Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process

• US 6,896,785 B2
• Filed: 04/15/2002
• Issued: 05/24/2005
• Est. Priority Date: 03/27/2002
• Status: Expired due to Term

• Current Assignee: Keronite International Ltd. (Curtiss-Wright Corporation)
• Original Assignee: Isle Coat Limited
• Inventors: Samsonov, Victor Iosifovich, Shatrov, Alexander Sergeevich
• Primary Examiner(s): King, Roy
• Assistant Examiner(s): Leader, William T.
• Application Number:
  US10/123,010
• Publication Number:
  US 20030188972A1
• Time in Patent Office: 1,135 Days
• Field of Search: 205/109, 205/148, 205/316, 205/333, 204/164
• US Class Current: 205/109
• CPC Class Codes: C25D 11/005 Apparatus specially adapted for electrolytic conversion coating apparatus in general for electrolytic coating C25D17/00
• CPC Class Codes: C25D 11/024 Anodisation under pulsed or modulated current or potential
• CPC Class Codes: C25D 11/026 Anodisation with spark discharge
• CPC Class Codes: C25D 15/00 Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
• CPC Class Codes: C25D 5/18 Electroplating using modulated, pulsed or reversing current
• CPC Class Codes: C25D 5/20 Electroplating using ultrasonics , vibrations
• CPC Class Codes: C25D 5/611 Smooth layers
• CPC Class Codes: C25D 5/617 Crystalline layers
• CPC Class Codes: C25D 5/627 Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance

Abstract

There is disclosed a process and apparatus for carrying out plasma electrolytic oxidation of metals and alloys, forming ceramic coatings on surfaces thereof at a rate of 2-10 microns per minute. The process comprises the use of high-frequency current pulses of a certain form and having a given frequency range, combined with the generation of acoustic vibrations in a sonic frequency range in the electrolyte, the frequency ranges of the current pulses and the acoustic vibrations being overlapping. The process makes it possible to introduce ultra-disperse powders into the electrolyte, with the acoustic vibrations helping to form a stable hydrosol, and to create coatings with set properties. The process makes it possible to produce dense hard microcrystalline ceramic coatings of thickness up to 150 microns. The coatings are characterised by reduced specific thickness of an external porous layer (less than 14% of the total coating thickness) and low roughness of the oxidised surface, Ra 0.6-2.1 microns.

Claims

1. A process for forming ceramic coatings on metals and alloys in an electrolytic bath fitted with a first electrode and filled with aqueous alkaline electrolyte, in which is immersed the article, connected to another electrode, wherein a pulsed current is supplied across the electrodes so as to enable the process to be conducted in a plasma-discharge regime, the process comprising the steps of:

i) supplying the electrodes with high-frequency bipolar pulses of current having a predetermined frequency range; and

ii) generating acoustic vibrations in the electrolyte in a predetermined sonic frequency range so that the frequency range of the acoustic vibrations overlaps with the frequency range of the current pulses.

2. A process according to claim 1, wherein the coating is formed on the metals Mg, Al, Ti, Nb, Ta, Zr, Hf and alloys thereof, and also on the compounds and composites Al—

Be, Ti—

Al, Ni—

Ti, Ni—

Al, Ti—

Nb, Al—

Zr, Al—

Al203, Mg—

A1203.

4. A process according to claim 1, wherein the acoustic vibrations cause aerohydrodynamic saturation of the electrolyte with oxygen.

5. A process according to claim 4, wherein the electrolyte is supplied with oxygen or air.

10. A process according to claim 1, wherein the plasma discharge regime is a plasma-electrolytic oxidation regime.

11. A process according to claim 1, wherein the ceramic coating is formed at a rate of 2 to 10 μ

m/min.

12. A process according to claim 1, wherein the current applied to the article has a current density of 3 to 200 A/dm2.

13. A process according to claim 12, wherein the current applied to the article has a current density of 10 to 60 A/dm2.

14. A process according to claim 1, wherein the current pulses have a pulse succession frequency of at least 500 Hz.

15. A process according to claim 14, wherein the pulse succession frequency is in a range of 1,000 to 10,000 Hz.

3. A process for forming ceramic coatings on metals and alloys in an electrolytic bath fitted with a first electrode and filled with aqueous alkaline electrolyte, in which is immersed the article, connected to another electrode, wherein a pulsed current is supplied across the electrodes so as to enable the process to be conducted in a plasma-discharge regime, the process comprising the steps of:

i) supplying the electrodes with high-frequency bipolar pulses of current having a predetermined frequency range; and

ii) generating acoustic vibrations in the electrolyte in a predetermined sonic frequency range so that the frequency range of the acoustic vibrations overlaps with the frequency range of the current pulse, wherein each current pulse has a form comprising an initial steep increase of current to a maximum over a time that is not more than 10% of the total duration of the pulse, followed by an initially rapid and then more gradual decrease in the current to 50% or less of its maximum.

6. A process for forming ceramic coatings on metals and alloys in an electrolytic bath fitted with a first electrode and filled with aqueous alkaline electrolyte, in which is immersed the article, connected to another electrode, wherein a pulsed current is supplied across the electrodes so as to enable the process to be conducted in a plasma-discharge regime, the process comprising the steps of:

i) supplying the electrodes with high-frequency bipolar pulses of current having a predetermined frequency range; and

ii) generating acoustic vibrations in the electrolyte in a predetermined sonic frequency range so that the frequency range of the acoustic vibrations overlaps with the frequency range of the current pulses, further comprising the step of introducing ultra-disperse solid particles into the electrolyte and creating a stable hydrosol by way of the acoustic vibrations.

7. A process according to claim 6, wherein the solid particles are not more than 5 μ

m in size.

8. A process according to claim 6, wherein the solid particles comprise compounds in the form of oxides, borides, carbides, nitrides, silicides and sulphides of metals.

9. A process according to claim 7, wherein the solid particles comprise compounds in the form of oxides, borides, carbides, nitrides, silicides and sulphides of metals.

16. A process for forming ceramic coatings on metals and alloys in an electrolytic bath fitted with a first electrode and filled with aqueous alkaline electrolyte, in which is immersed the article, connected to another electrode, wherein a pulsed current is supplied across the electrodes so as to enable the process to be conducted in a plasma-discharge regime, the process comprising:

supplying the electrodes with high-frequency bipolar pulses of current having a predetermined frequency range, wherein each current pulse has a form comprising an initial steep increase of current to a maximum over a time that is not more than 10% of the total duration of the pulse, followed by an initially rapid and then more gradual decrease in the current to 50% or less of its maximum.