PSI - Issue 40

Ekaterina A. Kazantseva et al. / Procedia Structural Integrity 40 (2022) 207–213 Kazantseva E.A. and Komarova E.G. / Structural Integrity Procedia 00 (2022) 000 – 000

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methods, micro-arc oxidation (MAO) is a prominent surface treatment for the formation of bioceramic-coating layers with beneficial physical, chemical, and biological properties on the metal substrates (Jian et.al., 2021). The structure and properties of MAO coatings can be widely controlled by adjusting process parameters such as applied voltage, frequency, processing time, and electrolyte composition. Recently, ultrasound (US) field has been employed during the MAO as an assist technique to regulate the morphological and structural features of the resultant MAO coating, which may also enhance its performance (Zhang et.al., 2021). Qu et.al. (2013) showed that the US improved the homogeneous distribution of micro-porous structure of MAO coatings, but did not change the phase composition of coatings. The effects of US on the morphology, phase composition, wear resistance and corrosion properties of the MAO coatings on Ti-6Al-4V alloy have been observed by Xie et.al. (2018), which is reported to be closely associated with the US parameters as well as electrolytic components. The influence of US vibration on the uniformity, microstructural feature, corrosion resistance, and in vitro biological properties of Cu-incorporated CaP/TiO 2 coatings were studied by Zhang et.al. (2021). It was shown, that the introduction of US vibration enhances the corrosion resistance, antibacterial capability, and cellular response of the Cu-incorporated CaP/TiO 2 coatings. In our previous works (Komarova et.al., 2019, and Kazantseva et.al., 2019), it was shown that the employing the US during the MAO led to the change of the surface and inner morphology of the coatings, to the increase of the coating’s thickness, roughness, and inner porosity, and to the decrease of the surface porosity. In addition, the applied US led to the coating’s structure transformation from the quasi -amorphous state to the amorphous-crystalline state. In this work, we continue those investigations and plan to study the elemental composition and the microstructure of the US-assisted MAO (UMAO) coatings. In this regard, the purpose of the work was to study the influence of the employing US with different powers and waveforms during the MAO on the formation of the elemental composition and the microstructure of the CaP coatings. 2. Materials and methods The sheet of commercially pure titanium (ASTM Grade 2) was cut into samples with the size of 10×10×1 mm 3 . Preliminary preparation of samples included mechanically polished using 120 – 1000 grit SiC abrasive papers; cleaning in the ultrasonic bath in distilled water and then in pure ethanol; air drying. MAO was carried out in pulsed anodic regime using the Micro-Arc 3.0 installation consisting of a pulsed DC power supply, titanium electrolytic bath as cathode, sample holder as anode, and PC for process control. In order to synthesize the CaP coatings, the electrolyte contained 5 wt.% of nano-sized Ca 10 (PO 4 ) 6 (OH) 2 , 7 wt.% of CaCO 3 , 27 wt.% of H 3 PO 4 , and distilled water as a balance (Komarova et.al., 2019, and Kazantseva et.al., 2019). The applied voltage, pulse duration, frequency, and oxidizing time were set to be 200 V, 100 μs, 50 Hz, and 10 min, respectively. In order to employ US during the MAO process, the electrolytic bath was supplemented with US devices generated pulsed or sinewave US current. The UMAO process carried out in three regimes: (i) control MAO without US; (ii) MAO with pulsed US (MAO/PUS) (P = 35 W, υ = 35 kHz); (iii) MAO with sinewave US (MAO/US) (P = 100 W, υ = 35 kHz). The surface and cross-sectional morphology of the coatings was analysed by scanning electron microscopy (SEM, Zeiss LEO EVO 50). Elemental composition was examined using electron dispersive X-ray spectroscopy (EDX) on the INCA system coupled to the SEM. Before SEM analysis, a thin layer of Cu was deposited on the samples with the dielectric CaP coatings. The deposited film provided sufficient electrical conductivity of the samples surface layer, which is necessary to prevent the formation and accumulation of electric charge on its surface. Coatings’ microstructure was observed by transmission electron microscopy (TEM, JEM 2100, JEOL), operating at 200 kV. A replica with the particles of the CaP coatings removed from the substrate was studied by TEM. The analysis of selected area electron diffraction (SAED) patterns was performed using the International Centre for Diffraction Data (ICDD) database as references. The SEM, TEM, and EDX studies were conducted in the “Nanotech” Common Center for Collective Use (ISPMS SB RAS, Tomsk, Russia). 3. Results and discussion Fig. 1 represents the SEM images of the cross-sectional MAO and UMAO coatings with the EDX scan lines of the elements (O, P, Ti , Ca) distribution through the coating’s thickness. All the coatings are characterized by a complex hierarchically organized porous structure. Firstly, there is a very thin dense oxide sublayer at the interface