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Publications (10 of 135) Show all publications
Sui, F. & Sandström, R. (2019). Creep strength contribution due to precipitation hardening in copper-cobalt alloys. Journal of Materials Science, 54(2), 1819-1830
Open this publication in new window or tab >>Creep strength contribution due to precipitation hardening in copper-cobalt alloys
2019 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, no 2, p. 1819-1830Article in journal (Refereed) Published
Abstract [en]

In spite of its huge technical significance, there does not seem to be consensus about how to model the precipitation contribution to the creep strength. Most contributions in the literature are based on a constant internal stress (also called back stress or threshold stress) from the precipitation. It is well-known and it will also be demonstrated in the paper that this assumption is at variance with observations except for some ODS alloys. There is, however, one model developed by Eliasson et al. (Key Eng Mater 171-174:277-284, 2000) that seems to be able to represent experimental data without the use of any adjustable parameters. It has successfully been applied to describe the creep strength of austenitic stainless steels. Due to the fact that various mechanisms contribute to the creep strength in these steels, the model has not been fully verified. The purpose of this paper is to apply the model to published creep data for Cu-Co alloys, where the precipitation totally dominates the strength contribution to validate the model. In the paper, it is demonstrated that the model can indeed describe the influence of applied stress, alloy composition and heat treatment for the three analysed Cu-Co alloys.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-239460 (URN)10.1007/s10853-018-2922-z (DOI)000448833200064 ()
Note

QC 20181128

Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2018-11-28Bibliographically approved
Zhang, J. & Sandström, R. (2019). Influence of W in solid solution on the creep rate of nickel. In: Qian, H; Brongers, M; Uddin, M (Ed.), PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE, 2018,: . Paper presented at ASME 2018 Pressure Vessels and Piping Conference, PVP 2018; Prague; Czech Republic; 15 July 2018 through 20 July 2018. AMER SOC MECHANICAL ENGINEERS
Open this publication in new window or tab >>Influence of W in solid solution on the creep rate of nickel
2019 (English)In: PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE, 2018, / [ed] Qian, H; Brongers, M; Uddin, M, AMER SOC MECHANICAL ENGINEERS , 2019Conference paper, Published paper (Refereed)
Abstract [en]

Ni and Ni-W binary alloys are basis for nickel based superalloys. For most nickel based superalloys, strengthening mechanisms include both solid solution hardening and precipitation hardening. W is a vital element to create solid solution hardening and to improve the creep strength. In spite of its wide usage to strengthening of high temperature alloys, the mechanisms for solid solution hardening are not fully quantified. From the assumption that it is due to the attraction of solute atoms to dislocations and formation of Cottrell atmosphere to slow down the motion of dislocations, a fundamental model has been formulated previously. In the present paper, the model is expanded by taking the stacking fault energy and strain induced vacancies into account. Important parameters in the model are the variation of the lattice constant and the shear modulus with alloying content. Models for these variations have been formulated as a function of solute content. Another important parameter is the maximum interaction energy between the dislocations and the solutes. The model can satisfactorily predict both the large difference in creep rate between pure Ni and Ni-W alloys and the comparatively smaller differences between the three investigated Ni-2W, Ni-4W and Ni-6W alloys.

Place, publisher, year, edition, pages
AMER SOC MECHANICAL ENGINEERS, 2019
Keywords
LATTICE-PARAMETERS; BEHAVIOR; MODELS
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-248107 (URN)000460998900048 ()2-s2.0-85056875021 (Scopus ID)
Conference
ASME 2018 Pressure Vessels and Piping Conference, PVP 2018; Prague; Czech Republic; 15 July 2018 through 20 July 2018
Note

QC 20190429

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-04-29Bibliographically approved
Sui, F. & Sandström, R. (2018). Basic modelling of tertiary creep of copper. Journal of Materials Science, 53(9), 6850-6863
Open this publication in new window or tab >>Basic modelling of tertiary creep of copper
2018 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 53, no 9, p. 6850-6863Article in journal (Refereed) Published
Abstract [en]

Mechanisms that are associated with acceleration of the creep rate in the tertiary stage such as microstructure degradation, cavitation, necking instability and recovery have been known for a long time. Numerous empirical models for tertiary creep exist in the literature, not least to describe the development of creep damage, which is vital for understanding creep rupture. Unfortunately, these models almost invariably involve parameters that are not accurately known and have to be fitted to experimental data. Basic models that take all the relevant mechanisms into account which makes them predictive have been missing. Only recently, quantitative basic models have been developed for the recovery of the dislocation structure during tertiary creep and for the formation and growth of creep cavities. These models are employed in the present paper to compute the creep strain versus time curves for copper including tertiary creep without the use of any adjustable parameters. A satisfactory representation of observed tertiary creep has been achieved. In addition, the role of necking is analysed with both uniaxial and multiaxial methods.

Place, publisher, year, edition, pages
SPRINGER, 2018
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-223768 (URN)10.1007/s10853-017-1968-7 (DOI)000424874900048 ()2-s2.0-85040081835 (Scopus ID)
Funder
Swedish Nuclear Fuel and Waste Management Company, SKB, 16884
Note

QC 20180307

Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-05-16Bibliographically approved
Sui, F., Sandström, R. & Wu, R. (2018). Creep Tests on Notched Specimens of Copper.
Open this publication in new window or tab >>Creep Tests on Notched Specimens of Copper
2018 (English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-228007 (URN)
Note

QC 20180523

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-05-23Bibliographically approved
Sui, F., Sandström, R. & Wu, R. (2018). Creep tests on notched specimens of copper. Journal of Nuclear Materials, 509, 62-72
Open this publication in new window or tab >>Creep tests on notched specimens of copper
2018 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 509, p. 62-72Article in journal (Refereed) Published
Abstract [en]

In Sweden, spent nuclear fuel is planned to be disposed off by placing it in canisters which are made of oxygen free copper alloyed with 50 ppm phosphorus. The canisters are expected to stay intact for thousands of years. During the long term disposal, the canisters will be exposed to mechanical pressure from the surroundings at temperatures up to 100 degrees C and this will result in creep. To investigate the role of the complex stress conditions on the canisters, creep tests under multiaxial stress state are needed. In the present work, creep tests under multiaxial stress state with three different notch profiles (acuity 0.5, 2, and 5, respectively) at 75 degrees C with net section stresses ranging from 170 MPa to 245 MPa have been performed. To interpret the experimental results, finite element computations have been conducted. With the help of the reference stress, the rupture lifetime in the multiaxial tests was estimated. The prediction was more precise for the higher acuities than for the lower one. In order to predict the creep deformation of the canisters for the long service period, fundamental creep models are considered. Previously developed basic models are used to compute the creep deformation in the multiaxial tests. Although the scatter is large, the agreement with the experiments is considered as acceptable, indicating that the basic models which have been successfully developed for uniaxial creep tests can also be used to describe multiaxial creep tests. Notch strengthening was observed for copper.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Multiaxial stress state, Creep, Notched specimen, Finite element modelling, Copper
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-234562 (URN)10.1016/j.jnucmat.2018.06.018 (DOI)000442483300007 ()2-s2.0-85048759534 (Scopus ID)
Funder
Swedish Nuclear Fuel and Waste Management Company, SKB
Note

QC 20180919

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-09-19Bibliographically approved
Xia, S., Lousada, C. M., Mao, H., Maier, A. C., Korzhavyi, P. ., Sandström, R., . . . Zhang, Y. (2018). Erratum: Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys (Front. Mater., (2018) 5, 53, 10.3389/fmats.2018.00053). Frontiers in Materials, 5, Article ID 73.
Open this publication in new window or tab >>Erratum: Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys (Front. Mater., (2018) 5, 53, 10.3389/fmats.2018.00053)
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2018 (English)In: Frontiers in Materials, ISSN 2296-8016, Vol. 5, article id 73Article in journal (Refereed) Published
Abstract [en]

In the original article, there was an error. An explanation should be inserted at the beginning of the section Thermodynamic Calculations, Paragraph 1, line 1: In this as well as the following paragraphs the authors refer to phases such as halite, spinel, corundum etc. It thereby solely referred to the structure type and not the respective mineral. In the original article, there was an error. The word "sfinancial" should be corrected to "financial" in the Acknowledgements section, Paragraph 1: The Carl Tryggers Stiftelse för Vetenskaplig Forskning is gratefully acknowledged for financial support. The authors apologize for these errors and state that they do not change the scientific conclusions of the article in any way. The original article has been updated.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-252249 (URN)10.1177/0956797615602271 (DOI)2-s2.0-85062450216 (Scopus ID)
Note

QC20190612

Available from: 2019-06-12 Created: 2019-06-12 Last updated: 2019-11-12Bibliographically approved
Sui, F. & Sandström, R. (2018). Fundamental Modelling of Mechanisms Contributing to Tertiary Creep in Copper AT 215 and 250°C. In: Proceedings of the ASME 2018 Pressure Vessels and Piping Conference: . Paper presented at ASME 2018 Pressure Vessels and Piping Conference, July 15-20, 2018, Prague, Czech Republic.
Open this publication in new window or tab >>Fundamental Modelling of Mechanisms Contributing to Tertiary Creep in Copper AT 215 and 250°C
2018 (English)In: Proceedings of the ASME 2018 Pressure Vessels and Piping Conference, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Extensive creep tests have been performed on oxygen free copper with 50 ppm phosphorus at both low and high temperatures. It is the candidate material for storage of spent nuclear fuel in Sweden. Basic models without fitting parameters have been formulated to reproduce primary and secondary creep. For a long time, only empirical models existed for fitting of tertiary creep. To understand the role of creep damage, including recovery, cavitation and necking, basic models that do not involve adjustable parameters are in urgent demand. Only recently, basic models taking the relevant mechanisms into account have been developed. These models were used to predict the tertiary creep for copper at 75°C. The modelled results were compared with experimental creep curves and good agreement has been found. In the present paper, the models are applied to creep tests at higher temperatures (215 and 250°C). A similar representation with good accuracy is obtained. This demonstrates that the fundamental model for back stress is applicable for the higher temperature tests as well. 

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-228012 (URN)2-s2.0-85056835819 (Scopus ID)
Conference
ASME 2018 Pressure Vessels and Piping Conference, July 15-20, 2018, Prague, Czech Republic
Note

QC 20180523

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2019-04-02Bibliographically approved
Xia, S., Lousada, C. M., Mao, H., Maier, A. C., Korzhavyi, P. ., Sandström, R., . . . Zhang, Y. (2018). Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys. Frontiers in Materials, 5, Article ID 53.
Open this publication in new window or tab >>Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys
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2018 (English)In: Frontiers in Materials, ISSN 2296-8016, Vol. 5, article id 53Article in journal (Refereed) Published
Abstract [en]

We performed a combined experimental and theoretical investigation of the oxidation behavior of pure Ni and of the following multi-component Ni-containing alloys with nearly equiatomic compositions: FeNi, CoFeNi, CoCrFeNi, and CoCrFeMnNi. The materials were exposed to air at ambient pressure and at a temperature of 800°C for 150 min, their weight-gain due to oxidation was continuously monitored and the products of oxidation were subsequently characterized by XRD. The most common oxides formed have spinel or halite structure and the materials resistance to oxidation increases as: FeNi < CoFeNi < Ni < CoCrFeMnNi < CoCrFeNi. We found further that the oxidation-resistance of the materials does not correlate linearly with the number of elements present, instead the type of elements impacts significantly the materials susceptibility to oxidative damage. Cr is the element that imparted higher resistance to oxidation while Mn and Fe worsened the materials performance. In order to better understand the mechanisms of oxidation we employed thermodynamic equilibrium calculations and predicted the phase stability of oxides of the elements that are present in the materials, in different ranges of temperature, composition and oxygen activity. Additionally, we determined the phase compositions for the thermodynamically stable oxides at 800°C. The results from the thermodynamic modeling are in good agreement with the experimental finds. The alloys with low resistance to oxidation such as CoFeNi and FeNi, form the Fe 3 O 4 spinel phase which tends to dominate the phase diagram for these materials. The presence of Cr increases the resistance to atomic rearrangement due to slow diffusion in the complex structure of Cr containing spinel phases. This causes the extremely high resistance to oxidation of the CoCrFeNi alloy. The presence of Mn in CoCrFeNi stabilizes the Mn 3 O 4 spinel, which reduces the oxidation-resistance of the alloys due to the high mobility of Mn.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
Keywords
High-entropy alloys, Nonlinear behavior, Oxidation, Single-phase multicomponent alloys, Thermodynamic calculations
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-247186 (URN)10.3389/fmats.2018.00053 (DOI)000443961600001 ()2-s2.0-85062451872 (Scopus ID)
Note

QC 20190506

Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-05-06Bibliographically approved
Xia, S., Lousada, C. M., Mao, H., Maier, A. C., Korzhavyi, P. ., Sandström, R., . . . Zhang, Y. (2018). Nonlinear Oxidation Behavior in Pure Ni and Ni-Containing Entropic Alloys (vol 5, 53, 2018). FRONTIERS IN MATERIALS, 5, Article ID 73.
Open this publication in new window or tab >>Nonlinear Oxidation Behavior in Pure Ni and Ni-Containing Entropic Alloys (vol 5, 53, 2018)
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2018 (English)In: FRONTIERS IN MATERIALS, ISSN 2296-8016, Vol. 5, article id 73Article in journal (Refereed) Published
Place, publisher, year, edition, pages
FRONTIERS MEDIA SA, 2018
Keywords
single-phase multicomponent alloys, oxidation, thermodynamic calculations, high-entropy alloys, nonlinear behavior
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-239990 (URN)10.3389/fmats.2018.00073 (DOI)000451624300001 ()
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Chen, K., Chen, X., Wang, Z., Mao, H. & Sandström, R. (2018). Optimization of deformation properties in as-cast copper by microstructural engineering. Part I. microstructure. Journal of Alloys and Compounds, 763, 592-605
Open this publication in new window or tab >>Optimization of deformation properties in as-cast copper by microstructural engineering. Part I. microstructure
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2018 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 763, p. 592-605Article in journal (Refereed) Published
Abstract [en]

The microstructural features required to optimize both the strength and ductility of copper are investigated by examining the as-cast pure Cu and Cu-(1.0e3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt %) alloys. Uniaxial tensile tests show that (Fe, Co)- or (Fe, Sn)-doping improves both the strength and ductility of pure copper. The microstructure evolution with Fe, Co, or Sn doping is characterized by using optical and scanning and transmission electron microscopies. The effects of Fe, Co, and Sn doping on the microstructure clearly show that (i) iron-rich nanoparticles are dispersed inside the grains. The spherical nanoparticles grow in size with increasing Fe content, and when the Fe content exceeds 2.0 wt %, the particles transition into a petal-like morphology. (ii) The microstructure of the alloys (grain size and morphology) is notably influenced by the Fe and Co contents, and the grain size is reduced from an average of 603 mu m in pure Cu to an average of 26 mm in the Cu-3.0Fe-0.5Co alloy. (iii) The addition of 1.5wt % Fe and 0.1wt % Sn dramatically reduces the grain size to an average of 42 mu m, and this reduction is correlated with the appearance of smaller spherical iron-rich nanoparticles. The evolution mechanisms of the iron-rich nanoparticles and grain structure under the alloying effect are discussed.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Casting, Copper, Microstructure design, Grain refinement, Iron-rich nanoparticle
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-234567 (URN)10.1016/j.jallcom.2018.05.297 (DOI)000442484300068 ()2-s2.0-85048149452 (Scopus ID)
Note

QC 20180919

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-09-19Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8494-3983

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