Evaluation of Nitriding, Nitrocarburizing, Organosilicon Interlayer, Diamond-Like Carbon Film and Duplex Plasma Treatment in the Wear and Corrosion Resistance of AISI 4340 Steel

Duplex treatments are performed to promote an additional property to a previous surface treatment to improve wear and corrosion resistance of the material, like the DLC film (diamond-like carbon) deposited on nitriding or nitrocarburizing surfaces on the AISI 4340 steel. The purpose of this work is to study the effect of the duplex treatment (nitriding + DLC and nitrocarburizing + DLC film deposition) on the wear and corrosion resistance of AISI 4340 steel. The nitrocarburizing treatments by plasma were performed with 80% N-2 + 17% H-2 + 3% CH4 at 400, 450, 500, 525 and 550 degrees C for 5 h. The nitriding treatment by plasma at 450 degrees C was performed with 80% N-2 + 20% H-2 for 5 h. The interlayer deposition was performed using hexamethyldisiloxane as a precursor. The deposition of DLC film was performed by DC-PECVD method using 90% CH4 + 10% Ar at 200 degrees C for 2 h. The duplex treatment was performed at the optimum temperature of the nitrocarburizing process. Micro-abrasive wear tests by fixed ball, and corrosion tests showed that all material treated presented lower wear volume and higher corrosion resistance than untreated material, but the duplex treatments provided greater wear and corrosion resistance than that observed on materials treated with only one type of treatment, showing that duplex treatment improves surface resistance of the AISI 4340 steel. The nitrocarburizing + DLC duplex treatment presented greater wear and corrosion resistance than nitriding + DLC duplex treatment, evidencing the great positive effect of carbon added to the treatment. (AU)