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The effect of Ni and Hf content on the microstructure, phase transformation, and hot workability of Ti-Ni-Hf high-temperature shape memory alloys (SMAs) were investigated. Twelve different Ti-xNi (x=49, 50.2, 50.5, 50.8 at%)-yHf (y=10, 12, 14 at%) SMA ingots were prepared by vacuum arc re-melting, and then analyzed by SEM, DSC, TEM, and XRD after heat treatment. Precipitation behavior was mostly dependent on Ni content rather than Hf content. The effect of homogenization treatment on the particle precipitation and phase transformation behavior was studied. We also found that hot workability was greatly dependent on the solidification structure of the austenite phase. (Received March 2, 2014)

keyword : shape memory alloys, phase transformation, precipitation, homogenization, texture

Indirect calibration of a nanoindentation system was performed by deriving a reference loading curve. This reference load-depth relationship was accomplished by assuming a perfect nanoindentation test on an ideal reference material; if all components in a nanoindentation system are well calibrated and the reference material has unique hardness and Young’s modulus, the indentation depth can be formulated with a function of the indentation load having two parts of contact and surrounding elastic depths. Substituting both the hardness and Young’s modulus of a fused silica into the derived function, the reference loading curve was plotted and directly compared with experimental data of the fused silica measured by two commercial nanoindenters. All indentation loading curves showed leftward shifts compared to the reference loading curve, and this is discussed, offering two reasons for the result, system compliance and indenter apex geometry.(Received January 6, 2014)

keyword : amorphous materials, mechanical properties, hardness test, indentation, calibration

A7003 alloy underwent T5 and T6 heat treatments (T5: 90 ℃ for 5 hrs and 150 ℃ for 16 hrs; T6: 470 ℃ for 3 hrs followed by artificial aging at 80 ℃ for 14 hrs, and 120 ℃ for 42 hrs); the tensile and fatigue properties of the treated materials were then examined. High-cycle fatigue tests were conducted at R (stress ratio)=0.1, and f (frequency)=20 Hz. The average grain size of A7003-T5 alloy was 3.8 μm, and that of A7003-T6 alloy was 4.1 μm. Both of the alloys were found to have MgZn2 (?), Fe-based intermetallic phases in their aluminum matrix. A7003-T6 alloy had finer MgZn2 (?) phases distributed more evenly than A7003-T5 alloy. Tensile test results showed that A7003-T6 alloy had higher strength (Y.S. & T.S.) and lower elongation compared to those of A7003-T5 alloy. High cycle fatigue results showed that A7003-T6 alloy had longer fatigue limit (320 MPa) than that (290 MPa) of T5 alloy. A7003-T6 alloy was found to perform better in all other fatigue stress conditions, too. Based on the observation of tensile and fatigue fracture surfaces, the correlations between microstructures made by heat treatments and mechanical/fatigue properties were also investigated along with the fatigue deformation mechanism of A7003 alloy.(Received April 22, 2014)

keyword : alloys, extrusion, Al7003, tensile test, scanning electron microscopy, microstructure

The effect of aging heat treatment was investigated in a HT9 steel for the Sodium-cooled Fast Reactor (SFR) fuel cladding tube. Aging heat treatment was carried out at 660℃ for up to 7000 hours and then microstructural analysis and mechanical tests, namely tensile and vickers hardness tests, were performed. The results showed that size of the carbide and lath were increased after aging, while the size of the prior austenite grain was not changed. Both the strength and hardness were decreased with aging, and these tendencies were similarly represented after the 3000 hours of aging. Based on the experimental results, the tempering parameter was modified and discussed with aging conditions.(Received May 16, 2014)

keyword : metals, aging, mechanical properties, HT9 steel

A sample with a composition of 95 wt% Mg-5 wt% TiCl3 (named Mg-5TiCl3) was prepared by reactive mechanical grinding, and its hydriding and dehydriding properties were examined. The activation of Mg-5TiCl3 was not required. Mg-5TiCl3 had an effective hydrogen-storage capacity of about 6.2 wt%. At the first cycle (n=1), the sample absorbed 5.77 wt% H for 5 min, 6.07 wt% H for 10 min, 6.17 wt% H for 30 min, and 6.19 wt% H for 60 min at 573 K under 12 bar H2. At n=1, the sample desorbed 0.03 wt% H for 2.5 min, 0.13 wt% H for 30 min, and 0.35 wt% H for 60 min at 573 K under 1.0 bar H2. Mg-5TiCl3 after reactive mechanical grinding contained Mg, β-MgH2, γ-MgH2, and TiH1.924. The XRD pattern of Mg-5TiCl3 dehydrided at the 4th hydriding-dehydriding cycle at 423-573 K contained β-MgH2, Mg, MgO, and TiH1.924. Mg-5TiCl3 had a higher initial hydriding rate and a larger quantity of hydrogen absorbed for 60 min than Mg-5TaF5, Mg-10Fe2O3, Mg-10MnO, and Mg, the hydrogen-storage properties of which were previously reported.(Received February 12, 2014)

keyword : hydrogen absorbing materials, mechanical alloying/milling, scanning electron microscopy (SEM), X-ray diffraction, TiCl3 addition

We studied the physical properties of CuInSe2(CIS) thin films fabricated using a cracked selenium (Se) source in the selenization processes. The crystalline CIS films were characterized by energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and a Hall effect measurement system. Precursors with the same amount of Se were prepared with a co-sputtering system equipped with Se Knudsen cells. The precursors were heated under four kinds of Se pressure conditions (0.02, 0.1, 1, 2 Pa) for 15 minutes at 425 ℃, which is a selenization process for crystalline CIS films. The low Se pressure conditions in selenization processes were more reactive than the higher Se pressure conditions. The Se pressure in selenization tends to increase the CIS grain size, which was confirmed by investigation of the surface morphology of SEM and of the crystal size in the XRD. We found that the Se pressure in the selenization processes influences the preferred crystalline orientations and the electrical properties of CIS thin films.(Received May 8, 2014)

keyword : solar cells, sputtering, interfaces, X-ray diffraction, CuInSe2 film

In this study, we verify the relationship among the catalytic effect, electrical conductivity, and structure of vanadium borophosphate glasses that have a coincidence of BO3 and BO4 and a coincidence of V4+ and V5+. We prepared vanadium borophosphate glasses with various compositions, given by 70V2O5- xB2O3-(70-x) P2O5(x=0-10mol%), and analyzed the catalytic effect, electrical conductivity, FT-IR spectroscopy, X-ray photoelectron spectroscopy, thermal properties, density, and molar volume. In V2O5-P2O5 binary glasses, the electrical conductivity increased from 0. 4073 × 10?7/Ω to 20.167 × 10?7/Ω but the catalytic effect for oxidation reactions of linoleic and stearic acid decreased with an increasing B2O3. From these results, we can deduce that electrons shift from V4+ to V5+ with an increasing B2O3. FT-IR analysis showed an occurrence peak at 680 cm?1 and XPS analysis showed that a V4+ decrease and a V5+ increase are the basis of the electron shift from V4+ to V5+. We also verify the structure and change in properties from quantitative properties such as thermal properties, density, and molar volume.(Received May 16, 2014)

keyword : glasses, solidification, electrical conductivity, thermal analysis, catalytic effect

In this study, we re-verify the relationship between the structure and properties of cadmium phosphate glasses through the study of the optical and binding properties. We prepared cadmium phosphate glasses with various compositions, given by xCdO-(100-x)P2O5 (x=10-55 mol%), and analyzed their Fourier transform infrared spectra, X-ray photoelectron spectroscopy, optical band gap and other properties such as dissolution rate, thermal expansion coefficient, glass transition temperature, glass softening temperature. We found that the optical band gap and glass transition temperature decreased and thermal expansion coefficient increased with increasing CdO content. These results suggest that CdO acts as a network modifier in binary phosphate glass and weakens its structure. Futher, we found that the chemical durability and optical band gap is rapidly changed when the CdO content is more than 40 mol%. From these results, we can deduce that ionic bonding increases and covalent bonding decreases when the CdO content is more than 40 mol%.(Received Mary 16, 2014)

keyword : glasses, solidification, optical properties, thermal analysis, fourier transform infrared spectra

The energy conversion efficiency (ECE) of the Pt counter electrode (CE) was improved by microwave irradiation for 0-40 seconds. A 0.45 cm2 sized device with a glass/FTO/blocking layer/TiO2/dye/ electrolyte/microwave-100 nm Pt/glass was prepared. The photovoltaic properties, such as the short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and energy conversion efficiency (ECE), were characterized using a solar simulator and potentiostat. The stress of the Pt layer was examined by X-ray diffraction. The interfacial resistance and catalytic activity were examined by impedance and cyclic voltammetry. The change in surface roughness was examined by atomic force microscopy. The 100 nm Pt CE after microwave irradiation for 10 seconds showed a large compressive stress of over ?4.43×10?3. The measured energy conversion efficiencies of the dye-sensitized solar cell devices with the Pt only and microwave Pt (10 seconds) counter electrodes were 4.60% and 5.72%, respectively. As the microwave irradiation time was increased to more than 10 seconds, the ECE decreased to that of the as-deposited Pt CE due to a decrease in the surface area of the Pt layers. These results suggest that the use of a Pt catalytic layer with the appropriate microwave irradiation conditions may improve the efficiency of dye-sensitized solar cells.(Received June 2, 2014)

keyword : solar cells, sputtering, optical properties, solar simulator, microwave

Effect of elements Si, Mn, Sn on tensile and corrosion properties of Mg-4Zn-0.5Ca alloys were investigated. The results of tensile properties show that the yield strength, ultimate tensile strength and elongation of Mg-4Zn-0.5Ca alloy increased significantly with the addition of 0.6 wt% Mn. This is considered the grain refinement effect due to addition of Mn. However addition of 0.6 wt% Si decreased yield strength, ultimate tensile strength and elongation. The bio-corrosion behavior of Mg-4Zn-0.5Ca-X alloys were investigated using immersion tests and potentiodynamic polarization test in Hank``s solution. Immersion test showed that corrosion rate of Mg-4Zn-0.5Ca-0.6Mn alloy was the lowest rate and addition of 1.0 wt% Sn accelerated corrosion rate due to micro-galvanic effect in α-Mg/CaMgSn phases interface. And corrosion potential (Ecorr) of Mg-4Zn-0.5Ca-0.6Mn alloy was the most noble among Mg-4Zn-0.5Ca-X alloys.(Received April 2, 2014)

keyword : biomaterials, casting, corrosion, scanning electron microscopy (SEM), magnesium alloy