Anodic Plasma Electrolytic Nitrocarburizing of VT22 Titanium Alloy in Carbamide Electrolyte

Abstract

The influence of the carbamide concentration on the nitrocarburizing temperature and changes in the mass of titanium samples, which are related to the anodic dissolution and high-temperature oxidation of titanium in a vapor‒gas shell, is investigated. The modified layer structure is revealed to contain an external oxide layer (rutile) and an intermediate diffusion layer whose microhardness reaches 770 HV. It is demonstrated that an increase in the nitrocarburizing temperature stimulates growth in the oxide-layer thickness, and the diffusion-layer thickness depends on the carbamide concentration in the solution. It is found that, at 850°С, the surface roughness decreases from 1.0 to 0.3–0.5 μm and the wear rate reduces from 6.7 × 10–7 to (1.2–1.7) × 10–7 due to nitrocarburizing in an electrolyte incorporating 10–15 wt % ammonium chloride and 10–12.5 wt % carbamide.