Articles de revues : « Microstructures γ-γ' »

1

Mohanty, R. R., et Yong Ho Sohn. « Phase Field Modeling of Interdiffusion Microstructure in Ni-Cr-Al Diffusion Couples ». Materials Science Forum 595-598 (septembre 2008) : 199–206. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.199.

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Evolution of interdiffusion microstructures was examined in ternary Ni-Cr-Al solid-tosolid diffusion couples using two-dimensional (2D) phase field simulation. Utilizing Cahn-Hilliard and Allen-Cahn equations, multiphase diffusion couples containing of fcc-γ and B2-β solid solution phases were simulated with alloys of different compositions and phase contents. Chemical mobility as a function of composition with constant gradient energy coefficients was used in the simulation. Simulated microstructures in γ+β/γ and γ+β/γ+β diffusion couples were compared with the experimental microstructures reported in literature. As observed experimentally, the model predicted the recession of γ+β region in the γ+β/γ couple and a stationary interface in γ+β/γ+β couple. Concentration profiles developed across the diffusion couples demonstrated that the interdiffusion occurs in the γ phase as well as in the γ+β region. Formation of single-phase γ and β layers near the interface of γ+β/γ+β couples was also investigated using the volume fraction profile obtained from the simulated microstructure.

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Xue, Yan Peng, Xiao Guang Wang, Jin Qian Zhao, Zhen Xue Shi, Shi Zhong liu et Jia Rrong Li. « Effect of Heat Treatment on Microstructure Evolution in DD9 Single Crystal Turbine Blade ». Materials Science Forum 1072 (25 octobre 2022) : 95–102. http://dx.doi.org/10.4028/p-26qh91.

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The microstructural evolution of DD9 single crystal superalloy turbine blade was studied after heat treatment. In comparison to the as-cast microstructures where the sizes of the γ′ precipitates have an obvious difference between the dendritic core and interdendritic regions, the γ′ sizes of the heat-treated microstructures tend to be uniform and more cubic. And in the heat-treated microstructures, the γ′ sizes and the related size dispersion degrees of the dendritic cores are slightly increased, while those of the interdendritic regions are obviously decreased. After all, all the γ′ sizes follow the normal distribution law. With the raise of section thickness, the γ′ sizes tend to increase and the related size dispersion degrees are enhanced during the cooling process after heat treatment, and the γ-γ′ eutectics are dissolved, left little residual eutectics and pores.

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Guo, X., P. He, K. Xu, P. Y. Chen, B. Chen et S. B. Huo. « Microstructural evolution and liquation cracking in the partially melted zone of deposited ERNiCrFe-13 filler metal subjected to TIG refusion ». Welding in the World 65, n^o 5 (9 février 2021) : 825–32. http://dx.doi.org/10.1007/s40194-021-01073-8.

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AbstractThe microstructure of ERNiCrFe-13 multipass weld metal has been shown to contain Laves/γ or σ/γ eutectic constituents that can increase susceptibility to solidification and weld metal liquation cracking resulting from the low eutectic reaction temperature. Under poor heat dissipation conditions such as on the edge of large thickness welded components, a partially melted zone (PMZ) may form in the weld metal during multipass welding. The microstructural evolution and liquation cracking susceptibility of this PMZ in ERNiCrFe-13 multipass welds have received little attention. In the present study, a tungsten inert gas (TIG) refusion process is used to simulate a thermal cycle with a long elevated temperature dwell time in order to investigate the microstructural evolution and liquation cracking in the weld metal PMZ. The results show that the eutectic microstructures in the PMZ evolve into three eutectic morphologies after TIG refusion, including long linear chains extending perpendicular to the boundary between the refusion zone and PMZ, skeletal structures, and fine lamellar networks. This evolution contributes to constitutional liquation occurring at the γ/Laves and γ/σ interface. Nb and Mo play a leading role in the constitutional liquation of γ/Laves and γ/σ eutectic microstructures, respectively. Liquation cracking in the PMZ is shown to occur along the linear chain grain boundaries resulting from constitutional liquation.

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Ding, Qingqing, Hongbin Bei, Xinbao Zhao, Yanfei Gao et Ze Zhang. « Processing, Microstructures and Mechanical Properties of a Ni-Based Single Crystal Superalloy ». Crystals 10, n^o 7 (3 juillet 2020) : 572. http://dx.doi.org/10.3390/cryst10070572.

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A second-generation Ni-based superalloy has been directionally solidified by using a Bridgman method, and the key processing steps have been investigated with a focus on their effects on microstructure evolution and mechanical properties. The as-grown microstructure is of a typical dendrite structure with microscopic elemental segregation during solidification. Based on the microstructural evidence and the measured phase transformation temperatures, a step-wise solution treatment procedure is designed to effectively eliminate the compositional and microstructural inhomogeneities. Consequently, the homogenized microstructure consisting of γ/γ′ phases (size of γ′ cube is ~400 nm) have been successfully produced after a two-step (solid solution and aging) treatment. The mechanical properties of the resulting alloys with desirable microstructures at room and elevated temperatures are measured by tensile tests. The strength of the alloy is comparable to commercial monocrystalline superalloys, such as DD6 and CMSX-4. The fracture modes of the alloy at various temperatures have also been studied and the corresponding deformation mechanisms are discussed.

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Wang, Chan, Duoqi Shi et Shaolin Li. « A Study on Establishing a Microstructure-Related Hardness Model with Precipitate Segmentation Using Deep Learning Method ». Materials 13, n^o 5 (10 mars 2020) : 1256. http://dx.doi.org/10.3390/ma13051256.

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This paper established a microstructure-related hardness model of a polycrystalline Ni-based superalloy GH4720Li, and the sizes and area fractions of γ’ precipitates were extracted from scanning electron microscope (SEM) images using a deep learning method. The common method used to obtain morphological parameters of γ’ precipitates is the thresholding method. However, this method is not suitable for distinguishing different generations of γ’ precipitates with similar gray values in SEM images, which needs many manual interventions. In this paper, we employ SEM with ATLAS (AuTomated Large Area Scanning) module to automatically and quickly detect a much wider range of microstructures. A deep learning method of U-Net is firstly applied to automatically and accurately segment different generations of γ’ precipitates and extract their parameters from the large-area SEM images. Then the obtained sizes and area fractions of γ’ precipitates are used to study the precipitate stability and microstructure-related hardness of GH4720Li alloy at long-term service temperatures. The experimental results show that primary and secondary γ’ precipitates show good stability under long-term service temperatures. Tertiary γ’ precipitates coarsen selectively, and their coarsening behavior can be predicted by the Lifshitz–Slyozov encounter modified (LSEM) model. The hardness decreases as a result of γ’ coarsening. A microstructure-related hardness model for correlating the hardness of the γ’/γ coherent structures and the microstructure is established, which can effectively predict the hardness of the alloy with different microstructures.

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Prakash, Aruna, et Erik Bitzek. « Idealized vs. Realistic Microstructures : An Atomistic Simulation Case Study on γ/γ′ Microstructures ». Materials 10, n^o 1 (23 janvier 2017) : 88. http://dx.doi.org/10.3390/ma10010088.

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Pan, Qinghai, Yongfeng Sui, Peijiong Yu, Xinbao Zhao, Yuan Cheng, Quanzhao Yue, Yuefeng Gu et Ze Zhang. « Effect of Heat Treatment Schedules on Creep Performance of Ni-Based Superalloy Mar-M247 at 871 °C and 250 Mpa ». Metals 13, n^o 7 (14 juillet 2023) : 1270. http://dx.doi.org/10.3390/met13071270.

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The effects of heat treatment (H1 and H2) on the creep behavior and microstructures of Mar-M247 at 871 °C/250 MPa are studied. The results show that the as-cast microstructure is composed of eutectics, γ phase, γ’ phase, MC and M23C6 carbides, while new M6C appears in heat-treated microstructures, indicating the transformation of carbides after heat treatments. The Mar-M247 is excellent, with over 1500 h of creep life, and H1 is 48% higher than H2. The addition of post-brazing and diffusion heat treatment in H2 is detrimental to creep resistance; the two steps promoted the transformation of MC into M23C6 in advance. The increase and coarsening of M23C6 would consume more γ-phase-forming elements, weakening the solution strengthening at grain boundaries. As a result, the resistance of the grain boundary and γ/γ’ interface to dislocation motion is significantly reduced, leading to the cracks’ initiation and propagation along the grain boundaries.

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KONG, FANTAO, et YUYONG CHEN. « EFFECTS OF THERMO-MECHANICAL TREATMENTS ON MICROSTRUCTURE OF Ti-43Al-9V-Y ALLOY ». International Journal of Modern Physics B 23, n^o 06n07 (20 mars 2009) : 1009–13. http://dx.doi.org/10.1142/s0217979209060385.

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Ti -43 Al -9 V - Y alloy billets was prepared by the quasi-isothermal canned forging processing, and effect of heat treatment processes on the microstructure of as-forged Ti -43 Al -9 V - Y alloy was investigated. The results show that, as-forged Ti -43 Al -9 V - Y alloy has streamline microstructure including a large number of recrystallized grains and broken lamellae, and different heat treatment processes were employed to obtain different microstructures of Ti -43 Al -9 V - Y alloy. After heat treatment at 1250°C, the microstructure of as-forged Ti -43 Al -9 V - Y alloy becomes γ+ B 2 microstructure. Comparing with the microstructure after HT of 1250°C/30 min, the precipitation of B 2 lath phase in γ equiaxed grains increased and γ grains refined after HT of 1280°C/30min or 1320°C/30min. However, after the heat treatment of 1300°C/30 min, the duplex microstructures can be gained.

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Xu, Wen Yong, Zi Chao Peng, Mu Zi Li et Minh Son Pham. « Microstructure Analysis and Creep Behaviour Modelling of Powder Metallurgy Superalloy ». Materials Science Forum 913 (février 2018) : 134–40. http://dx.doi.org/10.4028/www.scientific.net/msf.913.134.

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Microstructure analysis of Ni-based superalloy FGH96 under different ageing treatments were carried out in order to understand the microstructure-creep strength relationships of the alloy. It was found that the volume fraction of tertiary γ′ and the mean γ-channel width was significantly varied with different ageing treatments, leading to the changes in creep behavior. The dislocation/γ′ shearing mechanisms were also changed with ageing treatment. The volume fractions of both secondary and tertiary γ′ and the mean γ-channel width were quantitatively analyzed by electron microscopy. The quantified microstructures were used for a crystal plasticity-based constitutive model. It was observed that the crystal plasticity model can accurately simulate experimentally observed creep behavior of aged samples showing significant secondary creep stage.

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Wang, Xiao-Yan, Meng Li et Zhi-Xun Wen. « The Effect of the Cooling Rates on the Microstructure and High-Temperature Mechanical Properties of a Nickel-Based Single Crystal Superalloy ». Materials 13, n^o 19 (24 septembre 2020) : 4256. http://dx.doi.org/10.3390/ma13194256.

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The as-cast alloy of nickel-based single-crystal superalloy was used as the research object. After four hours of solution treatment at 1315 °C, four cooling rates (water cooling (WC), air cooling (AC) and furnace cooling (FC1/FC2)) were used to reduce the alloy to room temperature. Four different microstructures of nickel-based superalloy material were prepared. A high-temperature tensile test at 980 °C was carried out to study the influence of various rates on the formation of the material’s microstructure and to further obtain the influence of different microstructures on the high-temperature mechanical properties of the materials. The results show that an increase of cooling rate resulted in a larger γ′ phase nucleation rate, formation of a smaller γ′ phase and a greater number. When air cooling was used, the uniformity of the γ′ phase and the coherence relationship between the γ′ phase and the γ phase were the best. At the same time, the test alloy had the best high-temperature tensile properties, and the material showed a certain degree of plasticity. TEM test results showed that the test alloy mainly blocked dislocations from traveling in the material through the strengthening effect of γ′, and that AC had the strongest hindering effect on γ′ dislocation movement.

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Wang, Xiao Guang, Jia Rong Li, Zhen Xue Shi et Shi Zhong Liu. « Effect of Solid Solution Heat Treatment on Microstructures of the Third Generation Single Crystal Superalloy DD9 ». Materials Science Forum 747-748 (février 2013) : 549–58. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.549.

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An observation was conducted on the microstructures of as-cast as well as solid solution treated the third generation single crystal superalloy DD9 using optical microscope and SEM. The effects of solid solution temperature and time on the eutectic fractions of γ/γ and size of γ of the alloy were investigated. The results showed that the microstructure of DD9 was uniform. W and Re segregated to the dendrite cores while Al, Ta and Nb were enriched in interdendritic regions during solidification. The eutectic fractions of γ/γ reduced with the solid solution temperature raising and the solid solution time prolonging. When solid solution temperature increased to 1340, the eutectic in the alloy was entirely dissolved. The size of γ in dendritic cores was consistent, however the size of γ in interdendritic regions was gradually decreased with the increase of solid solution treatment and time, eventually the sizes of γ were completely uniform at the temperature of 1340

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Wartbichler, Reinhold, Tobias Maiwald-Immer, Fabian Pürstl et Helmut Clemens. « Laser Powder Bed Fusion of Intermetallic Titanium Aluminide Alloys Using a Novel Process Chamber Heating System : A Study on Feasibility and Microstructural Optimization for Creep Performance ». Metals 12, n^o 12 (5 décembre 2022) : 2087. http://dx.doi.org/10.3390/met12122087.

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A laser powder bed fusion process operating at elevated temperatures is introduced capable of fabricating crack-free and dense intermetallic titanium aluminide alloy specimens as well as demonstrator components using a base plate heating up to 900 °C and a unique heating system of the uppermost powder bed layer up to 1200 °C. Two so-called 4th generation alloys, TNM and TNM+, were used for this study. The microstructure and its evolution during subsequent heat treatments were investigated and explained by employing scanning electron microscopy, hardness testing, X-ray diffraction, differential scanning calorimetry and thermodynamic equilibrium calculation. Selected specimens were subjected to creep tests at 750 °C. The microstructures after processing consist of extraordinarily fine lamellar γ-TiAl/α2-Ti3Al-colonies with globular γ and βo-TiAl grains for both the TNM and TNM+ alloy, exhibiting a microstructure gradient from the last consolidated powder layer down to the starting layer due to cellular reaction, which increases the amount of globular γ and βo at the boundaries of the γ/α2-colonies. During annealing in proximity to the γ-solvus temperature, banded microstructures might form, as the α-grain size is only partially controlled by heterogeneously distributed γ/β-phase, which stems from the process-related Al loss. Additionally, the occurrence of thermally-induced porosity is investigated. Optimizing the microstructure to a homogenized, almost fully lamellar microstructure, involved annealing in the β-single phase field region and led to improved creep properties. Finally, TNM demonstrator components with complex geometries, such as aero engine blades and turbocharger turbine wheels, are fabricated by employing the novel laser powder bed fusion process.

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Thi Chieu, Le, Sai Manh Thang, Nguyen Duong Nam et Pham Mai Khanh. « The Effect of Deformation on Microstructure of Cu-Ni-Sn Aging Alloys ». Key Engineering Materials 682 (février 2016) : 113–18. http://dx.doi.org/10.4028/www.scientific.net/kem.682.113.

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This paper presents the effect of deformation on the change of microstructure of Cu-15Ni-8Sn and Cu-9Ni-6Sn alloy during heat treatment. The samples were homogenized, quenched, cold-rolled at different thickness reduction, and aged. The effects of deformation on microstructures were observed by optical microscope and SEM. The spinodal decomposition after homogenized solid solution, deformation and aging of these alloys was observed. The results have shown that during aging, from the rich-tin zones formed by spinodal decomposition, produced phase γ. The microstructure included of α +γ. The deformation accelerated the aging process and rapid increased the diameter of formed phase γ.

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Quadir, M. Z., Y. Y. Tse, K. T. Lam et B. J. Duggan. « Rolling and Recrystallization Texture of Cold Rolled IF Steel : A Study from Low to High Deformation ». Materials Science Forum 467-470 (octobre 2004) : 311–16. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.311.

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IF steel was homogeneously cold rolled between 30-95% reduction in thickness. The global cold rolling textures showed a gradual strengthening of both stable α and γ components with increasing reduction until ~80% after which γ remained effectively unchanged but α components intensified until 95% reduction of thickness. Deformation Banded (DB) and also fragmented microstructures were found exclusively in γ grains up until about 85% reduction after which DB was unexpectedly detected in α grains, becoming significant after 95% reduction. This is in sharp contrast with the rather undifferentiated microstructures found in α grains at low to medium levels of deformation. At lower reductions the annealing texture was a weak α, but the γ component increased with rolling strain and became dominant at ~80% rolling deformation. A peak type γ recrystallisation texture with orientations ranging from {554}<225> to {111}<123> was found in the 95% rolled sample. In addition to this a {411}<148> component began to intensify, reading 5R at 95% reduction. Microstructural analysis showed that DB provided the lattice curvature for nucleation in the α fibre.

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Tetsui, Toshimitsu. « Effect of Microstructure on Impact Resistance and Machinability of TiAl Alloys for Jet Engine Turbine Blade Applications ». Metals 13, n^o 7 (5 juillet 2023) : 1235. http://dx.doi.org/10.3390/met13071235.

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The impact resistance and machinability of TiAl alloys, which are used for jet engine turbine blades, are critical for ensuring reliability and reducing manufacturing costs. This study investigated the effects of the microstructure on these properties using Ti–Al–Cr ternary alloys via Charpy impact tests at room temperature and 700 °C and performing cutting tests using a face mill with cemented carbide tools. As a result, it was confirmed that six types of typical microstructures of TiAl alloys, namely, fine FL, coarse FL, L + γ, γ, γ + β, and L + γ + β, could be formed by varying the Al and Cr concentrations and heat-treatment conditions. Impact resistance and machinability are each the exact opposite trends to the other, with coarse FL having the best impact resistance but poor machinability. Meanwhile, γ has the best machinability but the weakest impact resistance. L + γ has no major drawbacks, including creep strength. As the microstructure of TiAl4822, currently used in LEAP (leading edge aviation propulsion) engine blades, is almost a γ single-phase microstructure, we assumed that manufacturers chose this microstructure to improve machinability and thus reduce the cost. However, because the γ microstructure has the lowest impact resistance, caution should be exercised when applying it to other engines with different operating environment. On the other hand, the microstructure containing the β phase is inferior in all aspects, including creep strength. Thus, it is questionable to use TiAl-forged materials with a residual β phase in small-sized products that can be manufactured by casting.

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Maruyama, Naoki, T. Ogawa et M. Takahashi. « Recrystallisation at Intercritical Annealing in Low Carbon Steels ». Materials Science Forum 558-559 (octobre 2007) : 247–52. http://dx.doi.org/10.4028/www.scientific.net/msf.558-559.247.

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Subgrain growth in deformed ferrite and incomplete recrystallisation during intercritical annealing in low carbon (LC) steels was investigated by EBSD and FEGTEM/EDS. It was confirmed that fine dual phase (α+γ) microstructures could be obtained even without the addition of microalloying elements such as Nb and Ti, if the steels were heated above Ac1 temperature before the completion of primary recrystallisation and then intercritically annealed. The fine microstructure was found to be mainly due to the inhibition of primary recrystallisation, and also due to the inhibition of subgrain growth in deformed matrix by finely dispersed γ phase formed during heating. Mn segregation at α/γ interfaces seems to indicate that the kinetics of boundary migration in the existence of γ is controlled by the volume diffusion of substitutional alloying elements across the α/γ interfaces.

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Hausmann, D., C. Solís, L. P. Freund, N. Volz, A. Heinemann, M. Göken, R. Gilles et S. Neumeier. « Enhancing the High-Temperature Strength of a Co-Base Superalloy by Optimizing the γ/γ′ Microstructure ». Metals 10, n^o 3 (28 février 2020) : 321. http://dx.doi.org/10.3390/met10030321.

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Compositionally complex polycrystalline γ/γ′ CoNi-base superalloys, such as CoWAlloy2 (Co41-Ni32-Cr12-Al9-W5-Ti0.3-Ta0.2-Si0.4-Hf0.1-C-B-Zr) are interesting candidates for new high-temperature materials. To maximize their high-temperature strength, the γ/γ′ microstructure has to be optimized by adjusting the multi-step heat treatments. Various microstructures after different heat treatments were analyzed by scanning and transmission electron microscopy and especially in-situ small-angle neutron scattering during heat treatment experiments. The corresponding mechanical properties were determined by compression tests and hardness measurements. From this, an optimum γ′ precipitate size was determined that is adjusted mainly in the first precipitation heat treatment step. This is discussed on the basis of the theory of shearing of γ′ precipitates by weak and strong pair-couplings of dislocations. A second age hardening step leads to a further increase in the γ′ volume fraction above 70% and the formation of tertiary γ′ precipitates in the γ channels, resulting in an increased hardness and yield strength. A comparison between two different three-step heat treatments revealed an increase in strength of 75 MPa for the optimized heat treatment.

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Pinz, M., G. Weber, W. C. Lenthe, M. D. Uchic, T. M. Pollock et S. Ghosh. « Microstructure and property based statistically equivalent RVEs for intragranular γ−γ' microstructures of Ni-based superalloys ». Acta Materialia 157 (septembre 2018) : 245–58. http://dx.doi.org/10.1016/j.actamat.2018.07.034.

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Hashimoto, Keizo. « High-Temperature Tensile Properties of Ti-Al-X (X=Cr,W) Consisting of α₂, β and γ in Three Phases ». Materials Science Forum 706-709 (janvier 2012) : 1066–70. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1066.

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Gamma titanium aluminides (γ-TiAl) have been investigated extensively for more than 25 years, since they are considered to be candidate materials for advanced jet engine components, automobile exhaust valves, turbo-chargers, and so on. Many researchers have reported that the mechanical properties of γ-TiAl have been improved by micro-alloying and thermo-mechanical microstructure control. Recently, γ-TiAl entered a new era by being applied to low-pressure turbine blades in newly developed commercial jet engines. In order to spread their applications further, material durability and affordability have become key issues. The tensile properties of the Ti-Al-X (X=Cr or W) have been studied intensively at various strain rates and test temperatures in a vacuum atmosphere. It has been demonstrated that the additions of a few atomic percent of Cr or W to γ-TiAl shifts the phase stability drastically and creates relatively fine-grain microstructures consisting of α2+β+γ in three phases. Although the microstructures of Ti-46at%Al-2.7at%Cr and Ti-45at%Al-1.9at%W show similar morphology, the high-temperature mechanical properties of each indicate distinguishable properties. The former specimens have demonstrated the capability of super-plastic deformation at temperatures above 1323K; the latter specimens, however, have showed relatively higher tensile strength than those of the other specimens having ternary compositions (Ti-Al-X). The differences in the tensile properties of Ti-Al-X (X=Cr or W) have been discussed in conjunction with microstructures and the effects of solid-solution hardening due to W atoms.

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Larson, D. J., M. K. Miller, H. Inui et M. Yamaguchi. « Atom Probe Field Ion Microscopy of Poly Synthetically Twinned Titanium Aluminide ». Microscopy and Microanalysis 4, S2 (juillet 1998) : 102–3. http://dx.doi.org/10.1017/s1431927600020638.

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Two phase γ-based TiAl alloys are attractive for structural applications at high temperatures because they possess good elevated-temperature mechanical properties, low density, and good creep and oxidation resistance. The microstructures of these alloys consist of plates of the near equiatomic γ phase (L10-ordered structure) and the Ti3Al α2 phase (D019-ordered structure). It is of great interest to study the details of the lamellar α2+γ microstructure because the interface stability is the key to providing a usable high temperature material.Polysynthetically twinned (PST) TiAl crystals have been developed in order to systematically study the lamellar microstructure. These PST materials contain no high angle grain boundaries and have an single set of aligned lamellae of a α2 and γ phases, as shown in Fig. 1. Therefore, PST samples facilitate the study of the dependence of mechanical properties on lamellar structure by providing a known, consistent set of aligned lamellae.

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Zhang, Shuling, Ning Cui, Wei Sun et Qiucheng Li. « Microstructural Characterization and Crack Propagation Behavior of a Novel β-Solidifying TiAl Alloy ». Metals 11, n^o 8 (2 août 2021) : 1231. http://dx.doi.org/10.3390/met11081231.

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Novel β-solidifying TiAl alloys have great potential for engineering applications in the aerospace and automotive industries. The introduction of the β0 phase will inevitably affect crack propagation. However, the related mechanism is unclear. In this study, the crack propagation behavior of different β0-containing microstructures was systematically investigated by three-point bending tests. The results show that the coarse γ/α2 lamellar microstructure exhibits better fracture toughness than the fine-grain microstructure because large numbers of γ/α2 lamellar boundaries can effectively hinder crack propagation. The propagation direction depends largely on the orientation of the γ/α2 lamellae. When the angle between the crack propagation direction and the γ/α2 lamellar boundary is small, the crack tends to propagate along γ/α2 lamellae. When the angle is close to 90°, the crack generally propagates by the trans-lamellar mode. Moreover, the crack tends to traverse across the fine β0/γ duplex region due to the low resistance of fine grains in the crack propagation. The transgranular and intergranular modes are the main fracture mechanisms in the microstructure of the fine β0/γ grains. Some shear ligaments can also be identified in the lamellar microstructure and these can consume propagation energy. The enlarged image shows that the crack propagation direction can be changed by the β0 phase, owing to its high hardness. The crack tends to stop at the β0 phase region.

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Sumitani, Takahiro, Katsushi Tanaka et Haruyuki Inui. « Microstructural evolution of monocrystalline Co–Al–W-based superalloys by high-temperature creep deformation ». MRS Proceedings 1516 (2012) : 221–26. http://dx.doi.org/10.1557/opl.2012.1683.

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ABSTRACTCreep tests of monocrystalline Co–Al–W-based alloys with a tensile stress of 137 MPa at 1000 °C were carried out. The microstructures of the crept specimens were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The γ′ phase in the specimens was not only elongated along the stress direction as expected by the sign of the lattice misfit but also elongated in one of the <100> directions perpendicular to the stress direction. As a result, the shape of the γ′ phase is not a rod but a plate. In the TEM images, it was observed that many SISFs are induced in the γ′ phase by creep. A similar microstructure is also observed in Ni-based superalloys, but the microstructure was formed under relatively lower temperatures and higher applied stresses. The observation of numerous stacking faults in the γ′ phase is a clear indication that the γ′ phase precipitated in the present alloy is weaker than that in many modern Ni-based superalloys.

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Villanueva Bravo, Sergio, Kaoru Yamamoto, Hirofumi Miyahara et Keisaku Ogi. « Control of Carbides and Graphite in Cast Irons Type Alloy’s Microstructures for Hot Strip Mills ». Journal of Metallurgy 2012 (14 mars 2012) : 1–6. http://dx.doi.org/10.1155/2012/438659.

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The carbide and graphite formation and redistribution of alloy elements during solidification were investigated on high-speed steel (HS) and Ni-hard type cast irons with Nb and V. The crystallization of hypereutectic HSS proceeds in the order of primary MC, γ + MC, γ + M6C, γ + M7C3, and γ + graphite eutectic, in hypoeutectic alloys proceeds in the order of primary γ, γ + MC, γ + graphite, γ + M6C, and γ + M7C3 eutectic, and in Ni-hard proceeds in the order of primary γ, γ + MC, γ + M3C, and γ + graphite eutectic. The γ + graphite eutectic solidifies with the decrease of V, Nb, and Cr and the increase of Si and C contents in residual liquid during solidification. The behavior in graphite forming tendency in the residual liquid is estimated by the parameter ∑CLimi′. The eutectic graphite crystallizes at the solid fraction when ∑CLimi′ takes a minimum value. The amount of graphite increases with the decrease in ∑CLimi′ of initial alloy content in both specimens. Inoculation with ferrosilicon effectively increases the graphite content in both specimens.

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Yang, Wan Peng, Jia Rong Li, Shi Zhong Liu, Jin Qian Zhao, Zhen Xue Shi et Xiao Guang Wang. « Microstructures of Low Angle Boundaries of a Third Generation Single Crystal Superalloy DD9 ». Materials Science Forum 898 (juin 2017) : 413–21. http://dx.doi.org/10.4028/www.scientific.net/msf.898.413.

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The microstructures of low angle boundaries (LABs) of a third generation single crystal superalloy DD9 in as-cast state and after different heat treatment processes were studied by optical microscopy (OM) and field emission scanning electron microscopy (FESEM). The results showed that the as-cast LABs of DD9 alloy consisted of rod-like and bulk γ' phases with γ matrix between them, and there were eutectic γ-γ' precipitating at the LABs, as well as small amounts of discrete distribution of carbides. The γ' phase locateed at the grain boundaries was larger than that distributed on both sides of the grain boundaries. After the solution heat treatment, as-cast eutectic γ-γ' at LABs dissolved completely, and rod-like γ' phase was still found at some LABs. Meanwhile, the LABs were inclined to be straight compared to the as-cast state. The primary aging heat treatment made γ' phase at the LABs dissolved completely, and the secondary aging heat treatment resulted little change in the morphology of the LABs. Thus, the effect of the primary aging heat treatment on the microstructures of the LABs was greater than that of the secondary aging heat treatment.

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Hooghan, Tejpal Kaur, Russell F. Pinizzotto, John H. Watkins et Toru Okabe. « A study of a low copper dental amalgam by analytical transmission electron microscopy ». Journal of Materials Research 11, n^o 10 (octobre 1996) : 2474–85. http://dx.doi.org/10.1557/jmr.1996.0312.

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Analytical transmission electron microscopy was used to study specimens of a low-Cu dental amalgam (Velvalloy), prepared using the “wedge technique.” Analysis confirmed that the microstructure consists of a Ag2Hg3(γ1)/HgSn7−9(γ2) matrix surrounding unreacted Ag3Sn(γ) particles. In addition a hitherto uncharacterized reaction layer of fine grains between Ag3Sn(γ) and Ag2Hg3(γ1) is a mixture of Ag3Sn(γ), Ag–Hg–Sn (β1), Ag2Hg3 (γ1), and occasionally Cu6Sn5 (η′). An Ag–Hg–Sn (β1) phase was clearly identified for the first time. Since Velvalloy is a simple commercial dental amalgam, it is a reasonable starting point for characterizing more complex dental amalgam microstructures.

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Horton, J. A., C. T. Liu et M. L. Santella. « Microstructures of Ni3Al alloyed with iron ». Proceedings, annual meeting, Electron Microscopy Society of America 45 (août 1987) : 210–11. http://dx.doi.org/10.1017/s0424820100125956.

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The nickel aluminide, Ni3Al, is an ordered intermetallic alloy that exhibits an increase in yield stress with an increase in temperature. Recent efforts have alleviated the inherent grain boundary brittleness by microalloying with boron. Alloying additions such as iron can be used to further increase the high temperature yield stress.Microstructures and phase relationships in the aluminides were studied by transmission electron microscopy. A Ni3Al alloy with 10 at.% iron was single phase with the ordered Ll2 structure. Two alloys with 15% iron were found to contain a two-phase, γ + γ', cellular structure that consisted of small islands of crystallographically aligned ordered γ', surrounded by a “web” of disordered γ, Fig. 1. At 20% iron, the cellular structure encompasses nearly the entire specimen. Figure 2, a bright-field, dark-field pair of micrographs, shows the dislocation-cell structures (2a) and the ordered cellular structure (2b) present after tensile deformation at 600°C.

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Xue, Yanpeng, Xiaoguang Wang, Jinqian Zhao, Zhenxue Shi, Shizhong Liu et Jiarong Li. « Effect of Withdrawal Rate on Solidification Microstructures of DD9 Single Crystal Turbine Blade ». Materials 16, n^o 9 (27 avril 2023) : 3409. http://dx.doi.org/10.3390/ma16093409.

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Single crystal superalloys are widely used in the manufacturing of turbine blades for aero-engines due to their superior performance at high temperatures. The directional solidification process is a key technology for producing single crystal turbine blades with excellent properties. In the directional solidification process, withdrawal rate is one of the critical parameters for microstructure formation and will ultimately determine the blade’s properties. In this paper, the as-cast microstructures in the typical sections of a DD9 single crystal (SX) superalloy turbine blade were investigated with 3 mm/min and 5 mm/min withdrawal rates during the directional solidification process. With increased withdrawal rate, the dendrite morphologies tended to become more refined, and the secondary dendritic arms tended to be highly developed. The dendrite in the blade aerofoil section was more refined than that in the tenon section, given the same withdrawal rate. Additionally, with increasing withdrawal rates, the size and dispersity of the γ′ precipitates in the inter-dendritic (ID) regions and dendritic core (DC) tended to decrease; furthermore, the size distributions of the γ′ precipitates followed a normal distribution law. Compared with the ID regions, an almost 62% reduction in the average γ′ sizes was measured in the DC. Meanwhile, given the same withdrawal rate, at the blade’s leading edge closest to the heater, the γ′ sizes in the aerofoil section (AS) were more refined than those in the tenon section (TS). As compared with the decreasing cross-sectional areas, the increased withdrawal rates clearly brought down the γ′ sizes. The sizes of the γ–γ′ eutectics decreased with increasing withdrawal rates, with the γ–γ′ eutectics showing both lamellar and rosette shapes.

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Rojhirunsakool, Tanaporn, Duangkwan Thongpian, Nutthita Chuankrerkkul et Panyawat Wangyao. « Effect of Pre-Weld Heat Treatment Temperatures on TIG Welded Microstructures on Nickel Base Superalloy, GTD-111 ». Key Engineering Materials 658 (juillet 2015) : 14–18. http://dx.doi.org/10.4028/www.scientific.net/kem.658.14.

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Nickel-base superalloys have been used as high temperature materials in land-base gas turbine application. When subjected to long term, high temperature service, large crack propagation was observed. Typical refurbishment method of these turbines is carried out by using TIG welding followed by post-weld standard heat treatment. However, new crack initiation is found in the heat-affected zone after TIG welding. Pre-weld heat treatment has been discovered to improves final γ + γ’ microstructure. This study focuses on the effect of pre-weld heat treatment temperature on final γ + γ’ microstructure. Seven different conditions of pre-weld heat treatment temperature were investigated. Scanning electron microscopy studies were carried out after pre-weld and post-weld heat treatments to compare the γ + γ’ microstructure and capture microcracks. The best pre-weld heat treatment temperature produces uniform distribution of finely dispersed γ’ precipitates in the γ matrix without post-weld crack.

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Sun, W., X. Z. Qin, W. Wang, T. T. Wang, Yong An Guo, J. T. Guo, Lang Hong Lou et Lan Zhang Zhou. « Effects of Nb/Ti Ratio on the Microstructures of Two Experimental Ni-Based Cast Superalloys ». Materials Science Forum 747-748 (février 2013) : 629–35. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.629.

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Effects of Nb/Ti ratio on the microstructures of two experimental Ni-based cast superalloys of the Nb/Ti ratio 0.46 and 0.03 were investigated. The Nb/Ti ratio had a significant effect on the dendritic microstructures, especially the γ precipitate, of the two alloys under the as-cast condition. The amount and composition of primary MC carbides were closely related to the Nb/Ti ratio for that the Nb atoms have a stronger tendency to form the MC carbides than the Ti atoms. During thermal exposure, the primary MC carbides gradually degraded through two reactions: firstly MC + γ M6C + γ and then MC + γ M23C6+ γ. The Nb/Ti ratio had little influence on the reaction formation but obvious influence on the decomposition degree of the primary MC carbides decomposition. In addition, the second M6C and M23C6carbides on the boundaries (GBs) gradually formed a continuous chain during thermal exposure. The γ-free zones appeared along the GBs as the growth of the second carbides and γ precipitates on the GBs when thermal exposure time last up to 3000 h.

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Sakata, Masahiro, Jong Yeong Oh, Ken Cho, Hiroyuki Y. Yasuda, Mitsuharu Todai, Takayoshi Nakano, Ayako Ikeda, Minoru Ueda et Masao Takeyama. « Effects of Heat Treatment on Unique Layered Microstructure and Tensile Properties of TiAl Fabricated by Electron Beam Melting ». Materials Science Forum 941 (décembre 2018) : 1366–71. http://dx.doi.org/10.4028/www.scientific.net/msf.941.1366.

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In the present study, effects of heat treatment on microstructures and tensile properties of the cylindrical bars of Ti-48Al-2Cr-2Nb (at.%) alloy with unique layered microstructure consisting of equiaxed γ grains region (γ band) and duplex-like region fabricated by electron beam melting (EBM) were investigated. We found that it is possible to control width of the γ bands (Wγ) by heat treatments at 1100°C and 1190°C. The Wγ increases with decreasing heat treatment temperature. The bars heat-treated at 1190°C exhibit high elongation of 2.9% at room temperature (RT) with maintaining high strength. The RT elongation increases with increasing the Wγ because of increasing deformable regions. In contrast, the RT elongation of the bars decreases with increasing the Wγ when Wγ is very large. This is because the large γ band leads intergranular fracture. These results indicate that there is appropriate width for the γ band to obtain excellent tensile properties at RT.

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Lacaze, Jacques, et Alain Hazotte. « Directionally Solidified Materials : Nickel-base Superalloys for Gas Turbines ». Textures and Microstructures 13, n^o 1 (1 janvier 1990) : 1–14. http://dx.doi.org/10.1155/tsm.13.1.

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From the first forged turbine blades made of iron base alloys to the present nickel base single-grain turbine blades and vanes manufactured by directional solidification, an enormous amount of research has been directed to attaining the hottest possible combustion chamber temperatures in jet engines. Temperature has been increased by about 15 K each year for the last two decades, improving the thermodynamic efficiency of the engines. The more recent developments concern the manufacturing of single-grain parts made of nickel base superalloys with large amount of the γ′ hardening phase.This paper first presents the directional solidification process used to produce single-grain parts, the formation of as-cast microstructures and the defects that can arise during solidification. In the second part the thermal treatments that are applied to the nickel base superalloys in order to enhance their mechanical properties are detailed. The effect of crystallographic orientation and of the γ/γ′ microstructure on the mechanical properties is briefly presented, as well as the. microstructural changes that can possibly arise during service.

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Samal, MK. « Development of a model for simulation of micro-twin and corresponding asymmetry in high temperature deformation behavior of nickel-based superalloy single crystals using crystal plasticity-based framework ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 231, n^o 14 (22 mars 2016) : 2621–35. http://dx.doi.org/10.1177/0954406216639073.

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Development of reliable computational models to predict the high temperature deformation behavior of nickel-based superalloys is in the forefront of materials research. These alloys find wide applications in manufacturing of turbine blades and discs of aircraft engines. The microstructure of these alloys consists of the primary γ′-phase, and the secondary and tertiary precipitates (of Ni3Al type) are dispersed as γ′-phases in the gamma matrix. It is computationally expensive to incorporate the explicit finite element model of the γ-γ′ microstructure in a crystal plasticity-based constitutive framework to simulate the response of the polycrystalline microstructure. Existing models in literature do not account for these underlying micro-structural features which are important for simulation of polycrystalline response. The aim of this work is to develop a physically motivated multi-scale approach for simulation of high temperature response of nickel-based superalloys. At the lower length scale, a dislocation density-based crystal plasticity model is developed which simulates the response of various types of microstructures. The microstructures are designed with various shapes and volume fractions of γ′-precipitates. A new model for simulation of the mechanism of anti-phase boundary shearing of the γ′-precipitates, by the matrix dislocations, is developed in this work. The lower scale model is homogenized as a function of various micro-structural parameters, and the homogenized model is used in the next scale of multi-scale simulation. In addition, a new criterion for initiation of micro-twin and a constitutive model for twin strain accumulation are developed. This new micro-twin model along with the homogenized crystal plasticity model has been used to simulate the creep response of a single crystal nickel-based superalloy, and the results have been compared with those of experiment from literature. It was observed that the new model has been able to model the tension–compression asymmetry as observed in single crystal experiments.

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Qiao, Mengmeng, Tao Zhang et Ming Miao. « Minced Beef Meat Paste Characteristics : Gel Properties, Water Distribution, and Microstructures Regulated by Medium Molecular Mass of γ-Poly-Glutamic Acid ». Foods 13, n^o 4 (6 février 2024) : 510. http://dx.doi.org/10.3390/foods13040510.

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The influences of various m-γ-PGA (0.08–0.20%, w/w) concentrations on the properties of minced beef meat paste in terms of rheological properties, texture, moisture distribution, and microstructures were evaluated. The results indicated that m-γ-PGA enhanced the water-holding capacity, gel strength, texture, and whiteness of the minced beef meat paste. Based on the microstructural results, m-γ-PGA helped form a more organized and compact gel, thereby limiting the migration of water through the gel matrix. In contrast to the control group, the water-holding property, gel strength, and whiteness of minced meat paste gels with m-γ-PGA content of 0.12% increased from 75.89%, 584.51 g·cm, and 61.83 to 79.91%, 780.87 g·cm, and 62.54, respectively (p < 0.05), exhibiting the highest water-holding property and gel strength. Thus, m-γ-PGA exhibits great potential for minced meat paste products as a healthy gel water retainer and enhancer in low-fat meat products.

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Tian, Su Gui, Xiao Xia Wu, Hui Chen Yu, Hao Fang Sun et Ze Hui Jiao. « Microstructures and Creep Behavior of As-Cast TiAl-Nb Alloy ». Materials Science Forum 816 (avril 2015) : 572–77. http://dx.doi.org/10.4028/www.scientific.net/msf.816.572.

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By means of creep properties measurement and microstructure observation, an investigation was carried out to study the creep behaviors of the as-cast TiAl-Nb alloy at temperature near 910 oC. Results showed that the microstructure of as-cast TiAl-Nb alloy consisted of γ/α2 phases with the lamellar feature, and the boundaries with irregular serrated configuration consisted of single γ phase, and located in between the lamellar γ/α2 phases with different orientations. The as-cast TiAl-Nb alloy displayed a better creep resistance at high temperature and longer creep life. Compared to α2 -Ti3Al phase, the γ phase possessed a weaker strength, therefore, the crack was easily initiated along the boundaries at about 45° angles relative to the stress axis, and propagated along the boundaries parallel to the orientation of lamellar γ/α2 phases up to the occurrence of creep fracture. Thereinto, the tearing edges formed on the surface of the fracture being inclined with the lamellar γ/α2 phases are attributed to the α2-Ti3Al phase with better strength hindering the crack propagation during creep.

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Pan, Wan, Wang, Shen, Fu, Li, Dai et Yan. « An Investigation of Friction Coefficient on Microstructure and Texture Evolution of Interstitial-Free Steel during Warm Rolling and Subsequent Annealing ». Crystals 9, n^o 11 (27 octobre 2019) : 565. http://dx.doi.org/10.3390/cryst9110565.

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A Ti bearing interstitial-free steel was finishing rolled in the ferrite region with and without lubrication and microstructures, mechanical properties and textures evolution during warm rolling and subsequent annealing were investigated by OM, SEM, tensile test and ODF. The results show that the surface microstructure of the as-rolled specimen without lubrication is composed of dense shear bands, while the microstructures of the central layer of the as-rolled specimen without lubrication and the whole cross section of the as-rolled specimen with lubrication are elongated ferrite. Short-time annealing can make the non-lubricated rolling sample recrystallize, but the lubricated rolling sample cannot. After complete recrystallization, the microstructure of the surface layer of the as-annealed specimen without lubrication is finer than that of the center layer of the as-annealed specimen without lubrication and the whole section of the as-annealed specimen with lubrication. The mechanical properties of as-annealed sample without lubrication change significantly in the initial annealing stage, while that of as-annealed sample with lubrication remain unchanged until the end stage of annealing. The surface layers of the as-rolled samples have strong Goss component and weak γ fibre components, while the central layers have strong γ fibre components and moderate rotated cubic components. As annealing proceeds, the Goss components of the surface layer decrease and the γ fibre components increase. The rotated cubic components in the central layer are gradually transformed into γ texture.

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Galieva, E. V., E. Yu Klassman et V. A. Valitov. « Low-temperature superplastic deformation of the EK79 nickel-based superalloy with the mixed ultrafine-grained microstructure ». Frontier materials & ; technologies, n^o 1 (2024) : 19–27. http://dx.doi.org/10.18323/2782-4039-2024-1-67-2.

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One of the most effective ways to increase the processing plasticity of advanced superalloys (heat-resistant nickel-based alloys) is the formation of an ultrafine-grained (UFG) microstructure in bulk semi-finished products. Such a microstructure is a necessary condition for the manifestation of the structural superplasticity effect in the technological processes of manufacturing products from such superalloys. One of the most promising methods for producing UFG microstructures is thermomechanical treatment (TMT) according to the multiple isothermal forging scheme. It has been shown that the EK79 superalloy after TMT, with a gradual decrease in the processing temperature from 0.88 to 0.62 Ts (where Ts is the strengthening phase dissolution temperature) leads to the transformation of the initial microduplex fine-grained microstructure into a mixed UFG microstructure. Such a mixed UFG microstructure consists of: 1) relatively coarse (inherited from the fine-grain microstructure) particles – γ'-phase with a size of 3.0±0.8 μm; 2) γ-grains, and incoherent γ'-phase particles with a size of 0.3–0.5 μm; 3) strengthening coherent intragranular γ'-phase particles with a size of 0.05–0.1 μm, released upon cooling from the TMT temperature to room temperature. During uniaxial compression tests, the EK79 superalloy with such microstructure, demonstrates low-temperature superplasticity in the temperature range of 800–1000 °C. It has been found that an increase in the deformation temperature up to 1000 °C, leads to the increase of γ-phase grains to micron size. The maintenance of superplastic properties in the presence of relatively coarse incoherent particles in the microstructure of the second phase (γ'-phase) is apparently related to the fact that the deformation is localised in the UFG component.

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Probst-Hein, M., A. Dlouhy et G. Eggeler. « Superposition of external and internal stress components in γ/γ'-microstructures and their effect on γ-channel dislocations ». Le Journal de Physique IV 09, PR9 (septembre 1999) : Pr9–127—Pr9–136. http://dx.doi.org/10.1051/jp4:1999913.

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Singh, S., M. J. Mills et M. De Graef. « Dynamical scattering image simulations for two-phase γ–γ′ microstructures : A theoretical model ». Ultramicroscopy 185 (février 2018) : 32–41. http://dx.doi.org/10.1016/j.ultramic.2017.11.008.

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Kim, Won Yong. « High Temperature Strength of Ni-Al-Cr Based Alloys Containing Refractory Elements for Advanced Die Materials ». Materials Science Forum 539-543 (mars 2007) : 1589–94. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1589.

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Microstructures and mechanical properties of Ni3Al based intermetallic alloys produced by vacuum arc melting and vacuum induction melting were investigated in terms of phase analysis using scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffractometer and tensile test machine. The duplex microstructural feature consisting of γ’ matrix phase and small intermetallic dispersoids was observed to be distributed over the whole microstructure in the Zr and/or Mo-added samples. From the SEM-EDS analysis of the alloys, it is clearly confirmed that the Mo is solved both into γ’ matrix phase and intermetallic phase while Zr has a role to form an intermetallic Ni5Zr phase for the entire alloys investigated. The ultimate tensile strength of the present alloy was superior to iron-based and Ni-based die materials especially in the high temperature region. The mechanical results obtained will be discussed in correlation with microstructural observations, phase analyses.

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Oehring, Michael, V. Küstner, Fritz Appel et Uwe Lorenz. « Analysis of the Solidification Microstructure of Multi- Component γ-TiAl Alloys ». Materials Science Forum 539-543 (mars 2007) : 1475–80. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1475.

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Gamma titanium aluminide alloys often solidify peritectically and show a coarse, dendritic microstructure, which can lead to unacceptable mechanical properties in the as-cast condition. In view of the development of improved cast alloys, the dependence of the solidifying microstructure on the aluminum content and other alloying elements was investigated. The formation of the observed solidification microstructures is discussed in comparison with microstructure formation maps calculated by the NCU (nucleation and constitutional undercooling) model developed by Hunziker et al. [1].

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Doi, Minoru, Takao Kozakai, Tomokazu Moritani et Shizuo Naito. « Two-Phase Microstructures of Gamma+Gamma-Prime Formed by Phase-Separations due to Heat-Treatments of Elastically Constrained Ni-Al-Ti Alloys ». Materials Science Forum 539-543 (mars 2007) : 3006–11. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.3006.

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In the elastically constrained Ni-Al-Ti alloy system, three kinds of phase-separations, i.e. microstructure changes, take place to bring the two-phase state of γ+γ’ depending on the alloy compositions and heat treatments: 1) in Ni-8at%Al-6at%Ti, the phase-separation of γ phase takes place and γ’ particles appear in the γ matrix, 2) in Ni-13at%Al-9at%Ti, the phase-separation of γ’ intermetallic phase takes place and γ particles appear in the γ’ matrix, 3) in Ni-8.5at%Al-5.4at%Ti, the phase-separation of γ’ precipitate phase takes place and γ particles appear in the γ’ precipitate.

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Zhao, Qian, Yong Kang Zhang, Cheng Yun Cui, Xi Gui Cui et Jin Zhong Lu. « Microstructure of Laser Cladded Cobalt-Based Alloy Coating on T10 Tool Steel ». Key Engineering Materials 464 (janvier 2011) : 694–97. http://dx.doi.org/10.4028/www.scientific.net/kem.464.694.

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Co-based alloy coating was fabricated by powder feeding laser cladding on T10 tool steel. The microstructure and phase composition were investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results showed that the different solidification microstructures on the section, such as planar, cellular and dendrite formed from the interface to the surface. The main phase γ-Co and another phase Cr23C6 existed in the original coating, however, the main phase γ-Co was unchanged, and another phase was replaced by Cr7C3 accompanying with Co3C and Co4B precipitations after aging treatment.

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Zhang, Wei Guo, Xue Mei Yi et Chu Ang Feng. « Heat Treatment Microstructures of a Directionally Solidified Nickel Base Superalloy under High Temperature Gradient ». Materials Science Forum 788 (avril 2014) : 519–24. http://dx.doi.org/10.4028/www.scientific.net/msf.788.519.

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The heat treatment of a directionally solidified superalloy under high temperature gradient with different dendritic size was studied. The evolution rules of each phase in DZ125 alloy after heat treatment were analyzed. The results show that γ' phase presents cube and uniform distribution after heat treatment. Its size is about 0.4μm and its area ratio is about 65%. MC carbide transforms into MC(2) carbide with high concentration of Hf. The morphology of MC carbide changes from Chinese-script to block and its size reduces gradually with increasing solidification rate under directional solidification. There is bulk γ' phase around carbide. MC(2) carbide and γ' phase in the grain boundary form chain along grain boundary, and effectively retard grain boundary sliding. γ+γ' eutectic is basically eliminated by solution treatment and only a little γ+γ' eutectic exists around carbide.

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Yang, Shu Yu, Min Jiang et Lei Wang. « New-Type Co-Based Superalloys Designed by CALPHAD Method ». Materials Science Forum 816 (avril 2015) : 578–80. http://dx.doi.org/10.4028/www.scientific.net/msf.816.578.

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The phase equilibria of new-type Co-based superalloys which include the system of Co-Al-W were studied by CALPHAD method. It was shown that γ+γ' two-phase regions were existed in the calculated phase diagrams. The compositions of new-type Co-based superalloys which can obtain γ+γ' microstructures were predicted due to the calculated phase diagram. The mole fractions of the constituent phases of Co-Al-W-Ni-Cr alloys were calculated. The temperature of γ' phase began to precipitate at about 1050°C.

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Wang, Xin Mei, M. Y. Cao, S. W. Li, Z. Y. Yu et Z. F. Yue. « The Influence of γ/γ′ Morphology on the Rafting and Stress Distribution of Nickel-Based Superalloys Loaded in [0 0 1] Direction ». Materials Science Forum 895 (mars 2017) : 14–19. http://dx.doi.org/10.4028/www.scientific.net/msf.895.14.

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Two kinds of representative volume elements (RVEs) are introduced to represent the experimental γ/γ′ morphology to study the influences of microstructures on the creep behavior of [0 0 1]-oriented single crystal nickel-based superalloys under tensile loading. One RVE (RVE1) is consisted with one cuboidal γ′ phase surrounded by γ phase. The other (RVE2) is constructed by two cuboidal γ′ phases and one rectangle γ′ phase. A raft criterion is implemented into a user subroutine to predict the rafting type. The misfit stress is considered by different thermal expansion coefficients of the two phases. The rafting type is correctly predicted. The evolutions of the stresses distributions are discussed.

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Li, Jing Yuan, Sumio Sugiyama et Jun Yanagimoto. « Microstructural Evolution and Deformation Behavior of Stainless Steel in Semi-Solid State ». Solid State Phenomena 116-117 (octobre 2006) : 681–85. http://dx.doi.org/10.4028/www.scientific.net/ssp.116-117.681.

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Thixoforming or Semi-Solid Metal Forming offers many advantages in comparison with casting and conventional forging. The purpose of the present study is to provide the basic microstructure and deformation data for austenitic and ferritic stainless steel under mushy state. As well known, the stainless steels solidify in different modes according to the different chemical compositions. In this paper, microstructural evolution of austenitic stainless steel type 304 which solidifies in FA mode ( L → L +δ → L +δ +γ →δ +γ →γ ),austenitic stainless steel type 310S which solidifies in A mode ( L → L +γ →γ ), and ferritic stainless steel type 430 which solidifies in F mode ( L → L +δ →δ )are investigated during partial remelting by way of SIMA (Strain Induced Melted Activation). The results show that A and F mode of stainless steels melt directly at the grain boundary without phase transformation during reheating. A banded structure, originating from the primary dendritic segregation of the original ingots, is observed in type 310S steel during further heating. On the other hand, a perfect globular and insegregative two-phase semi-solid structure L +δ can be obtained while heated beyond the banded three-phase L +δ +γ semi-solid state in FA mode austenitic stainless steel type 304. This spheroidization can be attributed to the peritectic reaction occurred in the L +δ +γ semi-solid state. In addition, simple compression tests of these alloys in semi-solid state for varied combination of deformation rate and deformation temperature are conducted to examine the deformation behavior of stainless steel. Flow stress curves exhibit abrupt change in various alloys, even though in the same alloy such as type 304, various flow stresses are observed according to the difference in inner microstructure or morphology. Stress of type 310S steel shows the most reduction as the deformation temperature increasing at the same strain rate condition. The Liquid is centralized to periphery by the compression force in all deformed test pieces. Fracture, observed in all alloys except type 304 steel in globular L +δ semi-solid state, should be resulted from the lack of liquid in L +δ +γ state of type 304 steel and solidification crack in type 310S and type 430 steel. Deformation of solid particles occurs only in L +δ +γ state of type 304 steel. Last in this paper, various deformation mechanisms are proposed for various microstructures.

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Tsuno, Nobuyasu, Akihiro Sato, Katsushi Tanaka et Haruyuki Inui. « Evolution of Raft Structure during Creep Deformation of the Ni-Based Single-Crystal Superalloy TMS-138 ». Advanced Materials Research 278 (juillet 2011) : 19–24. http://dx.doi.org/10.4028/www.scientific.net/amr.278.19.

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The evolution of the raft structure in the Ni-based single-crystal superalloy TMS-138 crept at 1100 °C and 137 MPa has been investigated quantitatively by the Fourier analysis of scanning electron microscope (SEM) images. This method of analysis quantifies the extent of tilting of the γ/γ′ interface during creep deformation. The analysis is carried out on two different crystallographic planes, (100) and (110), on which SEM observations of deformation microstructures are made, to see if there is any difference in the results of analysis depending on observation planes. The tilt angle of the γ/γ′ interface, which is deduced by the Fourier analysis, increases with the accumulation of creep strain. The rate of the increase in the tilt angle is significantly large in the tertiary creep stage. The result of analysis does not depend significantly on crystallographic planes on which SEM observations of microstructures are made.

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Reyes Tirado, Fernando L., Jacques Perrin Toinin et David C. Dunand. « γ+γ′ microstructures in the Co-Ta-V and Co-Nb-V ternary systems ». Acta Materialia 151 (juin 2018) : 137–48. http://dx.doi.org/10.1016/j.actamat.2018.03.057.

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Clément, Nicole, Mustafa Benyoucef, M. Legros, Pierre Caron et Armand Coujou. « In Situ Deformation at 850°C of Standard and Rafted Microstructures of Nickel Base Superalloys ». Materials Science Forum 509 (mars 2006) : 57–62. http://dx.doi.org/10.4028/www.scientific.net/msf.509.57.

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An in situ study of the plastic deformation of <001> single crystals of an industrial superalloy has been performed at 850 °C in a TEM to observe directly the micromechanisms which control the deformation under the actual temperature and stress conditions experienced by this material in aeroengines. A comparison between the creation and propagation modes of moving dislocations in the standard microstructure after annealing and the rafted microstructure after 20 h of creep at 1050°C evidence the important role of the width of the γ channels as well as the strength of the γ/γ’ interface in controlling the shearing events of γ’ channels.

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Horton, J. A., et C. T. Liu. « Microstructures of Ni3Al alloys as a function of Cr and Al levels ». Proceedings, annual meeting, Electron Microscopy Society of America 47 (6 août 1989) : 306–7. http://dx.doi.org/10.1017/s0424820100153506.

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Several alloys based on boron-doped Ni3Al are undergoing alloy development for a wide range of potential uses. The microstructures of several of these alloys were characterized by transmission electron microscopy as a function of the chromium and aluminum levels. The series included alloys with 0 to 10 at. % Cr and with 15.6 to 21% Al, see Table I.In Ni-AI alloys with low aluminum content and in most Ni-Al alloys with chromium additions, a twophase γ’ plus γ structure resulted. The major phase (and matrix) was ordered γ’ and the minor phase disordered γ· Both phases appeared interconnected and were completely epitactic. The ordered phase was aluminum-enriched while the disordered phase was chromium-enriched. Within the disordered phase a reprecipitation of γ’ often occurred, depending on heat treatment, and gave an appearance of a “disordered web”. Typical x-ray energy dispersive spectroscopic (EDS) analyses are listed in Table II.

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