Enhancement of corrosion–mechanical wear resistance of metallic alloys by glow-discharge nitriding

Abstract

The aim of this work is to provide a comprehensive analysis of hydrogen-free nitriding and nitrocarburizing processes in a glow discharge, to summarize the regularities of nitride and carbonitride layer formation on steels and titanium alloys, and to evaluate their corrosion–mechanical wear resistance under conditions of sliding, fretting, cavitation, and exposure to aggressive media. Particular attention is given to the application of  model for interpreting the kinetics and energy mechanisms of diffusion processes. The study presents a comparative analysis of the structural–phase transformations during nitriding and nitrocarburizing in a hydrogen-free glow discharge and systematizes experimental data on microhardness, electrochemical behavior, and corrosion–mechanical wear resistance.

The methodological basis of the theoretical part is the energy-exchange model, which describes the influence of active plasma species on the diffusion rate and phase formation. It is shown that hydrogen-free nitriding provides intensified nitrogen diffusion, the formation of stable nitrides TiN, Ti₂N, ε-(Fe₂–₃N), γ′-(Fe₄N), and the elimination of hydrogen embrittlement. It is established that nitrocarburizing produces multilayer carbonitride structures with hardness values of 900–1300 HV and high adhesion to the substrate. The modified layers demonstrate a 3–6-fold increase in wear resistance, a 2.5–4-fold reduction in cavitation damage, and a significant decrease in corrosion current in NaCl and NaOH solutions. A transition of the dominant failure mechanisms from brittle and adhesive to plastic-deformation dominated modes has been identified. The obtained results confirm the experimentally observed regularities of carbonitride-layer formation and demonstrate the key role of ion bombardment in generating the defect-subzone .