Anisotropic Pinning-Effect of Inclusions in Mg-Based Low-Carbon Steel.

In this study, the effect of austenite grain size on acicular ferrite (AF) nucleation in low-carbon steel containing 13 ppm Mg is determined. The average austenite grain size was calculated using OM Leica software. Results show that the predicted and experimental values of austenite grain size are extremely close, with a deviation of less than 20 µm. AF formation is difficult to induce by either excessively small and large austenite grain sizes; that is, an optimal austenite grain size is required to promote AF nucleation probability. The austenite grain size of 164 µm revealed the highest capacity to induce AF formation. The effects of the maximum distance of carbon diffusion and austenite grain size on the microstructure of Mg-containing low carbon steel are also discussed. Next, the pinning ability of different inclusion types in low-carbon steel containing 22 Mg is determined. The in situ observation shows that not every inclusion could inhibit austenite grain migration; the inclusion type influences pinning ability. The grain mobility of each inclusion was calculated using in situ micrographs of confocal scanning laser microscopy (CSLM) for micro-analysis. Results show that the austenite grain boundary can strongly be pinned by Mg-based inclusions. MnS inclusions are the least effective in pinning austenite grain boundary migration.

Investigation of the Defect Structure of Congruent and Fe-Doped LiNbO3 Powders Synthesized by the Combustion Method.

Fe-doped LiNbO3 synthesized by the combustion method to seek new multiferroic materials exhibits room-temperature ferromagnetism, as reported in our previous work [1]. In this work, the defect structure of congruent and Fe-doped LiNbO3 (0.57-3.3 mol %) powders was investigated in detail by several methods. The molar ratio of [Li]/([Li]+[Nb]) was determined by the Curie temperature (Tc) via DSC. Two peaks of Tc were observed due to phase splitting [2], and the phase at lower Tc disappears as the Fe doping concentration increases. The coexistence of two different oxidation states of Fe ions in LiNbO3 was probed by XPS and UV-Vis spectroscopy. The Raman spectra exhibit displacements along the c axis of Li and Nb ions, and a deformation of the NbO6 framework owing to Fe doping. Several doping models were applied in the Rietveld refinement of powder X-ray diffraction collected by synchrotron radiation. The fitting by the Nb vacancy model leads to an improbably distorted structure of congruent LiNbO3. In Fe-doped LiNbO3, we conjecture that Li and Nb vacancies coexist in the lattice structure; Fe+2/Fe+3 ions are substituted for Li ions at the regular Li site and may push the anti-site NbLi ion back to the regular Nb site.

Inclusions properties at 1673 K and room temperature with Ce addition in SS400 steel.

Inclusion species formed in SS400 steel with Ce-addition was predicted by thermodynamic calculation. The analysis of the inclusion morphology and size distribution was carried out by applying Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM). Nano-Fe3O4 particles were also found in cerium-deoxidized and -desulfurized steel and their shapes were nearly spherical. The complex Ce2O3 inclusions covering a layer of 218 nm composed by several MnS particles with similar diffraction pattern. Most importantly, the complex Ce2O3 characterized by using TEM diffraction is amorphous in the steel, indicating that Ce2O3 formed in the liquid iron and then MnS segregated cling to it.

Determination and controlling of grain structure of metals after laser incidence: Theoretical approach.

There are serious questions about the grain structure of metals after laser melting and the ways that it can be controlled. In this regard, the current paper explains the grain structure of metals after laser melting using a new model based on combination of 3D finite element (FE) and cellular automaton (CA) models validated by experimental observation. Competitive grain growth, relation between heat flows and grain orientation and the effect of laser scanning speed on final micro structure are discussed with details. Grains structure after laser melting is founded to be columnar with a tilt angle toward the direction of the laser movement. Furthermore, this investigation shows that the grain orientation is a function of conduction heat flux at molten pool boundary. Moreover, using the secondary laser heat source (SLHS) as a new approach to control the grain structure during the laser melting is presented. The results proved that the grain structure can be controlled and improved significantly using SLHS. Using SLHS, the grain orientation and uniformity can be change easily. In fact, this method can help us to produce materials with different local mechanical properties during laser processing according to their application requirements.

Thermodynamic Calculation among Cerium, Oxygen, and Sulfur in Liquid Iron.

Thermodynamic calculation has been applied to predict the inclusion formation in molten SS400 steel. When the Cerium addition in liquid iron is 70 ppm and the initial Oxygen and Sulphur are both 110 ppm, the formation of oxides containing Cerium would experience the transformation from Ce2O3 to CeO2 and also the formation of sulfides containing Cerium would experience the transformation from CeS to Ce2S3 and then to Ce3S4. Below 2000 K the most thermodynamic stable matter is CeO2 and the less thermodynamic stable inclusion is CeS. Only when the amount of [O] is extremely low and the amount of [S] and [Ce] is relatively high, Ce2S3 has the possibility to form.

Direct Printing of 1-D and 2-D Electronically Conductive Structures by Molten Lead-Free Solder.

This study aims to determine the effects of appropriate experimental parameters on the thermophysical properties of molten micro droplets, Sn-3Ag-0.5Cu solder balls with an average droplet diameter of 50 µm were prepared. The inkjet printing parameters of the molten micro droplets, such as the dot spacing, stage velocity and sample temperature, were optimized in the 1D and 2D printing of metallic microstructures. The impact and mergence of molten micro droplets were observed with a high-speed digital camera. The line width of each sample was then calculated using a formula over a temperature range of 30 to 70 °C. The results showed that a metallic line with a width of 55 µm can be successfully printed with dot spacing (50 µm) and the stage velocity (50 mm∙s-1) at the substrate temperature of 30 °C. The experimental results revealed that the height (from 0.63 to 0.58) and solidification contact angle (from 72° to 56°) of the metallic micro droplets decreased as the temperature of the sample increased from 30 to 70 °C. High-speed digital camera (HSDC) observations showed that the quality of the 3D micro patterns improved significantly when the droplets were deposited at 70 °C.

Effects of Rare Earth Metals on Steel Microstructures.

Rare earth metals are used in semiconductors, solar cells and catalysts. This review focuses on the background of oxide metallurgy technologies, the chemical and physical properties of rare earth (RE) metals, the background of oxide metallurgy, the functions of RE metals in steelmaking, and the influences of RE metals on steel microstructures. Future prospects for RE metal applications in steelmaking are also presented.

Fabrication of Microdots Using Piezoelectric Dispensing Technique for Viscous Fluids.

A simple microfluidic control method that uses a piezoelectric dispenser head is developed to fabricate microdots. A glycerol mixture was used as the test fluid to simulate conductive metallic solutions. The orifice diameter of the dispenser was 50 µm. Investigations were conducted at room temperature (25 °C). For each bipolar waveform, fluid was extruded in the form of a stretching liquid column, which eventually retracted into the dispenser orifice. Microdots were obtained by governing the liquid transfer process between the dispenser orifice and the target surface, where the gap was smaller than the maximum extrusion length during liquid column formation. Three fluid behaviors were observed using high-speed imaging, namely extrusion, impact on the target surface, and pinch-off of liquid ligament. For gaps of below 70 µm, some of the fluid sticking on the target surface resulted in a microdot diameter of 26 µm (about half of the orifice diameter).

Local geometric and electronic structures of gasochromic VO(x) films.

VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V(4+) and V(5+) valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 °C, and the lamellar structure was eliminated at 400 °C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V(5+) and V(3+). Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H2 gas sensors.

Shape-controlled synthesis of silver nanocrystals by X-ray irradiation for inkjet printing.

A suite of silver (Ag) nanocrystals have been synthesized using a rapid water radiolysis approach via X-ray irradiation. Various shapes including spheroidal, prism, rod, and multifaceted nanoparticles can be produced by varying the initial concentration of polyvinylpyrrolidone (PVP) relative to silver nitrate (AgNO3). UV-visible spectroscopy and transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) have been used to characterize these Ag products. At an optimized reagent ratio, a mixture of high-aspect-ratio rods (tunable to ∼50) and spheroidal particles result. Such a mixture is proven to have highly beneficial melting point and dispersive properties suited to inkjet printing of conductive Ag lines. The resistivity of the printed lines decreases to 77.7 µΩ and 33.1 µΩ after heating to 200 and 350 °C.

Formation and morphology of Zn(2)Ti(3)O(8) powders using hydrothermal process without dispersant agent or mineralizer.

Synthesis of Zn(2)Ti(3)O(8) powders for attenuating UVA using TiCl(4), Zn(NO(3))(2)·6H(2)O and NH(4)OH as precursor materials by hydrothermal process has been investigated. The X-ray diffractometry (XRD) results show the phases of ZnO, anatase TiO(2) and Zn(2)Ti(3)O(8) coexisted when the zinc titanate powders were calcined at 600 °C for 1 h. When calcined at 900 °C for 1 h, the XRD results reveal the existence of ZnO, Zn(2)TiO(4), rutile TiO(2) and ZnTiO(3). Scanning electron microscope (SEM) observations show extensive large agglomeration in the samples. Transmission electron microscope (TEM) and electron diffraction (ED) examination results indicate that ZnTiO(3) crystallites formed with a size of about 5 nm on the matrix of plate-like ZnO when calcined at 700 °C for 1 h. The calcination samples have acceptable absorbance at a wavelength of 400 nm, indicating that the zinc titanate precursor powders calcined at 700 °C for 1 h can be used as an UVA-attenuating agent.

Chelating agent-assisted heat treatment of a carbon-supported iron oxide nanoparticle catalyst for PEMFC.

Iron complexes were supported on commercial carbon black and heat treated to create FeO(x)/C catalysts that showed a larger normalized current density and normalized power density than commercial Pt/C catalysts; the coordination number of the iron complexes used affected the formation of the active site for oxygen reduction in PEMFC.