Papers by Keyword: Grain Size

Abstract: Bi-Pb-Sr-Ca-Cu-O (BPSCCO) superconductors are recognized as a projectable high-temperature superconductor for high-efficiency electrical applications. The addition of Ti enhances the formation of the Bi-2223 phase from the BPSCCO superconductor. The process of producing BPSCCO superconducting materials with TiO₂ dopants is performed by the solid-state process and the production of wire rolling, consisting of bismuth (III) oxide powder (Bi₂O₃ = 99%), Strontium Carbonate powder (SrCO₃ = 99%), Calcium Carbonate powder (CaCO₃ = 99%), Copper Oxide powder (CuO₂ = 99%), Lead Oxide powder (PbO₂ = 98%) Bi: Pb: Sr: Ca: Cu ratio: 1.6: 0.4:2:2:3 doped by 1 %wt Titanium Oxide powder (TiO₂ = 98.5%). The variables used in this study were the comparison of the sintering method at 860°C for 24 hours and 820 °C calcination for 20 hours, and 850°C sintering for 20 hours. The superconductor characterization was tested through the X-Ray Diffraction (XRD) test, Scanning Electron Microscopy (SEM), and Resistivity test. XRD test results showed the formation of Bi₂Sr₂CuO₆ and Bi₂Sr₅Cu₃O₁₆ phase. SEM results showed an increase in grain size. The resistivity test results showed that all samples formed critical temperatures, 9.6 and 9.5K respectively.

Abstract: Thermally-induced phase transformation (PT) is of significance and value to the application of NiTi alloy components. Low-temperature aging (LTA) treatment was used to alter PT characteristics of NiTi alloys avoiding undesirable grain growth. Effect of LTA on PT of NiTi wires with a wide range of grain sizes from 34 nm to 8021 nm was investigated in this study. As the average grain size varies from 34 to 217 nm, the temperature of the B2↔R transformation increase as a result of LTA, and the increasing effect is more obvious at a larger grain size. For NiTi alloys with average grain sizes ranging from 523 to 1106 nm, transformation sequence changes from B2↔B19' to B2↔R due to LTA. For the sample with an average grain size of 2190 nm, the B2↔B19' transformation is replaced by B2↔R←B19' after LTA. When the average grain size is larger than 2190 nm, transformation sequence changes from B2↔B19' to B2↔R↔B19' after LTA. Transmission emission microscope observations reveal that the above-mentioned PT behavior correlates with the coupled effect of grain size and precipitation. The precipitation of Ni₄Ti₃ in the grains with a size smaller than ~150 nm is inhibited after LTA, the temperature of B2→R of samples with average GS smaller than ~150 nm still is elevated due to the inhomogeneous grain size of NiTi wires.

Abstract: The use of friction welding with mixing allows to obtain non-defectal compounds of both alloy AL25 and dispersed particles composite aluminum materials. It was found that in addition to changes in the grain structure of the α-Al solid solution, there are changes in the process of the release of particles of intermetallide phases, which can be traced in the morphology, medium size and chemical composition of particles of intermetallide phases of different natures. The change in the morphology of secondary phase particles is due to the difference in thermo mechanical influence in different areas of the formation of the compound when welding friction with mixing.

Abstract: The paper presents the results of studies of the profile of the impregnated diamond surface depending on the grain size and initial roughness of the matrix. The experiments were carried out by impregnating powders of different grit size into a matrix made of low-carbon low-alloy steel with HB180 hardness using a ball indenter. The roughness parameters were measured using a contact profilometer. The height and step parameters of roughness and the curve of the profile bearing length were evaluated. In studying the effect of grain size on the surface profile, it was found that the optimal grain size should be 0.5...0.8 of the initial surface mean spacing profile irregularities. The shape of the Abbott-Firestone curve in this case corresponds to a flat profile. Experiments carried out with varying the initial roughness of the samples confirmed the dependence of the optimum grain size on the mean spacing of the profile irregularities. The developed research procedure can be used to design technological processes of hardening parts, tools and accessories by diamond impregnation.

Abstract: The high-strength Al-Zn-Mg-Cu alloy has broad application prospects in high-end equipment manufacturing fields, such as aerospace, national defense and military industry, and transportation. However, the grains of Al-Zn-Mg-Cu alloy are coarse, and the grains further grow after heat treatment, which seriously reduces the mechanical property of alloy castings. Therefore, the study on reducing the grain size of the cast alloy was carried out by adding Zr element and applying electromagnetic stirring treatment technology, as well as suppressing the recrystallization of the aluminum alloy during the heat treatment process. The results show that adding Zr element reduced the grain size by 30%, the tensile strength increased by 50 MPa, and the elongation increased by more than 10%.

Abstract: Light-weight and high-strength aluminum alloy drill pipes are potential and promising to replace traditional steel drill pipes. In this study, the grain size and mechanical properties of aluminum alloy drilling pipe materials reinforced by in-situ TiB₂ particles were studied. The results showed when reinforced by in-situ TiB₂ particles the grain size of aluminum alloy materials was refined from 155 m to 57 m and ultimate tensile strength was increased from 590 MPa to 720 MPa. Besides, the results also indicated that the friction coefficient was reduced from 0.99 to 0.50 and thus the abrasion resistance of 7075 aluminum alloy was enhanced by 34 %. This study provided theoretical basis for the application of light-weight and high-strength aluminum alloy drill pipes in directional drilling and ultra-deep wells.

Abstract: The study analyzes the specifics of modern metal processing technologies. The results of laboratory research for samples made from structural steel St3 with various heat treatment are presented. The results of mechanical tests, measurements of the relaxation coercive field force are shown. The processes that occur with the structure during heat treatment are studied and described. It is made by x-ray diffractograms and images obtained with raster electron and optical microscopes. The influence of structural changes on the relaxation coercive field force and mechanical parameters is described.

Abstract: Ceria stabilized zirconia with critical grain size is found to exhibit higher strength and higher resistance towards low temperature moisture degradation, The mechanical properties are greatly influenced by the size of the tetragonal grains. The effectiveness of doping with MnO2 (0.2 to wt %) in retarding degradation mechanical properties of ceria stabilized tetragonal zirconia (Ce-ZrO2) was evaluated by pressureless sintering within a temperature range from 1250°C-1550°C. Impact of manganese oxide to the mechanical properties and ageing resistance to the Ce-ZrO2 is truly beneficial. 0.4 wt% MnO2 at 1450°C revealed that, the tetragonal grain size was not affected by dopant level.With optimum dopant the 3 mol% ceria (3Ce-ZrO2) ceramic demonstarted the Vicker hardness of 11.8 GPa , fracture toughnessof 10.0 MPam^1/2, flexural strength 920 MPa and Young modulus of 210 GPa. The 3Ce-ZrO2 doped with 0.4wt% MnO2 sintered 1450°C could be the best building block for biomedical applications.

Abstract: This paper presents the results of the investigation of the grain structure formation in the intermetallic compound Ni₃Al under conditions of its high-temperature synthesis under pressure in a powder mixture of nickel and aluminum of stoichiometric composition and the effect of grain size on the strength properties of the synthesized intermetallic compound. The grain structure was investigated by optical metallography, transmission electron microscopy, and EBSD analysis; the ultimate tensile strength of the intermetallic compound was investigated under the tension of the samples in the temperature range from 20 to 1000 °C. It was found that with a decrease in the grain size, not only does the tensile strength of the intermetallic compound multiply increases but also on the anomalous temperature dependence of the intermetallic compound strength there is a significant shift in the maximum strength value to the region of higher temperatures.

Abstract: The aim of this work was to analyze the recrystallization behavior of cold rolled Aluminum/graphene composites during annealing. The Aluminum/graphene composite was cold rolled firstly, and then annealed at different temperature (250°C, 300°C, 350°C, 400°C) and for various time (1 h, 2 h, 8 h, 32 h). Full recrystallization did not occur until the annealing temperature was above 300 °C. With annealing temperature increasing from 250 to 300°C, the hardness of the composites decreased from 49.6 to 27.6 HV. Grain growth were not observed at high annealing temperature and longer annealing time, which suggested that Graphene has strong pinning effect on the grain boundary of Aluminum.