Special Issue "Creep and High Temperature Deformation of Metals and Alloys"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (30 June 2019).

Special Issue Editors

Guest Editor
Prof. Dr. Stefano Spigarelli

Department of Industrial Engineering and Mathematical Sciences, Marche Polytechnic University, Via Brecce Bianche I-60131, Ancona, Italy
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Phone: +39 071 2204746
Interests: creep; high-temperature deformation and hot working; steels; aluminum alloys; metal matrix composites
Guest Editor
Prof. Dr. Elisabetta Gariboldi

Politecnico di Milano, Depaerment of Mechanical Engineering, Via La Masa 1, 20156,Milan, Italy
Website 1 | Website 2 | E-Mail
Phone: +39 02 23998224
Interests: creep; high-temperature behaviour of alloys, aluminum alloys; Phase Change Materials, composites, magnesium alloys

Special Issue Information

Dear Colleagues,

The occurrence of time-dependent deformation of metals and alloys under constant loads or stresses, a phenomenon termed “creep”, has been documented for at least two centuries. Yet, its real significance was appreciated only by the late 1940s, when some peculiar features of creep, such as the occurrence of plastic deformation under stresses well below yielding, were investigated in detail. The continuous development of dislocation theories later permitted to enlighten some specific features of creep deformation. Similarly, the same dislocation theories were used to provide a physical background to the study of metals and alloys response to hot working processes and also to explain and model stress relaxation effects. In parallel, many new creep-resistant materials have been developed, and new hot-working techniques introduced, but creep and hot-working studies proceeded, in most cases, independently of each other. Yet, in many cases, the mechanisms that control these phenomena are essentially the same.

The aim of this Special Issue is to highlight recent innovations introduced in the fields of creep and, from a wider perspective, on high-temperature deformation. Scholars are thus encouraged to submit research papers dealing on specific aspects of creep and high-temperature deformation or describing the response of metals and alloys by experimental techniques and/or modelling.

Prof. Dr. Stefano Spigarelli
Prof. Dr. Elisabetta Gariboldi
Guest Editors

Manuscript Submission Information

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Keywords

  • Creep
  • Hot working
  • Constitutive equations
  • Creep mechanisms
  • Microstructural features
  • Microstructural stability
  • Steels
  • Nickel-base superalloys
  • Light Alloys
  • Composites

Published Papers (14 papers)

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Research

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Open AccessArticle
The Influence of Niobium Additions on Creep Resistance of Fe-27 at. % Al Alloys
Metals 2019, 9(7), 739; https://doi.org/10.3390/met9070739
Received: 3 June 2019 / Revised: 26 June 2019 / Accepted: 27 June 2019 / Published: 30 June 2019
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Abstract
Results of creep tests of two Fe-27 at. % Al-based alloys with additions of 2.7 and 4.8 at. % of niobium conducted in the temperature range from 650 °C to 900 °C in the authors’ laboratory are presented. The purpose of the study [...] Read more.
Results of creep tests of two Fe-27 at. % Al-based alloys with additions of 2.7 and 4.8 at. % of niobium conducted in the temperature range from 650 °C to 900 °C in the authors’ laboratory are presented. The purpose of the study is to supplement previous work on Fe-Al-Nb alloys to obtain a more complete overview of creep properties from the dilute alloy with 1% of Nb up to the eutectic alloy with 10% of niobium. At higher temperatures and lower stresses, the creep resistance of the 10% niobium alloy is better than that of the lower niobium alloys. On the other hand, the eutectic alloy loses its preference at lower temperatures and higher deformation rates. This phenomenon is similar to that reported by Yildirim et al. for Fe-50 at. % Al-based alloys and is probably associated with an increased stress sensitivity of the eutectic alloy. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Influence of Different Annealing Atmospheres on the Mechanical Properties of Freestanding MCrAlY Bond Coats Investigated by Micro-Tensile Creep Tests
Metals 2019, 9(6), 692; https://doi.org/10.3390/met9060692
Received: 22 May 2019 / Revised: 16 June 2019 / Accepted: 17 June 2019 / Published: 19 June 2019
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Abstract
The mechanical properties of low-pressure plasma sprayed (LPPS) MCrAlY (M = Ni, Co) bond coats, Amdry 386, Amdry 9954 and oxide dispersion strengthened (ODS) Amdry 9954 (named Amdry 9954 + ODS) were investigated after annealing in three atmospheres: Ar–O2, Ar–H2 [...] Read more.
The mechanical properties of low-pressure plasma sprayed (LPPS) MCrAlY (M = Ni, Co) bond coats, Amdry 386, Amdry 9954 and oxide dispersion strengthened (ODS) Amdry 9954 (named Amdry 9954 + ODS) were investigated after annealing in three atmospheres: Ar–O2, Ar–H2O, and Ar–H2–H2O. Freestanding bond coats were investigated to avoid any influence from the substrate. Miniaturized cylindrical tensile specimens were produced by a special grinding process and then tested in a thermomechanical analyzer (TMA) within a temperature range of 900–950 °C. Grain size and phase fraction of all bond coats were investigated by EBSD before testing and no difference in microstructure was revealed due to annealing in various atmospheres. The influence of annealing in different atmospheres on the creep strength was not very pronounced for the Co-based bond coats Amdry 9954 and Amdry 9954 + ODS in the tested conditions. The ODS bond coats revealed significantly higher creep strength but a lower strain to failure than the ODS-free Amdry 9954. The Ni-based bond coat Amdry 386 showed higher creep strength than Amdry 9954 due to the higher fraction of the β-NiAl phase. Additionally, its creep properties at 900 °C were much more affected by annealing in different atmospheres. The bond coat Amdry 386 annealed in an Ar–H2O atmosphere showed a significantly lower creep rate than the bond coat annealed in Ar–O2 and Ar–H2–H2O atmospheres. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Development of the FE In-House Procedure for Creep Damage Simulation at Grain Boundary Level
Metals 2019, 9(6), 656; https://doi.org/10.3390/met9060656
Received: 20 April 2019 / Revised: 29 May 2019 / Accepted: 29 May 2019 / Published: 5 June 2019
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Abstract
A two-dimensional (2D) finite element framework for creep damage simulation at the grain boundary level was developed and reported. The rationale for the paper was that creep damage, particularly creep rupture, for most high temperature alloys is due to the cavitation at the [...] Read more.
A two-dimensional (2D) finite element framework for creep damage simulation at the grain boundary level was developed and reported. The rationale for the paper was that creep damage, particularly creep rupture, for most high temperature alloys is due to the cavitation at the grain boundary level, hence there is a need for depicting such phenomenon. In this specific development of the creep damage simulation framework, the material is modeled by grain and GB (grain boundary), separately, where smeared-out grain boundary element is used. The mesh for grain and grain boundary is achieved by using Neper software. This paper includes (1) the computational framework, the existing subroutines, and method applied in this procedure; (2) the numerical and programming implementation of the GB; (3) the development and validation of the creep software; and (4) the application to simulate plane stress Copper–Antimony alloy. This paper contributes to the development of finite element simulation for creep damage/rupture at a more realistic grain boundary level and contributes to a new understanding of the intrinsic relationship of stress redistribution and creep fracture. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Estimating the Influences of Prior Residual Stress on the Creep Rupture Mechanism for P92 Steel
Metals 2019, 9(6), 639; https://doi.org/10.3390/met9060639
Received: 13 May 2019 / Revised: 30 May 2019 / Accepted: 31 May 2019 / Published: 2 June 2019
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Abstract
Creep damage is one of the main failure mechanisms of high Cr heat-resistant steel in power plants. Due to the complex changes of stress, strain, and damage at the tip of a creep crack with time, it is difficult to accurately evaluate the [...] Read more.
Creep damage is one of the main failure mechanisms of high Cr heat-resistant steel in power plants. Due to the complex changes of stress, strain, and damage at the tip of a creep crack with time, it is difficult to accurately evaluate the effects of residual stress on the creep rupture mechanism. In this study, two levels of residual stress were introduced in P92 high Cr alloy specimens using the local out-of-plane compression approach. The specimens were then subjected to thermal exposure at the temperature of 650 °C for accelerated creep tests. The chemical composition of P92 specimens was obtained using an FLS980-stm Edinburgh fluorescence spectrometer. Then, the constitutive coupling relation between the temperature and material intrinsic flow stress was established based on the Gibbs free energy principle. The effects of prior residual stress on the creep rupture mechanism were investigated by the finite element method (FEM) and experimental method. A comparison of the experimental and simulated results demonstrates that the effect of prior residual stress on the propagation of micro-cracks and the creep rupture time is significant. In sum, the transgranular fracture and the intergranular fracture can be observed in micrographs when the value of prior residual stress exceeds and is less than the material intrinsic flow stress, respectively. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Influence of Excess Volumes Induced by Re and W on Dislocation Motion and Creep in Ni-Base Single Crystal Superalloys: A 3D Discrete Dislocation Dynamics Study
Metals 2019, 9(6), 637; https://doi.org/10.3390/met9060637
Received: 20 March 2019 / Revised: 23 May 2019 / Accepted: 25 May 2019 / Published: 1 June 2019
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Abstract
A comprehensive 3D discrete dislocation dynamics model for Ni-base single crystal superalloys was used to investigate the influence of excess volumes induced by solute atoms Re and W on dislocation motion and creep under different tensile loads at 850 °C. The solute [...] Read more.
A comprehensive 3D discrete dislocation dynamics model for Ni-base single crystal superalloys was used to investigate the influence of excess volumes induced by solute atoms Re and W on dislocation motion and creep under different tensile loads at 850 ° C. The solute atoms were distributed homogeneously only in γ matrix channels. Their excess volumes due to the size difference from the host Ni were calculated by density functional theory. The excess volume affected dislocation glide more strongly than dislocation climb. The relative positions of dislocations and solute atoms determined the magnitude of back stresses on the dislocation motion. Without diffusion of solute atoms, it was found that W with a larger excess volume had a stronger strengthening effect than Re. With increasing concentration of solute atoms, the creep resistance increased. However, a low external stress reduced the influence of different excess volumes and different concentrations on creep. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Nanoindentation Investigation on the Size-Dependent Creep Behavior in a Zr-Cu-Ag-Al Bulk Metallic Glass
Metals 2019, 9(5), 613; https://doi.org/10.3390/met9050613
Received: 1 May 2019 / Revised: 23 May 2019 / Accepted: 23 May 2019 / Published: 27 May 2019
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Abstract
Nanoindentation technology has been widely adopted to study creep behavior in small regions. However, nanoindentation creep behavior of metallic glass is still not well understood. In the present work, we investigated nanoindentation size effects on creep deformation in a Zr-based bulk metallic glass [...] Read more.
Nanoindentation technology has been widely adopted to study creep behavior in small regions. However, nanoindentation creep behavior of metallic glass is still not well understood. In the present work, we investigated nanoindentation size effects on creep deformation in a Zr-based bulk metallic glass at room temperature. The total creep strain and strain rate of steady-state creep were gradually decreased with increasing holding depth under a Berkovich indenter, indicating a length-scale-dependent creep resistance. For a spherical indenter, creep deformations were insignificant in elastic regions and then greatly enhanced by increasing holding strain in plastic regions. Strain rate sensitivities (SRS) decreased with increasing holding depth and holding strain at first, and then stabilized as holding depth was beyond about 500 nm for both indenters. SRS values were 0.4–0.5 in elastic regions, in which atomic diffusion and free volume migration could be the creep mechanism. On the other hand, evolution of the shear transformation zone was suggested as a creep mechanism in plastic regions, and the corresponding SRS values were in the range of 0.05 to 0.3. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Creep Buckling of 304 Stainless-Steel Tubes Subjected to External Pressure for Nuclear Power Plant Applications
Metals 2019, 9(5), 536; https://doi.org/10.3390/met9050536
Received: 19 April 2019 / Revised: 7 May 2019 / Accepted: 7 May 2019 / Published: 9 May 2019
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Abstract
The creep-buckling behaviors of cylindrical stainless-steel tubes subjected to radial external pressure load at elevated temperatures—800, 900, and 1000 °C—were experimentally investigated. Prior to the creep-buckling tests, the buckling pressure was measured under each temperature condition. Then, in creep-buckling experiments, the creep-buckling failure [...] Read more.
The creep-buckling behaviors of cylindrical stainless-steel tubes subjected to radial external pressure load at elevated temperatures—800, 900, and 1000 °C—were experimentally investigated. Prior to the creep-buckling tests, the buckling pressure was measured under each temperature condition. Then, in creep-buckling experiments, the creep-buckling failure time was measured by reducing the external pressure load for two different tube specimens—representing the first and second buckling modes—to examine the relationship between the external pressure and the creep-buckling failure time. The measured failure time ranged from <1 min to <4 h under 99–41% loading of the buckling pressure. Additionally, an empirical correlation was developed using the Larson–Miller parameter model to predict the long-term buckling time of the stainless-steel tube column according to the experimental results. Moreover, the creep-buckling processes were recorded by two high-speed cameras. Finally, the characteristics of the creep buckling under radial loading were discussed with regard to the geometrical imperfections of the tubes and the material properties of the stainless steel at the high temperatures. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
An Investigation into Creep Cavity Development in 316H Stainless Steel
Metals 2019, 9(3), 318; https://doi.org/10.3390/met9030318
Received: 1 February 2019 / Revised: 5 March 2019 / Accepted: 6 March 2019 / Published: 12 March 2019
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Abstract
Creep-induced cavitation is an important failure mechanism in steel components operating at high temperature. Robust techniques are required to observe and quantify creep cavitation. In this paper, the use of two complementary analysis techniques: small-angle neutron scattering (SANS), and quantitative metallography, using scanning [...] Read more.
Creep-induced cavitation is an important failure mechanism in steel components operating at high temperature. Robust techniques are required to observe and quantify creep cavitation. In this paper, the use of two complementary analysis techniques: small-angle neutron scattering (SANS), and quantitative metallography, using scanning electron microscopy (SEM), is reported. The development of creep cavities that is accumulated under uniaxial load has been studied as a function of creep strain and life fraction, by carrying out interrupted tests on two sets of creep test specimens that are prepared from a Type-316H austenitic stainless steel reactor component. In order to examine the effects of pre-strain on creep damage formation, one set of specimens was subjected to a plastic pre-strain of 8%, and the other set had no pre-strain. Each set of specimens was subjected to different loading and temperature conditions, representative of those of current and future power plant operation. Cavities of up to 300 nm in size are quantified by using SANS, and their size distribution, as a function of determined creep strain. Cavitation increases significantly as creep strain increases throughout creep life. These results are confirmed by quantitative metallography analysis. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Low Cycle Fatigue and Relaxation Performance of Ferritic–Martensitic Grade P92 Steel
Metals 2019, 9(1), 99; https://doi.org/10.3390/met9010099
Received: 12 December 2018 / Revised: 9 January 2019 / Accepted: 10 January 2019 / Published: 18 January 2019
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Abstract
Due to their excellent creep resistance and good oxidation resistance, 9–12% Cr ferritic–martensitic stainless steels are widely used as high temperature construction materials in power plants. However, the mutual combination of different loadings (e.g., creep and fatigue), due to a “flexible” operation of [...] Read more.
Due to their excellent creep resistance and good oxidation resistance, 9–12% Cr ferritic–martensitic stainless steels are widely used as high temperature construction materials in power plants. However, the mutual combination of different loadings (e.g., creep and fatigue), due to a “flexible” operation of power plants, may seriously reduce the lifetimes of the respective components. In the present study, low cycle fatigue (LCF) and relaxation fatigue (RF) tests performed on grade P92 helped to understand the behavior of ferritic–martensitic steels under a combined loading. The softening and lifetime behavior strongly depend on the temperature and total strain range. Especially at small strain amplitudes, the lifetime is seriously reduced when adding a hold time which indicates the importance of considering technically relevant small strains. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
The Effect of Normalizing Temperature on the Short-Term Creep Rupture of the Simulated HAZ in Gr.91 Steel Welds
Metals 2018, 8(12), 1072; https://doi.org/10.3390/met8121072
Received: 14 November 2018 / Revised: 12 December 2018 / Accepted: 14 December 2018 / Published: 16 December 2018
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Abstract
As-received Gr.91 steel tube was normalized at either 940 or 1060 °C for 1 h, followed by Ar-assisted cooling to room temperature, then tempered at 760 °C for 2 h. Those samples were designated as 940NT or 1060NT samples. An infrared heating system [...] Read more.
As-received Gr.91 steel tube was normalized at either 940 or 1060 °C for 1 h, followed by Ar-assisted cooling to room temperature, then tempered at 760 °C for 2 h. Those samples were designated as 940NT or 1060NT samples. An infrared heating system was used to simulate HAZ microstructures in the weld, which included over-tempering (OT) and partial transformation (PT) zones. The results of short-term creep tests showed that normalizing at higher temperature improved the creep resistance of the Gr.91 steel. By contrast, welding thermal cycles would shorten the creep life of the Gr.91 steel. Among the tested samples in each group, the PT samples had the shortest life to rupture, especially the 940NT-PT sample. The microstructures of the PT samples comprised of fine lath martensite and ferrite subgrains with carbides decorating the grain and subgrain boundaries. Excessive dislocation recovery, rapid coalescence of refined martensite laths, and growth of ferrite subgrains were responsible for the poorer creep resistance of the PT samples relative to those of the other samples. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
Creep Behaviour and Microstructural Characterization of VAT 36 and VAT 32 Superalloys
Metals 2018, 8(11), 877; https://doi.org/10.3390/met8110877
Received: 2 October 2018 / Revised: 22 October 2018 / Accepted: 23 October 2018 / Published: 27 October 2018
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Abstract
Superalloys are used primarily for the aerospace, automotive, and petrochemical industries. These applications require materials with high creep resistance. In this work, evaluation of creep resistance and microstructural characterization were carried out at two new nickel intermediate content alloys for application in aerospace [...] Read more.
Superalloys are used primarily for the aerospace, automotive, and petrochemical industries. These applications require materials with high creep resistance. In this work, evaluation of creep resistance and microstructural characterization were carried out at two new nickel intermediate content alloys for application in aerospace industry and in high performance valves for automotive applications (alloys VAT 32 and VAT 36). The alloys are based on a high nickel chromium austenitic matrix with dispersion of intermetallic L12 and phases containing different (Nb,Ti)C carbides. Creep tests were performed at constant load, in the temperature range of 675–750 °C and stress range of 500–600 MPa. Microstructural characterization and failure analysis of fractured surfaces of crept samples were carried out with optical and scanning electron microscopy with EDS. Phases were identified by Rietveld refinement. The results showed that the superalloy VAT 32 has higher creep resistance than the VAT 36. The superior creep resistance of the alloy VAT 32 is related to its higher fraction of carbides (Nb,Ti)C and intermetallic L12 provided by the amount of carbon, titanium, and niobium in its chemical composition and subsequent heat treatment. During creep deformation these precipitates produce anchoring effect of grain boundaries, hindering relative slide between grains and therefore inhibiting crack formation. These volume defects act also as obstacles to dislocation slip and climb, decreasing the creep rate. Failure analysis of surface fractures of crept samples showed intergranular failure mechanism at crack origin for both alloys VAT 36 and VAT 32. Intergranular fracture involves nucleation, growth, and subsequent binding of voids. The final fractured portion showed transgranular ductile failure, with dimples of different shapes, generated by the formation and coalescence of microcavities with dissimilar shape and sizes. The occurrence of a given creep mechanism depends on the test conditions. At creep tests of VAT 32 and VAT 36, for lower stresses and higher temperature, possible dislocation climb over carbides and precipitates would prevail. For higher stresses and intermediate temperatures shear mechanisms involving stacking faults presumably occur over a wide range of experimental conditions. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessCommunication
Application of the Taylor Equation to Five-Power-Law Creep Considering the Influence of Solutes
Metals 2018, 8(10), 813; https://doi.org/10.3390/met8100813
Received: 18 September 2018 / Revised: 5 October 2018 / Accepted: 8 October 2018 / Published: 11 October 2018
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Abstract
This study determines the feasibility of describing the flow stress within the five-power-law creep regime, using a linear superposition of a dislocation hardening term and a significant solute strengthening term. It is assumed that the solutes are randomly distributed. It was found that [...] Read more.
This study determines the feasibility of describing the flow stress within the five-power-law creep regime, using a linear superposition of a dislocation hardening term and a significant solute strengthening term. It is assumed that the solutes are randomly distributed. It was found that by using an energy balance approach, the flow stress at high temperatures can be well-described by the classic Taylor equation with a solute strengthening term, τo, that is added to the αMGbρ1/2 dislocation hardening term. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle
The Role of Glide during Creep of Copper at Low Temperatures
Metals 2018, 8(10), 772; https://doi.org/10.3390/met8100772
Received: 13 August 2018 / Revised: 13 September 2018 / Accepted: 18 September 2018 / Published: 27 September 2018
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Abstract
Copper canister will be used in Scandinavia for final storage of spent nuclear fuel. The copper will be exposed to temperatures of up to 100 °C. The creep mechanism at near ambient temperatures has been assumed to be glide of dislocations, but this [...] Read more.
Copper canister will be used in Scandinavia for final storage of spent nuclear fuel. The copper will be exposed to temperatures of up to 100 °C. The creep mechanism at near ambient temperatures has been assumed to be glide of dislocations, but this has never been verified for copper or other materials. In particular, no feasible mechanism for glide based static recovery has been proposed. To attack this classical problem, a glide mobility based on the assumption that it is controlled by the climb of the jogs on the dislocations is derived and shown that it is in agreement with observations. With dislocation dynamics (DD) simulations taking glide but not climb into account, it is demonstrated that creep based on glide alone can reach a quasi-stationary condition. This verifies that static recovery can occur just by glide. The DD simulations also show that the internal stress during creep in the loading direction is almost identical to the applied stress also directly after a load drop, which resolves further classical issues. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Review

Jump to: Research

Open AccessFeature PaperReview
Creep-Ductility of High Temperature Steels: A Review
Metals 2019, 9(3), 342; https://doi.org/10.3390/met9030342
Received: 27 February 2019 / Accepted: 14 March 2019 / Published: 18 March 2019
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Abstract
A number of measures of the creep-ductility of high temperature steels are reviewed with an ultimate focus on intrinsic creep-ductility. It is assumed that there will be a future requirement for the determination of long duration creep ductility values for design and product [...] Read more.
A number of measures of the creep-ductility of high temperature steels are reviewed with an ultimate focus on intrinsic creep-ductility. It is assumed that there will be a future requirement for the determination of long duration creep ductility values for design and product standards in the same way as there is currently for creep strength values. The determination of such information will require specialist modelling techniques to be applied to the complex nature of multi-temperature, multi-heat (multi-cast) data collations, and possible solutions are considered. In service, the exhaustion of creep-ductility is most likely to occur at stress concentrations, and for this, a knowledge of the multiaxial creep-ductility is required, and its relationship to uniaxial creep-ductility. Some practical applications requiring a knowledge of creep-ductility are reviewed. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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