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Beta-type titanium alloys contain high-cost alloy elements, and thus the manufacturing process using them is too expensive. In order to solve these problems, with making a good balance of mechanical properties in the titanium alloy, we added low-cost elements (Fe and Mo) rather than the high-cost beta-stabilizing elements (Nb and Zr). Furthermore, boron was added to the Ti alloy because that containing boron, exhibited greater stiffness and strength, along with good fracture resistance. In order to study phase transformation about these alloys, solution treatment and aging were conducted. The knowledge on the solution treatment of the Ti alloy is important for controlling the microstructure, being the key to enhancing the mechanical properties and nucleation sites. The result shows that β-solution treatment leads to a stable β-matrix and provides the greatest driving force for precipitation. This contributed to good ductility (about 900 MPa of ultimate strength with 25% elongation), in Ti-12.1Mo-1Fe (0A1F). However, Ti-12.1 Mo-1Fe-xB (0A1F-0.05B, 0A1F-0.1B) had more ductility than 0A1F. In the solution-treatmentplus- aging condition, the nano-size ω phase that precipitated at 350-450 ℃ resulted in great strength (above 1500 MPa with 2% elongation). When aged at 550 ℃, the 0A1F only precipitated α-phase, and had ductility of about 1100 MPa with 13% elongation. The specimens to which boron was added, had α and ω phases; so 0A1F-xB was more brittle than 0A1F when aged at 550 ℃. Consequently, the design-alloy exhibited good mechanical properties (i.e. strength and elongation). More detailed investigation is needed to determine its optimal mechanical properties.

keyword : alloys, aging, mechanical properties, tensile test

Corrosion data obtained from in-line inspection can be applied to assess present integrity as well as to predict future integrity of gas pipelines. This can be accomplished by using a combination of probabilistic analyses and simulation. With a deterministic method, failure models (e.g., NG 18 or ASME B31G)can only provide “Safe or Fail” criteria for corroded pipelines. However, a probabilistic method can offer “Probability of Failure (POF)” using the same models. This paper is focused on determining the POF for hypothetical corrosion-pit data of a gas pipeline. The study presented a ten-step procedure for obtaining the POF of a gas pipeline using three statistical methods (i.e., Monte Carlo, FOSM: First-Order Second-Moment, and FORM: First-Order Reliability Method). Furthermore, the coefficient of variance, regarding the value of POF sensitivity in relation to data variation, was mostly affected by the corrosion-depth parameter of the pit data.

keyword : gas pipeline, corrosion data, probability of failure, statistical method, Monte Carlo, FOSM, FORM

Plasma nitrocarburizing (PNC) treatment of quenching and tempering (QT)-treated SNCM220 steel samples was carried out at 570 ℃ for 5 hours in plasma-nitriding equipment. The PNC in a gas mixture of N2:H2:CH4 (85:13.75:1.25 by vol%) produced a compound layer composed mainly of ε-Fe2-3(N,C)-phase on the surface of SNCM220 steel. The thickness of the compound layer decreased with increasing CH4 content when N2 composition was fixed to 85%. The amount of ε-Fe2-3 (N,C)-phase in the compound layer increased with increasing CH4 gas content up to 1.25 vol%. When there was more than 1.5% CH4 in the gas mixture, the cementite phase started to form, which reduced the thickness of the compound layer. The gas carbo nitriding (GCN) treatment was performed at 860 ℃ for 2 hours followed by oil quenching at 130 ℃ and tempering at 180 ℃ for 2 hours. The GCN treatment produced a hardened layer with a martensite structure containing high carbon content (0.6 wt%). The effective case-depth (550 HV0.3) was about 300 μm. Compared with the GCN, the PNC and QT-treated SNCM220 steel had a higher surface- hardness (by 150-200 HV0.1), but lower near-surface hardness and bulk hardness (by 300-400 HV0.1). However, PNC treatment of QTtreated SNCM220 steel showed better wear resistance. This was due to a smaller worn-wear-track section and a lower friction-coefficient, compared with the result from GCN treatment. Therefore, in the very near future, it is expected that gas carbo nitriding treatment could be replaced by the combined QT+Plasma nitrocarburizing process for manufacturing vehicle parts.

keyword : plasma nitrocarburizing, metals, surface modification, wear, hardness test

Fe-(4.8, 9.2, and 14.3 wt%)Al alloy were significantly corroded at 600 and 700 ℃ for up to 60 h in a mixed gas consisting of 0.031 atm of H2O, 0.0044 atm of H2S, and balance of N2. The Fe-4.8Al alloy corroded rapidly, forming outer FeS scales and inner (FeS, Fe2AlO4)-mixed scales. These were formed because the sulfidation of Fe to form FeS in the outer scales facilitated the oxidation of Al to Fe2AlO4 in the inner scales. The Fe-(9.2, 14.3)Al alloys formed much thinner scales, which consisted primarily of outer FeS scales and inner Al2O3 scales that effectively provided corrosion resistance.(Received May 9, 2014)

keyword : metals, casting, oxidation, scanning electron microscopy, H2S corrosion, H2O corrosion

An expulsion phenomenon occurred during resistance spot welding of advanced high-strength steel sheets, and the effects of the Cr and Si contents on the expulsion limit current (CExp) were investigated. The correlation between CExp and the steel properties (e.g., resistivity, melting point, coefficient of thermal expansion, high-temperature yield-strength and viscosity), were evaluated, as were the qualities of the alloying elements. The CExp decreased with increasing Si contents. This resulted in a narrow range of acceptable welding current, as well as poor suitability for spot welding. On the other hand, the effects of Cr-contents on the CExp, and on the acceptable range of welding current were minimal (with content of 3 wt%). Thus, the suitability for spot welding was not affected by the Cr-Contents (at the experimental concentration). As Si-Contents increased, resistivity also increased and the melting point decreased. This resulted in easy melting of the base metal at a low welding current (low heat input) and in the rapid increase of the pressure due to the increased coefficient of expansion. However, the high-temperature yield-strength of the corona bond, which blocked the expulsion of the molten melt, also decreased. Consequently, the CExp of steel containing additional Si was lower than that containing Cr.

keyword : metals, welding, microstructure, optical microscopy, expulsion

Interfacial reaction of metal-ceramic joints is of great interest because of their potential applicability to components operating in high-temperature environments. In this work, Mo-41Re alloy with sputter-deposited SiC coating was annealed at 1300~1500℃, and the reaction at the alloy/SiC interface was investigated. On annealing at 1500℃, the element Mo in the Mo-41Re alloy significantly diffused toward the SiC layer, reacted with SiC, and formed a MoC layer. The reaction resulted in the depletion of Mo in the alloy adjacent to the surface. A brittle σ-MoRe phase that was detrimental to joint reliability, formed at a depth of 10~20 μm from the alloy surface. After annealing at lower temperature (1300℃), the σ-MoRe phase was formed less deep (3~5 μm), but with higher density, in the alloy. The reaction at both temperatures additionally resulted in Mo silicides and voids at the interface.(Received July 11, 2014)

keyword : Re alloy, ceramics, diffusion bonding, interfaces, transmission electron microscopy, TEM

Spent solder-stripping solutions containing tin, copper, iron, and lead in nitric acid solution, are by-products of the manufacture of printed-circuit boards. The recovery of these metals and the nitric acid, for re-use has economic and environmental benefits. In the spent solder-stripping solution, a systematic method to determine a suitable process for recovery of valuable metals and nitric acid was developed. Initially, more than 90% of the tin was successfully recovered as high-purity SnO2 by thermal precipitation at 80 ℃ for 3 hours. About 94% of the nitric acid was regenerated effectively from the spent solutions by diffusion dialysis, after which there remained copper, iron, and lead in solution. Leakage of tin through the anion-exchange membrane was the lowest (0.026%), whereas Pb-leakage was highest (4.26%). The concentration of the regenerated nitric acid was about 5.1 N.

keyword : tin, nitric acid, diffusion dialysis, recovery, solder stripping solution

ZnO thin films were first grown on Zn-coated Teflon substrates using a spin-coating method, with various post-heating temperatures. The structural and optical properties of the ZnO thin films were then investigated using field-effect scanning-electron microscopy, X-ray diffractometry, and photoluminescence (PL) spectroscopy. The surface morphology of these ZnO thin films exhibited dendritic structures. With increasing post-heating temperature, all samples preferentially exhibited preferential c-axis orientation and increased residual tensile stress. All of the films exhibited preferential c-axis orientation, and the residual tensile stress of those increased with increasing post-heating temperature. The near-band-edge emission (NBE) peaks were red-shifted after post-heating treatment at 400 ℃. The intensity of the deep-level emission (DLE) peaks gradually decreased with increasing post- heating temperature. Moreover, the narrowest ‘full width at half maximum’ (FWHM) and the highest intensity ratio of the NBE to the DLE for thin films, were observed after post-heating at 400 ℃. The ZnO thin films fabricated with the 400 ℃ post-heating process provided the highest crystallinity and optical properties.(Received March 04, 2014)

keyword : zinc oxide, teflon substrate, zn coating layer, spin coating, photoluminescence

Ultraviolet ozone (UVO) surface-treatment was carried out on fluorine-doped tin oxide (FTO) substrate prior to the growth of Cu2O thin-films by electrochemical deposition. This was done to improve their photo-electrochemical properties. We examined the effect of various durations of UVO surface-treatment on the morphological, structural, optical and photo-electrochemical properties of Cu2O thin-films. The effects were measured via field-emission scanning-electron microscopy (FE-SEM), X-ray diffraction (XRD), UV-visible spectroscopy and 3-electrode potentiostat, respectively. The highest photocurrent density (4.22 mA/cm2) was achieved with a 2-minute UVO surface-treatment.(Received August 19, 2014)

keyword : optoelectronic materials, surface modification, grain growth, scanning electron microscopy, SEM, photoelectrochemical

A dye-sensitized solar cell device with a structure of 0.45 cm2 effective area of glass/FTO/blocking layer/TiO2/N719 (dye)/electrolyte/100 nm Pt/glass was employed. The 100 nm-thick Pt counter-electrode deposited with an RF sputter-coater, was etched to induce strain using ion-beam-assisted etching (IBAE) with Ar ions for 0-180 seconds. In order to improve the energy-conversion efficiency of a dye-sensitized solar-cell device. The photovoltaic properties (e.g., short-circuit current density, open-circuit voltage, fill factor, and energy-conversion efficiency) were characterized using a solar simulator and potentiostat. The strain and interface resistance of the Pt thin-film were examined using x-ray diffraction and impedance. The surface roughness and impurity of the Pt thin-film were examined using atomic-force microscopy and x-ray photoelectron spectroscopy. The measured energy-conversion efficiencies of the DSSC devices, at IBAE times of 0 and 60 seconds, were 5.06% and 5.50%, respectively. The increase in efficiency with IBAE time resulted from the compressive strain field caused by IBAE treatment. Above 60 seconds, the decrease in efficiency was due to residual Ar ions. Our results imply that the use of an IBAE-treated Pt-catalytic layer, with appropriate etch time, improves the efficiency of dye-sensitized solar cells.(Received August 26, 2014)

keyword : dye sensitized solar cells, ion beam assisted etching, energy conversion efficiency, x-ray photoelectron spectroscopy, strain