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The effect of cold rolling on the microstructural evolution in 22Cr-0.2N micro-duplex stainless steel was investigated. The 22Cr-xNi-yMn-0.2N duplex stainless steel plates with various Ni and Mn contents were fabricated. The steels were vacuum induction melted and hot rolled, followed by annealing treatment at the temperature range of 1000-1100℃, in which both the austenite and ferrite phases were stable. The volume fraction of the ferrite phase depending on the alloy compositions of Ni and Mn increased with an increase in the annealing temperature. Grain growth in the ferrite phase occurred markedly after cold rolling followed by annealing, while fine recrystallised grains were still found in the austenite phase. A large number of martensite laths was found in the microstructure of cold rolled steels, which should be formed by straininduced martensite from the austenite phase. The intersections of stacking faults were revealed by TEM observation. The volume fraction of the martensite phase increased with an increase of the reduction ratio by cold rolling.

keyword : Duplex stainless steel, microstructure, deformation

TiAlCN coatings with various C contents were synthesized by unbalanced magnetron sputtering. The characteristics, the crystalline structure, surface morphology, hardness, and friction coefficient of the coatings as a function of the C content were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), a microhardness tester, and a wear test. In addition, their corrosion behaviors in a deaerated 3.5 wt% NaCl solution at 40℃ were investigated by potentiodynamic polarization tests. The results indicated that the Ti14.9Al15.5C30.7N38.9 coating had the highest hardness, elastic modulus, and a plastic deformation resistance of 39 GPa, 359 GPa, and 0.55, respectively, and it also had the lowest friction coefficient of approximately 0.26. Comparative evaluation of the TiAlCN coatings indicated that a wide range of coating properties, especially coating hardness, could be obtained by the synthesis methods and processing variables. The microhardness of the coatings was much higher than that from previously reported coating using similar magnetron sputtering processes. It was almost as high as the microhardness measured from the TiAlCN coatings (~41 GPa) synthesized using an arc ion plating process. The potentiodynamic test showed that the corrosion resistance of the TiAlCN coatings was significantly better than the TiAlN coatings, and their corrosion current density (icorr), corrosion potentials (Ecorr) and corrosion rate decreased with an increasing C content in the coatings. The much denser microstructure of the coatings due to the increased amount of amorphous phase with increasing C contents in the coatings could result in the the improved corrosion resistance of the coatings.

keyword : TiAlCN coatings, thin films, sputtering, corrosion, wear

Recently, as the interest in improving energy efficiency has grown, the demand for vehicle and machine parts that are resistant in high temperature corrosive conditions and abrasive environments has increased. Pack chromizing treatment of sintered steels is a profitable method that satisfies both corrosion resistance and low friction properties. Since austenitic stainless steels have good corrosion resistance but low mechanical hardness, if they are replaced by sintered steel parts with pack chromizing treatment, all the desirable properties such as low price, easy molding, high hardness, low frictional coefficient, and high corrosion resistance, can be obtained. The higher corrosion resistance of the chromized parts over that of the austenitic stainless steels was acquired by coating chromium carbides and a thin chromium oxides layer on the surface. Moreover, the surface morphology of chromized parts, which were composed of chromium rich phases and hardened chromium carbides by diffusing and alloying, had a peak-and-valley shape so that the dimple effect by the wrinkled morphology and high hardness induced a low friction coefficient.

keyword : Alloys, coating, wear, atomic force microscopy, AFM, sintered steel

Nano powders of Al2O3 and TiO2 compounds made by high energy ball milling were pulsed current activated sintered for studying their sintering behaviors and mechanical properties. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Nano-structured Al2TiO5 with small amount of Al2O3 and TiO2 was formed by sintering at 1300℃ for 5 minute, in which average grain size was about 96 nm. Hardness and fracture toughness of the nano-structured Al2TiO5 compound with a small amount of Al2O3 and TiO2 were 602 kg/mm2 and 2.6 MPa.m1/2, respectively.

keyword : Compound, nanostructure, sintering, Al2TiO5, mechanical properties

Direct reduction of Ta2O5 using liquid calcium was investigated. The experiment was conducted in a closed stainless steel chamber in an Ar atmosphere for 5-120 minutes. Most of Ta2O5 was reduced to a-Ta in 30 minutes above 1173 K and at a molar ratio of Ca and Ta2O5 above 10. The particles size increased with the reaction temperature, but it did not change much above 1223 K. The oxygen content of metal Ta was about 1 wt%.

keyword : Tantalum, Ta2O5, calcium, calciothermic, direct reduction

The microstructure, chemical composition, and lead isotope ratio of the Buddhist bell of Yongmoon Mountain Sangwonsa temple, which was selected as one of the three great bells of Korea by Japanese historians, were analyzed in order to estimate the origin of the material and the time of casting. The microstructure of the temple bell was composed of a copper matrix phase with α, a face centered cubit lattice structure, a δ phase with Cu41 (Sn, Ag, Sb)11 as the chemical structural formula, dispersed lead and Cu2S particles, and locally agglomerated fine particles. Through analysis of the chemical composition of the bell, a criterion (Pb: 0-3.0 wt%, Sn: 10-15 wt%) for distinguishing the bells of the Shilla dynasty from the bells of the Koryo Chosun dynasty is proposed, Examining the lead isotope ratio of 207Pb / 206Pb and 208Pb / 206Pb of the Buddhist bell of Sangwonsa temple proved that the bell was fabricated using raw materials in South Korea, which led to the conclusion that the bell was cast in Korea and the top board of the bell has been damaged by an unknown individual. The criteria of distinguishing the bells from the Shilla dynasty from the bells of the Koryo Chosun dynasty presented for the first time in this research is expected to aid in identifying and estimating the previously unclear production years of other bells.

keyword : Bell of Yongmoon Mountain Sangwonsa, microstructure, chemical composition, lead isotope ratio, criteria for distinguishing the bells

The effect of an AlN additive on the thermoelectric properties of SiC ceramics was studied. Porous SiC ceramics with 48-54% relative density were fabricated by sintering the pressed a-SiC powder compacts with AlN at 2100-2200˚C for 3 h in an Ar atmosphere. In the undoped specimens, the Seebeck coefficients were positive (p-type semiconducting) possibly due to a dominant effect of the acceptor impurities (Al, Fe) contained in the starting powder. With AlN addition, the reverse phase transformation of 6H-SiC to 4H-SiC was observed during the sintering process. The electrical conductivity of the AlN doped specimen was larger than that of the undoped specimen under the same conditions, which might be due to a reverse phase trans-formation. The Seebeck coefficient of the AlN doped specimen was also larger than that of the undoped specimen. The density of specimen and the amount of addition had significant effects on the thermoelectric properties.

keyword : A-SiC, AlN-doped, microstructure, electrical conductivity, seebeck coefficient, power factor

Al-doped ZnO (AZO) thin films were grown on quartz substrates by the sol-gel method. The effects of the Al mole fraction on the structural and optical properties of the AZO thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-VIS spectroscopy. The particle size of the AZO thin films decreased with an increase in Al concentrations. The optical parameters, the optical band gap, absorption coefficient, refractive index, dispersion parameter, and optical conductivity, were studied in order to investigate the effects of Al concentration on the optical properties of AZO thin films. The dispersion energy, single-oscillator energy, average oscillator wavelength, average oscillator strength, and refractive index at an infinite wavelength of the AZO thin films were affected by the Al incorporation. The optical conductivity of the AZO thin films also increased with increasing photon energy.

keyword : Zinc oxide, Al doping, Sol-gel, thin films, optical properties, scanning electron microscopy

Samples with compositions of 80 wt% Mg-14 wt% Ni-6 wt% Fe2O3 and 80 wt% Mg-14 wt% Ni-6 wt% Ti were prepared by mechanical grinding under hydrogen (reactive mechanical grinding). Their hydrogen absorptions during reactive mechanical grinding were examined. TGA and BET analysis were employed to investigate the hydrogen storage properties of the prepared alloys. TGA analysis of the Mg-14Ni-6Fe2O3 showed an absorbed hydrogen quantity of 6.91 wt% while that of Mg-14Ni-6Ti was 2.59 wt%. BET analysis showed that the specific surface areas of Mg-14Ni-6Fe2O3 and Mg-14Ni-6Ti after reactive mechanical grinding were 264 m2/g and 64 m2/g, respectively. The larger absorbed hydrogen quantity and the larger specific surface area of Mg-14Ni-6Fe2O3 after RMG than those of Mg-14Ni-6Ti after RMG showed that the effects of Fe2O3 addition are much stronger than those of Ti addition during reactive mechanical grinding.

keyword : Hydrogen absorbing materials, mechanical alloying/milling, microstructure, scanning electron microscopy, SEM, Fe2O3 or Ti addition

A dense nanostructured TiN-AlN composite was prepared from high-energy ball milled TiN-AlN mixture powders by pulsed current activated sintering (PCAS). A highly dense TiN-AlN bulk composite was obtained within 2 minutes at 1500℃ with the simultaneous application of 80 MPa pressure and pulsed current. The fine crystalline structure of the TiN-AlN mixture, which was obtained by high-energy milling, was effectively maintained during PCAS and resulted in the enhancement of the mechanical properties. The micro hardness and fracture toughness of TiN-AlN composite were 1780 kg/mm2 and 5 MPa.m1/2, respectively. The mechanical properties were higher than monolithic AlN or TiN.

keyword : Composites, nanostructured materials, sintering, mechanical properties