Method for Producing a Chromium Coating and a Coated Object

• US 20160333494A1
• Filed: 01/15/2014
• Published: 11/17/2016
• Est. Priority Date: 01/15/2014
• Status: Active Grant

• Current Assignee: Savroc Ltd.
• Original Assignee: Savroc Ltd.
• Inventors: Miettinen, Juha, Ris, Jussi
• Granted Patent: US 10,443,143 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: C23C 14/06 characterised by the coating material C23C14/0021 , C23C14/04 take precedence
• CPC Class Codes: C23C 16/45525 Atomic layer deposition [ALD]
• CPC Class Codes: C23C 28/021 including at least one metal alloy layer
• CPC Class Codes: C23C 28/027 including at least one metal matrix material comprising a mixture of at least two metals or metal phases or metal matrix composites, e.g. metal matrix with embedded inorganic hard particles, CERMET, MMC.
• CPC Class Codes: C23C 28/324 with at least one metal matrix material layer comprising a mixture of at least two metals or metal phases or a metal-matrix material with hard embedded particles, e.g. WC-Me
• CPC Class Codes: C23C 28/34 including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
• CPC Class Codes: C25D 3/06 from solutions of trivalent chromium
• CPC Class Codes: C25D 3/562 containing more than 50% by weight of iron or nickel or cobalt
• CPC Class Codes: C25D 5/14 two or more layers being of nickel or chromium, e.g. duplex or triplex layers
• CPC Class Codes: C25D 5/48 After-treatment of electroplated surfaces
• CPC Class Codes: C25D 5/50 by heat-treatment
• CPC Class Codes: C25D 5/627 Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance

Abstract

To produce a trivalent chromium based coating on an object, a layer of nickel phosphorus alloy is deposited on the object, an intermediate layer of another metal or metal alloy or ceramic is deposited on the NiP layer, and a chromium layer is deposited from a trivalent chromium bath on the intermediate layer. The coated object is subjected to one or more heat treatments to harden the coating and to produce multiphase layers including at least one layer containing crystalline Ni and crystalline Ni3P and at least one layer containing crystalline Cr. The intermediate layer can consist of copper, molybdenum, a metal alloy or a non-metallic solid, such as an oxide, nitride or carbide of a metal.

Claims

1. A method for producing a chromium coating on an object by trivalent chromium plating, the method comprising the steps of:

depositing a layer of nickel phosphorus alloy (NiP) on the object;

depositing an intermediate layer on the NiP layer, the intermediate layer consisting of another metal or metal alloy or ceramic;

depositing a layer of chromium from a trivalent chromium bath on the intermediate layer; and

subjecting the coated object to one or more heat treatments to harden the coating and to produce multiphase layers comprising at least one layer containing crystalline Ni and crystalline Ni₃P and at least one layer containing crystalline Cr.

2. A method according to claim 1, wherein the intermediate layer contains copper or an alloy of copper.

3. A method according to claim 1, wherein the intermediate layer contains molybdenum or an alloy of molybdenum.

4. A method according to claim 1, wherein the intermediate layer contains inorganic nonmetallic solid selected from the group comprising metal oxides, metal carbides, metal borides, metal nitrides, metal silicides, and mixtures thereof.

5. A method according to claim 1, further comprising the step of depositing a nickel strike layer on the object before depositing the NiP layer.

6. A method according to claim 1, wherein the phosphorus content of the NiP alloy is 1-15 w-%, preferably 3-12 w-%, more preferably 5-9%.

7. A method according to claim 1, wherein the temperature in the one or more heat treatments is 200-1000°

C., preferably 400-750°

C., more preferably 500-700°

C.

8. A method according to claim 1, wherein the coated object is subjected to two or more heat treatments and cooled after each heat treatment.

9. A method according to claim 8, wherein at least one of the heat treatments is carried out at a temperature between 500 and 700°

C.

10. A method according to claim 8, wherein the temperature in a first heat treatment is 200-500°

C., preferably 350-450°

C., and the temperature in a second heat treatment is 500-800°

C., preferably 650-750°

C.

11. A method according to claim 8, wherein the temperature in a first heat treatment is 500-800°

C., preferably 650-750°

C., and the temperature in a second heat treatment is 200-500°

C., preferably 350-450°

C.

12. A method according to claim 1, wherein the object to be coated is of metal and the hardening of the metal of the object is carried out at the same time as the coated object is heat-treated.

13. A method according to claim 12, wherein the object to be coated is of steel and the heat treatment is carried out at a temperature between 750 and 1000°

C., preferably 800-950°

C.

14. A method according to claim 1, comprising repeating the depositing steps two or more times to produce a multilayer coating containing at least two layers of NiP, at least two layers of Cr, and at least one intermediate layer, after which the multilayer-coated object is subjected to one or more heat treatments.

15. A method according to claim 1, further comprising the step of depositing a top layer on the coated and heat-treated object by thin film deposition, such as physical vapor deposition (PVD), chemical vapor deposition (CVD) or atomic layer deposition (ALD).

16. A method according to claim 1, further comprising the step of depositing a top layer on the coated object by thin film deposition, such as physical vapor deposition (PVD), chemical vapor deposition (CVD) or atomic layer deposition (ALD), before the step of subjecting the coated object to one or more heat treatments.

17. An object coated using a method according to claim 1, the coating comprising a multiphase layer containing crystalline Ni and crystalline Ni₃P, an intermediate layer containing another metal or metal alloy or ceramic, and a multiphase layer containing crystalline Cr.

18. A coated object according to claim 17, wherein the intermediate layer consists of copper or an alloy of copper.

19. A coated object according to claim 17, wherein the intermediate layer consists of molybdenum or an alloy of molybdenum.

20. A coated object according to claim 17, wherein the intermediate layer contains inorganic nonmetallic solid selected from the group comprising metal oxides, metal carbides, metal borides, metal nitrides, metal silicides, and mixtures thereof.

21. A coated object according to claim 17, comprising a top layer applied on the coated object by thin film deposition, such as physical vapor deposition, chemical vapor deposition or atomic layer deposition.

22. A coated object according to claim 21, wherein the top layer consists of a metal, metal alloy, ceramic, or diamond like carbon.

23. A coated object according to claim 17, having a Vickers microhardness value higher than 2000 HV.