Possibilities of Duplex Plasma Electrolytic Treatment for Increasing the Hardness and Wear Resistance of a Commercially Pure Titanium Surface

Abstract

The technology for duplex treatment of a commercially pure titanium surface is expected to increase hardness and wear resistance. This technology consists of sequential nitrocarburizing and polishing of the product in plasma electrolysis. The mechanism of duplex processing is revealed; it consists of strengthening the surface layers under diffusion saturation and controlled formation of the surface relief. The possibility of controlling the characteristics of the modified surface by combining various plasma technologies is shown. The morphological features of the surface and the surface layer after treatment were studied. The microhardness of the modified layer and the tribological properties of the surface were measured. It has been established that the samples with the highest surface layer hardness and a small thickness of the oxide layer on the surface have the highest wear resistance. After nitrocarburizing at 750 °C for 5 min, wear resistance increases by 4.3 times compared to pure material. If subsequent polishing is carried out at a voltage of 275–300 V for 3–5 min in chloride and fluoride electrolytes and 5–10 min in a sulfate electrolyte, then wear resistance can be further increased. This is achieved by removing the porous outer oxide layer.