Advanced Materials Research Vols. 887-888

Abstract: The components of corrosion products on rusted cast iron artifacts in a wet/dry atmospheric environment have been studied by micro-Raman spectroscopy. The observations show that microstructures of outer and inner interfaces are different; indicating that active corrosion occurred on the rusted specimen covered with many cracks and pores. The μRaman spectra of outer and inner layer results prove to be composed of three main iron oxyhydroxides. In addition, Fe₃O₄ only exists in the inner layer.

Abstract: The source of inclusion in IF steel end slabs after reducing the casting remnant were studied by means of total oxygen and nitrogen content analysis, original position analyzer for metal (OPA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Slims. The results show that: reducing the casting remnant have little influence on reoxidation in continuous casting process, the size of micro-inclusions are mostly smaller than 5 μm. The size of large-sized inclusions in end slab are mainly trapped in mold, they are mostly from 140 μm to 300 μm and over 300 μm, which accounted individually for 19.94% and 73.21% of total large-sized inclusions. In the end of a cast, decreasing the casting speed with slower speed changing rate can decrease the slag entrainment index of hot rolled coils from end slabs.

Abstract: Multiaxial fatigue life of 50CrVA spring steel standard specimens and eccentric specimens under proportional loading was studied with MTS 809 tension-torsion electro-hydraulic servo tester. Both kinds of specimens were calculated by the finite element software ABAQUS and the fatigue life of specimens were predicted based on the finite element results. The results show that the additional bending moment will obviously reduce the life of specimens; only the Manson-Halford model and modified Manson-Halford model can obtain satisfactory results in many prediction models selected.

Abstract: Austempering was applied to bearing steel to improve the performance. The effect of austenitizing temperature and time on isothermal quenching microstructure in bearing steel was investigated via microstructure observation and fracture analysis. The results show that with the increase of austenitizing temperature, the size of bainite plate and residual austenite content increase. Austenitizing at lower temperature, the samples has a fracture composite fracture morphology of polygon cleavage unit and even small dimple.The fracture morphology of sample austenitized at 1050 °C is quasi-cleavage fracture with bar cleavage unit which is corresponding to the coarse acicular microstructure. the size of bainite plate increase with increasing the austenitizing time. As the result of comprehensive effect of fine grain strengthening and dispersion strengthening, that the microhardness firstly increases, and then obviously decreases with the increase of austenitizing time.

Abstract: Quality molten metal needed to produce thin wall ductile iron (TWDI). Pig iron, as the major base material to produce quality molten metal, due to its high price, has been change with scraps. The use of scrap as major base material associates with more cleaning and chemical composition adjustment. The ITmk3 technology in iron making has successfully produced iron nugget. Iron nugget can be use to substitute pig iron due to its quality that is comparable to pig iron but lower in price. This research conducted to see the effects of carbon content in producing iron nugget. Limonite iron ores used in this research are part of laterite rocks taken from Sebuku Island in South Kalimantan, Indonesia. Variation made to weight of carbon mixed with laterite. Heating temperatures of direct reduction process are 700°C, 900°C, and 1000°C. The process times are 10, 20, and 30 minutes. XRF used in analysing Fe content in laterite and XRD is used in analysing result of direct reduction process. The result shows that increasing carbon content to certain condition will increase the rate of gasification process during direct reduction. The increase of gasification rate will result to higher Fe formation.

Abstract: (Na,Bi)TiO₃-BaTiO₃ lead free piezoelectric ceramics were fabricated with modification of CaCu₃Ti₄O₁₂ additives. The phase structure, morphology, dielectric and piezoelectric properties of prepared samples were investigated, respectively. It was found that CaCu₃Ti₄O₁₂ additives evidently improve the polarization properties of (Na,Bi)TiO₃-BaTiO₃ lead free ceramics and the obtained samples exhibit an excellent piezoelectric properties (electromechanical coupling factor K_p=31%, mechanical quality factor Q_m=151 and piezoelectric constant d₃₃=160pC/N). According to results, the effect of CaCu₃Ti₄O₁₂ additives on electrical properties of (Na,Bi)TiO₃-BaTiO₃ lead free piezoelectric ceramics is discussed.

Abstract: Microwave filters require dielectric ceramic resonators attached to ceramic supports via joining. Among the BaTiO₃, CaTiO₃, and Ba₂Ti₉O₂₀ based-dielectric ceramics prepared in our labs., the CaTiO₃ ceramics modified with NdAlO₃ and Al₂O₃ gave satisfactory dielectric properties: dielectric constant DK = 40.69, quality factor Qxf = 18842 GHz (fo = 6.551 GHz), and frequency temperature coefficient t_f = 2.542 ppm °C^-1. For replacing the hard-to-sinter Al₂O₃ based-ceramic supports, a glass-ceramic of the SiO₂-B₂O₃-P₂O₅-ZnO system was developed, leading to a low sintering temperature of 900 °C, and a low dielectric constant (<4). Finally, a Bi₂O₃-ZnO-SiO₂-Al₂O₃-CaO glass was used as a sealing agent to replace the traditional gluing consisting of an adhesive. The present work hinters that with proper sintering aids, one can produce multilayered and integrated resonators with and without embedded passive elements.

Abstract: 0.95(Na_0.95-xK_xLi_0.05)(Nb_0.90Sb_0.05Ta_0.05)O₃-0.05KNbO₃ lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, the effects of K/Na ratio on the structure and electrical properties of the ceramics were studied in detail. The results show that the addition of the pre-calcined KNbO₃ powder as sintering aid is very effective to improve the density and sinterability, and the ceramics could be well sintered at reduced temperature of 1060 °C as compared with the relatively higher sintering temperature of Li, Sb, Ta modified KNN ceramics reported in the literature at 1100-1220 °C. The ceramics with x=0.44 possess the optimal properties: d₃₃=231 pC/N, k_p= 47 %, P_r= 22 μC/cm², and E_c= 11.4 kV/cm.

Abstract: In order to further broaden the application field of calcined bauxite, using differential thermal analysis-thermo-gravimetry (DTA-TG), X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM) and other testing technology to study and analysis on the high temperature performance of calcined bauxite in this paper. The results show that the main crystal phases of calcined bauxite are corundum and mullite, appearance is layered, granular distribution. Due to the thermal performance of calcined bauxite is optimal, and is expected to be used for the field of high temperature solar thermal heat storage material.

Abstract: The microstructures of the Mg-6Zn-2Y alloy solidified under high pressures were investigated using scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The room-temperature compression behavior was analyzed through experiments, showing that the microstructures of the alloys are consisted of α-Mg and quasicrystal I-Mg3Zn6Y phases. With solidification pressure increasing, the microstructures were refined, and the morphologies of the inter-dendritic secondary phase were improved from continuous networks into long-island and granule. The compression strength, yielding strength and compressibility were increased significantly corresponding with solidification pressure, from 259.02 MPa, 230.39 MPa and 18.3% under ambient pressure to 361.43 MPa, 272.25 MPa and 33.1% under high pressure of 6 GPa. The cleavage planes are flat, and the cleavage steps are straight under ambient pressure. However, the cleavage planes are small and rough under 4-6 GPa; tearing dimples occur in the tearing area, indicating that the degree of cleavage fracture decreases under high pressure.