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Lithium–sulfur batteries with liquid electrolytes are discussed as the most promising post‐lithium‐ion‐battery technology in literature due to their high theoretical specific energy and first prototype cells delivering >470 Wh kg−1. Although several electrolyte and material concepts are developed that partially solve the issue of the so‐called shuttle mechanism, the most promising concept to genuinely confine sulfur species in the cathode is all‐solid‐state argyrodite–sulfur cathodes leading to almost theoretical active material utilization by maintaining reasonable sulfur loadings and electrolyte to sulfur ratios. However, this battery concept has so far not achieved reversible cycling against metallic lithium anodes as it requires high pressures for manufacturing, and ductile lithium metal creeps along the grain boundaries of the solid electrolyte particles leading to short cuts of the cells. Recent findings show that metallic lithium, however, can be stably cycled with dimethoxyethane/lithium‐bis(fluorosulfonyl)imide (DME/LiFSI)‐based electrolytes. Herein, for the first time, a semisolid concept is presented combining the benefits of an argyrodite‐based solid‐state cathode and a DME/LiFSI/hydrofluoroether‐based anolyte concept – in coin cells and first pouch cells. This disruptive approach enables projected specific energies higher than 600 Wh kg−1 at cell stack level. [ABSTRACT FROM AUTHOR]

Formation of creep pores and their transformation into creep cracks in the metal of welded joints of steam pipelines made of heat-resistant pearlite steels (12Kh1MF and 15Kh1M1F), with the long-term operation (over 270,000 h) under creep and low-cycle fatigue conditions (via repeated start-stop modes), largely depends on the structural and phase state of the welded joints. Welded joints are characterized by structural heterogeneity caused by welding heat. The heterogeneity increases with their further service life. This heterogeneity in the metal of welded joints is much greater than the heterogeneity of the base metal of the steam line, which has not been subjected to welding heat. In long-term operation, the structure of steam lines and their welded joints is transformed into a ferriticcarbide mixture at different rates. The rate of this transformation in the metal of welded joints is much higher than in the base metal of steam lines. It was found that the intensity of damage to the metal of welded joints by pores and creep cracks largely depends on the level of transformation of the initial structure into a ferritic-carbide mixture. It was found that creep pores are mainly formed along the boundaries of α-phase grains and, to a lesser extent, along the grain body. We studied the peculiarities of physical and chemical processes occurring in the metal of welded joints of steam pipelines. We established a link between the self-diffusion of alloying elements (chromium, molybdenum, and vanadium) and the movement of dislocations. It was found that pore nucleation in the metal of welded joints occurs mainly at the boundaries of ferrite and bainite grains, where the coagulating carbides M23C6 and M7C3 are located rather than along the grain body. In the process of diffusion movement, vacancies, by merging, are transformed into microcontinuities that move in the direction of vacancy movement. It was found that the formation of creep pores in the metal of welded joints largely depends on its structural and phase state. Creep pores are most intensively formed in areas where the structure consists of tempering bainite, ferrite, and coagulating globularized pearlite. It was found that with an increase in the metal deformation of the zone of thermal influence of welded joints, the formation of creep pores is accelerated. [ABSTRACT FROM AUTHOR]

Understanding and controlling interface friction are central to many science and engineering applications. However, frictional sliding is closely related to adhesion, surface roughness, surface chemistry, mechanical deformation of contact solids, which poses the major challenge to experimental studying and theoretical modeling of friction. Here, by exploiting the recent developed thermomechanical nanomolding technique, we present a simple strategy to decouple the interplay between surface chemistry, plastic deformation, and interface friction by monitoring the nanoscale creep flow of metals in nanochannels. We show that superhydrophobic nanochannels outperforming hydrophilic nanochannels can be up to orders of magnitude in terms of creep flow rate. The comparative experimental study on pressure and temperature dependent nanomolding efficiency uncovers that the enhanced creep flow rate originates from diffusion-based deformation mechanism as well as the superhydrophobic surface induced boundary slip. Moreover, our results reveal that there exists a temperature-dependent critical pressure below which the traditional lubrication methods to reduce friction will break down. Our findings not only provide insights into the understanding of mechanical deformation and nanotribology, but also show a general and practical technique for studying the fundamental processes of frictional motion. Finally, we anticipate that the increased molding efficiency could facilitate the application of nanoimprinting/nanomolding. Solid-solid interface friction usually becomes the bottleneck at micro/nanoscale. Here, Xiang and Liu show that the nanoscale creep flow rate of crystalline metals can increase by orders of magnitude when the contact metal is in diffusion deformation and the thermally activated boundary slip is active. [ABSTRACT FROM AUTHOR]

The γ U-Mo alloy has been selected for the conversion of U.S. High-Performance Research Reactor (HPRR) fuel from highly enriched uranium to low enriched uranium as a part of the effort to reduce nuclear proliferation risks. Although γ U-Mo alloys have the advantage of high uranium density and good overall irradiation performance, the irradiation-induced swelling and creep in the metal remain important design parameters since they influence the mechanical and thermal integrity of the fuel. To account for these design criteria, engineering scale models need fundamental properties, such as diffusion coefficients, as input. In this study, the diffusion of related species along grain boundaries in γ U-Mo fuel is quantified considering that grain boundaries act as sinks for point defects, nucleation sites for gas bubbles, avenues for Coble creep, etc. The diffusivities of U and Mo in selected grain boundaries of γ U-Mo alloys (γ U-7Mo, γ U-10Mo, and γ U-12Mo) are obtained utilizing molecular dynamics simulations for a temperature range of 600 K - 1200 K with an interval of 100 K. The structures analyzed include symmetric tilt, asymmetric tilt, and twist grain boundaries. The grain boundary diffusion coefficients of U and Mo in the examined γ U-Mo alloys are on the order of 10 − 14 to 10 − 11 m2 s−1. It is observed that the U diffusivity in the grain boundary is higher than the Mo diffusivity in all cases and that the increase in Mo content of the alloy correlates to a decrease in the grain boundary diffusion. Xe diffusion along γ U-10Mo grain boundaries is also calculated in this work, and the diffusivity of Xe in the γ U-10Mo grain boundaries is found to be 8 to 15 orders of magnitude higher than the intrinsic Xe diffusivity in γ U-10Mo depending on the temperature. The information gathered in this work can inform fuel swelling and creep models and help understand various other phenomena related to γ U-Mo fuel performance. [ABSTRACT FROM AUTHOR]

Since the fundamental works of Kachanov and Rabotnov, creep damage mechanics is an established field of research in solid mechanics. The starting point is the creep behavior of materials under moderate loads but elevated temperatures. The final stage of creep behavior is accompanied by damage and other microstructural changes such as embrittlement. In the present paper a detailed analysis of literature is given. A special focus is made on the different types of representation of damage by scalar, vectorial and tensorial variables. In addition, some Russian sources are presented which are not widely known yet. The survey is representative, but not complete - due to the large number of sources, it is not possible to provide a complete overview. Considering the huge number of parameters of tensorial damage variables which should be established experimentally in the second part of the paper a simple model for the high temperature creep and embrittlement in metals and alloys under conditions of the long-term usage is introduced. The model is an extension of R. Arutunyan’s model developed in the 90th of the last century. The extension includes the consideration of a compressible medium, the introduction of the mass conservation law and true stress, and definition of the damage parameter as a relative change in the density of the material. The parameters are experimentally estimated and the comparison of simulations and experiments is given. [ABSTRACT FROM AUTHOR]

A novel creep testing machine was designed to test austenitic steel foil AISI 347 under the elevated temperature of 700°C. The creep test was repeated in five stress levels from low‐stress 55 MPa to severe applied stress 220 MPa for 0.25 mm thickness samples. The machine was equipped with a shield inert gas injection system, and tests were repeated in a nonoxidative area. The creep rupture behavior of the foil is well represented using the modified three‐parameter Theta Projection Concept model. Each model parameter is best represented as a function of the applied stress. Comparison between the results of creep life in different mediums shows that the oxidation effect was the dominant phenomenon in the creep process. Moreover, avoiding oxidation affects the steady‐state stage growth, and afterward, the creep life was increased by more than 40%. Post analyses of ruptured creep samples compare the creep cavitation at triple grain boundaries in a different environment. Highlights: Novel testing machine and method to measure the creep deformation of metal foils.Creep behavior of AISI 347 steel foil under various stresses at laboratory air and in argon environments.The use of shielding inert gas and its capability to protect the foil surfaces from oxidation.Stablish relationship between the creep life and axial creep conditions using modified theta projection concept. [ABSTRACT FROM AUTHOR]

Surface-acoustic-wave (SAW) devices have been widely investigated over many years as demand has grown for information sensing above 1000°C. At such high temperatures, metal electrode creep occurs, thereby causing the transformation of an electrode from a continuous uniform film to a discontinuous film with hollows or isolated grains. In this study, 100 nm thick ITO conductive oxide film is deposited on 100 nm thick Pt film to form an ITO/Pt bilayer-film composite electrode for high-temperature SAW devices. According to this way, the conductive stability of the Pt film electrode at high temperature can be greatly improved. Compared with the initial value, the electrical conductivity of single-layer 100 nm thick Pt film decreases to 65.4% with the area fraction of Pt at 64.1%. Meanwhile, the electrical conductivity of ITO/Pt bilayer-film decreases to only 95% with the area fraction of Pt at 63.1%. Then, the enhancement of high-temperature conductive stability can be attributed to the added ITO conduction channels. These findings demonstrate a potential route to design multilayer electrodes that can operate above 1000°C with promising applications in SAW devices needing to operate at high temperatures. [ABSTRACT FROM AUTHOR]

• Study of creep rupture behaviour of the dissimilar welded joint of P92 steel and Inconel 617 alloy tested at 650 °C under the stress range of 120–200 MPa. • Study the microstructure evolution and hardness in each zone of the weldments after creep failure. • Study the mechanism of the creep failure mechanism for different fracture location, i.e. base metal, P92 FGHAZ and interfacial failure. The dissimilar welded joint (DWJ) comprising P92 steel and Inconel 617 (IN617) is frequently utilized in advanced ultra-supercritical (AUSC) boilers. In present work the creep rupture behaviour, rupture mechanism and microstructure evolution of DWJ of P92 steel and IN617 with Ni-based ERNiCrCoMo-1 filler, were examined at 650 °C under the stress range of 120–200 MPa. The results of the creep test indicated that the location of creep rupture varied across different testing conditions, encompassing areas such as P92 base metal and the fine-grained heat-affected zone (FGHAZ). The creep tested specimens within the stress range of 180–200 MPa exhibited failure originating from P92 base metal, predominantly influenced by plastic deformation. The failure manifested in a transgranular mode, driven by the formation, growth, and eventually coalescence of microvoids. The creep tested specimens within the stress range of 120–150 MPa displayed the characteristic ofType IV failure, primarily attributed to matrix softening and the absence of adequate precipitates to pin the PAGBs. Microstructural characterization unveiled the presence of microvoids along the PAGBs, facilitating microvoid nucleation primarily owing to the existence of the coarse brittle carbide phase. The growth of these microvoids over a period of time during tertiary stage of creep which lead to their coalescence and the formation of microcracks, ultimately resulting in premature intergranular failure. The specimen creep exposed at 650 °C under the lower stress of 120 MPa exhibited higher creep rupture life for 432 h. The SEM/EDS study of the crept sample of 120 MPa is also confirmed the presence of intermetallic laves phases in regions near the fracture tip and in the heat-affected zones (HAZs). Although the creep tested specimens at 150 MPa and 120 MPa exhibited failure in the FGHAZ and their elemental SEM/EDS analysis confirmed the presence of an oxide layer and notch formation near the interface of P92 base metal and ErNiCrCoMo-1 filler weld. The FESEM study revealed the growth of the oxide layer in the notch region, and it also showed the presence of multiple cracks and microvoids in the oxide layer. The formation and propagation of the oxide notch mainly led to the interfacial failure. The crept specimens subjected to 180 MPa and 200 MPa did not exhibit any cracks or microvoids in HAZs. However, specimens that failed under applied stresses of 120 MPa and 150 MPa revealed the presence of a high density of microvoids in the FGHAZ, inter-critical heat-affected zone (ICHAZ), and in the region of the coarse-grained heat-affected zone (CGHAZ) adjacent to the interface attached with an oxide layer. [ABSTRACT FROM AUTHOR]

Indentation testing is a common technique for characterizing the mechanical properties of materials. When it comes to assessing the yield behavior of metals, conical indentation is often favored due to its ability to induce significant plastic deformation at relatively shallow indentation depths. On the other hand, spherical indentation is typically chosen for evaluating metal creep behavior, as it helps minimize the influence of plastic deformation on creep measurements. In spherical indentation tests, the friction at the contact interface is particularly crucial, given the larger contact area and more pronounced slip zones. However, accurately determining the friction coefficient at the contact interface is a complex multi-scale challenge, with the exact coefficient varying based on specific testing conditions and surface treatments. Consequently, empirical friction coefficients are frequently employed, often without thorough justification. In this work, we proposed Bayesian inference method for obtaining the creep constitutive behavior of alloys through spherical indentation tests. Our model considers not only the complexity of creep law, but also the indentation friction, which is unable to consider in most spherical indentation tests with traditional treatment. By using experimental data of spherical indentation tests on 310S stainless steel and pure nickel alloy from literature, present study demonstrates the effectiveness of the Bayesian inference approach, with the inferred constitutive models exhibiting well agreement with uniaxial creep behavior. Furthermore, the method considers the friction coefficient as an extra factor in inferring creep constitutive behavior from indentation tests. [Display omitted] • Friction plays a crucial role for obtaining the creep constitutive behavior of alloys through spherical indentation tests • The Bayesian inference approach can provide a reliable way for obtaining material parameters by data-mining of experimental spherical indentation • The inferred constitutive models exhibited well agreement with the uniaxial creep tests [ABSTRACT FROM AUTHOR]

• Shear strain rate should be the independent variable in creep. • Dislocation creep is due to a single deformation mechanism not two. • Activation entropy is a component of the flow activation energy. • Results lie on similar activation energy – temperature curves. Previously published results on the power law creep of a selection of fcc, bcc and hcp pure metals are discussed using a modified Stokes – Einstein equation originally describing Newtonian viscosity of spherical particles in a fluid. Activation energy is modified to include terms representing activation enthalpy, activation entropy and the effect of strain rate. It is similar to the Dorn equation for power law creep but with strain rate rather than stress as the independent variable. Curves of activation energy vs shear rate are linear rather than having a discontinuity as have those with stress as independent variable. All metals have linear curves of activation energy at zero rate vs temperature, the slope of which reflects the activation entropy and is similar for all metals. Intercepts which represent activation enthalpy are dependent on lattice structure. [ABSTRACT FROM AUTHOR]

The electrical potential drop (EPD) technique has previously shown promising results using a combination of AC and DC EPD (or DCPD) on large pressure vessel creep tests, detecting final cracking as well as incipient creep cavitation damage in welded P91 steel, with DCPD showing subtle but steady rises of around 5% over ca 10,000 h of testing before rising exponentially at failure. The work presented here has attempted to shed light upon this using a simple numerical model. The model uses an array of spherical cavities to constrain the current path and hence raise the DCPD, however it was only able to show a modest rise in DCPD, and not match experimentally determined rises. Modelled DCPD values were a fifth of those experimentally observed, but both the nature of the model (simplified to aid timely computation) and the assumption that only cavitation is responsible for the changes seen, could be the reason for the discrepancies reported here. The possibility remains that other mechanisms are at play, which could magnify the measured DCPD – particularly those mechanisms that could be associated with embryonic or micro-crack formation, and these are discussed herein. [ABSTRACT FROM AUTHOR]

Creep rupture behavior of dissimilar weldments between FB2 and 30Cr1Mo1V heat-resistant steel by multipass welding at 783 K (510°C) under different stresses (260 to 420 MPa) was researched. The fitted creep rupture exponent is 14.53, and the 10,000 h extrapolating strength values predicted by the power law and Larson-Miller parameter show good agreement with experimental data. The samples exhibit a ductile fracture character and fracture in the weld fusion zone, which has a highly heterogeneous microstructure and grains with different morphologies and sizes and an obvious softening. There exist a decrease in the dislocation and precipitate density and an increase in the subgrain size in the weld metal after creep. The rupture is a transgranular fracture characterized by dimples as a result of microvoid coalescence. Laves phases along with copper-rich precipitates are observed in the vicinity of fracture surface, which creates a stress concentration that can cause transgranular fracture initiation. [ABSTRACT FROM AUTHOR]

The paper presents the results of the application of the refined calculation guidelines to the analysis of the stress-strain state and fracture resistance of the equipment elements of the NPP primary circuit system with WWER reactor, in particular, the cylindrical part and the zone of the reactor pressure vessel inlet nozzle, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft under the operating and emergency modes of thermomechanical loading. The calculation methodology is based on the use of the modern models and methods of solution to the nonlinear boundary tasks of non-isothermal thermal viscoplasticity and tasks of fracture mechanics using the refined mixed schemes of the finite element method with increased accuracy. They allow one to obtain reliable solutions to the tasks considering the deformation history of thermomechanical loading, modern concepts of fracture mechanics and approaches to the modeling of brittle-viscous fracture defects, irradiation swelling and creep of metal, as well as as the structural elements, under the conditions of elevated temperature, intensive neutron irradiation and nonstationary modes of thermomechanical loading. The authors obtained and analyzed the calculation results for the cylindrical part and zone of the inlet nozzle of the WWER-1000 reactor pressure vessel, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft using the proposed guidelines. The results imply the possibilities of the proposed recommendations and make it possible to analyze some general tendencies and features of the application of the refined calculation models to justify the strength and life extension of the NPP structural elements under investigation. [ABSTRACT FROM AUTHOR]

The simulation of the results of metal testing under creep conditions at the nonstationary complex stress state is considered. As an example, we consider the experimental data obtained by a group of Japanese scientists for testing tubular samples of stainless steel under the temperature of $650 ^{\circ}$C. The following article presents the test results for four different loading programs. These loading programs are various combinations of piecewise constant dependencies of tangential and normal stresses on time. The presented data was simulated using the hardening theory and the flow theory; two material constants used are determined from the condition of the minimum relative integral discrepancy between the experimental and theoretical values of the corresponding creep deformations. A comparison was made of the results of the simulation carried out with the results of the simulation of the same experimental data, carried out by other researchers using other theories. In these theories, a large number of material characteristics are used: from three to nine constants and additionally one material function. The advantage of the hardening theory and flow theory with only two material constants each compared to the other theories has been shown.

The fundamental mechanism underlying the formation of brazed joints involves the diffusion of elements between the base metal (BM) and the brazing filler metal (FM). The formation of brittle compounds in FM during the brazing process frequently results in a significant deterioration of the mechanical properties of the brazed joints. Ni and Cu elements exhibit infinite solubility, and the incorporation of Cu element results in a decrease in the liquidus temperature of FM, thereby enhancing its surface wettability on the BM. The present investigation involves the preparation of as-cast and amorphous FMs with varying Cu element concentrations to examine their material properties, such as weldability, wettability, thermophysical behavior, and creep resistance. The thermophysical and mechanical properties of the nickel-based filler metal BNi-2 were evaluated using the JMatPro software for material thermodynamic simulation and compared with data obtained from existing literatures. An analysis is conducted on the creep properties of a novel FM comprising of Ni, Cr, Fe, Si, B, and Cu. The results suggest that the thermophysical properties of BNi-2 filler are minimally impacted by the presence of Cr (6–8 wt%), Fe (2.5–3.5 wt%), Si (4–5 wt%), and B (2.75–3.5 wt%). Furthermore, alterations in the composition of Si and B elements have a significant impact on the distribution of γ and γ′ phases, consequently influencing the creep properties of the material. At 25 °C, the equilibrium phase of BNi-2 with different Cu contents indicates a gradual decrease in the content of γ phase, while the content of γ′ and Cu–Ni phases increases with an increase in Cu content. The BNi-2 filler with 3 % Cu exhibits the most favorable properties in terms of steady creep rate and fracture life compared to other fillers. This is attributed to the competitive equilibrium between the γ phase and Cu–Ni phase. The addition of 6 % Cu element results in the optimal wettability of the filler metal and creep resistance of the brazed joints. It is also observed that as the concentration of Cu reaches 9 %, there is a gradual increase in the FeB phase, a rise in the proportion of brittle compounds, and a decline in the amorphous forming ability. [ABSTRACT FROM AUTHOR]

We present a comparative study on oxidation behavior and failure mechanisms of conventional NiCoCrAl alloys doped with Y and Hf (CNA) and in-situ composite AlCoCrFeNi 2.1 eutectic high-entropy alloy doped with Y and Hf (ISC-EHEA) at 1300 °C. We demonstrate that the ISC-EHEA has much stronger resistance to surface rumpling and oxide spallation than CNA. Hybrid molecular dynamics (MD) and Monte Carlo (MC) simulations show that the diffusion coefficients of the metal elements in the Al-depletion layer of the ISC-EHEA are 50 % lower than those in the CNA. The low diffusion coefficients lead to low growth stress in the thermally grown Al 2 O 3 scale on the ISC-EHEA and improve the creep resistance of the metal in contact with the scale, thus preventing the occurrence of rumpling. The oxidation rate constant of the ISC-EHEA is ∼32 % lower in comparison to those of the CNA, which is attributed to the coarser columnar Al 2 O 3 grains that effectively mitigate grain boundary diffusion. The rumpling-free metal/oxide interface, the low residual stress and the low oxide growth rate for the ISC-EHEA result in strong resistance to scale spallation. Owing to the strong scale/alloy bonding at the interface and the build-up of strain energy during prolonged oxidation, damage in the Al 2 O 3 scale on the ISC-EHEA is initiated as surface cracks rather than interface decohesion. When re-oxidized at 1300 °C, the ingress of oxygen along the surface cracks results in fast growth of new oxides at the metal/oxide interface, which causes local stress concentration, interface crack propagation and scale spallation. [ABSTRACT FROM AUTHOR]

The effect of dislocation-RE atoms interactions on the creep behaviour has been studied via creep testing and HAADF-STEM analysis of two extruded alloys; Mg–0.5Ce and Mg–2Gd (wt%). Almost no Ce atoms are detected in the Mg matrix due to the low solid solubility and faster diffusion rate in as-extruded condition. However, Gd solute segregations are observed along dislocations and hexagonal dislocation patterns. Such segregations can not only pin the dislocation motion and enhance the creep strengthening via dislocation patterns, but also lead to dynamic precipitation. Thus, combing with the stress exponent values, the transition of creep mechanism between Mg–0.5Ce alloys and Mg–2Gd alloys has been found and dislocation-Gd atoms interactions are determined to be the main factor for superior creep resistance of Mg–2Gd alloys. [ABSTRACT FROM AUTHOR]

In this paper thermal analysis was applied to determine the "Critical Stress" of concrete, different from its ultimate strength, able to produce the first damage in the structures under compressive loads. The Critical Stress can be thought as the stress able to produce the beginning of fatigue rupture within the material. Several specimens of high strength concrete were tested in order to define the incipient crack phenomena, also in internal part of the specimen not accessible by direct inspections, with the aid of infrared thermography. A finite element analysis completes the study and compares, for the same static loading conditions, the stress state with the experimental thermographic images. The final results show as the coupling of normal compressive test and the acquisition of the thermal images can be a useful aid to estimate a security stress value, indeed the Critical Stress, before the Ultimate Serviceability Limit (SLU) of the structure, defined as the maximum load condition before its failure. [ABSTRACT FROM AUTHOR]

Internal friction is essential for nearly all solids to dissipate kinetic energy through internal mechanisms. The pioneering analyses by Zener (Phys. Rev. 60 (1941) 906-908) and Kê (Phys. Rev. 71 (1947) 533-546) demonstrated the existence of a single friction peak in the loss modulus spectrum of polycrystalline solids, which is attributed to viscous sliding in grain boundaries. In this study, we establish a continuum model coupled elastic deformation, viscous creep and diffusion in grain boundaries and reveal the existence of a second loss modulus peak resulted from viscous deformation within grain boundaries. The corresponding two frequencies when internal dissipation reaches its local maximum depend on grain size d , one is inversely proportional to d , and the other is proportional to d − 3. The effects of local elasticity and diffusion in grain boundaries on the loss modulus spectrum are examined and the condition when the two peaks emerge is identified. The findings can be applied to granular and porous materials, and complex rheology in geosciences, where internal dissipation is momentous for waves and seismic activities. Image, graphical abstract [ABSTRACT FROM AUTHOR]

High engineering critical current density JE of > 500 A/mm2 at 20 T and 4.2 K can be regularly achieved in Ag-sheathed multifilamentary Bi2Sr2CaCu2Ox (Bi-2212) round wire when the sample length is several centimeters. However, JE(20 T) in Bi-2212 wires of several meters length, as well as longer pieces wound in coils, rarely exceeds 200 A/mm2. Moreover, long-length wires often exhibit signs of Bi-2212 leakage after melt processing that are rarely found in short, open-end samples. We studied the length dependence of JE of state-of-the-art powder-in-tube (PIT) Bi-2212 wires and gases released by them during melt processing using mass spectroscopy, confirming that JE degradation with length is due to wire swelling produced by high internal gas pressures at elevated temperatures [A. Malagoli et al. Supercond. Sci. Technol. 24, 075016 (2011) and A. Malagoli et al. Supercond. Sci. Technol. 26, 055018 (2013)]. We further modeled the gas transport in Bi-2212 wires and examined the wire expansion at critical stages of the melt processing of as-drawn PIT wires and the wires that received a degassing treatment or a cold-densification treatment before melt processing. These investigations showed that internal gas pressure in long-length wires drives creep of the Ag sheath during the heat treatment, causing wire to expand, lowering the density of Bi-2212 filaments, and therefore degrading the wire JE; the creep rupture of silver sheath naturally leads to the leakage of Bi-2212 liquid. Our work shows that proper control of such creep is the key to preventing Bi-2212 leakage and achieving high JE in long-length Bi-2212 conductors and coils. [ABSTRACT FROM AUTHOR]

An improved model based on thermally activated dislocation glide is proposed to describe the dislocation detachment-controlled creep of extruded and annealed GlidCop Al-15 and extruded GlidCop Al-60 at 973 K as well as the threshold behavior observed at lower stresses. Unlike the customary analysis using the Rösler-Arzt approach, both steady-state and strain-transient stress reduction creep tests were performed to obtain the activation energies and the obstacle strengths for creep. In contrast to pure copper, the constant-structure creep rates of GlidCop were greater than the subsequent steady-state creep rates in all tests. This result supports the concept that dislocation detachment from particles, rather than dislocation-dislocation interactions, is rate-controlling. In addition, the constant-structure creep rates at the same reduced stresses were found to be greater at higher initial stresses. This observation is interpreted as evidence that a forward internal stress arising from inter-dislocation interactions near the particles acts on the ready-to-detach dislocations and scales with the initial stress. This forward stress and an explicit treatment of the stress dependence of mobile dislocation density were incorporated in the improved model. Furthermore, the operational activation area for dislocation glide was determined at constant temperature and structure, and the values are consistent with the interparticle distances multiplied by the Burgers vector, which further supports the interpretation of detachment controlled glide. Finally, the true threshold stress for creep is modeled as originating from thermodynamic back jumps of just-detached dislocations due to the attractive nature of the particle/matrix interface. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Experimental results are presented for damage accumulation in 10GN2MFA and 15Kh2MFA steels studied with the LM-hardness method at different stress states under cyclic loading at room and elevated temperatures that are consistent with the service conditions of structure elements. Damage accumulation kinetics is examined at primary and secondary creep stages in view of the multiaxial stress state and creep strain effects on the homogeneity coefficient. A higher level of initial strain on cyclic creep gives rise to more intensive damage accumulation in the metal, leading to the earlier onset of fracture in comparison with the smaller initial strain. Experimental critical homogeneity coefficients are given that correspond to the plastic strain stability loss when the stable deformation of the metal with its further fracture is affected by the reduction in the cross-section area and hardening modulus. The rate of homogeneity change in examined steels at different ratios of principal cycle stresses on cyclic creep is evaluated. The significant effect of a stress state at equilibrium between strain hardening and softening of the structure (specimen) metal at the secondary creep stage, is demonstrated. The effect of a stress state and temperature on damage accumulation kinetics of examined materials, in particular on the useful life of the metal on cyclic creep is established. [ABSTRACT FROM AUTHOR]

The paper presents a model of creep damage development in polycrystalline material. The model operates at two scales: micro and macro. The microscale is appropriate for simulation of the damage development phenomenon. Engineering structures operate and experimental tests are performed at the macroscale. For a polycrystalline material, damage development is strictly dependent on the structure of the material. At the microscale, the model uses a tool called cellular automata that enables the description of this dependence. The macroscopic results, required for comparison with the experimental results and for the analysis of engineering structures, are achieved by means of the finite element method. The model connects the cellular automata damage model with the deformation model implemented in the finite element system to realize the multiscale cellular automata finite element model. This connection is made using a nonlocal approach to avoid a solution dependence on the finite element mesh. The nonlocal grid method is considered the most suitable for the discrete cellular automata model. The model has been verified with the experimental results of a uniaxial tension test for copper at elevated temperature. The effectiveness and different variants of the nonlocal grid method for creep crack growth problems have been examined. [ABSTRACT FROM AUTHOR]

In this paper, the creep behavior due to interface diffusion in unidirectional fiber-reinforced metal matrix composites under general transverse loading conditions is studied. A micromechanics model is adopted to estimate the average stresses in fibers, which is demonstrated to be of reasonable accuracy by comparing with finite element analysis. The creep deformation due to interface diffusion is characterized by a tensor-form creep strain rate, which is related to the components of average stress in fibers and possesses incompressibility. The derived creep strain tensor is then introduced into fibers as eigenstrain to estimate the effect of creep strain on stress redistribution in composites. Eventually, the macroscopic creep strain of composites under constant external loads and the stress relaxation at fixed displacements due to interface diffusion are calculated by the incremental creep analysis procedures based on the average field theory. The effects of loading conditions on the overall creep behavior are examined in detail. Results of this study show that under the fixed strain condition, the initial biaxial stress ratio actually varies rather than remains unchanged during the stress relaxation process. In both constant stress and constant strain conditions, stresses in fibers have a propensity to approach hydrostatic stress state, thus suppressing the interface diffusion. These findings were not reported in previous researches and may bring new understanding on diffusion-induced creep deformation in metal matrix composite materials. [ABSTRACT FROM AUTHOR]

During operation, thermomechanical stresses occur in refractory linings. Under elevated stress and temperatures, these ceramics experience primary creep, which can further proceed to the secondary and tertiary creep stages. This necessitates a characterization of their three-stage creep behavior. Hence, two advanced uniaxial tensile and compressive creep testing devices are utilized. The Norton-Bailey creep equations and an inverse identification procedure are applied for the evaluation of the creep curves. To account for the full three-stage creep behavior in thermomechanical modelling activities, a creep-stage transition criterion is identified and subsequently implemented together with the Norton-Bailey creep-strain rate representations in a new developed creep model. The finite element simulation results from different creep testing procedures are in accordance with the corresponding experimental results of a magnesia-chromite refractory ceramic. The study also reveals the temperature-dependent asymmetrical creep behavior of the material in terms of the creep-strain rates and critical creep strains. [ABSTRACT FROM AUTHOR]

A compressive pre-straining of 0.05 was applied to two Mg–2Y alloy sheets with different initial textures along their normal directions. Creep behaviors of these sheets before and after the pre-straining were investigated at 493 K under stresses ranging from 20 to 100 MPa. The influence of pre-straining on creep behaviors was then discussed. The results show that the effects of pre-straining on creep behaviors of the two sheets are quite different. A profound strengthening effect of this pre-straining is observed on the creep resistance of the extruded sheet with creep strain decreased by half and steady strain rate reduced by 75% at most. By contrast, for the rolled sheet, the improvement of creep resistance by the pre-straining is negligible. The difference lies in the number of anomalous twins introduced by the pre-straining. After the pre-straining, considerable {10–12} anomalous twins have been introduced in the extruded sheet with a random initial texture, compared to the rolled one. Dislocation movements during the creep can be impeded by the large amounts of twins in the pre-strained extruded sheets, resulting in the obvious improved creep resistance. Meanwhile, different predominant dislocation mechanisms are found along different creep directions. Since a more excellent impeding effect of the twins is obtained on cross-slip, better improvement of the creep resistance can be achieved along the TD than along the ED of the pre-strained extruded sheet. • Pre-straining is successfully applied to Mg–2Y extruded and rolled sheets. • Anomalous twins are induced in the grains which have high activities for basal slip. • Considerable anomalous twins are induced in extruded sheet compared to rolled sheet. • Strong impeding effect of anomalous twins on dislocations enhances creep resistance. • Dislocations induced by work hardening have limited benefits for creep resistance. [ABSTRACT FROM AUTHOR]

Compressive creep anisotropic behaviors were observed for a hot-extruded Mg–3Al–1Zn alloy rod at 423 K. Heavy basal slip accelerated the creep rate along transverse and 45° directions. Inversely, strong interactions between high densities of prismatic dislocations and {10–12} twins enhanced the creep resistance along extrusion direction. Although twinning was reported to induce yield softening during uniaxial loading, it could be beneficial for creep resistance even applied stress over yield stress. • Hot-extruded AZ31 Mg rod has obvious compressive creep anisotropy at 423 K. • ED sample has the highest creep resistance compared to 45° and TD samples. • Heavy basal slip in 45° and TD samples leads to the fast creep strain increment. • Regardless of yield softening, twinning conduces to the creep process of ED sample. • Strong interactions of twins and prismatic dislocations resist strain increment. [ABSTRACT FROM AUTHOR]

A comprehensive quantitative whisker growth theory has been developed. In this theory whisker growth is controlled by the ratio of the long range grain boundary diffusion creep relaxation rate to the short range creep relaxation rate. The theory relies solely on solid state diffusion effects and does not require additional constraints or assumptions to explain whisker growth. It explains a number of heretofore relatively poorly explained and puzzling observations reported over the past 6 decades, including: (i) Sn films that are 1–10 μm thick are more susceptible to whisker growth than thinner or thicker films; (ii) Sn film contamination in the form of hydrocarbons, Cu, hydrogen, etc., tend to increase the whisker propensity; (iii) as-deposited Sn films tend to be more susceptible to whisker growth than fused films; (iv) postplate annealing tends to improve the whisker resistance; (v) whisker growth rate tends toward zero as the temperature exceeds 100 °C; (vi) whisker growth propensity depends upon the crystallographic orientation of the Sn film; and (vii) the large statistical variations reported in whisker density and incubation time. The theory predicts: (i) the magnitude of the as deposited film stress state is not fundamental to whisker growth; (ii) at high stresses where power law creep relaxation dominates, whiskers do not form.; (iii) whiskers occur in those regions of the film that are exposed to stresses lower than that required for power law creep; (iv) whiskers form when a quasiequilibrium stress state is achieved as the stress in the film tends toward zero; (v) anything that affects (limits or restrains) power law creep and its associated stress dissipation, such as grain boundary pinning, increases the propensity for whisker growth; (vi) pinning tends to increase the whisker propensity and increase the whisker growth rate; and (vii) films with certain crystallographic orientations and grain sizes are less prone to whisker growth, independent of the anisotropic thermomechanical properties, as a result of the anisotropic diffusion behavior of Sn. [ABSTRACT FROM AUTHOR]

Solid oxide cell (SOC) is an important technology for hydrogen energy utilization. Durability and reliability of metal components including interconnect and metal support of metal-supported SOC are key requirements for the massive production of SOCs. Metal corrosion and electrode poisoning caused by elements diffusion under high-temperature working conditions are two main issues. This review concentrates on the anti-corrosion technology of interconnects and metal supports. First, the characteristics of stainless-steel materials commonly used in SOCs and the corrosion mechanisms under oxidizing, reducing, and dual atmospheres are introduced. Relevant elements interdiffusion and metal creep degradation are presented. Then, typical protective coating materials incorporating reactive element oxides, perovskites, and spinels are reviewed. Two composite coatings having a mixture or bilayer structure are discussed. Deposition processes involving electroplating, electrophoresis, magnetron sputtering, pulsed laser deposition, electron beam evaporation, screen printing, sol-gel coating, and plasma spraying are summarized and compared. Finally, challenges and future research directions are highlighted. • Corrosion mechanisms of FSSs for SOCs and alloy design are presented. • Progress in spinel, perovskite, and REO coating materials are estimated. • Electrodeposition, PVD, wet process, and plasma spray are compared. • Corrosion of metal support and coating methods in MS-SOC are discussed. [ABSTRACT FROM AUTHOR]

The article presents the results of nonisothermal creep measurements of the Zr[SUB52.5]Ti[SUB5]Cu[SUB17.9]Ni[SUB14.6]Al[SUB10] bulk metallic glass in a wide range of heating rates well below and in the vicinity of the glass transition temperature T[SUBg]. It is shown that the shear viscosity η is strongly dependent on the heating rate &Tdot;: η increases linearly with &Tdot;[SUP-1] at T< T[SUBg], while an increase of η with &Tdot; is observed at T > T[SUBg]. It is argued that the heating rate dependence of the shear viscosity below the glass transition region is controlled by irreversible structural relaxation and can be quantitatively described by the directional structural relaxation model. A possible reason for the η(&Tdot;) dependence in the glass transition region is discussed. [ABSTRACT FROM AUTHOR]

It is experimentally established that the discontinuous creep of aluminum‒magnesium alloy AlMg6, deformed in an aqueous medium, is accompanied by discrete electrochemical emission: jumps of the sample electrode potential, which arise simultaneously with stress drops during the development of macroscopic step on the creep curve. It has been found (with the aid of high-speed video recording) that the electrode potential jump occurs simultaneously with nucleation and initial fast stage of deformation band widening. A possible mechanism of the occurrence of electrode potential jumps in an aluminum alloy under discontinuous creep conditions is discussed. [ABSTRACT FROM AUTHOR]

The creep mechanisms of Sn and Sn-1.8Ag along specific orientations are investigated by the constant-strain-rate nanoindentation method. Due to the anisotropy of Sn, the mechanical behaviors could be very different along different crystal orientations. For microelectronic applications, Ag is often added to Sn to increase its strength. Data from creep test show that Ag addition increases the stress exponent by 3, which indicates that the rupture time could be extended by Ag addition. Moreover, the creep rate of Sn (100) grain is lower than that of Sn (001) grain in a low stress regime, namely, that [100] in Sn would have better creep resistance for usual applications. After indentation, transmission electron images of Sn samples show that the slip systems are (1 1 ¯ 0) [ 11 1 ¯ ] in (100) grain and (101) [ 1 1 ¯ 1 ¯ ] in (001) grain. Lastly, Sn-1.8Ag has better performance along [100] in creep resistance due to greater hindrance of Ag atoms on dislocation motion and its critical threshold stress. [ABSTRACT FROM AUTHOR]

The hydrogen effect on room temperature creep of 310 S stainless steel was investigated by using nanoindentation. Hydrogen enhanced the primary creep of 310 S steel much more significantly compared with the steady-state creep, which was attributed to the interaction between hydrogen and dislocation. Hydrogen obviously decreased the indentation stress so as to promote the primary creep, while hydrogen had little effect on the steady-state creep due to the evolution from mobile dislocation to immobile dislocation. • Hydrogen enhances the primary creep more significantly than the steady-state creep. • Hydrogen obviously decreases the indentation stress and the pile-up around indentation during the primary creep. • Hydrogen has little effect on the steady-state creep due to the evolution from mobile dislocation to immobile dislocation. [ABSTRACT FROM AUTHOR]

A comparative study has been carried out on densification, microstructure, and creep with oxide-scale formation in ZrB 2 -20 vol.% SiC-(7, 10 or 14 vol.%) LaB 6 composite containing B 4 C and C as additives, and prepared by spark plasma sintering at 1800 °C under 70 MPa ram pressure. Addition of LaB 6 has promoted densification of composites by scavenging oxygen impurity, thereby increasing their hardness. Constant load compressive creep tests at 1300 °C under 47 and 78 MPa stresses have shown the lowest creep rate in the 10 vol.% LaB 6 composite. The stress exponents obtained for composites having 10 vol.% LaB 6 (∼1.3 ± 0.1) and 14 vol.% LaB 6 (∼2.6 ± 0.2) suggest respectively, grain boundary diffusion with intergranular glassy phase formation and dislocation glide as operating mechanisms. Intergranular cracking caused by grain boundary sliding appears as the damage mechanism. Oxide scales formed during creep exhibit greater thickness and defect concentration than those by isothermal exposure at 1300 °C within similar duration. [ABSTRACT FROM AUTHOR]

Influence of coarsening of precipitates on creep in metals and alloys has been studied experimentally and modelled in the past. However, a proper model to understand the role of plasticity and creep in the matrix to the kinetics of coarsening of misfitting precipitates is still missing. Such a model is developed based on a thermodynamic approach utilizing earlier solutions of mechanical interactions between the misfitting precipitates and the matrix. Numerical simulations demonstrate a significant retardation of the coarsening process controlled by power-law creep in the matrix within a wide range of its activity. Evolution of precipitate radii in the matrix with infinite yield stress for different activities of power low creep in the matrix. Curve 1 - an intensive creep, curve 9 - a sluggish creep. The intensity of creep for curves with neighbouring labels differ by factor of 10. Unlabelled Image [ABSTRACT FROM AUTHOR]

The paper presents the results of comparative studies of shortterm creep in tensile tests of the VT1-0 commercially pure titanium (analogue Grade 2 according to ASTM A485) and the VT5-1 alloy (analogue Grade 6 according to ASTM B265) in air and argon. Tests by the Dorn's method were carried out in a gas-tight chamber under constant pressure. The specimens were heated by passing alternating current. Empirical coefficients are determined in power dependences of the creep rate and the conventional creep strength on test temperature in the range from 673 to 1323 K for argon and air environment and nominal stress ranging between 4.45 and 9.36 MPa. It is found that heating in argon environment, as compared to heating in air, decreases the rate of short-term creep and increases creep strength at identical nominal stresses in the entire range of test temperatures. Calculations demonstrate that the energy of the activation of short-term creep does not depend on test conditions. This indicates that the deformation mechanism is unchanged. [ABSTRACT FROM AUTHOR]

The nickel-base superalloys are unsurpassed for hot sections of the gas turbine engines whose efficiency can be improved by developing new superalloys with enhanced properties. The artificial neural networks (ANN) method is utilized in alloy design of single-crystal nickel-base superalloys. The ANN method is especially powerful in applications where developing a physically sound model is challenging such as alloy design with multiple components. A design space of 45,000 alloy compositions is generated, and then a multilayer perceptron (MLP) feed-forward (FF) artificial neural network is used to predict the density and creep lives of these alloys. The ANN method is coupled with physics-based (PHACOMP) calculations to predict and then correlate the creep rupture life to the composition, precipitate volume fraction, topologically closed packed phases, temperature, and stress. Then, an experimental alloy composition is selected from the design space, and its solidification behavior is investigated by a thermodynamics (CALPHAD)-based software. Moreover, single-crystal rods of the experimental alloy are grown and machined into creep samples, which are creep tested at three different stress–temperature couples. A good match between the experimental results and the ANN predictions is displayed in scatter plots and in Larson–Miller plots for the experimental alloy and for selected, well-known commercial single-crystal alloys. As the correlation of the microstructure to mechanical properties is still in its infancy by thermodynamics and mechanics-based software, an integrated ANN modeling is shown to be a powerful tool for finding a composition and establishing relationships between the microstructure and properties of alloys. This, of course, can help reduce the material development cycle time as aimed by the Integrated Computational Material Engineering (ICME). [ABSTRACT FROM AUTHOR]

The microstructure evolution of fine-grained heat-affected zone (FGHAZ) of Gr.92 steel welded joint has been investigated during creep using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The microstructure evolution strongly depended on the applied stress level. At the stress level of 90 MPa, the grains of the FGHAZ were coarsened after creep. When the stress level decreased to 70 MPa, the grains of the FGHAZ were found to be further refined during creep owing to continuous dynamic recrystallization (subgrains rotation). This was verified by the increase in boundary length featuring random misorientation angles after creep. Recrystallized microstructure was only observed for the FGHAZ of welded joints after creep, but not for the Ac3 heat-affected zone (HAZ) simulated samples which exhibited homogeneous microstructure even at the low applied stress of 50 MPa. In high stress regime the creep strength of the welded joints was almost the same as that of Gr.92 steel owing to the mechanical constraint originating from the heterogeneous creep property of welds. In low stress regime, the creep strength of the welded joint was inferior to that of Gr.92 steel and approached that of the Ac3 HAZ simulated sample as the applied stress decreased. This was caused by the relaxation of the constraint owing to grain boundary sliding. Recrystallization was regarded as a sign of relaxation of constraint and deterioration of creep property for high-Cr heat-resistant steel welded joints. [ABSTRACT FROM AUTHOR]

Heritage data for the class of 9 to 12 wt pct Cr steels are studied using data science to quantify the statistically significant relationships among multiple processing/microstructure and performance variables. The effort is undertaken to find new martensitic steels for creep life of 10 5 hours or greater at 650 °C and 100 MPa using machine learning. Linear regression and lasso regression were utilized to identify alloying elements that contribute towards better creep strength. Visualization techniques such as t-distributed stochastic neighbor embedding and pair-wire element specific comparisons were utilized to explore information gaps that exist within the data and are in conflict with existing domain knowledge. Combining all results suggest that the next alloy design to be explored should be 9 wt pct Cr with high W (2 to 3 wt pct) and high Co (2 to 3 wt pct) for creep life of 10 5 hours or greater at 650 °C, 100 MPa. [ABSTRACT FROM AUTHOR]

An advancement can be seen in ultra-thin coatings used for the enhancement of material durability and lifespan. Among candidate materials, copper is used in various applications, such as micro sensors, nuclear fuel waste deposition canisters, and International Thermonuclear Experimental Reactor first walls. However, it is easily susceptible to metal creep, due to its exposure to harsh environments. In this study, graphene, a promising ultra-thin material, is tested as a single-layer coating substance used to enhance the creep property of copper. For measuring creep life, the small punch creep test methodology is adopted. Results show that, remarkably, the creep lifetime of copper increases by up to 19% with the use of the graphene coating. In testing, the heat-treated copper specimen without graphene was fractured at 45 hours, while the graphene-coated copper specimen was fractured at 55.4 hours. The finite element method also supports the experimental results obtained. [ABSTRACT FROM AUTHOR]

Abstract The microstructure evolution and creep property degradation of the Ni-based superalloy K417 were studied at different high-temperature thermal exposure conditions. The results showed that the equivalent radius of γ′ precipitates increased with the exposure time at all the temperatures and displayed spherical morphologies. Moreover, small blocky-type Cr-rich M 23 C 6 carbides were observed due to the decomposition of the primary MC after exposure to 950 °C for 200 h and 50 h both at 1000 °C and 1050 °C. The creep-rupture lifetimes deteriorated with increased exposure time and temperature due to γ′ precipitates coarsening and the decomposition of the primary carbides. Furthermore, a physically based analytical model was developed to describe the influence of the microstructural evolution of the γ′ precipitates on the residual creep lifetime. Highlights • The microstructure evolution behaviors of K417 were investigated. • The temperature-dependent γ′ precipitates degradation kinetics was built. • The lifetimes deteriorated as a result of microstructural degradation. • A novel analytical model was developed to correlate the γ′ precipitates degradation and residual creep lifetime. [ABSTRACT FROM AUTHOR]

Abstract Inconel 718 is a widely used nickel-based superalloy in aircraft engines during the past decades, whose elevated temperature strength derives from disc-shaped gamma double prime (γ″) in three perpendicular variants plus less spherical gamma prime (γ′) precipitates. In present work, we observed an abnormal γ″ variant with tailored orientation and shape in directly aged cold-rolled Inconel 718, creep tests proved its substantial benefits in improving creep resistance at 650 °C superior to commonly perpendicular γ″ variants. The results can provide new insights for processing optimization and second-particle configuration design to maximize the strengthening effect of γ″ phase in 718-type superalloys. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract It is well known the effectiveness of ausforming on increasing the dislocation density of fresh martensite. This work demonstrates, using atom probe tomography, that this increase in the dislocation density has a strong influence on the nucleation of nanoprecipitates during tempering. Therefore, ausforming might be a powerful processing route for the two-fold improvement of ferritic/martensitic steels where creep resistance is of paramount importance. Firstly, ausforming refines the martensitic microstructure (high strength and toughness), and secondly, it increases the number density of thermally stable nanoprecipitates (creep resistance). Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract In order to meet the 21st century challenges, the need to improve the high temperature load bearing capabilities or creep properties of nickel base superalloys is more important than ever. Thorough understandings of creep deformation micro-mechanisms are essential for improving high temperature performance of these alloys. Therefore, in the present study, creep deformation micro-mechanisms of CM 247 DS LC alloy used for fabricating turbine blades and vanes under relevant service conditions have been explored. The creep deformation behaviour at the investigated temperatures has been divided into three temperature regimes. In the lower temperature regime, a classical three stage creep curve is observed, i.e., primary creep followed by steady-state creep and then an accelerating creep stage leading to failure. While, in the intermediate temperature creep regime a relatively shorter secondary creep region is seen, in contrast, secondary creep stage is almost missing in the high temperature regime. Transmission electron microscopic (TEM) studies revealed that the deformation micro-mechanisms in the low temperature regime are dominated by γ′-precipitates shearing of anti phase boundary (APB) coupled dislocations pair. In the high temperature regime, the deformation is dominated by the extensive dislocation networks formation and severe γ′-rafting. In the intermediate temperature regime, the deformation micro-mechanisms are basically mixture of both low and high temperature deformation micro-mechanisms. The facts revealed by TEM observations were well supported by scanning electron based factographic and microstructural analysis. Highlights • Creep deformation mechanisms of the alloy changing with temperature. • Shearing of γ′ is the dominant creep deformation mode in the low temperature regime. • Dislocation networks and severe γ′-rafting is prevalent in the high temperature regime. • In the intermediate temperature regime, creep deformation is mixture of both. • Formation of N- type rafts prevents dislocations to enter inside γ′-precipitates. [ABSTRACT FROM AUTHOR]

Abstract Using the internal friction measurement, this work dealt with the change of dislocation configuration during the creep of 9Cr 1Mo steel at 873 K. At different creep times, specimens of this steel were firstly prepared by the interrupted test to simulate various creep states. Then, the internal friction of these specimens was measured by a dynamic mechanical analyzer (DMA) to characterize the dislocation configuration. Based on the analysis of internal friction results, it showed that both the density and distribution of diffusion-controlled dislocations vary continuously with creep time, and there has a density peak at the end of primary creep. Meanwhile, the kinetics of dislocation motions was introduced to study the evolution of dislocations during present creep in detail. In comparison with the calculated results, the movement mechanism of above diffusion-controlled dislocations was clarified successfully by the modeled dislocations. In addition, the present work offered a powerful tool to evaluate the configuration of dislocations rather than mobile dislocations. Highlights • The diffusion-controlled dislocations during creep of 9Cr-1Mo steel was successfully characterized using internal friction measurement. • It revealed that these diffusion-controlled dislocations are actually the immobile dislocations forming during creep. • The internal friction measurement offers a potential method to characterize the configuration of dislocations rather than mobile dislocations. [ABSTRACT FROM AUTHOR]