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1
Oruganti, Ram. "Creep and Material Design". Material Science Research India 9, n. 1 (20 giugno 2012): 169–71. http://dx.doi.org/10.13005/msri/090125.
Testo completoAbstract (sommario):
When a material is subjected to temperature and stress, it deforms slowly resulting in permanent shape change. If the same amount of stress were applied at room temperature, the material would not budge. This deformation at high temperature under low stresses is called creep. This phenomenon is important for OEM’S like GE etc. since turbine components are exposed to low stress and high temperature and the resulting shape change is not a desirable consequence. Apart from the change in shape, the components can eventually rupture leading to catastrophic consequences. So it is imperative that the nature of this phenomenon is understood well. Some of the questions to be answered are 1) What makes one material more resistant to creep that the other 2) How can a material’s creep resistance be improved 3) How can the current creep damage in a component be measured 4) Is it possible to say what fraction of the total life of a component has been consumed by creep.
2
Hyde, C. J., T. H. Hyde, W. Sun, S. Nardone e E. De Bruycker. "Small ring testing of a creep resistant material". Materials Science and Engineering: A 586 (dicembre 2013): 358–66. http://dx.doi.org/10.1016/j.msea.2013.07.081.
Testo completo
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Sklenička, Vàclav, Květa Kuchařová, Marie Kvapilová, Luboš Kloc, Jiří Dvořák e Petr Král. "High-Temperature Creep Tests of Two Creep-Resistant Materials at Constant Stress and Constant Load". Key Engineering Materials 827 (dicembre 2019): 246–51. http://dx.doi.org/10.4028/www.scientific.net/kem.827.246.
Testo completoAbstract (sommario):
Creep is defined as a time dependent component of plastic deformation. Creep tests can be performed either at constant load or at constant applied stress. Engineering creep tests carried out at constant load are aimed at determination of the creep strength or creep fracture strength, i.e. the data needed for design. The constant stress tests are important as a data source for fundamental investigations of creep deformation and fracture mechanisms and for finite element modelling of more complex stress situations. For some materials, the difference between the two type of testing can be very small, while for other materials is large, depending on the creep plasticity of the material under testing. The paper aims to compare the creep results of two different creep-resistant materials: the advanced 9%Cr martensitic steel (ASME Grade P91) and a Zr1%Nb alloy obtained by both testing methods and to clarify the decisive factors causing observed differences in their creep behaviour.
4
Sklenička, Vàclav, Květa Kuchařová, Jiří Dvořák, Marie Kvapilová e Petr Král. "Creep Damage Tolerance Factor λ of Selected Creep-Resistant Steels". Key Engineering Materials 754 (settembre 2017): 47–50. http://dx.doi.org/10.4028/www.scientific.net/kem.754.47.
Testo completoAbstract (sommario):
The creep damage tolerance factor λ as an important outcome of the continuum damage mechanics approach has been used to asses the creep fracture mode and the susceptibility of material to localized cracking at strain concentrations. In this work, using sets of our earlier published creep data of three advanced ferritic creep-resistant steels (T23 low alloy steel, P91 and P92 chromium steels) are analysed in terms of the creep damage tolerance factor λ. It was found that the value of the creep damage factor λ is not constant and depends on the creep loading conditions. The data analysis is followed by fractographic investigations, which is used to identify the creep fracture mode (s) experimentally.
5
Antipov, A. A., V. A. Gorokhov, V. V. Egunov, D. A. Kazakov, S. A. Kapustin e Yu A. Churilov. "NUMERICAL SIMULATION OF HIGH-TEMPERATURE CREEP OF ELEMENTS OF HEAT-RESISTANT ALLOYS STRUCTURES TAKING INTO ACCOUNT NEUTRON IRRADIATION EFFECTS". Problems of strenght and plasticity 81, n. 3 (2019): 345–58. http://dx.doi.org/10.32326/1814-9146-2019-81-3-345-358.
Testo completoAbstract (sommario):
The technique of numerical research on the basis of FEM processes of deformation and damage accumulation in the structural elements of heat-resistant alloys under conditions of high-temperature creep taking into account the influence of neutron irradiation is developed. The description of the mechanical behavior of the material is carried out within the framework of the previously developed general model of the damaged material and the creep model for non-irradiated heat-resistant alloys, supplemented by taking into account the effect of irradiation on the creep rate and the appearance of brittle fracture in a given range of temperature variation and irradiation intensity. The defining relations of the creep model of the irradiated material were obtained by modifying the creep model of the non-irradiated material: a material function was introduced, taking into account the effect of the flux of neutrons on the rate of thermal creep deformation; a material function was introduced that takes into account the effect of the neutron flux on the creep surface radius; A material function was introduced, which takes into account the effect of the neutron flux on the ultimate value of the dissipation energy at full power. To simulate the processes of brittle fracture during creep under neutron irradiation conditions, it is assumed that the destructive values of effective normal stresses are a function of temperature, flux of neutrons and the current value of accumulated creep. The material functions of the model were obtained from the results of basic experiments conducted at the Research Institute of Mechanics for the heat-resistant alloy without irradiation under consideration and the available experimental data on the study of the creep of this alloy during its irradiation. Based on the proposed model, a numerical method for solving problems of high-temperature creep of structures made of heat-resistant alloys under neutron irradiation was developed and implemented within the UPAKS computing complex. To verify and illustrate the capabilities of the developed methodological and software tools, a number of problems of modeling the processes of high-temperature creep and destruction of structural elements made of the high-temperature alloy under consideration are solved.
6
Hyun, Yang Ki, Soon Ho Won, Jae Ho Jang e In Bae Kim. "The Evaluation of Material Degradation in Modified 9Cr-1Mo Steel by Electrochemical and Magnetic Property Analysis". Key Engineering Materials 321-323 (ottobre 2006): 486–91. http://dx.doi.org/10.4028/www.scientific.net/kem.321-323.486.
Testo completoAbstract (sommario):
Evolution of microstructure due to service exposure to high temperature has a strong effect performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of Fe2Mo-type laves phases and coarsening of M23C6-type carbides are the primary cause of degradation of mechanical properties such as creep resistance, tensile strength and toughness. Therefore creep tests have been carried out on modified 9Cr-1Mo steels to examine the effect of aging and stress on the creep strength. Additionally vibrating sample magnetometer is used to measure hysteresis loop.
7
Brnic, Josip, Goran Turkalj, Sanjin Krscanski, Goran Vukelic e Marko Canadija. "Uniaxial Properties versus Temperature, Creep and Impact Energy of an Austenitic Steel". High Temperature Materials and Processes 36, n. 2 (1 febbraio 2017): 135–43. http://dx.doi.org/10.1515/htmp-2015-0174.
Testo completoAbstract (sommario):
AbstractIn this paper, uniaxial material properties, creep resistance and impact energy of the austenitic heat-resistant steel (1.4841) are experimentally determined and analysed. Engineering stress–strain diagrams and uniaxial short-time creep curves are examined with computer-controlled testing machine. Impact energy has been determined and fracture toughness assessed. Investigated data are shown in the form of curves related to ultimate tensile strength, yield strength, modulus of elasticity and creep resistance. All of these experimentally obtained results are analysed and may be used in the design process of the structure where considered material is intended to be applied. Based on these results, considered material may be classified as material of high tensile strength (688 MPa/293 K; 326 MPa/923 K) and high yield strength (498 MPa/293 K; 283 MPa/923 K) as well as satisfactory creep resistance (temperature/stress $ \to $strain (%) at 1,200 min: 823 K/167 MPa $ \to $0.25 %; 923 K/85 MPa $ \to $0.2 %).
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Yang, You, Xiao Dong Wang e Wei Feng Tang. "Study on the High Temperature Creep Behavior of 30Cr25Ni20 Heat-Resistant Steel". Key Engineering Materials 814 (luglio 2019): 157–62. http://dx.doi.org/10.4028/www.scientific.net/kem.814.157.
Testo completoAbstract (sommario):
The high temperature creep test of heat-resisting steel 30Cr25Ni20 for automobile exhaust manifolds was carried out, and the creep strain-time curves at 650°C and 700°C in the different loads were obtained. The effects of different creep temperature and stress on creep life of materials were studied. The microstructure of the fracture after creep was observed by scanning electron microscopy. Microstructures before and after creep at different temperatures were compared by optical microscopy. The results show that the creep fracture life of heat-resistant steel decreases with the increase of stress at the same temperature. The creep fracture life decreases with the increase of temperature at the same stress, too. The fracture of heat-resistant steel shows good high temperature plasticity and a ductile fracture after creep. The fracture dimples become deeper with the increase of stress. At 650°Cand 700°C, the stress exponent is 8.6 and 6, respectively. When the sample was subjected to high temperature creep at 700°C, the precipitates increase obviously and the reticular structure became very large. At this point, the internal structure of the material is destroyed, and the matrix structure becomes unevenly distributed. The failure of the internal structure leads to the dramatic increase of the creep strain, and the failure of the internal structure will be more serious with the deformation of the sample.
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Bauné, Emmanuel, E. Galand, B. Leduey, G. Liberati, G. Cumino, S. Caminada, A. Di Gianfrancesco e L. Cipolla. "Grades 92 and 23: Weldability Assessment and Long-Term Performances for Power Generation Applications". Materials Science Forum 580-582 (giugno 2008): 383–88. http://dx.doi.org/10.4028/www.scientific.net/msf.580-582.383.
Testo completoAbstract (sommario):
Increased efficiency and emission reduction in modern power plants lead to the use of new advanced materials with enhanced creep strength, with the objective to increase the steam parameters of power plants. With over ten years on market and wide experience related to its use, ASTM Grade 92 is becoming one of the most required materials when high service temperatures are reached (max. 610°C). Its composition, with 9%Cr and 1.5%W, gives rise to martensitic microstructures which offer very high creep strength and long term stability. The improved weldability and creep-strength between 500 and 580°C of the low alloy ASTM Grade 23, as well as a cost advantage over higher Cr materials in this temperature range, make it one of the possible candidates to meet the stringent requirements of modern power plants. Air Liquide Welding (ALW) has optimized and distributes a complete product family for the welding of Grades 23 and 92. TenarisDalmine (TD) focused on the development of Grade 23 tubes and pipes and is working on the development of Grade 92. A deep characterization work of the microstructural evolution and long term creep performances of these high temperature resistant materials was thus undertaken by ALW and TD, in collaboration with the Centro Sviluppo Materiali (CSM). The joint characterization program consisted in the assessment of welded joints creep properties. Welded joints were produced using the gas tungsten (GTAW), shielded metal (SMAW) and submerged arc welding (SAW) processes. Mechanical and creep properties of weldments were measured both in the as welded and post weld heat treated conditions and proper WPS’s were designed in a manner such that industrial production needs were satisfied. Short term creep resistance of cross weld specimens was measured to be within the base material acceptance criteria. Long term base material and cross weld creep performance evaluation are now in progress.
10
Brnic, Josip, Marino Brcic, Sebastian Balos, Goran Vukelic, Sanjin Krscanski, Mladomir Milutinovic e Miroslav Dramicanin. "S235JRC+C Steel Response Analysis Subjected to Uniaxial Stress Tests in the Area of High Temperatures and Material Fatigue". Sustainability 13, n. 10 (19 maggio 2021): 5675. http://dx.doi.org/10.3390/su13105675.
Testo completoAbstract (sommario):
Knowledge of the properties and behavior of materials under certain working conditions is the basis for the selection of the proper material for the design of a new structure. This paper deals with experimental investigations of the mechanical properties of unalloyed high quality steel S235JRC + C (1.0122) and its behavior under conditions of high temperatures, creep and mechanical fatigue. The response of the material at high temperatures (20–700 °C) is shown in the form of engineering stress-strain diagrams while that at creep behavior (400–600 °C) is shown in the form of creep curves. Furthermore, based on uniaxial fully reversed mechanical fatigue tests (R=−1), a stress-life (S-N) fatigue diagram has been constructed and the fatigue (endurance) limit of the material is calculated The experimentally determined value of tensile strength at room temperature is 534 MPa. The calculated value of the fatigue limit, also at room temperature, using the modified staircase method and based on the mechanical fatigue tests data, is 202 MPa. With regard to creep resistance, steel 1.0122 can be considered creep-resistant only at a temperature of 400 °C and at an applied stress not exceeding 50% of the yield strength corresponding to this temperature.
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Shrestha, Sachin L., Dhriti Bhattacharyya, Guangzhou Yuan, Zhijun J. Li, Elizabeth Budzakoska-Testone, Massey De Los Reyes, Michael Drew e Lyndon Edwards. "Creep resistance and material degradation of a candidate Ni–Mo–Cr corrosion resistant alloy". Materials Science and Engineering: A 674 (settembre 2016): 64–75. http://dx.doi.org/10.1016/j.msea.2016.07.032.
Testo completo
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ALTENBACH, HOLM, KONSTANTIN NAUMENKO e YEVGEN GORASH. "CREEP ANALYSIS FOR A WIDE STRESS RANGE BASED ON STRESS RELAXATION EXPERIMENTS". International Journal of Modern Physics B 22, n. 31n32 (30 dicembre 2008): 5413–18. http://dx.doi.org/10.1142/s0217979208050589.
Testo completoAbstract (sommario):
Many materials exhibit a stress range dependent creep behavior. The power-law creep observed for a certain stress range changes to the viscous type creep if the stress value decreases. Recently published experimental data for advanced heat resistant steels indicates that the high creep exponent (in the range 5-12 for the power-law behavior) may decrease to the low value of approximately 1 within the stress range relevant for engineering structures. The aim of this paper is to confirm the stress range dependence of creep behavior based on the experimental data of stress relaxation. An extended constitutive model for the minimum creep rate is introduced to consider both the linear and the power law creep ranges. To take into account the primary creep behavior a strain hardening function is introduced. The material constants are identified for published experimental data of creep and relaxation tests for a 12% Cr steel bolting material at 500°C. The data for the minimum creep rate are well-defined only for moderate and high stress levels. To reconstruct creep rates for the low stress range the data of the stress relaxation test are applied. The results show a gradual decrease of the creep exponent with the decreasing stress level. Furthermore, they illustrate that the proposed constitutive model well describes the creep rates for a wide stress range.
13
Cieśla, M., e G. Junak. "The Influence Of Load History On Durability Of P92 Steel Used For The Construction Of Energy Pipelines". Archives of Metallurgy and Materials 60, n. 3 (1 settembre 2015): 1853–58. http://dx.doi.org/10.1515/amm-2015-0316.
Testo completoAbstract (sommario):
Abstract The research material used in the study was the martensitic creep-resistant steel P92 used for the manufacture of pipes being part of power generation units subject to heavy load. The research problem focused on two issues. The first one was to analyze how the plastic deformation cumulated in the material in low-cycle fatigue conditions affects the characteristics of the material in creep conditions in a temperature of 600ºC. The other one was concerned with analysis of a reverse situation, i.e. how the initial plastic deformation of the material in creep conditions changes the mechanical characteristics of the steel under low-cycle fatigue conditions in a temperature of 600ºC.
14
Fedorova, Irina, Zhanna Yanushkevich, Andrey Belyakov e Rustam Kaibyshev. "Microstructure and Deformation Behavior of a Hot Forged 9%Cr Creep Resistant Steel". Advanced Materials Research 409 (novembre 2011): 672–77. http://dx.doi.org/10.4028/www.scientific.net/amr.409.672.
Testo completoAbstract (sommario):
The tempered microstructure and the creep behaviour were studied in an ultra low carbon 9%Cr martensitic creep resistant steel. The starting material was forged at 1050°C followed by air cooling and then tempered at a temperature of 750°C for 3 hours. This treatment resulted in the mean transverse lath size of about 240 nm; the dislocation density in lath interiors comprised 4 × 1014 m-2. The tempered martensite lath structure (TMLS) is characterised by homogeneous precipitation of numerous MX-type carbonitrides and a small amount of relatively coarse M23C6–type carbides. Three kinds of MX carbonitrides were observed in the tempered lath martensite structure. Those were plate-shaped particles with longitudinal size of about 15 nm and thickness of 3 nm; round-shaped particles of about 10 nm in diameter; and relatively large almost equiaxed particles with mean size of about 90 nm. The large MX particles were resulted from incomplete dissolution of such carbonitrides at 1050°C, while the nanoscale particles homogeneously precipitated during the tempering. The creep tests conducted at 650°C showed that the studied steel demonstrated superior creep resistance. Namely, the rupture time was about an order as long as that for P92-type creep resistant steel.
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Olszyna, Andrzej Roman, e Marek Kostecki. "Zirconium – Based Ceramic Targets for Producing Nanocrystalline Coatings Resistant to Heat and Thermal Creep". Journal of Nano Research 11 (maggio 2010): 89–94. http://dx.doi.org/10.4028/www.scientific.net/jnanor.11.89.
Testo completoAbstract (sommario):
Technology of thermal ceramic barriers (TBC) has been chiefly designed for materials with a single thermal barrier of the 7YSZ type. A high content of Y2O3 ensures a good phase stability of the YSZ material. In search for other alternative materials suitable for TBC, the material most often examined is modified zirconium oxide. The modification consists of stabilizing the ZrO2 powder with Y2O3 and doping it with La, Gd and Nd. This paper presents the results of studies on producing cathodic zirconium oxide-based ceramic targets intended for depositing refractory heat-resistant nano-crystalline TBC coatings. The targets are characterized by a high density (close to its theoretical value) and have a homogeneous phase and chemical structure.
16
Xu, Dao Fen, Chun Ping Du e Dong Ye. "Compressive Creep Behavior of Mg-4Al-1RE-1Ca-0.2Sr Alloy". Applied Mechanics and Materials 190-191 (luglio 2012): 431–34. http://dx.doi.org/10.4028/www.scientific.net/amm.190-191.431.
Testo completoAbstract (sommario):
The compressive creep behavior of Mg-4Al-1RE-1Ca-0.2Sr (AECJ411002) alloy was investigated at temperatures in the range of 125~175°C and different compressive stress in the range of 88~112MPa with special apparatus. The results show that the creep deformation increases with the increasing of temperature and compressive stress. There is linear logarithmic relationship between the steady creep rate and all the temperature and stress used. The steady creep rate obeys an empirical equation. The stress exponents are similar at different temperatures and the appearance activation energies are not greatly different under different stresses. Their average value is respectively 6.19 and 39.05kJ/mol. Material constant A is 4.18×10-14. The steady creep rate is controlled by a dislocation climb led by grain boundary sliding. The creep resistance enhances because of the heat-resistant phases Al2Ca and Al4Sr distributing at grain boundary.
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Naumenko, Konstantin, Holm Altenbach e Andreas Kutschke. "A Combined Model for Hardening, Softening, and Damage Processes in Advanced Heat Resistant Steels at Elevated Temperature". International Journal of Damage Mechanics 20, n. 4 (25 ottobre 2010): 578–97. http://dx.doi.org/10.1177/1056789510386851.
Testo completoAbstract (sommario):
Phenomenological constitutive equations that describe inelastic behavior of advanced steels at elevated temperature are developed. To characterize hardening, recovery, and softening processes, a composite model with creep-hard and creep-soft constituents is applied. The volume fraction of the creep-hard constituent is assumed to decrease toward a saturation value. This approach reproduces well the primary creep as a result of stress redistribution between constituents and tertiary creep as a result of softening. To describe the whole tertiary creep stage, a damage variable in the sense of continuum damage mechanics is introduced. The material parameters and the response functions in the model are calibrated against experimental creep curves for X20CrMoV12-1 steel. For the verification, simulations of the inelastic response are performed and the results compared with experimental data including creep under stress change conditions and stress-strain response under constant strain rate. Furthermore, the lifetime predictions are analyzed and compared with the published creep rupture strength data. The results show that the consideration of both softening and damage processes is necessary to characterize the long-term strength in a wide stress range. Finally, the model is generalized to the multi-axial stress state.
18
Sladká, Jana, Dagmar Jandová e Eva Chvostová. "Influence of Microstructural Changes in Creep Resistant Steel after Long-Term Creep Tests on the Shape of the Polarization Curves". Key Engineering Materials 647 (maggio 2015): 153–61. http://dx.doi.org/10.4028/www.scientific.net/kem.647.153.
Testo completoAbstract (sommario):
Creep resistance of the steel depends on chemical and structural composition and structural stability. Therefore it is necessary to check microstructural changes in material during the long-term service, however the necessary material analyses are generally destructive. The submitted contribution describes non-destructive electrochemical method for detection of some microstructural changes taking place during creep exposures. The shape of polarization curves are correlated to the microstructure of CB2 steel, the most promissing (9-12) %Cr martensitic steel for the cast components. The dynamic polarization curves were measured using samples in as received conditions and after long-term creep tests at 650°C. Microstructure was analysed using light and electron microscopy. The microstructure of the CB2 steel changed during creep exposures. In polarization curves additional peak appeared in the main passivation region and the curve shape changed also in the secondary passivation region. The curve changed in dependence on precipitation and growth of Laves phase particles.
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Dong, Jiling, Yinsheng He, Minsoo Kim e Keesam Shin. "Effect of Creep Stress on the Microstructure of 9–12% Cr Steel for Rotor Materials". Microscopy and Microanalysis 19, S5 (agosto 2013): 95–98. http://dx.doi.org/10.1017/s1431927613012415.
Testo completoAbstract (sommario):
AbstractHigh-chromium heat-resistant steel has been widely used as the key material to improve the condition of steam pressure and temperature in the modern high-efficiency power plants. Despite the use of the steel above 550°C for several decades, its major failure is owing to the creep fracture. In this study, the effect of creep stress on the microstructure in 9–12% Cr steel has been investigated microscopically, and it is clarified that the creep stress enhances precipitation of Laves phase and influences the lath width and dislocation density in lath interior.
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Lehockey, E. M., G. Palumbo, P. Lin e A. Brennenstuhl. "On the Relationship Between Grain-Boundary Character Distribution and Intergranular Corrosion". Proceedings, annual meeting, Electron Microscopy Society of America 54 (11 agosto 1996): 346–47. http://dx.doi.org/10.1017/s0424820100164192.
Testo completoAbstract (sommario):
Intergranular corrosion can under severe conditions lead to “grain-dropping” which results in significant material loss. It has been demonstrated that grain boundaries described by low-Σ CSL misorientations are more resistant to corrosion, cracking (SCC), and sliding (creep) than “general” boundaries, and that the frequency of these “special” boundaries can be enhanced offering the possibility of producing materials with improved bulk corrosion and creep properties. This contribution presents a model for predicting the effect of “special” boundaries on the extent of gross wastage from grain-dropping.For any grain to be ejected from the matrix, all of its bounding interfaces must be fully compromised. Assuming “special” grain boundaries are immune to corrosion and considering a material containing hexagonal prism grains with a diameter and length, d, it can be shown that the probability, X, of observing grain-dropping at a depth, L, through the material thickness is related to the “special” boundary fraction, Fsp, by:
21
Wiederhorn, Sheldon M., Ralph F. Krause, František Lofaj e U. Täffner. "Creep Behavior of Improved High Temperature Silicon Nitride". Key Engineering Materials 287 (giugno 2005): 381–92. http://dx.doi.org/10.4028/www.scientific.net/kem.287.381.
Testo completoAbstract (sommario):
New data are presented on the tensile creep behavior of silicon nitride sintered with Lu2O3. The data are compared with two earlier sets of data collected on the same material. The older sets gave results that are difficult to explain theoretically: a high value for the stress exponent, n=5.33, and no cavitation. The new set of data also gave no cavitation, but gave a stress exponent, n=1.81, that can be rationalized theoretically in terms of solution-precipitation creep of the silicon nitride grains. An analysis of variance showed that one of the earlier sets of data was statistically consistent with the newer set, whereas the other set of data was not. Combining the two sets of data that agreed statistically yields a consistent picture of creep with a low value of the stress exponent and no cavitation. The stress exponent for the combined set of data is n=1.87±0.48 (95 % confidence limits). The tensile creep mechanism of the silicon nitride containing Lu2O3, solution-precipitation, differs from those of other silicon nitrides, for which tensile creep has been attributed to cavitation. Enhancement of the creep resistance of the silicon nitride sintered with Lu2O3 may be a consequence of the fact that Lu2O3 produces a more deformation resistant amorphous phase at the two grain junctions, than do Y2O3 or Yb2O3. In parallel, reducing the amount of secondary phase below a critical limit, or increasing the viscosity of the two grain boundaries relative to three-grain junctions reduces the ability of the material to cavitate during creep, and forces the creep mechanism to change from cavitation to solution-precipitation.
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Błachnio, Józef. "The Effect of High Temperature on the Degradation of Heat-Resistant and High-Temperature Alloys". Solid State Phenomena 147-149 (gennaio 2009): 744–51. http://dx.doi.org/10.4028/www.scientific.net/ssp.147-149.744.
Testo completoAbstract (sommario):
Heat-resistant and high-temperature materials are used to manufacture components, devices, and systems operated at high temperatures, i.e. under severe heat loads. Gas turbines used in the power industry, the traction, marine, and aircraft engines, the aerospace technology, etc. are good examples of such systems. Generally, as the temperature increases, the mechanical strength of materials decreases. While making such materials, there is a tendency to keep possibly low thermal weakening. In the course of operating gas turbines, various kinds of failures/defects/ damages may occur to components thereof, in particular, to blades. Predominating failures/damages are those attributable to the material overheating and thermal fatigue, all of them resulting in the loss of mechanical strength. The paper has been intended to present findings on changes in the microstructure of blades made of nickel-base alloy due to high temperature. The material gets overheated, which results in the deterioration of the microstructure’s condition. The material being in such condition presents low high-temperature creep resistance. Any component, within which such an effect occurs, is exposed to a failure/damage usually resulting in the malfunctioning of the turbine, and sometimes (as with aero-engines) in a fatal accident. Failures/damages of this kind always need major repairs, which are very expensive.
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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.
Testo completoAbstract (sommario):
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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Mondal, A. K., Subodh Kumar, Carsten Blawert e Narendra B. Dahotre. "Effect of Laser Surface Treatment on Microstructure and Properties of MRI 230D Mg Alloy". Materials Science Forum 539-543 (marzo 2007): 1153–58. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1153.
Testo completoAbstract (sommario):
A creep resistant Mg alloy MRI 230D was subjected to laser surface treatment using Nd:YAG laser equipped with a fiber optics beam delivery system in argon atmosphere. The laser surface treatment produced a fine dendritic microstructure and this treatment was beneficial for the corrosion and wear resistance of the alloy. Long-term linear polarisation resistance and Electrochemical Impedance Spectroscopy measurements confirmed that the polarisation resistance values of laser treated material were twice as high as that for the untreated material. This improved behaviour was due to the finer and more homogenous microstructure of the laser treated surface. The laser treatment also increased surface hardness two times and reduced the wear rate by 25% due to grain refinement and solid solution strengthening.
25
Hebsur, Mohan G., Ivan E. Locci, S. V. Raj e Michael V. Nathal. "Influence of processing on the microstructure and mechanical properties of a NbAl3-base alloy". Journal of Materials Research 7, n. 7 (luglio 1992): 1696–706. http://dx.doi.org/10.1557/jmr.1992.1696.
Testo completoAbstract (sommario):
A multiphase oxidation resistant composition (Nb–67Al–7Cr–0.5Y–0.25W) based on NbAl3 was prepared by both induction melting and rapid solidification processing (RSP), followed by grinding to 75 μm powder and consolidating by powder metallurgy techniques (hot pressing, hot isostatic pressing, and Ceracon pressing). Constant strain rate compression tests conducted on consolidated materials in the temperature range 300–1300 K indicated that the RSP material exhibited significantly higher strength and ductility than the induction melted alloy up to 1200 K. Bend strengths measured on induction melted material were significantly lower than the corresponding compressive strengths, suggesting the brittle, flaw-sensitive nature of this alloy. The NbAlCrYW alloy exhibits a brittle-to-ductile transition around 1000 K. The constant load creep tests conducted on the induction melted alloy in the 1200–1300 K temperature range indicated that this alloy shows a power law creep dependency with a stress exponent, n, of 3.2. It was found that the specific strength of this alloy is competitive with other aluminide intermetallics.
26
Anopuo, Okechukwu, Yuan Ding Huang, Norbert Hort, Karl Ulrich Kainer e Petra Maier. "Modeling Bolt Load Retention of Ca Modified AS41 Using Compliance-Creep Method". Materials Science Forum 690 (giugno 2011): 278–81. http://dx.doi.org/10.4028/www.scientific.net/msf.690.278.
Testo completoAbstract (sommario):
Adequate quantification of the degree of fastener clamp load retained at bolted joint of Mg-Al alloys is crucial to develop new elevated temperature resistant Mg-alloys. Several attempts have been made in the past to model Bolt Load Retention (BLR) behaviour of Mg-alloys using different approaches. It must be mentioned that whereas these models attempt to predict BLR of the alloys investigated, the results of the models differ in most cases with the experiments by great margin. The BLR behaviour of Mg-alloy is geometry and material dependent. This means that, the configuration of the test sample, the compliance of the bolt/joint and creep response of the material under investigation play important role in determining the joint response under load and temperature. In this work, BLR and creep behaviour of Ca modified AS41 is investigated and compared to that of Mg4Al and AS41. A compliance-creep approach is used to model the response of these Mg-Al alloys at bolted joints. The model prediction of the BLR response and experimental results as obtained in this work are in good agreement. AS41+0.15 % Ca shows improved creep and BLR properties up to 175 °C. A correlation between the microstructures, creep and BLR results reveal that the formation of a ternary CaMgSi phase is responsible for the improved elevated temperature behaviour.
27
Cheruvu, N. S. "Development of a Corrosion Resistant Directionally Solidified Material for Land Based Turbine Blades". Journal of Engineering for Gas Turbines and Power 120, n. 4 (1 ottobre 1998): 744–50. http://dx.doi.org/10.1115/1.2818462.
Testo completoAbstract (sommario):
Advanced turbines with improved efficiency require materials that can operate at higher temperatures. Availability of these materials would minimize cooling flow requirements, and, thus, improve the efficiency of a turbine. Advanced processing. such as directional solidification (DS), can improve temperature capability of the majority of Ni based superalloys. However, results of earlier work on IN-738 reveal that the DS process does not significantly improve temperature capability of this alloy. A research program was initiated to develop a corrosion resistant Ni-based DS blade material for land based turbines. In this program, eight heats with varied Cr, Al, Ti, Ta, and W contents were selected for evaluation. Screening tests performed on these heats in the DS condition include tensile, creep, and corrosion. The Results of experimental heats were compared with those of IN-738 in the equiaxed condition. From these results, two chemistries offering approximately 100°F temperature advantage at typical row I turbine blade operating stress were selected for castability and further mechanical property evaluation. Several row 1 solid and cored turbine blades were successfully cast. The blades were evaluated for grain structure and mechanical properties. Tests were also conducted to evaluate the effects of withdrawal rates on properties. These results are summarized in this paper.
28
Qiao, Kun, Anping Zhu, Baoming Wang, Chengrui Di, Junwei Yu e Bo Zhu. "Characteristics of Heat Resistant Aluminum Alloy Composite Core Conductor Used in overhead Power Transmission Lines". Materials 13, n. 7 (31 marzo 2020): 1592. http://dx.doi.org/10.3390/ma13071592.
Testo completoAbstract (sommario):
The heat resistant aluminum alloy wire composite material core conductor (ACCC/HW) which was used in overhead transmission lines is developed and studied in this work. The composite material core is carbon fiber/glass cloth reinforced modified epoxy resin composite. Tensile stress tests and stress-strain tests of both composite core and conductor are taken at 25 °C and 160 °C. Sag test, creep test and current carrying capacity test of composite conductor are taken. The stress of composite conductor are 425.2 MPa and 366.9 MPa at 25 °C and 160 °C, respectively. The sag of conductor of 50 m length are 95 mm, 367 mm, and 371 mm at 25 °C, 110 °C, and 160 °C, respectively. The creep strain are 271 mm/km, 522 mm/km, and 867 mm/km after 10 years under the tension of 15% RTS (Rated Tensile Strength), 25% RTS and 35% RTS at 25 °C, and 628 mm/km under 25% RTS at 160 °C, according to the test result and calculation. The carrying capacity of composite conductor is basically equivalent to ACSR (Aluminum Conductor Steel Reinforced). ACCC/HW is suitable in overhead transmission lines, and it has been used in 50 kV power grid, according to the results.
29
Golański, Grzegorz, Adam Zieliński, Marek Sroka e Jacek Słania. "The Effect of Service on Microstructure and Mechanical Properties of HR3C Heat-Resistant Austenitic Stainless Steel". Materials 13, n. 6 (13 marzo 2020): 1297. http://dx.doi.org/10.3390/ma13061297.
Testo completoAbstract (sommario):
The physical metallurgical tests were performed on the test samples made of HR3C steel, taken from a section of a pipeline in the as-received condition and after approximately 26,000 h of service at 550 °C. In the as-received condition, the test material had austenitic microstructure with numerous large primary Z-phase precipitates inside the grains. The service of the test steel mainly contributed to the precipitation processes inside the grains and at the grain boundaries. After service, the following precipitates were identified in the microstructure of the test steel: Z-phase (NbCrN) and M23C6 carbides. The Z-phase precipitates were observed inside the grains, whereas M23C6 carbides - at the boundaries where they formed the so-called continuous grid. The service of the test steel contributed to the growth of the strength properties, determined both at room and elevated temperature (550, 600 °C), compared to the as-received condition. Moreover, the creep properties of HR3C steel after service were higher than those of the material in the as-received condition. The increase in the strength properties and creep resistance was connected with the growth of strengthening of the test steel by the precipitation of Z-phase and M23C6 carbides.
30
Pasternak, Jerzy, e Janusz Dobrzanski. "Properties of Welded Joints on Superheater Coils Made from New Generation High Alloy Martensitic Steels Connected to Austenitic Creep-Resisting Steels and Supper Alloy Grades, for Supercritical Parameters". Advanced Materials Research 278 (luglio 2011): 466–71. http://dx.doi.org/10.4028/www.scientific.net/amr.278.466.
Testo completoAbstract (sommario):
The continuously developing power generation sector, including boilers with supercritical parameters, requires applications of new creep-resistant steel grades for construction of boilers steam superheater components. Therefore, this paper contains selected information, results of the research and implementation process including: - evaluation, comparison of requested properties of base material and welded joints, such as tensile strength, impact strength and technological properties, - destructive examinations with evaluation of welded joints and HAZ structure and hardness distribution, - influence of manufacturing process in large boilermaker conditions and after simulated operation. A new creep-resistant steels to be used, in order to comply with the operational requirements, as to assure the appropriate reliability and safety of the boiler equipment in operation process. This document presents a simplified analysis of martensitic steels from group 9-12% Cr (T91, T92, HCM12A, VM12) and austenitic steels Cr-Ni (TP347FG, SUPER 304H, HR3C), having the chemical composition as presented in tables 1 and 2, which are to be applied for steam superheater components.
31
Wieczorska, Agata. "The Process of Regenerative Heat Treatment of the Valve Chamber of the Steam Turbine". Journal of KONES 26, n. 3 (1 settembre 2019): 243–48. http://dx.doi.org/10.2478/kones-2019-0079.
Testo completoAbstract (sommario):
Abstract Steel castings are often used in the construction of valve chambers of steam turbines. Stringent requirements are set due to the continuous operation of the material at elevated temperatures, in the order of 300°C to 600°C. The material of the valve chamber must be resistant to fatigue-creep changes as well as corrosion. This material must be also resistant to dynamic damage which occures when the turbine is starting and stopping. Dynamic damage is induced by a short-lasting but intense accumulation of localized stresses. The castings of the valve chambers of the steam turbine are usually made from the “three-component” type CrMoV-cast steel. Mentioned castings of the valve chamber are continuously subjected to high temperatures, either constant and periodically variable stresses. Due to this, the degradation process of material of the castings is taking place. It is caused by physicochemical processes such as: creep, relaxation, thermal fatigue, corrosion, erosion and changes in material properties, e.g. displacement of the critical point of brittleness. Finally, first cracks and deformations can be observed in the material during the operation. The art presents the process of revitalization technology of the steam turbine valve chamber which was subjected to long-term operation at high temperatures. The revitalization process is aimed at improving the plastic properties of the material and, as the result, extending its service life. The research presented in the article show that impact strength of the chamber material after revitalization is very high. Also the strength properties of the valve chamber, after revitalization, are high and in line with the requirements. The study show that the revitalization of the valve chamber was carried out correctly and restored the material to plastic deformation.
32
Gsellmann, Bernadette, Dilek Halici, Mihaela Albu, Coline Beal e Bernhard Sonderegger. "Combination of Microstructural Investigation and Simulation during the Heat Treatment of a Creep Resistant 11% Cr-Steel". Materials Science Forum 879 (novembre 2016): 625–30. http://dx.doi.org/10.4028/www.scientific.net/msf.879.625.
Testo completoAbstract (sommario):
This work deals with the microstructural evolution of creep resistant martensitic/ferritic 11% Cr-steel during thermomechanical treatment from an experimental as well as modeling point of view. The creep resistance of this material group is highly dependent on the precipitate status. The initial precipitate status is controlled by the chemical composition of the alloy and the heat treatment after casting or hot rolling. It is therefore of utmost interest to understand and model the precipitate kinetics during this process. Once the microstructural evolution has been modeled successfully, only minimum effort is required to computationally test variants in the composition or heat treatment in order to optimize the process. In this work, the material was hot rolled, austenitized and subsequently annealed. All heat treatments have been performed during dilatometry tests. In order to investigate the microstructural evolution during the process, specimens were extracted at definite stages of the treatment. The specimens were then investigated applying various microscopical techniques in order to quantify the microstructural features (grain size, martensite lath width and precipitate data). The experimental data were then compared to thermodynamic simulations (MatCalc). General data such as nucleation sites for precipitates were taken from literature, grain size and martensite lath widths from the experimental data. Simulations include equilibrium calculations and precipitate kinetic simulations. In general, the simulations showed good agreement with the experimental findings, with minor room for improvements. The work thus lays a solid ground for future improvements of the heat treatment process.
33
Mitrovic, Radivoje, Dejan Momcilovic, Olivera Eric, Ivana Atanasovska e Nenad Hut. "Study on impact properties of creep-resistant steel thermally simulated heat affected zone". Thermal Science 16, n. 2 (2012): 513–25. http://dx.doi.org/10.2298/tsci111006142m.
Testo completoAbstract (sommario):
The steam pipe line (SPL) and steam line material, along with its welded joints, subject to damage that accumulates during operation in coal power plants. As a result of thermal fatigue, dilatation of SPL at an operating temperature may lead to cracks initiation at the critical zones within heat affected zone (HAZ) of steam pipe line welded joints. By registration of thermal cycle during welding and subsequent HAZ simulation is possible to obtain target microstructure. For the simulation is chosen heat resisting steel, 12H1MF (designation 13CrMo44 according to DIN standard). From the viewpoint of mechanical properties, special attention is on impact toughness mostly because very small number of available references. After simulation of single run and multi run welding test on instrumented Charpy pendulum. Metallographic and fractographic analysis is also performed, on simulated 12H1MF steel from service and new, unused steel. The results and correlation between microstructure and impact toughness is discussed, too.
34
Birosz, Márton Tamás, Mátyás Andó e Sudhanraj Jeganmohan. "Finite Element Method modeling of Additive Manufactured Compressor Wheel". Journal of The Institution of Engineers (India): Series D 102, n. 1 (13 febbraio 2021): 79–85. http://dx.doi.org/10.1007/s40033-021-00251-8.
Testo completoAbstract (sommario):
AbstractDesigning components is a complex task, which depends on the component function, the raw material, and the production technology. In the case of rotating parts with higher RPM, the creep and orientation are essential material properties. The PLA components made with the material extrusion process are more resistant than VeroWhite (material jetting) and behave similarly to weakly cross-linked elastomers. Also, based on the tensile tests, Young’s modulus shows minimal anisotropy. Multilinear isotropic hardening and modified time hardening models are used to create the finite element model. Based on the measurements, the finite element method simulation was identified. The deformation in the compressor wheel during rotation became definable. It was concluded that the strain of the compressor wheel manufactured with material extrusion technology is not significant.
35
Dymáček, Petr, Denisa Bártková, Vít Horník, Luděk Stratil, Bohuslav Mašek e Jiří Svoboda. "New Generation of ODS Alloys". Key Engineering Materials 810 (luglio 2019): 113–18. http://dx.doi.org/10.4028/www.scientific.net/kem.810.113.
Testo completoAbstract (sommario):
Excellent creep strength of the ODS steels is associated with an attractive interaction between dislocations and oxides. The aim of this study is to explore the Fe-Al-O and Fe-Al-Cr-Y-O systems with high oxygen content (up to 1.5 wt %) represented by alumina or yttria oxides (up to 5 vol. %) to identify the potentials of the new generation of ODS alloys. The basic material is prepared from Fe and 10 or 11 wt. % of Al. Theoretical models showed stability of Al oxides even above 1000°C, while practical results show coarsening with time at these temperatures. Stability of Y oxides is about 200°C higher, so there is a potential to have stable creep resistant alloy in range of 1000-1200°C.
36
Wortman, D. J., E. C. Duderstadt e W. A. Nelson. "Bond Coat Development for Thermal Barrier Coatings". Journal of Engineering for Gas Turbines and Power 112, n. 4 (1 ottobre 1990): 527–30. http://dx.doi.org/10.1115/1.2906199.
Testo completoAbstract (sommario):
The use of thermal barrier coatings on high-pressure turbine components can improve gas turbine efficiency through reduction of cooling airflow. However, to reduce cooling airflow, a highly reliable thermal barrier coating is required. This increased reliability will be achievable through several complimentary approaches: material and process development, life prediction method development, and engine service experience. The results of bond coat material development, which has increased the thermal cycle life of plasma spray thermal barrier coatings, are presented. Improvements were achieved by two methods: (1) use of creep-resistant bond coat compositions, and (2) overaluminiding of the bond coat.
37
Igwemezie, V. C., C. C. Ugwuegbu e U. Mark. "Physical Metallurgy of Modern Creep-Resistant Steel for Steam Power Plants: Microstructure and Phase Transformations". Journal of Metallurgy 2016 (30 novembre 2016): 1–19. http://dx.doi.org/10.1155/2016/5468292.
Testo completoAbstract (sommario):
The fact that the microstructure of steel depends on its composition and the heat treatment given to it has been heavily exploited in the design of steel for power plant applications. To obtain a steel that can function at the higher temperature where power plants operate without failure for extended life, heat treatment is needed to produce fine and highly stable dispersion of carbides, nitrides, and intermetallic compounds in the microstructure of the material. A significant contribution also comes from solid solution strengthening by substitutional solutes. We review here various types of phases, microstructures, functions, and interacting effects of the various alloying elements in the design of steel for modern power plant application.
38
Cui, Hui Ran, Feng Sun, Lan Ting Zhang, Ai Dang Shan e Jian Sheng Wu. "Effect of W on Deformation Resistance of Co-Bearing 12Cr Ferrite Heat-Resistant Steel for USC Steam Turbines". Materials Science Forum 650 (maggio 2010): 199–204. http://dx.doi.org/10.4028/www.scientific.net/msf.650.199.
Testo completoAbstract (sommario):
12Cr heat resistant steels with different concentration of Co and W, while Mo equivalent (Mo+1/2W) was fixed at 1.6, were prepared by arc-melting and hot rolling. Mechanical properties were evaluated by tensile tests conducted with the strain rate 2×10-5S-1 at 575oC, 600oC and 625oC instead of time-consuming creep tests. The results show that when Co content is fixed, the steel with 1.5 wt% W is found having the best deformation resistance which is strong work hardening and slow strain softening. Apparent activation energy of the steel with 3.1 wt% Co and 1.5 wt% W is in the range of 370~413 kJ/mol, higher than those of the other steels in our study, which are close to the self-diffusion activation energy of iron (239 kJ/mol). Therefore, the steel with 3.1 % Co and 1.5% W is suggested as a potential candidate material for 625oC~650oC class USC steam turbines.
39
Sukhov, D. I., S. V. Nerush, I. Yu Efimochkin, F. N. Karachevchev e I. A. Bogachev. "PRODUCTION OF MMC BASED ON VZh159 ALLOY BY SELECTIVE LASER MELTING". Aviation Materials and Technologies, n. 2 (2021): 62–72. http://dx.doi.org/10.18577/2713-0193-2021-0-2-62-72.
Testo completoAbstract (sommario):
The paper considers manufacturing of metal matrix composites (MMC) by means of selective laser melting. The heat-resistant nickel-based Ni–Cr–Mo–Nb–Al alloy was chosen as a matrix material, the Y2O3 oxide was chosen as a strengthener. After mechanical alloying the obtained powder was used in SLM for the production of a material. The synthesized material’s condition was examined after the SLM process and after hot isostatic pressing (HIP). In the structure the areas containing Y, Al and O-based compounds were found. The creep-rupture tests of samples after HIP and heat treatment were performed and the results were explained by fractographic analysis.
40
Brnic, Josip, Goran Turkalj, Marko Canadija, Sanjin Krscanski, Marino Brcic e Domagoj Lanc. "Deformation behaviour and material properties of austenitic heat-resistant steel X15CrNiSi25-20 subjected to high temperatures and creep". Materials & Design 69 (marzo 2015): 219–29. http://dx.doi.org/10.1016/j.matdes.2014.12.062.
Testo completo
41
Priarone, Paolo Claudio, Stefania Rizzuti, Giovanna Rotella e Luca Settineri. "Technological and Environmental Aspects in Milling of γ-TiAl". Advanced Materials Research 223 (aprile 2011): 340–49. http://dx.doi.org/10.4028/www.scientific.net/amr.223.340.
Testo completoAbstract (sommario):
Gamma-titanium aluminides present an attractive combination of low density, high melting temperature, good oxidation and burn resistance, high modulus and strength retention at elevated temperatures, and good creep properties. For this reason they are promising candidates as advanced structural materials for high temperature applications. However due to their high strength, high hardness and brittleness at room temperature, g-TiAl alloys are regarded as difficult-to-cut materials. Many efforts have been done during the last 20 years to introduce TiAl-based alloys into the aerospace and automotive market as engineering components. But for the application and diffusion of this new heat-resistant light-weight material for high performance components, a deeper knowledge of their machinability is still required. In this context, and given the increasing attention to the environmental aspects related to the manufacturing processes, the present research work is aimed at investigating two key aspects: the influence of cutting parameters and cooling conditions, on tool wear, surface finishing and power consumption in milling operations of a g-TiAl alloy.
42
Lu, Qi, Wei Xu e Sybrand van der Zwaag. "A Material Genomic Design of Advanced High Performance, Non-Corroding Steels for Ambient and High Temperature Applications". Materials Science Forum 783-786 (maggio 2014): 1201–6. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.1201.
Testo completoAbstract (sommario):
This work presents an artificial intelligence based design of a series of novel advanced high performance steels for ambient and high temperature applications, following the principle of the materials genome initiative, using an integrated thermodynamics/kinetics based model in combination with a genetic algorithm optimization routine. Novel steel compositions and associated key heat treatment parameters are designed both for applications at the room temperature (ultra-high strength maraging stainless steel) and at high temperatures (ferritic, martensitic and austenitic creep resistant steels). The strength of existing high end alloys of aforementioned four types are calculated according to the corresponding design criteria. The model validation studies suggest that the newly designed alloys have great potential in outperforming existing grades.
43
Rinaldi, Antonio, Giuseppe Barbieri, Eduard Kosykh, Peter Szakalos e Claudio Testani. "Materials for High Temperature Liquid Lead Storage for Concentrated Solar Power (CSP) Air Tower Systems". Materials 14, n. 12 (12 giugno 2021): 3261. http://dx.doi.org/10.3390/ma14123261.
Testo completoAbstract (sommario):
Today the technical limit for solar towers is represented by the temperature that can be reached with current accumulation and exchange fluids (molten salts are generally adopted and the max temperatures are generally below 600 °C), even if other solutions have been suggested that reach 800 °C. An innovative solution based on liquid lead has been proposed in an ongoing experimental project named Nextower. The Nextower project aims to improve current technologies of the solar sector by transferring experience, originally consolidated in the field of nuclear plants, to accumulate heat at higher temperatures (T = 850–900 °C) through the use of liquid lead heat exchangers. The adoption of molten lead as a heat exchange fluid poses important criticalities of both corrosion and creep resistance, due to the temperatures and structural stresses reached during service. Liquid lead corrosion issues and solutions in addition to creep-resistant material selection are discussed. The experimental activities focused on technical solutions adopted to overcome these problems in terms of the selected materials and technologies. Corrosion laboratory tests have been designed in order to verify if structural 800H steel coated with 6 mm of FeCrAl alloy layers are able to resist the liquid lead attack up to 900 °C and for 1000 h or more. The metallographic results were obtained by mean of scanning electron microscopy with an energy dispersive microprobe confirm that the 800H steel shows no sign of corrosion after the completion of the tests.
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Golański, Grzegorz, Jacek Słania, Marek Sroka, Paweł Wieczorek, Michał Urzynicok e Ryszard Krawczyk. "Microstructure and Mechanical Properties of Modern 11%Cr Heat-Resistant Steel Weld Joints". Materials 14, n. 12 (21 giugno 2021): 3430. http://dx.doi.org/10.3390/ma14123430.
Testo completoAbstract (sommario):
In addition to good high-temperature creep resistance and adequate heat resistance, steels for the power industry must have, among other things, good weldability. Weldability of such steels is one of the criteria determining whether or not the material is suitable for applications in the power industry. Therefore, when materials such as martensitic steel Thor 115 (T115) are introduced into the modern power industry, the quality and properties of welded joints must be assessed. The paper presents the results of metallographic and mechanical investigations of T115 martensitic steel welded joints. The analysis was carried out on joints welded with two filler metals: WCrMo91 (No. 1) and EPRI P87 (No. 2). The scope of the investigations included: microstructural investigations carried out using optical, scanning and transmission electron microscopy and mechanical testing, i.e., Vickers microhardness and hardness measurement, static tensile test and impact test. The macro- and microstructural investigations revealed correct structure of the weld, without welding imperfections. The microstructural investigations of joint No. 1 revealed a typical structure of this type of joint, i.e., the martensitic structure with numerous precipitates, while in joint No. 2, the so-called Nernst’s layers and δ-ferrite patches were observed in the weld fusion zone as well as the heat affected zone (HAZ). The mechanical properties of the test joints met the requirements for the base material. A slight influence of the δ-ferrite patch on the strength properties of joint No. 2 was observed, and its negative effect on the impact energy of HAZ was visible.
45
Chen, Shao Hsien, Sen Chieh Su, Po Chun Chang, Shuo Yan Chou e Kong King Shieh. "The Machinability of MAR-M247 Superalloy". Advanced Engineering Forum 1 (settembre 2011): 155–59. http://dx.doi.org/10.4028/www.scientific.net/aef.1.155.
Testo completoAbstract (sommario):
Nickel-base superalloy is a special super heat resistant alloy developed by U.S in 1970s. It is mainly applied to turbine parts as well as high-temperature components. Nickel-base superalloys exhibit an excellent high strength, low thermal conductivity and creep resistance as well as work hardening. It is the most difficult to be machined with high-speed cutting among different sorts of high-temperature superalloys and is a material presenting multifold challenges for machining. The purpose of this study aims at the machinability of Nickel-base alloys. Engineering statistical analysis was employed to observe the cutting speeds, feed rates and surface roughness at first place. The researcher further applied the half-normal probability plot (HNPP), Pareto analysis and ANOVA to identify the cross effects and probed into the characteristics of Nibase alloy.
46
Grzywna, P., e D. Kukla. "Evaluation of Strain Distribution for the P91 Steel under Static Load Using Espi System". Advances in Materials Science 14, n. 4 (1 dicembre 2014): 28–39. http://dx.doi.org/10.2478/adms-2014-0019.
Testo completoAbstract (sommario):
AbstractThe goal of the research was to evaluate the change of displacement/strain phases in the P91 steel under static load conditions. Undertaken tests were aimed at estimation and analysis of the impact of the material state, which was subjected to loading conditions, on the distribution of stress pattern using ESPI system. Specimen made of high temperature creep resistant steel X10CrMoVNb9-1 (P91) used as a construction material for boiler steam feed heaters, vapor tanks, pressure vessels and vapor pipelines, is used in the service conditions of temperature range up of 650°C. Test samples were taken from two P91 steel pipes. One sample came from a segment of a pipeline transporting fresh vapor in time 80 000 h, under the pressure of 8.4 MPa and temperature 540 °C. The second sample was the same material but in the delivery state.
47
Shriwastwa, Bharat B., e Arun Kumar. "Influence of Copper on Redistribution Behaviour of Boron in Titanium Stabilized and Low Carbon Steel as Observed by Neutron Induced Alpha Autoradiography". Advanced Materials Research 794 (settembre 2013): 502–6. http://dx.doi.org/10.4028/www.scientific.net/amr.794.502.
Testo completoAbstract (sommario):
Boron content and its distribution play a significant role in modifying the metallurgical and mechanical properties of many steels and alloy at lower level of concentration. Precipitation of boron at the grain boundaries, have shown to improve the creep strength in titanium stabilized steel, high temperature ductility in low carbon corrosion resistant steel and the hardenability in low carbon steel in general. Titanium-stabilized steel (DIN 1.4970), was developed as a possible material for fast breeder sodium-cooled nuclear reactor core components for its superior creep strength, high micro-structural stability and elevated void swelling resistance. It is well known that, helium produced during neutron irradiation through the 10B(n,α)Li7 reaction, affects the mechanical properties and the amount of void swelling in nuclear reactor materials. Two nos. of Ti-stabilized steel samples with 40ppm boron and 2ppm boron (DIN 1.4970 & DIN1.4970LB steel) were analyzed for boron re-distribution behavior during different thermo-mechanical treatment using a technique known as Neutron Induced Alpha Autoradiography (NIAA). This technique is a well known technique, and widely used for revealing the spatial distribution of boron in the materials with a resolution approaching to ppm level. This technique has also been used to detect the influence of copper addition on boron distribution pattern in steel specimen. Mapping of boron autoradiography of Low carbon steels containing 20ppm of boron with and without copper was able to demonstrate this behavior. Boron track mapping of Low carbon steel without copper, in solution annealing treatment, show the uniform distribution of boron throughout the matrix, whereas when the similar steel with 1.48% copper was mapped, it shows the precipitation of boron at the grain boundaries.
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Chen, Zhong Bing, Yi Shi Lv, Wei Shi, Quan You Qi e Hai Bo Wang. "Review of Reheat Crack in Welded Joint of Low Alloy Heat-Resistant Steels". Key Engineering Materials 730 (febbraio 2017): 15–20. http://dx.doi.org/10.4028/www.scientific.net/kem.730.15.
Testo completoAbstract (sommario):
The current research status of reheat crack in welded joint of low alloy heat-resistant steels are outlined. Some new phenomena discovered in engineering in recent years are summarized, and related problems that remain to be studied are also presented. Reheat crack in welded joint is occurred frequently during postweld heat treatment (PWHT) or in service at elevated temperature. Mainly four mechanisms leading to reheat crack, respectively, impurity segregation grain boundary weakening, precipitation hardening, creep rupture and no-precipitation zone weakening have been generally accepted now. Several essential factors consist of parent material chemical composition, microstructure and thickness of welded joint, filler material, preheat and postheat procedures, welding energy input, PWHT parameter, and stress and strain and so on. Theoretical calculation methods, criterion of RoA (Reduction of Area) and several experimental methods are put forward to evaluate reheat crack susceptibility. Based on new issues emerged in engineering, problems of concerning reheat crack are necessary to be researched, which include at least mechanism and influence factors of new multi-element composite strengthening heat-resistant steels, the mitigation measures for increasing wall thickness weldment, the root cause analysis and prevention methods of conventional low alloy heat-resistant steels for long term service.
49
Dudek, Rainer, Peter Sommer, Andreas Fix, Joerg Trodler, Sven Rzepka e Bernd Michel. "Reliability investigations for high temperature interconnects". Soldering & Surface Mount Technology 26, n. 1 (28 gennaio 2014): 27–36. http://dx.doi.org/10.1108/ssmt-10-2013-0030.
Testo completoAbstract (sommario):
Purpose – Because of the need for electronics use at temperatures beyond 150°C, high temperature resistant interconnection technologies like transient liquid phase (TLP) soldering and silver sintering are being developed which are not only replacements of high-lead solders, but also open new opportunities in terms of temperature resistance and reliability. The paper aims to address the thermo-mechanical reliability issues that have to be considered if the new interconnection technologies will be applied. Design/methodology/approach – A TLP soldering technique is briefly introduced and new challenges concerning the thermo-mechanical reliability of power devices are worked out by numerical analysis (finite element simulation). They arise as the material properties of the interconnect materials differ substantially from those known for soft solders. The effective material responses of the new materials are determined by localized unit cell models that capture the inhomogeneous structure of the materials. Findings – It is shown that both the TLP solder layer and the Ag-sinter layer have much less ductility and show less creep than conventional soft solders. The potential failure modes of an assembly made by TLP soldering or Ag sintering change. In particular, the characteristic low cycle fatigue solder failures become unlikely and are replaced either by metallization fatigue, brittle failure of intermetallic compound, components, or interfaces. Originality/value – A variety of new failure risks, which have been analyzed theoretically, can be avoided only if they are known to the potential user of the new techniques. It is shown that an optimal reliability will be strongly dependent on the actual assembly design.
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Ebhojiaye, R. S., Patrick E. Amiolemhen e Akii O. A. Ibhadode. "Development of Hybrid Composite Material of Palm Kernel Shell (PKS) and Periwinkle Shell (PS) Particles in Pure Aluminium Matrix". Solid State Phenomena 278 (luglio 2018): 54–62. http://dx.doi.org/10.4028/www.scientific.net/ssp.278.54.
Testo completoAbstract (sommario):
Lightweight engineering materials that are strong, durable, wear and corrosion resistant are required nowadays in the field of engineering, especially in the automobile industry. This study was to develop a hybrid composite material of palm kernel shell (PKS) and periwinkle shell (PS) particles as reinforcements in pure aluminium matrix. The central composite design (CCD) of the response surface methodology (RSM) was used to carry out the design of experiment (DoE). Stir casting method was used to fabricate the specimens. The DoE gave 20 runs (experimental samples) which were replicated three times each, bringing the total number of runs to 60 for each of the six responses considered, and 360 specimens were fabricated in all. Three experimental values were obtained for each of the 120 runs for the wear rate, creep rate, density, tensile strength, hardness and melting temperature. The average values were determined and recorded. Control specimens with 100 wt. % pure aluminium matrix, 0 wt. % of PKS and PS reinforcement particles were prepared. The results showed that the reinforcement particles had significant improvement on mechanical properties of the pure aluminium.