Preparation of epitaxial and polycrystalline bismuth titanate thin films on single crystal (100) MgO by chemical solution deposition

Epitaxial and polycrystalline Bi₄Ti₃O₁₂ thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi₄Ti₃O₁₂ may be suppressed by the formation of a titanium-rich phase such as Bi₂Ti₂O₇ owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C.     

Effects of iron catalyst on the formation of crystalline domain during carbonization of electrospun acrylic nanofiber

To investigate the effects of introducing the iron compound on the carbonization behavior polyacrylonitile (PAN)-based electrospun nanofibers were carbonized with or without iron(III) acetylacetonate (AAI) over the temperature range of 900–1500 °C in nitrogen atmosphere. The morphological characteristics of the carbon nanofibers were investigated using X-ray diffractometer (XRD), Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrical conductivity of the carbon nanofiber web was measured by four-point probe method. The iron catalyst had a profound effect on the crystal structure of the carbonized nanofiber. In the presence of AAI the nanofibers carbonized at 1300 °C developed graphite structure, which could be obtained at the temperature higher than 2000 °C in the absence of the catalyst. The in-plane size of the graphite crystals (L_a) was measured to be about 6.5 nm by Raman spectroscopy and the (0 0 2) spacing by XRD was 0.341 nm.     

Superplastic deformation and crystallization behavior of Cu54Ni6Zr22Ti18 metallic-glass sheet

Superplastic deformation and crystallization behavior of a Cu₅₄Ni₆Zr₂₂Ti₁₈ metallic glass were investigated. A maximum elongation of 650% was obtained at 733 K at 1 × 10⁻² s⁻¹ from the sheet fabricated by squeeze copper-mold casting method. At low strain rates, the strain-rate-sensitivity exponent value was close to 1, suggesting that Newtonian-like behavior governed the plastic flow. At a high strain rate around 10⁻² s⁻¹, a transition from Newtonian to non-Newtonian behavior took place with decrease in m value. Large strain hardening by crystallization occurred during the course of deformation. The strain hardening was found to be caused by crystallization according to the analyses of the relation of true stress vs. testing time, T-T-T diagram and DSC characteristics. The time periods up to the strain before strain hardening at 733 K for the Cu₅₄Ni₆Zr₂₂Ti₁₈ metallic glass were similar to that of the Zr₆₅Al₁₀Ni₁₀Cu₁₅ metallic glass at 696 K as 180–300 s (3–5 min). This coincidence could be explained by comparison of their T-T-T diagrams showing that the incubation times for crystallization of the Cu BMG at 733 K and for Zr BMG at 696 K are similar.     

Effect of low-cycle fatigue on the hot ductility of plain carbon steel

In a continuous casting steelmaking operation, the surface of a slab is under a condition that can be characterized as high-temperature, low-cycle fatigue in which the tensile and compressive stress is repeatedly developed. For this reason, for the evaluation of the hot ductility of a slab, considering the fatigue deformation is more feasible before a tensile or compressive test. In this study, the effects of low-cycle fatigue on the hot ductility of steels with a carbon content of 0.06–0.8 wt.% are investigated at various temperatures. For a carbon content of 0.06%, there were no significant differences between the RA values from a simple tensile test and those from a tensile test after fatigue deformation. The tendency of ductility deterioration with fatigue deformation is evident in 0.1 %C steel, and is due to the deformation-induced ferrite film that forms around the prior austenite grain. Conversely, high carbon steel containing 0.8 %C did not show a recovery of hot ductility in a low temperature region, and the specimen on which the tensile was measured after fatigue showed a higher hot ductility in the low temperature region, which is thought to result from the pearlite refinement effects. As the results obtained in this work showed noticeable differences in the hot ductility of carbon steel through the test conditions, it is suggested that for more accurate data, fatigue deformation be adopted in which the temperature range in an unbending operation is determined in the steelmaking factory.     

Densification and compressive strength ofin-situ processed Ti/TiB composites by powder metallurgy

In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB₂, B₄C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB₂ or B₄C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100, 1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB₂ compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of the composite made from TiB₂ reactant powder was higher than that of the composite made from B₄C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between matrix and reinforcement made from TiB₂ reactant powder was better than that made from B₄C.     

Effects of Rare Earth Metal addition on the cavitation erosion-corrosion resistance of super duplex stainless steels

Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance.     

Process for dense 2D SiC fiber-SiC matrix composites

A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated. The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of >98%. The 2D SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength.     

Morphological analysis and classification of types of surface corrosion damage by digital image processing

This paper examines a new concept of corrosion surface damage analysis by using the digital image processing. Corrosion phenomena are analyzed using a digital value for morphological surface damages instead of electrochemical methods. Initial images are characterized by three categories: color, texture and shape features. To calculate corrosion surface damages color we use the interpretation of HIS model. For the texture attributes, the method of co-occurrence matrix is used. Five types of corrosion damage are examined. Multidimensional scaling procedure is used to define the classification plane. This study suggests a probabilistic method of decision-making. This analysis develops a method for automated identification system of corrosion damages and is supposed to be more advantageous than that of electrochemical techniques.     

Development of the active balancing device for high-speed spindle system using influence coefficients

A high-speed spindle can be very sensitive to rotating mass unbalance which has harmful effect on many types of rotating machinery. Therefore, the balancing procedure is certainly needed to reduce vibration in all high-speed rotating systems. In this study, an active balancing program using influence coefficient method and an active balancing device of an electro-magnetic type with both simple and reliable structures were applied to the developed high-speed spindle system. A gain scheduling control using influence coefficients of the reference model was proved to be effective in balancing the spindle system although its characteristics were changed. The stability of reference influence coefficients was verified by experiments with frequency response functions. The active balancing experiment of the manufactured spindle system using an active balancing program and device was also performed efficiently during the operation. As a result, controlled unbalance responses after balancing work were below the vibration limit at all rotating speed ranges including critical speeds.     

Boron distribution in a low-alloy steel

Boron distribution in a low-alloy steel (15B26:0.25C-0.29Cr-0.03Ti-0.028Al-0.0016B) has been characterized employing Fission Track Etching (FTE) method. The characteristics of boron distribution with variation of cooling rate after austenitization and through case-hardened depth after carburization were analyzed. Hardenability of 15B26 steel was also evaluated through Jominy-end-quench test and the results are as follows: It was observed that, in austenitized 15B26 steel, boron was distributed uniformly over the whole area of specimen with a little segregation along the austenite grain boundaries at higher cooling rates and boron precipitates were formed in the intergranular as well as transgranular regions at lower cooling rates. Jominy equivalents (HRC 35) of 15B26 steel were fairly increased between the Jominy temperatures of 820°C and 850°C, which might result from the increase of the amount of soluble boron in austenite due to the dissolution of borocarbides between 820°C and 850°C. In carburized 15B26 steel, the different through thickness features of boron distribution from the carburized surface were found; coarse nodular boron precipitates up to the depth of 150 μm; uniform distribution of dissolved boron between 150~650 μm; and segregation of boron atoms along grain boundaries in the regions deeper than 650 μm.