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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were independent on the employing US and were following: O (66- 70 аt.%); P (14 -16 at.%); Ti (11- 13 аt.%); Ca (4 5 аt.%). It can be due to the fact that US vibrations improved the mass transport of al l elements in the electrolyte and their number increased in the coating, but the percentage ratio remained unchanged. The low content of precipitated Ca (4- 5 аt.%) led to the low atomic Ca/P ratio equaled to 0.3. Thus, both MAO and UMAO coatings are calciu m deficient. However, Qu et. al (2013) showed that employing the US led to the increase of the Ca/P ratio from 0.2 to 0.4. Previously, X-ray diffraction (XRD) studies revealed that the MAO coatings were in the quasi-amorphous state (Komarova et.al., 2019). At the same time, the UMAO coatings contained an amorphous phase and a small amount (≤ 6 vol. %) of microcrystalline phases of monetite (CaHPO 4 ) and β - calcium pyrophosphate (β -Ca 2 P 2 O 7 ). For those phases, the Ca/P ratio was equal to 1.0. The amorphous phase can be represented by the CaP substance containing Ti cations. The bright field (BF) and dark field (DF) TEM images with SAED patterns of fragments of both the MAO and UMAO coatings are shown in Fig. 3. The low contrasting BF TEM micrographs reveal the absence of phase separation as well as homogeneous amorphous microstructure of all the coatings (Fig. 3 a, d, g). It is confirmed by the SAED patterns consisting of both blurred diffuse halo which belongs to short-range ordering structure and reflexes which belong to the different crystals (Fig. 3 b, e, h). The interpretation of the SAED patterns reveals the complex polyphase composition with the following crystalline phases: CaHPO 4 with the triclinic lattice (ICDD #00-009- 0080), β -Ca 2 P 2 O 7 with the tetragonal lattice (ICDD #00-009-0346), TiO 2 (anatase) with the tetragonal lattice (ICDD #00-021-1272). At the same time, these phases and an additional high- temperature (>1170°С) metastable phase α -Ca 2 P 2 O 7 (ICDD #00-009-0345) were detected in the UMAO coatings. This may be due to the local increase in the temperature of the phase formation in the channels of micro-discharges under the action of the ultrasonic field. The DF TEM images show a predominantly low contrasting homogeneous amorphous microstructure, including individual nano- crystallites (≤ 100 nm) at the external boundaries of the coating s’ particles (Fig. 3 c, f, i). The equiaxial crystallites in (̅112) reflection of the CaHPO 4 phase, crystallites in (150) and (002) reflections of the α -Ca 2 P 2 O 7 phase are observed in the BF TEM images. The TiO 2 anatase reflexes observed on SAED patterns corresponded to the internal oxide sublayer in the interface between the CaP coating and the Ti substrate. These results are in the good agreement with the previous XRD data (Komarova et.al., 2019). 4. Conclusion The influence of the employing US with different powers and sinewaves during the MAO on the formation of the elemental composition and the microstructure of the CaP coatings was studied. It was shown that the quantitative elemental composition of the coatings did not change under the employing US and was as follows: O (66- 70 аt.%); P (14-16 at.%); Ti (11- 13 аt.%); Ca (4 - 5 аt.%). The TEM revealed the amorphous-crystalline microstructure in the coatings regardless of the application of US during the MAO. The nano- crystallites of the CаHPO 4 , β - Cа 2 P 2 O 7 , and TiO 2 (anatase) were observed in the coatings. In addition to these phases, a high- temperature metastable phase α - Ca 2 P 2 O 7 was detected in the UMAO coatings. The elemental composition and the microstructure of the UMAO coatings did not depend on the US power (35 W and 100 W) and waveform (sine, pulsed). Acknowledgements The work has been financially supported by the Russian Science Foundation (Project No. 21-73-10265). References Jian, S.Y., Aktug, S. L., Huang, H. T., Ho, C. J., Lin, S.Y., Chen, C.H., Wang, M.W., Tseng, C.C., 2021. The potential of calcium/phosphate containing MAO implanted in bone tissue regeneration and biological characteristics. International Journal of Molecular Sciences 22(9), 4706 doi:10.3390/ijms22094706 Kazantseva, E. A., Komarova, E. G., Sharkeev, Yu. P., 2019. Effect of ultrasound during micro-arc oxidation on the porous ptructure and adhesion strength of the calcium phosphate coatings. AIP Conference Proceedings 2067, 020155. doi: 10.1063/1.5132022 Komarova, E.G., Kazantseva, E.A., Sedelnikova, M.B., Sharkeev, Yu.P., 2019. Influence of ultrasonic field during micro-arc oxidation on the structure and properties of calcium phosphate coatings. IOP Journal of Physics: Conference Series 1393, 012098. doi: 10.1088/1742 6596/1393/1/012098