Method for plasma-assisted and multi-step continuous preparation of diffusion layer/amorphous carbon film composite coating and use thereof

A method for plasma-assisted and multi-step continuous preparation of a diffusion layer/amorphous carbon film composite coating, the method comprising the following steps:

• S1, pretreating a substrate by polishing a surface of a substrate steel material to a mirror surface, and cleaning in alcohol and an acetone solution for later use;
• S2, performing plasma diffusion with high-temperature carbon/nitrogen ion by putting a sample obtained in step S1 into a plasma chemical heat treatment furnace to allow diffusion, introducing hydrogen or argon and heating, introducing a source gas for the diffusion after the heating is completed, controlling a gas pressure and a flow rate of the source gas, and conducting heat preservation of the diffusion;
• S3, performing plasma activation with argon ion under gradient cooling by after the heat preservation of the diffusion in step S2 is completed, stopping introducing the source gas for the diffusion, introducing argon while controlling a flow rate and a pressure of the argon, gradually reducing the flow rate and the pressure of the argon, reducing a voltage, and realizing argon ion bombardment while a furnace temperature is lowered;
• and
• S4, performing plasma coating with low-temperature carbon ion by, when the furnace temperature drops to not more than 200° C., applying the voltage, introducing a carbon source gas and hydrogen, controlling a gas pressure and flow rates of the carbon source gas and the hydrogen, depositing an amorphous carbon film, cooling the sample to a room temperature with the furnace after the depositing is completed, and taking out the sample;
• wherein the performing plasma diffusion with the high-temperature carbon/nitrogen ion in step S2 is plasma nitriding;
• wherein the heat treatment furnace in step S2 is operated at 400° C. to 600° C.;
• wherein the performing plasma activation with the argon ion under gradient cooling in step S3 comprises multi-step plasma activation with the argon ion having the following stages:
• S31, conducting plasma activation at a flow rate of the argon of 20 sccm, a gas pressure of 100 Pa, and a voltage of 780 V for 30 min;
• S32, conducting plasma activation at a flow rate of the argon of 15 sccm, a gas pressure of 100 Pa, and a voltage of 750 V for 30 min;
• S33, conducting plasma activation at a flow rate of the argon of 10 sccm, a gas pressure of 80 Pa, and a voltage of 700 V for 30 min;
• and
• S34, conducting plasma activation at a flow rate of the argon of 5 sccm, a gas pressure of 60 Pa, and a voltage of 600 V, and conducting the plasma coating with the low-temperature carbon ion in step S4 when the furnace temperature drops to not more than 200° C.;
• wherein the carbon source gas in step S4 is propane;
• wherein the depositing in step S4 is conducted at less than 200° C., a voltage of 750 V to 850 V, and a pressure of less than 100 Pa.