Study on the technology of surface strengthening Ti–6Al–4V alloy by near-dry multi-flow channel electrode electrical discharge machining

Abstract

Titanium alloy has excellent performance and wide application prospects in the aerospace, energy, chemical industry, and other areas. However, low hardness and poor wear resistance severely limit the application range of titanium alloys. Therefore, in the present research, multi-flow channel electrode and gas-liquid atomization medium are used for surface strengthening of Ti–6Al–4V alloy by electrical discharge machining (EDM). Benefiting from the multi-flow channel electrode, the gas-liquid atomization medium passes into the discharge gap uniformly. Under the environment of transient high-temperature and high-pressure generated by discharge, the ionized element N and molten titanium in the atomizing medium are induced to undergo in-situ synthesis reactions and generate a nitride reinforcement layer. Influence parameters such as peak current, pulse on time (Ton), and pulse off time (Toff) on the surface characteristics are optimized through single-factor experiments. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) are adopted to investigate the hardness and wear resistance characteristics of the strengthening surface. The results indicate that a continuous and uniform reinforcement layer with fewer defects can be obtained. TiN and other hard phases are observed in the strengthened surface. The hardness of the strengthening layer is about 3–5 times as much as that of the substrate, and the wear resistance is increased by more than 40 %. Electrochemical analysis shows that the corrosion tendency of the strengthened layer decreased by 72 % compared to that of the substrate.