Research

13 pages, 5359 KiB

Open AccessArticle

Influence of Cryo-Processing and Post-SPD Annealing on Creep Behavior of CP Titanium

by Jiri Dvorak, Petr Kral, Andrey G. Kadomtsev, Vladimir I. Betekhtin, Maria V. Narykova, Marie Kvapilova and Vaclav Sklenicka

Materials 2022, 15(5), 1646; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15051646 - 22 Feb 2022

Cited by 2 | Viewed by 1226

Abstract

The commercial purity of VT1-0 titanium was processed by the rolling process and executed at elevated, room, and cryo-temperatures. These processings led to the formation of an ultrafine-grained microstructure, with the mean grain size at a nanometer level. Some of these materials were [...] Read more.

The commercial purity of VT1-0 titanium was processed by the rolling process and executed at elevated, room, and cryo-temperatures. These processings led to the formation of an ultrafine-grained microstructure, with the mean grain size at a nanometer level. Some of these materials were statically annealed at a temperature of 823 K for 1 h, which led to significant subgrains and grain coarsening. The constant load creep tests in tension were carried out in argon on all states of materials, at temperatures of 648–723 K and different ranges of applied stresses. From the value of the steady-state creep rate, the control creep mechanisms were determined. The microstructure analyses were carried out via SEM and TEM. It was found that titanium prepared at elevated and room temperatures have a higher creep strength than titanium prepared at cryo-temperatures. Furthermore, the post-SPD —annealing led to a significant decrease in the creep properties. The influence of the preparation temperature on the difference of the creep behavior were discussed and explained using the microstructure analyses of the tests’ samples. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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15 pages, 5079 KiB

Open AccessArticle

Creep Resistance of S304H Austenitic Steel Processed by High-Pressure Sliding

by Petr Kral, Jiri Dvorak, Vaclav Sklenicka, Zenji Horita, Yoichi Takizawa, Yongpeng Tang, Lubomir Kral, Marie Kvapilova, Pavla Roupcová and Jakub Horvath

Materials 2022, 15(1), 331; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15010331 - 03 Jan 2022

Cited by 5 | Viewed by 1523

Abstract

Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated [...] Read more.

Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500–700 °C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500 °C. However, a further increase in creep temperature to 600 °C and 700 °C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600 °C and its formation was enhanced after recrystallization at 700 °C. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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15 pages, 9722 KiB

Open AccessArticle

Multiscale Characterization of an Oxide Scale Formed on the Creep-Resistant ATI 718Plus Superalloy during High-Temperature Oxidation

by Adam Kruk, Aleksander Gil, Sebastian Lech, Grzegorz Cempura, Alina Agüero and Aleksandra Czyrska-Filemonowicz

Materials 2021, 14(21), 6327; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14216327 - 23 Oct 2021

Cited by 2 | Viewed by 1740

Abstract

The ATI 718Plus^® is a creep-resistant nickel-based superalloy exhibiting high strength and excellent oxidation resistance in high temperatures. The present study is focused on multiscale 2D and 3D characterization (morphological and chemical) of the scale and the layer beneath formed on the [...] Read more.

The ATI 718Plus^® is a creep-resistant nickel-based superalloy exhibiting high strength and excellent oxidation resistance in high temperatures. The present study is focused on multiscale 2D and 3D characterization (morphological and chemical) of the scale and the layer beneath formed on the ATI 718Plus superalloy during oxidation at 850 °C up to 4000 h in dry and wet air. The oxidized samples were characterized using various microscopic methods (SEM, TEM and STEM), energy-dispersive X-ray spectroscopy and electron diffraction. The 3D visualization of the microstructural features was achieved by means of FIB-SEM tomography. When oxidized in dry air, the ATI 718Plus develops a protective, dense Cr₂O₃ scale with a dual-layered structure. The outer Cr₂O₃ layer is composed of coarser grains with a columnar shape, while the inner one features fine, equiaxed grains. The Cr₂O₃ scale formed in wet air is single-layered and features very fine grains. The article discusses the difference between the structure, chemistry and three-dimensional phase distribution of the oxide scales and near-surface areas developed in the two environments. Electron microscopy/spectroscopy findings combined with the three-dimensional reconstruction of the microstructure provide original insight into the role of the oxidation environment on the structure of the ATI 718Plus at the nanoscale. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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47 pages, 21192 KiB

Open AccessArticle

Effect of Neutron Irradiation on the Mechanical Properties, Swelling and Creep of Austenitic Stainless Steels

by Malcolm Griffiths

Materials 2021, 14(10), 2622; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14102622 - 17 May 2021

Cited by 19 | Viewed by 3902

Abstract

Austenitic stainless steels are used for core internal structures in sodium-cooled fast reactors (SFRs) and light-water reactors (LWRs) because of their high strength and retained toughness after irradiation (up to 80 dpa in LWRs), unlike ferritic steels that are embrittled at low doses [...] Read more.

Austenitic stainless steels are used for core internal structures in sodium-cooled fast reactors (SFRs) and light-water reactors (LWRs) because of their high strength and retained toughness after irradiation (up to 80 dpa in LWRs), unlike ferritic steels that are embrittled at low doses (<1 dpa). For fast reactors, operating temperatures vary from 400 to 550 °C for the internal structures and up to 650 °C for the fuel cladding. The internal structures of the LWRs operate at temperatures between approximately 270 and 320 °C although some parts can be hotter (more than 400 °C) because of localised nuclear heating. The ongoing operability relies on being able to understand and predict how the mechanical properties and dimensional stability change over extended periods of operation. Test reactor irradiations and power reactor operating experience over more than 50 years has resulted in the accumulation of a large amount of data from which one can assess the effects of irradiation on the properties of austenitic stainless steels. The effect of irradiation on the intrinsic mechanical properties (strength, ductility, toughness, etc.) and dimensional stability derived from in- and out-reactor (post-irradiation) measurements and tests will be described and discussed. The main observations will be assessed using radiation damage and gas production models. Rate theory models will be used to show how the microstructural changes during irradiation affect mechanical properties and dimensional stability. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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25 pages, 8213 KiB

Open AccessEditor’s ChoiceArticle

Thermodynamic Modelling and Microstructural Study of Z-Phase Formation in a Ta-Alloyed Martensitic Steel

by Florian Riedlsperger, Bernadette Gsellmann, Erwin Povoden-Karadeniz, Oriana Tassa, Susanna Matera, Mária Dománková, Florian Kauffmann, Ernst Kozeschnik and Bernhard Sonderegger

Materials 2021, 14(6), 1332; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14061332 - 10 Mar 2021

Cited by 3 | Viewed by 2738

Abstract

A thermokinetic computational framework for precipitate transformation simulations in Ta-containing martensitic Z-steels was developed, including Calphad thermodynamics, diffusion mobility data from the literature, and a kinetic parameter setup that considered precipitation sites, interfacial energies and dislocation density evolution. The thermodynamics of Ta-containing subsystems [...] Read more.

A thermokinetic computational framework for precipitate transformation simulations in Ta-containing martensitic Z-steels was developed, including Calphad thermodynamics, diffusion mobility data from the literature, and a kinetic parameter setup that considered precipitation sites, interfacial energies and dislocation density evolution. The thermodynamics of Ta-containing subsystems were assessed by atomic solubility data and enthalpies from the literature as well as from the experimental dissolution temperature of Ta-based Z-phase CrTaN obtained from differential scanning calorimetry. Accompanied by a comprehensive transmission electron microscopy analysis of the microstructure, thermokinetic precipitation simulations with a wide-ranging and well-documented set of input parameters were carried out in MatCalc for one sample alloy. A special focus was placed on modelling the transformation of MX into the Z-phase, which was driven by Cr diffusion. The simulation results showed excellent agreement with experimental data in regard to size, number density and chemical composition of the precipitates, showing the usability of the developed thermokinetic simulation framework. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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16 pages, 14935 KiB

Open AccessEditor’s ChoiceArticle

Effect of Ti Content on the Microstructure and High-Temperature Creep Property of Cast Fe-Ni-Based Alloys with High-Al Content

by Gokul Obulan Subramanian, Changheui Jang, Ji Ho Shin and Chaewon Jeong

Materials 2021, 14(1), 82; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14010082 - 26 Dec 2020

Cited by 4 | Viewed by 1977

Abstract

The cast Fe-Ni-based austenitic heat-resistant alloys with 4.5 wt% Al and varying Ti content were developed for high-temperature application. With increase in Ti content, strength of model alloys increased gradually at 700 °C and 750 °C. At 750 °C, alloys with 35Ni–(2~4)Ti composition [...] Read more.

The cast Fe-Ni-based austenitic heat-resistant alloys with 4.5 wt% Al and varying Ti content were developed for high-temperature application. With increase in Ti content, strength of model alloys increased gradually at 700 °C and 750 °C. At 750 °C, alloys with 35Ni–(2~4)Ti composition showed a significant increase in creep rupture life compared to 30Ni–1Ti alloy, attributed to the increase in γ’-Ni₃(Al,Ti) precipitates due to higher Ni and Ti content. Among the 35Ni–(2~4)Ti alloys, increasing Ti content from 2 to 4 wt% gradually increased the creep rupture life in the as-cast condition. The creep rupture life was improved after solution annealing treatment, however, the beneficial effect of higher Ti content was not evident for 35Ni–(2~4)Ti alloys. After solution annealing, interdendritic phases were partially dissolved, but coarse B2-NiAl phases were formed. The size and amount of coarse B2-NiAl phases increased with Ti content. In the creep-tested specimens, creep void nucleation and crack propagation were observed along the coarse B2-NiAl phases, especially for high-Ti alloys. Therefore, the beneficial effect of the increase in γ’-Ni₃(Al,Ti) precipitates for high-Ti alloys on creep property was limited due to the detrimental effect of the presence of coarse B2-NiAl phases. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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17 pages, 15201 KiB

Open AccessArticle

The Effect of Predeformation on Creep Strength of 9% Cr Steel

by Petr Král, Jiří Dvořák, Wolfgang Blum, Václav Sklenička, Zenji Horita, Yoichi Takizawa, Yongpeng Tang, Lenka Kunčická, Radim Kocich, Marie Kvapilová and Marie Svobodová

Materials 2020, 13(23), 5330; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13235330 - 25 Nov 2020

Cited by 6 | Viewed by 1703

Abstract

Martensitic creep-resistant P92 steel was deformed by different methods of severe plastic deformation such as rotation swaging, high-pressure sliding, and high-pressure torsion at room temperature. These methods imposed significantly different equivalent plastic strains of about 1–30. It was found that rotation swaging led [...] Read more.

Martensitic creep-resistant P92 steel was deformed by different methods of severe plastic deformation such as rotation swaging, high-pressure sliding, and high-pressure torsion at room temperature. These methods imposed significantly different equivalent plastic strains of about 1–30. It was found that rotation swaging led to formation of heterogeneous microstructures with elongated grains where low-angle grain boundaries predominated. Other methods led to formation of ultrafine-grained (UFG) microstructures with high frequency of high-angle grain boundaries. Constant load tensile creep tests at 873 K and initial stresses in the range of 50 to 300 MPa revealed that the specimens processed by rotation swaging exhibited one order of magnitude lower minimum creep rate compared to standard P92 steel. By contrast, UFG P92 steel is significantly softer than standard P92 steel, but differences in their strengths decrease with increasing stress. Microstructural results suggest that creep behavior of P92 steel processed by severe plastic deformation is influenced by the frequency of high-angle grain boundaries and grain coarsening during creep. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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11 pages, 4035 KiB

Open AccessArticle

Fundamental Improvement of Creep Resistance of New-Generation Nano-Oxide Strengthened Alloys via Hot Rotary Swaging Consolidation

by Jiří Svoboda, Lenka Kunčická, Natália Luptáková, Adam Weiser and Petr Dymáček

Materials 2020, 13(22), 5217; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13225217 - 18 Nov 2020

Cited by 16 | Viewed by 1679

Abstract

New-generation oxide dispersion-strengthened (ODS) alloys with a high volume fraction of nano-oxides of 5% are intended to become the leading creep- and oxidation-resistant alloys for applications at 1100–1300 °C. Hot consolidation of mechanically alloyed powders by intensive plastic deformation followed by heat treatment [...] Read more.

New-generation oxide dispersion-strengthened (ODS) alloys with a high volume fraction of nano-oxides of 5% are intended to become the leading creep- and oxidation-resistant alloys for applications at 1100–1300 °C. Hot consolidation of mechanically alloyed powders by intensive plastic deformation followed by heat treatment of the alloys are the key aspects for achieving top creep properties, typically ensured by a coarse-grained microstructure strengthened with homogeneously dispersed, very stable yttrium nano-oxides. The rotary swaging method proves to be favourable for hot consolidation of the new-generation ODS alloy presented. Compared to specimens consolidated by hot rolling, consolidation by hot rotary swaging predetermines the formation of coarse grains with a very high aspect ratio during subsequent secondary recrystallization. Such a grain morphology increases the creep strength of the new-generation ODS alloy considerably. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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11 pages, 3081 KiB

Open AccessArticle

Influence of Hot Consolidation Conditions and Cr-Alloying on Microstructure and Creep in New-Generation ODS Alloy at 1100 °C

by Jiří Svoboda, Natália Luptáková, Milan Jarý and Petr Dymáček

Materials 2020, 13(22), 5070; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13225070 - 10 Nov 2020

Cited by 10 | Viewed by 1497

Abstract

The coarse-grained new-generation Fe-Al-Y₂O₃-based oxide dispersion strengthened (ODS) alloys contain 5 vol.% homogeneously dispersed yttria nano-precipitates and exhibit very promising creep and oxidation resistance above 1000 °C. The alloy is prepared by the consolidation of mechanically alloyed powders via [...] Read more.

The coarse-grained new-generation Fe-Al-Y₂O₃-based oxide dispersion strengthened (ODS) alloys contain 5 vol.% homogeneously dispersed yttria nano-precipitates and exhibit very promising creep and oxidation resistance above 1000 °C. The alloy is prepared by the consolidation of mechanically alloyed powders via hot rolling followed by secondary recrystallization. The paper presents a systematic study of influence of rolling temperature on final microstructure and creep at 1100 °C for two grades (Fe-10Al-4Y₂O₃ and Fe-9Al-14Cr-4Y₂O₃ in wt%) of new-generation ODS alloys. The hot rolling temperatures exhibit a rather wide processing window and the influence of Cr-alloying on creep properties is evaluated as only slightly positive. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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