C, mixed together, were added after every 30 minutes of plating. The plating continued for 3 hours.
After 3 hours, the panels were removed from the bath, and measured for deposit thickness. The heat treatment was at
7S0°F for ninety minutes. The panels measured .0347 inches before plating and .040? inch after plating, showing a total thickness increase of .006 inch, or ,003 inch per side, or a deposition rate of .001 inch per hour.
11

The panels were continuous without any blotches, and free from porosity. The panels were then cut, mounted, cross-sectioned and checked for hardness in accordance to standard micro hardness test studies. The coating could then be examined in the profile showing the interface area between the coating and substrate. This area was free of voids and foreign matter.
The hardness of the coated panels was measured, using a Knoop indentor with a 100-gram load. The hardness values before heat treatment was about 950 to about 1050. The hardness values after heat treatments vere as follows; 1545, 1685, 1610, 1785, 1660, 1710, 1690, 1820, 1730, and 1710. If the highest and lowest value were dismissed and the remaining values averaged to a final hardness value of 1697. This shows that the novel plating composition produces reproducible high hardness values. This is at least 25% harder than other nickel boron coatings in the prior art and, therefore, manifested as much as a 300% improvement in wear resistance.
The remaining plated samples wers analyzed using XCp technology to find the quantitative composition of the coating. The ICP results (X-ray) showed a composition of 95.5% nickel and 4.5% boron and trace elements with a probable error of 5%. Before heat treatment: the coating was a nickel/boron alloy. After heat treatmant the coating had a dispersion of nickel boride in the nickel/boron alloy.
Heat-treated coatings in accordance with the present invention have been found to have a Kroop hardness value of between about 1400 and to about 2200. These values are higher than the best hardness values previously reported for nickel boron electxoless coatings.
The present invention of using lead tungstate was compared to prior art nickel-plating baths using thallium as the stabilizer. In Bellis, US Patent Number 3,574,447, example: 3 produced a coating of nickel 93%; boron 3.5%; thallium 3.5% with a knoop hardness of 900-l000. In Klein, US Patent Number 3,295,999, example 2 produced a coating of
12

nickel 93%, boron 4%, and thallium 3% with a knoop hardness of 1000-1100. In McComas, US Patent Number: 5,109,613 example 1, produced a coating of nickel 90% cobalt 4% boron 4%; thallium 2% with a knoop hardness of 1200-1300. The knoop hardness of the Bellis and McComas coatings before heat treatment was measured to be less than about 925.
These comparisons show the unexpected results of using lead tungstate as the stabiliser by achieving Knoop hardness from 1335 to 2200 after heat treatment and 950- 1050 before heat treatment with a continuous- coating free from any blotches.
The concentration of lead tungstate in the bath was varied producing the following results. In grams per gallon of lead tungstate in , the bath:, at 00115 grams the bath was unstabler at .003 grams a slight improviwnent was observed; at .008 grams the deposition rate was uncontrollable with mild drop out after 10 minutes; at .0104 grams the bath was unstable with severe seed out; at .013 grams the bath was unstable with severe seed out; at .0116 grams the bath was unstable with seed out; at .0182 grams the bath was initially unstable but corrected it self in time; at .0208 grams good results; at . 05 grams excellent results; at .56 grams good results; at .06 grams good results; at .365 grams good results but slow deposition rates; at .07 grams same results; at .09 grams slower deposition rate; at .1 grams. slower deposition rates of about .0004 mils per hour; at .2 grams slow deposition rates of about .0003 mil/hour; at .3 grams same; at .4 grams plating stops.
At about .0104 grams to about .014 grams per gallon of lead tungstate a non uniform coating was observed. The coating covered the surface with blotches. The structure of the costing was irregular. When the Lead tungstate in the bath ancreased above about 0.0142 the coating become continuous and uniform The blotches disappeared.
13

These results show that the cpncentration of lead tungstate in the bath can range betweer. about .0142 to 0.30 grams per gallon of plating bath. The preferred concentration range is from about .0128 grams to about .2 grams.
with respect to the above description then, it is to be realized that the optimum proportions, process steps, and ingredients of the invention, to include variations in size/ materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those described in the specification are intended to be encompassed by the present invention.
Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will ;:eadily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be :resorted to, falling within the scope of the invention-How that the invention has been described,
14

WE CLAIM:
1. A coaling composition containing nickel and boron comprising a nickel horide dispersed in a nickel/boron alloy wherein (ho nickel is 67.5 to 97.0 wt%, and the boron is 2.5 to 10 wt% and the coaling has a Knoop hardness greater than 1385 and wherein ihe coaling is continuous and free from blotches.
2. A coating composition containing nickel and horon as claimed in claim I. wherein said wear resisiani coaling comprises from 93 to 97 wt% nickel and 7 to 3 wt% horon.
.V A coating composition containing nickel and horon as claimed in claim 2. wherein said wear resistant coaling has a Knoop hardness of at least ahoul 1400 lo about 2200.
4. A coating composition containing nickel and horon as claimed in claim I. wherein said wear resistant coating has a thickness from ahout .001 to .04 inch.
5. A coating composition containing nickel and horon as claimed in claim I. wherein cobalt is substituted for nickel up to ahoul 50% of the nickel.
6. A coaling hath for providing a hard, wear and corrosion resisiani. ductile coating on a substrate, said bath having a pH of 10 to 14 and comprising. (I )0. I 75 to 2.10 moles per gallon of coaling hath of nickel ions:
(2) an effective amount of lead lungstate to stabilize the bath and to form a continuous coating free from blotches without any substantial deposition of lead lungsiate in the coaling:
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(3) an effective amount: of metal ion complexing agent (which includes ethylenediamine. dicthylene triamine, tricrhylcne leiramine. the organic acids, oxalic acids, citric acid, tartaric acid and ethylene diamine tetra acetic acid'and the water soluble salts as herein described), in an amount sufficient to inhibit precipitation of said metal ions from the coating bath:
(4) an effective amount of a borohydride (such as sodium horohydride & sodium triniethoxyborohydride) reducing agent; and
(5 ) optionally up to I .05 moles per gallon of cobalt.
7. The coaling bath as claimed in claim 6, wherein the bath containing about 0.0156 to about 3 grams per gallon lead lungstate as a stabilizer.
8. The coaling bath as claimed in claim 6, wherein the metal ion complexing agent is selected from the group of ethylenediamine, diethylene triamine. triethvlene teiramine the organic acids, oxalic acids, citric acid, tartaric acid and ethylene diamine terra acetic acid and the water soluble salts as herein described and ammonia.

9. The coating bath as claimed in claim S, wherein the metal ion complexing agent is ethylenediamine.
10. The coaling bath as claimed in claim 7 wherein the borohydride reducing agent is selected from the group consisting of sodium borohydride. potassium borohydride. sodium trimethoxyborohydride. and potassium trimeihoxyborohydride.
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1 1. The coaling bath as claimed in claim 10 wherein the borohydride reducing agent is sodium borohydride.
1.2. The coaling hath as claimed in claim. UK wherein the borohydride concentration is about .01 7 to about .035 moles per gallon.
13. The coating bath as claimed in claim 6 wherein the concentration of metal

ion complexing compound is from about 2.26 lo about 6.795 moles per gallon of coaling both.
14. The coaling bath as claimed in claim 7 wherein the nickel ion concentration is about 0.35 to about. 1.57 moles per gallon.
15. The coating bath as claimed in claim 6 wherein the lead tumgstate ion concentration is about. .0182 to about 0.25 grams per gallon.
lb. A method for depositing a metal coating containing nickel, and boron on a substrate, said method composing: providing a plating bath according to claim 6; immersing said substrate to be coaled into said bath; and electrolessly depositing the coating on the substrate.
17. The method as claimed in claim 16, wherein the pH of said bath prior to coating is adjusted to between about 12 and 14. which can be accomplished by addition of any of a wide variety of alkaline salts of solutions thereof. Preferred chemical agents for establishing and maintaining bath pH are the alkali metal hydroxides, particularly sodium and potassium hydroxide, and ammonium hydroxide.
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18. The method as claimed in claim 16 wherein the metal ion completing agent comprises a compound selected from the group consising of ethylenediamine, water soluble sails of tartaric acid and ammonia
19. The method as claimed in claim 18 wherein the metal ions complexing agent is elhylenediamine.
20. The method as claimed in claim 16 wherein the borohydride reducing
agent is seleeted from the group consisting, of sodium borohydride, potassium
borohydride. sodium trimethoxyborohydride. and potassium
trimethoxyborohydride.
21. The meihod as claimed in claim 20 wherein the borohydride is reducing agent is sodium borohydride.
22. The meihod as claimed in claim 16 where in the metal coaling is heat-treated.
23. A coaling bath lor providing a hard, wear and corrosion resistant, ductile coating on a substrate, said bath having a pH. of about 12 to about 14 and comprising:
(I) about 0.35 to about 1.57 moles per gallon of coaling bath of nickel ions;
(2 ) about 0.0208 to aboul .08 grams per gallon lead lungstate as a stabilizer:
(3)about 3.3 to about 3.8 moles per gallon of metal ion complexing agent
to inhibit precipitation of said metal ions from the coating, bath: (4) about .045 lo about .08 moles per gallon of a borohydride reducing agent; and
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(5) optionally cobalt.
24. A coaling composition as claimed in any of the claims I to 5 wherein said coaling comprises 67.5 to 97 wt% nickel. 2.5 to 10 wt% boron, said coating having thiekness in excess 0.0003 inch and a Knoop hardness of at cast about 950-1050 and wherein said coating has not been heat treated and the coating is continuous, and blotch free.
25. The coating bath produced according to claim 6. wherein the bath is formed by combining the ingredicnts (1). (2). (3), (4) and optionally (5).
26. A coating composition as claimed in any of the claims 1 io 4, wherein the coaling has a ihiekness in excess of .00025 inch
27. A coaling bath for providing a hard, wear and corrosion resistant", ductile coating on a substrate as claimed in claim 23, wherein the substrate is a metal such as nickel, cobalt, iron, steel, aluminum, zinc palladium, platinum, copper, brass, chromium, tungsten, titanium, tin, silver carbon, graphite and their alloys thereof.
28. An article, having a continuous wear-resistant amorphous coaling free from blotches, consisting essentially of a nickel boride dispersed in a nickel/ boron alloy wherein the nickel is 67.5 to 97.0 wt%. and the boron is 02.5 to 10 wt% and the coating has a Knoop hardness greater than about 1385.
Dated this 18th day of October 2000

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A coating composition containing nickel and boron and method for coating the same using a coating bath that provides a hard, wear and corrosion resistant, ductile coating on a substrate, said bath having a pH of about 10 to 14 and comprising: (I) about 0,175 to about 2,10 moles per gallon of coating bath of nickel ions; (2) an effective amount of lead rungstate to stabilize the bath and to form a continuous coating free from blotches without any substantial deposition of lead tungstate in the coating; (3) an effective amount of metal ion complexfng agent in an amount sufficient to inhibit precipitation of said metal ions from the coating bath ; and (4) an effective amount of a borohydride reducing agent.

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Patent Number

200935

Indian Patent Application Number

IN/PCT/2000/00415/KOL

PG Journal Number

N/A

Publication Date

19-Jan-2007

Grant Date

19-Jan-2007

Date of Filing

18-Oct-2000

Name of Patentee

MCCOMAS TECHNOLOGIES AG.,

Applicant Address

POSSARTSTRASE 20,D-81679 MUNCHEN,

Inventors:

#	Inventor's Name	Inventor's Address
1	MCCOMAS, EDWARD	20 EAST WILMOT STREET,RICHMOND HILL,ONTARIO L4B 1C8,

PCT International Classification Number

B23B15/00;C23C18/50

PCT International Application Number

PCT/US99/10032

PCT International Filing date

1999-05-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	09/074,703	1998-05-08	U.S.A.
2	09/306,848	1999-05-07	U.S.A.