Surface Characteristics, Properties and Wear Resistance OF TIB2 BASED Hard-Alloy Coatings Obtained by Electrospark Deposition at Negative Polarity on Ti6Al4V Alloy

In the present work, the possibilities of improving the surface properties of titanium alloy Ti6Al4V by electrospark deposition (ESD) at negative polarity were investigated. The coatings were deposited with a TiB2-TiAl-based hard-alloy electrode with nano-sized additives of NbC and ZrO2. The effect of polarity in ESD at low pulse energy (0.01-0.07 J) on the surface roughness, thickness, composition and structure of coatings was studied by profilometric, metallographic, XRD, SEM and EDS methods. In both polarities, dense and uniform coatings were obtained with roughness and thickness, which could be varied by changing the ESD modes within the range Ra=1.5÷4.5 µm, d= 6÷20 µm and microhardness from 9 to 12 GPa, respectively. It was found that the negative polarity coatings obtained are denser and uniform with higher thickness, lower roughness, finer structure, and lower coefficient of friction, and can be successfully used to reduce the surface roughness and defects of 3D printed titanium alloy. Abrasion and erosion wear tests showed that the wear resistance of coated titanium surfaces at both polarities was 2.2 to 3.5 times higher than that of the substrate. Coatings deposited in positive polarity demonstrated higher resistance to abrasive wear, while those in negative polarity are more resistant to erosive wear.