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Advanced structural materials, materials for extreme conditions УДК 669.245 DOI: 10.17277/jamt.2023.01.pp.070-082
The influence of ultrafine-grained structure on solid-state weldability and formability of precipitation-hardening nickel-based superalloys
© Elvina V. Galieva3^, Ekaterina Yu. Klassmana, Vener A. Valitova'b, Egor M. Stepukhov3,b, Radim R. Gabbasovb, Rinat V. Safiullina, Ramil Ya. Lutfullina,b
a Institute for Metals Superplasticity Problems of the RAS, 39, Khalturina St., Ufa, 450001, Russian Federation, Ufa University of Science and Technology, 32, Z. Validi Sr., Ufa, 450000, Russian Federation
И galieva_elvina_v@mail.ru
Abstract: The formation of an ultrafine-grained (UFG) structure of a mixed type in the EK61 superalloy provides the
manifestation of the low-temperature superplasticity effect. It can be successfully implemented in an innovative process of
pressure welding (PW) to obtain solid-state joints (SSJ) in a combination of EK61 and EP975 superalloys characterized by
different types of hardening phases. According to the energy-dispersive analysis resultsin the process of PW in vacuum
-4 -1
under low-temperature and rate superplasticity conditions (Т = 850 °С, s = 10 s ) the interdiiffusion of alloying elements occurs between the joined EK61 and EP975 superalloys. As a result of the interdiiffusion, a narrow transition zone of diffusion interaction is formed, the width of which is 3 ^m. The effect of heat treatment (HT) on the change in the phase composition in the SSJ and its strength in welded specimens in a combination of EK61//EP975 superalloys has been studied. It is shown that HT leads to expansion of the diffusion interaction zone by 4.6 times (3 to 14 ^m). According to the results of mechanical tensile tests at room temperature, it was found that the strength of welded samples after PW reaches a value of 0.8 of the strength of the EK61 superalloy being joined, and after the following HT it remains at the same level. The influence of the strain on the microstructure and microhardness changes of sheet blanks from the EK61 superalloy with a UFG structure subjected to superplastic forming (SPF) into a cylindrical matrix under low-temperature superplasticity conditions has been studied.
Keywords: nickel-based superalloys; ultrafine-grained structure; superplasticity; pressure welding; solid-state joint.
For citation: Galieva EV, Klassman EYu, Valitov VA, Stepukhov EM, Gabbasov RR, Safiullin RV, Lutfullin RYa. The influence of ultrafine-grained structure on solid-state weldability and formability of precipitation-hardening nickelbased superalloys. Journal of Advanced Materials and Technologies. 2023;8(1):070-082. D0I:10.17277/jamt.2023.01. pp.070-082
Влияние ультрамелкозернистой структуры на свариваемость в твердофазном состоянии и формуемость дисперсионно-твердеющих суперсплавов на основе никеля
© Э. В. ГалиевааИ, Е. Ю. Классмана, В. А. Валитова'Ь , Е. М. Степухова'Ь, Р. Р. ГаббасовЬ, Р. В. Сафиуллина, Р. Я. Лутфуллина'Ь
а Институт проблем сверхпластичности металлов РАН, ул. Ст. Халтурина, 39, Уфа, 450001, Российская Федерация, Уфимский университет науки и технологий, ул. З. Валиди, 32, Уфа, 450000, Российская Федерация
И galieva_elvina_v@mail.ru
Аннотация: Показано, что формирование в суперсплаве ЭК61 ультрамелкозернистой (УМЗ) структуры смешанного типа обеспечивает проявление эффекта низкотемпературной сверхпластичности, который может быть успешно реализован в инновационном технологическом процессе сварки давлением для получения
твердофазных соединений (ТФС) в сочетании суперсплавов ЭК61 и ЭП975, характеризующихся различным типом
упрочняющей фазы. По результатам энергодисперсионного анализа установлено, что в процессе сварки
давлением в вакууме в температурно-скоростных условиях низкотемпературной сверхпластичности (Т = 850 °С, -4 -1
s = 10 с ) между соединяемыми сплавами ЭК61 и ЭП975 в результате протекания процессов взаимной диффузии легирующих элементов формируется узкая переходная зона диффузионного взаимодействия, ширина которой составляет 3 мкм. Изучено влияние термической обработки на изменение фазового состава в зоне ТФС и его прочность в сварных образцах в сочетании суперсплавов ЭК61//ЭП975. Показано, что термическая обработка приводит к расширению зоны диффузионного взаимодействия в 4,6 раза (от 3 до 14 мкм). По результатам механических испытаний на растяжение при комнатной температуре установлено, что прочность сварных образцов после сварки давлением достигает величины 0,8 от прочности соединяемого сплава ЭК61, а после термической обработки сохраняется на том же уровне. Исследовано влияние степени деформации на изменение микроструктуры и микротвердости листовых заготовок из сплава ЭК61 с УМЗ структурой, подвергнутых формовке в цилиндрическую матрицу в условиях низкотемпературной сверхпластичности Установлено, что после сверхпластической формовки (СПФ) в модельных отформованных образцах сохраняется однородная равноосная УМЗ структура дуплексного типа, параметры которой и значения микротвердости сохраняются на одном уровне после различных степеней деформации при формовке.
Ключевые слова: никелевые сплавы; ультрамелкозернистая структура; сверхпластичность; сварка давлением; твердофазное соединение.
Для цитирования: Galieva EV, Klassman EYu, Valitov VA, Stepukhov EM, Gabbasov RR, Safiullin RV, Lutfullin RYa. The influence of ultrafine-grained structure on solid-state weldability and formability of precipitation-hardening nickel-based superalloys. Journal of Advanced Materials and Technologies. 2023;8(1):070-082. D01:10.17277/jamt. 2023.01.pp.070-082
1. Introduction
Superalloys (heat-resistant nickel alloys) are widely used for the manufacture of various parts of aircraft gas turbine engines: compressor and turbine disks, rotor and nozzle blades, and other parts [1-4]. At present, for modern and promising aircraft engine building, the problems of increasing the energy efficiency of gas turbine engines and the efficiency of their production are very relevant. The first problem of increasing the energy efficiency of a gas turbine engine can be solved not only by creating new compositions of high-temperature materials with improved characteristics of heat-resistant properties [1-4], but also by developing and implementing new technical solutions related to the use in the design of a gas turbine engine bimetallic parts, such as "blisk" and "disk-shaft" [4-8]. Another problem of increasing the efficiency of production of parts, including bimetallic ones, for gas turbine engines can be solved through the development and implementation of new resource-saving technologies based on the use of the superplasticity effect [8-13].
As is known [1-4], the achievement of the required level of heat resistance in complexly alloyed nickel-based superalloys is achieved by separating coherent particles of strengthening phases, such as Ni3Nb or Ni3(Al, Ti). It should be noted that the presence in the coarse-grained matrix (y-phase) of superalloys of a significant amount (the volume fraction of y'-phase is 55-60 %) of dispersed coherent particles of the strengthening Ni3(Al, Ti) phase leads
to a sharp decrease in their technological plasticity. Therefore, for the manufacture of parts from superalloys, it is advisable to use the promising technology of superplastic deformation [9, 10]. Its implementation can be achieved by obtaining in semi-finished products from superalloys a finegrained (1-10 ^m) or ultrafine-grained (UFG) structure of a duplex type (with a grain and phase size of less than 1 ^m), which is formed in the process of preliminary thermomechanical treatment (TMT) of such materials [9-11, 14-22].
It follows from the analysis of the scientific literature that various methods are used to obtain solid-state joints (SSJ) from metals and alloys, as well as nickel-based superalloys. In [23], using the example of Inconel 718 alloy, the efficiency of using inertial friction welding in welding with Inconel 718, Incoloy909, U720LI, Rene88DT alloys was shown. However, according to the results of the research, the authors showed that in the SSJ zones there are areas where the dissolution of the 5-phase and the Y '-phase particles occurred. The width of such a zone reaches 500 ^m, which leads to a decrease in hardness. When assessing the weldability of the EP742 alloy by the method of linear friction welding, the authors of [24] showed that macrodefects in the form of lack of penetration and discontinuities in the zone of the welded joint are not observed. At the same time, there are many pores along grain boundaries and in triple junctions, as well as chains of coarse carbide precipitates, leading to a decrease in the strength of
the welded joint and contributes to the initiation and development of cracks during welding.
The studies [25-27] were devoted to the effect of rotational friction welding and heat treatment on the properties of wrought nickel-based superalloys. Thus, it was shown in [25] that a high level of properties of welded joints of the VZh172 alloy with the EK79 alloy (0.80-0.96 of the strength of a less strong alloy) is achieved during welding both with subsequent complete heat treatment and in the heat-strengthened state. The work [27] is devoted to the study of weldability of homogeneous and dissimilar combinations of semi-finished products of high-temperature nickel alloy VZh159 by rotational friction welding.
The data presented in [28] are of interest. This paper provides an overview of the weldability of a wide range of nickel-based superalloys and aluminides. In another work [29], the features of the formation of diffusion bonding of heat-resistant alloys with each other and with structural steels, the issues of manufacturing technology for rotors of small-sized gas turbine engines and reinforcement of shroud shelves of aircraft engine blades are considered.
Of particular interest is the patented diffusion welding technology [30], which can be used to fabricate bimetallic structures consisting of a combination of stainless steel + titanium alloy or titanium alloy + nickel alloy materials in almost many industries. A feature of this method is that the welded bimetallic structures are made of materials that form intermetallic phases between themselves. An intermediate layer in the form of a porous tape of ultrafine metal powder (UFMP) was placed between the materials to be welded. Diffusion welding was carried out at a temperature of 0.85-0.9 of the temperature of formation of intermetallic phases of the metal of the intermediate layer with one of the welded materials and between the welded materials. The intermediate layer of UFMP minimizes the formation of intermetallic compounds, which avoids embrittlement of the diffusion joint while maintaining its tensile strength. In another method of diffusion welding [31], for the manufacture of parts from powder heat-resistant nickel alloys, after assembling the elements for welding, they are evacuated and heated to a temperature not exceeding the solvus temperature by more than 10 °C. A welding force of 1.5-2.5 kg-mm was applied with a holding time of 1.5-2 hours. Then the welding force was removed and the holding time was carried out for 2 hours.
The disadvantages of many well-known widely used methods, such as diffusion welding [6, 7, 28-33], are the duration of the process and high
homologous temperatures, which in many cases are close to pre-melting temperatures, at which the process of obtaining SSJ is carried out. The methods of inertial, linear and rotational friction welding [23-27] are characterized by intense deformation heating up to the melting of the materials being joined, which has a negative effect on the structure of the SSJ zone and its strength.
One of the most promising methods for producing bimetallic joints from hard-to-deform superalloys is pressure welding (PW) using superplastic deformation, which makes it possible to obtain SSJ from various alloys [8-10, 12-13, 34-43]. At the same time, a sufficient condition for obtaining a high-quality joint is the manifestation of the superplasticity effect in at least one of the materials being joined [8, 12, 34, 36-43]. The use of welded structures not only saves metal, but also reduces the weight of the resulting parts. However, there is a problem of joining dissimilar alloys, since brittle inclusions may appear in the weld zone [12, 13]. In this regard, much attention is paid to research aimed at obtaining high-quality permanent joints from superalloys, as well as the development of innovative methods for manufacturing bimetallic parts with the required set of operational properties.
In [41], a method was developed for obtaining SSJ intermetallic alloys of the VKNA type based on the NisAl intermetallic compound with a single-crystal structure with wrought alloys of the EP975 type with an initial fine-grained structure of the microduplex type, under conditions of high-temperature (T = 1125-1175 °C) superplasticity. The co-authors of this patent in [8, 36-41] showed that SSJ between EP975//VKNA-25 alloys can be obtained in a wide temperature-speed range of superplasticity (1075-1175 °C). It has been established that the strength of welded samples obtained by PW at temperatures of 1125 and 1175 °C (Vacuum Р = 5-10 Pa) corresponds to the strength of the VKNA-25 intermetallic alloy. All samples tested at room temperature failed along the VKNA-25 alloy being joined.
In a recently published study [43], it was shown that the pressure welding method is an effective method for obtaining SSJ superalloys of the EK61 and EP975 types with various types of hardening phase. It was found that in the process of pressure welding at a temperature of 925 °C, the UFG structure is transformed into a fine-grained structure with a grain size of 1.5 ^m. This temperature corresponds to the upper temperature limit of manifestation of superplasticity of the EK61 alloy with UFG structure. It is of interest to assess the possibility of obtaining SSJ at a much lower
temperature of 850 °C, at which the EK61 alloy with a mixed-type UFG structure demonstrates the maximum characteristics of low-temperature superplasticity [44, 45]. However, such data are not available in the scientific literature.
The study of formability is an important element for determining the process characteristics of sheet materials with an ultrafine grain structure. As is known [46-62], in order to assess the formability of superplastic materials, most researchers conduct experiments using the methods of molding into special cylindrical or conical matrices. In the case of forming into a cylindrical matrix, either spherical or cylindrical specimens can be obtained. Moreover, the formed material is deformed in a wide range of strain rates. The main task of such experiments is to establish the optimal modes of superplastic forming (SPF), which can later be used to develop a technology for obtaining real thin-walled parts.
The use of low-temperature superplasticity is also important for the fabrication of parts of complex geometry from hard-to-deform superalloys by the SPF method. Thus, in [34], using the example of the Inconel 718 alloy, it was shown that the use of sheet semi-finished products with an UFG structure (~ 0.3 ^m) makes it possible to reduce the flow stress level by a factor of 1.5 compared to the fine-grained state (~ 6.0 ^m). Due to the implementation of the effect of low-temperature joint venture, it is possible to reduce the temperature of the SPF process of sheet blanks made of Inconel 718 alloy to 900 °C.
The aim of this study is to generalize the new results and those previously obtained to evaluate the effectiveness of the effect of deformation under conditions of low-temperature superplasticity of the EK61 superalloy on its formability, as well as on the formation of SSJ with the EP975 superalloy with a different type of hardening phase.
2. Materials and Methods
2.1. Characteristics of the developed alloys
The wrought heterophase nickel-based superalloys EK61 (KhN5 8MBYuD) and EP975 (KhN59KVYuMBT), which differ in chemical and phase composition, and the type of hardening phase,
were chosen as materials for the study. Table 1 shows the chemical composition of the studied superalloys, which fully complies with TU 14-1-50-45-91 (for the EK61 alloy) and Russian Standard 5632-2014 (for the EP975 alloy). The EK61 alloy is characterized by a high content of niobium (5%) and a low content of aluminum and titanium. The EP975 alloy, on the contrary, has a high total content of aluminum and titanium (7.2 %) and a reduced amount of niobium. These differences in the content of such alloying elements determine significant differences in the phase composition, type of the hardening phase, its morphology, and precipitation kinetics in the investigated EK61 and EP975 alloys.
In the EK61 alloy, as well as in its foreign analogue, the Inconel 718 alloy [2], hardening is achieved due to the precipitation inside the grains of the y-phase (a solid nickel-based solution with an FCC lattice) of the strengthening y"-phase based on the Ni3Nb intermetallic compound. The strengthening y''-phase is not isomorphic to the matrix (y-phase, FCC), since it has a different type of crystal lattice -a body-centered tetragonal (bct.) lattice. It is released inside the grains of the y-phase in the form of nanosized coherent disk-shaped particles with an ordered structure of the DO22 type. According to the data of [2], the y''-phase is metastable because, during long-term aging at an elevated temperature (more than 650 °C), it transforms into a 5-phase (Ni3Nb) of a lamellar form with an orthorhombic lattice. During deformation-heat treatment of the plates, the 5-phases undergo fragmentation with subsequent spheroidization of the fragments [21]. In the initial state, the EK61 alloy was billets 80 mm in diameter and 90 mm high, cut from a hot-deformed rod 80 mm in diameter with an initial coarse-grained structure: the average grain size of the y-phase is ~ 62 ^m, inside which coherent nanosized (~ 40 nm) particles are homogeneously isolated metastable strengthening y''-phase based on Ni3Nb intermetallic compound.
In another studied wrought alloy EP975, heat-resistant characteristics were observed after the final heat treatment, as a result of which there was a homogeneous precipitation inside large (50-150 ^m)
Table 1. Chemical composition of EK61 and EP975 superalloys (heat-resistant nickel alloys) (wt. %)
Alloy Al Cr Co/Fe W/V Mo Ti Nb Cu C La EK61 1.0 16.6 15.0 Fe 0.5 V 3.9 0.8 5.0 0.5 <0.05 EP975 4.8 8.2 15.1 Co 10.2W 1.2 2.4 1.5 - 0.06 <0.01
grains of the matrix (y-phase, nickel-based solid solution) coherent (0.2-0.4 pm) particles of the strengthening y'-phase based on Ni3(Al, Ti) intermetallic compound [1, 4]. In the EP975 alloy, both phases (grains of the y-phase and dispersed particles of the y'-phase) had the same type of face-centered cube crystal lattice. Billets from the EP975 alloy 40x50x70 mm in sizewere used as the starting material; they were cut from forgings with a diameter of 400 mm and a thickness of 40 mm, in which a uniform fine-grained structure of the microduplex type was formed during high-temperature TMT: the average grain size of the y-phase was 6-8 pm, along the boundaries and in the triple junctions of which large (2-3 pm) incoherent particles-grains of the y'-phase were observed. In the microduplex structure, inside the grains of the y-phase, there were dispersed (0.1-0.2 ^m) coherent particles of the strengthening y'-phase, which usually precipitate upon cooling from the forging temperature to room temperature. The volume fraction of the recrystallized microduplex structure exceeded 80 %.
2.2. Thermo-mechanical treatment of mixed-type UFG structure in EK61 alloy
To obtain a UFG structure of a mixed type in the EK61 alloy, TMT was carried out in the temperature range (0.93-0.65) 7g (where is the dissolution temperature of the 5-phase) for the EK61 alloy) using the scheme of multiple isothermal forging (MIF), developed at IMSP RAS [9]. TMT of blanks was carried out with a gradual decrease in temperature in the above range on a hydraulic press with a force of 6.3 MN, equipped with an isothermal stamp block.
At each temperature, at least 5-fold pressing was carried out with successive rotation of the deformation axis by 90°. The strain rate was s ~ 10-2 - 10-3 s-1.
Experiments on pressure welding under conditions of superplasticity of one of the materials being joined (EK61) were carried out on cylindrical specimens with dimensions: diameter di = 157 mm for both alloys and height h0 = 20 mm for the EK61 alloy and 15 mm for the EP975 alloy. Pressure welding was carried out on a Shenck Trebel type RMS100 testing machine equipped with a UVSD-1 high-temperature pressure welding unit developed at IMSP RAS (Fig. 1).
This setup includes a high-temperature furnace (with a working temperature of up to 1250 °C), strikers made of an intermetallic alloy of the VKNA-1B type, a vacuum pumping system including a fore-vacuum and diffusion pumps to ensure a vacuum in the container with samples at a level of 5-10 Pa. This unit was developed earlier in the course of research led by Dr. V.A. Valitov on topics of RFBR projects No. 13-08-12200\15 (2014-2016) and RSF projects No. 18-19-00685 (2018-2020).
Pressure welding of cylindrical specimens in a combination of EK61//EP975 alloys was carried out under temperature and rate conditions of superplasticity of the EK61 alloy at a temperature of 850 °C and an initial strain rate of 10-4 s-1. Samples of EK61//EP975 pairs were placed in a sealed container made of stainless steel, in which, during the entire process, the LED was passed through a gas outlet tube connected to a vacuum system. The strength of SSI EK61//EP975 at elevated (650 °C) and room temperatures was evaluated in comparison with the less high-temperature EK61 superalloy.
(o)
(b)
(c)
Fig. 1. The working zone of the furnace of the UVSD-1 installation for high-temperature pressure welding based on the RMS-100 testing machine from SCHENK (a, b) and samples before and after pressure welding in sealed containers (c)
2.3. Mechanical tests
Mechanical tests were carried out on an Instron 5982 testing machine. Superplastic formability was studied according to the original technique [30] using special equipment for SPF of sheet blanks into a cylindrical matrix with a diameter of 30 mm [60-62], the diagram of which is shown in Fig. 2.
To study the formability, the investigated sheet blank was hermetically welded with an auxiliary sheet along the contour. A fitting was welded to the auxiliary sheet, to which a pressure supply device is attached. The pressure of the working gas can vary in the range from 0 to 6 MPa. The welded package with the investigated sheet blank was installed in the tooling. The equipment was placed in an electrically heated oven and heated. The SPF of polished sheets 40x40 mm in size and 0.7 mm thick with an UFG structure made of the EK61 alloy was carried out according to the modes developed earlier in [45].
The SPF was carried out in the temperature-speed mode of low-temperature superplastic deformation of the EK61 alloy with a UFG structure of a mixed type: at a temperature of 850 °C with a deformation rate of 3 • 10-3 s-1. During heating, a vacuum (1.3-0.13 Pa) was created in the inner cavity of the blank to prevent oxidation of the surface under study. After reaching the required temperature, the working gas is fed into the internal cavity of the blank according to a special law - P = fx), where t is the forming time [60, 61]. After the completion of the SPF process, the tooling was disassembled and formed cylinders were cut out. On the obtained samples, the deformation relief was examined, the thickness distribution was examined, and the equivalent tensile strain was found. When using interchangeable dies with a depth of 5, 10 and 15 mm, the equivalent deformation was from 10 to 800 %.
2.4. Analytical methods
Microstructural studies were carried out on a Mira 3LMH scanning electron microscope (TESCAN, Czech Republic). The fine structure was studied using a JEM-2000EX transmission electron microscope at an accelerating voltage of 160 kV. Energy dispersive analysis (EDA) was performed on a Vega 3SBH scanning electron microscope (TESCAN, Czech Republic). Microhardness measurements were carried out on an MHT-10 Microhardness Tester.
3. Results and Discussion
3.1. Certification of the microstructure of the investigated alloys
The microstructure of the EK61 alloy after TMT using the MAIF scheme is shown in Fig. 3. In the EK61 alloy (Fig. 3a, b), a mixed-type UFG structure is formed in the entire volume of the deformed material, in which the UFG component is close to the nanoduplex type in morphology and size.
The grain size of the y-phase and the incoherent particles of the S-phase was ~ 0.3-0.8 ^m, the volume fraction of the S-phase was VS ~ 24 %. In this case, along with the UFG component, individual relatively large particles of the S-phase (shown by red arrows)
Fig. 2. Tooling scheme for SPF sheet blanks in cylindrical
matrix: P - forming gas pressure; H - forming depth can be 5, 10, 15 mm; D - diameter of the cylindrical hole in the matrix (30 mm)
vNf '
t ; 0X3
Fig. 3. The initial microstructure of the superalloys under investigation: a, b - EK61; c, d - EP975
up to ~ 2 pm in size are observed in the alloy structure, the fraction of which is V§ ~ 5 %. Relatively large particles are preserved and are "hereditary", i.e. previously formed at the stage of formation of the microduplex structure.
3.2. Pressure welding of nickel alloys in combination of alloys EK61//EP975 under conditions of low-temperature superplasticity of the EK61 alloy
Figure 4 shows the microstructures of the alloys to be joined and the SSJ zone after PW (a) and subsequent heat treatment (b). In general, the entire deformation was localized in the less strong EK61 alloy, in which an UFG structure was formed before pressure welding, which ensured the implementation of the effect of low-temperature superplasticity during pressure welding.
According to the results of the research, it was found that the UFG structure of the EK61 alloy during pressure welding at a temperature of T = 850 °C is thermally stable, individual large particles of the S-phase are preserved in the structure (Fig. 4a). After welding and heat treatment, it was found that the UFG structure of the EK61 alloy is transformed into a CG structure (Fig. 4b). The microstructure of the EP975 alloy is thermally stable, no significant microstructural changes occurred during the heat treatment (Fig. 4b).
This is evidenced by the preservation of the type and parameters of the fine-grained structure of the microduplex type, which is identical to the initial state of the microstructure of the EP975 alloy before pressure welding (Fig. 3d). It is important to note that intragranular dispersed particles of the y-phase, no
larger than 0.4 pm in size, present in the microduplex structure, are retained at the studied pressure welding temperature of 850 °C and, accordingly, can affect the formation of SSJ of opposite alloys in the EK61//EP975 combination.
Figure 5 shows the results of the energy-dispersive analysis of the SSJ zone of alloys in the EK61//EP975 combination after pressure welding and heat treatment, where the dashed lines indicate the boundaries of the diffusion zone. It is important to note that the processes of mutual diffusion of alloying elements are affected by the difference in the chemical composition of the alloys being joined, as well as the difference in the atomic radius (rat) of the alloying elements. Nickel EP975 alloy is enriched with Co (rat = 0.125 nm), W (rat = 0.140 nm), in comparison with EK61 alloy, and depleted in Fe (rat = 0.127 nm) and Cr (rat = 0.128 nm). Therefore, apparently, the diffusion of Co (rat =0.125 nm) from the nickel alloy EP975 into the EK61 alloy proceeds actively. In this case, counter diffusion of iron and chromium is observed.
Thus, a detailed study of the results of energy-dispersive analysis indicates that, during pressure welding of two wrought superalloys EP975 and EK61 with a different type of hardening phase, the formation of SSJ occurs by diffusion with the formation of a y-solid Ni-based solution. The chemical composition of the solid solution in the SSJ zone is intermediate between the chemical compositions of the joined alloys. As a result of pressure welding at a temperature of 850 °C, a diffusion interaction zone is formed, the width of which is approximately 3 pm.
(a) (b) Fig. 4. Microstructure of SSJ zone: a - after PW; b - after PW and following HT
Diffusion zone
Diffusion zone
pm
Fig. 5. Distribution of alloying elements in welded samples in a combination of EK61//EP975 superalloys after PW (a), as well as following HT (b)
The results of the microhardness study of welded samples in the combination of EK61//EP975 alloys after pressure welding and heat treatment are shown in Fig. 6.
After heat treatment, the microhardness of the EP975 alloy being joined far from the SSJ zone had the same values as after pressure welding. The microhardness of the less heat-resistant EK61 alloy after heat treatment increased to the level of the microhardness of the EP975 alloy. The microhardness values that were determined in the SSJ zone were not entirely correct. This is due to the fact that the diameter of the indenter print when measuring microhardness was approximately 20 pm, although the width of the diffusion interaction zone did not exceed 14 pm even after heat treatment. Therefore, the indenter print includes not only the SSJ zone, but also the adjacent areas of the EK61 and EP975 materials being joined, which undoubtedly affects the obtained microhardness value in this area of the welded sample.
The results of mechanical testing of welded blanks according to the uniaxial tension scheme are presented in Table 2.
4,5
ro 4
Q.
(D 3,5
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m 2,5
c
"a
ro 2
sz 1,5
o
o 1
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0,5
0 -
i
t-1
+ cl
EK61
SSJ
EP975
Fig. 6. Microhardness in welded samples in combination of EK61//EP975 superalloys after PW and PW + HT
The analysis of the tested samples showed that the fracture in the welded specimens occurred along the SSJ zone. It has been established that the strength in samples obtained by welding at Т = 850 °C at room temperature is 0.8 of the strength of the EK61 alloy (Table 2). Tests at a temperature of 650 °C showed that the joint strength is 0.35 of the strength of the EK61 alloy (Table 2).
A comparative analysis of the above results with the data obtained by the authors earlier and published in [43] is of interest. In this paper, pressure welding of EK61 and EP975 alloys was carried out at a temperature of 925 °C, which is 75 °C higher than the temperature of pressure welding of the same alloys in similar structural states. The lower pressure welding temperature of 850 °C, which was used in this work, affected not only the width of the SSJ zone, but also the strength of the welded samples. A decrease in pressure welding temperature from 925 to 850 °C led to a significant decrease in the width of the diffusion interaction zone from 20 pm to 3 pm, which did not exceed 14 pm even after heat treatment. At the same time, the strength of the welded samples at room temperature (1170 MPa) turned out to be significantly higher than that of the samples after pressure welding at 925 °C (908 MPa). Although the test results at elevated temperature (T = 650 °C) showed the opposite result. The strength (455 MPa) of welded samples obtained by pressure welding at 850 °C turned out to be lower than after PW at 925 °C (664 MPa). At the same time, it should be noted that the level of SSJ strength achieved in both cases may be quite sufficient for obtaining real designs of bimetallic parts from opposite superalloys using SSJ in the form of a conical surface. It is assumed that during the operation of such bimetallic parts, the SSJ will be subjected to the action mainly of compressive stresses, rather than tensile stresses.
Table 2. Mechanical properties of welded joints and EK61 and EP975 superalloys
Condition
ob, mpa o0.2, mpa
5, %
t °c
1 tests, ^
(SSJ) PW, T = 850 °C 1170 1070 19
(SSJ) PW + HT, T = 850 °C 1140 970 20 20
EK61, the initial state UFG 1490 1030 33
EP975, the initial state FG 1690 1130 40
(SSJ) PW, T = 850 °C (SSJ) PW + HT, T = 850 °C EK61, the initial state UFG EP975, the initial state FG
455 1110 1300 1460
360 780 870 990
20 2 55 22
650
c m
5 mm 10 mm
15 mm
(a) (b) (c)
Fig. 7. Samples after superplastic forming at T = 850 °C to the different depth: a - microstructure (forming H = 5 mm); b - general view of the samples after SPF; c - microstructure (forming H = 15 mm)
3.3. Superplastic forming of nickel alloy EK61 with UFG structure
According to the results of experiments described in detail in [62], as well as those carried out in this work, it is shown that low-temperature superplastic deformation of the EK61 UFG alloy by a mixed-type structure can be successfully implemented under various deformation schemes (compression, tension), including the formation of sheet samples. Implementation of the effect of low-temperature superplasticity of the EK61 alloy has good formability without cracking even at low temperature T = 850 °C and strain rate s = 3-10-3 s-1. The formed model samples had a regular cylindrical shape [62] and were characterized by good filling of the die cavity (Fig. 7b).
The microstructural analysis of the material of hollow samples after the completion of the SPF (Fig. 7a, c) showed that the structure is duplex in all
cases, the equiaxiality of the grains of the y-phase was preserved. With an increase in the degree of deformation during SPF, some coarsening of the grains and a change in the phase composition were observed: at a forming depth of H = 5 mm, the grain size of the y-phase was ~ 1.72 ^m (Fig. 7a), at H = 10 mm ~ 2.0 ^m, and at H = 15 mm ~ 2.4 ^m (Fig. 7c), and the volume fraction of the S-phase was ~ 20 %.
Due to the increase in the grain size of the y-phase from 0.3-0.8 to ~1.7 - 2.4 ^m during the SPF process, a decrease in the microhardness of the material was observed (Table 3).
It is interesting to note that the values of microhardness after SPF were significantly lower than in a similar material after pressure welding (Fig. 4). Apparently, this is due to a significant difference in the stress-strain state that occurs in the compression scheme implemented during pressure welding compared to the tension scheme observed in SPF.
Table 3. Microhardness of EK61 superalloy before and after of superplastic forming
Sample condition Microhardness,
(forming depth H), mm GPa
The initial state (before forming) 4.2
5 3.4
10 3.5
15 3.6
In the latter case, the most favorable conditions were observed for the realization of the effect of superplastic deformation and softening of the deformed material.
Compared with the results of a study [34] previously carried out on the foreign alloy Inconel 718, which is the closest analogue of the domestic alloy EK61 in terms of chemical and phase composition, the latter succeeded in additionally lowering the SPF temperature by 50°C.
Thus, the results of the study showed that sheet blanks from the EK61 alloy with a preliminarily prepared UFG structure had good superplastic formability and, therefore, can be in demand for the manufacture of various complex-profile thin-walled products by the SPF method.
4. Conclusion
As a result of the experimental studies, it was found that pressure welding under conditions of low-temperature superplasticity is an effective method for obtaining SSJ from EK61 and EP975 nickel alloys with various types of hardening phase. It is shown that in the process of pressure welding at a temperature of 850°C between the alloys being joined, as a result of the processes of mutual diffusion of alloying elements, a transition zone of diffusion interaction is formed, the width of which is ~3 ^m. The strength of the SSJ compound EK61//EP975 at room temperature reaches 0.8 of the strength of the EK61 alloy. Macrodeformation of model hollow specimens during SPF proceeds relatively uniformly and uniformly. With an increase in the degree of deformation (holding time) during SPF, a certain coarsening of grains from ~0.3 to ~2.4 ^m is observed, which is consistent with a decrease in the microhardness values of the samples under study. The obtained data testify to the high superplastic properties of the EK61 alloy with the UFG structure and make it possible to recommend it for use in innovative technological processes of pressure welding to obtain SSJ from superalloys, as well as low-temperature SPF for shaping various types of
hollow products of complex configuration for aerospace technology. The results obtained can be used to optimize scientific and technical solutions related to the development of innovative deformation technologies based on the use of the superplasticity effect to obtain, for example, bimetallic parts of a disk-shaft gas turbine engine, and are also relevant in the creation of resource-saving technologies for forming hollow products of complex configuration.
5. Funding
The research work on pressure welding EK61//EP975 was supported financially by the Grants Council of the President of the Russian Federation (Presidential Scholarship for Young Researchers and Postgraduates SP-4002.2022.1).
The SPF experiments were carried out within the framework of the State Assignment of the IMSP RAS No. 122011900474-5.
6. Acknowledgements
Electron microscopic studies were carried out at the collective service center of the IMSP RAS "Structural and physical-mechanical studies of materials".
7. Conflict of interests
The authors declare no conflict of interest.
References
1. Kishkin ST. Creation, research and application of heat-resistant alloys: Selected works (To the 100-th anniversary of the birth). Moscow: Nauka; 2006. 407 p. (In Russ.)
2. Sims Ch, Stoloff T, Hagel V. Heat-resistant materials for aerospace and industrial power plants. Moscow: Metallurgiya; 1995. 568 p. (In Russ.)
3. Reed RC. The superalloys: Fundamentals and Applications. New York: Cambridge University Press; 2006. 372 p.
4. Logunov AV. Heat-resistant nickel alloys for blades and disks of gas turbines. Moscow: "Gas turbine technologies" Publ. house; 2017. 854 p. (In Russ.)
5. Magerramova LA. The use of bimetallic blisks, manufactured by HIP from granulated and foundry nickel superalloys, to increase the reliability and service life of gas turbines. Vestnik Ufimskogo gosudarstvennogo aviatsionnogo tekhnicheskogo universiteta. 2011;15(4(44)):33-38. (In Russ.)
6. Lyushinsky AV, Nikolich EV, Zhloba AA, Kharkovsky SV, Borovsky AV. Diffusion welding of nickel-based heat-resistant alloys. Svarochnoye proizvodstvo = Welding International. 2014;(5):25-28. (In Russ.)
7. Lyushinsky AV. Diffusion welding of dissimilar materials. Moscow: Akademiya; 2006. 208 p. (In Russ.)
8. Povarova KB, Valitov VA, Ovsepyan SV, Drozdov AA, Bazyleva OA, Valitova EV. Study of the properties and choice of alloys for discs with blades ("Bliskov") and the method of their connection. Metally = Russian Metallurgy (Metally). 2014;(5):61-70. (In Russ.)
9. Mulyukov RR, Imaev RM, Nazarov AA, Imaev MF, Imaev VM. Superplasticity of ultrafine-grained alloys: experiment, theory, technology. Moscow: Nauka; 2014. 284 p. (In Russ.)
10. Kaibyshev OA, Utyashev FZ. Superplasticity, structure refinement and processing of hard-to-form alloys. Moscow: Nauka; 2002. 438 p. (In Russ.)
11. Novikov II, Portnoy VK. Superplasticity of alloys with ultrafine grains. Moscow: Metallurgiya; 1981. 167 p. (In Russ.)
12. Lutfullin RYa. Superplasticity and solid-phase bonding of nanostructured materials. Part I. Influence of grain size on solid-phase weldability of superplastic alloys.
Pis'ma o materialakh = Letters on Materials. 2011;1:59-64. (In Russ.)
13. Lutfullin RYa, Mukhametrakhimov MKh, Valitov VA, Mukhtarov ShKh, Klassman PA, Astanin VV. Nanostructuring and solid-phase welding of hard-to-machine alloys. Perspektivnyye materialy = Inorganic Materials: Applied Research. 2011;(12):295-300. (In Russ.)
14. Kaibyshev OA, Utyashev FZ, Valitov VA. Influence of the content of y'-phase on the modes of preparation of the structure and superplasticity of heat-resistant nickel alloysMetallovedeniye i termicheskaya obrabotka metallov = Metal Science and Heat Treatment. 1989;(7):40-44. (In Russ.)
15. Kaibyshev OA, Valitov VA, Salishchev GA. Influence of the state of the y'-phase and hot deformation conditions on the formation of a microduplex structure in a heat-resistant nickel alloy..Fizika metallov i metallovedenie = The Physics of Metals and Metallography. 1993;75(4):110-117. (In Russ.)
16. Valitov VA, Utyashev FZ, Mukhtarov ShKh. Formation of microcrystalline structures and superplastic properties of nickel based alloys. Materials Science Forum. 1999;(304-306):79-84. DOI:10.4028/www. scientific.net/MSF.304-306.79
17. Portnoy VK, Alalykin AA, Novikov II. Formation of an ultrafine-grained structure in heat-resistant nickel alloys during hot deformation. In: Metal science and processing of non-ferrous alloys: a collection of scientific articles. Moscow: Nauka; 1992. 229 р. (InRuss.)
18. Kaibyshev OA, Valitov VA, Salishchev GA. Processing method for precipitation-hardening nickelbased alloys. Russian Federation patent 2,041,284. 09 August 1995. (In Russ.)
19. Utyashev FZ, Kaibyshev OA, Valitov VA. Method for manufacturing axisymmetric parts and methods for manufacturing blanks from multiphase alloys for its implementation (options). Russian Federation patent 2,119,842. 10 October 1998. (In Russ.)
20. Valitov VA. Superplasticity of heat-resistant nickel alloys with micro-, submicro- and nanocrystalline structure and prospects for its use for obtaining complex profile parts. Tyazheloye mashinostroyeniye. 2007;(4):23-28. (In Russ.)
21. Valitov VA. Deformation-heat treatment - an effective method for obtaining an ultrafine-grained and nanocrystalline structure in nickel alloys. Pis'ma o materialakh = Letters on Materials. 2013;3:50-55. (In Russ.).
22. Yang X, Chen S, Wang B, Li X, Wang B, Tian Y. Revealing the superplastic deformation behavior of cold-rolled Inconel 718 alloy at high strain rates. SSRN Electronic Journal. 2022. D01:10.2139/ssrn.4073483
23. Roder1 O, Helm D, Neft S, Albrecht J, Luetjering G. Mixed INCONEL® alloy 718 inertia welds for rotating applications - Microstructures and mechanical properties. In Proceedings of the International Symposium on Superalloys and Various Derivatives. Minerals, Metals and Materials Society, 2-5 October 2005, Pittsburgh, Pennsylvania. 2005:649-658. DOI: 10.7449/2005/ Superalloys_2005_649_658
24. Bychkov VM, Selivanov AS, Medvedev AYu, Supov VA, Bolshakov B O, Grin RR, Musin FF. Investigation of weldability of high-temperature nickel alloy EP742 by the method of linear friction welding. Vestnik Ufimskogo gosudarstvennogo aviatsionnogo tekhnicheskogo universiteta. 2012;16(7)(52):112-116. (In Russ.)
25. Lukin VI, Kovalchuk VG, Samorukov ML, Gridnev YuM, Zhegina IP, Kotelnikova LV. Study of the influence of friction welding parameters and heat treatment on the quality of welded joints of heat-resistant wrought nickel alloys. Svarochnoye proizvodstvo = Welding International. 2011;(4):26-30. (In Russ.)
26. Lukin VI, Kovalchuk VG, Samorukov ML, Gridnev YuM. Investigation of the influence of the technology of rotational friction welding of wrought heat-resistant nickel alloy VZh175 on the structure and strength characteristics of welded joints. Vestnik MGTU im. N.E. Baumana. Seriya „Mashinostroyeniye". 2011;S2: 114-121. (In Russ.)
27. Samorukov ML, Sviridov AV, Rassokhina LI, Bityutskaya ON. Rotational friction welding of cast and wrought semi-finished products of high-temperature nickel alloy VZh159. Trudy VIAM. 2020;1:15-23. DOI: 10.18577/2307-6046-2020-0-1-15-23 (In Russ.)
28. DuPont JN, Lippold JC, Kiser SD. Welding Metallurgy and Weldability of Nickel-Base Alloys. John Wiley & Sons, Inc; 2009. Available from: http://sv.20file.org/up1/1068_0.pdf.
29. Grishin IS. Diffusion welding of heat-resistant alloys between themselves and with structural steels. Kuibyshev: KuAY; 1981. 35 p. (In Russ.)
30. Lyushinsky AV, Fedorova ES. Method of diffusion welding. Russian Federation patent 2,720,267. 28 April 2020. (In Russ.)
31. Lyushinsky AV, Fedorova ES, Zhelonkina OG, Yarochkina GE. Method for diffusion welding of nickelbased powder heat-resistant alloy. Russian Federation patent 2,555,279. 07 October 2015. (In Russ.)
32. Liu J, Cao J, Lin X, Song X, Feng J. Microstructure and mechanical properties of diffusion bonded single crystal to polycrystalline Ni-based superalloys joint. Materials and Design. 2013;49:622-626. DOI:10.1016/j.matdes.2013.02.022
33. Shirzadi AA, Wallach ER. New method to diffusion bond superalloys. Science and Technology of Welding and Joining. 2004;9(128):37-40. DOI: 10.1179/136217104225017125
34. Valitov VA, Mukhtarov ShKh, Lutfullin RYa, Safiullin RV, Mukhametrakhimov MKh. Microstructure and properties of nanostructured alloy 718. Advanced Materials Research. 2011;278:283-288. DOI: 10.4028/ www.scientific.net/AMR.-278.283
35. Kruglov A, Enikeev F, Lutfullin R. Superplastic forming of a spherical shell out of a welded envelope. Materials Science and Engineering: A. 2002;323(1-2):416-426. D0I:10.1016/s0921-5093(01)01376-4
36. Drozdov A A, Povarova KB, Valitov VA, Galieva EV, Arginbaeva EG, Bazyleva OA, Bulakhtina MA, Raevskikh AN. Effect of the temperature of pressure welding of a wrought EP975 nickel alloy and a single-crystal intermetallic VKNA-25 alloy on the structure and properties of the welded joints. Russian Metallurgy (Metally). 2020;2020(7) :752-759. D0I:10.1134/S003602952007006X
37. Galieva EV, Povarova KB, Drozdov AA, Valitov VA. Structure and properties of the solid-phase joints of a wought EP975 nickel alloy and a single-crystal intermetallic VKNA-25 alloy formed by pressure welding at a strain of 24% under the superplasticity of the EP975 alloy. Russian Metallurgy (Metally). 2018;2018(11):1067-1073. DOI: 10.1134/S003602951811006X.
38. Drozdov A A, Povarova KB, Valitov VA, Bazyleva OA, Galieva EV, Bulakhtina MA, Arginbaeva EG. Effect of the deformation during pressure welding of a wrought EP975 nickel alloy and a single-crystal intermetallic VKNA-25 alloy on the structure and properties of the welded joints. Russian Metallurgy (Metally). 2019;2019(11): 11951204. DOI:10.1134/ S0036029519110041
39. Drozdov AA, Valitov VA, Povarova KB, Bazyleva OA, Galieva EV, Ovsepyan SV. Formation of solid-phase joints of a heat-resistant disc nickel alloy with an ultrafine-grained structure and a Ni3Al-based single-crystal bladed alloy. Pis'ma o materialakh = Letters on Materials. 2015;5(2):142-146. DOI: 10.22226/2410-3535-2015-2-142-146(In Russ.)
40. Povarova KB, Valitov VA, Drozdov AA, Bazyleva OA, Galieva EV, Arginbaeva EG. Formation of gradient structures in the zone of joining a deformable nickel alloy and a single-crystal intermetallic alloy during thermos-diffusion pressure welding and subsequent heat treatment. Russian Metallurgy (Metally). 2018;2018(1): 42-50. DOI:10.1134/S0036029518010111
41. Valitov V, Povarova K, Bazyleva O, Drozdov A, Ovsepyan S, Galieva E. Research of solid compound formation during thermal deformation effect on intermetallic Ni3Al-alloy with a heat-resistant alloy EP975 and influence on the physical, mechanical and performance properties. Materials Science Forum. 2016;838-839:523-527. DOI: 10.4028/www.scientific.net/ MSF.838-839.523
42. Valitov VA, Mulyukov RR, Ospennikova OG et al. Method for manufacturing a bimetallic product. Russian Federation patent 2,608,118. 13 January 2017. (In Russ.)
43. Galieva EV, Bikmukhametova AA, Valitov VA. Formation of a solid-phase joint from dissimilar alloys based on nickel EK61 and EP975. Fundamental'nyye problemy sovremennogo materialovedeniya. 2022;19(3): 394-401. DOI: 10.25712/ASTU. 1811-1416.2022.03.012 (In Russ.)
44. Galieva EV, Klassman EYu, Gabbasov RR, Stepukhov EM, Valitov VA. Low-temperature superplastic deformation of EK61 and EP975 wrought nickel-based superalloys with an ultrafine-grained structure. Pis'ma o materialakh = Letters on Materials. 2023;13(1):79-84. D0I:10.22226/2410-3535-2023-1-79-84
45. Valitova EV, Lutfullin RYa, Valitov VA. Influence of the rate and temperature of deformation on the microstructure and properties of the ultrafine-grained XN58MBYUD weldable alloy. Perspektivnyye materialy = Inorganic Materials: Applied Research. 2013;15:30-34. (In Russ.)
46. Lederich RJ, Sastry SML, Hayse M, Mackay TL Superplastic Formability Testing. Journal of Metals. 1982;34:16-20. D0I:10.1007/BF03338067
47. Akhunova AH, Dmitriev SV. Optimization of the shape of matrices for test superplastic forming of sheet blanks. Deformation and destruction of materials. 2009;11:40-44. (In Russ.)
48. Beck W. Results of in-house cone-cup testing of low to high temperature SPF-alloys. Materials Science Forum. 2004;447-448:145-152. D0I:10.4028/www. scientific.net/MSF.447-448.145
49. Ghosh AK, Hamilton CH. On constant membrane stress test for superplastic metals. Metallurgical Transactions A 1111. 1980;1915-1918. DOI: 10.1007/ BF02655109
50. Zhang B, Bate P, Ridley N, Dover S. Modeling of superplastic behaviour of AA5083. 4th European Conference on Superplastic Forming Euro SPF'05: Book of Papers, Manchester. UK 22-24 June 2005 Midland Hotel. 2005:173-178.
51. Sorgente D, Tricarico L. Pressure profile optimization on a superplastic aluminium alloy. Materials Science Forum. 2012;735:383-395. D0I:10.4028/www. scientific.net/MSF.735.383
52. Barnes AJ, Raman H, Lowerson F, Edwards D. Recent application of superformed 5083 aluminum alloy in the aerospace industry. Materials Science Forum. 2012;735:361-371. D0I:10.4028/www.scientific.net/MSF. 735.361
53. Marinho EP, Sakata A, Prados EF, Batalha GF. Instrumentation and control of a bulge test on a superplastic Pb-Sn alloy. Materials Science Forum. 2012;735:224-232. D0I:10.4028/www.scientific.net/MSF. 735.224
54. Carpenter AJ, Barnes AJ, Taleff EM. High-temperature deformation of magnesium elektrontm 43. Materials Science Forum. 2012;735:93-100. D0I:10.4028/ www. scientific.net/MSF.735.93
55. Dai G, Jarrar F, 0zturk F, Sheikh-Ahmad J. 0n the effect of the complexity of the constitutive model in simulating superplastic forming. Defect and Diffusion Forum. 2018;385:379-384. D0I:10.4028/www.scientific. net/DDF.385.379
56. Guo M, Tan M, Song X, Chua B. Numerical and experimental investigation on the hybrid superplastic forming of the conical Mg alloy component. Defect and Diffusion Forum. 2018;385:391-396. D01:10.4028/www. scientific.net/DDF.385.391
57. Kumaresan G, Kalaichelvan K. Formability analysis on superplastic forming of AZ91 magnesium alloy sheet. Defect and Diffusion Forum. 2018;385:437-442. D0I:10.4028/www.scientific.net/DDF.385.437
58. Langdon TG. Langdon.The background to superplastic forming and opportunities arising from new developments. Solid State Phenomena. 2020;306:1-8. DOI: 10.4028/www.scientific.net/SSP.306.1
59. Padmanabhan KA, Balasivanandha S.P, Mulyukov RR, Nazarov A, Imayev RM, Ghosh S. Chowdhury. Superplasticity. Common basis for a near-
ubiquitous phenomenon. Heidelberg: Springer-VERLAG GMBH; 2018. p. 526.
60. Safiullin RV, Enikeev FU, Lutfullin RYa. The method of estimation of strain in superplastic forming of thin-sheet materials. Kuznechno-shtampovochnoye proizvodstvo. 1994;(4):8-10. (In Russ.).
61. Safiullin RV, Enikeev FU. Determination of thinning characteristics during sheet forming processes. Superplasticity and Superplastic Forming. 1995. IOP Conf. Ser.: TMS Annual Meeting: Proceedings. 1995:213217.
62. Safiullin RV, Valitov VA, Lutfullin RYa, Galieva EV, Klassman EYu. Superplastic forming of EK61 nickelbased superalloy with ultrafine-grained structure. Pis'ma o materialakh = Letters on Materials. 2022;12(4s):439-444. D0I:10.22226/2410-3535-2022-4-439-444
Information about the authors / Информация об авторах
Elvina V. Galieva, Cand. Sc. (Eng.), Researcher, Institute for the problems of superplasticity of metals of the Russian academy of sciences (IMSP RAS), Ufa, Russian Federation; ORCID0000-0002-1074-6274; e-mail: galieva_elvina_v@mail.ru
Ekaterina Yu. Klassman, Postgraduate, Engineer, IMSP RAS, Ufa, Russian Federation; ORCID 00000003-1984-5137; e-mail: klassman@mail.ru
Vener A. Valitov, D. Sc. (Eng.), Leading Researcher, IMSP RAS, Ufa, Russian Federation; ORCID 00000002-1349-6047; e-mail: valitov_va@mail.ru
Egor M. Stepukhov, Student, Ufa University of Science and Technology (UUST), Ufa, Russian Federation; e-mail: egorstepukhov@mail.ru
Radim R. Gabbasov, Student, UUST, Ufa, Russian Federation; e-mail: awesome.radim@yandex.ru
Rinat V. Safiullin, Cand. Sc. (Eng.), Leading Researcher, IMSP RAS, Ufa, Russian Federation; ORCID 0000-0002-4555-052X; e-mail: dr_rvs@mail.ru
Ramil Ya. Lutfullin, D. Sc. (Eng.), Chief Researcher, IMSP RAS, Ufa, Russian Federation; ORCID 00000003-4638-3206; e-mail: lutfullin.ramil@imsp.ru
Галиева Эльвина Венеровна, кандидат технических наук, научный сотрудник, Институт проблем сверхпластичности металлов Российской академии наук (ИПСМ РАН), Уфа, Российская Федерация; ORCID 0000-0002-1074-6274; e-mail: galieva_ elvina_v@mail.ru
Классман Екатерина Юрьевна, аспирант, инженер, ИПСМ РАН, Уфа, Российская Федерация; ORCID 0000-0003-1984-5137; e-mail: klassman@ mail.ru
Валитов Венер Анварович, доктор технических наук, ведущий научный сотрудник, ИПСМ РАН, Уфа, Российская Федерация; ORCID 0000-00021349-6047; e-mail: valitov_va@mail.ru
Степухов Егор Михайлович, студент, Уфимский университет науки и технологий (УУНиТ), Уфа, Российская Федерация; e-mail: egorstepukhov@mail.ru
Габбасов Радим Рифкатович, студент, УУНиТ, Уфа, Российская Федерация; e-mail: awesome. radim@yandex.ru
Сафиуллин Ринат Владикович, кандидат технических наук, ведущий научный сотрудник ИПСМ РАН, Уфа, Российская Федерация; ORCID 0000-0002-4555-052X; e-mail: dr_rvs@mail.ru
Лутфуллин Рамиль Яватович, доктор технических наук, главный научный сотрудник, ИПСМ РАН, Уфа, Российская Федерация; ORCID 0000-00034638-3206; e-mail: lutfullin.ramil@imsp.ru
Received 20 February 2023; Accepted 13 April 2023; Published 26 May 2023
Copyright: © Galieva EV, Klassman EYu, Valitov VA, Stepukhov EM, Gabbasov RR, Safiullin RV, Lutfullin RYa, 2023. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
