Friction- and wear-reducing coating

1. A coating comprising:

a first layer of a ceramic orthorhombic boride-based alloy represented by the general formula AlMgB 14 —X and having a thickness of from greater than 1 micron to less than or equal to 3 microns;

wherein X is present in an amount of from 0 to 70 parts by weight based on 100 parts by weight of said ceramic orthorhombic boride-based alloy and is a doping agent selected from the group of Group IV elements and borides and nitrides thereof; and

a second layer disposed on said first layer and including amorphous carbon present in a gradient concentration that increases with a distance from said first layer;

wherein the coating has a hardness of from 10 to 20 GPa;

wherein the coating has a coefficient of friction of less than or equal to 0.12.

2. The coating of claim 1 , wherein said first layer has a hardness of from 30 to 40 GPa.

3. The coating of claim 1 , wherein said second layer has a hardness of from 10 to 25 GPa.

4. The coating of claim 1 , wherein said coating does not substantially degrade at a temperature of less than or equal to 1,000° C.

5. The coating of claim 4 , wherein said coating has a wear rate of less than or equal to 2×10 −7 mm 3 /N·m as measured in accordance with ASTM G99-05.

6. A coating comprising:

a first layer of a ceramic orthorhombic based-boride alloy represented by the general formula AlMgB 14 —X and having a thickness of from 1.25 to 3 microns;

wherein X is present in an amount of from 0 to 70 parts by weight based on 100 parts by weight of said ceramic orthorhombic boride-based alloy and is a doping agent selected from the group of Group IV elements and borides and nitrides thereof; and

a second layer disposed on said first layer and including amorphous carbon present in a gradient concentration that increases with a distance from said first layer and having a thickness of from 0.1 to 1.5 microns;

wherein the coating has a hardness of from 10 to 20 GPa;

wherein the coating has a coefficient of friction of less than or equal to 0.12.

7. The coating of claim 6 , wherein said first layer has a hardness of from 30 to 40 GPa.

8. The coating of claim 7 , wherein said second layer has a hardness of from 10 to 25 GPa.

9. A method of coating a substrate, the method comprising the steps of:

cleaning the substrate;

forming a first layer of a ceramic orthorhombic boride-based alloy represented by the general formula AlMgB 14 —X and having a thickness of greater than 1 micron to less than or equal to 3 microns on the substrate;

wherein X is present in an amount of from 0 to 70 parts by weight based on 100 parts by weight of the ceramic orthorhombic boride-based alloy and is a doping agent selected from the group of Group IV elements and borides and nitrides thereof; and

depositing a second layer onto the first layer to form a coating on the substrate, wherein the second layer includes amorphous carbon present in a gradient concentration that increases with a distance from the first layer;

wherein the coating has a hardness of from 10 to 20 GPa;

wherein the coating has a coefficient of friction of less than or equal to 0.12.

10. The method of claim 9 , wherein said depositing is further defined as increasing a concentration of amorphous carbon in the second layer with a distance from the first layer so that amorphous carbon is present in the second layer in the gradient concentration.

11. The method of claim 9 , wherein said depositing is further defined as sputtering the first layer with a target material including carbon.

12. The method of claim 9 , wherein said depositing is further defined as decomposing a carbon-based gas in the presence of the first layer.

13. The method of claim 9 , wherein said cleaning is further defined as etching the substrate.

14. The method of claim 9 , wherein said forming is further defined as physical vapor depositing the first layer.

15. The method of claim 14 , wherein said physical vapor depositing is further defined as sputtering the substrate with a target material represented by the general formula AlMgB 14 —X;

wherein X is present in an amount of from 0 to 70 parts by weight based on 100 parts by weight of the ceramic orthorhombic boride-based alloy and is a doping agent selected from the group of Group IV elements and borides and nitrides thereof.