Simultaneous duplex process of TiN coating and nitriding by active screen plasma nitriding

Abstract

Nitriding steel sample SACM 645 was nitrided by active screen plasma nitriding (ASPN) using a titanium screen to form simultaneously TiN coating/nitrogen-diffusion layer on the sample surface. ASPN experiments were carried out using a DC plasma-nitriding unit. The sample was placed on the sample stage in a floating potential and a cathodic potential. A titanium double screen was mounted on the cathodic stage around the sample stage. ASPN treatments at 0%-bias and 100%-bias were performed in a nitrogen–hydrogen atmosphere with 75% N2+25% H2 for 0–54 ks at 873K under 100Pa. After nitriding, the nitrided microstructure was examined with a scanning electron microscope, glow discharge optical emission spectroscopy and X-ray diffraction studies. In addition, the hardness of the surface and the cross‐sections of the nitrided sample were measured using a Vickers microhardness tester under a 0.1-N load. The thickness of the TiN layer grew linearly with increasing nitriding time. In this case, the deposition rate of the TiN layer was 0.22μm/h. The nitrided layer formed by ASPN at 100%-bias consisted of a TiN compound layer followed by a nitrogen-diffusion layer.