US 3674447 A
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United States Patent U.S. Cl. 29196.6 18 Claims ABSTRACT OF THE DISCLOSURE Metallic compositions and substrates coated therewith having improved wear resistance and other properties are provided. In a preferred embodiment, the coating comprises an intimate dispersion of hard nickel-boride (Ni B) or nickel phosphide (Ni P) in a soft matrix of nickel and thallium. The coating is prepared by chemical reduction of nickel and thallium salts using borohydrides such as sodium borohydride and dimethylamine borane (DMAB) or sodium hypophosphite. The proportions of the metals in the preferred coating are about 99.4 to 82 percent by weight nickel, about 0.1 to 12 percent by weight boron or phosphorus and about 0.5 to 6 percent by weight thallium. Cobalt can be used as well as the preferred nickel. In the metallic compositions, abrasionresistant particles such as metal carbides can be present in the soft matrix of nickel and thallium. The coating can be heat-treated at 300 to 500 C. to achieve optimum metallurgical structure. Shaped structures subject to wear, such as piston rings and bearings, and structures subjected to cutting action, such as twist drills, are particularly benefited by the coatings.
BACKGROUND OF THE INVENTION Field of invention This invention relates to metallic compositions and coatings possessing high hardness and low friction and wear, and more particularly to nickel-born or phosphorus-thallium alloy coatings having these properties.
Prior art The reductive plating of nickel or cobalt on various substrates to produce functional, decorative, coated articles is well known in the art. Such coatings are prepared by reducing nickel or cobalt salts using borohydrides such as dimethylamine borane or sodium borohydride, or sodium hypophosphite as reducing agents. While uses for such prepared articles have been limited to decorative applications, there is a desire to extend the uses of reductive plated articles to other areas.
One such area of interest is hard, wear-resistant coatings which can replace the compete with commercial hard chrome. Although U.S. Pat. 3,045,334 issued to T. Berzins on July 24, 1962 discloses that nickel-boron reductive coatings do possess hardness, they have been found to be of insuflicient hardness and wear resistance to be of commercial significance.
It has been found by the present invention that a controlled amount of thallium uniformly dispersed throughout the coating gives the requisite hardness and wear resistance. Although U.S. Pat. 3,295,999 issued to Heinz G. Klein and Eberhard Zirngiebl on Jan. 3, 1967, discloses the use of thallium nitrate and thallium arsenate to 3,674,447 Patented July 4, 1972 stabilize borohydride plating baths, there is no mention that thallium is contained in the coatings or that thallium confers beneficial properties to the coatings.
SUMMARY OF THE INVENTION According to the present invention there is provided a metallic composition comprising: a soft matrix of nickel or cobalt and thallium, and finely divided hard particles dispersed therein; said composition containing about 99.4 to 82 percent by weight nickel or cobalt, about 0.5 to 6 percent by weight thallium and about 0.1 to 12 percent by weight of boron or phosphorus. Some abrasion-resistant particles such as metal carbides and nitrides can also be present.
There is also provided a coated article in which the coating has low friction and wear, and high hardness comprising: a substrate and a coating on at least one surface of the substrate comprising nickel or cobalt with boron or phosphorus and containing thallium, said coating being about 99.4 to 82 percent by Weight of nickel or cobalt, about 0.1 to 12 percent by weight boron or phosphorus and about 0.5 to 6 percent by weight thallium.
DETAILED DESCRIPTION OF THE INVENTION The coated articles of the present invention can be prepared by chemically depositing an alloy of nickel or cobalt with boron or phosphorus onto a substrate from plating solutions described in U.S. Pat. 3,338,726, issued to Talivaldis Berzins on Aug. 29, 1967, U.S. Pat. 3,096,182, issued to Talivaldis Berzins on July 2, 1963 and U.S. Pat. 2,658,841, issued to G. Gutzeit and Abraham Krieg on Nov. 10, 1953, also containing thallium salts from which thallium metal will also be chemically deposited. These patents describe chemical plating using dimethylamine borane, sodium borohydride and sodium hypophosphite, respectively, as reducing agents. Of these, borohydride baths are preferred and a sodium borohydride bath is most preferred due to its faster plating rate. Since the compositions of these baths are well known to those skilled in the art, they will not be described; however, the contents of the above patents describing the bath compositions are incorporated by reference.
The thallium can be employed in the form of any water-soluble salt which is not antagonistic to the plating process and from which thallium will also be chemically deposited. For instance, the chlorides, sulfates, formates, carbonates and acetates of thallium are satisfactory with thallium sulfate being preferred. The exact concentration of thallium salts in the bath varies with the reducing power of the bath. In general, to achieve the required 0.5 to 6 percent by weight of thallium in the alloy plate requires about 10 to 60 mg./l. of thallium sulfate. Too low a concentration of thallium is ineffective while too high a concentration produces coatings with high thallium content, and thus with inferior properties. A preferred thallium content is 1 to 5 percent with best results achieved at a thallium level of 2 to 3 percent. Further, when the thallium content of the bath increases, a catalytic surface becomes more passive and eventually no plating occurs.
Coating of the surfaces of substrates occurs by placing in contact with the plating solutions such substrates the surface of which is composed of nickel, cobalt, iron, steel, aluminum, zinc, palladium, platinum, copper, brass, manganese, chromium, molybdenum, tungsten, titanium, tin,
silver, carbon or graphite, or mixtures thereof. Articles having these surfaces that can be plated for improved wear or cutting action include piston rings, bearings, hydraulic rams, pistons, shafts, chain-saw parts, twist drills, reamers, taps, punches, dies and abrasive particles. These materials function catalytically to cause a reduction of the nickel or cobalt ion to the hard particles of nickel or cobalt alloy by the reducing agent present and thereby deposit such alloys in a uniform layer on the metal surfaces. Nonmetallic materials such as ceramaceous materials and various plastics can have their surfaces rendered catalytic by sensitizing techniques known to those skilled in the art, i.e., dipping the ceramic or plastic articles in a solution of stannous chloride and then contacting the treated surface with a solution of palladium chloride.
In carrying out the plating process on metallic substrates, the article to be plated is properly prepared by degreasing, alkaline cleaning and acid pickling according to standard practice in the electroplating industry. The cleaned article is then immersed in a suitable volume of hot, aqueous plating solution. Almost immediately, hydrogen bubbles can be observed forming on the catalytic surfaces of the immersed article, and escaping in a steady stream from the solution, while the surface of the article is slowly coated with a metallic plate. The plating is continued until the metal ions are depleted from solution or until the borohydride is consumed in the plating process.
The nickel or cobalt-boron-thallium and nickel or cobalt-phosphorus-thallium alloys of the invention are characterized by an essentially amorphous structure. Thus, essentially no crystalline nickel or cobalt, or thallium is detected by X-ray examination using CuKa radiation.
Alloy plates useful in the present invention contain about 99.4 to 82 percent by weight, preferably about 98 to 89 percent, nickel or cobalt; about 0.1 to 12 percent by weight, preferably about 1 to 6 percent, boron or phosphorus; and about 0.5 to 6 percent by weight, preferably about 1 to 5 percent, thallium. These elements are uniformly dispersed and distributed throughout the coating. The thallium forms with the nickel or cobalt a soft matrix in which hard particles of nickel or cobalt borides, or nickel or cobalt phosphides, are intimately dispersed. These latter hard particles are produced when the asplated coating is subjected to the preferred heat-treatment.
Although the thallium-containing alloy coatings possess greater hardness and wear resistance than the same coatings without thallium, the hardest and best wearing coatings are obtained when the coatings are heat-treated. The coated articles are heat-treated by heating to a temperature within the range of 200 to 600 C., preferably 300 to 500 0., for times of 1 minute to 16 hours, preferably 15 minutes to 4 hours to produce some nickel or cobalt boride or phosphide in the plate as shown by X-ray examination. Suitable means of heat-treating are a forced oven with an air or inert atmosphere or immersion in a salt bath. Alternatively, if the surface can be cold-worked, a hardening of the plate results. It has been found that greater than 6 percent thallium gives coatings in which the hardness deteriorates during heating, whereas coating of preferred thallium content shows essentially no deterioration of hardness.
The thallium-containing alloy plates are bright, very hard, uniform in thickness, free of porosity and have a high degree of ductility. These plates also exhibit low friction and wear properties. The plates of the invention are less brittle than similar plates without thallium. It has been found that unsupported coating films were more coherent, flexible and tough when they fell within the preferred composition limits of the invention. Such unsupported films were produced by plating one side of copper foil 5 mils in thickness and then dissolving the copper by alternate immersions in a polysulfide bath and then a cyanide bath. Coating films of the preferred com- '4 position can be creased without cracking and can be isolated in sizeable areas without porosity.
The alloy content of the plates is determined by wet chemical methods after selective dissolution of the plate from copper in warm 2M nitric acid. Nickel and thallium are determined by atomic absorption methods on the resulting solution by comparison with a series of known solutions. The boron is present in the solution as boric acid and is separated from the other metal ions by passing the solution through a column packed with a cation-exchange resin like Amberlite IR 120 manufactured by Rohm and Haas Company. The boric acid content of the efiluent is then determined titrimetrically in the presence of mannitol, using a pH meter to indicate the endpoint.
Plates of the present invention display improved wear resistance in the ASTM Test D 2714 using the LFW-l wear testing device. In this test, a small plated steel block is contacted under pressure with a rotating ring of standard tool steel. The resulting scar is measured accurately after a specific number of cycles has elapsed. The usual test conditions are 35,000 cycles at 72 r.p.m., a load of 630 pounds, and mineral oil as the lubricant. Under these conditions, plates of the preferred composition show onetenth less wear than the lubricated wear of commercial chromium electroplate.
The coefiicient of friction is determined in conjunction with the wear resistance test. It is the frictional force at the line of contact as read on the load indicator, divided by the load, which is usually 630 pounds.
Another practical wear test is to measure the number of holes than can be cut in 0.75 inch alloy steel of Rockwell B 68 hardness by a 0.25 inch twist drill (Cleveland) plated with a thallium-containing alloy plate of the present invention operating at 2250 r.p.m. and 5 inches per minute. The plates of the preferred composition increased unlubricated tool life in this test by a factor of 10. All holes were counted until the tool broke.
Hardness of the thallium-containing alloy plates is determined with a load of grams on a Knoop hardness measuring device. The preferred plates are harder than commercial hard chromium electroplate with values in excess of 900 Knoop or Rockwell C 60.
While the preferred plate is limited to a duplex structure of hard nickel or cobalt boride, or nickel or cobalt phosphide dispersed in a softer nickel or cobalt and thallium matrix, the invention is also applicable to the use of other hard refractory or abrasion-resistant particles dispersed in a soft nickel or cobalt and thallium matrix. These abrasion-resistant particles can be dispersed in the matrix by themselves or, when the coating is given the preferred heat-treatment, the hard nickel or cobalt boride, or nickel or cobalt phosphide is also present. Suitable finely divided hard particles are metal oxides such as aluminum oxide, metal carbides such as Cr C silicon carbide, titanium carbide, calcium carbide and boron carbide, metal nitrides like boron nitride and natural abrasives such as diamond dust, garnet, quartz, emery and corundurn. Finely divided particles of these materials should preferably have particle sizes under 20 microns; however, particle size is not critical. Particles up to 1000 microns in size can be used. A coated article may be produced by reductive plating of the fine particles followed by pressure sintering by powder metallurgical methods.
The invention can be further understood by referring to the following examples in which parts and percentages are by weight unless otherwise indicated:
EXAMPLE 1 This example shows the beneficial effect of thallium upon the hardness and wear properties of as-plated nickelalloy coatings. In these tests, standard alpha blocks were treated first in a variety of plating baths; then further blocks were treated in the same baths but with added thallium sulfate. The coatings were selected so that the coating thickness was about 2 mils. The steel blocks were given a standard pretreatment consisting of degreasing, alkaline cleaning and acid picklin Coating adhesion was judged to be good in all cases. In all cases, the hardness and lubricated wear properties of the coatings were improved by the presence of thallium. The data is summarized in Table I. Plates 0.1 mil thick were also applied to inch twist drills (Cleveland) that were free of any oxide or other surface benefication. The presence of thallium in the coating significantly increased the number of holes that could be out before tool breakage as seen in Table I. The drills were not lubricated in these tests. Tests were conducted as previously described.
TABLE I.UTILITY OFC THALLIUM IN NICKEL ALLOY OATIN GS Drill life, Coating analysis, Knoop holes percent hard- Coeffi- Wear cut to ness cient of scar, break- Batli Ni B P 'Il KH u friction mil 3 age N0'1E.Bath #1 20 g./l. NiC1z.6H-z0, 40 g. [1. NaOH, 60 g./l. C2Hz (NH 0.5 g./l. NaBHi; 15 mgJl. TlzsOi; 92 C., pH 14; h #2 0 g./l. nickel acetatejHgo, 25 g./l. sodium citrate, 25 g./l. lactic acid, 0.05 g./l. thicdiglycolic acid, 2.5 g./1. DMAB; 10 mgJl. T12SO4265 0., pH 6.5; Bath #3 20 g./l. NiSOJ. 6H2O, 10 g./l. citric acid, 2.5 g./.l. DMAB, 1 mgJl. 2- rnercaptobenzothiazole; l5 mg./l. TlzSOi: 65 0., pH 5.5; Bath #4 40 g./l.
NiSOi. 61140, 65 g.fl.(NHi)2S04, 30 g./l. succinic acid, 30 g./l. sodium acetate, 50 g./l. NaHzPOz; 15 mg./l. Tl2S04192 0., pH 9.5.
EXAMPLE 2 This example illustrates the further beneficial effect heat-treatment has upon the properties of the plates described in Example 1. A standard heat-treatment of minutes at 325 C. was employed for all samples. This data is summarized in Table II.
TABLE II.UTILIT TREATED AT 325 C. FOR 20 MINUTES Mg./l. T12SO4 in bath Percent T1 in coating No heat-treatrnentz Hardness, KH 709 741 767 727 708 Duetility Poor Fair Good Fair Poor Friction coefiieient. 0. 15 0. 12 0. 12 0. 12 0. 14 Wear sear, mil 3 8, 000 2, 100 2, 500 3, 600 5, 000 Holes cut to breakage. 3 5 2 After 20 minutes at 325 0.:
Hardness, KH 774 1, 055 1, 022 889 794 Ductility Poor Good Good Fair Poor Friction coefficient- 0.11 0.09 0.09 0. 10 O. 12 Wear scar, mil 3 3, 100 475 540 785 2, 200 Holes cut to breakage 8 75 95 35 12 EXAMPLE 4 This example illustrates the influence of thallium upon coating hardness as a function of heat-treatment. Mild steel panels were treated at 92 C. in the baths of Example 3 to a thickness of 2 mils. It is clear that the optimum thallium content ensures high hardness without substantial deterioration over a broader range of temperatures as shown in Table IV.
TABLE IV.HEAT-TREATMENT AND COATING HARDNESS, KHioo MgJl. T12SO4 in bath Norm-An optimum temperature exists between 325 and 400 C. to
achieve maximum hardnesss.
Y OF THALLIUM IN NICKEL-ALLOY COATINGS HEAT- Ooating analysis, Knocp Coetfi- Drill life percent hardcient Wear holes cut Heat uess scar to Bath N1 B P 'Il treated KHmo friction mil 3 breakage 1 93 3 No 780 0.11 2,000 5 93 3 Yes 1, 025 0. 09 450 120 3 92 3 No 785 0.10 1,250 6 92 3 Yes 1, 040 0. 09 395 4 92 2 No 745 0.12 9,600 7 92 2 Yes 975 0. 10 1, 425 24 EXAMPLE 3 EXAMPLE 5 This example illustrates that a critical thallium content exists for optimum hardness and wear properties. Samples of mild steel, S-mil copper foil, alpha blocks and twist drills were plated in a bath consisting of 30 g./l. NiCl .6H O, 40 g./l. NaOH, 60 g./l. C H (NH 0.5 g./l. NHBH4 and varying amounts of 11 50 at 92 C. It was observed that no plating occurred at Tl SO levels greater than 0.26 g./l. Tests were conducted as previously This example shows that the metallic composition of the invention containing finely divided industrial diamonds exhibits improved grinding efficiency. Catalytically activated industrial diamonds held on a l20-mesh screen were immersed in Bath #1 of Example 1 until the weight of the sample increased 50 percent (60% cladding). The clad diamonds were then converted into a grinding wheel by imbedding the particles onto a plastic disc. It was described. Table III summarizes the data on these tests. found that the grinding efiiciency (amount of metal removed per gram of diamond) was increased about 30% when compared with unclad diamonds.
Silicon carbide, alumina, graphite and silica particles were also clad successfully using the same bath and same catalytic pretreatment (stannous chloride dip bath followed by a palladium chloride dip bath).
What is claimed is:
1. A coated article in which the coating has low friction and wear, and high hardness comprising: a substrate and a coating on at least one surface of the substrate comprising a metal selected from the group consisting of nickel and cobalt with an alloying element selected from the group consisting of boron and phosphorus and containing thallium, said coating being about 99.4 to 82 percent by weight of said metal, about 0.1 to 12 percent by weight of said alloying element and about 0.5 to 6 percent by weight thalium.
2. The coated article of claim 1 wherein the thallium is uniformly distributed throughout the coating and the coating is essentially free of crystalline metal and thallium.
3. The coated article of claim 2 wherein a portion of the metal is combined with the alloying element as hard particles selected from the group consisting of metal boride and metal phosphide dispersed in a matrix of said metal and thallium.
4. The coated article of claim 3 wherein the coating contains about 98 to 89 percent by weight of said metal, about 1 to 6 percent by weight of said alloying element and about 1 to percent by weight thallium.
5. The coated article of claim 4 wherein the substrate is a metallic substrate.
6. The coated article of claim 5 wherein the metallic substrate is a ferrous substrate.
7. The coated article of claim 6 wherein some nickel and boron are combined as nickel boride in the coating.
8. The coated article of claim 2 wherein the coated article is heat-treated at a temperature within the range of about 300 to 500 C.
9. The coated article of claim 2 wherein the coated article is heat-treated at a temperature within the range of about 200 to 600 C.
10. The coated article of claim 3 wherein finely divided abrasion-resistant particles are also present in the composition.
11. A metallic composition comprising: a soft matrix of a metal selected from the group consisting of nickel and cobalt, and thallium, and finely divided hard particles dispersed therein; said composition containing about 99.4
8 to 82 percent by weight of said metal, about 0.5 to 6 percent by weight thallium and about 0.1 to 12 percent by weight of an alloying element selected from the group consisting of boron and phosphorus.
12. The metallic composition of claim 11 wherein a portion of the metal is combined with the alloying metal as hard particles selected from the group consisting of metal boride and metal phosphide dispersed in a matrix of said metal and thallium.
13. The metallic composition of claim '12 wherein finely divided abrasion-resistant particles are also present in the composition.
14. The metallic composition of claim 13 wherein the finely divided abrasion resistant particles are selected from the group consisting of metal carbides, metal oxides, metal nitrides and diamond dust.
15. A metallic composition comprising: a soft matrix of nickel and thallium, and hard nickel boride dispersed therein; said composition containing about 98 to 89 percent by weight nickel, about 1 to 5 percent by weight thallium and about 1 to 6 percent boron.
16. A coated article in which the coating has low friction and wear, and high hardness comprising: a ferrous substrate and a coating on at least one surface of the substrate comprising nickel boride dispersed in a soft matrix of nickel and thallium, said coating being about 98 to 89 percent by weight nickel, about 1 to 5 percent thallium and about 1 to 6 percent boron, said coated article heat-treated at a temperature within the range of about 300 to 500 C.
17. The coated article of claim 5 in a form of cutting tool.
18. The coated article of claim 16 in a form subject to lubricated wear.
References Cited UNITED STATES PATENTS 2,872,312 2/1959 Eisenberg 117100 B X 3,045,334 7/1962 Berzins 29194 3,295,999 1/ 1967 Klein et al. 106l 3,617,363 11/1971 Metzger et al. 117-130 E L. DEWAYNE RUTLEDGE, Primary Examiner J. M. DAVIS, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,674,447
DATED I JULY 4, 1972 INVENTOR(S) I HAROLD EDWARD BELLIS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 5, line 28, and column 5, line 71, change "C H (NH t0 C H (NH a Signed and Scaled this Eighteenth Day f March 19 0 [SEAL] Arrest:
SIDNEY A. DIAMOND I Arresting Oflicer Commissioner of Patents and Trademarks