Showing papers on "Creep published in 2016"
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13 Jul 2016
TL;DR: Part I Radiation Damage: The Radiation Damage Event, Displacement of Atoms, Damage Cascade, Point Defect Formation and Diffusion, and Damage Cascade as mentioned in this paper, Part II Physical Effects of Radiation Damage, 6 Radiation-Induced Segregation, 7 Dislocation Microstructure, 8 Irradiation-induced Voids and Bubbles, 9 Phase Stability Under Irradiated, Unique Effects of Ion Irradiations, 11 Simulation of Neutron IRradiation Effects with Ions, and Part III Mechanical Effects of radiation Damage.
Abstract: Part I Radiation Damage -- 1 The Radiation Damage Event -- 2 The Displacement of Atoms -- 3 The Damage Cascade -- 4 Point Defect Formation and Diffusion -- 5 Radiation-Enhanced and Diffusion Defect Reaction Rate Theory -- Part II Physical Effects of Radiation Damage -- 6 Radiation-Induced Segregation -- 7 Dislocation Microstructure -- 8 Irradiation-Induced Voids and Bubbles -- 9 Phase Stability Under Irradiation -- 10 Unique Effects of Ion Irradiation -- 11 Simulation of Neutron Irradiation Effects with Ions -- Part III Mechanical Effects of Radiation Damage -- 12 Irradiation Hardening and Deformation -- 13 Irradiation Creep and Growth -- 14 Fracture and Embrittlement -- 15 Corrosion and Stress Corrosion Cracking Fundamentals -- 16 Effects of Irradiation on Corrosion and Environmentally Assisted Cracking -- Index. .
949 citations
TL;DR: It is reported that Ti-45Al-8Nb single crystals with controlled lamellar orientations can be fabricated by directional solidification without the use of complex seeding methods, and could provide expanded opportunities for higher-temperature applications, such as in aeronautics and aerospace.
Abstract: Increasing the temperature of jet engines requires materials that are stable against degradation. Towards this goal, growth of TiAl alloys with high strength and ductility, as well as superior creep resistance, is reported at high temperatures.
431 citations
TL;DR: In this article, the authors present a comprehensive review of the mechanism of crack formation and propagation, compressive strength, modulus of elasticity, stress-strain behavior, tensile strength (TS), flexural strength, drying shrinkage, creep, electrical resistance, and chloride migration resistance of high performance fiber reinforced concrete.
Abstract: In recent years, an emerging technology termed, “High-Performance Fiber-Reinforced Concrete (HPFRC)” has become popular in the construction industry. The materials used in HPFRC depend on the desired characteristics and the availability of suitable local economic alternative materials. Concrete is a common building material, generally weak in tension, often ridden with cracks due to plastic and drying shrinkage. The introduction of short discrete fibers into the concrete can be used to counteract and prevent the propagation of cracks. Despite an increase in interest to use HPFRC in concrete structures, some doubts still remain regarding the effect of fibers on the properties of concrete. This paper presents the most comprehensive review to date on the mechanical, physical, and durability-related features of concrete. Specifically, this literature review aims to provide a comprehensive review of the mechanism of crack formation and propagation, compressive strength, modulus of elasticity, stress–strain behavior, tensile strength (TS), flexural strength, drying shrinkage, creep, electrical resistance, and chloride migration resistance of HPFRC. In general, the addition of fibers in high-performance concrete has been proven to improve the mechanical properties of concrete, particularly the TS, flexural strength, and ductility performance. Furthermore, incorporation of fibers in concrete results in reductions in the shrinkage and creep deformations of concrete. However, it has been shown that fibers may also have negative effects on some properties of concrete, such as the workability, which get reduced with the addition of steel fibers. The addition of fibers, particularly steel fibers, due to their conductivity leads to a significant reduction in the electrical resistivity of the concrete, and it also results in some reduction in the chloride penetration resistance of the concrete.
350 citations
TL;DR: It is shown that nanocrystalline copper–tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability, including in the aerospace, naval, civilian infrastructure and energy sectors.
Abstract: A nanocrystalline copper–tantalum alloy with high strength and extremely high-temperature creep resistance is achieved via a processing method that creates clusters of atoms within the alloy that pin grain boundaries. Reducing the grain size of a metal is one way of increasing its strength, but it can often have detrimental effects on other mechanical properties. The resistance to slow irreversible deformation known as creep, for example, can be greatly diminished, owing to the relatively large volume of the material that is in the form of grain boundaries between the nanocrystalline constituents. Kristopher Darling et al. describe a family of nanostructured alloys that combine high strength with extremely high creep resistance. Key to this achievement is a processing strategy that creates tiny clusters at the grain boundaries, stabilizing the nanocrystalline grains against sliding, rotation and diffusional growth, and so greatly enhancing their resistance to creep. Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size1. However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper2,3. The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation3. Here we show that nanocrystalline copper–tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength4,5, which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10−6 per second—six to eight orders of magnitude lower than most nanocrystalline metals—at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of microstructurally stable structural alloys with high strength and creep resistance for various high-temperature applications, including in the aerospace, naval, civilian infrastructure and energy sectors.
204 citations
TL;DR: In this article, a multistage grain scale approach to microstructure-sensitive fatigue crack formation and growth is presented which uses Fatigue Indicator Parameters (FIPs) to correlate these processes.
196 citations
TL;DR: In this paper, the β-solidifying so-called TNM alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in atomic percent), is presented.
Abstract: After more than 30 years of fundamental research and development activities intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in aerospace and automotive industries. The advantages of this class of innovative high-temperature lightweight materials are their low density, their good strength and creep properties, as well as their oxidation resistance up to 750 °C. A drawback, however, is their limited ductility at room temperature, which is reflected by a low plastic strain at fracture. Advanced engineering TiAl alloys, such as the β-solidifying so-called TNM alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in atomic percent), are complex multi-phase materials which can be processed by ingot or powder metallurgy, precision casting methods as well as additive manufacturing. Each production process leads to specific microstructures which can be altered and optimised by thermomechanical processing and/or subsequent heat treatments, whereby the knowledge of t...
171 citations
TL;DR: In this article, surface observations were used to elucidate the deformation mechanisms responsible for the superplastic effect in Ti-6Al-4V. The authors used a scanning electron microscope to perform high-temperature in-situ tests for tensile and shear deformation modes.
162 citations
30 Sep 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the creep properties of a polycrystalline nickel-based superalloy produced via selective laser melting were investigated, and it was shown that the additively manufactured material showed superior creep strength compared to conventional cast and wrought material.
Abstract: The creep properties of a polycrystalline nickel-based superalloy produced via selective laser melting were investigated in this study. All heat treatment conditions of the additively manufactured material show superior creep strength compared to conventional cast and wrought material. The process leads to a microstructure with fine subgrains. In comparison to conventional wrought material no Niobium rich δ phase is necessary to control the grain size and thus more Niobium is available for precipitation hardening and solid solution strengthening resulting in improved creep strength.
160 citations
10 May 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions.
Abstract: To achieve high thermal efficiency, modern day thermal power plants operate at higher operating temperature and pressure which necessitates use of steels with high creep rupture strength such as modified 9Cr-1Mo steels. In the present study, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions. The main focus has been to study the effect of heat treatment temperature ranging from 623 K to 1033 K (350–760 °C) on P91 steel. Further, the effect of furnace cooling, water quenching, tempering at 1273 K (1000 °C) and austenitizing on the mechanical properties and microstructure has been studied. The techniques used for material characterization were scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction. For low tempering temperature, i.e. 623 K (350 °C), M 23 C 6 , M 3 C, M 7 C 3, and MX precipitates have been observed with high yield strength (YS), tensile strength (UTS), hardness and low toughness. In the high temperature range, 923–1033 K (650–760 °C), fine MX, M 7 C 3 , M 23 C 6 , M 2 X, and M 3 C precipitates have been observed with low YS, UTS, hardness and high toughness. The steel tempered at 1033 K (760 °C) was observed to be having best combination of YS, UTS, hardness, toughness and ductility.
160 citations
TL;DR: In this paper, the deformation behavior of CoCrFeMnNi high-entropy alloys (HEAs) was systematically explored through a series of spherical nanoindentation creep experiments.
154 citations
TL;DR: A new ‘phase-transformation strengthening' mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C is introduced.
Abstract: Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO2 emissions. Here we introduce a new ‘phase-transformation strengthening’ mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ′ to η phase along stacking faults in γ′ precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties. Nanoscale processes may directly impact macroscopic mechanical behaviour. Here authors describe a ‘phase-transformation strengthening’ mechanism in nickel-based high temperature alloys, allowing suppression of deleterious deformation processes at elevated temperatures by specific alloying elements.
TL;DR: In this article, a series of triaxial compression and creep tests were conducted on frozen loess under different confining pressure and temperature conditions in order to study the rate-dependent mechanical behaviors.
07 Mar 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel has been investigated using optical metallography and scanning electron microscopy (SEM).
Abstract: Mechanical properties of creep enhanced ferritic (CSEF) steels is affected by various parameters, the solutionizing temperature is one of them. The present work demonstrates the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel. Optical metallography (OM) and Scanning electron microscopy (SEM) were carried out to study the microstructure of P91 steel in different heat treatment conditions. In order to determine the precipitates present in microstructure; X-ray analysis was performed. Moreover, the influence of solutionizing temperature on the mechanical properties (strength, hardness and impact toughness) has also been studied.
TL;DR: In this article, computational alloy thermodynamics coupled with strength modeling have been employed to explore a new generation reduced activation ferritic-martensitic (RAFM) steels, which were designed to significantly increase the amount of MX nanoprecipitates, which are manufacturable through standard and scalable industrial steelmaking methods.
TL;DR: In this paper, a modified strain energy density exhaustion model was proposed to predict the tension hold-only creep-fatigue life for high temperature components, which exhibits high accuracy due to the reasonable evaluation of creep damage.
TL;DR: In this paper, the authors measured elasticity, anelasticity, and viscosity of polycrystalline aggregates at near-solidus temperatures ranging from below to above the solidus temperature.
Abstract: Elasticity, anelasticity, and viscosity of polycrystalline aggregates were measured at the near-solidus temperatures ranging from below to above the solidus temperature (Tm). The result shows that the mechanical effects of the partial melting are twofold; changes just below the solidus temperature in the absence of melt and changes at the solidus temperature due to the onset of partial melting. As homologous temperature (T/Tm) increases from about 0.92 to 1, high-frequency part of the attenuation spectrum significantly grows. Viscosity of the grain boundary diffusion creep is also reduced in this temperature range. These changes are caused by a solid-state mechanism and have a large amplitude even for the samples which can generate very small amounts of melt at the solidus temperature. At the onset of melting, further increases in the elastic, anelastic, and viscous compliances occur. These changes are caused by the direct effects of the melt phase and are very small for the samples with very small melt fractions. Mechanical properties of a partially molten aggregate are determined by these twofold changes, and when melt fraction is small, the former changes are dominant. We performed a parameterization of the present experimental results and applied the obtained empirical formula to the seismic tomographic data in the upper mantle. The present model explains well the steep reduction of the seismic shear wave velocity in the oceanic lithosphere just below the solidus temperature.
TL;DR: In this paper, a selection of experimental results of creep tests found in the scientific literature are used to highlight the nonlinearity, multi-axiality, hydration, and thermal and drying effects.
01 Jan 2016
TL;DR: The fundamentals of creep in metals and alloys is available in our book collection and an online access to it is set as public so you can get it instantly as mentioned in this paper. But it does not have a physical copy.
Abstract: Thank you for reading fundamentals of creep in metals and alloys. Maybe you have knowledge that, people have search hundreds times for their chosen novels like this fundamentals of creep in metals and alloys, but end up in infectious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they juggled with some harmful virus inside their computer. fundamentals of creep in metals and alloys is available in our book collection an online access to it is set as public so you can get it instantly. Our digital library saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the fundamentals of creep in metals and alloys is universally compatible with any devices to read.
TL;DR: In this article, a series of cyclic heart-shaped and cyclic triaxial undrained tests were performed on Shanghai clay through simultaneously varying the torsional shear stress and the normal stresses.
TL;DR: In this paper, a creep recovery shear rheological protocol was applied to fresh cement pastes and a viscosity bifurcation behavior was observed through applying a range of creep stresses.
TL;DR: In this article, the authors studied the time dependent behavior of a geopolymer concrete and compared the predictions made using Eurocode 2 with those made by Eurocode 3 for OPC concrete.
Abstract: The main purpose of this research is to study the time dependent behaviour of a geopolymer concrete. The geopolymer binder is composed of 85.2 % of low calcium fly ash and only 14.8 % of ground granulated blast furnace slag. Both drying shrinkage and creep are studied. In addition, different curing conditions at elevated temperature were used. All experimental results were compared to predictions made using the Eurocode 2. The curing regime plays an important role in the magnitude and development of both creep and drying shrinkage of class F fly ash based geopolymer concrete. A minimum of 3 days at 40 °C or 1 day at 80 °C is required to obtain final drying shrinkage strains similar to or less than those adopted by Eurocode 2 for ordinary Portland cement (OPC) concrete. Creep strains were similar or less than those predicted by Eurocode 2 for OPC concrete when the geopolymer concrete was cured for 3 days at 40 °C. After 7 days at 80 °C, creep strains became negligible.
08 Feb 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the plastic-deformation mechanism and mechanical properties evolution of single-phase Al0.1CoCrFeNi high-entropy alloy (HEA) were studied under high pressure torsion (HPT) under a pressure of 6 GPa through 1 and 2 revolutions.
Abstract: High pressure torsion (HPT) under a pressure of 6 GPa through 1 and 2 revolutions have been used to follow the evolution of microstructures and properties in an Al0.1CoCrFeNi high-entropy alloy (HEA). The plastic-deformation mechanisms of the HEA include dislocation slip at low strains and twinning at high strains at room temperature. The planar dislocation slip on the normal face-centered-cubic slip system, {111}〈110〉, and nanoscaled deformation twins with a thickness from several nanometers to 40 nm, accompanied with some secondary twins. The hardness of the Al0.1CoCrFeNi HEA increases from 135 Hv at hot-isostatic pressed (HIPed) state to about 482 Hv after HPT processing. The HEAs have a relatively high initial hardness and high work hardening, compared with traditional alloys. The creep resistance of the HEA processed by HPT was determined by a nanoindentation technique. The strain rate sensitivity, m, increases with the decreasing of grain size, for smaller activation volume and the dominant deformation mechanism changing from the dislocation slip to grain-boundary slide. The present results give the plastic-deformation mechanism and mechanical properties evolution of single-phase HEA processed by HPT at room temperature.
TL;DR: In this paper, the elastic stiffness and the creep properties of ordinary Portland cement pastes conditioned at 20°C were characterized by means of a power-law expression including elastic and creep moduli, as well as a creep exponent.
TL;DR: In this article, the authors focused on studying the time-dependent properties of recycled concrete, especially shrinkage and creep behaviour, and showed that the use of pre-saturated recycled aggregates leads to different time-dependency in shrinkage.
TL;DR: In this article, the authors measured the uniaxial power-law creep response from nanoindentation on commercial purity aluminum alloy at a number of temperatures up to 550°C and found that the activation energy for creep was 140.2KJ/mol/K.
TL;DR: In this paper, the microstructure, crystal structure, creep behavior and mechanism of AlxCoCrFeNi (x is in molar ratio) high entropy alloys were examined.
TL;DR: In this article, the effect of postwelding heat treatment (PWHT) and weld groove designs on the overall microstructure and mechanical properties of P91 steel pipe welds produced by the gas tungsten arc welding process was studied.
Abstract: The martensitic creep-resistant steel designated as ASTM A335 for plate and as P91 for pipe is primarily used for high-temperature and high-pressure applications in steam power plants due to its excellent high-temperature properties such as high creep strength, high thermal conductivity, low thermal expansion, and so on. However, in the case of welded joints of such steels, the presence of an inter-critical heat-affected zone (IC-HAZ) can cause the joint to have lower creep strength than the base metal. In the present study, the effect of post-welding heat treatment (PWHT) and weld groove designs on the overall microstructure and mechanical properties of P91 steel pipe welds produced by the gas tungsten arc welding process was studied. Various regions of welded joints were characterized in detail for hardness and metallographic and tensile properties. Sub-size tensile samples were also tested to evaluate the mechanical properties of the weld metal and heat-affected zone (HAZ) with respect to PWHT. After PWHT, a homogenous microstructure was observed in the HAZ and tensile test fracture samples revealed shifting of the fracture location from the IC-HAZ to the fine-grained heat-affected zone. Before PWHT, the conventional V-grooved welded joints exhibited higher tensile strength compared to the narrow-grooved joints. However, after PWHT, both narrow- and V-grooved joints exhibited similar strength. Fractography of the samples indicates the presence of carbide precipitates such as Cr23C6, VC, and NbC on the fracture surface.
TL;DR: In this paper, a nonlinear damage creep constitutive model of high-stress soft rock is defined in series with the improved Burgers model, Hooke model and St. Venant model.
Abstract: Rock engineering especially deep rock engineering undergoing long-term effects of external loading and gravity all or most may gradually damage deformation or creep deformation accumulation, leading rock structures to damage, crack, such as severe plastic deformation or even progressive failure. In this paper, based on the nonlinear damage creep characteristics of rock and damage variable, a new nonlinear damage creep constitutive model of high-stress soft rock is defined in series with the improved Burgers model, Hooke model and St. Venant model. This new nonlinear damage creep constitutive model can work out fairly reasonably explanations for the soft rock creep deformation. A series of uniaxial compression creep tests were performed to study the creep damage characteristics of typical soft rock in Jinchuan No.2 Mine in the northwest of China. Using the increment step loading and single-step loading, the results of creep experiments and nonlinear damage creep constitutive model results are very consistent in this study. The new model not only can reflect the whole course of creep deformation, but also can reasonably describe the soft rock under different initial creep stage, steady-state creep stage and accelerated creep stage. Therefore, the new nonlinear creep damage model is a reasonable reference model for the research of soft rock creep.
TL;DR: Using the magnetron sputtering technique, two typical high-entropy alloy (HEA) films, namely CoCrFeNiCu (Al-0) with a face-centered cubic (fcc) structure and Al-25 with a bodycentered cubic structure were prepared by alloy targets as discussed by the authors.
Abstract: Using the magnetron sputtering technique, two typical high-entropy alloy (HEA) films namely CoCrFeNiCu (Al-0) with a face-centered cubic (fcc) structure and CoCrFeNiCuAl25 (Al-25) with a body-centered cubic (bcc) structure were prepared by alloy targets The as-deposited HEA films have a columnar-growth mode and nanocrystalline grains The creep behaviors of both HEA films were systematically investigated by nanoindentation with a Berkovich indenter The bcc Al-25 exhibited a stronger creep resistance than the fcc Al-0 In addition, with the increase of holding load and/or loading rate, the creep deformation was significantly enhanced in the fcc Al-0 Interestingly, it was almost history-independent in the bcc Al-25 The creep characteristics of HEA films could be related to the distinct lattice structures, which apparently affect the kinetics of plastic deformation The strain rate sensitivity (SRS) and activation volume of the dislocation nucleation were carefully estimated for both HEA films In view of the large differences of activation volumes between Al-0 and Al-25, we present discussions to explain the observed creep characteristics in HEA films (C) 2015 Published by Elsevier Ltd
TL;DR: In this paper, the effect of crystallinity and crystalline forms (ratio of the less ordered α and the more ordered α crystalline form) of injection moulded Poly(Lactic Acid) (PLA) was analyzed on the mechanical, thermo-mechanical, Heat Deflection Temperature (HDT) and creep properties.