A CHROMIUM-CONTAINING COATING, A METHOD FOR ITS PRODUCTION AND A COATED OBJECT

• US 20170159198A1
• Filed: 07/11/2014
• Published: 06/08/2017
• Est. Priority Date: 07/11/2014
• Status: Active Grant

• Current Assignee: Savroc Ltd.
• Original Assignee: Savroc Ltd.
• Inventors: MIETTINEN, Juha, RAISA, Jussi
• Granted Patent: US 10,487,412 B2
• Time in Patent Office: Days
• CPC Class Codes: C23C 18/1653 Two or more layers with at least one layer obtained by electroless plating and one layer obtained by electroplating
• CPC Class Codes: C23C 18/1692 Heat-treatment
• CPC Class Codes: C23C 18/1834 Use of organic or inorganic compounds other than metals, e.g. activation, sensitisation with polymers
• CPC Class Codes: C23C 18/36 using hypophosphites
• CPC Class Codes: C23C 28/021 including at least one metal alloy layer
• CPC Class Codes: C23C 28/322 only coatings of metal elements only
• 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 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 5/617 Crystalline layers
• CPC Class Codes: C25D 5/625 Discontinuous layers, e.g. microcracked layers
• CPC Class Codes: C25D 5/627 Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance

Abstract

The invention relates to a chromium-based coating comprising at least one layer rich in crystalline phase or phases of nickel (Ni) and/or Ni compounds, and at least one layer rich in crystal-line phase or phases of chromium (Cr) and/or Cr compounds, Cr being electroplated from a trivalent chromium bath. The coating is characterized in that the it further comprises one or more crystalline phases of chromium-nickel-phosphorus (CrNiP), which CrNiP phase has been produced by heat treating a coating comprising at least one layer of nickel-phosphorus (NiP) and at least one layer of Cr. The invention also relates to a method for producing a chromiumbased coating and to a coated object.

Claims

1. A chromium-based coating comprising at least one layer rich in crystalline phase or phases of nickel (Ni) and/or Ni compounds, and at least one layer rich in crystalline phase or phases of chromium (Cr) and/or Cr compounds, Cr being electroplated from a trivalent chromium bath, characterized in that the coating further comprises one or more crystalline phases of chromium-nickel-phosphorus (CrNiP), which CrNiP phase has been produced by heat treating a coating comprising at least one layer of nickel-phosphorus (NiP) and at least one layer of Cr.

2. A chromium-based coating according to claim 1, wherein the crystalline CrNiP phase(s) form(s) an interface layer between a layer rich in crystalline phase(s) of Ni and/or Ni compounds and a layer rich in crystalline phase(s) of Cr and/or Cr compounds.

3. A chromium-based coating according to claim 1, wherein at least one of the layers is a multiphase layer.

4. A chromium-based coating according to claim 1, wherein the chromium-based coating is a multilayer coating comprising at least two layers rich in crystalline phase or phases of Ni and/or Ni compounds and at least two layers rich in crystalline phase or phases of Cr and/or Cr compounds.

5. A chromium-based coating according to claim 1, wherein at least one of the layers rich in crystalline phase or phases of Ni and/or Ni compounds comprises a crystalline Ni₃P phase.

6. A chromium-based coating according to claim 1, wherein the crystalline CrNiP phase(s) is/are a component(s) of at least one multiphase layer.

7. A chromium-based coating according to claim 1, wherein at least one of the layers is a multiphase layer and comprises, in addition to crystalline Cr, at least one of the following:

crystalline CrNiP, crystalline CrNi, crystalline Ni, chromium carbide or chromium oxide, or a combination thereof.

8. A chromium-based coating according to claim 1, wherein the layer closest to the surface of the coating comprises crystalline Cr.

9. A chromium-based coating according to claim 1, wherein the layer closest to the surface of the coating comprises NiP or crystalline Ni₃P.

10. A chromium-based coating according to claim 1, wherein the atomic ratio of the CrNiP phase is, for example, Cr_10.08Ni_1.92P₇, Cr_0.75Ni_0.25P, Cr₁Ni₁P₁, Cr_2.4Ni_0.6P, Cr_0.65Ni_0.35P_0.10 or Cr_1.2Ni_0.8P or any combination thereof.

11. A chromium-based coating according to claim 1, wherein the CrNiP phase comprises tetragonal CrNiP and/or orthohrombic CrNiP.

12. A chromium-based coating according to claim 1, wherein the thickness of at least one of the crystalline chromium-containing layers is 0.05-20 μ

m, preferably 0.3-10 μ

m, more preferably 2-7 μ

m.

13. A chromium-based coating according to claim 1, wherein at least one of the CrNiP-containing layers is an interface layer.

14. A chromium-based coating according to claim 1, wherein the thickness of the coating is 0.5-200 μ

m.

15. A chromium-based coating according to claim 1, wherein the hardness of the coating is at least 1,500 HV_0.005, preferably at least 2,000 HV_0.005 on a Vickers microhardness scale.

16. A chromium-based coating according to claim 1, wherein the Taber index of the coating measured by the Taber abrasion test according to ISO 9352 is below 2, preferably below 1.

31. A coated object, characterized in that it comprises a coating according to claim 1.

32. A coated object according to claim 31, wherein the coated object is a gas turbine, shock absorber, hydraulic cylinder, linked pin, a ball valve or an engine valve.

17. A method for producing a chromium-based coating on an object by trivalent chromium plating, the method comprising the steps of

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

b) depositing a layer of chromium from a trivalent chromium bath on the object; and

c) subjecting the coated object to at least one heat treatment at a temperature of 650-950°

C., preferably at a temperature of 750-900°

C., to amend the mechanical and physical properties of the coating and to produce a CrNiP phase.

18. The method according to claim 17, wherein the at least one heat treatment in step c) is induction heating or furnace heating.

19. The method according to claim 17, wherein the heat treatment of step c) is induction heating and the object is cooled by cooling liquid 0.1-60 seconds, preferably 0.5-10 seconds, more preferably 0.8-1.5 seconds, after the end of the heating.

20. The method according to claim 17, wherein the method comprises an additional step d) of depositing a top layer after step c) by thin film deposition, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD) or electroplating or electroless plating.

21. The method according to claim 17, wherein the method comprises an additional step d) of depositing a top layer before step c) by thin film deposition, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD) or electroplating or electroless plating.

22. The method according to claim 17, wherein the steps a) and b) are repeated at least once before step c) to produce a multilayer coating containing at least two layers rich in crystalline phase or phases of nickel (Ni) and/or Ni compounds and at least two layers rich in crystalline phase or phases of chromium (Cr) and/or Cr compounds.

23. The method according to claim 17, wherein the steps a), b) and c) are repeated at least once.

24. The method according to claim 17, wherein the method comprises an additional step i) before step a) to improve the adhesion between the adjacent layers.

25. The method according to claim 24, wherein step i) comprises depositing a strike layer.

26. The method according to claim 25, wherein step i) further comprises treating the object with an strong acid, preferably with 30% (w/w) hydrochloric acid, before depositing the strike layer.

27. The method according to claim 17, 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.

28. The method according to claim 17, wherein the object to be coated is a hardened steel rod and wherein step i) is performed first, then step a), then step b), then step c), wherein step c) comprises first heating at 300-500°

C. and then at 750-870°

C., and wherein the method comprises the further step of cooling with a cooling liquid within 60 seconds, preferably within 10 seconds, more preferably within 1.5 seconds from the end of step c).

29. The method according to claim 28, wherein the method comprises a further step of tempering at a temperature of 200-400°

C. after cooling with a cooling liquid.

30. The method according to claim 28, wherein the hardened steel rod is a rod of a shock absorber or a rod of a hydraulic cylinder.