Investigation of the properties of oxide coatings on titanium alloys obtained by plasma electrolytic oxidation

Abstract

The use of structures made of titanium and its alloys, which have improved corrosion, physical and mechanical properties, are in demand in many industries. In this regard, the processes of modifying the surface of metals are of interest. One of the modern and promising methods of metal surface treatment is plasma electrolytic oxidation. Currently, there is a problem of widespread use of this process when DC modes are used in the implementation of the process. This is due to the large consumption of electricity. The purpose of this work is to study the morphological and corrosion properties of oxide coatings obtained in the pulsed anodecathode mode on titanium alloys VT1-0 and VT5 in various electrolyte solutions. Modification of the surface of titanium alloys was carried out at the duration of the anode current pulse of 250 ± 25 microseconds, the duration of the cathode current pulse of 5 ± 0.5 ms, the repetition frequency of the anode and cathode pulses of 50 ± 0.5 Hz. Alkaline solutions served as electrolytes. Oxide coatings obtained in various electrolytes are characterized by different porosity and coating thickness. Coatings with a finely porous structure, with an average pore diameter from 0.09 microns to 0.4 microns, and larger pore sizes of 0.6 – 0.7 microns were obtained. The porosity of the coatings ranges from 6.12% to 12.2%. According to the data of energy dispersion analysis, it was found that the structure of oxide coatings includes both components of the processed metal and components of the electrolyte solution. The main components, in this case, are oxygen and processed metal, as well as other elements such as boron, phosphorus, aluminium, fluorine, sodium, silicon and others. Corrosion tests according to GOST 9.308-85 under the influence of neutral salt mist at a temperature of (35 ± 2) °C with 1500 hours in the Ascott CC 450 chamber, it was shown that there was no corrosion damage to the coatings.