Cumulative effect of FexN phases, roughness parameters, and asperity geometry on the anti-wear properties of low-temperature plasma nitrided Ti-Nb stabilized IF steel

Abstract

Plasma-driven surface modification techniques like plasma nitriding (PN) are trending, especially for steel products. It is advantageous due to the higher order of process control and superior quality of property enhancement of the surface. This technique often employs a high processing temperature, which is one of its metallurgical and economical limitations. One of the renowned solutions is the implementation of lower processing temperatures. The current work is based on the low-temperature plasma nitriding of Ti-Nb stabilized interstitial-free steel at different processing temperatures ranging from 400 ºC to 500 ºC. The role of Fe_xN phases, surface roughness parameters, and asperities geometry are thoroughly studied with respect to the anti-wear properties of the surface. The formation of γ′-Fe₄N and ε-Fe_2–3N are detected in the XRD plot, whereas α″-Fe₁₆N₂ is confirmed in microscopy. The sample treated at 450 ºC presents the best anti-wear properties compared to other samples, primarily due to the presence of prominent ε-Fe_2–3N phase and blunt surface asperities. A maximum reduction in wear volume of about 3 times the base value is recorded in the wear test. The microscopic and elemental analyses are conducted on the wear scars, wear debris, and counter-body worn-out surfaces to study the wear mechanism comprehensively. The work tries to illustrate the wear mechanisms schematically to understand the conceptual grounds associated with such theories. The spectrometric analysis in the depth direction is also performed, and it detects the trace of nitrogen up to about 7 µm depth for 500 ºC nitriding conditions.