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Alloys containing the β/B2 phases of Ti-45Al-3Mo, Ti-45Al-3Mo-2Nb and Ti-45Al-5Mo were prepared using an vacuum arc-melting machine. Heat-treatments were carried out at 1250 ℃ in an Ar atmosphere. The temperature of 1250 ℃ is the temperature region of phase α + γ + (β/B2), and the heat treatment condition which improves mechanical properties by decreasing the fraction of the β/B2 phase. The presence of the β/B2 phase can result in relatively weakness at high temperatures and collapses the lamellar structure of the α₂ / γ phase during heat treatment. The transient oxidation behaviors of Ti-45Al-(3, 5)Mo-(2Nb) (at%) alloys were investigated in an ambient atmosphere at 900 and 1000 ℃. Initial oxidation behaviors and oxidation resistance of the three alloys were compared at 1000 ℃. The oxidation resistance of the Ti-45Al- 3Mo-2Nb alloy containing Mo and Nb was the most remarkable among the three alloys at 900 ℃ and 1000 ℃. At the same time, Si pack cementation coated Ti-45Al-3Mo-2Nb alloys and oxidation behavior were also analyzed. The phase sequences of the multilayers of τ₂ / Ti₅Si₄ / TiAl₃ / TiAl₂ /TiAl were observed on the substrate. Also, a diffusion pathway of the silicide coating layers in the ternary phase diagram of Ti-Al-Si was proposed. The oxidation resistance of the silicide coated TiAl alloys was improved during the oxidation tests at 1000 ℃. (Received December 10, 2018; Accepted January 16, 2019)

keyword : TiAl, oxidation, coatings

This study investigated and compared the tensile and high-cycle fatigue properties of AISI 1045 steel and Cr electroplated AISI 1045 steel. First, tensile and fatigue specimens were machined from AISI 1045 steel (substrate), and two kinds of Cr electroplating layers with different layer thickness were applied. The substrate, AISI 1045 steel consisted of an a-Fe matrix and pearlite, and the two Cr electroplating layers were measured to have thicknesses of 13.1 μm and 53.9 μm, respectively. The Cr layer did not show signs of peeling from the substrate, but initial micro cracks were present within the Cr electroplating layer. Tensile test results confirmed that the Cr electroplated specimens had similar yield strengths and tensile strengths to those of the substrate AISI 1045 steel, but elongation decreased significantly. High cycle fatigue results confirmed that the fatigue limit (~107 cycles to fatigue failure) of the substrate steel was 600 MPa, and the fatigue limit decreased significantly to 500 MPa (13.1 μm thickness) and 325 MPa (53.9 μm thickness) as the Cr electroplating layers were formed. This study also observed fracture surfaces of tensile and high cycle fatigue fractured specimens, and the deformation mechanisms of the Cr electroplated steel were suggested in connection with microstructures. (Received January 4, 2019; Accepted January 28, 2019)

keyword : Cr plating, AISI 1045 steel, indentation, microstructure, tensile, high cycle fatigue

This study on the chlorination of ilmenite ore was carried out using chlorine gas and coke as the chlorinating and reduction agents in a static bed reactor for the selective removal of iron. The effect of the amount of coke, the partial pressure of the chlorine gas and the reaction temperature were investigated. It was found that the iron removal ratio increased with the amount of coke, p_C12 and temperature. As the chlorination reaction progresses, the number of pores in the particles are increased, and the reactant gas can penetrate through the pores. The rate equations of the gas-solid reaction were applied to examine the experimental data. It was confirmed that the rate controlling step changed at 1123 K. At 1123 K and above, the reaction rate was controlled by the chemical reaction, and below 1123 K, it was controlled by the rate of diffusion through the product layer. The activation energy controlled by the rate of diffusion through the product layer was calculated to be 193.18 kJ/mol below 1123 K. (Received October 1, 2018; Accepted January 21, 2019)

keyword : ilmenite, selective chlorination, kinetics, activation energy, titanium dioxide

Aluminum dross results from the re-melting of used aluminum cans, and is a valuable resource containing alumina. In general, aluminum dross contains oxides of Al, Ca, Fe, Mg, Si and Ti and some salts. As a continuation of the previous work to recover pure alumina from the dross, the effect of employing ultrasound wave in the NaOH solution was investigated to improve the leaching percentage of alumina from the mechanically activated dross. The use of ultrasound improved the leaching percentage of alumina from 35% to 60% and resulted in a leaching solution where the purity of aluminate ion was 99%. Among the optimum conditions (5 M NaOH, 50 ℃, 4 h, pulp density of 100 g/L and ultrasonic power 100 W), leaching time had a remarkable effect on the dissolution of alumina in the presence of ultrasound. The combined effect of ultrasound and the addition of CaCl₂ and organic acids to the NaOH solution was also investigated. Roasting of the black dross with CaCl₂ followed by ultrasound leaching did not improve the leaching percentage of alumina. The presence of organic acids in the NaOH solution increased the leaching percentage of alumina as well as silica, and thus was not favorable for recovering pure aluminate solution from the black dross. (Received December 4, 2018; Accepted January 18, 2019)

keyword : black dross, ball milling, NaOH leaching, alumina, ultrasound wave

During the extraction of metal ions from a weak acidic chloride solution by ionic liquids consisting of an organophosphorus extractant and Aliquat 336, the equilibrium pH is sometimes observed to be higher than the initial pH. To compare the hydrogen ion extraction behavior of tertiary and quaternary amines, Alamine 336, Aliquat 336 and their mixture with Cyanex 272, and an ionic liquid (prepared by mixing Cyanex 272 and Aliquat 336, R₄NA) were employed in solvent extraction experiments at a pH range from 0.05 to 5. R4NA showed the highest extraction percentage of hydrogen ions. The initial pH of the chloride solution had a great effect on the extraction of hydrogen ions and the equilibrium pH value produced by these extractants. The order of hydrogen ion extraction was R₄NA>Alamine 336>mixture of Alamine 336 and Cyanex 272. The addition of sodium chloride improved phase separation. The solvent extraction reaction of hydrogen ions with R4NA in the chloride solution was verified by applying a slope analysis method to the extraction data. UV-Vis and FT-IR spectra indicated a strong interaction between the hydrogen ions and R₄NA during the extraction. The obtained results provide some information on the change in solution pH during the extraction of metal ions from weak acidic solution by an ionic liquid (R₄NA). (Received December 31, 2018; Accepted January 18, 2019)

keyword : solvent extraction, hydrogen ion, ionic liquids, aliquat 336, cyanex 272

Amorphous oxide semiconductors have attracted much attention due to their good electrical properties with wide band gaps and low cost process, which are used as backplanes for displays. However, there are some issues regarding low temperature process with high mobility and printing capability. The inkjet method is an attractive technology for high resolution printing with drop-on-demand patterning. Doping is a useful technology to control semiconductor properties. We prepared zinc-doped metal-oxide semiconductors using the inkjet-printing technique at a low temperature of 200 ℃. The In₂O₃ formulation with various doping concentrations of zinc during the inkjet process was thoroughly investigated. For the case of In₂O₃ TFT, the electrical properties were influenced by the concentration of zinc. The lower zinc concentration exhibited better TFT electrical properties due to the suitable suppression of carriers. The threshold voltage of the metal oxide TFT was negatively shifted with zinc doping concentrations. The 0.025M Zn doped In₂O₃ TFT showed the best performance, which was similar to In₂O₃ TFT, and exhibited a more positively shifted threshold voltage under hysteresis and positive bias stress. When the doping concentration of zinc was 0.025 M, the TFT demonstrated a mobility of 1.80 cm²/Vs, an on-to-off current ratio of 1.49 × 10⁷, a threshold voltage of -3.26 V and a subthreshold slope of 0.3 V dec^-1. (Received November 19, 2018; Accepted January 26, 2019)

keyword : inkjet print, metal-oxide, TFT, doping effect

In the present work, MgH₂ was doped with Zn(BH₄)₂, Ni, and/or Ti to improve its hydrogen absorption and release features. Samples were prepared by grinding in a planetary ball mill in a hydrogen atmosphere. To increase the hydrogen absorption and release rates without significantly sacrificing hydrogenstorage capacity the additive percentages were less than 10 wt%. The activation of these samples was not necessary. M2.5Z2.5N had the largest quantity of hydrogen absorbed in 60 min, Q_a (60 min), at the number of cycles, NC, of one (NC=1), followed in descending order by M5Z2.5N2.5T and M1Z. M5Z2.5N2.5T had the highest initial release rate, followed in descending order by M2.5Z2.5N and M1Z. M5Z2.5N2.5T had the highest initial release rate and M1Z had the largest quantity of hydrogen released in 60 min, Q_d (60 min) at NC=2. The sample without Ni (M1Z) had the lowest initial release rate at NC=2. Among these samples, M2.5Z2.5N had the best hydrogen absorption and release properties. Grinding MgH₂ with Zn(BH₄)₂, Ni, and/ or Ti in hydrogen is believed to create defects, induce lattice strain, generate cracks, and reduce the particle sizes. The formed hydrides β-MgH₂, γ-MgH₂, and TiH_1.924 are believed to help produce finer particles in the sample by being pulverized during grinding in hydrogen. The formed Zn and TiH_1.924 and the NaCl remained unreacted during cycling. It was deemed that the formed Mg₂Ni phase contributed to the increases in the initial hydrogen absorption and release rates and the improvement in cycling performance by absorbing and releasing hydrogen itself.

keyword : hydrogen absorbing materials, mechanical milling, hydrogen, microstructure, effects of Zn(BH₄)₂ and transition metal addition

In this study, we analyzed the chemical composition of Al-Si cast alloys from microstructural images, using image recognition and machine learning. Binary Al-Si alloys of Si = 1~10 wt% were cast and prepared as reference images in the dataset used for machine learning. The machine learning procedure was constructed with Inception V3 model. Repeated training to relate the microstructural images to their chemical composition was carried out, for up to 10,000 steps, to increase the reliability of the analysis. The peaks of similarity existed in the dataset with chemical compositions corresponding to the known target composition. The heights of the peaks became higher and the distribution of similarity became sharper with further training steps. This means that the weighted average of the chemical composition approached the target composition with increasing training steps. The correctness of the analysis increased with training steps up to 10,000, then was saturated. It was found that the chemical composition outside the dataset range could not be analyzed correctly. Analysis of the compositions between the datasets showed incorrect but reasonable results. The reliability of the chemical composition analysis using machine learning and image recognition developed in this study will increase when a vast range of reference images are collected and verified. (Received January 10, 2019; Accepted January 28, 2019)

keyword : artificial intelligence, image recognition, chemical composition, microstructure, aluminum alloy

The hot stamping process is beneficial for fabricating high strength automotive parts without spring back. To suppress high temperature oxidation and decarburization, it is necessary to coat the hot stamping steel. In the present work, the performance of galvannealed coated (GA) hot stamped steel was evaluated. During cyclic corrosion tests, the steel substrate began to corrode after the heat treated galvannealed coating fully corroded, because a Zn alloyed coating provides cathodic protection. In order to be applied to the automotive body-in-white, GA coated hot stamped steel must overcome drawbacks such as liquid metal embrittlement (LME) due to the low melting temperature of the Zn, and low or limited weldability due to the thick surface ZnO layer. The results of this study showed that an increase in the α-Fe(Zn) phase fraction of the coating was an effective way to prevent LME. In addition, the resistance spot weldability of GA hot stamped steel can be improved by removing the thick Zn oxide layer by sand blasting. (Received October 17, 2018; Accepted January 18, 2019)

keyword : hot stamping, galvannealed coating, cathodic protection, liquid metal embrittlement, resistance spot welding