GB2182055A

GB2182055A - Improvements relating to electrodeposited coatings

Info

Publication number: GB2182055A
Application number: GB08526546A
Authority: GB
Inventors: John Foster; Eric Charles Kedward; Francis John Honey
Original assignee: Baj Ltd
Current assignee: Baj Ltd
Priority date: 1985-10-28
Filing date: 1985-10-28
Publication date: 1987-05-07
Also published as: GB2182055B; GB8526546D0

Abstract

Apparatus and process for the electrodeposition of a composite coating in which a vessel containing a plating solution and insoluble particles is divided by a partition (6) having an opening (13) at the bottom and a weir (14) at the top, thus dividing the vessel into a working zone (9) and a return zone (11). The article to be coated (16) is placed in the working zone and gas is admitted adjacent the bottom of the return zone. The gas rises in the return zone and thus produces a circulation flow of the solution and particles which is generally upwards in the return zone and generally downwards in the working zone. <IMAGE>

Description

SPECIFICATION Improvements relating to electrodeposited coatings This invention relates to apparatus and processes for the electrodeposition of composite coatings which consist of a metal matrix containing particles, in which processes the particles are co-deposited with the metal from a solution in which the particles are insoluble.

The invention is primarily concerned with the electrodeposition of coatings incorporating ceramic particles but the particles may also be of cermet or metal. Such coatings may be used for various purposes including wear and abrasion resistance, corrosion and oxidation resistance and improvement in coefficient of friction (lubricity) and anti-fretting and anti-galling properties. In certain cases the coatings themselves may constitute the final product so that the process is one of electroforming.

The process comprises electroplating in a bath containing insoluble particles dispersed in the electrolyte, the particles being co-deposited with the metal deposited from the electrolyte.

There is described in GB-A-1 218 179 a process for the electrodeposition of a composite coating comprising a metal matrix containing particles, the particles being co-deposited with the metal from a solution in which the particles are insoluble, and in which process the solution is circulated through the container in which electrodeposition takes place, gas being admitted to the container to produce a generally upward flow of solution and gas in the vicinity of the surface of which deposition is occurring. In the preferred apparatus for carrying out the process, the solution is withdrawn from the container near the top and is returned to the container at the bottom, circulation being produced by a pumping system which includes a pump which is external to the container, the gas being admitted to the suction duct.The overall flow in the vicinity of the workpiece to be coated is thus essentially upwards although the effect of the gas is to produce some degree of turbulence so that locally and for short intermittent periods the flow may be in other directions.

According to one aspect of the present invention, in a process for the electrodeposition of a composite coating comprising a metal matrix containing particles, the particles being co-deposited from a slurry of plating solution and particles which are insoluable therein, gas is admitted to the solution at a location to produce circulation in the solution generally upwards in one zone and generaly downwards in a second zone and the workpiece is located in the second zone.

It has been found that with this process, particles of a larger size can be incorporated, this in turn leading to the ability to incorporate a higher proportion of particulate material in the deposited matrix. It has been found that particle loadings in the solution needed to produce required coating compositions are less than in the method particularly described in the previously mentioned GB-A 1 218 179.

Preferably the workpiece is rotated about an axis which is horizontal or has a horizontal component so that all surfaces to be coated face the downwardly directed flow from time to time.

The process may be electrolytic or electroless but for most applications an electrolytic process will be used.

According to another aspect of the invention, apparatus for the electro-deposition of a composite coating comprises a vessel the interior of which is divided by a partition into a working zone and, alongside the working zone, a smaller return zone, means interconnecting the two zones adjacent the bottom of the vessel, a weir connecting the two zones at a level above the interconnecting means, means for mounting a workpiece in the working zone, and gas admission means adjacent the bottom of the return zone.

Preferably the weir is a broad crested weir which may extend across the entire width of the vessel. The vessel may have a downwardly tapering lower section and the interconnecting means may be afforded by the partition stopping short of the bottom of the vessel.

As with the invention described in the abovementioned GB-A-1 218 179, the present invention may be used for deposition of many different composite coatings examples of which include nickel, cobalt, copper, chromium, and tungsten-cobalt alloy as the metal matrix and zirconium diboride, moiybdenum disulphide and tungsten carbide as the insoluble particles. The composite coatings may incorporate a solid lubricant for cases where the coating is to act as a bearing, using the term broadly to cover any relative movement between adjacent surfaces between which a load is transmitted. For example, graphite particles may be incorporated in the coating to provide a three-component coating of metal matrix, ceramic particles and graphite particles.

Plating may take place on any substrate which can be plated including, for example, steel, non-ferrous metals including light alloy components and plastics, glass and composited materials where such material have been rendered conductive either by incorporation of appropriate materials or by precoating with a conductive material.

The invention may be performed in various ways but one form of apparatus and a method of coating using the apparatus will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of the appa ratus; Figure 2 is a side elevation of the apparatus; and Figure 3 is a front elevation of the apparatus.

The apparatus shown in the drawings, comprises a vessel or container 1 having a parallelepiped shaped upper portion 2 and a downwardly tapering lower portion 3 in the form of an inverted pyramid which is skewed so that one side face 4 forms a continuation of one side face 5 of the upper portion.

The vessel 1 contains a partition 6 which lies in a vertical plane parallel to the side faces 4 and 5 of the vessel and makes contact at its side edges 7 and 8 with the adjacent vertical and sloping faces of the vessel.

The partition thus divides the vessel into a larger working zone 9 and a smaller return zone 11. At its bottom, the partition 6 terminates at a horizontal edge 12 above the bottom of the vessel to afford an interconnection 13 between the working zone 9 and the return zone 11. At its top, the partition 6 terminates at a horizontal edge 14 below the top edges of the vessel 1.

At the bottom of the return zone 11 there is an air inlet 15 which is connected to an air pump (not shown). Mounted in the working zone 9 is a jig 16 to which the workpiece to be coated is mounted, the jig 16 being mounted for rotation about a horizontal axis parallel to the plane of the partition and motor means (not shown) is provided to rotate the jig.

When the apparatus is to be used for electrolytic plating, conductors are provided to apply a voltage to the workpiece mounted on the jig 16 relative to an anode which is suspended in the working zone.

To use the apparatus, to codeposit a coating on a workpiece, the workpiece is mounted on the jig 16 which is positioned in the vessel as shown. Before or after the positioning of the jig, the vessel is filled to a level 17 above the top edge 14 of the partition 6 with a plating solution containing particles to be codeposited. Air is admitted to the inlet 15 and this rises up the return zone 11, raising solution and entrained particles. At the top of the return zone, the air escapes and the solution and particles flow over the broad crested weir formed by the top edge 14 of the partition and flow down past the workpiece on the rotating jig 16. At the bottom of the working zone 9, the particles tend to settle and slide down the inclined sides of the vessel towards the interconnection 13 where they are again entrained in the solution and carried round again.

As the downwardly travelling particles in the working zone 9 encounter the workpiece, they tend to settle on the workpiece where they become embedded in the metal which is being simultaneously plated out.

One particular class of composite coatings which may be produced by the apparatus described is that comprising a matrix of Ni, Co or NiCo with particles of CrAIY. It has been found that good quality coatings containing up to 30% by weight of particles can be produced using only 1 gram per litre of particles in the solution. This may be compared with the figure of 5% quoted in the Examples described in the aforementioned GB-A-1 218 179.

Claims

1. A process for the electrodeposition of a composite coating comprising a metal matrix containing particles in which process the particles are co-deposited in which process the particles are co-deposited with the metal from a solution in which the particles are insoluble, and in which process gas is admitted to the solution at a location to produce circulation in the solution generally upwards in one zone and generally downwards in a second zone and the workpiece is located in the second zone.

2. A process as claimed in Claim 1 in which the gas is air.

3. A process as claimed in Claim 1 or Claim 2 in which the workpiece is rotated about an axis which is horizontal or has a horizontal component.

4. Apparatus for the electro-deposition of a composite coating comprising a vessel the interior of which is divided into a working zone and, alongside the working zone, a smaller return zone by a partition, means interconnecting the two zones adjacent the bottom of the vessel, a weir connecting the two zones at a level above the interconnecting means, means for mounting a workpiece in the working zone, and gas admission means adjacent the bottom of the return zone.

5. Apparatus as claimed in Claim 4 which includes a cathode located in the vessel and means for applying a voltage between the cathode and a workpiece in the working zone.

6. Apparatus as claimed in Claim 4 or Claim 5 in which the wire is a broad crested weir.

7. Apparatus as claimed in Claim 4 or Claim 5 or Claim 6 in which the vessel has a downwardly tapering lower section.

8. Apparatus as claimed in any of Claims 4 to 7 in which the interconnecting means is afforded by the partition stopping short of the bottom of the vessel.

9. A process for the electrodeposition of composite coatings which is carried out substantially in the manner described herein.

10. Apparatus for the electrodeposition of a composite coating constructed and arranged to operate substantially as described herein with reference to the accompanying drawings.