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Start Over Author "A. Tehranchi" Publisher elsevier b.v.
145 results on '"A. Tehranchi"'

10. Segregation at prior austenite grain boundaries: The competition between boron and hydrogen.

Author

Hachet, Guillaume, Tehranchi, Ali, Shi, Hao, Prabhakar, Manoj, Wei, Shaolou, Angenendt, Katja, Zaefferer, Stefan, Gault, Baptiste, Sun, Binhan, Ponge, Dirk, and Raabe, Dierk

Subjects
*AB-initio calculations, *CRYSTAL grain boundaries, *THERMAL desorption, *DISLOCATION density, *THERMODYNAMIC equilibrium
Abstract

The interaction between boron and hydrogen at grain boundaries has been investigated experimentally and numerically in boron-doped and boron-free martensitic steels using thermal desorption spectrometry (TDS) and ab initio calculations. The calculations show that boron and hydrogen are attracted to grain boundaries but boron can repel hydrogen. This behavior has also been observed using TDS measurements, with the disappearance of one peak when boron is incorporated into the microstructure. Additionally, the microstructure of both steels has been studied through electron backscattered diffraction, synchrotron X-ray measurements, and correlative transmission Kikuchi diffraction-atom probe tomography measurements. While they have a similar grain size, grain boundary distribution, and dislocation densities, pronounced boron segregation into PAGBs is observed for boron-doped steels. It indicates that boron in PAGBs is responsible for the disappearance of the TDS peaks for the boron-doped steel. Then, the equilibrium hydrogen concentration in different trapping sites has been evaluated using the Langmuir–McLean approximation. This thermodynamic model shows that the distribution of hydrogen is identical for all traps when the total hydrogen concentration is low for boron-free steel. However, when it increases, traps of the lowest segregation energies (mostly PAGBs) are firstly saturated, which promotes failure initiation at this defect type. This finding partially explains why PAGBs are the weakest microstructure feature when martensitic steels are exposed to hydrogen-containing environments. [Display omitted] • Pronounced segregation of B in PAGBs is observed when it is inserted in steel. • TDS curves show an additional peak for LC compared to B-LC. • DFT calculations show that the interaction of H with B is repulsive in GB. • The diffusion of hydrogen is higher for B-LC steel compared to LC. • C H at thermodynamic equilibrium is determined using theoretical models. [ABSTRACT FROM AUTHOR]

Published
2024
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47. Precise calculation of electrical capacitance by means of quadruple integrals in method of moments technique.

Author

Sarkarati, Saeed, Tehranchi, Mohammad Mehdi, and Mehrshahi, Esfandiar

Subjects
*MOMENTS method (Statistics), *ELECTRIC capacity, *INTEGRALS, *ANALYTICAL solutions, *CAPACITORS
Abstract

In this paper, the capacitance of a parallel plate air-gap rectangular capacitor, and a unit cube capacitor have been calculated. Because of its generality and simplicity, the method of moments (MOM) Technique is utilized. In order to improve the accuracy of the calculations, the use of quadratic integrals instead of binary integrals has been proposed. A neat form is provided for the analytical solution of the integrals required for the method of moment. The results show that there is a very small error in calculating the capacity even with coarse boundary division. The described formulas and codes can easily be used for similar purposes. [ABSTRACT FROM AUTHOR]

Published
2023
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