X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... 567–575 EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUE PROPERTIES OF NICKEL-BASED SINGLE-CRYSTAL SUPERALLOY DD419 VPLIV TEMPERATURE IN AMPLITUDE DEFORMACIJE NA LASTNOSTI MALO-CIKLI^NEGA UTRUJANJA MONO-KRISTALINI^NE SUPER ZLITINE NA OSNOVI NIKLJA VRSTE DD419 Xiaoming Du 1* , Weiye Dong 1 , Xiang Zhu 1 , Jide Liu 2 , Zhijun Wang 3 , Tianfu Li 3 1 School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, People’s Republic of China 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China 3 China Institute of Atomic Energy, Beijing 102413, People’s Republic of China Prejem rokopisa – received: 2024-04-25; sprejem za objavo – accepted for publication: 2024-08-20 doi:10.17222/mit.2024.1169 High-temperature and low-cycle fatigue tests were conducted on a nickel-based single-crystal superalloy DD419 under total strain-controlled conditions at 760 °C and 980 °C. The fatigue properties of the alloy are discussed by analysing the fatigue test data. Fracture morphology and dislocation structure were observed using scanning electron microscopy and transmission elec- tron microscopy. At the same strain amplitude, the results indicate that the plastic deformation of the alloy is larger at 980 °C compared to 760 °C. This leads to a lower fatigue strength and shorter fatigue life, along with more severe damage. The value of the strain amplitude affects the cyclic stress response behaviour of the alloy. Under low strain amplitudes, the cyclic stress re- sponse behaviour differs between 760 °C and 980 °C. The hysteresis loop exhibits similar shapes at 760 °C and 980 °C, with an increase in the area as the strain amplitude rises. The fatigue fracture analysis indicates that micropores on the surface are the primary fatigue sources at 760 °C, while oxides on the surface are the main fatigue source at 980 °C, leading to cracking due to multiple sources. Moreover, transmission electron microscopy reveals that the deformation mechanism involving dislocations at 760 °C primarily occurs through plane slip and wave slip, whereas at 980 °C, dislocations mainly move through cross slip and climb. Keywords: nickel-based single-crystal superalloy, low-cycle fatigue, temperature, strain Avtorji v ~lanku opisujejo visoko-temperaturne teste malo-cikli~nega utrujanja preizku{ancev iz Ni monokristalini~ne superzlitine vrste DD419 v pogojih popolne deformacije pri 760 °C in 980 °C. Avtorji v ~lanku opisujejo trajno dinami~ne lastnosti izbrane zlitine na osnovi dobljenih rezultatov preizkusov. Morfologije prelomov preizku{ancev so avtorji ~lanka opazovali s pomo~jo vrsti~ne in presevne elektronske mikroskopije (SEM in TEM). Pri enaki amplitudi deformacije so rezultati preizkusov pokazali, da je plasti~na deformacija preizku{ancev ve~ja pri 980 °C kot tista dobljena pri 760 °C. To posledi~no vodi do ni`je trajne trdnosti, kraj{e `ivljenske dobe izbrane zlitine in k njenim bolj nenadnim poru{itvam. Vrednosti deformacijske amplitude vplivajo na cikli~ni napetostni odgovor izbrane zlitine. V pogojih nizkih deformacijskih amplitud se cikli~na napetostna odgovora pri 980 °C in pri 760 °C razlikujeta med seboj. Oblika histerezne zanke je pribli`no enake oblike pri obeh temperaturah in z nara{~anjem amlitude se pove~uje njen presek. Na trajnostnih prelomih preizku{ancev testiranih pri 760 °C so na povr{ini mikro pore, kar je tudi primarni vzrok za utrujanje materiala. Na preizku{ancih testiranih pri 980 °C pa je primarni vzrok za odpoved materiala zaradi utrujanja prisotnost oksidnih vklju~kov. Nadalje avtorji ugotavljajo na osnovi TEM preiskav, da mehanizem deformacije pri 760 °C primarno poteka z drsenjem dislokacij po drsnih ravninah in s pomo~jo valovitega drsenja. Pri 980 °C pa deformacija poteka s pomo~jo pre~nega drsenja in plezanja dislokacij. Klju~ne besede: mono-kristalini~na superzlitina na osnovi Ni, malocikli~no utrujanje, temperatura, deformacija 1 INTRODUCTION Nickel-based single-crystal (SX) superalloys have be- come essential materials for hot-end components, espe- cially turbine blades, because of their superior mechani- cal properties. 1–3 Turbine blades are subjected to substantial thermal stress, as well as high-temperature conditions characterized by intense centrifugal forces and asymmetric alternating loads during an actual opera- tion. Low-cycle fatigue (LCF) damage is the primary cause of the blade material failure. Consequently, it is necessary to consider the LCF behaviour of SX superalloys. Extensive studies have been conducted on the effects of cyclic frequency, strain rate, strain range, holding period, predeformation, corrosive environment, and testing temperature on high-temperature LCF. 4–7 Fan et al. conducted a study on the impact of temperature and strain amplitude on the fatigue life of the DD10 alloy. The findings indicate that the LCF life of the DD10 alloy is influenced by temperature. In the low strain range, the LCF life at 760 °C surpasses that at 980 °C, while in the high strain range, the opposite trend is observed. The for- mation mechanism of fatigue fractures in the DD10 alloy varies with temperature. 8 Ding et al. investigated the de- formation mechanism of an SX superalloy at different Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 567 UDK 669.24:537.226.86:620.178.3 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(5)567(2024) *Corresponding author's e-mail: du511@163.com (Xiaoming Du) temperatures. They provided a detailed analysis of the effects of microscopic dislocation motion in three tem- perature ranges (T 750 °C, 850 °C T 900 °C, and T 1000 °C) on the properties and deformation behav- iour of the alloy. 9 At present, the DD419 alloy has been shown to ex- hibit exceptional mechanical properties at high tempera- tures. However, there have been few studies on the ef- fects of various temperatures and strain ranges on the LCF properties of the alloy. Therefore, this paper investi- gates the relationships between temperature, strain am- plitude, and LCF properties of the DD419 alloy. The pur- pose of this study is to comprehensively understand the effect of temperature on the LCF behaviour, fatigue frac- ture characteristics, and dislocation morphology of DD419 alloy. In this paper, the results can provide valu- able references for a practical application of single-crys- tal superalloys in the engineering field. 2 EXPERIMENTAL PART The experimental alloy used in this work is a sec- ond-generation SX superalloy, DD419, which contains 6.8 % Cr, 9.3 % Co, 6.5 % W, 1.0 % Mo, 3.0 % Re, 5.8 % Al, 1.1 % Ti, 6.5 % Ta, 0.09 % Hf, and Ni in bal- ance (by weight). A single-crystal superalloy billet (pur- chased) was fabricated using a vacuum induction furnace with the high-rate solidification (HRS) technique. The single-crystal superalloy billet underwent the standard heat treatment, which included a solution treat- ment at 1300 °C for9hinair,andatw o-step aging treat- ment. The first step involved aging at 1150 °C for 4 h, followed by the second step at 870 °C for 14 h, with both steps being followed by air-cooling. LCF samples were cut from the billet using an electric discharge machine and then machined into LCF specimens with a diameter of 6 mm and a gauge length of 72 mm. The specimens with a diameter of 6 mm were used for the LCF tests. The orientation of the test bar deviat- ing from [001] was within 8°, as determined by the X-ray backscattering Laue method. A servo-hydraulic testing machine was used to conduct fatigue tests at 760 °C and 980 °C with a total strain amplitude of 1.4 %. The constant strain control loading mode was employed, utilizing a triangular waveform. The strain rate was 0.006 s –1 , and the strain ratio was R = 0.05. The tempera- ture fluctuation over the gauge length was maintained within ±2 °C; all the tests were performed in air. After conducting the LCF tests, the fracture surfaces were ex- amined using a scanning electron microscope (SEM) (TESCAN Maia3). The dislocation was observed using a transmission electron microscope (TEM) (Tecnai G2 F30) operating at an acceleration voltage of 120 kV. 3 RESULTS AND DISCUSSION 3.1 LCF life Figure 1 illustrates the relationship between the total strain amplitude and the fatigue life of the alloy at the two temperatures. At both temperatures, the life de- creases with an increase in strain amplitude. The slope of t /2–2 N f curve at 760 °C is greater than that at 980 °C, indicating that N f is more sensitive to a strain variation at 760 °C. In other words, the influence of temperature on the fatigue life becomes more significant with higher strain amplitudes. The total strain amplitude in LCF testing under a strain control can be expressed as the sum of the elastic and plastic strain amplitudes, as expressed with the Man- son-Coffin equation below: 0 ΔΔ Δ te p f fff 222 22 =+= + ' ()' () E NN bc (1) where t /2, e /2 and p /2 represent the total strain amplitude, the elastic strain amplitude, and the plastic strain amplitude, respectively. N f is the number of cycles to failure; f ' and f ' are the fatigue strength and ductility coefficient, respectively; b and c are the material’s con- stants for the selected alloy; and E is Young’s modulus. Figure 2 shows the fitting curves for e /2–2 N f and p /2–2 N f for the alloy at 760 °C and 980 °C. The fitted fatigue parameters are listed in Table 1. The specific form of the Manson-Coffin equation at 760 °C and 980 °C is as follows: Δ t ff 2 00570 2 00571 2 0 2388 0 3899 =+ −− .() .() .. NN (2) Δ t ff 2 00233 2 00589 2 0 1784 0 6173 =+ −− .() .() .. NN (3) It can be seen from Figure 2 that at all testing strain levels, the values of the plastic strain amplitude for alloy DD419 are much smaller than the elastic strain ampli- tude at both temperatures, being similar to most SX superalloys. 10–12 As e /2–2 N f and p /2–2 N f have no X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... 568 Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 Figure 1: Relation curves for fatigue life and total strain amplitude at different temperatures intersection points, there is no transition fatigue life (N tf ) where e /2 = p /2. 13 The references suggest that elas- tic strain plays a dominant role in the fatigue failure of the alloy, 8 and that there is a strong correlation with fa- tigue life. Table 1: Fatigue parameters of DD419 at different temperatures Temperature (°C) f ’ (MPa) f ’ bc E (GPa) 980 °C 2049 0.0589 –0.1784 –0.6173 88 760 °C 6180 0.0051 –0.2388 –0.3899 108 In Table 1, it is demonstrated that f ' decreases with increasing temperature. This implies that as the tempera- ture increases, the fatigue strength of the alloy decreases, leading to a shorter fatigue life. In short, this is consis- tent with the relationship between the total strain ampli- tude and fatigue life of the alloy shown in Figure 1. 3.2 Cyclic stress response behaviour Figure 3 presents the cyclic stress response behav- iour for DD419 tested at 760 °C and 980 °C at various strain amplitudes ( /2). In Figure 3a, under a 0.475 % strain amplitude, the cyclic stress response behaviour is shown at 760 °C and 980 °C. At 760 °C, the cyclic stress response behaviour first exhibits a brief softening stage, then transitions to a hardening stage, where it remains X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 569 Figure 3: Cyclic stress response curves for three different strain am- plitude fatigue tests at 760 °C and 980 °C: a) 0.475 %, b) 0.570 %, c) 0.713 % Figure 2: Strain amplitude versus the number of failure cycles at dif- ferent temperatures: a) 760 °C, b) 980 °C stable for an extended period in the middle of LCF, and then it experiences a sudden failure in the later stage. At 980 °C, the cyclic stress response shows a small differ- ence, characterized by a progression of hardening, fol- lowed by softening, then a stable stage, and finally an abrupt failure. On Figures 3ba n d3c, at strain amplitudes of 0.570 % and 0.713 %, the cyclic stress response curves exhibit similar trends at 760 °C and 980 °C. There are no obvious cyclic hardening and softening stages; the mate- rial basically maintains the cyclic stability throughout the LCF process. The difference in the curve is that the number of cycles before the alloy finally fails decreases as the temperature increases. This indicates that the higher the temperature, the lower is the LCF life of the alloy. By comparing Figures 3a to 3c, it can be seen that at low strain amplitudes, the difference in the temperature also creates a difference in the cyclic stress response be- haviour, but at high strain amplitudes, the temperature difference has almost no impact on the alloy’s cyclic stress response behaviour. Under three different strain amplitudes, the connection between the stress amplitude and fatigue life is also shown to be linear: the higher the stress amplitude, the shorter is the fatigue life. This is due to the fact that a higher strain amplitude will need a higher stress amplitude to create deformation, which will result in a shorter fatigue life. 3.3 Hysteresis loops and plastic strain energy Under strain-controlled fatigue loading, materials usually enter a stable cyclic stage at around half of their fatigue life. 14 Figure 4 shows hysteresis loops at around the half-life cycle for different strain amplitudes at two temperatures. Due to an asymmetric applied strain ratio (R = 0.05), the hysteresis loops of the DD419 alloy are asymmetric about the origin but symmetric about the strain axis during the half-life period. At 760 °C, the shape of the hysteresis loops does not change significantly and approximates a straight line for all strain amplitudes. This suggests that the alloy’s LCF process mainly involves elastic deformation, with very limited plastic deformation and damage. As the strain amplitude increases, the area of the hysteresis loops gradually expands, indicating increased plastic deforma- tion and reduced fatigue life. At 980 °C, the area of the hysteresis loop obviously increases compared to 760 °C. Simultaneously, this area increases with the strain ampli- tude. The area enclosed by hysteresis loops serves as a measure of the plastic strain energy value. Its physical meaning is that the larger the area of a hysteresis loop, the greater is the energy dissipation during plastic defor- mation, which makes the material more prone to fatigue damage and a lower life. 15 Generally, the value of plastic strain energy is obtained by integrating the area of the hysteresis loop. Previous studies revealed that the value X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... 570 Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 Figure 5: Relationship between strain amplitude and plastic strain en- ergy of the alloy Figure 4: Hysteresis loops of alloys at different strain amplitudes: a) 760 °C, b) 980 °C X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 571 Figure 7: Fracture topography at 980 °C: a) 0.475%, b) 0.570%, c) 0.713% Figure 6: Fracture topography at 760 °C, a) 0.475%, b) 0.570%, c) 0.713% of the plastic strain energy is primarily influenced by crystal orientation, as well as average stress and strain amplitude. 16 Figure 5 illustrates the relationship between the strain amplitude and measured plastic strain energy. It is observed that the plastic strain energy increases with an increase in the strain amplitude at different temperatures. According to the principle of energy conservation, the energy expended in fracturing each sample remains con- stant. Therefore, a higher plastic strain energy consumed per cycle indicates a reduced number of cycles. This sug- gests that fatigue life diminishes with increasing strain amplitude, which is consistent with the findings of the strain-life curve. 3.4 Fracture behaviour Fracture morphologies of specimens after the LCF fracture under different strain amplitudes and tempera- tures are shown in Figures 6 and 7. A typical fatigue fracture surface includes a fatigue source, fatigue exten- sion zone, and transient fault zone. 17,18 Illustrations on the right show enlarged details of the three zones. As shown in Figure 6, at 760 °C the division between the zones is obvious. The cross-section of the fracture after fatigue still remains circular, which is typical of brittle fracture. There is no significant difference in the fatigue fracture morphology under different strain amplitudes. The main fatigue sources (aI, bI, and cI) all stem from surface defects (such as porosity and casting defects). Secondary fatigue sources can also be observed around the main fatigue sources, indicating multiple fatigue sources. This is because the slip system operated by the single-crystal superalloy at 760 °C is the octahedral slip system, and the slip can occur in different directions. 19 After a fatigue source appears, the crack gradually expands and eventually forms an expansion zone. At this time, there are traces of metal slip and some torn edges in the expansion zone (aII, bII, and cII). Based on the microscopic expansion pattern, it can be inferred that the crack growth is of an open type. When the stress contin- ues to increase, it leads to the eventual fracture of the al- loy and the formation of a transient fault zone within the fracture. It is found that the macroscopic morphology of transient fault zones is rough, and microscopic cleavage steps are formed (aIII, bIII, and cIII). Therefore, the frac- ture of the alloy at 760 °C is a cleavage fracture. 20 As shown in Figure 7, from a macro perspective, the fracture morphology at 980 °C is also composed of three parts, but the boundaries of each region are not clearly defined. The fracture shape after fatigue shows no obvi- ous elongation or necking phenomenon, which is charac- teristic of typical brittle fractures. The crack propagation traces on Figure 7 are more pronounced than those at 760 °C, and multiple crack sources can also be observed. From a microscopic perspective, fatigue cracks are initi- ated at the edge oxide of the sample (aI, bI, and cI) when the strain amplitudes are (0.475, 0.570, and 0.713) %. This occurs because the high temperature leads to the formation of a significant oxide layer on the alloy’s sur- face. This, in turn, causes stress concentration on the sur- face, creating a source of fatigue that initiates cracking. There are also oxidation traces and metal slip traces in the fatigue extension zone (aII, bII, and cII), and the slip traces indicate the direction of crack propagation. The morphology of the instantaneous fracture zone is basi- cally the same as that at 760 °C. The macroscopic ap- pearance is relatively rough, and cleavage steps can be clearly observed under the microscope (aIII, bIII, and cIII). It is concluded that the fracture mechanism of the alloy at 980 °C is still a cleavage fracture. In summary, under the same strain amplitude, changes in the temperature affect the location of fatigue source initiation but do not significantly impact other morphologies and fracture mechanisms. Similarly, at a constant temperature, variations in the strain amplitude do not alter the primary morphology of each region. Figures 8 and 9 show transmission electron micros- copy (TEM) images of the dislocation morphology after the LCF testing at a strain amplitude of 0.475 % and temperatures of 760 °C and 980 °C, respectively. The TEM morphology reveals that the main structures ob- X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... 572 Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 Figure 8: Microscopic morphology of dislocations at 760 °C: a) sample 1, b) sample 2 served after the LCF tests are the matrix phase and the strengthened ' phase. Additionally, the transmission electron microscopy (TEM) morphology reveals highly uneven curved dislocation lines within the matrix chan- nels of the DD419 alloy, which is consistent with the dis- location distribution characteristics observed in LCF fracture samples of other superalloys. 21 At 760 °C, the ' phases in Figure 8a are uniformly distributed with a distinct cubic shape. No angular disso- lution or rafting phenomenon is observed, indicating that no creep damage occurred during the fracture of the sample. Some short dislocations are dispersed within the ' phase, and their shearing of the ' phase diminishes the strengthening effect of the ' phase. It is also observed that a large number of screw dislocations continuously move into the matrix channel through cross slip and eventually plug up at the / ' interface, contributing to the work hardening. Notably, in Figure 8b, a large num- ber of slip bands composed of irregular dislocations and a small number of wavy dislocations can be clearly ob- served. The existence of wavy dislocations is a typical characteristic of wavy slip. 22 Therefore, the fracture mechanism of LCF at moderate temperatures exhibits characteristics of plane slip and wave slip, which is con- sistent with previous research findings. 23 In addition, a small number of stacking faults were found in the phase, which reduces the alloy’s resistance to plastic de- formation and leads to a rapid initiation of microcracks. In Figure 9, the presence of angular dissolution or rafting of the ' phase suggests that creep damage oc- curred during the fracture of the specimen at 980 °C. Ad- ditionally, short dislocations cut into the ' phase (Fig- ure 9a), and many high-density dislocations form a large number of dislocation networks that tangle around the / ' interface (Figure 9b). According to previous stud- ies, 24,25 this is the typical dislocation network structure in the primary stage of creep damage, and the density and morphology of dislocation networks play a crucial role in strengthening SX superalloys. At this point, due to the increase in the temperature, thermal activation becomes stronger, causing the stacking faults to disappear, leading to a change in the dislocation motion mode. The disloca- tions clustered at the / ' interface continue to move around the ' phase through climbing, and then proceed to advance through slippage or cross-slip mechanisms, resulting in a uniform distribution of dislocations. There- fore, the stress concentration in the phase is reduced, and the local hardening effect caused by dislocation en- tanglement is cancelled out. This demonstrates cyclic stability in the cyclic stress response curve (Figure 3). Temperature plays a crucial role in the movement of dislocations and the formation of dislocation structures in nickel-based superalloys. Figure 10 shows the effect of temperature on the microscopic deformation mecha- nism of the alloy. 26 As shown in Figure 10, the disloca- tion movement mode changes from planar slip to wave slip at 760 °C. Some of the screw dislocations move out- ward around the ' phase in an arch shape through cross slip, while more dislocations accumulate at the / ' inter- face. Finally, the accumulated dislocations will still pass through the ' phase, leading to strain localization. When X. DU et al.: EFFECTS OF TEMPERATURE AND STRAIN AMPLITUDE ON LOW-CYCLE FATIGUEP ROPERTIES ... Materiali in tehnologije / Materials and technology 58 (2024) 5, 567–575 573 Figure 10: Effect of temperature on the microscopic deformation mechanism of the alloy Figure 9: Microscopic morphology of dislocations at 980 °C: a) sample 1, b) sample 2 the temperature reaches 980 °C, the edge of the ' phase dissolves significantly. As the stacking fault energy (SFE) increases, the stacking fault disappears, and the mismatch stress at the / ' interface rises. This leads to the formation of a large number of dislocation networks due to the accumulated dislocations at the / ' interface, increasing the difficulty of cutting the ' phase. In addi- tion, under the influence of thermal activation, the newly formed dislocations can move and traverse the ' phase through climbing. They can then advance through glide or cross slip on the matrix channel {111} plane, ensuring a uniform distribution of dislocations. 4 CONCUSIONS 1) The LCF life of DD419 alloy is significantly influ- enced by temperature. Elastic deformation plays a cru- cial role in determining the LCF life of alloys at 760 °C and 980 °C. However, when compared to 760 °C, at 980 °C, the alloy shows increased plastic deformation, leading to reduced fatigue performance, shorter lifespan, and more severe damage. 2) The cyclic stress response behaviour of alloys at two different temperatures varies significantly. At low strain amplitudes, temperature differences can also lead to variations in the cyclic stress response behaviour of al- loys. However, at high strain amplitudes, temperature differences have a minimal impact on the cyclic stress re- sponse behaviour of alloys. The hysteresis loop of alloys typically stabilizes near the half-life. As the strain ampli- tude increases, the plastic strain energy gradually rises, leading to a decrease in the fatigue life and performance. 3) At 760°C and 980°C, the fatigue fracture exhibits multiple fatigue sources, and the transient fracture zone displays cleavage steps, indicating a cleavage fracture. At 760 °C, fatigue source mainly initiates at surface de- fects. The fatigue source at 980 °C is mainly surface ox- ide. 4) At 760 °C, the alloy exhibits short dislocations and shearing of the ' phase within slip bands, along with wavy dislocations near the / ' interface. Hence, the LCF deformation mechanism of the alloy at 760 °C combines characteristics of both planar slip and wavy slip. At 980 °C, high-temperature creep damage mainly occurs in ma- trix dislocations and interface dislocations, with only a few dislocations passing through the ' phase. The defor- mation mechanism mainly involves cross slip and climb around the ' phase. Acknowledgment This research was funded in 2023 by the Liaoning Provincial Applied Basic Research Project (2023JH2/ 101300233), National Natural Science Foundation of China (No. 12375305), and Basic Research Projects of Higher Education Institutions in Liaoning Province (JYTZD20230004, JYTMS20230193). 5 REFERENCES 1 L. Liu, J. Meng, J. L. Liu, T. Jin, X. D. Sun, H. F. Zhang, Effects of crystal orientations on the cyclic deformation behavior in the low cy- cle fatigue of a single crystal nickel-base superalloy, Materials & De- sign, 131 (2017), 441–449, doi:10.1016/j.matdes.2017.06.047 2 Z. X. Shi, X. G. Wang, S. Z. Liu, J. R. Li, Low cycle fatigue proper- ties and microstructure evolution at 760 °C of a single crystal super- alloy, Progress in Natural Science: Materials International, 25 (2015), 78–83, doi:10.1016/j.pnsc.2015.01.009 3 L. B. Yang, X. N. Ren, C. C. Ge, Q. Z. Yan, Status and development of powder metallurgy nickel-based disk superalloys, Int. J. Mater. 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