CORROSION RESISTANT CARBON COATINGS

Abstract

The invention provides substrates with a multi-layer coating, comprising in order: i) the substrate; ii) a seed layer; ill) a barrier layer deposited via a CVD method; and iv) a functional layer deposited via a PVD method, and methods of making such coatings. The coatings of the invention have been shown to possess good resistance to corrosion.

Claims

1. A metallic substrate with a multi-layer coating, comprising in order: i) the metallic substrate; ii) a seed layer; iii) a barrier layer comprising DLC deposited via a CVD method; and iv) a functional layer comprising ta-C deposited via a PVD method; and wherein the overall thickness of the coating is 5 μm or less.

2. A coated substrate according to claim 1 comprising multiple alternating barrier layers and functional layers.

3. A coated substrate according to claim 2 comprising alternating layers of up to 10 barrier layers and up to 10 functional layers.

4. A coated substrate according to claim 1 which further comprises an intermediate layer between the seed layer ii) and the barrier layer iii).

5. A coated substrate according to claim 4 wherein the intermediate layer comprises ta-C.

6. A coated substrate according to claim 1 wherein the total thickness of all barrier layers in the substrate is up to 1.0 μm.

7. A coated substrate according to claim 1 wherein the total thickness of all barrier layers in the substrate is from 0.05 μm to 0.5 μm.

8. A coated substrate according to claim 1 wherein the thickness of the functional layer is from 0.1 μm to 3 μm.

9. A coated substrate according to claim 1 wherein the thickness of the seed layer is from 0.05 μm to 2 μm.

10. A coated substrate according to claim 1 wherein the functional layer(s) is/are deposited by FCVA.

11. A coated substrate according to claim 1 wherein the seed layer is formed from Cr, W, Ti, NiCr, Si or mixtures thereof.

12. A coated substrate according to claim 1 wherein the substrate is a steel substrate.

13. A coated substrate according to claim 12 wherein the substrate comprises stainless steel, HSS, tool steel or alloy steel.

14. A coated substrate according to claim 1 wherein the substrate comprises Ti, an alloy of Ti, Al or an alloy of Al.

15. A coated substrate according to claim 1, comprising at least 2 barrier layers and at least 2 functional layers.

16. A coated substrate according to claim 1, comprising at least 3 barrier layers and at least 2 functional layers.

17. A substrate according to claim 1 comprising in order: i) a steel substrate; ii) a seed layer having a thickness from 0.05 μm to 2 μm; iii) a barrier layer deposited by a CVD method, the barrier layer comprising DLC and having a thickness of 3 μm or less; and iv) a layer comprising ta-C deposited by CVA and having a thickness of from 0.1 μm to 3 μm.

18. A substrate according to claim 1 comprising in order: i) a steel substrate; ii) a seed layer having a thickness from 0.05 μm to 2 μm; iii) an intermediate layer comprising ta-C having a thickness of from 0.1 μm to 1.0 μm; iv) a barrier layer deposited by a CVD method, the barrier layer comprising DLC and having a thickness of 2 μm or less; and v) a layer comprising ta-C deposited by CVA and having a thickness of from 0.1 μm to 3 μm.

19. A method of coating a substrate, the method comprising: i) providing a metallic substrate; ii) depositing onto the substrate a seed layer; iii) depositing onto the substrate a layer of DLC having a thickness of 5 μm or less via a CVD method; and iv) depositing onto the substrate a layer of ta-C via a PVD method.

20. A method according to claim 19, for making a coated substrate according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0098] FIG. 1A shows an uncoated steel substrate (comparative example) following corrosion testing as described in Example 2.

[0099] FIG. 1B shows a ta-C-coated steel substrate (comparative example) following corrosion testing as described in Example 2.

[0100] FIG. 1C shows a steel substrate coated with a coating of the invention following corrosion testing as described in Example 2.

[0101] FIG. 1D shows a DLC-coated steel substrate (comparative example) following corrosion testing as described in Example 2.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

[0102] The protocol for making corrosion resistant films according to the invention is provided below: [0103] a. A high speed steel (HSS) substrate is first prepared for coating by ultrasonic cleaning with a detergent. The substrate is then rinsed with deionised water and then dried (in accordance with standard cleaning processes used in the vacuum industry). [0104] b. The cleaned HSS substrate is placed in a vacuum chamber having sputtering, CVD and FCVA targets/sources. [0105] c. The chamber is pumped down to reduce the pressure to less than 1×10.sup.−5 Torr (0.00133 Pa), and heated to between 150° C. and 200° C. [0106] d. Ion cleaning is conducted in the chamber in order to activate the surface of the substrate to promote adhesion. [0107] e. Seed layer deposition: Sputtering, 100° C.-150° C., NiCr targets, layer thickness=1.0 μm. [0108] f. Barrier layer deposition: Plasma Assisted CVD, C.sub.2H.sub.2 (flow rate=100 sccm) and Ar (flow rate=200 sccm), bias voltage=600V, bias current=8 A, bias duty cycle=50%; layer thickness=0.2 μm. [0109] g. Functional layer deposition: FCVA, <100° C., solid graphite target, coating thickness=1.3 μm.

[0110] Sputtering, CVD and FCVA targets and sources are well-known and commercially available.

Example 2—Corrosion Resistance Testing

[0111] A salt spray test was used to determine the corrosion resistance of the coatings of the invention (as produced in Example 1) compared to uncoated and DLC coated substrates.

[0112] Test materials: [0113] a. Uncoated high speed steel W.sub.6Mo.sub.5Cr.sub.4V.sub.2 substrate (without surface treatment). Hardness=746.9 HV [0114] b. Ta—C coated high speed steel W.sub.6Mo.sub.5Cr.sub.4V.sub.2. Coating thickness=2.3 μm. Hardness=2212 HV. The coating was prepared according to the method of Example 1, with the omission of barrier layer deposition step (f). [0115] c. High speed steel W.sub.6Mo.sub.5Cr.sub.4V.sub.2 coated with ta-C coating of the invention (see Example 1). Coating thickness=2.5 μm. Hardness=2317 HV [0116] d. High speed steel W.sub.6Mo.sub.5Cr.sub.4V.sub.2 substrate coated with DLC only. Coating thickness=2.5 μm. Hardness=1540 HV.

[0117] Salt Spray Conditions: [0118] Salt solution concentration: (5±1)% NaCl [0119] pH=6.5-7.2 [0120] Salt spray settling rate: (1-2 mL)/80 cm.sup.2; [0121] Temperature inside the salt spray box: 35±2° C.; [0122] Spray 1 min every 10 minutes;

[0123] Results: [0124] a) Uncoated—Obvious rust of the surface after 10 minutes (see FIG. 1A) [0125] b) Ta—C coated—Visible, erasable rust after 18 hours (see FIG. 1B). When subjected to a scratch test, the coating showed a critical load of 38.66N. [0126] c) Invention—No obvious rust after 100 hours (see FIG. 1C). When subjected to a scratch test, the coating showed a critical load of 30.60N. [0127] d) DLC coated—No obvious rust after 100 hours (see FIG. 1D). When subjected to a scratch test, the coating showed a critical load of 20.22N.

[0128] As an indication of the wear-resistance of the coatings, a Taber abrasion test was conducted on test materials b), c) and d), with the following conditions: [0129] Instrument: Taber Linear Abraser TLA 5700 [0130] Abradant: CS-17 Wearaser® [0131] Test Load: 1 kg weight [0132] Cycle Speed: 60 cycles/min [0133] Stroke Length: 15 mm

[0134] No visible scratches were seen on either test material b) and c) following 30,000 cycles of the taber test. However, visible scratches were seen on test material d) following only 5,000 cycles of the taber test.

[0135] The coatings of the invention therefore show improved corrosion resistance compared to uncoated substrates and substrates coated with DLC alone. The coatings of the invention also have comparable hardness and wear resistance properties to ta-C-only coated substrates and have superior hardness and wear resistance properties comparted to DLC-only coated substrates.

Example 3—Further Protocol

[0136] A protocol for is described below for coating a high speed steel substrate with a coating of the invention.

[0137] Step 1: First the substrate is cleaned using industrial cleaning agents and ultrasonic cleaning, rinsed with pure water and then dried. Such a cleaning process is commonly used in the vacuum coating industry and is conducted to remove oil stains and dirt on the substrate surface prior to coating.

[0138] Step 2: The substrate is loaded and clamped into the coating chamber and the chamber is heated to a temperature of 130° C. and depressurized to a pressure from 1.0×10.sup.−3 Pa to 4.0×10.sup.−3 Pa.

[0139] Step 3: Plasma cleaning is conducted in order to activate the substrate surface for coating (e.g. ion cleaning USES, for example using a linear ion source device as described in Chinese patent application no. 201621474910.4)

[0140] Step 4: A seed layer is coated onto the activated substrate via a magnetron sputtering process. A negative bias pulse (150V-600V) is applied to the substrate and a working pressure of Argon of 150 sccm to 300 sccm is used. The seed layer can be formed from NiCr, Ti, Si, Cr, W or combinations of these metals with carbon or nitrogen. The thickness of the seed layer may be from 0.3 μm to 1.5 μm.

[0141] Step 5: Optionally a ta-C intermediate layer is deposited on top of the seed layer. The ta-C is deposited using an FCVA process (e.g. as described in Chinese patent application no. 201621474910.4) using a graphite target and by applying a negative pulse bias of 500V to 2000V to the substrate. The thickness of this ta-C layer is typically from 0.2 μm to 1.5 μm.

[0142] Step 6: A DLC layer is applied onto the seed layer (if no ta-C intermediate layer is deposited in Step 5) or on top of the ta-C layer (if a ta-C intermediate layer is deposited in Step 5). The DLC is deposited via a plasma-assisted chemical vapour deposition process using argon and a carbon source gas (such as methane, acetylene, ethane or other hydrocarbon gases). Deposition is conducted at a chamber pressure of 0.4 Pa to 2 Pa with a pulse negative substrate bias of 300V to 800V. The thickness of this layer is typically greater than 0.5 μm

[0143] Step 7: Finally, a ta-C layer is deposited. The ta-C is deposited using an FCVA process (e.g. as described in Chinese patent application no. 201621474910.4) using a graphite target and by applying a negative pulse bias of 500V to 2000V to the substrate. The thickness of this ta-C layer is typically from 0.4 μm to 1.0 μm.

Example 4—Further Coatings

[0144] Further coated substrates of the invention were prepared with the following structures, using the protocol described in Example 3.

[0145] Coating 4A: [0146] High Speed Steel Substrate [0147] NiCr (1.0 μm) [0148] Ti (0.2 μm) [0149] Ta—C (1.0 μm) [0150] DLC (1.0 μm) [0151] Ta—C (0.5 μm)

[0152] Overall coating thickness is 3.7 μm.

[0153] Coating 4B: [0154] High Speed Steel Substrate [0155] NiCr (1.0 μm) [0156] Ti (0.2 μm) [0157] Ta—C (0.4 μm) [0158] DLC (1.0 μm) [0159] Ta—C (1.0 μm)

[0160] Overall coating thickness is 3.6 μm.

[0161] Coating 4C: [0162] High Speed Steel Substrate [0163] NiCr (1.0 μm) [0164] Ti (0.2 μm) [0165] Ta—C (0.5 μm) [0166] DLC (0.2 μm) [0167] Ta—C (0.5 μm) [0168] DLC (0.2 μm) [0169] Ta—C (0.5 μm)

[0170] Overall coating thickness is 3.1 μm.