발간논문

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Pseudoelasticity behaviour and passivetion treatment on the shape memory alloys are known to have a great deal of influence on the stability of transformation temperature, shape recovery and improvement of corrosion resistance characteristics in their practical applications. The present work was aimed to examine the pseudoelasticity characteristics by tensile test, and corrosion resistance characteristics by corrosion test in Ti-Ni-X(X-Al, Cu) alloys with/ without passivation treatment. The results of this study are as follows, 1. The results of tensile test for Ti-Ni-X(X-Al, Cu) alloys show that the shape recovery is nearly perfect in martensite state and critical stress for slip is increased with increasing strain. Also, the pseudoelasticity behaviour appears in Ti_(50.0)Ni_(40.0)Cu_(10.0) alloy by unloading at temperature above Af and Ti_(50.0)Ni_(49.0)Al_(10.0) alloy by cold working over 25%. 2. The results of the anodic polarization corrosion test show that the corrosion resistance characteristics of Ti-Ni based alloys can be increased by application of passivation treatment and Ti-Ni-X(X=Al, Cu) alloys has better corrosion resistance characteristics than Ti-Ni equiatomic composition alloy.

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Hg_(0.8)Cd_(0.2)Te epitaxial layers were grown by an LPE(liquid phase epitaxy) process. As-grown Hg_(0.8)Cd_(0.2)Te showed p-type conductivity with a carrier concentration of 8.8×10^(17)㎝^(-3). Annealings of as-grown Hg_(0.8)Cd_(0.2)Te wafers in Hg-atmosphere were performed over the temperature range 200 to 430℃. Annealings below 300℃ resulted in n-type conductivity with carrier concentrations from 10^14 to 10^15 cm^-3 and showed a maximum value at about 260℃. p→in type conversion temperature is thought to be determined by Hg-interstitials rather than residual donor impurities. The phase boundary of Hg_(0.8)Cd_(0.2)Te on the metal-rich side could be obtained.

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On the development of ferrochrome production process by coal, the chromite pellets with carbon(l0, 15 and 20 wt%) were reduced at the temperature range of 1,200 to 1,400℃ for confirming the effects of temperature and carbon content. The chromite pellets with carbon were rapidly reduced at temperature above 1,100℃, and the reduction rate of the chromite pellets with carbon was increased in proportion to the carbon content and temperature. When the chromite pellets are reduced above 1,350℃, the reduction of MgO in gangue mineral becomes significant.

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The electrical resistivity was measured on Al-Li and Al-Sc systems annealed and aged at various temperatures to determine the equilibrium solubility of Li and Sc in aluminium. The residual resistivity for Li and Sc in aluminium was determined to be 0.79μΩ㎝/at% in Al-Li system and 3.8μΩ㎝/at% in Al-Sc system, respectively. These values are influenced to the determination of the solute concentration in matrix. The Li and Sc concentration in matrix due to coarsening of the precipitates linearly increases with t^(-⅓). The Li and Sc concentration in equilibrium with the precipitates of infinite size, i. e, the equilibrium solubility of Li and Sc in aluminium is given by applying Ostwald ripening theory developed by Adrell. The values of the equilibrium solubility of Li and Sc in aluminium were determined to be 4.60 at% at 493K ; 4.93 at% at 513K in AI-Li system and 0.008 at% at 673K ; 0.013at% at 703K ; 0.019 at% at 733K in Al-Sc system, respectively.

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To investigate the effects of the cooling rates of hot bands on the magnetic induction of AIN-based high permeability grain-oriented silicon steels, specimens prepared by vacuum induction melting were hot-rolled to 2.3㎜ in thickness and subsequently cooled with various rates. The cooling rates of hot bands used in this study were 120℃/sec(water quenching), 50℃/sec(oil quenching)and 10℃/sec(air quenching).The dependency of the magnetic induction on the cooling rate was examined in terms of such metallurgical factors as distribution of AIN ppt., microstructures and textures in the hot hands and the decarburized sheets. When the cooling rate was 50℃/sec, the magnetic induction was found to be superior to those obtained at the specimens of the lower and higher cooling rates. In case of the lower cooling rate(10℃/sec), large number of agglomerated AIN precipitates were distributed, resulting in poor magnetic induction. In spite of uniform and fine AIN distribution in the specimens of the higher cooling rate(120℃/sec), more improved magnetic induction was not achieved. The main reason for the deterioration of magnetic induction at the higher cooling rate specimens was thought to be the increase unfavorable texture components in the primary recrystallized sheet., such as (100)〔110〕 and (112)〔110〕.

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In this study, a direct in-situ observation of fracture and crack tip deformation behavior under a wedge loading has been carried out in a scanning electron microscope (SEM) using an HSLA steel and an AISI 4340 steel. A specially designed wedge loading stage was adapted in an SEM for the observation of crack propagation on the surface of small double cantilever beam (DCB) specimens. The results for the HSLA steel with simulated microstructures of the heat affected zone of welding show that the formation of shear bands is primarily responsible for the initiation of microcrack at notch tip and crack propagation. A fracture mechanism for the local brittle zone (LBZ) phenomena has also been identified as the initiation of microvoids by the interfacial decohesion between the ferrite matrix and martensite islands. For the 4340 steel, voids were first observed to form around the large MnS inclusions and the plastic deformation became localized into intense shear bands between these voids as they grew. The failure eventually occurred along these shear bands, although fine microvoids would form around alloy carbides within the shear hands. This in-situ SEM technique has been found very useful for studying the microstructural aspects of crack initiation and crack growth behavior on the surface

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The magnetic properties of Fe-Co-Nd-B magnet were examined using rapidly solidified amorphous powders of Nd (Fe_(0.92)-xCo_xB_(0.08))_(5.5)+y wt% ZrB₂composition. Magnets were prepared by sintering the crystallized powders, and cold isostatic pressing followed by sintering. In the as-spun magnet alloys, coercivity increases as the y increases up to x=0.17 when B/Nd ratio is constant. However, above the x=0.22, the maximum coercivity was obtained when y=2 and iHc=17.4 kOe at that composition. Curie temperature has been found to increase almost linearly with the addition of Co in the range of x=0.07∼0.22, and the maximum Tc was 491℃ when x=0.22. Laves phase, Nd(Fe_(0.5)Co_(0.5))₂always form in the sintered magnet(where x ＞ 0.17) prepared by both powder metallurgy process and cold isostatic pressing followed by sintering.

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The presence of Laves phase has been found in melt spun Fe-Co-Nd-B magnetic alloy as well as in sintered magnet of the same composition. In the melt spun Nd(Fe_(0.92-x) Co_xB_(0.08))_(5.5) alloy, the Laves phase forms after crystallization treatment when x is larger than 0.17. When x corresponds to 0.22 in the sintered Nd(Fe_(0.92-x)Co_xB_(0.08))_(5.5) magnet, the Laves phase of Nd(Fe_(0.5)Co_(0.5))₂corresponds to 15 vol% of the magnet. It is proposed that the presence of certain amount of Laves phase activate the liquid phase sintering to have a high remanence while an excessive Laves phase deteriorates the coercivity in the Fe-Co Nd-B alloys prepared by both rapid solidification and powder metallurgy processing

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This paper describes the results on the formation of iron powders using the waste pickling liquor of steel. 1) The formation of iron powders is easily proceeded when the iron oxides and iron hydroxides precipitated at pH 12-13 in the pickling liquor are reduced for 1 hour under conditions of the flow rate of 0.3 1/min of hydrogen at 750℃. The particle size of the iron powders is in the range of 1-5 ㎛ and they have saturation magnetization of 178.5emu/g at 8 kOe which is equivalent to 82% of the theoretical value of pure Fe. 2) As the result of filtering from the pickling liquor of steel, the residue concentrates of the filtrate solution were conformed to be mainly of Cl, Cr^(3-), Cr^(64), and Zn with their concentrations of 3282, 0.077, 0.084 and 0.035 ppm, respectively. Accordingly. it may not be a problem as a foul water of urban.

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Removal of antimoy, arsenic, tin and bismuth in the system of molten cryolite and lead has been investigated in order to develop a new pyrometallurgical lead refining process. Experiments were carried out in an argon atmosphere using 300g of molten lead containing metal elements, such as Sb, As, Sn and Bi, and oxygen. The temperature for this experiments was fixed at 700℃ to satisfy conditions for both the fluidity of flux and the stability of magnesia crucible. The antimony, tin and arsenic contents in molten lead were reduced rapidly from approximately 1,000 to 40 ppm, 30 ppm and 35 ppm, respectively at added oxygen of 0.2wt%, However, the cryolite flux had little effect on the removal of bismuth. A brief thermodynamic analysis was carried out to estimate the solubility products of impurity oxides in molten lead and experimental results were discussed according to the analysis.

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