Papers by Keyword: Electron Microscopy

Abstract: Liquid phase separation is a common phenomenon observed in various types of condensed matter, including metals. The microstructure of Co-Cr-Mn-Fe-Ni-Cu and Co-Cr-Fe-Mn-Ni-Ag high entropy alloys (HEAs) with liquid phase separation was investigated. Dual fcc phases were observed in CoCrFeMnNiAg, CoCrFeMnNiCu, and CoCrFeMnNiCu₂ HEAs. A macroscopically phase separated structure formed via liquid phase separation was observed in CoCrFeMnNiAg HEA, and conventional dendritic structures were observed in CoCrFeMnNiCu and CoCrFeMnNiCu₂ HEAs.

Abstract: The article reviews the results of experimental studies of microstructure and redistribution of alloying elements in heat-resistant alloy HN45VMTYUBR during laser beam welding (alloy produced according to GOST 5632-14). Impression of laser emission on redistribution of alloying elements throughout the depth of a welding seam is demonstrated. Analysis covers the microstructure of several welding and heat-affected zones and redistribution of the alloying elements in these zones. Increase in tungsten content in weld root is detected. Redistribution of alloying elements in welding zones is proven to impact strength characteristics of the seam.

Abstract: The paper dwells upon the specifics of worn spots being formed on a silicon-carbide crystal in microscratching of iron, cobalt, and nickel. Analysis was done using a Versa 3D dual-beam electron microscope. The chemical composition of worn spots was studied by local X-ray microanalysis. It was found out that the amount of metal transferred to the silicon-carbide worn spot was associated with the electron structure of metal atoms.

Abstract: Zn-Mg alloys containing up to 5.28 wt.%Mg were prepared by gravity casting. Light and scanning electron microscopy with energy-dispersive X-ray spectrometry were used to characterize their as-cast microstructure as compared to that of pure zinc. The alloy with 3.60 wt.%Mg was found to be eutectic. Phase identification by X-ray diffractometry suggested that the eutectic Mg-rich phase wasMg₂Zn₁₁ with two types of intermetallic compounds, including Mg₂Zn₁₁ and MgZn₂, present in the alloy with 5.28 wt.%Mg. The microhardness increased with increasing Mg content from 41 HV for pure zinc to 266 HV for the alloy with 5.28 wt.%Mg. The electrochemical behavior of the alloys was studied by potentiodynamic polarization test at room temperature using 8.5 M KOH solution as electrolyte. Hydrogen evolution was generally postponed for the cases of Zn-Mg alloys as compared to pure zinc. The corrosion potential (E_corr) was not significantly affected by Mg addition into Zn, while the corrosion current density (i_corr) was significantly increased, especially for the case of the alloy with 3.60 wt.%Mg, as compared to that of pure zinc. It can be proposed that, due to its relatively higher hydrogen overpotential and uniform corrosion in KOH solution, the eutectic alloy with 3.60 wt.%Mg can be an alternative to pure zinc for use as anode in applications related to alkaline electrolyte.

Abstract: The microrelief of the contact, free sides and cuts of three metal alloys with various niobium contents were studied. It is shown that samples with high niobium content are X-ray amorphous, the alloys FeCu₁Si₁₆B₆, FeCu₁Nb₃Si₁₆B₆are characterized by an amorphous-crystalline structure. The change in the magnetic characteristics and electrical resistance of alloys in the course of thermomagnetic annealing is studied. It is shown that an increase in the Nb content in an alloy increases its temperature stability and the temperature of the onset of crystallization processes.

Abstract: Since the mechanism of Sn-whisker growth is closely related with the behavior of deformation and recrystallization, understanding of the behavior is very important to establish the measure for mitigation of whisker growth. In this work, microstructural changes after heavy deformation by scratching were characterized by EBSD for a single crystal of β-Sn, and the following results were obtained. Three types of crystal grains appear immediately after the deformation; small grains in aggregation, large serrated grains and rim-grains. The small grains are considered to be formed by dynamic recrystallization. They continue to grow at a room temperature over a lengthy period of time. The large grain has a certain crystallographic relationship with the matrix where <100> axes of the large grain and the matrix are almost parallel to each other. The serrated boundaries of large grain are so stable that the large grain does not show a grain growth process. The stable boundary is considered to promote a continuous growth of whiskers.

Abstract: Conventional (CCT) and accelerated (ACT) creep tests of a weld joint made of COST F and COST FB2 steels were carried out over a temperature range from 550 °C to 650 °C. Fracturing of the crept specimens was located in the heat affected zone (HAZ) of the F steel. Two specimens were selected after CCT and ACT for quantitative evaluation of the precipitates and compared to the weld joint in as-received conditions. Scanning and transmission electron micrographs were used to measure the precipitate size. Both methods were compared and the accuracy of the results was discussed. It was concluded that ACT can simulate the precipitation of chromium carbides and structure recovery during long term creep exposures. However, precipitation of Laves phase during CCT was not recorded after ACT. Therefore, it is difficult to use ACT in this experiment for estimating the long term creep strength.

Abstract: The research presents the atomic structure investigation of amorphous rapidly quenched Co₅₈Ni₁₀Fe₅Si₁₁B₁₆ at.% alloys. The alloys were quenched with linear velocity of cooper wheel surface from 22 to 38 m/s. We found a nonlinear dependence of local atomic ordering from linear velocity of cooling wheel. The average lateral density of ordered atomic clusters of 5 nm size changes from 4% to 8%. The amorphous alloy with metastable disordered structure with lower level of free energy is more stable against the external conditions. This approach can be used to determine the best technological parameters for preparing amorphous metallic alloy with metastable structure.

Abstract: Effect of the alloy initial structure before remelting on the melt viscosity, its state prior to crystallization, and on processes occurring in the alloy in solid state during its subsequent treatment was investigated using EK77 alloy. The study was performed by means of torsional oscillation of the melt with crucible, scanning electron microscopy, and optical metallography.

Abstract: This paper presents experimental results revealed on the samples type 2024 aluminum alloy used in aeronautics. Adequate characterization of 2024 aluminum alloys with special destination (aviation) was achieved by combined investigations:(i) wet chemical analysis, (ii) spectrochemical analysis, (iii) X-ray diffraction and (iv) electron microscopy. The main conclusion that emerges from the investigations carried out on aluminum samples revealed that: (a) alloys fits in terms of composition with the standard specification for 2024, in all cases; (b) microstructure vary in fineness of grain, but meets the requirements of aviation rules; the investigated microstructures have been appreciated as adequate of aluminum alloys type "2024".