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The effects of Ti and Y2O3 addition on the microstructure and mechanical properties of a 15Cr-1Mo steel were evaluated. The 15Cr-1Mo and 15Cr-1Mo-0.3Ti-0.35Y2O3 steels were prepared by a mechanical alloying, hot isostatic pressing and hot rolling processes. Microstructural observation of these steels indicated that the Ti and Y2O3 addition to 15Cr-1Mo steel acted to refine a grain size and to form nano-sized oxide particles such as an Y2Ti2O7. As a result, the yield and tensile strengths at room temperature and at 700 ℃ were considerably enhanced. Considerable improvement of creep properties at 700 ℃ was also observed. These improvements could be mainly attributed to the formation of nano-sized oxide particles as well as the refined grain size. It is thus concluded that the Ti and Y2O3 addition to the 15Cr-1Mo steel would be very effective in improving the mechanical properties especially at high temperatures. (Received December 05, 2014)

keyword : 15Cr-1Mo steel, oxide dispersion strengthend, ODS, oxide particles, Y2Ti2O7

This paper investigates with the mechanical properties of Al alloy samples coated by plasma electrolytic oxidation (PEO) using a phosphate electrolyte with a Na2WO4 solution. Under an A Ccondition of 60Hz, PEO coatings were applied for 300 seconds at a current density of 100mA/cm2. Microstructural observations of the PEO-coated samples revealed that the size and fraction of the micro-pores remained nearly constant while WO3 and W were additionally in corporated in the oxide layer using the Na2WO4 solution. During PEO coating, the Na2WO4 solution dissociated into Na+ and WO4 2- and the high dielectric voltage exceeding the ignition voltage activated the electrochemical reactions of WO4 2- in the anode, leading to the formation of WO3 and W. The incorporation of WO3 and W is expected to lead to enhancement of the hardness and wear resistance of the PEO-coated Al sample. (Received October 08, 2014)

keyword : Al alloy, coating, plasma electrolytic oxidation, mechanical properties, scanning electron microscopy, SEM

The effect of sputter target power and substrate bias voltage on the deposition of silicon carbide thin film was investigated. Films were deposited using unbalanced magnetron sputtering method with sintered silicon carbide target connected to a direct current electric power from 50 to 200 W. Ar gas was used as a sputtering gas. The distance between the target and the substrate was 7.5 cm and the deposition pressure was 3 m Torr. We used a Si single crystal wafer as a substrate, which was heated at 450℃. The substrate bias voltage was varied between 0 and -100V. Deposited films consisted of columnar grains with several nm width, which formed a texture whose orientation was influenced by the bias voltage. Most of the grains were crystalline which was confirmed by transmission electron microscopy. The hardness measured by a nano-indentation method showed a super-hardness of about 50 GPa. (Received September 17, 2014)

keyword : thin films, sputtering, microstructure, transmission electron microscopy, TEM

Nanocomposite CrZrSiN thin films were deposited with various substrate bias voltages from 0 to -200 V using unbalanced magnetron sputtering. The crystalline structure, microhardness, microstructure, and adhesion properties of the CrZrSiN thin films were evaluated by X-ray diffraction, Fischer scope, field-emission scanning electron microscopy, and a scratch tester. The surface roughness and deposition rate decreased with an increase in the substrate bias voltage. The substrate bias voltage increased and the hardness increased to 36 GPa at -100 V, then decreased to 32 GPa as the substrate bias voltage further increased to -200V. The CrZrSiN thin films maintained their hardness up to 800℃ while the hardness of CrZrN film decreased rapidly over 500℃. The critical load (Lc3) increased from 8 N to 35 N up to a substrate bias voltage of -100 V, while the critical load decreased to 8 N with further increase of the substrate bias voltage. (Received February 07, 2015)

keyword : thin films, plasma deposition, mechanical properties, transmission electron microscopy, TEM

Ti nanopowder was prepared by high energy ball milling. The milled Ti and CNT powders were then simultaneously synthesized and consolidated using high frequency induction heated sintering (HFIHS) within one minute under applied pressure of 80 MPa. The milling did not induce any reaction between the constituent powders. Meanwhile, HFIHS of the Ti-CNT mixture produced a Ti-TiC composite according to the reaction (0.94Ti + 0.06CNT→ 0.88Ti + 0.06TiC, 0.88Ti + 0.12CNT→ 0.76Ti + 0.12TiC). Highly dense nanocrystalline Ti-TiC composites with a relative density of up to 99.5 % were obtained The hardness and the fracture toughness of the dense Ti-6.4 mole% TiC and Ti-13.6 mole% TiC produced by HFIHS were also investigated.

keyword : rapid sintering, composite materials, nanomaterials, mechanical properties

The alloying behavior of Ni-Co-Cr nano-sized powders was studied via a polymer solution approach as a substitute method for mechanical alloying processes. Metal nitrate salts were dissolved in distilled water with a 5 wt% polyvinyl alcohol (PVA) solution, and the homogeneous sols were dried to gels and heated under a reducing atmosphere consisting of an argon-hydrogen (Ar-N2) gas mixture. In this study, the effects of processing parameters, specifically PVA content, composition of the gas mixture, and heating temperature, on alloying behavior were examined. The PVA ensured a homogeneous distribution of metal ions in the solution and it resulted in nano-sized metal particles after heating at 500 ℃. In particular, nano-sized Ni particles were oxidized when they were exposed to air after the heat treatment. However, a Ni-Co alloy was observed at higher heating temperature of 700 ℃, showing significant particle growth. Nano-sized Cr particles were not alloyed and instead oxidized to Cr2O3, showing a relative smaller particle size when they were exposed to air after heating at 700℃ and higher. In general, the metal particle sizes decreased as the H2 concentration increased in the gas mixture. (Received December 08, 2014)

keyword : alloys, powder processing, crystallization, transmission electron microscopy, TEM, polymer solution route

A uniaxial hot compression test was carried out under a strain rate range of 10-3~1/s at a temperature range of 533~653K to evaluate the flow stress features of ZAM631 Magnesium (Mg) alloy. The peak value of flow stress increased with increasing strain rate at constant temperature. In contrast, an increase in the deformation temperature at a constant strain rate resulted in a decrease of the peak value of the flow stress. Microstructure examination of the specimens showed that dynamic recrystallization (DRX) took place in both compressed and extruded specimens. The flow stress information was further used to simulate the indirect extrusion process for the ZAM631 alloy. Non-isothermal finite element simulations were carried out by a rigid plastic finite element method. Extrusion deformation behaviors such as temperature, strain rate and strain were compared at different locations of the deformed billet during extrusion. (Received December 30, 2014)

keyword : alloys, extrusion, microstructure, compression test, finite element method

In the present study, extraction and separation possibilities have been established for boron and lithium from Uyuni salar brine. Diols were shown to be effective extraction reagents for boron. The present scientific study was developed with 2, 2, 4-trimethyl-1, 3-pentanediol (TPD) as an extractant system. For fixing the diluent system, various diluents were tested and it was found that chloroform is a better diluent for boron extraction. Further, experimental studies on the extraction equilibrium time, pH influence, and phase ratio effects on boron extraction were conducted and the conditions for boron recovery and lithium separation were optimized. The McCabe Thiele diagram was established to optimize the number of extraction stages for boron extraction. Finally, stripping studies of boron from the loaded organic phase using various salts were performed. Received October 31, 2014)

keyword : boron, extraction, recovery, separation, uyuni salar brine, lithium, diol

Used was a sample with a composition of 86 wt% MgH2+10 wt% Ni+2 wt% NaAlH4+2 wt% Ti prepared by milling under H2 (reactive mechanical grinding) and then kept in a glove box for two months. The variations of its hydrogen-storage characteristics with hydriding-dehydriding cycling were investigated and compared with those of a sample just after reactive mechanical grinding. The hydriding-dehydriding cycling was performed between hydriding (at 593 K under 12 bar H2) and dehydriding (at 623 K in vacuum). The quantities of hydrogen absorbed for 2.5, 5, 10, and 60 min increased rapidly as the number of cycles, n, increased from n=1 to n=3. This is believed to be due to the predominance of the removal of the adsorbed gases and the destruction of oxide layers among the effects of hydriding-dehydriding cycling. From n=3 to n=15, Ha (2.5 min) and Ha (5 min) increased slowly and Ha (10 min) and Ha (60 min) decreased slowly. (Received July 15, 2014)

keyword : hydrogen absorbing materials, mechanical alloying/milling, microstructure, scanning electron microscopy, SEM, transition metals and sodium alanate-added MgH2

In this study, we grew TiO2 nanorods on TiO2-film buffered FTO substrate using modified chemical bathdeposition (M-CBD). The TiO2 buffer layer was grown by spin coating method with different RPM (revolutions per minute) values and deposition cycles. We investigated the effects of the RPM values and the deposition cycles on the morphological, structural and photoelectrochemical properties of TiO2 nanorods. In this work, we have also found that the morphological and structural properties of TiO2 nanorods affected the photoelectrochemical properties of TiO2 nanorods. And the maximum photocurrent density of 0.34 mA/cm2 at 0.6V (vs.SCE) was obtained from the buffer layer deposition process condition of 4,000 RPM and two-times buffer layer depositions. (Received July 29, 2014)

keyword : photoelectrochemical, buffer layer, spin coating, nanorods, photocurrent density, semiconductors, chemical synsthesis, coating, crystal structure, scanning electron microscopy, SEM