Variable hardness nanocomposite coating
A variable hardness nanocomposite coating and method for its production. The variable hardness nanocomposite coating can be applied as a single layer on metallic engine components that require a break-in to achieve physical mating of interacting surfaces thereby reducing friction and optimizing engine performance. The single layer nanocomposite coating has a relatively higher carbon content and lower hardness at the surface region and a relatively lower carbon content and relatively higher hardness region as one proceeds towards a surface of the metal component being coated.
1 . A method of coating a metal part for an engine with a magnetron sputtering system having a process chamber including a magnetron and a Ti target comprising:
placing said metal part having a surface into said process chamber;
reducing gas pressure in said chamber;
supplying an inert gas to said process chamber and generating a plasma for said inert gas;
supplying nitrogen to said process chamber;
supplying both a gas containing carbon and silicon and a carbon containing gas to said process chamber;
sputtering titanium from a magnetron target in said process chamber;
depositing only a single continuous layer of Ti—Si—C—N coating on said metal part surface at a thickness in the range of 5.0 μm to 40 μm including a carbon amorphous phase, wherein an exposed surface region of said coating has a hardness that increases from said coating surface region down to said surface of said metal substrate.
2 . The method of claim 1 wherein said gas containing carbon and silicon comprises hexamethyldisilizane and/or tetramethylsilane.
3 . The method of claim 1 wherein said carbon containing gas comprises acetylene.
4 . The method of claim 1 wherein said surface region of said coating has a hardness in the range of 5.0 GPa to 10.0 GPa and increases to a value of greater than 10.0 GPa to 30.0 GPa below said surface region and down to said surface of said metal part.
5 . The method of claim 1 wherein said coating has a thickness of 40.0 μm and said surface region of said coating has a thickness in the range of up to 5.0 μm.
6 . The method of claim 1 wherein said coating has a thickness of 20.0 μm and said surface region of said coating has a thickness in the range of up to 5.0.
7 . The method of claim 1 wherein said relatively higher hardness portion of said coating provides a wear rate of less than 10×10 −6 mm 3 /N/m.
8 . The method of claim 1 wherein said relatively higher hardness portion of said coating has a coefficient of friction of less than 0.15.
9 . The method of claim 1 wherein said coating comprises 35-49 atomic percent titanium, 1-5 atomic percent of silicon, 17-50 atomic percent of carbon, and 19-35 atomic percent of nitrogen.
10 . The method of claim 1 wherein said gas containing carbon and silicon is introduced at a flow rate set at an initial value of 0 sccm and increased to 6 sccm as the single continuous layer nanocomposite coating is deposited and the carbon containing gas in introduced at a flow rate set at an initial value of 0 sccm and increased to 50 sccm as the single continuous layer nanocomposite coating is deposited.
11 . The method of claim 1 wherein said coating comprises a Si—N amorphous phase and the carbon amorphous phase and a Ti—C—N crystalline phase.
12 . The method of claim 1 wherein the metal part is a gear, piston ring, or camshaft for an engine.