Papers by Keyword: Fe-Cr Alloy

Abstract: This present work dealt with the effect of surface roughness on the scales growth of Fe-15Cr alloy. Surface morphologies and oxidation kinetics reveal that there was no obvious influence of surface roughness on the oxide-scale growth of Fe-15Cr alloy except for the initial oxidation stage of 1 h. However, there was an obvious influence on the oxide-scale spallation and microstructure, especially under the mutual function of temperature changes and surface roughness.

Abstract: A computer simulation of atomic displacement cascades in Fe-9at.%Cr binary alloy has been performed by molecular dynamics method for temperature of 300 K and cascade energies from 100 eV to 20 keV. The average number of Frenkel pairs produced in cascade has been calculated. The data on point defect clusterization have been obtained. Obtained evaluations of effective fraction of surviving defects are well approximated by the sum of power and linear functions of cascade energy. Increased chromium fraction in the self-interstitial (SIA) configurations has been observed and has been explained by combination of two factors: positive binding energy of Cr atom with SIAs and mobility of SIA configuration. The diffusion coefficient of single SIA configuration in the matrix of pure bcc Fe has been evaluated for the temperature range of 300 – 1000 K. We have prepared 100 group neutron cross-sections of effective displacement generation in Fe-9at.%Cr binary alloy. It has been shown that effective dpa generation rate can be 2-3 times lower than corresponding rates of conventional dpa generation rate.

Abstract: Nanostructured iron based alloy, elaborated from pure elemental powders by mechanical milling at high energy was studied. The materials obtained were characterized by several techniques, such as X-ray diffraction (XRD), which allowed the dissolution of chromium in the iron phase as a function of milling time. The peaks indicate that the obtained solid solution has the body centred cubic (bcc) structure, for a speed of 250 rpm after 24 hours milling time. The Williamson - Hall analysis method was used to exploit the recorded XRD patterns. The crystallite size of about 14 nm and the microstrain of about 0.90% were obtained for 48 hours of milling. Scanning electron microscopes (SEM) and EDX analysis have confirmed the refining of milled particles as a function of milling time and the homogenization of our powders. The measurement of reflection coefficient has revealed an increase in the microwave absorption versus milling time and has confirmed the formation of our alloy during 24 hours of milling.

Abstract: The influence of magnetic interactions on high temperature thermodynamic stability of Fe-Cr binary system has been analysed in the light of accurate isothermal calorimetry measurements (400-1473 K) on Fe-20wt.%Cr alloy. The onset of two successive principal transformations namely, (i) α(Fe-rich bcc)+α(Cr rich bcc)α(HT bcc) at 702±10 K; and (ii) α_ferroα_para at 925 ±10 K, with their associated enthalpy effects (Δ^oH_mag = 2 kJ mol ^-1; C_p^mag = 20 J mol^-1 K^-1) have been clearly delineated by the measured enthalpy variation with temperature. A precise quantification of magnetic contribution to high temperature thermodynamic stability has been attempted using physically based modelling approach.

Abstract: The first wall material in a nuclear fusion reactor endures a series of complex processes, resulting in irradiation damage of its structural materials and eventually questioning its operative safety. Experimental and computer simulation are currently applied to search for irradiation damage. We used, the Material Studio software to model and calculate the crystal structure and mechanical properties, and the CASTEP module, primitive cell of iron, Fe-Cr alloy and Fe-Cr alloy with defects to calculate, analyze, and obtain the values of elastic constants and Young’s modulus. Our results showed that addition of Cr atom to conventional first wall metal materials of nuclear reactor, enhanced endurance by increasing the values of elastic constant and Young’s modulus, but distorted the symmetry of the crystal structure. We preliminarily prove and predict the possibility of the changes of mechanical properties of Low-activation martensite/ferrite under irradiation effects.

Abstract: Abstract. Binary Fe-11.62wt%Cr alloys were investigated in as-received state as well as after a two step helium ion implantation at different energies (100 keV and 250 keV) with doses up to 3.12×10¹⁸ cm^-2. In order to study changes in alloys in dependence on the temperature, thermal annealing was performed at temperatures of 400, 475, 525 and 600 °C and specimens were afterwards measured by a pulsed low energy positron system (PLEPS). Annealing out of defects at lower temperatures was not as significant as expected, and we also encountered difficulties with defect identification. However, an apparent decrease of defect size was observed in the specimen annealed at a temperature of 600 °C.

Abstract: A plate of Fe-30Cr (wt%) were subjected to isothermal furnace at 600 °C in flowing CO2 gas at total pressure of approximately 1 atm. The reacted samples morphology and microstructure were characterized by using visual inspection, optical microscope, SEM and EDAX. The weight change measurement showed a fluctuating result during the exposure. The significant weight loss was observed after five hours exposure due to oxide scale exfoliation. Formation of different oxide and element presents on the interface of the specimen such as Cr2O3, C and Fe3C were revealed by X-ray diffraction and with supported by EDAX analysis. This behavior of the high temperature corrosion on Fe-30Cr was discussed based on morphology and microstructure observation.

Abstract: The turtle shell, as the oldest amphibian, has developed a rigid calcified shell to protect the soft body against environmental pressures and predators. The paper has studied the effect of microstructure on the mechanical behavior of the turtle shell. Furthermore the porous Fe-Cr based alloy was manufactured by the method of powder metallurgy. The results showed that turtle shell was composed of the element of Ca, P, C, Cl and Na etc. The microstructure of turtle shell is a sandwich structure typical of flat bones with the compact layer, the spongy layer with many pores and the fibrous inner layer. The unique structure affected the mechanical behavior of turtle shell very seriously. The sandwich structure can absorb the energy during transferring load, and very little energy is transferred to the endocortical bony and the internal organs. In this sense the soft part of turtle shell was protected by the shell. The porous Fe-Cr based alloy was manufactured by powder metallurgy and the pores are irregular and the porosity of alloy Fe-Cr is 19.4%. The microhardness of Fe-20Cr is 77.5 HV.

Abstract: Manganese-cobaltite spinel coatings were produced on Fe-Cr alloys for the improvement of the chemical and mechanical stability of solid oxide fuel cell (SOFC) interconnects. It was found by thermal investigation, i.e., the microscopy of various samples that were heat-treated in air at 800 °C, that the screen-printed coating more effectively inhibited oxide scale growth than the sputtered coating. The reason why the manufacturing method of the spinel coating affected the oxide scale growth rate was investigated. It was demonstrated that the oxide scale in both the samples after annealing in air at 800 °C for 5000 h comprised MnCr₂O₄ and Cr₂O₃ with no difference in composition. However, the interface between the alloy and the oxide scale was deeper and rougher and had a larger grain size because of the high oxygen diffusivity in the sputtered coating. In contrast, in the screen-printed sample, the dense spinel layer above the oxide scale blocked oxygen diffusion into the alloy, so the oxide scale growth rate was lower and the interface between the alloy and oxide scale remained flat even after thermal treatment. Introducing a reduction treatment in the manufacturing process made the Mn-Co spinel layer denser and further inhibited the oxide scale growth. Moreover, the addition of Li as a sintering aid into the Mn-Co spinel was found to even more effectively inhibit the oxide scale growth.

Abstract: Void formation in a duplex scale formed on Fe-5Cr alloy at 773 K has been elucidated by oxygen chemical potential distribution, the flux of oxide ion and its divergence. The calculation predicts that voids preferentially form at the interface between inner and outer scales in the low oxygen partial pressure in which the predominant defect of iron is interstitial ion. The flux of oxide ion changes discontinuously at this interface and the divergence of the flux gives voids. Calculated volume fraction of voids at this interface is in good agreement with that has been measured.