Wear Resistant Diamond Coating And Method Of Application

Abstract

A process for producing an extremely hard and wear resistant coating on a basis metal comprising the electro-deposition of fine grained diamonds and diamond particles in a metal matrix upon said basis metal. The coating comprises a uniform electrolytic deposit of a metal matrix having embedded therein diamonds and diamond particles ranging between 0.01 micron to 30 microns in size.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of electroplating and more particularly to the electrodeposition of fine to micro-fine diamonds and diamond particles on a basis metal. The imvention also relates to an electrolytic deposit of a metal matrix having occluded therein fine to micro-fine diamonds and diamond particles and to the plating baths from which the coating are deposited.

2. Description of the Prior Art

It is well known in the electroplating field that the dispersion of certain solid and bath insoluble particles in an electroplating bath will result in the deposition on the basis metal of a coating of the metal of the electroplating bath having dispersed therein the particles of the solid material. The usual procedure has been to suspend in a nickel electroplating bath finely divided particles of certain metals and/or the bath insoluble oxides or salts of these metals. The coating thus produced usually enhances the appearance of the plated article or serves to protect the basis metal from corrosion. However, prior to the present invention, it was not known in the art to electrodeposit a metal matrix having embedded therein very fine diamonds upon the surface of an element to produce an extremely hard and wear resistant coating.

Previously, when it was desired to apply a diamond containing coating to the surface of an article, such as a grinding wheel dresser or the like, the surface was first coated with an adhesive and diamond particles were then sprinkled thereon or manually embedded therein. The diamonds were then rolled or pressed through the adhesive up against the surface of the article. This method, as well as the coating produced thereby, have several major disadvantages. One of these is that minor irregularities may be produced because of the differences in particle size which are inherent in any screening or sizing operations of the diamond particles. Another is the difficulty encountered in accurately positioning the diamonds so that their apexes project the desired amount out of the surface of the adhesive. A third is the difficulty of producing a coating containing more than one layer of diamonds embedded therein.

SUMMARY OF THE INVENTION

The present invention comprises a method of forming a wear resistant coating on an article by the electro-deposition of fine and micro-fine diamond particles upon said article. The article to be plated is made a cathode and a layer which consists essentially of metal and of diamond particles is applied to the surface of the article by simultaneously electroplating said metal and electrophoretically depositing said diamonds from a bath consisting essentially of a salt or acid containing the metallic ion or radical in solution and of said diamonds in suspension.

The plate deposited by this method consists of a metal matrix containing occluded diamond particles. The diamonds are evenly and uniformly distributed throughout the metal matrix thus forming a uniform and continuous plate. The thickness of the deposit can be varied and is dependent on the factors of current strength and the time the article is left in the electrolyzed bath. The density or concentration of the diamonds occluded in the metal matrix can be varied by varying the amount of diamonds present in the plating bath. It is possible to obtain a very thin metal coating containing one layer of diamond particles or a thicker metal coating containing a plurality of layers.

The plating baths of the present invention consist of aqueous solution of the common electroplating metals such as cadmium, antimony, bismuth, chromium, cobalt, copper, gold, indium, iron, lead, nickel, palladium, platinum, rhodium, silver, tungsten, tin, zinc and the like. The metals are present in the form of soluble salts or acids. Various additives such as leveling and brightening agents may be added to these baths. The diamonds are suspended in the baths in the form of fine particles having an average diameter of from between sub-micron size to 30 microns, although sub-micron size particles, particles having an average diameter of less than 1 micron, are preferred as they produce fine and smooth plate. Diamond particles above 15 microns in diameter produce some roughness, especially on shelf areas where the particles can settle. With most of the baths the maximum improvement in wear resistance of the articles is attained when about 50 to 150 carats (10 to 30 grams) per liter of the fine diamond particles are dispersed in the baths.

The coating formed by this method is extremely tough and wear resistant due to the occluded diamonds. Any articles that come in contact with other surfaces, such as the wear, cutting or grinding surfaces of tools, tool parts, taps, knives, saws, die punches, gauges, shears, engine components and the like can be coated with this coating to prolong their useful operating lives by reducing wear and to reduce friction. Thus, for example, it has been found that a cigarette filter cutting blade coated with the diamond plate has a useful operating life up to four times greater than an untreated blade. It has also been found that the frictional forces between two surfaces coated with the coating of the present invention are substantially reduced.

The present invention also includes the electroplate comprising a metal matrix containing occluded diamond particles which is produced by the aforementioned method. Likewise included in the present invention are the various plating baths containing suspended therein the fine and micro-fine diamond particles. This invention also relates to various articles, such as cutting blades, drills, die punches, bearings, and the like having deposited on their surface a plate comprising a metal matrix containing occluded diamond particles.

The present invention has many advantages over other previous types of coatings. One of these lies in the extreme hardness possessed by the coating, said hardness due to the presence of diamond particles. Another advantage is that the diamond particles are uniformly distributed throughout the metal matrix. Still another advantage resides in the fact that the diamonds being deposited in the coating electrophorically rather than manually as in the prior art, they are generally of the same size, are accurately positioned, and are identically oriented in the matrix.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In practice the article to be coated is made the cathode and immersed in a plating bath containing soluble metal salts or acids of the matrix metal. The cathode consists essentially of the matrix metal. The diamonds, which have been pretreated, are suspended in the bath in the form of fine bath insoluble particles and are kept in suspension by a period of initial agitation which is terminated when the solution is electrolyzed. The average particle diameter of the diamonds can be between 0.01 micron and 30 microns and preferably should not be greater than 15 microns. This particle size has been found to be preferred and advantageous, with the most preferred particle being of sub-micron size averaging from about .01 to about 1 micron.

The concentrations of the diamond particles depend upon the type of bath in which they are dispersed and the density of the diamonds desired in the matrix. Thus in a Watts type nickel bath a concentration of 100 carats (20 grams) per liter is found to give optimum results, producing a nickel matrix containing 40 percent diamond particles. In a chrome bath, on the other hand, it has been found that for optimum results a diamond concentration of about 150 carats per liter is necessary.

It has been found that the untreated diamonds may tend in some instances to agglomerate in the solution and to form roughness and lumpiness in the plate. To overcome this problem the diamonds are subjected to a special treatment before being introduced into the plating bath. The treatment consists of cleaning the diamonds by immersing them in hydrochloric acid. The diamonds are then cleaned a second time by immersion in a solution of sodium hydroxide. After the diamonds have been cleaned they are soaked in a solution of coumarin sulfate and sulfuric acid. The amount of time that the diamonds are soaked in the coumarin sulfate can be as long as 24 hours. The diamonds are then rinsed several times in water and thereafter are soaked in a wetting agent of the anionic type. After exposure to the wetting agent the diamonds are again rinsed with water. Finally the diamonds are air-dried and added to a concentrated solution of metallic salt or acid of the bath to be added immediately to the bath or stored for a period of time. Alternatively the treated diamonds can be added directly to the bath rather than to a concentrated solution of metal salt or acid of the metal. The treated diamonds are suspended in the bath at random and do not tend to agglomerate but plate out as discrete and individual particles.

The preferred metal matrix is one consisting essentially of nickel. But other metals, depending upon the purpose to which the coated surface is to be put, can be used. Among these metals are those that are used in the more common types of plating baths: antimony, bismuth, cadmium, chromium, cobalt, copper, gold, indium, iron, lead, palladium, platinum, silver, tungsten, tin and zinc.

Both natural and synthetic or man-made diamonds can be used in the present invention. It has been found, however, that the man-made diamonds plate out faster than do the natural diamonds. Thus, under identical conditions a solution having suspended therein man-made diamonds will produce a plate having a slightly greater diamond density than a plate produced from a solution having suspended therein natural diamond particles. This phenomena is greatly increased when the cathode is polarized. In order to increase the density of the diamond particles in the matrix, in other words to increase the rate of co-deposition of diamonds, a magnet is attached to the cathode. The synthetic diamonds will then plate out at a rate approximately 25 to 50 percent higher than if the cathode was not polarized. The plate thus deposited will contain 25 to 50 percent more diamonds per unit area than one formed with an unpolarized electrode. However, if natural diamonds are used in a plating bath having a magnet attached to the cathode, the rate of co-deposition of the diamonds is not appreciably increased. This is thought to be a function of the mechanism by which the particles plate out. Although this mechanism is not clearly understood, it is possible that the adsorption of hydrogen ions and nickel ions by the particles would give the particles a positive charge and in this way they would tend to plate out. In addition, while naturally occurring diamonds are not semi-conductors, the man-made diamonds, due to the presence of small metal particles therein, are semi-conductors. Adding a magnet to the cathode also tends to produce a situation wherein two forces are acting on the synthetic diamonds; magnetic and electrical, while with natural diamonds only the electrical force is acting upon the diamonds. Nevertheless, regardless of the mechanism of the co-deposition of these particles and independent of whether they are naturally occurring or made-made, the deposition of the particles starts immediately and they plate out as uniform dispersions in the metal plate. Thus at any point in the plating procss the surface of the metal plate has distributed over its surface very many fine diamond particles in various stages of being embedded in the surface.

Below are listed examples of the baths of this invention in which the diamond particles are used.

EXAMPLE I

Grams/liter NiSO.sub.4 300 - 450 NCl.sub.2 30 - 75 H.sub.3 BO.sub.3 30 - 45 Diamond particles, .01 to 1 micron average diameter 1 - 20 pH = 2.5 - 4.0

EXAMPLE II

Grams/liter SbS.sub.3 40 - 60 Na.sub.2 CO.sub.3 90 - 110 Diamond particles, .01 to 15 microns average diameter 1 - 20

pH = 2.0 - 5.0 EXAMPLE III Grams/liter BiO 30 - 50 HClO.sub.4 100 - 110 Diamond particles, .01 to 30 microns average diameter 1 - 20 pH = 2.0 - 5.0

EXAMPLE IV

Grams/liter CrO.sub.3 250 - 450 H.sub.2 SO.sub.4 1.25 - 2.5 Lead Anode Cathode current density, amp/sq. ft., 60 - 100 pH = acidic diamond particles, .01 to 30 microns average diameter 10 - 30

EXAMPLE V

Grams/liter CoSO.sub.4.sup.. 7H.sub.2 O 500 NaCl 17 H.sub.3 BO.sub.3 45 Cathode current density, amp/sq.ft., 30 - 165 diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE VI

Grams/liter Cu SO.sub.4.sup.. 5H.sub.2 O 150 - 300 H.sub.2 SO.sub.4 50 - 75 pH = acidic Cathode current density, amp/sq.ft., 15 - 40 diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE

VII Grams/liter KAu (CN).sub.2 2.1 KCN 15 Na.sub.2 HPO.sub.4.sup.. 12H.sub.2 O 4 Cathode current density, amp/sq.ft., 1 - 5 diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE

VIII Grams/liter In.sub.2 O.sub.3 200 H.sub.2 SO.sub.4 250 H.sub.2 SO.sub.4 120 - 200 Platinum anodes Cathode current density, amp/sq. ft., 18 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE IX

Grams/liter FeSO.sub.4.sup.. 7H.sub.2 O 160 FeCl.sub.2.sup.. 2H.sub.2 0 30 - 40 NH.sub.4 Cl 20 - 25 Cathode current density, amp/sq. ft., 50 pH = 3 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE

X Grams/liter Pb (OH).sub.2 PbCO.sub.3 150 HF (50 per cent) 240 H.sub.3 BO.sub.3 105 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XI

Grams/liter Palladium diamino nitrite 10 NH.sub.4 NO.sub.3 100 Na NO.sub.3 10 NH.sub.4 OH 50 (cc) Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XII

Grams/liter Platinum diamino nitrite 10 NH.sub.4 NO.sub.3 100 NaNO.sub.2 10 NH.sub.4 OH 50 (cc) pH = 2 - 2.5 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XIII

Grams/liter SnCl.sub.2 30 - 50 NiCl.sub.2 240 - 320 NH.sub.4 HF.sub.2 60 NH.sub.4 OH - to pH of 2.0 - 2.5 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XIV

Grams/liter AgCN 35 KCN 37 K.sub.2 CO.sub.3 38 Cathode current density, amp/sq. ft., 1 - 2 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XV

Grams/liter NaCN 90 CdO 30 Cathode current density, amp/sq. ft., 10 - 15 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XVI

Grams/liter Sodium tungstate 38 Sodium hydroxide 60 Dextrose 60 Diamond particles, .01 to 30 microns average diameter 1 - 20

EXAMPLE XVII

Grams/liter __________________________________________________________________________ Zn (CN).sub.2 60 NaCN 23 NaOH 53 Cathode current density, amp/sq. ft., 8 - 20 Diamond particles, .01 to 30 microns average diameter 1 - 20

In addition to the contents of the various plating baths as set forth in the above examples, the plating baths may also contain materials such as "addition agents" employed in small amounts to affect the crystalline nature of the deposit, brighteners, leveling agents, buffers to keep the solution at the desired pH, and salts which can increase the conductivity of the baths if the salt or acid containing the metallic ion or radical is not sufficiently conductive. The concentrations and proportions of the above, as well as the ingredients given in the foregoing examples, may be varied to produce different results. Thus for example, a common nickel plating solution may have the metal ion in the shape of NiSO.sub.4, NH.sub.4 Cl, or (NHhd 4).sub.2 SO.sub.4 to increase the conductivity of the bath; NiCl.sub.2 to assist anode corrosion; H.sub.3 BO.sub.3 which acts as a buffer to maintain the pH of the solution; a wide range of high-molecular-weight organic "addition agents" such as organic sulfon compounds, examples of which are O or P-Toluene sulfonamide, o-Benzoyl sulfamide, O-benzoyl sulfimide, naphthalene, mono-, di-, or tri-sulfonic acid, sulfonated aryl aldehydes, etc. to give smoother and finer grained deposits; and brighteners such as cadmium sulfate. In the case of a tin bath the tin salt may be furnished by Na.sub.2 SnO.sub.3, the conducting salt by NaOH which also assists anode corrosion, the addition agent to effect the deposit being glucose or other organic materials. The bismuth bath may contain glue and cresol as addition agents; the cadmium bath may contain glue, casein, molasses and gorilac as addition agents; the silver bath may contain small amounts of CS.sub.2 as a brightener; and the tin bath may contain sodium acetate as a buffer.

The co-deposition rate of the diamonds is dependent on the size of the particles, their concentration in the solution, and the current density. Thus, for example, one carat of diamonds of 5 microns average diameter in 5 milliliters of solution will plate out in such a manner that a 90 percent diamond concentration will result in a plate one mil thick. Diamond particles up to 15 microns in size can be plated out at a current density as low as 2 amps/sq. ft. However, diamond particles larger than 30 microns are deposited with greater difficulty, even at high current densities.

As mentioned previously, the preferred metal matrix is one consisting essentially of nickel. The diamond particles can be suspended in a variety of nickel baths. However, all of these baths are of the same general type, i.e., nearly neutral or slightly acid solutions in which the nickel is present principally as a single salt, usually the sulfate. One bath which has been found especially effective contains 40 - 50 ounces per gallon of NiSO.sub.4, 5 - 6 ounces per gallon of NiCl.sub.2, 5 - 6 ounces per gallon of H.sub.3 BO.sub.3, 100 carats per liter of diamond particles of an average diameter of 0.01 to 15 microns, and a pH of 3 - 6. This bath is operated at a current density of 50 amps/sq. ft. and leveling agents such as sulfonated aryl aldehydes are maintained at 0.7%. Another nickel bath which produces excellent results consists of 45 - 60 ounces per gallon of NiSO.sub.4, 8 - 10 ounces per gallon of NiCl.sub.2, 5 - 6 ounces per gallon of H.sub.3 BO.sub.3, 1 ounce per gallon of NH.sub.4 Cl, 100 carats of diamond particles of 0.01 to 30 microns average diameter, and a brightening agent of the sulfonimide type. The bath is operated at a current density of 40 amps/sq. ft., at a temperature of 150.degree.- 160.degree. F., and at a pH of 2.5 - 3.0. Still another nickel bath which has been found to be useful contains 26 ounces per gallon of NiSO.sub.4, 3.3 ounces per gallon of NH.sub.4 Cl, 4 ounces per gallon of H.sub.3 BO.sub.3, 100 carats per liter of micro-fine diamond particles, and a pH of 5.6 - 5.9. This bath is operated at a current density of 25 - 50 amps/sq. ft. at a temperature of 110.degree.- 140.degree. F. A nickel bath which has been found to produce extremely fine grained nickel is one which contains 26 ounces per gallon of NiSO.sub.4, 23 ounces per gallon of NiCl, 2 ounces per gallon of NH.sub.4 Cl, 5 - 6 ounces per gallon of H.sub.3 BO.sub.3, and a pH of 1.5. This bath is operated at a current density of 25 - 100 amps/sq. ft. and contains 115 - 120 carats per liter of fine to micro-fine diamond particles.

It will be noticed that all four of these nickel baths have a high metal (nickel) ion content. Furthermore, "fine" diamond particles are, for the purposes of this invention, defined as those particles having an average diameter of from 1 micron to 30 microns, while "micro-fine" diamonds are those having an average diameter of from 0.01 micron to 1 micron. With the aforementioned nickel baths operated under the described conditions a plate is formed which comprises approximately 60 percent nickel and 40 percent diamonds. This ratio can be varied as desired by changing the concentration of the diamond particles. The thickness of the plate can also be varied by varying the time and current density.

The plate produced from the above described nickel baths has excellent adhesion to the substrate surfaces. Microscopic examination of the surface of the plate shows an "orange peel" effect. That is to say, the surface of the plate resembles an orange peel in that rather than being uniformly even it possesses concavities and convexities. The diamond particles are distributed evenly throughout the concave and convex surface areas. It is the presence of the concave and convex surface areas that is thought to be responsible for decreasing the frictional forces between a surface in contact with the electroplated article. It is believed that air or oil and other lubricating agents are trapped in the concavities and thus have a lubricating or buoying effect when the two surfaces are in contact with each other. It is also likely that the nickel oxidizes to form a thin film of nickel oxide, especially on the convex areas, which also acts as a lubricant, thereby further reducing the frictional force.

The diamond particles are found to be aligned in a uniform configuration throughout the entire matrix. The diamond particles are all aligned with their sharp, uneven or ragged edges directed toward the substrate surface while their rounded or even ends are aligned facing outwardly from the substrate metal and the matrix. Thus it is the smooth or rounded ends of the diamond particles rather than the sharp or ragged edges which come into contact with a corresponding surface. This too reduces the frictional forces as well as insuring that the contacting surface will not be scored or scratched by the diamonds' rough edges.

If desired, the diamond containing plate, which can be as thin as .000039 inch or as thick as 0.25 inch but which is usually kept at a thickness of 0.0001 inch, can be given a final chromium plate of about 0.2 mil thickness to protect the softer nickel or other matrix metal.

Claims

I claim:

1. A method for electrodepositing a composite wear-resistant plate consisting essentially of metal and diamond particles on the surface of an element comprising making said element a cathode in an electroplating bath of said metal having suspended therein diamond particles in the form of fine powder having a particle size from about 0.01 to about 30 microns average diameter and electrolyzing said bath with externally applied current of sufficient density to electrophoretically deposit said diamond particles and said metal in a composite plate on said surface while said diamond particles are suspended in said bath and while at the same time keeping said bath in a quiescent state.

2. The method as set forth in claim 1 wherein the metal is selected from the group consisting of antimony, bismuth, cadmium, chromium, cobalt, copper, gold, indium, iron, lead, nickel, palladium, platinum, silver, tungsten, tin and zinc.

3. The method as set forth in claim 1 wherein said diamonds are from approximately 0.01 micron to 15 microns average diameter.

4. The method as set forth in claim 1 wherein said diamonds are from approximately 0.01 micron to 1 micron average diameter.

5. The method as set forth in claim 1 wherein said bath contains suspended therein about 150 carats per liter of diamond particles.

6. The method as set forth in claim 1 and further including the step of pretreating the diamond particles by washing the diamond particles, soaking said particles in a wetting agent of the anionic type, and rinsing said particles in water before suspending said particles in said bath.

7. The method as set forth in claim 1 wherein the metal is essentially nickel and wherein said bath comprises at least one nickel salt selected from the group consisting of nickel sulfate and nickel chloride.

8. The method as set forth in claim 1 wherein said diamond particles are particles of synthetic diamonds and further including magnetizing the cathode.

9. A composite wear resistant electroplate on a metal surface comprising diamond particles in a metal matrix, said particles having relatively smooth and ragged surfaces and having an average particle diameter of from about 0.01 to 30 microns and being electrophoretically deposited in the matrix in a spatially oriented pattern wherein said smooth surfaces of said particles are directed outwardly from said metal surface and said ragged surfaces are directed inwardly toward said metal surface,made by a method comprising making said metal surface a cathode in an electroplating bath of said metal having suspended therein said diamond particles and electrolyzing said bath while said particles are in suspension and while keeping said bath in a quiescent state with externally applied current of sufficient density to electrophoretically deposit said diamond particles and metal on said surface in a composite electroplate.

10. The electroplate as set forth in claim 9 wherein said diamond particles are washed before being suspended in said electroplating bath.

11. The electroplate as set forth in claim 9 wherein said diamond particles are particles of synthetic diamonds and the method of making includes magnetizing the cathode.