Papers by Keyword: Phase Composition

Abstract: Changes in thermal expansion during heating of hot-extruded tube made of VT23 titanium alloy (Ti-5.45 Al-4.7 V-2.45 Mo-1.1 Cr-0.7 Fe, wt. %) were analyzed. The volume effect of α→β-transformation, β-transus temperature as well as the volume fraction of α-and β-phase formed during heating were calculated based on the received data of dilatometric analysis. Results obtained were compared to thermodynamic calculations and published data. The change in the CTE value of VT23 alloy upon heating to 975 °C was estimated, and the explanation of different CTE values obtained in the present study and published data was proposed.

Abstract: The AlCrFeNi alloys has successfully synthesized with the composition of Al, Cr, Fe, and Ni at 25 atomic percent. The synthesis of this material is to obtain an alloy intended as nuclear fuel cladding for a research reactor with high uranium density. The AlCrFeNi alloys made from pressed powder then sintered at temperatures of 800, 900, and 1000 °C with a dwelling time for one hour. Sintering process was conducted in inert atmosphere. The obtained alloys were analyzed using the X-ray diffraction (XRD) for phase analysis and the Scanning Electron Microscope (SEM) for morphological observation and elemental analysis. From the diffraction pattern, the three alloys synthesized had the dominant B2 phase. Alloys sintered at 800 °C and 900 °C show the FCC phase linear in composition value with the sintering temperature. From the diffraction pattern, a theoretical density value is also obtained. The results indicate that the alloy with the only B2 phase has the lowest density of 5.932 g/cm³. From the SEM micrographs, it can be seen that the morphology of the alloys have relatively large cracks. The elemental analysis results to confirm the alloy's phase composition obtained a ratio of Al and Ni, which only allows the B2+FCC phases to form.

Abstract: Metallurgical characteristics of iron ore agglomerates of various basicity (reducibility, strength after reduction (LTD_+6.3), temperatures of the beginning and ending of softening) have been investigated. The phase composition (XRD) of iron ore agglomerates and their microstructure were analyzed by optical microscopy. Various dependences of influence of the basicity of iron ore agglomerates on their metallurgical characteristics with respect to the proportion of phase components that have been obtained. It has been shown that an increase in the proportion of stabilized silicoferrite (SFCA) in the agglomerate has a positive effect on their strength after reaction, which will further increase the productivity of the blast furnace and significantly reduce dust emission.

Abstract: In modern scientific and engineering expertise there are a few methods for graphical computational analysis related to decision making. However, few of them are devoted to materials science and the determination of the complex of properties separately and simultaneously. This research proposes a decision analysis approach tested for the basic properties of BH11 steel. With the help of the approach the tendencies as technological regimes in the change of the microhardness Hv, the relative wear resistance Kv and the connected nitride zone δnz are established. A model for the phase composition is derived, which interprets all observed trends and technological regimes for the relatively minimal and relatively maximal studied values. Thus, the efficiency of the technology in processing the considered steel is associated with the structure and properties of ion nitrided layers, which as a research is the main task of materials science.

Abstract: The structure, the phase composition and microhardness over the section of welded joints aged at 500 and 550 °C have been studied by means of structural and microdurometric analyzes. The welded joints of OT4-VT23, VT6-VT23 and VT19-VT23 titanium alloys pairs were obtained by the argon-arc welding with a nonconsumable tungsten electrode. It has been established that the aging at 500 °C for 8 hours promotes the decomposition of metastable phases (b, a”) which formed after welding in the welded joint of VT19-VT23 titanium alloys pair. The decomposition process leads to strengthening of the main zones of the welded joint (except for the parent metal of VT23 alloy) and provides a favorable smooth change of microhardness in the joint during the transition from one alloy to another. The aging at 500 and 550 °C during 8 hours of the welded joints of OT4-VT23, VT6-VT23 titanium alloys pairs also led to the development of the decomposition of metastable phases (b, a”, a’) in the weld and heat affected zones of the alloys being joined, but did not provide the required monotonic change in microhardness over the cross section of the joint.

Abstract: The paper presents the results of the determination of the effect of a photocatalytic composite material (PCM) with the composition SiO₂‒TiO₂ on the main properties of white Portland cement: heat release during hydration, phase composition and microstructural features of cement stone, pressure strength and self-cleaning ability. PCM was synthesized by a sol-gel method based on tetrabutoxytitanium and finely dispersed diatomite powder and 15% cement was added instead. The presence of PCM in the cement system provided the reduction of the induction period of cement hydration, consolidation of the microstructure of the cement stone with the products of the pozzolanic reaction, the ability to photocatalytic self-cleaning of the cement stone surface.

Abstract: Radioluminescence technologies are at the front line of the optic and electronic studies. Effective, self-contained and safe radioluminescent light sources can find their application in space industry, in medicine and in military technologies. The question of the performance improvement of the solid-state radioluminescent light sources (SRLS) without raising the included activity of working radionuclide can be solved by upgrading the phosphor crystalline structure. The electron-beam treatment for zinc-sulphide phosphors initial batch has been studied in a wide range of concentrations of the activating agent (Cu) for improving the radioluminescent performances of the phosphors, for creating the structural defects that form centers of luminescence. The changes of the phase composition were investigated under different synthesis conditions. It is revealed that electron-beam treatment of the initial batch leads to the growth of the wurtzite phase content in zinc-sulphide phosphors synthesized below the phase transition temperature. The changes of the phase content promote the spectral redistribution under the tritium beta-excitation. It is obviously the reflection of the fact of «green» luminescence centers rearrangement between the volume of the crystal and its surface. The correlations between structural configuration and performances of ionizing luminescence were found. Electron beam treatment gave the 20% increase of brightness of the radioluminescence. The achieved enhancement of luminescence performances allows the development of advanced tight-packed SRLS with minimal radioactivity and high energy-light conversion.

Abstract: It is shown that microarc oxidation (MAO) makes it possible to increase the size of aluminum alloy details by forming dense ceramic coatings (MAO-coatings) on them. Found that MAO-process a duration of 50...80 minutes in a liquid solution according to conventional technology allows you to increase the size of the details made of deformable alloy AMg3 and D16 by 78...80 % of the thickness formed on them MAO-coating and MAO-process in solution of corundum particles opens the possibility of increasing the same details by 98...100 % of the thickness formed on them more thick MAO coating. Revealed that increasing solution temperature from 15 to 45 оС leads to a reduction in the thickness of MAO coating and an even more significant reduction in growth dimensions, as well as to reduce the quality of their surfaces. It is shown that the removal of the outer layers of MAO coatings to a thickness of 20 ... 25 μm by grinding contributes to a significant reduction in the roughness of the surfaces of details. It is confirmed that MAO coatings obtained in liquid solution and in solution with corundum particles have a similar mainly polycrystalline structure, but MAO coatings obtained in solution with corundum particles differ in greater thickness and higher corundum content (α-Al₂O₃). It is established that the outer layers of MAO coatings are characterized by a relatively low content of modifications of crystalline aluminum oxide, so after their removal, the strength properties of the surfaces of details also improve. The principal possibility of increasing the size of details made of deformable aluminum alloys by 150 μm with ensuring high quality of their surfaces is proved.

Abstract: The post-sintering properties of walling high-calcium ceramics based on clay-containing raw materials in low-temperature roasting depend on the chemical-mineralogical composition of clay with different contents of iron, calcium-containing and alkaline oxides that contribute to the formation of new crystalline phases, which provide for the production of low-density ceramic material with high-strength properties.

Abstract: This article discusses the ways of intensification of the oxidation process with the formation of surface properties necessary to increase the service life of one of the parts of an internal combustion engine - a cylinder made of cast aluminum alloy. A brief overview of existing technologies for hardening the aluminum surface is presented. Environmentally friendly options are proposed for using the potential of processes that have accumulated energy within an electrolytic cell by activating the interelectrode gap and forming an oxide with desired properties. The main difference from the existing model approaches of oxide formation lies in the parallel excitation of the main participant in the process, oxygen, in order to dominate it over other, oxygen-containing donors. Ways of using the energy of cavitation phenomena due to acoustic resonance in an electrolytic solution are proposed. Redistribution of the field potential by replacing a flat cathode with a pointed one changed the conductivity conditions in the interelectrode gap as a result of the electroconvective action. The structure of the oxide layer, phase changes, and physical properties confirming the originality of oxide coatings have been investigated.