IMPROVED COATING PROCESSES

Abstract

A method of depositing a coating on a substrate comprises simultaneously depositing a first material via a CVA process and a second material via a sputtering process; also described are coatings obtained therefrom and coated substrates.

Claims

1. A method of depositing a coating on a substrate, the method comprising simultaneously depositing a first material via a CVA process and a second material via a sputtering process, characterised in that the first material comprises to-C.

2. A method according to claim 1 of depositing a coating comprising a first material and a second material on a substrate, the method comprising: i) depositing the first material via a CVA process to form a lower layer; ii) simultaneously depositing the first material via the CVA process and the second material via a sputtering process to form a transition layer; and iii) depositing the second material via a sputtering process to form an upper layer.

3. A method according to claim 1 of depositing a coating comprising a first material and a second material on a substrate, the method comprising: i) depositing the second material via a sputtering process to form a lower layer; ii) simultaneously depositing the first material via the CVA process and the second material via a sputtering process to form a transition layer; and iii) depositing the first material via a CVA process to form an upper layer.

4. A method according to claim 1, wherein the CVA process is FCVA.

5. A method according to claim 1, wherein the first material consists of to-C.

6. A method according to claim 1, wherein the second material is selected from Ti, Cr, Si, Zr, C, W and alloys and compounds thereof.

7. A method according to claim 1, further comprising depositing a seed layer onto the substrate prior to coating it with the first and second materials, and optionally wherein the seed layer has a thickness of from 0.1 μm to 0.5 μm.

8. A method according to claim 1, wherein the substrate is a metallic substrate.

9. A method according to claim 8 wherein the substrate is a steel substrate.

10. A method according to claim 2 wherein the first layer has a thickness of 0.2 μm to 1.5 μm, and/or the second layer has a thickness of 0.1 μm to 0.3 μm.

11. A method according to claim 1 wherein the coating has a thickness of from 0.5 μm to 5 μm.

12. A method according to claim 11 wherein the coating has a thickness of from 1.0 μm to 3.0 μm.

13. A method according to claim 1 wherein the coating takes place in a chamber at a pressure of 0.5 Pa or less.

14. A coated substrate obtainable from a method according to claim 1.

15. A substrate coated with a coating, wherein the coating comprises: i) a layer deposited via a sputtering process; ii) a transition layer between (i) and (iii) deposited by a process comprising simultaneous CVA deposition and a sputtering process; and iii) a ta-C layer deposited by CVA deposition.

16. A coating apparatus comprising: a substrate station, for location of a substrate to be coated; a CVA station, for depositing ta-C via CVA onto the substrate; a sputtering station, for depositing material via a sputtering process onto the substrate; and a control unit that is capable of operating the CVA and sputtering stations simultaneously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The invention is now illustrated with reference to the accompanying drawings in which:

[0116] FIG. 1 is a schematic diagram showing the structure of the coating of the invention described in Example 1 (not to scale).

EXAMPLES

Example 1

[0117] A first example of the coating of the invention (see FIG. 1, 10) was prepared as described below:

TABLE-US-00002 Layer Thickness SPT* (14) 0.3 μm ta-C + SPT* (13) 0.4 μm ta-C (12) 0.8 μm Substrate (11) - SUS304 Steel Total Thickness ~1.5 μm   (determined by CAR2)

[0118] SPT*—a range of materials deposited by sputtering was used to form a range of coatings with different coloured uppermost layers:

TABLE-US-00003 SPT* material Colour CrSiC Charcoal CrWC Black CrAlSiCN Blue CrN Silver

[0119] i. Start FCVA ta-C deposition first, gradually increasing input Ar pressure to a pressure of between 0.5 to 1.0 mTorr ;

[0120] ii. Keep the pressure constant steady and begin magnetron sputtering;

[0121] iii. After a certain time (e.g. a time period sufficient to generate a co-deposited layer with a thickness of about 400 nm), stop FCVA coating and continue sputtering to form the top layer

Example 2

[0122] The hardness of the coatings prepared in Example 1 were determined by using a nanoindenter (CSM NHT2). These values were compared with the hardness of coatings produced using sputtering only (i.e. sputtering the SPT material directly onto the substrate).

TABLE-US-00004 CrSiC CrWC CrAlSiCN CrN Hardness (HV) SPT only 680 500 660 1200 (Comparative Examples) SPT & ta-C 1250 950 1100 1530 (Example 1)

Example 3—Cross Hatch

[0123] To check the level of adhesion of the coating to the substrate, a cross hatch test was conducted based on the ASTM D-3359 Test Method B. A lattice pattern with grid dimensions of 1.0 mm by 1.0 mm was cut into the surface of the coating. Pressure sensitive 51596 was then applied to the cut coating and removed.

[0124] In both the coatings of Example 1 and the corresponding Comparative Coatings (containing only a sputtered layer of the SPT material), the peel-off area was less than 5%.

Example 4—Steel Wool Abrasion Test

[0125] As an indication of the wear-resistance of the coatings of Example 1, a Taber abrasion test was conducted on the coatings, with the following conditions: [0126] Instrument: Taber Linear Abraser Test [0127] Abradant: Steel Wool [0128] Test Load: 500g weight [0129] Cycle Speed: 60 cycles/min [0130] Stroke Length: 5 mm

[0131] After 400 cycles, there were no noticeable scratches on the surface of the coatings of Example 1. When corresponding substrates coated with only the SPT materials (i.e. without the ta-C layer or the transition layer containing ta-C and SPT) were subject to the same conditions, visible scratches were observed.

Example 5—Blue Jean Abrasion Test

[0132] As an indication of the wear-resistance of the coatings of Example 1, a Taber abrasion test was conducted on the coatings, with the following conditions: [0133] Instrument: Taber Linear Abraser Test [0134] Abradant: Levis blue jean material [0135] Test Load: 500 g weight [0136] Cycle Speed: 60 cycles/min [0137] Stroke Length: 5 mm

[0138] After 1000 cycles, there were no noticeable scratches on the surface of the coatings of Example 1. When corresponding substrates coated with only the SPT material (i.e. without the ta-C layer or the transition layer containing ta-C and SPT) were subject to the same conditions, visible scratches were observed.

Example 6—Salt Spray Test

[0139] As an indication of the corrosion-resistance of the coatings of Example 1, a salt spray test was conducted on the coatings. The salt spray test was based on ASTM B117: Standard

[0140] Practice for Operating Salt Spray (Fog) and comprised spraying a 5% salt water solution onto the coated substrates at a temperature of 35° C.

[0141] After 72 hours, there were no visible signs of rust or degradation of the coatings of Example 1. When corresponding substrates coated with only the SPT material (i.e. without the ta-C layer or the transition layer containing ta-C and SPT) were subject to the same conditions for 72 hours, corrosion was observed.

[0142] As can be seen in the Example above, coatings of the invention can have increased hardness, wear resistance and corrosion resistance compared to the comparative coatings.