Articoli di riviste: "Creep mechanism"

1

Shinya, Norio. "Creep fracture mechanism map." Bulletin of the Japan Institute of Metals 26, n. 8 (1987): 801–8. http://dx.doi.org/10.2320/materia1962.26.801.

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2

Li, J., e A. Dasgupta. "Failure-mechanism models for creep and creep rupture". IEEE Transactions on Reliability 42, n. 3 (1993): 339–53. http://dx.doi.org/10.1109/24.257816.

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3

Hou, Qing Yu, e Jing Tao Wang. "Deformation Mechanism in the Mg-Gd-Y Alloys Predicted by Deformation Mechanism Maps". Advanced Materials Research 146-147 (ottobre 2010): 225–32. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.225.

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Deformation mechanism maps at 0-883 K and shear strain rate of 10-10-10+6 s-1 were built from available rate equations for deformation mechanisms in pure magnesium or magnesium alloys. It can be found that the grain size has little effect on the fields of plasticity and phonon or electron drag, though it has important influence on the fields of power-law creep, diffusion creep, and Harper-Dorn creep in the maps within the present range of temperature, strain rate, and grain size. A larger grain size is helpful to increase the field range of power-law creep but decrease that of diffusion creep when the grain size is smaller than ~204 μm. Harper-Dorn creep dominates the deformation competed to diffusion creep in the grain size range of ~204-255 μm. The maps include only plasticity, phonon or electron drag, and power-law creep when the grain size is higher than ~255 μm, then the grain size has little influence on the maps. Comparison between the reported data for the Mg-Gd-Y alloys and the maps built from available rate equations, it can be conclude that the maps are an effective tool to predict or achieve a comprehensive understanding of the deformation behavior of the Mg-Gd-Y alloys and to classify systematically their discrepancies in the deformation mechanism. However, differences exist in the deformation mechanisms of the alloys observed by the reported data and that predicted by the maps. Therefore, refinement of the maps from the viewpoint of mechanical twining, DRX, and adiabatic shear are necessary.

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4

Sun, Zhihui, Baoshu Liu, Chenwei He, Lu Xie e Qing Peng. "Shift of Creep Mechanism in Nanocrystalline NiAl Alloy". Materials 12, n. 16 (7 agosto 2019): 2508. http://dx.doi.org/10.3390/ma12162508.

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We have examined the effects of temperature, stress, and grain size on the creep process including creep strain, crystal structure, dislocations and diffusions of nanocrystalline NiAl alloy through molecular dynamics simulations. A smaller grain size accelerates the creep process due to the large volume fraction of grain boundaries. Higher temperatures and stress levels also speed up this process in terms of dislocation changes and atom diffusion. In both primary creep and steady-state creep stages, atomic diffusion at the grain boundary could be seen and the dislocation density increased gradually, indicating that the creep mechanism at these stages is Coble creep controlled by grain boundary diffusion while accompanied by dislocation nucleation. When the model enters the tertiary creep stage, it can be observed that the diffusion of atoms in the grain boundary and in the crystal and the dislocation density gradually decreases, implying that the creep mechanisms at this stage are Coble creep, controlled by grain boundary diffusion, and Nabarro–Herring creep, controlled by lattice diffusion.

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5

Liu, Guo Jun. "Research on Mechanism of Concrete Creep". Applied Mechanics and Materials 670-671 (ottobre 2014): 441–44. http://dx.doi.org/10.4028/www.scientific.net/amm.670-671.441.

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Under sustained loads with a fixed value, the deformation of concrete will continue to increase as time increases; this phenomenon is called creep of concrete. Currently, there are several theories to explain the phenomenon of concrete creep, viscoelasticity theory, seepage theory, viscous flow theory, plastic flow theory, micro-fractures theory and internal forces balance theory. Above models mostly studied linear creep of concrete under low stress status. This paper mainly research on concrete creep mechanism, and pointed out the advantages and limitations of the various theories, which has a guiding significance for theoretical research.

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Sun, Qiang, Hong Fei Duan, Lei Xue e Li Qin. "The Micro-Mechanism Analysis on Rock Creep Damage". Advanced Materials Research 194-196 (febbraio 2011): 2031–34. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.2031.

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Rock creep is a hot topic and key point in engineering geology. Based on renormalization group theory, the rock creep instability of micro-mechanism can be described as follow: with the expanding and interaction of micro-cracks and the main fault forms, which leads to failure. Comparing with the similarity of rock creep and rock compression process, and combining results of rock creep process, it is shown that there a distinct pertinence between different stages of rock creep. The relationship characteristics of different evolutionary stages can be used to provide scientific foundation for rock creep.

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7

Zhao, Fei, Jie Zhang, Chenwei He, Yong Zhang, Xiaolei Gao e Lu Xie. "Molecular Dynamics Simulation on Creep Behavior of Nanocrystalline TiAl Alloy". Nanomaterials 10, n. 9 (28 agosto 2020): 1693. http://dx.doi.org/10.3390/nano10091693.

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TiAl alloy represents a new class of light and heat-resistant materials. In this study, the effect of temperature, pressure, and grain size on the high-temperature creep properties of nanocrystalline TiAl alloy have been studied through the molecular dynamics method. Based on this, the deformation mechanism of the different creep stages, including crystal structure, dislocation, and diffusion, has been explored. It is observed that the high-temperature creep performance of nanocrystalline TiAl alloy is significantly affected by temperature and stress. The higher is the temperature and stress, the greater the TiAl alloy’s steady-state creep rate and the faster the rapid creep stage. Smaller grain size accelerates the creep process due to the large volume fraction of the grain boundary. In the steady-state deformation stage, two kinds of creep mechanisms are manly noted, i.e., dislocation motion and grain boundary diffusion. At the same temperature, the creep mechanism is dominated by the dislocation motion in a high-stress field, and the creep mechanism is dominated by the diffusion creep in the low-stress field. However, it is observed to be mainly controlled by the grain boundary diffusion and lattice diffusion in the rapid creep stage.

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8

Kasum, Kasum, Fajar Mulyana, Mohamad Zaenudin, Adhes Gamayel e M. N. Mohammed. "Molecular Dynamics Simulation on Creep Mechanism of Nanocrystalline Cu-Ni Alloy". Jurnal Fisika Flux: Jurnal Ilmiah Fisika FMIPA Universitas Lambung Mangkurat 18, n. 1 (26 febbraio 2021): 67. http://dx.doi.org/10.20527/flux.v18i1.8548.

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Creep mechanism is an essential mechanism for material when subjected to a high temperature and high pressure. It shows material ability during an extreme application to maintain its structure and properties, especially high pressure and temperature. This test is already done experimentally in many materials such as metallic alloys, various stainless steel, and composites. However, understanding the creep mechanism at the atomic level is challenging due to the instruments limitation. Still, the improvement of mechanical properties is expected can be done in such a group. In this work, the creep mechanism of the nanocrystalline Cu-Ni alloy is demonstrated in terms of molecular dynamics simulation. The result shows a significant impact on both temperature and pressure. The deformation supports the mechanisms as a result of the grain boundary diffusion. Quantitative analysis shows a more substantial difference in creep-rate at a higher temperature and pressure parameters. This study has successfully demonstrated the mechanism of creep at the atomic scale and may be used for improving the mechanical properties of the material.

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9

Osborne, J. W. "Creep as a Mechanism for Sealing Amalgams". Operative Dentistry 31, n. 2 (1 febbraio 2006): 161–64. http://dx.doi.org/10.2341/05-18.

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Clinical Relevance Creep may be a major factor in amalgam sealing from microleakage. Creep expansion causes amalgam to fill in the tooth/amalgam interface gap and causes the restoration to extrude out of the preparation.

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10

Nabarro, F. R. N. "The mechanism of Harper-Dorn creep". Acta Metallurgica 37, n. 8 (agosto 1989): 2217–22. http://dx.doi.org/10.1016/0001-6160(89)90147-8.

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11

Тукмакова, А. С., Н. И. Хахилев, Д. Б. Щеглова, В. Д. Насонов, А. П. Новицкий, И. А. Сергиенко e А. В. Новотельнова. "Анализ механизмов уплотнения термоэлектрических порошков скуттерудитов и сплавов Гейслера в процессе активированного полем спекания". Физика и техника полупроводников 55, n. 12 (2021): 1132. http://dx.doi.org/10.21883/ftp.2021.12.51695.10.

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The analysis of the shrinkage rate of powders, based on the power-law creep model of a porous body, was carried out in this paper to calculate the compaction parameters of CoSb3-based skutterudites and Fe2VAl-based Heusler alloys within field-activated sintering. It was indicated that this method, which had already been used for metal and ceramic powders, is applicable for thermoelectric powders. The values of strain rate sensitivity were obtained, and the corresponding powder compaction mechanisms have been defined. The main creep mechanism for skutterudites was found to be a dislocation climb, that later was replaced by grain boundary sliding, and the last sintering stage was associated with diffusional creep. The main creep mechanism for Heusler alloys was grain boundary sliding, later replaced by diffusional creep.

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12

Camin, Bettina, e Lennart Hansen. "In Situ 3D-µ-Tomography on Particle-Reinforced Light Metal Matrix Composite Materials under Creep Conditions". Metals 10, n. 8 (1 agosto 2020): 1034. http://dx.doi.org/10.3390/met10081034.

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In transportation light metal matrix composites (L-MMCs) are used increasingly due to their improved creep resistance even at higher application temperatures. Therefore, the creep behavior and failure mechanisms of creep loaded particle reinforced L-MMCs have been investigated intensively. Until now, creep damage analyses are usually performed ex situ by means of interrupted creep experiments. However, ex situ methods do not provide sufficient information about the evolution of creep damage. Hence, in situ synchrotron X-ray 3D-µ-tomography investigations were carried out enabling time and space resolved studies of the damage mechanisms in particle-reinforced titanium- and aluminum-based metal matrix composites (MMCs) during creep. The 3D-data were visualized and existing models were applied, specifying the phenomenology of the damage in the early and late creep stages. During the early stages of creep, the damage is determined by surface diffusion in the matrix or reinforcement fracture, both evolving proportionally to the macroscopic creep curve. In the late creep stages the damage mechanisms are quite different: In the Al-MMC, the identified mechanisms persist proportional to creep strain. In contrast, in the titanium-MMC, a changeover to the mechanism of dislocation creep evolving super-proportionally to creep strain occurs.

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13

Kawasaki, Megumi, e Terence G. Langdon. "Characteristics of High Temperature Creep in Pure Aluminum Processed by Equal-Channel Angular Pressing". Materials Science Forum 638-642 (gennaio 2010): 1965–70. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.1965.

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High purity aluminum was processed by equal-channel angular pressing (ECAP) to reduce the grain size to ~1.3 m. Tensile specimens were cut from the as-pressed billets and these specimens were tested under conditions of high temperature creep. The results show excellent creep properties with a well-defined region of steady-state flow. The flow behavior is analyzed by comparing the creep data with the predicted behavior for different fundamental creep mechanisms and by plotting a deformation mechanism map to provide a visual representation of the creep properties.

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14

Asada, Yasuhide, e Masatsugu Yaguchi. "Mechanistic Approach for Creep-Fatigue Evaluation of 9Cr-1Mo-V-Nb Steel". Journal of Engineering Materials and Technology 117, n. 4 (1 ottobre 1995): 356–60. http://dx.doi.org/10.1115/1.2804725.

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A mechanistic model was developed to describe the creep-fatigue interaction of 9Cr-1Mo-V-Nb steel based on a damage mechanics approach. The model assumes that each of the fatigue and creep damage consists of basic damages with a size and density. The mechanism of the creep-fatigue interaction is considered to be an early growth of a size of fatigue basic damage from a creep basic damage formed prior to fatigue loading. The model interprets well the experimental creep-fatigue life under complex strain histories.

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15

Yamamoto, Masato, e Takashi Ogata. "Microscopic Damage Mechanism of Nickel-Based Superalloy Inconel 738LC Under Creep-Fatigue Conditions". Journal of Engineering Materials and Technology 122, n. 3 (1 marzo 2000): 315–20. http://dx.doi.org/10.1115/1.482803.

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Creep-fatigue damage in Inconel 738LC was clarified by in-situ observation and a new creep-fatigue life prediction model was proposed based on the mechanism identified. Creep-fatigue tests on standard specimens show that the tensile hold creep-fatigue lives were reduced to 60 to 80 percent and those in the compressive hold condition were reduced to 20 to 40 percent of the fatigue life of the same total strain condition. In-situ creep-fatigue tests on miniature specimens show that grain boundary sliding could be observed under the compressive strain hold condition and under the tensile strain hold condition grain boundary cavity damage and grain boundary sliding were observed. These mechanisms are regarded as the main cause of the damage acceleration under the creep-fatigue loading conditions. Therefore, the new creep-fatigue life prediction model, which is based on the nonlinear damage accumulation method, employed two damage acceleration parameters “dsl” and “dcr,” which represent grain boundary sliding damage and grain boundary cavity damage, respectively. Creep-fatigue lives of the test results were well predicted by the proposed model. [S0094-4289(00)01203-2]

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16

Tian, Su Gui, Xin Wang, Chen Liu e Wen Ru Sun. "Influence of Phosphorus and Boron on Creep Behavior and Fracture Mechanism of GH4169 Superalloy". Materials Science Forum 747-748 (febbraio 2013): 672–77. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.672.

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By means of creep properties measurement and microstructure observation, the influence of the traces P, B on creep behaviors and fracture mechanism of GH4169 alloy was investigated. Results showed that during creep the twinning was thought to be the main deformation mechanism of GH4169 alloy, however the deformation mechanisms of alloy containing P, B were the twinning and slipping of dislocations activated within the grains. And the fact that the slipping of dislocations activated within the grain can delay the stress concentration in the local regions to restrain the initiation of the cracks to improve the creep resistance of the alloy. Compared to GH4169 alloy, the fracture of GH4169G alloy displayed the non-smooth surface. The adding traces P, B were segregated in the region near the boundary, which may promote the particle-like δ phase precipitated along the boundary to restrain the boundaries slipping and the cracks propagation. This was thought to be the main reason for enhancing the strength of the boundary and prolonging the creep life.

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17

Shibutani, Tadahiro, Qiang Yu e Masaki Shiratori. "A Study of Deformation Mechanism During Nanoindentation Creep in Tin-Based Solder Balls". Journal of Electronic Packaging 129, n. 1 (12 maggio 2006): 71–75. http://dx.doi.org/10.1115/1.2429712.

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As the shrinkage and integration of devices, the creep behavior of tin-based alloys becomes important with microscales. In this paper, the behavior of creep deformation in solder alloys during a nanoindentation test was examined. Nanoindentation creep test was carried out for tin-based solder balls. Obtained results summarized as follows: (i) The stress exponent for power-law creep estimated can be evaluated from the evolution of hardness. These values obtained in the early stage corresponds with that of bulk within the range of high strain rate. (ii) The stress sensitivity decreases after stress relaxation in nanoindentation creep tests. The saturated value is 1 in three solder balls. (iii) The morphology of indented surface consists of three parts: initial indentation, power-law creep, and granular surface. It suggests that the transition from power-law creep to diffusion creep takes place. (iv) Finite element method analysis reveals stress and strain concentration appears in the vicinity of the tip. Strain field remains self-similar as the indentation proceeds. (v) The gradient of triaxial stresses below the tip in a nanoindentation test accelerates the creep strain rate due to the diffusive flow, relatively.

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Chiu, Huai Yi, Chen Ming Kuo e Huei Sen Wang. "Creep Behavior of 409L and 436 Ferritic Stainless Steels Applied for Automotive Exhaust System". Applied Mechanics and Materials 302 (febbraio 2013): 252–57. http://dx.doi.org/10.4028/www.scientific.net/amm.302.252.

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In order to investigate the creep behavior and understand its deformation mechanism of automotive exhaust pipe materials, this study conducted creep experiments of 409L and 436 ferritic stainless steels at both 600°C and 750°C under different stress levels. After creep tests, crept specimens were analyzed on the microstructure and fracture surfaces by the use of scanning electron microscopy. From creep data, two important material coefficients, namely, M of Monkman-Grant relationship and K of Coble creep equation are calculated for predicting the material creep life. Results show the creep resistance of 436 stainless steel is better than that of 409L stainless steel, because the 436 stainless steel has more Ni, Cr, and Mo contents. As the creep mechanism, all tests show grain boundary diffusion or Coble creep is the dominate deformation mechanism, except at higher temperature 750 °C and higher stress levels.

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Xu, Xiang, Peter Binkele, Wolfgang Verestek e Siegfried Schmauder. "Molecular Dynamics Simulation of High-Temperature Creep Behavior of Nickel Polycrystalline Nanopillars". Molecules 26, n. 9 (29 aprile 2021): 2606. http://dx.doi.org/10.3390/molecules26092606.

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As Nickel (Ni) is the base of important Ni-based superalloys for high-temperature applications, it is important to determine the creep behavior of its nano-polycrystals. The nano-tensile properties and creep behavior of nickel polycrystalline nanopillars are investigated employing molecular dynamics simulations under different temperatures, stresses, and grain sizes. The mechanisms behind the creep behavior are analyzed in detail by calculating the stress exponents, grain boundary exponents, and activation energies. The novel results in this work are summarized in a deformation mechanism map and are in good agreement with Ashby’s experimental results for pure Ni. Through the deformation diagram, dislocation creep dominates the creep process when applying a high stress, while grain boundary sliding prevails at lower stress levels. These two mechanisms could also be coupled together for a low-stress but a high-temperature creep simulation. In this work, the dislocation creep is clearly observed and discussed in detail. Through analyzing the activation energies, vacancy diffusion begins to play an important role in enhancing the grain boundary creep in the creep process when the temperature is above 1000 K.

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Dragatogiannis, Dimitrios A., Elias P. Koumoulos, Ioannis A. Kartsonakis e Costas A. Charitidis. "Deformation mechanism during nanoindentation creep and corrosion resistance of Zn". International Journal of Structural Integrity 7, n. 1 (1 febbraio 2016): 47–69. http://dx.doi.org/10.1108/ijsi-07-2014-0034.

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Purpose – The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. There is a lot of work in the field of nanoindentation in order to understand the dynamic effects on nanomechanical properties. The paper aims to discuss these issues. Design/methodology/approach – The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on hot dip galvanized (HDG) steel, is discussed through nanoindentation. Findings – Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro-materials and systems. The corrosion resistance was studied by electrochemical impedance spectroscopy (EIS) and localized EIS. Originality/value – The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on HDGsteel, is discussed through nanoindentation. Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro- materials and systems. The corrosion resistance was studied by EIS and localized EIS.

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Nanko, Makoto, Manabu Sato, Koji Matsumaru e Kozo Ishizaki. "Densification Mechanism of Fine Ni-20Cr Powder during Pulsed Electric Current Sintering". Materials Science Forum 510-511 (marzo 2006): 818–21. http://dx.doi.org/10.4028/www.scientific.net/msf.510-511.818.

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Microstructure observation and kinetic analysis were conducted on fine Ni-20Cr powder (spherical shape and 5 m in average particle diameter) to understand the sintering mechanism of fine metallic powder during pulsed electric current sintering (PECS). Insulation of the sample during PECS was carried out to investigate the influences of pulsed electric current passing through the sample. Temperature at the sample/die interface was measured as sample temperature. Pulsed electric current did not influence densification. The microstructure observation revealed that the necks between particles had very small curvature radius, which means the neck formation by compressive deformation of particles owing to creep. As results of the kinetic analysis of the densification, the creep rate of fine Ni-20Cr powder was two digits larger than the extrapolated values of the steady-state creep on PECS of coarse Ni-20Cr powder and creep tests reported previously. The larger creep rate of fine Ni-20Cr powder during PECS may be influenced by not only smaller grain size of powder particles but also contribution of the initial creep, which was faster than the steady-state creep.

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Kvapilová, Marie, Květa Kuchařová, Karel Hrbáček e Vàclav Sklenička. "Creep Processes in MAR-M247 Nickel-Base Superalloy". Solid State Phenomena 258 (dicembre 2016): 603–6. http://dx.doi.org/10.4028/www.scientific.net/ssp.258.603.

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Creep processes in MAR-M247 Nickel - Base Superalloy were studied at elevated temperatures. The stress exponents of creep rate n and time to fracture m indicate power-low (dislocation) creep regime and suggest the same controlling mechanism for the creep deformation and fracture. The variation of values of parameter n within the interval of applied stress may indicate changes in the rate-controlling creep deformation mechanism. The possibility of using of Monkman-Grant relationship for creep life prediction was demonstrated.

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Liu, Dezheng, Yan Li, Xiangdong Xie, Guijie Liang e Jing Zhao. "Estimating the Influences of Prior Residual Stress on the Creep Rupture Mechanism for P92 Steel". Metals 9, n. 6 (2 giugno 2019): 639. http://dx.doi.org/10.3390/met9060639.

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Creep damage is one of the main failure mechanisms of high Cr heat-resistant steel in power plants. Due to the complex changes of stress, strain, and damage at the tip of a creep crack with time, it is difficult to accurately evaluate the effects of residual stress on the creep rupture mechanism. In this study, two levels of residual stress were introduced in P92 high Cr alloy specimens using the local out-of-plane compression approach. The specimens were then subjected to thermal exposure at the temperature of 650 °C for accelerated creep tests. The chemical composition of P92 specimens was obtained using an FLS980-stm Edinburgh fluorescence spectrometer. Then, the constitutive coupling relation between the temperature and material intrinsic flow stress was established based on the Gibbs free energy principle. The effects of prior residual stress on the creep rupture mechanism were investigated by the finite element method (FEM) and experimental method. A comparison of the experimental and simulated results demonstrates that the effect of prior residual stress on the propagation of micro-cracks and the creep rupture time is significant. In sum, the transgranular fracture and the intergranular fracture can be observed in micrographs when the value of prior residual stress exceeds and is less than the material intrinsic flow stress, respectively.

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Meng, Dejian, Lijun Zhang, Xiaotian Xu, Yousef Sardahi e Gang S. Chen. "Sensing and Quantifying a New Mechanism for Vehicle Brake Creep Groan". Shock and Vibration 2019 (26 febbraio 2019): 1–10. http://dx.doi.org/10.1155/2019/1843205.

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This paper investigates the creep groan of a vehicle’s brake experimentally, analytically, and numerically. Experimentally, the effects of acceleration on caliper and strut, noise, brake pressure, and tension are measured. The results show that the measured signals and their relevant spectra broadly capture the complex vibrations of creep groan. This includes the simple stick-slip, severe stick-slip vibrations/resonances, multiple harmonics, half-order harmonics; stick-slip-induced impulsive vibrations, steady/unstable vibrations, and their transitions. Analytically, a new mathematical model is presented to capture the unique features of half-order harmonics and the connections to fundamental stick-slip/resonant frequency and multiple harmonics. The analytical solution and the experimental results show that the vibro-impact of the brake pad-disc system can be triggered by severe stick-slip vibrations and is associated with instable, impulsive stick-slip vibration with wideband. The induced stick-slip vibro-impact can evolve into a steady and strong state with half-order, stick-slip fundamental, and multiple-order components. This new mechanism is different from all previously proposed mechanisms of creep groan in that we also view some type of creep groan as a stick-slip vibration-induced vibro-impact phenomenon in addition to conventional stick-slip phenomena. The new mechanism comprehensively explains the complex experimental phenomena reported in the literature. Numerically, the salient features of phase diagrams of instable stick-slip and vibro-impact are examined by using a seven-degree-of-freedom brake system model, which shows that the phase diagrams of the dynamics of creep groan with and without vibro-impact are substantially different. The phase diagram of the dynamics with vibro-impact is closer to the experimental results. In contrast to existing mechanisms, the proposed new mechanism encompasses the instable stick-slip nature of creep groan and elaborates the inherent connections and transition of the spectrogram. The new knowledge can be used to attain critical improvements to brake noise and vibration analysis and design. By applying the proposed new model in addition to existing models, all experimental phenomena in creep groan are elaborated and quantified.

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YAN, Ming. "Mechanical Mechanism of Creep-thermal Fatigue Interaction". Chinese Journal of Mechanical Engineering 45, n. 01 (2009): 111. http://dx.doi.org/10.3901/jme.2009.01.111.

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Watanabe, Hiroshi, e Tadashi Inoue. "Creep Behavior for Combined Rouse-Reptation Mechanism". Nihon Reoroji Gakkaishi 32, n. 3 (2004): 113–16. http://dx.doi.org/10.1678/rheology.32.113.

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Zhou, Q., G. Itoh e T. Yamashita. "Creep mechanism of aluminum alloy thin foils". Thin Solid Films 375, n. 1-2 (ottobre 2000): 104–8. http://dx.doi.org/10.1016/s0040-6090(00)01234-7.

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Parthasarathy, Triplicane A., Tai-Il Mah e Kristen Keller. "Creep Mechanism of Polycrystalline Yttrium Aluminum Garnet". Journal of the American Ceramic Society 75, n. 7 (luglio 1992): 1756–59. http://dx.doi.org/10.1111/j.1151-2916.1992.tb07193.x.

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Irfan, T. Y. "Mechanism of creep in a volcanic saprolite". Quarterly Journal of Engineering Geology and Hydrogeology 27, n. 3 (agosto 1994): 211–30. http://dx.doi.org/10.1144/gsl.qjegh.1994.027.p3.03.

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Yan, Jingli, Yangshan Sun, Feng Xue, Jing Bai, Shan Xue e Weijian Tao. "Creep deformation mechanism of magnesium-based alloys". Journal of Materials Science 43, n. 21 (novembre 2008): 6952–59. http://dx.doi.org/10.1007/s10853-008-2968-4.

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Ekaputra, I. M. W., e Gunawan Dwi Haryadi. "Karakteristik Laju Regangan Melar pada Baja Tahan Karat Austenitic 316L". ROTASI 19, n. 4 (3 ottobre 2017): 201. http://dx.doi.org/10.14710/rotasi.19.4.201-205.

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Abstract (sommario):

In this study, the creep strain rate characteristics of austenitic 316L stainless steel was investigated from the uniaxial creep-rupture test. The tests were conducted under various applied load levels with a constant temperature at 525oC. The creep exponent was obtained by applying a Norton’s law equation on a regression line of creep strain rate vs. stress curve. The steel clearly showed an instantaneous primary stage, following with the secondary and tertiary stages on the creep curve. It was found that the creep rupture time decreased systematically with an increase in the stress. The secondary stage of creep curve almost dominated the creep’s lifetime. Therefore, the creep strain rate was determined from the minimum strain rate on this stage. The obtained creep exponent indicated that the responsible creep mechanism was grain boundary sliding or diffusional creep mechanism

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32

Lin, Sheng, Xian Fen Xu, Cheng Wang e Jian Xin Ye. "Analysis of Creep and Shrinkage Mechanism of Bridge Considering the Effect of Shrinkage on Creep Stress Reduction". Advanced Materials Research 255-260 (maggio 2011): 781–85. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.781.

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The effect of concrete shrinkage and creep on the deformation of the bridge structure is posing a serious issue with increasing numbers of large-span bridges are being built. At the moment, only the creep coefficient is usually considered for calculating bridge creep, without taking other factors into consideration. This paper, based on aging theory, considers the influence of shrinkage on creep stress reduction, by simplifying the formula of creep strain under discrete load by using the integral mean-value theorem and deriving the formula of concrete creep strain. Taking a continuous rigid frame bridge for example, the paper calculated the creep considering creep stress reduction under shrinkage, which showed that the method can well predict the final shrinkage and creep values of large-span concrete bridge.

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33

Li, Jiachun, Ning Tian, Ping Zhang, Fang Yu, Guoqi Zhao e Ping Zhang. "Creep Damage and Deformation Mechanism of a Directionally Solidified Alloy during Moderate-Temperature Creep". Crystals 11, n. 6 (7 giugno 2021): 646. http://dx.doi.org/10.3390/cryst11060646.

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Abstract (sommario):

Through creep performance tests, microstructural observations, and contrast analysis of the dislocation configuration, the deformation and damage mechanism of the directionally solidified nickel-based superalloy during creep at moderate temperatures was investigated. The findings suggested that the deformation of the alloy in the late stage of creep at moderate temperatures involved dislocations slipping in the γ matrix and shearing into the γ′ phase. The super-dislocations sheared into the γ′ phase could either be decomposed to form a <112> super-Shockley incomplete dislocation plus superlattice intrinsic stacking fault (SISF) configuration, or it could slip from the {111} plane to the {100} plane and decompose to form a dislocation configuration of the Kear–Wilsdorf (K-W) lock plus antiphase domain boundary (APB). The configurations of the dislocations could inhibit the slipping and cross-slipping of dislocations to enhance the alloy creep strength, which is thought to be one reason that the alloy displayed good creep resistance. In the late creep stage, the primary/secondary slipping systems were alternately activated, and the interaction of the slipping traces caused micro-holes to appear on the interface of the γ/γ′ phases at the intersection areas of the two slipping systems. The micro-holes gathered and grew to form micro-cracks, which extended along the grain boundary at 45° to the stress axis until creep rupture occurred. These were the damage and fracture characteristics of the alloy in the late stage of creep at moderate temperatures.

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34

Shi, X. Q., Z. P. Wang, Q. J. Yang e H. L. J. Pang. "Creep Behavior and Deformation Mechanism Map of Sn-Pb Eutectic Solder Alloy". Journal of Engineering Materials and Technology 125, n. 1 (31 dicembre 2002): 81–88. http://dx.doi.org/10.1115/1.1525254.

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Abstract (sommario):

In this study, a large number of creep tests were carried out using miniature specimens in order to investigate the creep behavior of 63Sn/37Pb eutectic solder alloy over a wide temperature range from −40 to 150°C and stress range from 0.75 to 70 MPa. Based on dislocation and diffusion theories, two unified constitutive models were developed to describe the dislocation-controlled and diffusion-controlled creep behaviors observed. It was found that the two models accurately predict the experimental data. A deformation mechanism map was established for this eutectic solder alloy in order to interpret the creep mechanism under different temperature and loading conditions.

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35

Jiang, Li Wu, Shu Suo Li e Mei Ling Wu. "Investigation on Creep Mechanism of a Ni₃Al-Based Single Crystal Superalloy IC6SX under 760°C/540MPa". Materials Science Forum 747-748 (febbraio 2013): 804–9. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.804.

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Abstract (sommario):

The creep behaviors of a Ni3Al-base single crystal superalloy IC6SX prepared by spiral grain selection method was studied systematically under the testing condition of 760/540MPa. The microstructure evolution, movement of dislocations, formation of the dislocation networks and dislocation configuration during the creep process were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the creep performance of the single crystal alloy IC6SX is excellent under 760/540MPa. The experimental results showed that the creep curve of the Ni3Al-base single crystal superalloy IC6SX was divided into three stages, including decelerating creep stage, steady-state creep stage and accelerated creep stage. The microstructure and the dislocation configuration were different at different stage during the creep and the raft microstructure has not been formed. The creep mechanism was main slipping characterized by dislocation glide mechanism.

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36

Naveena, P. Parameswaran, K. Laha e M. D. Mathew. "Study on creep deformation mechanism of 316LN stainless steel from impression creep tests". Materials at High Temperatures 31, n. 2 (maggio 2014): 180–84. http://dx.doi.org/10.1179/1878641314y.0000000012.

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37

LI, Han, Wen-bo DU, Jian-hui LI, Shu-bo LI e Zhao-hui WANG. "Creep properties and controlled creep mechanism of as-cast Mg-5Zn-2.5Er alloy". Transactions of Nonferrous Metals Society of China 20, n. 7 (luglio 2010): 1212–16. http://dx.doi.org/10.1016/s1003-6326(09)60280-6.

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38

SHINYA, Norio, Junro KYONO e Hideaki KUSHIMA. "Creep Fracture Mechanism Map and Creep Damage of Cr-Mo-V Rotor Steel". Tetsu-to-Hagane 92, n. 5 (2006): 327–33. http://dx.doi.org/10.2355/tetsutohagane1955.92.5_327.

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39

Cieśla, M., F. Binczyk, M. Mańka e R. Findziński. "The Influence of Macrostructure of Nickelbased Superalloys IN713C and MAR 247 on the Characteristics of High-temperature Creep". Archives of Foundry Engineering 14, n. 4 (1 dicembre 2014): 11–16. http://dx.doi.org/10.2478/afe-2014-0077.

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Abstract (sommario):

Abstract The study consisted in assessing the influence of surface and volume modification on the characteristics of high-temperature creep of castings made of waste products of nickel-based superalloys IN 713C and the MAR-247. The results of high-temperature creep tests performed under conditions of two variants of research were analysed. The characteristics of creep according to variant I were obtained on the basis of earlier studies of these alloys with the parameters T=982°C, σ=150MPa [1]. Variant II included carrying out creep tests of alloy IN713C with the parameters T=760°C, σ =400MPa and alloy MAR247 with the parameters: T=982°C, σ=200MPa.Developed creep characteristics were compared with the results of these alloys with the parameters according to variant I of the study. It was observed that the conditions of experiments carried out depending upon the value of the creep test temperature and stress with the creep stability depends on the size of the macrograin (I variant of the studies) or such influence was not observed (II variant of the studies). Stability of samples with coarse structure in variant I of creep tests was significantly higher than the samples with fragmented grain. It was found that the observed stability conditions are dependent on the dominant deformation mechanisms under creep tests carried out - diffusion mechanism in variant I and a dislocation mechanism in variant II of the study. The conditions for the formation and growth of the cracks in the tested materials, including the morphological characteristics of their macro-and microstructure were tested

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40

Chatzidakis, Stylianos, Miltiadis Alamaniotis e Lefteri H. Tsoukalas. "Creep Rupture Forecasting". International Journal of Monitoring and Surveillance Technologies Research 2, n. 2 (aprile 2014): 1–25. http://dx.doi.org/10.4018/ijmstr.2014040101.

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Abstract (sommario):

Creep rupture is becoming increasingly one of the most important problems affecting behavior and performance of power production systems operating in high temperature environments and potentially under irradiation as is the case of nuclear reactors. Creep rupture forecasting and estimation of the useful life is required to avoid unanticipated component failure and cost ineffective operation. Despite the rigorous investigations of creep mechanisms and their effect on component lifetime, experimental data are sparse rendering the time to rupture prediction a rather difficult problem. An approach for performing creep rupture forecasting that exploits the unique characteristics of machine learning algorithms is proposed herein. The approach seeks to introduce a mechanism that will synergistically exploit recent findings in creep rupture with the state-of-the-art computational paradigm of machine learning. In this study, three machine learning algorithms, namely General Regression Neural Networks, Artificial Neural Networks and Gaussian Processes, were employed to capture the underlying trends and provide creep rupture forecasting. The current implementation is demonstrated and evaluated on actual experimental creep rupture data. Results show that the Gaussian process model based on the Matérn kernel achieved the best overall prediction performance (56.38%). Significant dependencies exist on the number of training data, neural network size, kernel selection and whether interpolation or extrapolation is performed.

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41

Xiao, Lai Rong, Xi Min Zhang, Yan Wang, Wei Li, Quan Sheng Sun e Zhan Ji Geng. "High Temperature Creep Behavior of Zn-1.0Cu-0.2Ti Alloy". Advanced Materials Research 287-290 (luglio 2011): 769–76. http://dx.doi.org/10.4028/www.scientific.net/amr.287-290.769.

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Abstract (sommario):

In the present work, Zn-1.0Cu-0.2Ti alloy was prepared by melt casting and extruding processes. High temperature creep property of the alloy was determined using electronic creep relaxation testing machine. Microstructures of the alloy before and after creep test were observed and its high temperature creep mechanism was discussed. The results show that the steady-state creep rate of the alloy increases with temperature and stress. The logarithm of steady-state creep rate (ln) shows a linearity relationship with the logarithm of the stress (lnσ) and reciprocal of temperature (1/T). The stress exponent and apparent activation energy for creep have been determined to be 5.10 and 83.7 kJ/mol, separately. The predominant mechanism is mainly self-diffusional creep. The second phases on the grain boundary can block the slip of grain boundary and dislocation motion which can improve creep resistance of the alloy.

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42

Ishikawa, H. "Relation Between Cyclic Creep and Pure Creep on Copper". Journal of Engineering Materials and Technology 109, n. 3 (1 luglio 1987): 221–25. http://dx.doi.org/10.1115/1.3225967.

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Abstract (sommario):

The behavior of a pure copper subject to pure creep and cyclic creep under imposed load is examined at room temperature, and at 200°C, 300°C, and 400°C to show the relation between these two kinds of phenomena. Plots of observed strain, not against number of cycles, but against time are available for the direct comparison between cyclic creep and pure creep. This unified treatment shows that the instantaneous strain affects the succeeding mechanism of both pure creep and cyclic creep. As the result, these two kinds of phenomena are essentially identified, and pure creep could be regarded as the extreme aspect of cyclic creep.

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43

Robles-Arellano, Karen D., e Lukas Bichler. "Creep Deformation of 10 mol% La₂O₃ + YSZ Ceramic Composite Prepared by Spark Plasma Sintering". Materials Science Forum 783-786 (maggio 2014): 1087–92. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.1087.

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Abstract (sommario):

Development of creep-resistant 8mol% Yttria-stabilized Zirconia (YSZ) ceramic has received much interest due to its potential use in fuel cells and thermal barrier coatings. In this research, Spark Plasma Sintering was used to develop a high-density 10 mol% La203 + YSZ composite. Compressive creep testing was performed at 1300 oC at 45 – 78 MPa load. The mechanism of plastic deformation of the composite was studied using Scanning Electron Microscopy and X-Ray Diffraction. The results suggest that lattice diffusion and grain boundary sliding were the active creep mechanisms.

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44

Kvapilová, Marie, Vaclav Sklenička, Jiří Dvořák e Petr Král. "An Evaluation of Creep Mechanisms in Ultrafine-Grained Metals". Key Engineering Materials 465 (gennaio 2011): 382–85. http://dx.doi.org/10.4028/www.scientific.net/kem.465.382.

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Abstract (sommario):

Our earlier published creep data are analyzed for ultrafine-grained pure aluminium and copper processed by equal-channel angular pressing (ECAP). The analysis demonstrates conclusively that creep occurs in the investigated materials after ECAP by the same mechanism as in conventional coarse-grained materials with intergranular dislocation glide and climb as the dominant rate-controlling flow process. Under creep conditions examined in this work diffusion creep is not important in pure aluminium and copper because the ultrafine grains are unstable at elevated and/or high temperature creep and the grains grow sufficiently to preclude any significant contribution from Nabarro-Herring or Coble creep.

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45

Liu, Dan, e Dirk J. Pons. "Development of a stress-based creep-fatigue equation: Accommodating pure-fatigue to pure-creep for the high-cycle loading regime". International Journal of Damage Mechanics 27, n. 9 (9 ottobre 2017): 1397–415. http://dx.doi.org/10.1177/1056789517735678.

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Abstract (sommario):

Background The creep-fatigue damage in low-cycle regime has been described by a strain-based creep-fatigue equation through integrating creep effect into fatigue damage. Need There is a need to develop a creep-fatigue equation which describes the stress-controlled creep-fatigue behaviour in high-cycle regime. Approach This stress-based creep-fatigue equation was developed through superposing a fatigue mechanism with a creep mechanism. This creep-fatigue equation was then validated on GP91 casting steel. The creep-fatigue data were transformed to the reference condition and collapsed into one power-law curve with good quality. Outcomes This result verified the formulas of the fatigue component and the creep component, and demonstrated the method of extracting the coefficients. The full-range characteristic of this creep-fatigue equation is discussed. In addition, the introduction of the compatibility presents a better description of the reference condition. Originality A new creep-fatigue equation is provided with demonstrably good ability to cover the full range of conditions from the pure-fatigue condition to the pure-creep condition for the high-cycle regime. The method of extracting the coefficients is also provided.

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46

Gareh, Salim, e Zakaria Boumerzoug. "HEAT TREATMENT EFFECT ON THE CREEP OF INDUSTRIAL COPPER WIRE". Acta Metallurgica Slovaca 22, n. 3 (27 settembre 2016): 181. http://dx.doi.org/10.12776/ams.v22i3.725.

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Abstract (sommario):

<p class="Default">Creep behavior of copper wire, produced by wiredrawing process in ENICAB Biskra, has been investigated by creep tests at 340°C under the stress 98,108 and 118 MPa. In this investigation, three samples have been tested: copper drawn wire non heat treated, and heat treated at 600°C and 700°C. Microstructure after the creep test was observed by optical microscopy to understand the rupture mechanism. We have found that the sample heat treated at 600 °C had a longer creep life. We have also deduced that the dislocation creep was the creep deformation mechanism of the drawn copper. SEM observations of fractured surfaces after creep tests of drawn copper wire non heat treated and treated 10 min at 600 ° C under stress of 118 MPa.</p>

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47

Wang, Minqing, Jinhui Du e Qun Deng. "The Mechanism of Creep during Crack Propagation of a Superalloy under Fatigue–Creep–Environment Interactions". Materials 13, n. 19 (4 ottobre 2020): 4418. http://dx.doi.org/10.3390/ma13194418.

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Abstract (sommario):

In this study, we examine the mechanism of fatigue-crack propagation in 718Plus superalloy at 704 °C under fatigue–creep–environment interactions, in this case, a new turbine disc material used in aero-engines at high temperatures. The effect of creep on the fatigue-crack propagation of the superalloy at high temperature was also researched. There was an unusual inhibitory effect on the propagation of fatigue cracks in 718Plus alloy, in which the propagation rate of fatigue cracks decreased with the increase of creep time through exploration of dwell-fatigue-crack growth (DFCG) test with different creep times. In particular, under lower stress intensity factor range (ΔK) conditions, the fatigue-crack growth rate with a 90 s hold-time was one order of magnitude lower than that with a 5 s hold-time. Conversely, the gap between the two DFCGs gradually decreased with the increase of ΔK and the creep effect became less apparent. The mechanism of crack propagation in 718Plus alloy under two creep conditions was investigated from a viewpoint of the microstructure, oxidation rate at high temperature and crack path morphology under different conditions.

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48

Li, Zhenrong, Chunlei Ma, Sugui Tian, Liqing Chen e Xianghua Liu. "Deformation Mechanisms of Tandem Hot Rolled GH4169 Superalloy during Creep". High Temperature Materials and Processes 33, n. 1 (1 febbraio 2014): 71–75. http://dx.doi.org/10.1515/htmp-2013-0024.

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Abstract (sommario):

AbstractBy means of direct aged treatment, creep property measurement and high resolution TEM microstructure observation, the deformation mechanisms of Tandem Hot Rolled GH4169 superalloy during creep are investigated. Results show that, after direct aging treatment, fine γ″ particles with different sizes and shapes dispersedly precipitate in the alloy, which is one of important factors for the alloy possessing good creep resistance. And the deformation mechanisms of the alloy are that the deformed twinnings with different orientations are activated on {111} plane by pole mechanism, thereinto, the twinning dislocation may continuously slip around a pole axis dislocation on the twinning planes when the applied stress exceeds the critical value, and the twinnings may multiply by the dislocation reactions and mutual indemnification. As creep goes on, the denser dislocations with single or double orientations slip in the different twinnings, which play an important role of coordinating the grain deformation to enhance the creep resistance of the alloy.

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49

Baskin, Don, Jeff Wolfenstine e Enrique J. Lavernia. "Elevated temperature mechanical behavior of CoSi and particulate reinforced CoSi produced by spray atomization and co-deposition". Journal of Materials Research 9, n. 2 (febbraio 1994): 362–71. http://dx.doi.org/10.1557/jmr.1994.0362.

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Abstract (sommario):

Monolithic CoSi and TiB2 reinforced CoSi materials were produced by spray atomization and co-deposition. The creep behavior of both materials at elevated temperature was investigated. The unreinforced material of grain size ≍25 μm exhibited a stress exponent of three, activation energy for creep of 320 kJ/mole, dislocation substructure of homogeneously distributed dislocations, and inverse creep transients upon stress increases. These results suggest that the creep behavior of CoSi is controlled by a dislocation glide mechanism. In contrast, the reinforced material of a finer grain size (≍10 μm) exhibited a stress exponent of unity, activation energy for creep of 240 kJ/mole, and negligible creep transients upon stress increases, suggesting that the creep behavior of the reinforced material is controlled by a diffusional creep mechanism. The creep resistance of the reinforced material was lower than that for the unreinforced material. This is a result of the finer grain size and higher porosity in the reinforced material.

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50

Dan, Zhenhua, Jiafei Lu, Hui Chang, Ping Qu, Aifeng Zhang, Zhigang Fang, Yuecheng Dong, Ying Wang e Lian Zhou. "High-Stress Compressive Creep Behavior of Ti-6Al-4V ELI Alloys with Different Microstructures". MATEC Web of Conferences 321 (2020): 11007. http://dx.doi.org/10.1051/matecconf/202032111007.

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Abstract (sommario):

Influence of initial microstructure of Ti-6Al-4V ELI alloys on their compressive creep behavior at ambient temperature was investigated with applying compression stresses from 695 to 1092 MPa The experimental results show that the basketweave alloys have better compressive creep resistances than those duplex ones. The constitutive equations in steady-state compressive creeps of duplex or basketweave structure are calculated to be =2.77×10-15(σ-710)2.1 and =2.36×10-14(σ-740)1.7 by fitting the linear regression creep curves after uniaxial compression tests. The noticeable compressive creep strains occur when the applied compression stresses are higher than the threshold stresses, i.e. 710 MPa for duplex Ti-6Al-4V ELI alloys and 740 MPa for basketweave alloys. Microstructural analysis indicates that the creep deformation of Ti-6Al-4V ELI alloys at ambient temperature is mainly controlled by dislocation slip. The creep behavior of Ti-6Al-4V ELI alloy with duplex microstructure is controlled by dislocation slip, like slip dislocations with a-type Burgers vector sliding on the basal or prismatic planes and a few c+a type dislocation sliding on the pyramidal planes. While creep mechanism for basketweave ones is dislocation glide controlled by c+a type Burgers vector sliding on the pyramidal planes and a-type sliding on the basal or prismatic planes.

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