발간논문

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For fuse element fabrication with glass-ceramic substrate, photoetching technic was applied. To control copper layer thickness on glass-ceramic substrate, continuous electroless plating rates were monitored using QCM method. Plating rates were 0.6∼l㎛/hr, which value increased with Rochelle Salts addition. At 0.1%HF, 2min etching condition, adhesion between glass-ceramic and copper layer was most favorable. Etching factor value was most favorable at 1.8kgf/min injection pressure and 2.5M/L of etchant concentration. Fuse element design of stepped layer was a little effective for arc duration and preventing fuse temperature from rising suddenly.

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Using a vacuum consumable arc melting furnace, the methods of adding oxygen and iron to pure titanium and the effects of these additives on the mechanical properties of titanium were studied. The chemical composition and mechanical properties of ASTM grads 1, 3 and 4 were used as targets in the experiments. Addition of oxygen in the form of Ti-10wt% O master alloy gave more consistent results than in the form of TiO₂. Iron was added in the form of powder. Under the pressure employed in the main experiment about 20% and 50% of oxygen and iron were found to be a loss in the process of melting, respectively. As a result oxygen and iron contents of the grades 3 and 4 turned out to be a little higher than expected, giving rise to the much higher ultimate tensile strength and yield strength but slightly higher reduction in area than the lower ASTM limits. The grade 1 to which nothing was added was satisfactory both in the chemical composition and mechanical properties.

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Synthesizing conditions of Sr-ferrite by hydrothermal method have been studied as function of process parameters such as SR^(+2) to Fe^(+3), (Fe^(+2)) mole ratio, pH, reaction temperature and reaction time. In the studied range Sr-ferrite powders could by synthesized by using Fe^(+3) as precursor, The optimum condition was as follows ; pH 13, Fe^(+3): SR^(+2)=0.12 : 0.07 mole, reaction temperature : 250℃, reaction time : 60 minutes. The mean particle size of synthesized powders was about 2㎛ with hexagonal plate shape. The saturation magnetization, remanence and coercive force were 62.1 emu/g, 3077G and 1.8KOe respectively.

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The main purpose of this study is to investigate the characteristics of huh temperature exposure on microstructure and fracture behavior of an SiC continuous fiber reinforced Al composite. After the specimens of 6061 Al-SiC fiber composite were exposured at 600℃ for 100∼300 hours in air, microstructure observations, AES in-situ fracture tests, tensile tests, and fracture surface observations were conducted. As the exposure time increased, the interfacial reaction layer grew and was found to be controlled by diffusion. The tensile strength of 6061 Al-SiC fiber composite and pull-out length of the fibers were decreased with increasing exposure time. The interfacial reaction layer and carbon coating layer were fractured in the early stage of deformation and acted on the surface of the fiber as a micronotch, thereby they promoted cracking of fibers.

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Rapidly solidified SmFe7+xMx(M=Mo, V. Ti) compounds were found to crystallize in the Sm(Fe, M)7 based stable magnetic phase by introducing a second transition element into the Sm-Fe binary system. The Sm(Fe, M)7 phase exhibits a high Curie temperature(Te= 355℃) with a quite high intrinsic coercivity(He= 3~6 kOe). The Sm(Fe, M)7 phase remains stable even after annealing once formed during rapid solidification. The primary reason for the high coercive force is due to the fine grain size(2000~8000 Å) of the magnetic Sm(Fe, M)7 matrix phase and the enhanced Curie temperature is attributed to a extended solid-solubility of the additive transition elements in Fe matrix causing a volume expansion of the Sm(Fe, M)7 cell.

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The mechanical properties in a series of low carbon Fe-(15.5∼18.5)%Cr-10%Ni ternary stainless steels with two phase structure of deformation-induced martensite(α′) and reversed austenite(γ) after annealing for 0.6ks in the temperature range of 750 to 1100K were investigated as a function of α′ content and γ stability with transformation-induced plasticity(TRIP). All the steels almost transform to lath α′ from γ by 90% cold rolling and show α′ structure below γ content of 10%. The increase of Cr contents increases γ stability and hence decreases γ′ content in the same reduction of area. The deformed α′ rapidly reversed to γ in the temperature range of 773 to 873K and then the reversion was completed at about 1073K. The reversed γ has a ultrafine grain diameter of 0.5㎛. As a result of ultrafine grain structure of γ, the (α′ + γ) mixed structure was more stabilized. The good combination of high strength and elongation was obtained from the mixed structure containing a higher amount of retained α′ with decreasing Cr content. For example, for 15.5%Cr-10%Ni steel the proof stress of 0.79GPa and ultimate true tensile stress of 1.06GPa were obtained with elongation of 30%. The elongation caused by TRIP in the mixed structure was greatly affected by transformation behavior to α′ from γ in the initial stage of deformation.

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Fatigue crack propagation behavior of a two-phase (α₂+β) Ti₃Al-Nb alloy has been investigated. Various heat treatments were used to vary the volume fraction and the morphology of α₂ phase. Results show that the volume fraction and morphology of α₂ phase have large influence on the fatigue crack propagation behavior. Fine colony structure shows no variation in the fatigue crack propagation rate as α₂ volume fraction changes. On the other hand, equiaxed structure and basket-weave structure shows the increased crack growth resistance as α₂ volume fraction decreases. Such increased crack growth resistance is attributed primarily to a tortuous morphology of crack path which rsuslts in a reduction in the crack driving force from crack deflection and roughness-induced crack closure mechanism. Quantitative metallography and experimental crack closure mesurements are presented to substantiate such interpretations.

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The aging behavior of Cu-bearing HSLA steels was studied by using differential scanning calorimetry (DSC), transmission electron microscopy and hardness tester. Two heat evolution peaks were observed during DSC scans over the temperature range of 25∼590℃ at a heating rate of 5℃/min. The peaks appeared in low(241∼319℃ : HSLA-A, 224∼310℃ : HSLA-B) and high temperature (514℃∼ 590℃ : HSLA-A, 451∼558℃ : HSLA-B) are attributed to the formation of coherent Cu-clusters and noncoherent ε-Cu phase, respectively. And at a rapid heating rate over 7.5℃/min, another peak between these two peaks was observed in the temperature range of 300∼370℃. This peak is conjectured to be due to the formation of 9R martensite structures proposed by Othen et al. It will be necessary further research to identify this peak clearly. It was confirmed that as aging proceeds, the coherent bcc Cu-clusters transform to noncoherent fcc ε-Cu phase. In the case of the aging to peak hardness at 300℃ and 400℃, the coherent Cu-clusters contributed to the hardening. As aging time and temperature increase over peak hardness, noncoherent ε-Cu are formed and hardness decreases. The activation energy due to the formation of coherent bcc Cu-clusters in HSLA-B steel is 55㎉/mole. And those due to the formation of nonchorent ε-Cu phase in HSLA-A and HSLA-B steels are 59㎉/mole and 51㎉/mole, respectively. These are similiar to the activation energy(58㎉/mole) for the solute diffusion of Cu in α-Fe.

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A better fuel efficiency can be achieved by the reaction of CO and H₂ gas produced at the surface of iron bath injected with oxygen gas from lance tip. In this study, the post combustion phenomena in an iron-bath smelter were studied by a numerical method in order to find effective process conditions. The computation simulation for a turbulent gaseous combustion was carried out by the use of k-ε turbulent model, f-g turbulent mixing model and Gibbs energy minimization method for the analysis of the post combustion phenomena in a bath type smelting reduction process. It has been assumed that there is a main nozzle at lance tip and three side nozzles at the side of lance. The effects of lance height, oxygen velocity and side nozzle were studied. the efficiency of post combustion phenomena was found to be better when it happened at higher lance height, lower blowing velocity at the 45˚ angle of side nozzle than other cases.

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The adhesion strength of do magnetron sputtered TiN or Al coatings on polished high speed steel(HSS) substrates have been measured by two new methods. The most critical problem for the application of new developed three point bend test and modified shear test is to prepare a sample with a notch which initiates crack propagation at the coating/substrate interface. Three point bend test and modified shear test provide interface fracture toughness K_c and interface shear strength τ_B, respectively. These data were compared with results obtaind by the scratch test in order to show the applicability of the individual techniques for the determination of the adhesion strength. The results obtaind so far demonstrate that the new methds are good applicable to measuring the adhesion strength of various coating systems.

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