Friction reduced and wear resistant coating, preparation method thereof and piston ring

1. A coating able to reduce friction and wear, wherein the coating is located on a surface of a substrate and the coating comprises an adhesive layer, a transition layer, a gradient layer and a function layer in sequence in a direction away from the surface of the substrate, wherein

the gradient layer is a CrMo x N layer in which Mo content progressively increases from 2.0-3.0 wt % to 3.0-6.0 wt %; and

the function layer comprises at least one cyclical layer, each cyclical layer comprises a first CrMo x N layer and a second CrMo x N layer in sequence from bottom to top, and a Mo content of the first CrMo x N layer is lower than a Mo content of the second CrMo x N layer.

2. The coating of claim 1 , wherein the first CrMo x N layer has a Mo content of 3.0 wt % to 6.0 wt %; and

the second CrMo x N layer has a Mo content of 10.0 wt % to 15.0 wt %.

3. The coating of claim 1 , wherein the function layer comprises 4 to 20 cyclical layers.

4. The coating of any one of claim 1 , wherein the adhesive layer is a Cr layer.

5. The coating of claim 1 , wherein the transition layer is a CrN layer and/or a Cr2N layer.

6. The coating of claim 1 , wherein the substrate is a piston ring made of steel and/or cast iron.

7. The coating of any one of claim 1 , wherein the coating has a thickness of 10 μm to 80 μm.

8. The coating of claim 1 , wherein the function layer has a thickness of 7.5 μm to 55 μm.

9. The coating of claim 1 , wherein a ratio of the thickness of the second CrMo x N layer to that of the first CrMo x N layer is (2-3):1.

10. The coating of claim 1 , wherein the adhesive layer has a thickness of 0.5 μm to 3 μm.

11. The coating of claim 1 , wherein the transition layer has a thickness of 1 μm to 11 μm.

12. The coating of claim 1 , wherein the gradient layer has a thickness of 1 μm to 11 μm.

13. A piston ring provided with the coating of claim 1 .

14. A preparation method of the coating of claim 1 , comprising the following steps:

(1) cleaning the surface of the substrate to obtain a cleaned substrate;

(2) depositing the adhesive layer on the surface of the substrate by using a multi-arc ion plating device;

(3) depositing the transition layer on a surface of the adhesive layer by using the multi-arc ion plating device;

(4) depositing the gradient layer on a surface of the transition layer by using the multi-arc ion plating device; and

(5) depositing the at least one cyclical layer on a surface of the gradient layer by using the multi-arc ion plating device to form the function layer and obtain the coating.

15. The preparation method of claim 14 , wherein the cleaning in the step (1) comprises the following steps:

(a) degreasing the surface of the substrate, subjecting the surface of the substrate to ultrasonic cleaning, drying the substrate, loading the substrate into the multi-arc ion plating device, heating the substrate to 380° C. to 450° C., and then vacuumizing the multi-arc ion plating device to below 5.0×10 −3 Pa; and

(b) passing 99.99% pure Ar to the multi-arc ion plating device, letting Ar ions bombarding and cleaning the surface of the substrate at a negative bias voltage of −800 V to −1200 V.

16. The preparation method of claim 14 , wherein process conditions for the depositing the adhesive layer in the step (2) comprise: a metal Cr target as a cathode, Ar as a working reactant gas, a cathode current of 80 A to 120 A, a pressure of 1 Pa to 2 Pa, and a negative bias voltage of −17 V to −23 V applied to the substrate;

process conditions for the depositing the transition layer in the step (3) comprise: a metal Cr target as a cathode, N 2 as a working reactant gas, a cathode current of 80 A to 120 A, a pressure of 4 Pa to 6 Pa, and a negative bias voltage of −30 V to −40 V applied to the substrate; process conditions for the depositing the gradient layer in the step (4) comprise a metal Cr target and a metal CrMo target as a cathode, N 2 as a working reactant gas, a pressure of 4 Pa to 6 Pa, a negative bias voltage of −30 V to −40 V applied to the substrate, and a progressively increased CrMo cathode current from 30 A to 45 A to 40 A to 55 A; and

process conditions for the depositing the at least one cyclical layer in the step (5) comprise: a metal Cr target and a metal CrMo target as a cathode, N 2 as a working reactant gas, a pressure of 4 Pa to 6 Pa, a negative bias voltage of −30 V to −40 V applied to the substrate, and a CrMo cathode current of 40 A to 55 A, for depositing the first CrMoxN layer; and then a metal Cr target and a metal CrMo target as a cathode, N 2 as a working reactant gas, a pressure of 4 Pa to 6 Pa, a negative bias voltage of −30 V to −40 V applied to the substrate, and a CrMo cathode current of 80 A to 95 A, for depositing the second CrMoxN layer.

17. The preparation method of claim 14 , wherein the step (5) comprises depositing 4 to 20 cyclical layers.

18. The preparation method of claim 14 , wherein total duration of deposition process of the step (2) to the step (5) is 8 h to 39 h.

19. The preparation method of claim 14 , comprising the following steps:

(1) cleaning the surface of the substrate to obtain the cleaned substrate, wherein the cleaning comprises:

(a) degreasing the surface of the substrate, subjecting the surface of the substrate to ultrasonic cleaning, drying the substrate, loading the substrate into the multi-arc ion plating device, heating the substrate to 380° C. to 450° C., and then vacuumizing the multi-arc ion plating device to below 5.0×10 −3 Pa; and

(b) passing the 99.99% pure Ar to the multi-arc ion plating device, letting Ar ions bombarding and cleaning the surface of the substrate at the negative bias voltage of −800 V to −1200 V;

(2) depositing the adhesive layer, a Cr layer, on the surface of the substrate under the following process conditions: a metal Cr target as a cathode, Ar as a working reactant gas, a cathode current of 80 A to 120 A, a pressure of 1 Pa to 2 Pa, and a negative bias voltage of −17 V to −23 V applied to the substrate;

(3) depositing the transition layer, a CrN layer and/or a Cr 2 N layer, on the Cr layer under the following process conditions: a metal Cr target as a cathode, N 2 as a working reactant gas, a cathode current of 80 A to 120 A, a pressure of 4 Pa to 6 Pa, and a negative bias voltage of −30 V to −40 V applied to the substrate;

(4) depositing the CrMo x N layer in which Mo content progressively increases under the following process conditions: a metal Cr target and a metal CrMo target as a cathode, N 2 as a working reactant gas, a pressure of 4 Pa to 6 Pa, a negative bias voltage of −30 V to −40 V applied to the substrate, and a progressively increased CrMo cathode current from 30 A to 45 A to 40 A to 55A;

(5) depositing the first CrMo x N layer under the following process conditions: a metal Cr target and a metal CrMo target as a cathode, N 2 as a working reactant gas, a pressure of 4 Pa to 6 Pa, a negative bias voltage of −30 V to −40 V applied to the substrate, and a CrMo cathode current of 40 A to 55 A; and then depositing the second CrMo x N layer under the following process conditions: a metal Cr target and a metal CrMo target as a cathode, N 2 as a working reactant gas, a pressure of 4 Pa to 6 Pa, a negative bias voltage of −30 V to −40 V applied to the substrate, and a CrMo cathode current of 80 A to 95 A; and

(6) repeating the step (5) for 4 to 20 cycles until the end of a process duration, and taking out the substrate after a furnace temperature is lower than 150° C., to obtain the coating on the surface of the substrate,

wherein total duration of deposition process from the step (2) to the step (5) is 8 h to 39 h.