Bortnytska M. Formation regularities and properties of ion-plasma coatings based on MAX phases

Bortnytska M.O. Formation regularities and properties of ion-plasma coatings based on MAX phases - Qualification scientific work on the rights of manuscript. Dissertation for the degree of Doctor of Philosophy in specialty 104 - Physics and Astronomy (Field of Knowledge 10 - Natural Sciences) - National Research Center "Kharkiv Institute of Physics and Technology" of the National Academy of Sciences of Ukraine, Kharkiv, 2024. Surface modification technologies are widely used as an effective way to improve the complex characteristics of materials. MAX phases, which combine the properties of ceramics and metals due to their special nanolayered structure and combined type of bonding, are a promising material for multifunctional coatings resistant to high-temperature oxidation, corrosion, wear, irradiation, etc. However, the high synthesis temperatures of MAX phases are an important obstacle to their widespread use. Application of ion-plasma methods of physical deposition can significantly reduce the synthesis temperature due to the high energy of the particles that form the coating. Therefore, it is important to develop simple and economical processes for the synthesis of coatings using a multicomponent cathode that provides MAX phase stoichiometry. The presented thesis is aimed at studying the regularities of the structure formation of ion-plasma coatings deposited from cathodes based on MAX phases of the Ti-Al-C system and establishing the relationship between the parameters of their synthesis, chemical composition, structure and physical and mechanical properties. For the first time, comprehensive comparative studies of the composition, structure and properties of coatings deposited by different ion-plasma methods from cathodes based on MAX phases of the Ti-Al-C system, which were made by hot pressing powder mixtures, were carried out. The processes of deposition of high-quality coatings up to 10 μm thick on technologically significant substrates by the following methods were worked out: ion sputtering using an arc gas plasma source, vacuum arc deposition, and magnetron sputtering. X-ray fluorescence analysis, scanning electron microscopy with an X-ray energy dispersive microanalysis system, Auger spectroscopy, and X-ray diffraction analysis were used to study the composition and structure of cathodes and deposited coatings. The following material properties were determined: nanohardness and Young's modulus, wear resistance and cavitation resistance, fretting fatigue resistance, oxidation resistance and electrical conductivity. It has been shown that the MAX phase of Ti2AlC belongs to the hard-to-spray materials. The sputtering coefficient of a target based on Ti2AlC with Ar+ ions is 1.5 times lower than that of titanium targets and decreases from 0.7 to 0.2 atoms/ion when the ion energy decreases from 1200 to 400 eV. As a result of bombardment with Ar+ ions, phase transformations occur on the target surface associated with the decay of the MAX phase and selective sputtering of light elements. It has been established that when using a cathode (target) based on the MAX phase of Ti2AlC, magnetron coatings have a chemical composition close to that of the cathode and a columnar nanostructure regardless of the discharge power in the range of 600-2800 W. The elemental composition of ionic and vacuum-arc coatings at a substrate potential of 50 V also practically corresponds to the cathode composition, but with an increase in potential to 100-200 V, the relative aluminium content in the coatings drops sharply due to selective sputtering. The main phase in such coatings is a solid solution of aluminium in the TiC crystal lattice, which has a cubic structure such as NaCl, due to the low temperature of the substrate (≤ 450℃), the mismatch of stoichiometry and the low energy of the particles forming the coating. It has been found that the formation of the MAX phases Ti2AlC and Ti3AlC2 in vacuum-arc coatings is facilitated by the use of a cathode with a high aluminium content and an increase in the power of ion bombardment of the growth surface with heavy ions, which is achieved by introducing argon into the vacuum chamber and/or doping the cathode material with niobium (replacing 10-20 at.% Ti). No increase in the MAX phase content was observed when the cathode material was alloyed with tin (replacing up to 50 at% Al). In the case of alloying with both elements, tin suppresses the effect of niobium on increasing the content of the MAX phase and stabilises the structure of TiC carbide. It has been found that the vacuum-arc coating Ti0.65Al0.07C0.28 with a two-phase structure of solid solutions based on TiC+(α-Ti) has a wear resistance and cavitation resistance 1.5-2 times higher than the widely used TiN coating. With a friction coefficient of 0.5-0.6, the specific wear rate of the Ti0.65Al0.07C0.28 coating is 1.26 × 10-4 mm3/Nm at room temperature and decreases to 7.18 × 10-5 mm3/Nm at 500°C.