Synthesis of TiN on SAE 1080 steel via plasma deposition with cathodic cage at cathodic and floating potential

This work investigated the deposition of titanium nitride (TiN) films on SAE 1080 steel using the cathodic cage plasma deposition (CCPD) technique. The innovation of this study lies in the evaluation of the simultaneous duplex process (thermochemical diffusion and hard film deposition in a single step) and in the direct influence of electrical potentials (cathodic and floating) and temperatures (400 and 450 °C) on the tribological performance of the steel. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy, microhardness, Rockwell C adhesion, and microabrasive wear tests. The XRD results confirmed the efficient formation of the hard structural phases Fe2N, Fe4N, and Ti2N. SEM analysis quantified disparities in surface morphology: Treatment at cathodic potential generated significantly thicker films of 6.366 ± 0.75 μm (400 °C) and 5.193 ± 0.45 μm (450 °C), though less uniform due to the edge effect. In contrast, the floating potential produced highly homogeneous films with grain refinement, but with reduced thicknesses of 1.727 ± 0.27 and 1.113 ± 0.14 μm at respective temperatures. In the mechanical tests, the samples at cathodic potential showed the largest increases in surface microhardness, reaching 748.54 ± 93.21 HV (400 °C) and 831.28 ± 87.2 HV (450 °C) compared to 245.63 ± 28.25 HV for the base material, a benefit attributed to the formation of a nitrogen diffusion zone underlying the film. All conditions demonstrated excellent adhesion quality (HF1 level). In the tribological tests under an 8 N load, the property gradient of the cathodic potential ensured the lowest rates and accumulated volumes of microabrasive wear. However, the films generated at floating potential exhibited wear resistance lower than that of the base material, resulting from the fragmentation of the deposited film that generated abrasive debris in the tribo-contact. The coefficient of friction remained below 0.8 for all conditions, with the lowest value recorded for the DP400F sample. It is concluded that the CCPD technique is viable for surface modification of SAE 1080 steel, with the cathodic potential configuration being the most efficient for applications requiring high hardness and wear resistance.