NICKEL ALLOY PLATING

Abstract

A nickel-boron coating deposited on a substrate which comprises nickel, boron and a material selected from bismuth, tin, tellurium, selenium, indium and gallium.

Claims

1-14. (canceled)

15. A method of depositing a nickel-boron coating comprising at least 75% wt nickel, wherein the method comprises contacting the substrate with a coating solution having a pH of at least 11 comprising: a source of nickel ions; a reducing agent comprising a source of boron ions; a complexing agent; and a stabilizer agent comprising a source of ions selected from bismuth ions, tin ions, tellurium ions, selenium ions, indium ions and gallium ions.

16. The method of claim 15, wherein the substrate comprises steel.

17. The method of claim 15, wherein the deposition speed of the nickel-boron coating on the substrate is at least 10 m/h.

18. The method of claim 15, wherein the coating solution is lead-free and thallium-free.

19. The method of claim 15, wherein the coating solution is phosphorus-free.

20. The method of claim 15, wherein the coating solution has one or more of the following features (a) through (d): (a) a concentration of the complexing agent in the range 50 to 70 g/l; (b) a concentration of the reducing agent in the range 0.25 to 1 g/l; (c) a concentration of the nickel ions from the source of nickel ions in the range 20 to 30 g/l; (d) a concentration of the stabilizer agent in the range 10 to 25 mg/l.

21. The method of claim 15, comprising preparing the coating solution by: providing an alkaline solution comprising the source of nickel ions, the complexing agent and the stabilizer; adding the reducing agent to the alkaline solution to form the coating solution.

22. The method of claim 15, further comprising heat treating the nickel-boron coating after its deposition.

23. The method of claim 22, wherein the heat treating comprises a heat treatment which lasts at least 30 minutes at a temperature of at least the crystallisation temperature of the nickel-boron coating.

24. The method of claim 22, wherein the heat treating is carried out at a temperature of at least 280 C. and less than 500 C.

25. The method of claim 15, wherein the nickel-boron coating comprises at least 85% wt of nickel.

26. The method of claim 15, wherein the nickel-boron coating comprises (in % wt): at least 85% wt of nickel; boron in the range 1.0 to 10% wt; and a material selected from bismuth, tin, tellurium, selenium, indium, gallium and combinations of two or more thereof, in the range 0.1-5% wt.

27. The method of claim 15, wherein the nickel-boron coating is free of at least one of lead, thallium, and phosphorus.

28. The method of claim 15, wherein the nickel-boron coating is free of lead, thallium, and phosphorus.

29. The method of claim 26, wherein the nickel-boron coating has one of the following features (a) through (h): (a) a thickness of at least 2 m; (b) a wear tracks width of 500 m; (c) a specific wear rate of 4 m.sup.2/N; (d) a friction coefficient of 0.35; (e) a cross section hardness of 700 hv.sub.100; (f) a roughness Ra of 1 m; (g) a roughness Rp of 0.7 m; (h) a critical load for first damage Lc of at least 15N (scratch test).

30. The method of claim 15, wherein the reducing agent comprises a borohydride.

31. The method of claim 15, wherein the complexing agent comprises ethylene diamine.

32. The method of claim 15, wherein, during the deposition of the nickel-boron coating, the coating solution has a temperature of at least 80 C. and less than 120 C.

33. A method of depositing a nickel-boron coating on a substrate, wherein the nickel-boron coating comprises at least 85% wt of nickel, boron in the range 1.0% wt to 10% wt, and a material selected from bismuth, tin, tellurium, selenium, indium, gallium and combinations of two or more thereof, in the range 0.1-5% wt, and the method comprising contacting the substrate with a coating solution having a pH of at least 11, the coating solution comprising: a source of nickel ions; a reducing agent comprising a source comprising a borohydride ; a complexing agent comprising ethylene diamine; and a stabilizer agent comprising a source of ions selected from bismuth ions, tin ions, tellurium ions, selenium ions, indium ions and gallium ions; and wherein the coating solution is lead-free, thallium-free and phosphorus free.

34. The method of claim 33, wherein the coating solution has: a concentration of the complexing agent in the range 50 to 70 g/l; a concentration of the reducing agent in the range 0.25 to 1g/l; a concentration of the nickel ions from the source of nickel ions in the range 20 to 30 g/l; and a concentration of the stabilizer agent in the range 10 to 25mg/l.

Description

[0073] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing of which:

[0074] FIG. 1 illustrates samples of coatings submitted to a neutral salt fog test.

[0075] An aqueous alkaline solution (pH 13.5-14.2) for the preparation of a coating solution is prepared comprising: [0076] about 24 g/L nickel chloride as a source of nickel ions; [0077] about 60 g/L ethylene diamine as a complexing agent; [0078] about 0.02 g/L of bismuth tungstate oxide as a stabilizer agent (source of bismuth ions); and [0079] sodium hydroxide to obtain the desired pH.

[0080] In order to provide a substantially homogeneous solution and coating, a stir bar is immersed in the aqueous solution and subjected to a rotating field by a magnetic stirrer so that the stir bar rotates in the aqueous solution at a spin rate of about 300 rpm. The magnetic stirrer operates continuously during the preparation of the alkaline solution and during the depositing process.

[0081] A first steel substrate is cleaned prior the deposition step. The steel substrate is manually ground on 1200 and 4000 SiC paper sequentially (it may also be possible to use 500 and 1200 MESH SiC paper sequentially), degreased with acetone, rinsed in distilled water and dried. The steel substrate is then activated by a pickling treatment which consists of activating the substrate by immersing it in a 30% acidic solution of HCl (also known as pickle liquor) during about 3 minutes in order to remove possible impurities at the exposed surface of the sample. The steel substrate is then rinsed in distilled water to provide a prepared sample ready for coating deposition.

[0082] When the pickling treatment is almost over, the coating solution is prepared by adding a reducing agent consisting of sodium borohydride to the alkaline solution with the alkaline solution at a temperature of 95 C. The concentration of reducing agent in the coating solution is about 0.6 g/L.

[0083] Immediately after adding the reducing agent to the alkaline solution to form the coating solution, the first prepared sample is immersed in the coating solution during about 1 hour to deposit a nickel-boron coating on the exposed surface of the sample.

[0084] At the end of the deposition step, the first sample is removed from the coating solution and rinsed with distilled water and dried in air. Alternatively, it may be dried inert gas, such as nitrogen.

[0085] The nickel-boron coating has a chemical composition of about 90.7% wt of nickel, about 6.4% wt of boron and about 3% wt of bismuth. In order to determine the chemical composition of a deposited coating, one method is to dissolve a portion of the sample in aqua regia. Aqua regia is a mixture of (molar ratio) of nitric acid and (molar ratio) of hydrochloric acid. Once the portion of the sample is dissolved, the resulting solution is analysed by ICP (Inductively coupled plasma optical emission spectrometry). Alternatively, the chemistry is measured by glow-discharge optical emission spectroscopy.

[0086] The nickel-boron deposited coating has a thickness of about 15.1 m. Table 1 below shows comparative data between the nickel-boron deposited coating from a coating solution comprising bismuth ions (hereinafter NiB-Bi) and a nickel-boron deposited coating having a thickness of about 15.42 m obtained from a comparable coating solution comprising lead ions (hereinafter NiB-Pb) instead of bismuth ions:

TABLE-US-00001 TABLE 1 NiBBi NiBPb Cross section hardness (MPa, hv.sub.100) 865.21 859.80 Roughness Ra (m) 0.26 0.20 Roughness Rp (m) 0.60 0.49 Critical load for first damage Lc (N) 16 30 Friction coefficient 0.37 0.41 Wear tracks width (m) 351 323 Specific wear rate Ws (m.sup.2/N) 3.23 2.53

[0087] The NiB-Bi nickel-boron coating of this example has properties comparable with a nickel-boron coating deposition with a coating solution using a lead stabilizer. Furthermore, first tests of corrosion resistance, using a measure of current density with respect of potential, seem to show that the nickel-boron-bismuth coating has better corrosion resistance than the nickel-boron-lead coating.

[0088] A coating from a coating solution comprising tin ions Ni-B-Sn (hereinafter NiB-Sn) was deposited on a second steel substrate which had been prepared to provide a sample ready for coating deposition in the same way as that described for the first steel substrate above. The second steel substrate, following its preparation was immersed during about 1 h in a coating bath having the following composition:

TABLE-US-00002 TABLE 2 Nickel chloride 24 g/l Sodium hydroxide 39 g/l Ethylenediamine 60 ml/l Tin chloride 0.10 g/l Sodium borohydride 0.602 g/l Bath temperature 95 C. Bath pH 12.5

[0089] The nickel-boron deposited coating had a thickness of about 18.3 m.

[0090] Table 3 below shows comparative data between the NiB-Sn coating and the NiB-Pb coating having a thickness of about 15.42 m shown in the previous comparative example.

TABLE-US-00003 TABLE 3 NiBSn NiBPb Cross section hardness (MPa, hv.sub.100) 794 859.80 Roughness Ra (m) 0.62 0.20 Roughness Rp (m) 2.90 0.49 Critical load for first damage Lc (N) 30 30 Friction coefficient 0.33 0.41 Wear tracks width (m) 323 Specific wear rate Ws (m.sup.2/N) 0.11 2.53

[0091] Table 4 below shows information on corrosion resistance. Each sample was submitted to salt fog spray test using a neutral salt spray in accordance with ASTM B117. The amount of corrosion of the surface was quantified by image analysis, software Image J, using a SEM, with respect of the exposed surface. The samples are illustrated in FIG. 1. The time to decomposition and palladium test values are determined using the tests below:

Time to decomposition test: a plating bath free of any samples for deposition, is submitted to plating conditions, notably to a plating bath temperature of 95 C. The time to decomposition represents the time before the plating bath starts to react spontaneously (i.e. starts forming nickel powder).
Palladium test: palladium chloride PdCl.sub.2 having a concentration of about 650 mg/l is added dropwise over about 25 s to the plating bath once the plating bath reached the plating condition and a plating bath temperature of 951 C. Sufficient magnetic stirring (about 400 rpm) was used to dissipate any concentration gradient due to the addition of PdCl2. The amount of palladium chloride added to the plating bath is 0.5 ml per 100 ml of plating bath solution. The time required for the plating bath solution to be decomposed was recorded. The end point, i.e. the onset of bath decomposition, was when the solution became opaque. The values of time to decomposition and palladium test of table 4 below are the mean values of 5 tests.

TABLE-US-00004 TABLE 4 NiB-lowSn NiB-midSn NiB-highSn NiBPb NiB NiBBi (see Note 1) (see Note 2) (see Note 3) Time to decomposition (s) 21500 19800 15000 21600 25200 27000 Palladium test (s) 204 190 189 178 211 247 Thickness (m) 16.02 10.1 15.0 14.5 18.3 20.8 Ra (m) 0.32 0.22 0.26 0.93 0.62 0.39 Hardness hk.sub.50 854 704 839 668 842 867 Lc (N) 25 23 16 28 30 18 Friction coefficient 0.45 0.48 0.45 0.42 0.35 0.51 Specific wear rate Ws 0.63 0.81 0.67 0.81 0.11 1.29 (m.sup.2/N) Duration of salt fog spray 240 240 240 240 240 240 and 504 test (hours) Corroded surface (%) 21.1 3.9 32.6 66.6 17.6 6.4 (240 h) and 9.3 (504 h) Note 1: deposition with concentrations of tin chloride of 0.05 g/L. Note 2: deposition with concentrations of tin chloride of 0.10 g/L. Note 3: deposition with concentrations of tin chloride of 0.20 g/L.