Wear behavior of DLC film on plasma nitrocarburized AISI 4140 steel by pulsed DC PACVD: Effect of nitrocarburizing temperature

• Adhesion and wear behavior of DLC film on nitrocarburized steel was studied.
• Plasma nitrocarburizing was done on 500 °C and 550 °C.
• Nitrocarburizng improved adhesion of the DLC film on AISI 4140 steel.
• Nitrocarburizing at 550 °C provided better interlocking sites that resulted in better adhesion of the DLC film.
• Burnishing wear and graphitization were two main wear mechanisms of DLC film.

DLC films were produced on nitrocarburized AISI 4140 steel at 110 °C by a pulsed DC PACVD method. Plasma nitrocarburizing (PNC) at 500 °C and 550 °C was used as an intermediate layer. SEM, roughness, micro-Raman spectroscopy and XRD analysis were employed to investigate the microstructure, surface roughness, various carbon phases and nitrided phase of the films. Furthermore, Rockwell C indentation tests were conducted to evaluate the adhesion of DLC films grown onto plasma nitrocarburized substrates. The friction and wear behavior of the treated samples were studied by pin-on-disk method. Results confirmed that plasma nitrocarburizing improved adhesion of the DLC films to the steel substrate. Also, the DLC sample that was deposited on the PNC (550) showed lower friction coefficient and lower wear rate compared to DLC sample that was grown on the PNC (500) sample. Burnishing wear was main wear mechanism in PNC (550)-DLC sample.