Process For Electroless Metallizing Incorporating Wear-resisting Particles

Abstract

There are disclosed processes for electroless metallizing workpieces to provide thereon a metal coating incorporating therein nonmetallic wear-resisting particles and the coated workpieces produced by such processes, the processes comprising contacting the workpieces with an electroless metallizing bath consisting of an aqueous solution of a metal salt and an electroless reducing agent therefor and a quantity of nonmetallic wear-resisting particles, wherein the particles are essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, the particles being present in the bath in an amount by weight no greater than about four times the weight of the metal in the bath expressed as free metal, and maintaining the particles in suspension throughout the bath during the metallizing of the workpiece; the electroless coating with the wear-resisting particles therein may be heat treated by heating to an elevated temperature in the range 100.degree. C. to 600.degree. C. for one hour or more further to harden the coating.

Description

The present invention is directed to processes for electroless metallizing workpieces wherein the resultant metal coating has incorporated therein wear-resisting particles.

It is an important object of the present invention to provide a process for electroless metallizing a body to provide thereon a metal coating incorporating therein wear-resisting particles so as to provide a highly wear-resistant coating on the body to protect such bodies that are subject to wear by reason of sliding contact, rubbing contact, and the like in use; the process comprising contacting the body with the electroless metallizing bath consisting essentially of an aqueous solution of the metal salt and an electroless reducing agent therefor and a quantity of wear-resisting particles, wherein the particles are essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, the particles being present in the bath in an amount by weight no greater than about 4 times the weight of the metal in the bath expressed as free metal, and maintaining the particles in suspension throughout the bath during the metallizing of the body, thereby to produce on the surface of the body a coating of metal having the particles uniformly dispersed therethrough.

Another object of the invention is to provide a process of electroless metallizing of the type set forth wherein the wear-resisting particles have dimensions in the range 0.01 micron to 100 microns, a further preferred range being from about 0.5 micron to about 25 microns, the particles being maintained in suspension in the bath by mechanical agitation in the bath or by passing the bath with the particles therein across the body, or by streams of minute bubbles of gases passing through the bath or by agitation of the body within the bath.

Still another object of the invention is to provide a process of the type set forth and further comprising the step of heating the coating to an elevated temperature for a sufficient period of time to heat-harden the coating, a typical coating being heat-hardened by heating to a temperature in the range from about 100.degree. C. to about 600.degree. C. for about 1 hour.

Still another object of the invention is to provide a process of the type set forth which is particularly suited for applying wear-resistant coatings to bodies formed of a material selected from the group consisting of aluminum, magnesium, copper, beryllium and their alloys, whereby additional heat-hardening of the coating is not required to provide adequate wear-resistance in the coating.

Further features of the invention pertain to the particular arrangement of the steps of the processes and the compositions of the bath used therein and of the wear-resistant coatings produced thereby, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification and to the several illustrative examples set forth therein.

In accordance with the present invention, there is provided a workpiece or article of manufacture having an outer surface that is to carry the desired wear-resistant coating, the outer surface typically being one that will be subject to sliding contact or rubbing contact with another surface, whereby to subject it to substantial wearing and bearing pressures. First, the workpiece is cleaned using one of several well-known cleaning methods, after which the workpiece is contacted with an electroless metallizing bath containing a quantity of wear-resisting particles, the bath being for example a conventional chemical nickel plating bath of the nickel cation-hypophosphite anion type, and the particles being essentially insoluble in the plating bath and noncatalytic and inert with respect thereto and being present in the bath in an amount by weight no greater than about four times the weight of the metal in the bath expressed as free metal. During the plating process, the wear-resisting particles are maintained in suspension throughout the bath, whereby after a suitable time interval there is produced on the surface of the workpiece a coating of the metal, such as nickel, having uniformly dispersed therethrough a quantity of the wear-resisting particles. Thereafter the workpiece may be subjected to a heat-hardening step in order to render the composite coating thus produced intimately bonded thereto and of harder and more wear-resistant character.

The term "wear-resistant coating" as used herein refers to a coating, the properties of which changed in any manner whatsoever to increase the wear-resistant properties thereof; for example, the term includes increasing the hardness of the coating by the incorporating therein materials that are intrinsically harder than the coating itself; on the other hand, the term as used herein may include coatings wherein a lubricating material, such as molybdenum disulfide, has been added to the coating so that the lubricated surface of the coating wears longer due to the lubricating properties thereof. Finally, it will be understood that the term"wear-resistant coating" may also refer to a coating which embodies both particles which are intrinsically harder than the coating and particles which add a lubricating property to the coating.

While the processes of the present invention are fundamentally independent of the composition of the workpiece, ordinarily the workpiece is formed of an industrial metal, such for example, as steel, although the workpiece may be formed of a nonmetallic material. In the last mentioned instance, the workpiece is first subjected to pretreatment in order to activate the surface thereof so that it may subsequently receive the electroless metallized coating that is inherently produced in the metallizing process. When the metallizing metal is nickel, pretreatment may be that as disclosed in U.S. Pat. No. 2,690,401, granted on Sept. 28, 1954 to Gregoire Gutzeit, William J. Crehan and Abraham Krieg, and in U. S. Pat. No. 2,690,402 granted on Sept. 28, 1954 to William J. Crehan.

The processes of the present application are particularly beneficial in providing wear-resistant coatings on workpieces formed of materials, such as aluminum, magnesium, copper, or beryllium which are not readily heat hardenable and which ordinarily are not heated after fabrication thereof, the inventive coating having wear-resistant properties such that additional treatment thereof is not necessary to provide a satisfactory wear-resistant surface.

It will be understood that a large number of metallizing processes of the electroless type may be utilized including electroless nickel processes, electroless cobalt processes and electroless copper processes. The invention is of particular applicability in the case of electroless nickel processes, specifically those using hypophosphite anions as the electroless reducing agent. Furthermore, the electroless metallizing process in the case of electroless nickel is independent of the particular composition of the nickel plating bath of the nickel cation-hypophosphite anion type that is employed in the chemical nickel plating step, whereby a wide variety of these conventional chemical nickel plating baths may be employed; which plating baths inherently produce coatings essentially comprising by weight about 85 percent to 97 percent nickel and about 3 percent to 15 percent phosphorus.

The plating bath disclosed in U.S. Pat. No. 2,822,294, granted on Feb. 4, 1958 to Gregoire Gutzeit, Paul Talmey and Warren G. Lee is particularly recommended due to its simplicity and economy. More particularly, this plating bath is of the nickel cation-hypophosphite anion type, also containing lactic anion and having a pH in the acid range 3.0 to A typical example of this chemical nickel plating bath useful in the present invention has the following composition: --------------------------------------------------------------------------- EXAMPLE 1

NiSO.sub.4 .6H.sub.2 0 0.08 mole/1. NaH.sub.2 PO.sub.2.H.sub.2 O 0.23 mole/1. Lactic anion 0.30 mole/1. Propionic anion 0.03 mole/1. Lead ion 1 part per million pH 4.6 __________________________________________________________________________

a quantity of the above plating bath was placed in a plating vessel having a magnetic stirrer therein, after which there was added thereto 1 percent by weight of the solids in the plating bath of 600 grit silicon carbide particles, it being noted that the nickel content of the bath on the solid basis expressed as nickel metal is about 0.5 percent. A steel workpiece having a bearing surface thereon was then placed in the plating bath while the silicon carbide particles were maintained in agitated suspension throughout the plating bath, and while the temperature of the plating bath was maintained in the general range 93.degree. C. to 98.degree. C. After about an hour, there was present on the exposed surfaces of the workpiece about one mil of a wear-resistant coating comprising electroless nickel and a quantity of the silicon carbide particles embedded in and distributed therethrough. The coating that is inherently produced by the particular plating bath essentially comprises by weight about 86 percent nickel and about 9 percent phosphorus, and about 5 percent silicon carbide.

The surface of the coated workpiece was rough and dull in appearance and had a hardness in the nickel-phosphorus alloy area of 525 V.P.N. (Vickers Pyramid Number). The Taber Wear Index (TWI) was determined and was found to be 4.7. The Taber Wear Index is defined as the loss of weight in mg. per 1000 revolutions of two CS-10 rubber wheels under a 1000 grams load, a TWI of 5 representing a loss in thickness of about 0.01 mil of coating. By contrast an electroless nickel coating made using the bath of example 1 without the addition of wear-resisting particles thereto has a TWI of 15.2 whereby the coating of the present invention incorporating therein the silicon carbide wear-resisting particles materially imposes the wear-resistance of the coating, the improvement being essentially by a factor of 3.

In the chemical nickel plating bath of example 1, the absolute concentration of hypophosphite in the bath expressed in mole/liter may vary within the range from about 0.15 to about 1.20, and ratio between the nickel cations and hypophosphite anions in the bath expressed in molar concentrations may vary within the range from about 0.25 to about 1.60. The lactic anion serves as a complexing agent and may be derived from lactic acid or salts thereof, the absolute concentration of lactic ions in the bath expressed in mole/liter being within the range from about 0.25 to about 0.60. The bath also includes an exalting additive, namely, the propionic anion, which has a concentration in the bath expressed in mole/liter in the range from about 0.025 to about 0.060. Other exalting additives may be used in place of the propionic anion, the exalting additive being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids, including three to five carbon atoms and salts thereof. Further details of the composition of the bath and the method of using the same are set forth in the aforementioned U.S. Pat. No. 2,822,294 and the disclosure thereof is incorporated herein by reference.

The silicon carbide particles useful in the process of example 1 may have a particle size in the range from about 0.5 micron to about 25 microns, in order to obtain good suspension of the particles in the plating bath and in order to to obtain uniform distribution of the particles in coating. Smaller particles inhibit the plating action, due to close packing, while larger particles are kept dispersed in the plating bath only with extreme difficulty. The concentration of the silicon carbon carbide particles in the plating bath should not exceed about 4 times the weight of the nickel metal present in the bath expressed as free metal, although smaller concentration of the silicon carbide particles may be utilized, it being understood that the volume of silicon carbide in the coating will be a function of the concentration of the silicon carbide particles in the plating bath as well as the effectiveness of the dispersion thereof. In example 1, the silicon carbide comprises about 15 percent by volume of the wear-resistant coating, although it will be understood that the volume of the silicon carbide particles may vary from as little as 1 percent up to as much as 40 percent of the volume of the coating.

Other thicknesses of the coating may be provided, and the coating may have a thickness in the range from about 5 microns to about 200 microns or more if desired.

Summarizing, with respect to example 1 above, there is provided a process of "electroless" plating of a nickel-phosphorus alloy coating on a workpiece, the coating containing silicon carbide particles distributed therethrough and being a relatively thick "dispersion hardened" metal deposit. The expression "electroless plating" as used herein refers to the plating of metal coatings without the application of an external electrical current, and preferably by a chemical reduction of the electroless metal utilizing an electroless reducing agent for the metal, thereby to accomplish a process of electroless metallizing. The term "dispersion hardened" as used herein refers to the described metal coatings in which are embedded inert solid particles during the laying down of the metal coating, the particles being partially or completely embedded in and held in position by the coating.

The lead content of the nickel plating bath of example 1 performs the important function of stabilizing the bath during the plating operation. It will be understood that other types of stabilizers and other amounts of stabilizers may be advantageously utilized in connection with the present invention, suitable such stabilizers being disclosed in U.S. Pat. No. 2,762,723 granted Sept. 11, 1958 to Paul Talmey and Gregoire Gutzeit, the disclosure of that patent being incorporated herein by reference.

Alkaline nickel plating baths may be utilized advantageously in the present invention, and particularly when coating certain plastics and certain metals such as magnesium, examples of suitable alkaline baths being set forth in U.S. Pat. No. 3,211,578 granted Oct. 12, 1965 to Gregoire Gutzeit, the disclosure thereof being incorporated herein by reference.

In general any nonmetallic particle may be utilized as a wear-resisting particle in the process of example 1, it simply being necessary that the particles be essentially insoluble in the plating bath and that the particles be noncatalytic and inert with respect to the reducing of the metal salt by the electroless reducing agent therefor. In this connection it is pointed out that a wide variety of such nonmetallic wear-resisting particles may be used, and more specifically, there may be used the following: kaolin; glass flour, talc, synthetic organic plastic resin powders; and oxides, carbides, nitrides, borides, silicides, sulfides, silicates, sulfates, carbonates, phosphates, oxalates or fluorides of aluminum, boron, chromium, hafnium, molybdenum, silicon, titanium, tantalum, vanadium, tungsten, zirconium, nickel, magnesium calcium, barium, strontium, cerium, iron or manganese. The particle size of the wear-resisting particles may be of the order of 0.01 micron to 100 microns, a preferred size being in the range from about 0.5 micron to about 25 microns.

Furthermore, the particles must be essentially insoluble in the plating bath, i.e., must have a very low solubility therein on the order of no more than about 0.01 mole per liter. In addition, the wear-resisting particles must be noncatalytic and inert with respect to the reducing agent and the reaction of the reducing agent with the coating metal in the bath, and also the particles must not interfere with or stop the plating reaction. The concentration of the wear-resisting particles in the plating bath is preferably in the range from about 0.1 percent by weight of the solids to about 2 percent by weight of the solids, but in any event not more than 4 times the weight of the electroless plating metal in the bath when the weight of the metal is expressed as the free or reduced metal. In certain instances it may be desirable to provide an acid or solvent wash to the particles before the addition thereof to the plating bath, thereby to avoid contamination and to increase the stability of the plating bath.

Other suitable methods of maintaining the wear-resisting particles in suspension may be used in addition to that described above with respect to example 1. For example, a mixture of the plating solution and the wear-resisting particles may be advantageously pumped through the bottom of the plating vessel, the bottom of the plating vessel being dish-shaped and symmetrical, whereby a uniform stream of the plating bath with the wear-resisting particle suspended and entrained therein is passed or flooded across the surfaces of the workpiece being coated.

Another advantageous system for maintaining the wear-resisting particles in suspension is to provide a symmetrical plating bath having dispersed in the bottom thereof a spider including a number of very small gas outlets therein. In this manner very fine air bubbles can be introduced into the plating bath via the spider, the air bubbles serving to hold the wear-resisting particles in suspension throughout the plating solution. Other gases such as nitrogen, or one of the noble gases, may be used in place of air.

Yet another method of maintaining the wear-resisting particles in suspension is to agitate and move the workpiece within the plating solution, such movement of the workpiece causing currents in the plating solution which tend to hold the wear-resisting particles in suspension. Each of the above-mentioned alternative methods of maintaining the wear-resisting particles in suspension has been successfully utilized in conjunction with the process of example 1 above.

It will be appreciated that the process of example 1 is particularly useful when applied to workpieces having surfaces that are to be employed in sliding applications, such as slide bearings, motor housings, shafts, and the like. It will be understood, however, that the incorporation of the wear-resisting particles in the electroless deposited metal coating affects other properties of the coating in addition to the hardness and wear-resistance thereof. In general the physical, chemical and electrochemical properties of the coating are affected including the coefficient of friction, the temperature stability of the coating, the oxidation stability of the coating, the corrosion stability of the coating, the reflectivity and/or gloss thereof, etc.

Turning now to a consideration of the electroless chemical nickel plating baths useful in the present invention, there are a number of suitable available compositions, such for example, as disclosed in U.S. Pat. No. 2,532,283, granted on Dec. 5, 1950 to Abner Brenner and Grace E. Riddell, U.S. Pat. No. 2,658,841, granted on Nov. 10, 1953 to Gregoire Gutzeit and Abraham Krieg, or U.S. Pat. No. 2,658,842 granted on Nov. 10, 1953 to Gregoire Gutzeit and Ernest J. Ramirez.

The following are additional examples of such baths useful in the present invention. --------------------------------------------------------------------------- EXAMPLE 2

Nickel chloride 30 g./1. Sodium acetate 13 g./1. Sodium hypophosphite 10 g./1. pH 4 Temperature 95.degree. C. __________________________________________________________________________

a plating bath as set forth above was placed in a symmetrical plating vessel and there was added 240 grit silicon carbide particles in an amount equal to 2 percent of the solids in the plating bath. After an hour of plating, a rough dull coating having a thickness of 0.65 mil was provided on a workpiece disposed therein, the plating solution being continuously agitated by stirring to hold the silicon carbide particles in suspension therein. The resultant coating has the valuable properties as set forth both with respect to the coating of example 1. --------------------------------------------------------------------------- EXAMPLE 3

Nickel sulfate 30 g./1. Sodium citrate 100 g./1. Ammonium chloride 50 g./1. Sodium hypophosphite 10 g./1. pH 8-10 Temperature 95.degree. C. __________________________________________________________________________

The plating process of example 1 was repeated utilizing the bath of the above composition, there being produced on the workpiece an electroless nickel coating having the silicon carbide particles uniformly dispersed therethrough, the coating possessing the valuable properties described with respect to example 1.

The hardness of the electroless nickel coatings incorporating therein the silicon carbide particles as described in conjunction with examples 1 to 3 above can be further hardened and rendered even more wear-resistant by a heat treatment of the coating after deposition thereof. There is disclosed in U.S. Pat. No. 2,908,419, granted on Oct. 13, 1959 to Paul Talmey and William J. Crehan a suitable heat treatment process to increase the hardness of such electroless nickel coatings, and the disclosure of that patent is incorporated herein by reference. The electroless nickel portion of the coatings of examples 1 to 3 may contain from about 85 percent to about 97 percent nickel and from about 3 percent to about 15 percent phosphorus by weight, certain of the baths such as that of example 1 actually providing compositions in the range from 88 percent to 94 percent nickel and from about 6 percent to about 12 percent phosphorus by weight. The electroless nickel coating more specifically after heat treatment constitutes a stable solid characterized by the presence of substantial microcrystals of nickel phosphide dispersed in a matrix of nickel metal and having a resultant hardness as high as 1200 V.P.N. the hardness varying down to about 575 V.P.N. depending upon the heating temperature and time.

The following is an example of the heat treatment of the novel coating of example 1.

EXAMPLE 4

A workpiece having a coating thereon produced as in example 1 was gradually heated in an oven from 100.degree. C. to 400.degree. C. for a period of 1 hour. At the end of the hour it was found that the hardness of the electroless nickel portion of the coating was 1,081 V.P.N. and the wear-resistance was 1.9 TWI. This compared with a TWI of 4.2 for the electroless nickel coating alone without the addition of the wear-resisting particles thereto.

It will be appreciated that the coatings of examples 2 and 3 above can be likewise heat-hardened by processing in accordance with example 4 herein, and further as explained in the U.S. Pat. No. 2,908,419 referred to above.

It has been found that sulfides are also useful as wear-resisting particles in the present invention, the following being examples of the use of molybdenum sulfide particles as the wear-resisting particles.

EXAMPLE 5

The plating bath and the coating process of example 1 were duplicated but the plating bath had disposed therein 1 percent weight of the dry solids of granulated molybdenum disulfide having an average particle size of about 50 microns. There resulted from one hour of plating a coating having a thickness of 0.78 mil and possessing a rough texture. The hardness of the electroless nickel coating was 508 V.P.N. and the wear-resistance thereof was 4.9 TWI. The coated workpiece made in accordance with example 5 had good lubricating properties imparted thereto by the molybdenum disulfide and possessed the other advantages and properties as described above with respect to example 4.

The coating of example 5 may also be heat-hardened, an example of such a process being as follows:

EXAMPLE 6

workpiece with the coating of example 5 thereon was further processed and heat treated as in example 4 above to provide a heat-hardened coating having a hardness of 1018 V.P.N. and a wear resistance of 1.1 TWI.

Metal oxides are examples of other wear-resisting particles which are useful in carrying out the processes of the present invention. The following is an example utilizing aluminum oxide particles:

EXAMPLE 7

The plating bath and process of example 1 was utilized but there was substituted for the silicon carbide particles aluminum oxide particles having a size of about 0.5 micron, and having a concentration by weight of about 1 percent of the dry solids in the plating bath. There was produced a bright coating of electroless nickel having dispersed therethrough the aluminum oxide particles, 0.6 mil of the coating being produced in one hour's time. The hardness of the coating in the nickel area was 572 V.P.M. and the wear-resistance thereof was 9.8 TWI. The wear-resistant coating made in accordance with example 7 had the other desirable properties of the coating produced by the process of example 1 as set forth above.

The process of example 7 was repeated utilizing a concentration of the aluminum oxide particles of 0.1 percent by weight on a dry basis of the solids in the plating bath. There resulted after one hour of plating a coating having a thickness of 0.6 mil and a hardness of 627 V.P.N. In another process in accordance with example 7, the aluminum oxide particles were present in the plating bath in a concentration of 2 percent by weight on a dry basis of the solids, there resulting a rough coating having a thickness of 0.43 mil and a hardness of 642 V.P.N. In yet another variation of the process of example 7, the aluminum oxide particles utilized had a size of 0.05 micron and a concentration of 1 percent in the bath, thereby to produce after one hour a bright coating having a thickness of 0.67 mil and a hardness of 612 V.P.N.

Finally, there was carried out a variation of the process of example 7, wherein the aluminum oxide particles had a size of 1 micron and were present in a concentration of 1 percent in the bath, there resulting after 1 hour of plating a rough coating having a thickness of 0.52 mil and a hardness of 572 V.P.N.

The coatings made in accordance with example 7 may also be heat-treated to improve the wear-resistant properties thereof, the following being an example of such a process.

EXAMPLE 8

A workpiece coated in accordance with the process of example 7 was heat-treated in accordance with the process of example 4, the resultant coating having a hardness of 1049 V.P.N. and a wear-resistance of 4.6 TWI.

A wide variety of metal oxides may be utilized in the place of aluminum oxide in examples 7 and 8, and more specifically, titanium oxides may be utilized to provide a dull rough coating having a thickness of 0.54 mil after 1 hour of plating and a hardness of 572 V.P.N. Tin oxide powder substituted for the aluminum oxide in example 7 provided after 1 hour a bright coating having a thickness of 0.59 mil and a hardness of 536 V.P.N. While chromium oxide when substituted in example 7 in the form of a liquid containing particles of 0.5 micron size after 1 hour produced a dull smooth coating having a thickness of 0.69 mil and a hardness of 525 V.P.N.

Silicas having a small particle size comprise another class of materials that are particularly useful as wear-resisting particles in the processes of the present invention, examples of which are as follows:

EXAMPLE 9

The process of example 1 was repeated using the bath thereof but substituting silica as the wear-resisting particles therein, the silica utilized being that sold under the trade designation "Syloid 244" and having a particle size in range 1-5 microns. After 1 hour of plating with a 1 percent concentration of the silica in the bath on a dry weight basis, there was produced a bright coating having a thickness of 0.76 mil, a hardness of 525 V.P.N. and a wear-resistance of 14.6 TWI. Comparable results were obtained utilizing other synthetic silicas including that sold under the trade designation "Syloid 266" and that sold under the trade designation "QUSO G-30 ".

The coating of example 10 can be further hardened by heat treatment thereof and the following is as example:

EXAMPLE 10

A workpiece carrying a coating made in accordance with example 9 was heat treated in accordance with example 4, and there resulted a coating having a hardness of 1064 V.P.N. and a wear-resistance of 6 TWI.

The present invention is also particularly useful in applying wear-resistant coatings to aluminum castings and forgings which cannot be heat-hardened, but which have surfaces that must be wear-resistant. The following is an example of the application of a wear-resistant coating to an aluminum workpiece:

EXAMPLE 11

The plating bath of example 1 was modified by adding thereto 0.5 grams per liter of potassium fluoride dihydrate, the preferred concentration being in the range from about 0.001 to about 0.04 mol./liter. An aluminum workpiece was then coated in accordance with the process of example 1 to provide thereon a rough dull coating having a thickness after 1 hour of plating of 0.54 mil, a hardness of 508 V.P.N. and a wear-resistance of 4.5 TWI. It will be appreciated that this workpiece has a bearing surface provided by the coating that is materially more wear-resistant than either the aluminum metal or the electroless nickel plate without the addition of the silicon carbide particles thereto.

In certain instances, it is possible to heat treat aluminum base workpieces, the following being an example of such a heat treatment:

EXAMPLE 12

The aluminum workpiece of example 11 was heated to 175.degree. C. for 1 hour to provide a heat-hardening of the coating thereon. More specifically, the coating now had a hardness of 724 V.P.N. and a wear-resistance of 3.2 even after this mild heat treatment of the workpiece.

As noted above, the workpiece of examples 11 and 12 are rough and dull in appearance. It has been found that if the surface of the coating of example 11, i.e., without heat-treatment, is honed or lapped to render the surface smooth, the wear-resistance thereof is improved and more specifically the TWI is decreased to about 2.2.

Other carbides are useful as wear-resisting particles when applied to aluminum base workpieces, the following being an example thereof:

EXAMPLE 13

The process of example 11 was repeated, but there was substituted for the silicon carbide particles therein tungsten carbide particles having a size of 400 mesh maximum, the tungsten carbide being that sold under the trade designation "Haynes Alloy No. 956." The tungsten carbide particles were utilized in a concentration of 1 percent of the dry solids in the bath, and after 1 hour of plating, there was provided a rough coating having a thickness of 0.45 mil, a hardness of 593 V.P.N., and a wear-resistance of 6.6 TWI.

The coating of example 13 can also be further hardened by heat treatment thereof, the following being an example:

EXAMPLE 14

The aluminum workpiece with the coating of example 13 thereon was heat treated by being heated to a temperature of 270.degree. C. for 16 hours. The heat treated coating was found to have a hardness of 1,145 V.P.N. and a wear-resistance of 2.1 TWI.

Certain metal sulfides may also advantageously be incorporated in electroless nickel plating applied to aluminum base alloys, the following being an example thereof:

EXAMPLE 15

The process of example 5 was repeated by substituting an aluminum base workpiece for the steel workpiece thereof, whereby there was provided after 1 hour of plating a rough coating having a thickness of 0.78 mil, a hardness of 606 V.P.N. and a wear-resistance of 2.7.

The workpiece of example 15 if heat treated can have the hardness of the coating thereon increased, the following being an example:

EXAMPLE 16

The aluminum base workpiece carrying the coating of example 15 was heated to 270.degree. C. for a period of 8 hours to provide a heat-hardened coating having a hardness of 927 V.P.N. and a wear-resistance of 1.5 TWI.

In the above examples, metallizing baths have been illustrated wherein nickel cations have been chemically reduced by hypophosphite anions. It will be understood that other electroless reducing agents may be utilized, the following being an example thereof:

EXAMPLE 17

There was provided an electroless nickel plating bath having the following composition and characteristics:

Nickel chloride 30 g./1. Sodium citrate 10 g./1. Sodium acetate 20 g./1. Sodium succinate 20 g./1. N-diethylborazane 30 ml./1. Lead chloride 0.01 g./l. Methanol 50 ml./l. pH 6 Temperature 65.degree. C.

a quantity of silicon carbide particles was added to the above plating bath with a concentration of 1 percent of the dry ingredients in the bath, the silicon carbide having a size of grit 600. A steel workpiece was immersed in the plating bath and the particles were held in suspension by stirring of the bath. After 1 hour, there was provided a coating of electroless coating on the workpiece, the coating having dispersed therein silicon carbide particles. The coating had all of the useful characteristics and advantages described above with respect to the coating produced by the process of example 1.

Other borazane reducing agents may be used in place of that set forth in example 17 above. In general, any aklkyl-borazane may be used, another preferred reducing agent being dimethyl-borazane. Also useful is sodium borahydride.

The present invention is also applicable to processes wherein other metals are plated by electroless plating, the following being examples of the plating of cobalt coatings on steel workpieces and incorporating in the coatings wear-resisting particles, all in accordance with the present invention.

EXAMPLE 18

There was formulated an electroless cobalt plating solution having the following composition and characteristics:

Cobalt chloride 35 g./1. Sodium acetate 20 g./1. Sodium hypophosphite 10 g./1. pH 4.5 Temperature 95.degree. C.

there was added to this solution 1 percent by weight of the dry ingredients thereof of silicon carbon particles having the size of 600 grit. After 1 hour of plating during which the solution was thoroughly agitated uniformly to suspend the silicon carbide particles, there was produced on the surface of the workpiece an electroless cobalt coating having uniformly dispersed therethrough silicon carbide particles. The resultant coating had the desirable characteristics described above with respect to the coating produced by the process of example 1.

EXAMPLE 19

A plating solution having the following composition and characteristics was formulated:

Cobalt sulfate 30 g./l. Sodium citrate 110 g./l. Ammonium chloride 45 g./1. Sodium hypophosphite 12 g./l. pH 9 Temperature 95.degree. C.

There was added to the plating solution silicon carbide particles in a concentration of 1 percent of the dry ingredients of this plating solution, the particles having the size of 600 grit. A steel workpiece was placed in the plating solution and the solution was vigorously stirred to suspend the silicon carbide particles uniformly therethrough; after an hour, there was produced on the surface of the workpiece a coating of electroless cobalt having silicon carbide particles uniformly dispersed therethrough. The coating had all of the desirable characteristics and advantages of the coating of the process of example 1, described above.

Two electroless metals may be codeposited from an electroless plating solution as is known in the art and such plating solutions are useful in carrying out the process of the present invention, the following being examples thereof:

EXAMPLE 20

An electroless plating solution was formulated having the following composition and characteristics:

Nickel chloride 20 g./1. Cobalt chloride 10 g./1. Sodium citrate 20 g./1. Sodium hypophosphite 10 g./1. pH 4.2 Temperature 95.degree. C.

to the plating solution there was added silicon carbide particles in a concentration of 1 percent of the dry ingredients by weight, the particles having the size of 600 grit. A steel workpiece was immersed in the plating solution while the plating solution was vigorously stirred so as uniformly to suspend the silicon carbide particles throughout the volume thereof. After an hour of plating, there was provided on the workpiece a nickel-cobalt coating having uniformly dispersed therethrough silicon carbide particles. The resultant coating had the several desirable properties and characteristics discussed above with respect to the coating produced by the process of example 1.

EXAMPLE 21

An electroless plating solution was formulated having the following composition and characteristics:

Nickel sulfate 25 g./l. Cobalt chloride 5 g./l. Ammonium chloride 60 g./l. Sodium hypophosphite 15 g./l. pH 9.5 Temperature 95.degree. C.

to this plating solution was added silicon carbide particles in a concentration of 1 percent by weight of the dry ingredients therein, the particles having a size of 600 grit. A steel workpiece was immersed in the plating solution while the solution was vigorously agitated to maintain the silicon carbide particles in suspension throughout the solution during the coating of the workpiece. After an hour, the workpiece had thereon a nickel-cobalt coating having silicon carbide particles uniformly dispersed therethrough. The coating was wear-resistant and had the desirable properties and characteristics discussed above with respect to the coating produced by the process of example 1.

It will be understood that the hardness and wear-resistance of the coatings of examples 17 through 21 can be improved by heat treatment thereof, i.e., by the heating thereof to an elevated temperature for a sufficient period of time to effect a heat-hardening thereof.

The following is an example of yet another electroless metal and an electroless plating solution useful in carrying out the present invention:

EXAMPLE 22

An electroless plating bath was formulated having the following composition and characteristics:

Copper sulfate 20 g./l. Triethanolamine 100 g./l. Formaldehyde solution 20 ml./l. pH 12.5 Temperature 25.degree. C.

there was added to the electroless plating solution silicon carbide particles in a concentration of 1 percent by weight of the dry ingredients in the solution, the silicon carbide particles having a size of 600 grit. A steel workpiece was immersed in the plating solution and the solution was vigorously agitated to maintain the silicon carbide particles in suspension throughout the solution during the coating of the workpiece, After an hour, the workpiece had an appreciable coating thereon of copper having dispersed uniformly therethrough silicon carbide particles. The resultant coating had the hardness and wear-resistance and other desirable properties and characteristics discussed above with respect to the coating provided by the process of example 1.

The following are yet other examples of workpieces which may be successfully coated utilizing the present invention, the chemical composition being other than the steel and aluminum given in the above specific examples.

EXAMPLE 23

The process of example 1 was repeated using a workpiece consisting of copper with essentially the same results in regard to the wear-resistance of the coating obtained.

EXAMPLE 24

The process of example 1 was repeated using a workpiece consisting of brass with essentially the same results in regard to the wear-resistance of the coating obtained.

EXAMPLE 25

Example 25

The process of example 1 was repeated using a workpiece consisting of beryllium alloy with essentially the same results in regard to the wear-resistance of the coating obtained.

Example 26

The process of example 1 was repeated using a workpiece consisting of nickel with essentially the same results in regard to the wear-resistance of the coating obtained.

EXAMPLE 27

The process of example 17 was repeated using a workpiece of magnesium. The coating had all of the characteristics described above with respect to the wear-resistance of the coating of example 17.

Yet other wear-resisting particles may be utilized advantageously in the present invention as follows:

EXAMPLE 28

The electroless plating bath of example 1 was utilized in the process of example 1, but 1 percent by weight on the dry basis of boron nitride was substituted for the silicon carbide therein. The coating obtained after one hour of plating had much improved wear-resistance due fundamentally to the lubricating properties of the boron nitride particles.

EXAMPLE 29

The plating solution and the process of example 1 were repeated but there was substituted for the silicon carbide therein 1 percent by weight of "Microthene FN-510," a polyethylene resin powder having a particle size in the range less than 30 microns. There was obtained an electroless metal coating which had improved wear-resistance due to the incorporation of the plastic particles therein.

It will be understood that the wear-resisting properties of the coatings made in accordance with the present invention may be derived from both the incorporation of hard particles therein and the incorporation of lubricating particles therein. The following is an example of such a process and coating derived therefrom.

EXAMPLE 30

The plating bath and the process of example 1 were utilized but there was in addition added thereto 1 percent by weight on a dry basis of molybdenum disulfide having a particle size of about 50 microns. The resultant coating had much improved wear-resistance, the wear-resistance being imparted thereto both by the hard silicon carbide particles and the lubricating molybdenum disulfide particles.

From the above, it will be seen that there have been provided processes for electroless metallizing of workpieces to provide thereon metal coatings incorporating therein wear-resisting particles, which processes fulfill all of the objects and advantages set forth above. In addition, the processes provide coated workpieces with the improved coatings thereon, all in accordance with the objects set forth above.

While there have been described what are at present considered to be certain preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Claims

What is claimed is:

1. A process of electroless metallizing a body to provide on the surface thereof a metal coating incorporating therein wear-resisting particles, which process comprises contacting the surface of said body with a stable electroless metallizing bath consisting essentially of an aqueous solution of a metal salt and an electroless reducing agent therefor and a stabilizer for said bath and a quantity of wear-resisting particles, wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto; said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about 4 times the weight of the metal in said bath expressed as free metal, and maintaining said particles in suspension throughout said bath during the metallizing of said body for a time sufficient to produce a coating having a thickness of at least about 5 microns, thereby to produce on the surface of said body a coating of the metal having said particles uniformly dispersed therethrough.

2. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles are silicon carbide particles.

3. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles are tungsten carbide particles.

4. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles are molybdenum sulfide particles.

5. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles are silica particles.

6. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles are aluminum oxide particles.

7. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles have dimensions in the range from about 0.01 micron to about 100 microns.

8. The process of electroless metallizing set forth in claim 1, wherein said wear-resisting particles have dimensions in the range from about 0.5 micron to about 25 microns.

9. The process of electroless metallizing set forth in claim 1, wherein said particles are maintained in suspension throughout said bath by mechanically agitating said bath and said particles.

10. The process of electroless metallizing set forth in claim 1, wherein said particles are maintained in suspension throughout said bath by passing said bath with said particles therein past said body.

11. The process of electroless metallizing set forth in claim 1, wherein said particles are maintained in suspension by streams of minute bubbles of gases passing through said bath.

12. The process of electroless metallizing set forth in claim 1, wherein said particles are maintained in suspension throughout said bath by agitation of said body within said bath.

13. The process of electroless metallizing set forth in claim 1, and further comprising the step of heating said coating to an elevated temperature for a sufficient period of time to heat-harden said coating.

14. A process for coating the surface of a body with a nickel coating incorporating therein wear-resisting particles, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of nickel salt and a reducing agent therefor and a stabilizer for said bath and a quantity of wear-resisting particles, wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about 4 times the weight of nickel in said bath expressed as nickel metal, and maintaining said particles in suspension throughout said bath during the coating of said body for a time sufficient to produce a coating having a thickness of at least about 5 microns, thereby to produce on the surface of said body a coating of nickel having said particles uniformly dispersed therethrough.

15. The process of coating set forth in claim 14, wherein said reducing agent is a hypophosphite.

16. The process of coating set forth in claim 15, wherein the absolute concentration of hypophosphite in said bath expressed in mole/liter is within the range 0.15 to 1.20, and the ratio between nickel and hypophosphite in said bath expressed in molar concentrations is within the range 0.25 to 1.60.

17. The process of coating set forth in claim 15, wherein said bath also includes a complexing agent selected from the group consisting of lactic acid and slats thereof.

18. The process of coating set forth in claim 17, wherein the absolute concentration of lactic ions in said bath expressed mole/liter is within the range 0.25 to 0.60.

19. The process of coating set forth in claim 15, wherein said bath also includes an exalting additive selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including three to five carbon atoms and salts thereof.

20. The process of coating set forth in claim 19, wherein the absolute concentration of said exalting additive in said bath expressed in mole/liter is within the range 0.025 to 0.060.

21. The process of coating set forth in claim 15, wherein said bath also includes a complexing agent selected from the group consisting of lactic acid and slats thereof, and an exalting additive selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including three to five carbon atoms and salts thereof.

22. The process of coating set forth in claim 21, wherein the absolute concentration of lactic ions in said bath expressed in mole/liter is within the range 0.25 to 0.06, and the absolute concentration of said exalting additive in said bath expressed in mole/liter is within the range 0.025 to 0.060.

23. The process of coating set forth in claim 15, and further comprising the step of heating said coating to an elevated temperature for a sufficient period of time to heat-harden said coating.

24. The process of coating set forth in claim 23, wherein the coating is heated to a temperature in the approximate range 100.degree. C. to 600.degree. C. throughout a time interval of at least about 1 hour.

25. The process of coating set forth in claim 14, wherein said reducing agent is an alkyl-borazane.

26. A process of applying a nickel coating incorporating therein wear-resisting particles to the surface of a body essentially formed of a material selected from the group consisting of aluminum and its alloys, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite and a stabilizer for said bath and a quantity of wear-resisting particles and wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect to the reduction of the nickel salt by the hypophosphite, said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about four times the weight of nickel in said bath expressed as nickel metal, and maintaining said particles in suspension throughout said bath during the metallizing of said body for a time sufficient to produce a coating having a thickness of at least about 5 microns thereby to produce on the surface of said body a coating of nickel having said particles uniformly dispersed therethrough.

27. The process of coating as set forth in claim 26, wherein said bath additionally consists essentially of a fluoride, wherein the absolute concentration of fluoride anions in said bath expressed in mole/liter is in the range from about 0.001 to about 0.04.

28. A process of applying a nickel coating incorporating therein wear-resisting particles to the surface of a body essentially formed of a material selected from the group consisting of magnesium and its alloys, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite and a stabilizer for said bath and a quantity of wear-resisting particles, and wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect to the reduction of the nickel salt by the hypophosphite, said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about four times the weight of nickel in said bath expressed as nickel metal, and maintaining said particles in suspension throughout said bath during the metallizing of said body, for a time sufficient to produce a coating having a thickness of at least about 5 microns, thereby to produce on the surface of said body a coating of nickel having said particles uniformly dispersed therethrough.

29. A process of applying a nickel coating incorporating therein wear-resisting particles to the surface of a body essentially formed of a material selected from the group consisting of beryllium and its alloys, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite and a stabilizer for said bath and a quantity of wear-resisting particles, and wherein said particles are nonmetallic and being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about 4 times the combined weight of the nickel and the cobalt in said bath expressed as nickel metal and cobalt metal, and maintaining said particles in suspension throughout said bath during he coating of said body for a time sufficient to produce a coating having a thickness of at least about 5 microns, whereby to produce on the surface of said body a coating of a nickel-cobalt alloy having said particles uniformly dispersed therethrough.

30. A process of applying a nickel coating incorporating therein wear-resisting particles to the surface of a body essentially formed of a material selected from the group consisting of copper and its alloys, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite and a stabilizer for said bath and a quantity of wear-resisting particles, and wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect to the reduction of the nickel salt by the hypophosphite, said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about four times the weight of nickel in said bath expressed as nickel metal, and maintaining said particles in suspension throughout said bath during the metallizing of said body for a time sufficient to produce a coating having a thickness of at least about 5 microns, thereby to produce an the surface of said body a coating of nickel having said particles uniformly dispersed therethrough.

31. A process of coating the surface of a body with a cobalt coating incorporating therein wear-resisting particles, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of a cobalt salt and a reducing agent therefor and a stabilizer for said bath and a quantity of wear-resisting particles, wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about four times the weight of the cobalt in said bath expressed as cobalt metal, and maintaining said articles in suspension throughout said bath during the coating of said body for a time sufficient to produce a coating having a thickness of at least from 5 microns, thereby to produce on the surface of said body a coating of cobalt having said particles uniformly dispersed therethrough.

32. The process of coating set forth in claim 30, and further comprising the step of heating said coating to an elevated temperature for a sufficient period of time to heat-harden said coating.

33. A process of coating the surface of a body with a nickel-cobalt alloy incorporating therein wear-resisting particles, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of nickel salt and cobalt salt and a reducing agent therefor and a stabilizer for said bath and a quantity of wear-resisting particles, wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, said particles,

34. The process of coating set forth in claim 33, and further comprising the step of heating said coating to an elevated temperature for a sufficient period of time to heat-harden said coating.

35. The process of coating said coating set forth in claim 34, wherein said coating is heated is the approximate range 100.degree. C. to 600.degree. C. throughout a time interval of at least about 1 hour.

36. A process of coating the surface of a body with a copper incorporating therein wear-resisting particles, which process comprises contacting the surface of said body with a stable bath consisting essentially of an aqueous solution of a copper salt and a reducing agent therefor and a stabilizer for said bath and a quantity of wear-resisting particles, wherein said particles are nonmetallic and essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, said particles being present in said bath in an amount by weight in the range from about 0.1 percent to about 2 percent of the solids in said bath and no greater than about four times the weight of the copper in said bath expressed as copper metal, and maintaining said particles in suspension throughout said bath during the coating of said body for a time sufficient to produce a coating having a thickness of at least about 5 microns, thereby to produce on the surface of said body a coating of copper having said particles uniformly dispersed therethrough.

37. The process of coating set forth in claim 36, wherein said reducing agent is formaldehyde.