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Low-cycle fatigue (LCF) tests of the nickel-based superalloy Haynes 282 from a large forged ingot were conducted at 25 and 750 °C with total strain ranges from 0.7 to 1.7%. Compared with other tests on this alloy, it was found that the LCF properties showed similar results at room temperature, but improved number of cycles to failure at high temperatures. The number of cycles at a given total strain range showed no large differences between the core and rim positions. By comparing with two other types of low γ′ volume fraction nickel-based superalloys, Haynes 282 gave the best LCF properties at high temperatures. The reason may be due to the dominating transgranular fracture in the current work. A mixture of intergranular and transgranular fractures had been observed in the other alloys. The results demonstrate that heavy components of Haynes 282 can be produced with good LCF properties. [ABSTRACT FROM AUTHOR]

Diffusion controlled cavity growth models tend to exaggerate the growth rate. For this reason it is essential to take into account the restrictions caused by creep rate of the surrounding material, so called constrained growth. This has the consequence that the stress that the cavities are exposed to is reduced in comparison to the applied creep stress. Previous constrained growth models have been based on linear viscoplasticity. To avoid this limitation a new model for constrained growth has been formulated. Part of the work is based on a FEM study of expanding cavities in a creeping material. Compared with the previous constrained cavity growth models, the modified one gives lower reduced stresses and thereby lower cavity growth rates. By using recently developed cavity nucleation models, the modified creep cavity growth model can predict the cavity growth behaviour quantitatively for different types of austenitic stainless steels, such as 18Cr10Ni, 17Cr12NiNb and 17Cr12NiTi. [ABSTRACT FROM AUTHOR]

Creep rupture prediction is always a critical matter for materials serving at high temperatures and stresses for a long time. Empirical models are frequently used to describe creep rupture, but the parameters of the empirical models do not have any physical meanings, and the model cannot reveal the controlling mechanisms during creep rupture. Fundamental models have been proposed where no fitting parameters are involved. Both for ductile and brittle creep rupture, fundamental creep models have been used for the austenitic stainless steel Sanicro 25 (23Cr25NiWCoCu). For ductile creep rupture, the dislocation contribution, solid solution hardening, precipitation hardening, and splitting of dislocations were considered. For brittle creep rupture, creep cavitation models were used taking grain boundary sliding, formation, and growth of creep cavities into account. All parameters in the models have been well defined and no fitting is involved. MatCalc was used for the calculation of the evolution of precipitates. Some physical parameters were obtained with first-principles methods. By combining the ductile and brittle creep rupture models, the final creep rupture prediction was made for Sanicro 25. The modeling results can predict the experiments at long-term creep exposure times in a reasonable way. [ABSTRACT FROM AUTHOR]

Exploring efficient non-precious metal cathode catalysts is attracting ever-increasing interest in the development of direct borohydride fuel cell (DBFC). Herein, a cobalt-based nitrogen-doped bamboo-like graphene tube (Co-NGT) is prepared as an efficient cathode catalyst. The Co-NGT consists of bamboo-like graphene tubes (40–130 nm in diameter and ∼10 μm in length), as well as cobalt nanoparticles (50–100 nm in diameter) confined in the graphene tubes. The Co-NGT shows an onset reduction potential of 0.964 V and an almost four-electron pathway towards oxygen reduction reaction, as well as a negative shift of 8 mV in half-wave potential after 10,000 CV cycles. The Tafel slope of the Co-NGT catalyst is 47 mV decade−1, which is by ca. 37.8 mV decade−1 smaller than for Pt/C. A DBFC using the Co-NGT cathode yields the biggest power density of 453 mW cm−2 at 60 °C and a life span of over 120 h. The excellent electrocatalytic properties and superior durability of Co-NGT catalyst arise from the highly graphitized NGT, providing strong interaction with Co nanoparticles and mitigating the agglomeration of Co nanoparticles. Our study guides for composition and structural design of high-efficient cathode catalysts of DBFC. [Display omitted] • The Tafel slope of Co-NGT towards ORR is 47 mV dec−1. • The half-wave potential is only 8 mV negative shift of Co-NGT after 10,000 CV cycles. • Maximum power density of 453 mWcm−2 is achieved by DBFC using Co-NGT cathode. [ABSTRACT FROM AUTHOR]

• In situ XANES was used to reveal the valence evolution of Fe-based electrocatalysts toward ORR. • In situ XRD was used to reveal the phase transition of Fe-based electrocatalysts during ORR. • A Fe2+/3+ redox transition was both found in Fe-PPy-C and FeS-PPy-C. • The Fe, FeS and Fe 2 O 3 were all converted to FeOOH during ORR in Fe-based electrocatalysts. • The ORR activities of Fe-based electrocatalysts are governed by their static structure. [Display omitted] The commercialization of fuel cells relies largely upon the development of highly active non-precious metal electrocatalysts. Insufficient understanding of the reaction mechanism of Fe-based electrocatalysts towards oxygen reduction reaction (ORR) limits the further improving of its catalytic performance. Herein the valence state and phase transformation of three Fe-based electrocatalysts comprising different valences of iron during the ORR in alkaline medium are investigated by in situ synchrotron radiation X-ray absorption and diffraction studies in direct borohydride fuel cell. There is a dynamic structure associated with the 'Fe2+/3+' redox transition confirmed by in situ X-ray absorption near edge structure spectra in Fe-PPy-C and FeS-PPy-C. The metallic Fe, FeS, and Fe 2 O 3 of the three Fe-based electrocatalysts are all converted to FeOOH during ORR. The local structure of Fe atoms and valence transition barrier contribute to most of the ORR activities of the three Fe-based electrocatalysts. [ABSTRACT FROM AUTHOR]

Piezocatalysts have attracted much attention due to their excellent degradation ability for organics. In this work, three types of BaTiO 3 (BTO) nanostructures, including hydrothermally synthesized nanocubes (NCs), sol-gel calcined nanoparticles (NPs), and electrospun nanofibers (NFs), are prepared for catalyzing the dye degradation. Compared with the NCs and NPs, the NFs exhibit a higher piezocatalytic degradation performance due to the large specific surface area, fine crystal size, and easy deformation structure. Moreover, the kinetic factors, including initial dye concentration, ionic strength, ultrasonic power, and applied action, influencing the degradation performance of the BTO NFs are analyzed deeply. A high degradation rate constant of 0.0736 min -1 is achieved for rhodamine B, which is superior compared with the previous reports. The excellent stability of BTO NFs is demonstrated by the cycling tests, where a high degradation efficiency of 97.6% within 110 min is still obtained after the third cycle. Furthermore, the mechanism of piezocatalysis revealed that the hydroxyl and superoxide radicals are the main reactive species in the degradation process. This work is of importance for the development of high-performance piezocatalysts and highlights the potential of piezocatalysis for water remediation.