**2. Materials and Methods**

### *2.1. Coating Production*

Ti-6Al-4V alloy samples (Grade V, max. wt.%: 5.5–6.7 Al, 3.5–4.0 V, 0.25 Fe, 0.2 O, 0.05 N, 0.08 C, bal. Ti) (Scope Metals Group Ltd., Israel) with a surface area of 62 cm2 were grounded up to abrasive paper grits #1200 and subjected to the ultrasonic cleaning in acetone.

The MAO process was carried out by MP2-AS 35 power supply (Magpulls, Sinzheim, Germany) with the follow electrical parameters: Imax = 5 A, Umax = 1000 V. Electrical parameters were pulsed (symmetric bipolar square pulse) at a frequency from 200 to 1000 Hz. Names of the experimental samples and their current pulse parameters listed in Table 1. The process was carried out in electrolyte contained sodium carbonate (Na2CO3, Sigma Aldrich, St. Louis, MO, USA) = 10 g/L and sodium metasilicate pentahydrate (Na2SiO3·5H2O, Sigma Aldrich, St. Louis, MO, USA) = 2 g/L. The process was conducted at 30 ◦C; in a water-cooled glass vial for 15 min. The examined alloy served as a working electrode and a stainless-steel sheet served as a counter electrode. The anodic current density was set at 0.05 A/cm2 and the applied voltage was 250 V, with the duty cycle 50% and symmetrical anode/cathode pulse. Electrical parameters of the process were recorded by Scope Meter 199C, 200 MHz, 2.5 GS s−<sup>1</sup> (Fluke, Everett, WA, USA).


