*3.3. Phase Analysis*

The XRD pattern of the alloy Ti-6Al-4V surface after MAO treatment is shown in Figure 4.

XRD investigation evaluated the presence of the following phases in the obtained oxide-based coating: titanium dioxide in the form of rutile [28] and intermetallic of Al0.3Ti1.7 [29]. They were expected to be formed in the coating, rutile due to the oxidation process and Ti/Al intermetallic resulting in the noticeable presence of Al in the alloy. XRD measurements evaluated that no new phase was formed during the process and no impurities were detected in the coating.

The cross section line scan and the microstructure of the Ti-6Al-4V alloy treated by MAO are shown in Figure 5.

**Figure 4.** X-ray diffraction pattern of the alloy Ti-6Al-4V surfaces after MAO treatment.

**Figure 5.** EDS line scan of the alloy Ti-6Al-4V after MAO treatment (**a**) and its cross section microphotograph obtained by SEM (**b**). Arrow indicates the direction of the EDS line scan analysis. Points in images attributed to: 1—base alloy; 2—oxide layer; 3—resin.

SEM micrograph, jointly with the EDS line scan, indicated that the obtained oxide layer is uniform and its thickness is about 2.5 μm. Moreover, the elemental analysis detected only components that fit the composition of the expected oxide layer and no additional impurities. Usually, impurities are detected in the coating after the process that is carried out in the aqueous electrolyte. Aliasghari et al. detected the presence of phosphorous in the coating formed on Ti by the MAO process in an electrolyte containing phosphoric acid [30].
