A physically-based constitutive model for high temperature microstructural degradation under cyclic deformation

An enormous amount of research had been dedicated to exploring the nanotechnology over the past decade. The fast-paced development of nanomaterial production has enhanced the application of zinc oxide (ZnO) in a wide variety fields. ZnO nanoparticles can be obtained mechanically or chemically for commercial use. However, the environmental issues raised by these techniques have been brought to the world’s attention. Nowadays, green synthesis of ZnO nanoparticles is of particular interest in the research field aiming to mitigate environmental problems. In this green approach, natural based materials such as plant extract, microbes, fungus and algae are used as bio-reductants and bio-stabilizers due to their enrichment in bioactive phytochemicals. Numerous studies have proven that the green synthesis is facile and feasible to produce ZnO nanopowder with advanced properties as compared to the chemically synthesized ZnO nanoparticles. In order to make the green synthesized ZnO nanoparticles more applicable in a wide range of uses, surface modification using metal and non-metal ions are applied to alter and improve the properties of ZnO nanoparticles. The findings available currently represent an excellent initial step towards the promising green approach in the synthesis of ZnO nanoparticles and additional work should be undertaken to exploit the application of green synthesis in the commercial platform.

Facile green synthesis of ZnO nanoparticles using natural-based materials: Properties, mechanism, surface modification and application

A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels

Corrosion of Ceramic and Composite Materials

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.

https://www.mdpi.com/1996-1944/13/22/5217/pdf

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

Oxide-dispersion-strengthened (ODS) Fe-Al-Y2O3-based alloys (denoted as FeAlOY) containing 5 vol. % of nano-oxides have a potential to become top oxidation and creep-resistant alloys for applications at temperatures of 1100–1300 °C. Oxide dispersoids cause nearly perfect strengthening of grains; thus, grain boundaries with limited cohesive strength become the weak link in FeAlOY in this temperature range. One of the possibilities for significantly improving the strength of FeAlOY is alloying with appropriate elements and increasing the cohesive strength of grain boundaries. Nearly 20 metallic elements have been tested with the aim to increase cohesive strength in the frame of preliminary tests. A positive influence is revealed for Al, Cr, and Y, whereby the influence of Y is enormous (addition of 1% of metallic Y increases strength by a factor of 2), as it is presented in this paper.

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Substantial Improvement of High Temperature Strength of New-Generation Nano-Oxide-Strengthened Alloys by Addition of Metallic Yttrium

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.

https://www.mdpi.com/1996-1944/13/22/5070/pdf

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

The stress relaxation behavior of the P91 martensitic steel is tested for the temperature range 400–600 °C in order to investigate the plastic deformation and fracture processes. The repeated relaxation tests are performed on the tensile specimens at the stress level of 95% of the ultimate tensile stress. The deformation mechanisms are analyzed in terms of an activation volume, dislocation density and velocity, a thermal stress component and a strain rate hardening. The deformation is driven by the dislocation glide. Short range interactions between dislocations and a lattice become dominant at the studied temperature range. The dislocations are able to overcome a pinning effect by the thermal activation at 600 °C.

Deformation and fracture behavior of the P91 martensitic steel at high temperatures

N. Luptáková, Academy of Sciences of Czech Republic, Institute of Physics of Materials, Brno, Czech Republic F. Pešlová, University of Alexander Dubcek in Trencin, Slovakia J. Kliber, VŠB – Technical University of Ostrava, Faculty of Metallurgy and Materials Engineering, Ostrava, Czech Republic The given paper is closely connected with the process of the manufacturing of ZnO. The purity of the metal zinc has crucial influence on the quality of ZnO. ZnO can be produced by pyrometallurgical combustion of zinc and hard zinc. But this mentioned method of preparation leads to the creation of the enormous amount of waste including chemical complexes. On the basis of the occurrence of the residual content of other elements, it is possible to make prediction about the material behavior in the metallographic process. The input and finally materials were investigated and this investigation was done from the aspect of structural and chemical composition of the materials.

Natália Luptáková

Papers

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

Substantial Improvement of High Temperature Strength of New-Generation Nano-Oxide-Strengthened Alloys by Addition of Metallic Yttrium

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

Deformation and fracture behavior of the P91 martensitic steel at high temperatures

The study and microstructure analysis of zinc and zinc oxide