GB2218111A

GB2218111A - Coating metallic substrates by the PVD process

Info

Publication number: GB2218111A
Application number: GB8905734A
Authority: GB
Inventors: Michael Baltz; Klaus Schulze-Berge; Siegfried Bastian; Hulmut Erhart; Hartwig Petersen
Original assignee: SURPRO OBERFLAECHEN; LPW Chemie GmbH
Current assignee: SURPRO OBERFLAECHEN; LPW Chemie GmbH
Priority date: 1988-03-18
Filing date: 1989-03-13
Publication date: 1989-11-08
Anticipated expiration: 2009-03-13
Also published as: JPH0277585A; HK141294A; DE3809139C2; GB2218111B; GB8905734D0; CH677366A5; DE3809139A1

Description

2 2; 18 111 COATING METALLIC SUBSTRATES BY THE PU PROCESS The invention

relates to the application to metallic substrate materials of coatings produced by the PU process. PU stands for physical vapour deposition. It embraces both functional and decorative coatings. The common coating materials include borides, carbides, nitrides, oxides and silicides of metallic elements in subgroups 4 to 6 of the periodic system, viz., titanium, hafnium and vanadium, niobium, tantalum and chromium, molybdenum and tungsten, individually or in combinations. Particular interest centres on the carbides, nitrides and oxides of the subgroup 4 elements, since apart from the high hardness and wear resistance of such coating materials, which can be several times greater than those of hard chromium deposits, they can exhibit attractive decorative colourations resembling for example gold in the TiN case and anthracite in the TiC case. The coating materials in question can also contain suitable admixtures of other elements such as aluminium, cobalt, gold, carbon, copper, nickel and/or palladium, which extend the range of colourations to blue, green, red or silvery tints. Furthermore, the PU process can be used to deposit metallic materials such as aluminium, titanium, zirconium, platinum or gold, so that suitable equipment having more than one sputtering source can also produce combination coatings. Titanium for example can be superficially oxidised by subsequent chemical or electrochemical treatment, so that colourations extending over the full spectrum range can be produced. Moreover, the PU process can even deposit amorphous and/or diamond-like carbon, in order for example to produce particularly low-friction and slow-wearing sufaces.

The PVD process has proved succesful in many branches of technology (cf. GB-PS 2 123 039) and has led to substantial improvements in the quality of the coated products, provided that the substrate material itself is sufficiently corrosionresistant when the coated products are exposed to corrosive environments, as is the case when PVD coatings of titanium carbide or nitride are applied to austenitic chromium-nickel steel or solid titanium substrates. However, if the substrate material has too little corrosion resistance, or no resistance whatever, to the specific corrosive environments, then corrosion damage will eventually ensue in service. Thi s applies for example to metallic substrate materials such as aluminium, lead, copper, magnessium, nickel, silver, steel and zinc or their respective alloys such as brasses, bronzes, German silver, Monel, Alpacca, zinc pressure diecasting alloys, lead spincasting alloys and so on. Corrosion damage still ensues when such substrate materials have already been provided with an electrolytically or chemically deposited underlayer of the matte, bright, semi-bright or semi-matte type consisting of chromium, -copper, copper alloy, nickel, nickel alloy, silver or tin alloy or a combination thereof. The term nickel or nickel alloy coating includes the disperse Ni, Ni-P and Ni-B types. The same problem arises with galvanised synthetic materials such as, for example, ABS (acrylonitrile-butadiene-styrene) or mixed polymerisates such as polycarbonate/ABS (e.g., Bayblend - Bayer, Lever-kusen), V polypropylene etc., which are usually provided with an initial non- electrolytic metallic layer or chemically deposited copper, nickel- phosphorus or nickel-boron, an interlayer of bright copper and bright to semi-matte nickel and a final layer of bright chromium.

Corrosion damage arises because coatings applied by the PVD process, in the commonly used thickness range of 0.3 - 1 micron, are porous or microfissured, particularly if the deposition temperature is low and the environment has not been purified; they have a high pinhole concentration and can have a very high positive electrochemical potential. The source of the high pinhole concentration lies in the preferred spike crystal growth normal to the substrate surface, which is characteristic of the PVD deposition process; the spikes are incapable of spreading out sufficiently over the substrate surface and thereby forming a continuous uniform coating layer. These coating defects can disappear given a sufficient coating thickness, but this remedy would not be cost effective from the equipment productivity viewpoint, since the deposition rate in the PVD process is extremely low. Moreover, one can only adopt very low PVD processing temperatures in the range 100-1200C in many cases notably when coating synthetic materials, to avoid heating the latter to their Vicat softening point. In view of the extremely low processing temperatures, the PVD process is incapable in the majority of applications of producing truly sound coatings.

One could consider suppressing damaging corrosion phenomena by providing an interlayer of a very noble metal such as gold or platinum, which could not be deposited by the normal electroplating techniques, or at least which would not adhere tenaciously to a chormium-plated surface. Apart from the high costs this would involve, such interlayers would- be extremely soft, particularly in the case of gold, and could very easily be damaged in the course of applying further layers by the PVD process. Moreover, it is particularly deleterious to interpose a layer of low micro-hardness beneath a hard outer layer. Furthermore, tests have shown that interlayer materials such as gold often give rise to tenacity problems when coatings applied by the PVD process are mechanically loaded in shear.

Accordingly, the object of the invention is to improve the corrosion resistance and mechanical tenacity of PVD coatings in finishes comprising a substrate material having little or no corrosion resistance and a coating applied by the PVD process.

According to the present invention, a method of applying a coating to a metallic substrate material of little or no corrosion resistance by the PVD process comprises using an interlayer of palladium-nickel alloy containing 30-90 wt.% preferably 60-85 wtJ of palladium, deposited from an aqueous electrolyte containing palladium and nickel ammines at a palladium concentration in the range 2-20 g/l and a nickel concentration in the range 5-30 9/1, together with optional conductivity salts and organic additives which can contain sulphur, and wherein the electrolyte components are selected so that any sulphur precipitated with the alloy has a valency exceeding two.

The additives in the electrolyte can be aliphatic, unsaturated and/or heterocyclic sulphonates, optional conductivity salts, selected aromatic sulphonimides as tensile stress reducers and/or anti-corrosion additives, together with non-ionic and/or anion-active wetting agents, characterised in that the added aliphatic, unsaturated and/or heterocyclic sulphonates consist of one or more alkali salts (more particularly sodium salts) of vinyl- allyl-, propin-, methallyl- and/or N-benzylpyridinium-2-ethyl sulphonic acids, N-pyridiniumpropylsulphobetain and/or Npyridiniummethylsulphobetain.

The metallic substrate material can be aluminium, lead, copper, magnesium, nickel, silver, steel, zinc, alloy materials based thereon such as brass, bronze, German silver, Monel, Alpacca, zinc pressure diecasting alloys or lead spincasting alloys, in their common technical forms. Different substrate materials can be provided with, or different optical effects or technical properties can be obtained by, electrolytically or chemically depositing additional layers of matte, bright, semi-bright or semi-matte copper, copper alloy, nickel, nickel alloy, silver or tin alloy or combinations thereof. The term nickel and nickel alloy layers includes the disperse, Ni-P and Ni-B types. Alternatively, the metallic substrate material can itself be an electroplate coating on a galvanisable synthetic material component, including single or combined layers of matte, bright, semi-bright or semi-matte copper, copper alloy, nickel, nickel alloy, silver or tin alloy. It is obvious that the palladium-nickel alloy cannot be deposited by the usual electroplating processes, at least as a tenacious coating on chromium-pl;ted substrates.

Palladium-nickel alloy coatings adapted and produced in the specified manner are surprisingly immune from damage when handled in conformity with the invention, even when the interlayer in question is applied extremely thinly. The palladium-nickel layer has a far higher micro- hardness, and resists possible damage during subsequent PVD processing much better than a comparable interlayer of pure gold. Even if the substrate material usually suffers severe corrosion in service, the problems disappear when the features of the invention are adopted. The palladium-nickel alloy coatings used in the special manner of the invention are in themselves known (of. DE-PS 31 08 508 and DE-PS-32 32 735). Moreover, there are no adhesion problems when the coating applied by the PVD process is loaded mechanically in shear.

According to a preferred embodiment of the invention, described in a different formulation, the invention relates to a process for the application of a PVD coating to a substrate material having little or no corrosion resistance, whereby an interlayer of a palladium-nickel alloy is first applied to the substrate material, by deposition from an aqueous solution containing palladium and nickel ammines at a palladium concentration in the range 2-20 g/l and a nickel concentration in the range 5-30 g/l, together with added aliphatic, unsaturated and/or heterocyclic sulphonatesq optional S conductivity salts, selected aromatic sulphonimides as tensile stress reducers and/or anti-corrosion additives (benzene-acidsulphonimide and/or benzene-sulphonyl resin) and further nonionic and/or anion-active wetting agents the palladium to nickel ratio in the electrolyte being so adjusted that the electrolytically deposited alloy has a palladium content in the range 30-90 wt.%, preferbly 60-85 wt.%, and the additive consisting of an aliphatic, unsaturated and/or heterocyclic sulphonate of the alkali salt type, more particularly such as one or more of the sodium salts of vinyl-, allyl-, propin-, methallyland/or N-benzylpyridinium-2-ethyl-sulphonic acids, N-pyridiniumpropylsulphobetain and/or N- pyridiniummethylsulphobetain.

The introduction already referred to known coatings for application by the PVD process. It is within the scope of the invention to use PVD coatings consisting of borides, carbides, nitrides, oxides and/or silicides of metallic elements in subgroups 4 to 6 of the periodic system, individually or in combination. More particularly they can be carbides, nitrides and/or oxides of subgroup 4 elements, such as TiN or TiC or mixtures of different substances, which can furthermore contain certain amounts of aluminium, cobalt, gold, carbon, copper, nickel and/or palladium. Alternatively, the PVD coatings can be of a metallic nature, such as aluminium, titaniumt zirconium, gold, platinum and so o n. They can even consist of amorphous and/or diamond-like carbon.

Evidently, if may also be necessary, depending on the nature of the substrate material, to provide another electrolytically deposited coating bef ore applying the palladium-nickel interlayer, in order for example to improve the surface finish of the substrate material by smoothing coatings, to ensure the adequate tenacity of the palladiumnickel layer, to attain special semi-bright surface effects, or in the case of synthetic materials to attain an adequate thermal shock resistance within the coated composite product by providing a copper underlayer of maximum possible thickness. The range likewise includes the disperse nickel, Ni-P and Ni-B coating types, which provide outstandingly hard underlayers for example. It is also evident that when coating electroplated synthetic materials the PVD processing temperature must be adjusted to conform to their Vicat softening point limits. - Palladium- nickel coatings cannot be applied by conventional electroplating means, at least because of their lack of tenacity to surfaces which have not been chromium-plated.

In order to ensure that the palladium-nickel interlayer is absolutely or substantially free from pores, its thickness is preferably adjusted in conformity with the surface finish of the substrate material and/or the electrolytically deposited underlayer thereon, and should be at least 0.1 micron. The coating thickness 'is preferably adjusted to the depth of roughness grooves on the substrate material or the underlayer deposited thereon. In other words, the palladium-nickel interlayer thickness is increased as the roughness grooves on the substrate surfaces become deeper. Average coating thicknesses lie in the range 0.5 to 5 microns. The PVD coating should preferably have a thickness in the range 0.1 to 5 microns, more preferably 0.3 to 1 micron. It is obvious that the PVD processing parameters should preferably be so adjusted that the coating will contain an absolute minimum of continuity defects (porosity, microfissures, pinholes).

The invention and the advantages accruing therefrom will now be discussed with reference to typical embodiments thereof.

ExampIg 1 Sheets of grade Ms 58 brass are cleaned, electrolytically degreased and pickled in conformity with the known rules of electroplating technology; they are then electroplated to thickness of ca. 1 micron in a copper cyanide bath, ca. 7 microns in a bright nickel bath and ca. 0.3 mirons in a sulphuric acid bright chromium bath.

Before applying PVD coating, the prepared sheets are cleaned ultrasonically, first in emulsifier-containing Freon (Du Pont product TWD 602) and f inally in Freon TF, prior to applying a TiN layer ca. 0.5 microns thick by the PVD process. The cleaning in Freon products prior to PVD coating is to be recommended as a means of removing any and all dirt and fingermarks before fixing in the special carrier frames for the PVD process.

The processed test sheets are then subjected to various corrosion tests, each of 72 hours duration, in condensate alternating with an atmosphere containing S02 test SFW 2.0 S, DIN 50 018, or acetic acid/salt-spray test ESS, DIN 50 021. The test sheets suffer serious pitting corrosion, with ca. 2-3 pores/cm2. Some of the test sheets are usually corroded all through.

Example

The bright chromium layer of test sheets prepared in a similar manner to those in Example 1 is replaced by a layer 1 to 1.5 microns thick of the palladium-nickel alloy of the invention; the rest of the coating treatments remain the same. They now remain sound after any of the 72 hour corrosion tests.

Palladium-nickel electrolytes in accordance with the invention can contain:

6 g palladium as 9 g nickel as g conductivity salt as 2.5 g sodium allysulphonate, optionally together with EPd(NH3)43C12 [Ni(NH3)63S04 M4)2S04 g benzene-acid-sulphonimide, sodium salt or:

2 g benzene-sulphonyl resin and as wetting agent:

0.5 g nonylphenolethoxylate (23 EO) NH40H to maintain a pH of 8-8.5, water to make up to 1 litre; z electrolyte temperature 25 - 300C gentle workpiece agitation cathode current density 1 AMm2 immersion period 4 - 6 minutes anodes of platinised titanium or graphite.

The non-ionic wetting agent can be replaced by selected anion-active tensides based on alkyl- and alkylarylether sulphonates such as 1 g/1 H 3C(CH2)12/14-0-(CH2-CH2-0)n-CH2-CH2-CH2-SO3K, with n = 11.

Since such wetting agents have no cloudiness point, it is now possible to use bath temperatures of for example 40500C. This simultaneously further improves the brightness of the coating.

Example

The substrate material used in Examples 1 and 2 is replaced by grade C 45 WN 1.0503 steel. The results are the same, i.e., a Pd/Ni interlayer is essential because of the corrosion problems.

Example 4

An additional 0.1 microns of 23 ct-gold/nickel alloy is sputtered on the final PU coating of titanium nitride. The corrosion problems in Example 1 are even further aggravated, whereas the Pd/Ni interlayer as used in Example 2 to replace the bright chromium interlayer eleminates the corrosion phenomena entirely.

Example 5

Titanium nitride can be replaced by titanium carbide, 1 titanium-aluminium carbonitride, titanium metal etc. The same corrosion differences as those between Examples 1 and 2 are again obtained.

Example 6

A test sheet of Bayblend T 45 MN is first nickel plated by the usual chemical process used in elec.troplating technology and the chemically deposited Ni-P coating is prestrengthened electrolytically in a Wattstype bath. Next, 20 - 30 microns of bright copper and 10 microns of semibright nickel are deposited in sulphuric acid-type baths. If a final PU coating is applied directly on the semi-bright nickel plate, the corrosion resistance tests as in Example 1 again result in failure. However, as soon as an interlayer of palladium/nickel is applied as in Example 2, corrosion resistance is immediately fully restored.

E x a mp--1-e 7 The bright chromium layer of thickness 0.3 microns, as used in Example 1, is replaced by 0.1 microns of pure gold deposited electrolytically in a conventional bath, and the M cover layer is then applied. Apart from their poor corrosion resistance, the specimens fail durability tests in a burnishing drum or using conventional polishing agents: the hard outer coating is systematically sheared off the gold interlayer. When one uses the palladium/nickel interlayer of the invention, the M cover layer becomes outstandingly tenacious; thus, the gold interlayer is too sensitive to shearing forces.

E.xaaxpl-c 8 I 2 1 For applications which make no special demands with respect to superior decorative brightness in the Palladium/nickel interlayer, and more particularly for any technical applications, it is equally possible to use Palladium/nickel electrolytes which contain no aliphatic, unsaturated and/or heterocyclic sulphonates and no aromatic sulphonimides. The palladium/nickel interlayer still produces the necessary corrosion resistance, and at the same time makes the subsequently applied PVD coating outstandingly tenacious, provided that any sulphur co-deposited therewith has a valency exceeding two. The electrolyte composition is:

6 g palladium as g nickel as Pd(NH3)4 CL2 Ni(NH 3)6S04 or (H2NS03)23i. 4H20 - 100 g conductivity salt as M4)2S04 or H2NS03NH4 optionally together with, as a wetting agent:

1 g H3C-(CH2)12/14-0-(CH2-CH2-0)n-CH2-CH2-CH2-SO3 K, with n = 11 NH4CH to maintain a pH of 8 - 8.5, water to make up to 1 litre; electrolyte temperature 40 - 500C gentle workpiece agitation cathode current density 1 A/dm2 immersion period 4 - 6 minutes anodes of platinised titanium or graphite.

The specimens are tested as described in Example 2 and give the same results as those in Example 2.

A

Claims

1 A method of applying a coating to a metallic substrate material of little or no corrosion resistance by the PVD process comprising using an interlayer of palladium-nickel alloy containing 30 - 90 wt.% of palladium, deposited from an aqueous electrolyte containing palladium and nickel ammines at a palladium concentration in the range 2-20 g/l and a nickel concentration in the range 5-30 g/l, wherein the electrolyte components are selected so that any sulphur precipitated with the alloy has a valency exceeding two.

2. A method as in Claim 1, wherein the palladiumnickel alloy contains 60 85 wt.% of palladium.

3. A method as in Claim 1 or Claim 2, wherein the electrolyte contains conductivity salts and organic additions which contain sulphur.

4. A method as in any one of Claims 1 to 3, wherein the electrolyte contains, as additives, aliphatic, unsaturated and/or heterocyclic sulphonates, selected aromatic sulphonimides as tensile stress reducers and/or anti-corrosion additives, together with non-ionic and/or anionactive wetting agents, the added aliphatic, unsaturated and/or heterocyclic sulphonates consisting of one or more alkali salts of vinyl-, allyl-, propin-, methallyl- and or N-benzylpyridinium-2-ethyl sulPhonic acids, N-pyridiniumpropylsulphobet6in and/or Npyridiniummethylsulphobetain.

5. A method as in any one of Claims 1 to 4, wherein the metallic substrate material is aluminium, lead, copper, magnesium, nickel, silver, steel, zinc or an alloy material 4 V based thereon, and wherein it is further provided with an electrolytically or chemically deposited layer or layers of matte, bright, semi-bright or semi-matte copper, copper alloy, nickel, nickel alloy, silver or tin alloy or combinations thereof.

6. A method as in any one of Claims 1 to 4, wherein the metallic substrate material is itself an electroplate coating on a galvanisable synthetic material, more particularly single or combined layers of matte, bright, semibright or semi-matte copper, copper alloy, nickel, nickel alloy, silver or tin alloy.

7. A method as in any one of Claims 1 to 6, wherein the coating applied by the PVD process consists of one or more borides, carbides, nitrides, oxides and/or silicides of subgroup 40 to 6 elements of the periodic system.

8. A method as in Claim 7, wherein the coating applied by the PVD process can contain certain amounts of additional aluminium, cobalt, gold, carbon, copper, nickel and/or palladium.

9. A method as in any one of Claims 1 to 6, wherein the coating applied by the PVD process consists of metallic aluminium, titanium, zirconium or tantalum, which can be subsequently superficially oxidised by chemical or electrochemical means.

10. A method as in any one of Claims 1 to 6, wherein the coating applied by the PVD process consists of amorphous and/or diamond-like carbon.

11. A method as in any one of Claims 1 to 10, 4 wherein in order to produce an absolutely or at least substantially pore- free palladium-nickel interlayer, its thickness is adjusted to the depth of the roughness grooves on the substrate material and/or the electrolytically deposited underlayer thereon, and is at least 0.1 microns.

12. A method as in Claim 11, wherein the average thickness of the palladium-nickel interlayer is in the range 0.5 to 5 microns.

13. A method as in any one of Claims 1 to 12, wherein the thickness of the coating applied by the PVD process is in the range 0.1 to 5 microns.

14. A method as in Claim 13, wherein the thickness of the coating applied by the PVD process is in the range 0.3 to 1 micron.

15. A method as in any of Claims 1 to 14, more particularly for applying coatings having technical functions wherein the combination of a palladium-nickel interlayer and the cover coating applied by the PVD process is a substitute for hard chromium finishes.

Published 1989 at The Patent Office.Stale House.6671 High R0ITJc"r-Lo_-. don V.CiR 4TP. Further copiesmaybe obtainedfrOln ThePatentOffice Sales Branch, St Mary Cray, Orpington. Kent BP_9 3RD. Printea by W'iltiplex techniques ltd, St Mary Cray. Kell.. Con. 1167 1 l