Fine structure features of Ni-Al coatings obtained by high velocity atmospheric plasma spraying

Vol. 26 No. 3 2024 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.

OBRABOTKAMETALLOV Vol. 26 No. 3 2024 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Aff airs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary

Vol. 26 No. 3 2024 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Sukhov A.V., Sundukov S.K., Fatyukhin D.S. Assembly of threaded and adhesive-threaded joints with the application of ultrasonic vibrations...................................................................................................................................... 6 Baraboshkin K.A., Adigamov R.R., Yusupov V.S., Kozhevnikova I.A., Karlina A.I. Thermomechanical rolling in well casing production (research review)......................................................................................................................... 24 Dwivedi R., Somatkar A., Chinchanikar S. Modeling and optimization of roller burnishing of Al6061-T6 process for minimum surface roughness, better microhardness and roundness................................................................................ 52 Ilinykh A.S., Pikalov A.S., Miloradovich V.K., Galay M.S. Experimental studies of rail grinding modes using a new high-speed electric drive...................................................................................................................................................... 66 Karlina Yu.I., Konyukhov V.Yu., Oparina T.A. Assessment of the possibility of resistance butt welding of pipes made of heat-resistant steel 0.15C-5Cr-Mo................................................................................................................................... 79 Gimadeev M.R., Stelmakov V.A., Shelenok E.A. Product life cycle: machining processes monitoring and vibroacoustic signals fi lterings.................................................................................................................................................................... 94 EQUIPMENT. INSTRUMENTS Zakovorotny V.L., Gvindjiliya V.E., Kislov K.V. Information properties of frequency characteristics of dynamic cutting systems in the diagnosis of tool wear....................................................................................................................... 114 Ablyaz T.R., Blokhin V.B., Shlykov E.S., Muratov K.R., Osinnikov I.V. Features of the use of tool electrodes manufactured by additive technologies in electrical discharge machining of products....................................................... 135 Sidorov E.A., GrinenkoA.V., ChumaevskyA.V., Panfi lovA.O., Knyazhev E.O., NikolaevaA.V., CheremnovA.M., Rubtsov V.E., Utyaganova V.R., Osipovich K.S., Kolubaev E.A. Patterns of reverse-polarity plasma torches wear during cutting of thick rolled sheets..................................................................................................................................... 149 MATERIAL SCIENCE Semin V.O., Panfi lov A.O., Utyaganova V.R., Vorontsov A.V., Zykova A.P. Corrosion properties of CuAl9Mn2/ER 321 composites formed by dual-wire-feed electron beam additive manufacturing................................ 163 Dewangan R., Sharma B.P., Sharma S.S. Investigation of hardness behavior in aluminum matrix composites reinforced with coconut shell ash and red mud using Taguchi analysis............................................................................ 179 Saprykina N.А., Saprykin A.А., Sharkeev Y.P., Ibragimov E.А. The eff ect of technological parameters on the microstructure and properties of the AlSiMg alloy obtained by selective laser melting......................................................... 192 Burdilov A.A., Dovzhenko G.D., Bataev I.A., Bataev A.A. Methods of synchrotron radiation monochromatization (research review).................................................................................................................................................................. 208 Burkov A.A., Dvornik M.A., Kulik M.A., Bytsura A.Yu. Wear resistance and corrosion behavior of Cu-Ti coatings in SBF solution..................................................................................................................................................................... 234 Pugacheva N.B., Bykova T.M., Sirosh V.A., MakarovA.V. Structural features and tribological properties of multilayer high-temperature plasma coatings........................................................................................................................................ 250 Sharma B.P., Dewangan R., Sharma S.S. Characterizing the mechanical behavior of eco-friendly hybrid polymer composites with jute and Sida cordifolia fi bers.................................................................................................................... 267 Kornienko E.E., Gulyaev I.P., Smirnov A.I., Plotnikova N.V., Kuzmin V.I., Golovakhin V., Tambovtsev A.S., Tyryshkin P.A., Sergachev D.V. Fine structure features of Ni-Al coatings obtained by high velocity atmospheric plasma spraying.................................................................................................................................................................... 286 EDITORIALMATERIALS 298 FOUNDERS MATERIALS 307 CONTENTS

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Fine structure features of Ni-Al coatings obtained by high velocity atmospheric plasma spraying Elena Kornienko 1, а, *, Igor Gulyaev 2, b, Alexandr Smirnov 1, c, Natalya Plotnikova 1, d, Viktor Kuzmin 2, e, Valeriy Golovakhin 1, f, Alexandr Tambovtsev 2, g, Pavel Tyryshkin 2, h, Dmitry Sergachev 2, i 1 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation 2 Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, 4/1 Institutskaya str., Novosibirsk, 630090, Russian Federation a https://orcid.org/0000-0002-5874-5422, e.kornienko@corp.nstu.ru; b https://orcid.org/0000-0001-5186-6793, gulyaev@itam.nsc.ru; c https://orcid.org/0000-0003-3746-8793, micros20t@mail.ru; d https://orcid.org/0000-0002-8005-1128, n.plotnikova@corp.nstu.ru; e https://orcid.org/0000-0002-9951-7821, vikuzmin57@mail.ru; f https://orcid.org/0000-0003-3396-8491, golovaxin-valera@mail.ru; g https://orcid.org/0000-0003-1635-9352, alsetams@gmail.com; h https://orcid.org/0009-0009-8125-6772, pavel99730@gmail.com; i https://orcid.org/0000-0003-2469-5946, dsergachev@itam.nsc.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2024 vol. 26 no. 3 pp. 286–297 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.3-286-297 ART I CLE I NFO Article history: Received: 14 June 2024 Revised: 14 July 2024 Accepted: 07 August 2024 Available online: 15 September 2024 Keywords: High velocity atmospheric plasma spraying Coating Ni-Al HV-APS Funding The work was carried out within the framework of the state assignment of ITAM SB RAS. Acknowledgements The research was carried out on the equipment of the Collective Use Center “Structure, Mechanical and Physical Properties of Materials”. ABSTRACT Introduction. Development of Ni-Al intermetallic compounds is one of the priority directions of modern machine building. Due to such characteristics as high heat resistance, high temperature strength, and low density, nickel aluminides are used as functional coatings in the aerospace industry. The main methods of Ni-Al coating surfacing are High-Velocity Oxygen-Fuel and High-Velocity Air-Fuel spraying (HVOF and HVAF), atmospheric plasma spraying (APS) and its modification such as High-Velocity Atmospheric Plasma spraying (HV-APS) which provides non-equilibrium cooling conditions. Since there are eight different intermetallic compounds, as well as martensite transformation, Ni-Al coatings is quite interesting to study. The work purpose is to study the features of the martensitic structure in HV-APS coatings, and also to establish the effect of heating temperature on its decomposition. Materials and methods. Ni-Al coatings were surfaced onto a low-carbon steel substrate using the HV-APS method. Studies of the fine structure of the coatings were carried out using transmission electron microscopy (TEM). In addition, the influence heating temperature on structural transformations of the coatings was analyzed. Results and discussion. Two types of particles are formed in HV-APS coatings: with a dendritic and granular structure. The most part of HV-APS coatings consists of particles with a two-phase grain structure (NiхAl1-х and γ’-Ni3Al grains). Only NiхAl1-x grains undergo martensitic transformation at cooling. Martensite in large grains (sizes greater than 500 nm) has a lamellar structure, while small grains are completely transformed into one martensite plate. In addition, the coatings contain grains in which martensite plates (NiхAl1-х) and β-phases alternated. It is shown the behavior of martensitic plates at colliding with each other, as well as with the γ′-Ni3Al grain. Heating up to 400 °C contribute the begins of martensite decomposition in individual grains with the release of a secondary phase; after heating up to 600 °C all martensite dissolves. For citation: Kornienko E.E., Gulyaev I.P., Smirnov A.I., Plotnikova N.V., Kuzmin V.I., Golovakhin V., Tambovtsev A.S., Tyryshkin P.A., Sergachev D.V. Fine structure features of Ni-Al coatings obtained by high velocity atmospheric plasma spraying. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 3, pp. 286–297. DOI: 10.17212/19946309-2024-26.3-286-297. (In Russian). ______ * Corresponding author Kornienko Elena E., Ph.D. (Engineering), Associate Professor Novosibirsk State Technical University, 20 Prospekt K. Marksa, 630073, Novosibirsk, Russian Federation Tel.: +7 383 346-53-59, e-mail: e.kornienko@corp.nstu.ru

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Introduction Nowadays, intermetallic materials design for structural purposes is one of the priority areas for the development of modern mechanical engineering. Due to the combination of characteristics such as high heat resistance and thermal conductivity, the ability to maintain strength and rigidity at high temperatures and relatively low density [1–3], nickel aluminides are used as materials for components of aircraft engines, gas turbines and heat exchangers [4–6]. It is vital that Ni-Al system alloys, being high-temperature materials, have low ductility and fracture toughness at room temperature [6] and this limits its use as bulk parts. In turn, one of the solutions to this problem is the use of nickel aluminides as functional coatings. In general, the main methods of applying Ni-Al coatings are high-velocity oxygen-fuel spraying (HVOF) [7–9], highvelocity air-fuel spraying (HVAF) [9, 10], atmospheric plasma spraying (APS) [11–14] and also its modification such as high-velocity atmospheric plasma spraying (HV-APS). There are eight stable and metastable intermetallic compounds in the Ni-Al system [15], the most promising of which are aluminides located in the nickel-rich part of the phase diagram, such as γ΄-Ni3Al and β-NiAl (Fig. 1) [3, 16, 17]. β-NiAl solid solutions have a wide range of homogeneity (43–70 at. % Ni at 1,400 °C), which decreases to 45–60 at. % Ni at a room temperature [3, 16]. Cooling of the β-phase in the range of high Ni concentrations is accompanied by the formation of a mixture of β- and γ΄-phases, while grains of the β-NiAl phase often have different chemical compositions. The martensitic transformation B2 → L10 occurs in β-phase crystals containing more than 62.3 at. % Ni. The onset temperature of this transformation (Ms) varies, according to various sources, from −200 to ~ 650 or 900 °C [17–19] depending on the Ni concentration. Subsequent heating of alloys from 62.5–68.0 at. % Ni promotes the separation of the Ni5Al3 phase or the metastable Ni2Al phase [20–22]. As a rule, coatings with a similar composition are often used as a bonding layer between the base material and a ceramic heat-shielding coating (YSZ) [23]. Chen et al. [24] discovered that the martensitic transformation occurring in the metal sublayer can cause the destruction of the ceramic coating due to changes in volume during the transformation of the β-phase into martensite. Thus, the study of the structural-phase state, as well as the understanding of structural transformations are priority tasks in the Ni-Al coatings design, since both functional and mechanical, as well as technological properties will depend on this. The purpose of this work is to study the features of the martensitic structure of Ni-Al coatings obtained by the HV-APS method. To achieve this purpose, the following tasks were solved: • study of the coatings structure; • study of the features of the martensitic structure depending on the grain size; • study of the behavior of martensitic plates when colliding with other structural components; • study of the influence of heating temperature on the structure of the coatings. Materials and methods Ni-Al coatings 500–600 µm thick were spraying on discs from low carbon steel with a diameter of 20 mm and a thickness of 8 mm. The particle size of powder was 40–100 µm, chemical composition was 75 at. % Ni and 25 at. % Al. To apply the coatings, we used the Termoplasma 50 plasma spraying installation, Fig. 1. Part of Ni-Al phase diagram

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 equipped with an HV-APS plasma torch. The supersonic spraying mode using air as the working gas ensures the speed of the sprayed particles at a level of 500 m/s and higher. Optimal modes for high-velocity spraying Ni-Al powder are presented in our previous work [25]. To analyze the structural state of the coatings, a scanning electron microscope (Carl Zeiss EVO50 XVP with an EDS X-Act microanalyzer) and a transmission electron microscope (FEI Tecnai G2 20 TWIN) were used. Transverse sections of coatings were the samples for SEM as well as foils, cut from the middle of the coatings, were the samples for TEM. Ni-Al coatings were kept for 1 hour at temperatures of 300, 400, 500 and 600 °C (air cooling) to study the structural transformations that occur upon heating. Results and discussion Previously, we have shown that HV-APS coatings are characterized by the presence of several zones that differ in structure [25]. Fig. 2 shows SEM image and scheme of the microstructure of the HV-APS coating in the initial state. The chemical composition of all areas was determined using micro-X-ray spectral analysis. According to the data obtained, there are particles, the central part of which is the β-NiAl intermetallic compound (section 1 in Fig. 2), surrounded by a single-phase layer of the β-NiAl phase enriched in Ni (referred to as the NixAl1-x phase) (section 2 in Fig. 2). The structure of section 3 in Fig. 2 is dendritic: the chemical composition of the dendrites coincides with the composition of the layer (section 2), and the chemical composition of the interdendritic space corresponds to theγ’-Ni3Al phase. We considered the fine structure of these areas more thoroughly in our work [25]. As a rule, the particles with a similar structure are not common for HV-APS coatings. Predominant particles are particles with two-phase structure consisting of NixAl1-x and γ’-Ni3Al grains (section B in fig. 2). Fig. 3 shows TEM images of section 4. It can be seen that NixAl1-x grains undergo a shear martensitic transformation, during which the high-temperature B2 structure transforms into the low-temperature L10 structure, while the γ΄-Ni3Al grains do not change. There are also one-phase areas consisting only of grains of the γ΄-Ni3Al phase (fig. 3, b). The shape of the grains in section 4 is non-equiaxial, which is typical for material cooled under non-equilibrium conditions. The grain sizes usually do not exceed 500 nm, although sometimes larger γ΄-Ni3Al grains are formed. Such grains often have deformation twins (Fig. 3, c) and stacking faults (Fig. 3, d). a b Fig. 2. SEM image (a) and scheme (b) of HV-APS coatings: 1 – β-NiAl phase; 2 – layer of NiхAl1-х; 3 – area with dendritic structure: NiхAl1-х dendrites, interdendritic region (γ′-Ni3Al phase); 4 – area with grain structure: both NiхAl1-х and Ni3Al grains

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Martensite in HV-APS coatings is lamellar (Fig. 4), but depending on the size of the grains in which the transformation occurs, it looks different. For example, martensite formed in large NixAl1-x grains consists of plates located in a twinned orientation relative to each other (Fig. 4, a). The distance between microtwins may be from 0.5 nm (Fig. 4, b) to several nanometers (fig. 4, a). The martensite-martensite interface can be located both inside the former NixAl1-x grain and outside it (Fig. 4, c). Unlike large grains (greater than 500 nm), fine grains completely transform into one microtwinning plate (Fig. 4, d). Sometimes there are martensitic grains in which, even with the use of a dark field, it is not possible to detect microtwins in pairs of parallel plates, and these plates appear to be single crystals (Fig. 5). According to data of local chemical analysis, adjacent plates have different chemical compositions. The Ni content in plates with microtwins (type 1) is 77.4 at. %, which corresponds to the NixAl1-x phase, while the Ni content in plates without microtwins (type 2) is 52.5 at. %, which corresponds to the β-phase. Martensite plates can behave differently when collide with each other or with other phases. For example, growth of individual thin plates growing in different directions often does not stop. These plates pass through each other and only the area of its intersection is rearranged (Fig. 4, a). Fig. 6, a, b shows that when a martensitic plate collides with a γ΄-Ni3Al grain, it does not penetrate into it, but continues to transform. On the other hand, Fig. 6, c shows martensitic plates that seem to have grown inside the γ΄-Ni3Al grain. Apparently, in this case, the NixAl1-x plates appeared first, around which the γ΄-Ni3Al phase later formed. Some plates change the direction of its growth, deviating to the side at collision with obstacle (Fig. 6, d). Deformation and elastic distortions occur in areas near curved plates, which contrast is visible near the bend. Fig. 3. Bright field TEM images of HV-APS coatings: a – two-phase area of NiхAl1-х + γ΄-Ni3Al; b – one-phase area of γ΄-Ni3Al; c) twins in γ΄-Ni3Al; d – stacking faults in γ΄-Ni3Al with diffraction pattern а b c d

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 a b Fig. 5. TEM image of martensite with different types of plates: a – bright field image; b – dark field image Fig. 4. Bright field TEM images of martensite: a–c – lamellar martensite in coarse grains of NiхAl1-х; d – lamellar martensite in fine grains of NiхAl1-х а b c d

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Fig. 6. Interaction of martensite with other phases: a, b – collision of martensite plate with grain γ΄-Ni3Al; c – growth of martensite plates into grain; d – martensite plate deformation; a, c, d – bright field; b – dark field а b c d It was shown above that the temperature of martensitic transformation in Ni-Al alloys is determined by the chemical composition of the material. Coating heating at 400–600 °C allows obtaining information about structural changes in the material. We do not observe any noticeable changes at lower heating temperatures. Fig. 7 demonstrates TEM images of the microstructure of HV-APS coatings after heating at 400 and 500 °C. According to structural studies, the beginning of the reverse transition of L10 martensite to the B2 structure is observed at 400 °C. In addition, a secondary phase in the form of elongated disks segregates along the boundaries of microtwins (Fig. 7, a). In some cases, only part of the martensite plate undergoes transformation. This can be explained by differences in the chemical composition within the same crystal. An increase in temperature to 500 °C leads to further decomposition of martensite plates and the growth of an already precipitated secondary phase (Fig. 7, b). The secondary phase in grains, where martensite has completely transformed, is oriented in one direction. The formation of the secondary phase is characteristic only for NixAl1-x grains and is absent in grains of the γ΄-Ni3Al phase (Fig. 7, b) and β-NiAl plates (fig. 7, c). The internal structure of β-NiAl plates is characterized by a relatively uniform distribution of dislocations. Finally, heating to these temperatures does not lead to any noticeable structural changes in small grains of the NixAl1-x phase (fig. 7, d). A significant increase in the width of grain boundaries is observed in two-phase regions after heating at 600 °C (Fig. 8, a, b). The shape of the γ′-Ni3Al and NixAl1-x grains approaches equiaxial, which indicates the occurrence of recrystallization processes. A growth of the secondary phase with increasing temperature

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Fig. 7. Bright field images of coating structure after heating 400 (a, c, d) and 500 °С (b) а b c d is not observed. The structure also contains martensite crystals in which the L10 → B2 transformation has completely occurred. Fig. 8, c, d shows bright-field and dark-field images of former martensite plates. Data of dark-field analysis confirms the presence of the secondary phase in former martensite plates, the chemical composition of which corresponds to the NixAl1-x phase (Fig. 8, d). The completely transformed plates are separated from each other by low-angle boundaries. Conclusions There are two types of particles in HV-APS coatings: with a dendritic and grain structure. The center of particles with a dendritic structure consists of the β-NiAl phase surrounded by a one-phase layer of the NixAl1-x phase and a layer of dendrites (NixAl1-x) with interdendritic space (γ’-Ni3Al). Most of the coatings are particles with a grain structure (NiхAl1-x and γ’-Ni3Al grains). Only NixAl1-x grains experience martensitic transformation when the particles are cooled. In the large grains, larger than 500 nm, martensite consists of plates in a twinned orientation relative to each other, while small grains are completely transformed into one microtwinning plate. In addition, there are grains in which martensite and β-phase plates alternated. The collision behavior of martensitic plates is different. Thin plates at collision pass through each other and only the area of its intersection is rearranged. When a martensitic plate collides with an already formed γ΄-Ni3Al grain, the plate continues to transform without penetration. If martensitic plates were formed first, the γ΄-Ni3Al phase is formed around it. In addition, thin plates at collision with an obstacle can be deflected.

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 When heated to 400 °C in large grains of NixAl1-x, the beginning of the reverse transition of L10 martensite to B2 structure with the secondary phase formation along microtwins is observed. No changes are observed in small grains of the NixAl1-x phase, γ΄-Ni3Al grains and β-NiAl plates. After heating to 600 °C, the shape of the γ’-Ni3Al and NixAl1-x grains approaches equiaxial, which indicates the occurrence of recrystallization processes. The secondary phase is oriented in one direction in NixAl1-x grains. The martensite crystals in large grains are completely transformed into the B2 structure, although it retained its orientation. References 1. Bochenek K., Basista M. Advances in processing of NiAl intermetallic alloys and composites for high temperature aerospace applications. Progress in Aerospace Sciences, 2015, vol. 79, pp. 136–146. DOI: 10.1016/j.paerosci.2015.09.003. 2. Müller M., Enghardt S., Kuczyk M., Riede M., López E., Brueckner F., Marquardt A., Leyens C. Microstructure of NiAl-Ta-Cr in situ alloyed by induction-assisted laser-based directed energy deposition. Materials & Design, 2024, vol. 238, p. 112667. DOI: 10.1016/j.matdes.2024.112667. 3. Zhou L., Mehta A., Cho K., Sohn Y. Composition-dependent interdiffusion coefficient, reduced elastic modulus and hardness in γ-, γ′- and β-phases in the Ni-Al system. Journal of Alloys and Compounds, 2017, vol. 727, pp. 153–162. DOI: 10.1016/j.jallcom.2017.07.256. 4. Darolia R. Ductility and fracture toughness issues related to implementation of NiAl for gas turbine applications. Intermetallics, 2000, vol. 8 (9–11), pp. 1321–1327. DOI: 10.1016/S0966-9795(00)00081-9. Fig. 8. TEM images of coating structure after heating 600 °С: a, b – two-phase area; c, d – prior martensite plates; a, b, c – bright field; d – dark field а b c d

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OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 24. Chen M.W., Glynn M.L., Ott R.T., Hufnagel T.C., Hemker K.J. Characterization and modeling of a martensitic transformation in a platinum modified diffusion aluminide bond coat for thermal barrier coatings. Acta Materialia, 2003, vol. 51, pp. 4279–4294. DOI: 10.1016/S1359-6454(03)00255-6. 25. Kornienko E., Gulyaev I., Smirnov A., Nikulina A., Ructuev A., Kuzmin V., Tuezov A. Microstructure and properties of Ni-Al coatings obtained by conventional and high-velocity atmospheric plasma spraying. Results in Surfaces and Interfaces, 2022, vol. 6, p. 100038. DOI: 10.1016/j.rsurfi.2022.100038. Conflicts of Interest The authors declare no conflict of interest.  2024 The Authors. Published by Novosibirsk State Technical University. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0).

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