Papers by Keyword: Phase Structure

Abstract: In order to explore the influence of V, Mo and Zr elements on Al_0.5TiNb-based refractory high-entropy alloys. Three alloys Al_0.5TiNbV_0.5, Al_0.5TiNbZr_0.5 and Al_0.5TiNbMo_0.5 were used as experimental materials in this paper. The phase structures, microstructures and mechanical properties of the three designed alloys were analyzed by using X-ray diffraction, optical Olympus metallographic microscope and mechanical performance testing. The results show that the three designed alloys are composed of BCC phase solid solution. There was no formation of intermetallic compounds. The yield strength of Al_0.5TiNbZr_0.5 and the compressive plastic strain of Al_0.5TiNbV_0.5 reached the maximum value of 1340 MPa and 7.86%, respectively. This might be attributed to four effects of high-entropy alloys and the strengthening effect of dendrites. The dendrite content of Al_0.5TiNbZr_0.5, Al_0.5TiNbMo_0.5 and Al_0.5TiNbV_0.5 decreases successively. There are coarse grain boundaries in the microstructure of Al_0.5TiNbV_0.5, which contribute to improvement of compressive plasticity.

Abstract: Ni–Co alloy coatings were electrodeposited at various cobalt amounts on pretreated steel substrates. The co-deposition phenomenon of Ni-Co alloys was described as anomalous behaviour. Different techniques including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), X-ray diffraction (XRD) and potentiodynamic polarization were used to characterize the alloy coatings. EDX results showed that the Co content increase with the enhancing of Co amount. SEM images have shown that the increase of Co amount leads grain developing from large grain to branched grain form and that goes through spherical and pyramidal, this implies that the grain size of these alloy coatings is greatly affected by Co amount in the electrolyte baths. XRD patterns revealed that the phase structure of Ni–Co coatings is dramatically changed from fcc into hcp structure with the increase of Co amount. The electrochemical properties of Ni-Co alloy coatings evaluated in 3.5% NaCl solution reveal that Ni–34.32 wt.% Co alloy exhibits better corrosion resistance compared to pure Ni and other Ni–Co alloy coatings.

Abstract: Compared with SBR latex, waterborne epoxy resin has obvious advantages. The cured epoxy resin emulsified asphalt material has stronger mechanical properties, but it is less used in asphalt modification applications. Aiming at this problem, this paper uses waterborne epoxy resin as the modified material of emulsified asphalt, and carries out performance characterization and road performance evaluation of waterborne epoxy resin modified emulsified asphalt and its mixture under different dosages. Fluorescence microscopic analysis of waterborne epoxy asphalt with a content of 8wt%, 15wt%, 30wt%, and 50wt%, respectively, shows that the resin content should not exceed 30wt% to ensure the performance of asphalt. The bonding properties of SBR modified emulsified asphalt and waterborne epoxy resin modified emulsified asphalt with different dosages at 20 °C and 60 °C were analyzed. The results show that the tensile strength and oblique shear of waterborne epoxy modified emulsified asphalt. The strength is higher than SBR modified emulsified asphalt, and its high temperature resistance is better than SBR modified emulsified asphalt material. The road performance analysis was carried out on the mixture prepared by the aqueous epoxy modified emulsified asphalt with the content of 0wt%, 8wt%, 15wt% and 30wt% respectively. The results show that with the increase of waterborne epoxy content, the Marshall stability, splitting strength and high temperature rutting resistance of the mixture increase more obviously. The freeze-thaw splitting strength of the waterborne epoxy resin mixture is 13% higher than that of the pure emulsified asphalt mixture, and the splitting strength is also significantly improved. Due to the high stiffness of the waterborne epoxy resin after curing, the maximum bending strain of the mixture is reduced, and the recommended dosage is not more than 30% by weight. On the whole, the introduction of waterborne epoxy resin could greatly improve the strength and road performance of the asphalt, and could be used as a proper road repair material.

Abstract: In this work, Bi₂Fe₄O₉ superfine particles were prepared by hydrothermal method and effects of hydrothermal conditions on the microstructure of Bi₂Fe₄O₉, especially the concentration of OH^- ([OH^-]) in initial solutions, were investigated. The results showed that [OH^-] had obvious influences on the growth of Bi₂Fe₄O₉ under the same hydrothermal temperature and hydrothermal time. Phase structure of Bi₂Fe₄O₉ unchanged with the increase of [OH^-] and maintained orthorhombic structure. Besides, the microstructure of Bi₂Fe₄O₉ was carefully studied through transmission electron microscopy (TEM). The results suggested that the mechanism of Bi₂Fe₄O₉ growth was Ostwald ripening. In conclusion, Bi₂Fe₄O₉ superfine particles with good morphology and microstructure can be successfully synthesized when the concentration of OH^- is 2 mol/L and hydrothermal conditions are 240 °C for 6h.Keywords: Bi₂Fe₄O₉, hydrothermal method, phase structure, growth mechanism Topic code numbers: C2

Abstract: The Nd_7.69Fe_92.31-xTi_x (x = 0, 4, 8, 12) alloy were prepared by arc smelting and high energy ball milling method. The morphology and phase structure of the powders were analyzed by Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and the effect of the Ti content on microwave absorbing properties of the powders were measured by a vector network analyzer (VNA). The results reveal that the samples mainly consisted of Nd₂Fe₁₇ and α-Fe crystal structure. The minimum absorption peak frequency shifts to lower frequency region firstly and then shifts to higher frequency region with the increasing amount of Ti content. The minimum reflection loss of Nd_7.69Fe_84.31Ti₈ powder is-31.35 dB and the bandwidth of R < -5 dB reach 3.6 GHz when the coating thickness is 2.0 mm. With the increasing of the coating thickness, the minimum reflectivity peak value of the Nd_7.69Fe_84.31Ti₈ moves to lower frequency region and the minimum reflection loss increase firstly and then decrease. And the minimum reflection value of Nd_7.69Fe_84.31Ti₈ alloy can reach to-38.74 dB (microwave absorption rate 99.99%) at 5.68 GHz, and the bandwidth of R < -10 dB reach 1.12 GHz with the best matching thickness of 2.2 mm.

Abstract: In the research, the properties of potassium sodium niobate – barium titanate [(1-x)K_0.02Na_0.98NbO₃–(x)BaTiO₃: (1-x)KNN–(x)BT] ceramics prepared by molten salt method with various molecular weight of BT or x are 0 and 0.05 were investigated. The calcined powders of pure K_0.02Na_0.98NbO₃ and (0.95) K_0.02Na_0.98NbO₃-(0.05) BaTiO₃ were pressed and sintered at 1250 – 1325 °C and 1225 – 1300 °C for 2h, respectively. It was found that, the samples showed phase structure changing from monoclinic to orthorhombic with small amount BaTiO₃ addition. The densification of K_0.02Na_0.98NbO₃ ceramics and dielectric properties were improved with the addition of BaTiO₃. The (0.95)K_0.02Na_0.98NbO₃–(0.05)BaTiO₃ ceramics sintered at 1250 °C showed maximum density and dielectric constant (∼8035), which was even comparable with that of K_0.02Na_0.98NbO₃ ceramics sintered at 1225 – 1300 °C.

Abstract: The article covers an intelligent technology-based functional materials quality control process. It justifies the need for computer pattern recognition methods application in fabric analysis based on specimen digital photos taken in the course of quality control sampling. A two-level phase structure classification algorithm, that allows recognition of classes by teaching on a predefined known structures template array, is suggested. A working example is made of an algorithm application in the analysis of phase distribution on a photo of a hardened steel microsection with prescribed strength properties.

Abstract: Al_1.3FeCoNiCuCr high entropy alloy (HEA) coatings were prepared by pre-placed laser cladding on 921A steel substrate, and the study on the phase transition of the Al_1.3FeCoNiCuCr coating due to the introduction of Mn was conducted. The combination of TEM and XRD results showed that the Al_1.3FeCoNiCuCr HEA coatings without Mn addition typically consisted of two kinds of grains, i.e., one is composed of only FCC phase, and the another is a mixture of BCC and FCC phases. The two phases were of similar ratio in the coatings, while nanoparticulate precipitates were observed in the bcc phase. When 3 wt. % Mn was introduced into the alloy, the coatings consisted of also FCC and BCC phase. However, most of the grains were in FCC phase, while the BCC phase with a lath shape only distributed between the FCC phases. High hardness nanobanded precipitates were observed in the FCC phase. It is clearly revealed that the phase structure of Al_1.3FeCoNiCuCr coatings undergoes a dramatic transition due to the introducing of Mn.

Abstract: (Sm_1-xNd_x)₂Ce₂O₇ ceramics was synthesized by solid reaction method at 1873K for 10h in the present investigation. The density, phase structure, thermal conductivity and thermal expansion coefficient of (Sm_1-xNd_x)₂Ce₂O₇ ceramics were studied by the Archimedes method, X-ray diffraction (XRD), laser-flash and pushing rod. The (Sm_1-xNd_x)₂Ce₂O₇ ceramics have pure fluorite-structure. The thermal conductivity of (Sm_1-xNd_x)₂Ce₂O₇ ceramics decreased with an increase of Nd₂O₃ content at identical temperature conditions, and the thermal expansion coefficient increased with increasing Nd-doping content. The synthesized (Sm_1-xNd_x)₂Ce₂O₇ ceramics can be explored as an ideal candidate material for future thermal barrier coatings.

Abstract: The results of the X-ray phase and thermodynamic analysis of phase formation in the Zr-Y-O system which is the initial material for formation of yttrium of stabilized ceramics on the basis of dioxide of zirconium are presented. It is established that the material is multiphase and contains monoclinic, cubic and tetragonal modifications of dioxide of zirconium which weight ratios differ considerably.