Effects of the duty factor on the surface characteristics of the plasma nitrided and diamond-like carbon coated high-speed steels

The purpose of this study is to investigate the effects of the duty factor on the surface characteristics of plasma nitrided and diamond-like carbon (DLC) coated high-speed steels. In the duplex treatment, pulsed plasma nitriding was performed with N2 and H2 gases at 530°C for 4 h. Duty factors were controlled within the range from 0.1 to 1 by varying both the pulse-on time and the pulse-off time. Plasma-assisted chemical vapor deposition equipment was used for the deposition of DLC films. Since the adhesion of the film to the substrate is of primary importance for the industrial application of duplex layers, the critical load was measured by the scratch test method. Properties of the nitrided and duplex treated layer were analyzed by using optical microscopy, scanning electron microscopy, X-ray diffractometry, atomic force microscopy and micro-Vickers hardness measurement. It was found that surface roughness increased with increasing duty factor for all the nitrided and duplex treated surfaces. The critical load to failure decreased with increasing substrate roughness.