Tribo-Mechanical Behavior of Films and Modified Layers Produced by Cathodic Cage and Glow Discharge Plasma Nitriding Techniques

Two surface modification techniques, the glow discharge plasma nitriding (GDPN) and the cathodic cage plasma nitriding (CCPN), were compared regarding the mechanical and tribological behavior of layers produced on AISI 316 stainless-steel surfaces. The analyses were carried out at the micro/nanoscale using nanoindentation and nanoscratch tests. The nitriding temperature (degrees C) and time (h) parameters were 350/6, 400/6, and 450/6. Morphology, structure, and microstructure were evaluated by X-ray diffraction, scanning electron and optical interferometry microscopies, and energy-dispersive X-ray spectroscopy. GDPN results in stratified modified surfaces, solidly integrated with the substrate, with a temperature-dependent composition comprising nitrides (gamma'-Fe4N, epsilon-Fe2+xN, CrN) and N-solid solution (gamma(N) phase). The latter prevails for the low treatment temperatures. Hardness increases from similar to 2.5 GPa (bare surface) to similar to 15.5 GPa (450 degrees C). The scratch resistance of the GDPN-modified surfaces presents a strong correlation with the layer composition and thickness, with the result that the 400 degrees C condition exhibits the highest standards against microwear. In contrast, CCPN results in well-defined dual-layers for any of the temperatures. A top 0.3-0.8 mu m-thick nitride film (most epsilon-phase), brittle and easily removable under scratch with loads as low as 63 mN, covers a gamma(N)-rich case with hardness of 10 GPa. The thickness of the underneath CCPN layer produced at 450 degrees C is similar to that from GDPN at 400 degrees C (3 mu m); on the other hand, the average roughness is much lower, comparable to the reference surface (Ra similar to 10 nm), while the layer formation involves no chromium depletion. Moreover, edge effects are absent across the entire sample ' s surface. In conclusion, among the studied conditions, the GDPN 400 degrees C disclosed the best tribo-mechanical performance, whereas CCPN resulted in superior surface finishing for application purposes.

Automated summary

Two surface modification techniques, glow discharge plasma nitriding (GDPN) and cathodic cage plasma nitriding (CCPN), were compared for the mechanical and tribological behavior of layers produced on AISI 316 stainless-steel surfaces. GDPN resulted in stratified modified surfaces with temperature-dependent composition, while CCPN produced well-defined dual-layers. GDPN at 400°C demonstrated the best tribo-mechanical performance, while CCPN provided superior surface finishing for application purposes.