Synthesis of Ti-Al intermetallic coatings via electrospark deposition in a mixture of Ti and Al granules technique

In this paper, the results of studies of the formation of Ti-Al intermetallic coatings on a Ti6Al4V alloy by the electric spark deposition method in a mixture of titanium and aluminum granules are presented. Five mixtures of granules with an aluminum concentration of 24 to 88 at% were prepared. As the concentration of aluminum in the mixture of granules increased, the phase composition of the corresponding coatings changed from alpha Ti and titanium rich aluminides to aluminum aluminides rich and Al. According to EDS analysis, with an increase of the aluminum content in the mixture of granules from 24 to 88 at.% its concentration on the surface of the coatings increased from 19 to 68 at.%. The main mechanism of Ti-Al coatings formation at electrospark granule deposition is convective mixing of melted materials of granules and substrate. Potentiodynamic polarization tests in a 3.5% NaCl solution showed that coatings can improve the corrosion resistance of the Ti6Al4V alloy. A high-temperature corrosion test for 100 h at 900 degrees C showed that coated samples were oxidized 1.1-3.4 times less than initial Ti6Al4V substrate. The best oxidation resistance properties showed the coating with the highest aluminum content. Electric spark granule deposition increase microhardness of Ti6Al4V alloy up to 6.4-9.4 GPa. The wear resistance of the coatings at dry sliding with 10 and 25 N loads was 4-27 and 6-36 times higher, respectively, than wear resistance of the initial alloy. The wear rate of coatings decreased with increasing titanium concentration.