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The relationship between the tensile properties and the microstructure in a dual phase steel containing 0.2%C and 1.5%Si was studied. Specimens were intercritically annealed at 790℃ for 8min. and then, isothermally transformed at 320∼480℃ for various times. The effect of the retained austenite on the tensile properties and TRIP phenomena was studied. The steels examined in the present investigation were found to exhibit upper and lower bainites. In the lower bainite region, morphology of the retained austenite was finely dispersed film type, but, in the upper bainite region, bulky type retained austenite was examined. Steels transformed in the lower bainite region showed better tensile property than steels transformed in the upper bainite region, because film type retained austenite in the lower bainite was more stable than bulky type retained austenite in the upper bainite during deformation of the specimens.

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The mechanical behaviors of a wrought high strength aluminium alloy containing 4.5 Zn, 2.0 Mg, and 0.12 Zr in wt.% have been examined as a function of the concentration of chromium in the range of 0.02∼0.2wt.%. It has been reported that the chromium forms Cr-dispersoids called E-phase(Al_(18)Mg₃Cr₂) in AI-Zn-Mg alloys. The size of these Cr-dispersoids is known to be depended on the content of chromium. The alloy containing 0.1 wt.% Cr has the small spherical Cr-dispersoids. However, the Cr-dispersoids are long rod-Like in the alloy with 0.2wt.% Cr. Because these Cr-dispersoids inhibit the motion of dislocations within the grain, the strength is increased. However, increment in strength is higher in the alloy with 0.1 wt.% Cr than in that with 0.2 wt.% Cr. The reason of the above phenomena may be resulted from the decrease of planar slip and increase cross slip due to the spherical Cr-dispersiods in the alloy with 0.1 wt.% Cr. The fracture toughness of the alloy depends on the shape and size of the Cr-dispersoids. The small spherical dispersoids increase the fracture toughness but the long rod-like dispersoids reduce it.

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Effects of SO₄^=, Cl^- and SCN^- concentration on the corrosion behavior of sensitized AISI 316 stainless steel in various aqueous electrolytes were investigated electrochemically. Passive film breakdown potential (E_b) and induction time(IT) for pit nucleation of solutionized-sensitized AISI 316 stainless steel specimens were measured upon exposure to deaerated solution with different SO₄^=, Cl^- and SCN^- concentrations at 25℃ After the anodic polarization treatments, the morphology of corrosion pits was inspected by scanning electron microscopy. It was found that E_b gradually increased as more H₂SO₄ was added to 0.5M HCl solution and the highest E_b was obtained when 0.3M H₂SO₄ was added. Then E_b slowly decreased as SO₄^= concentration increased. In the both cases of Cl^- addition to 0.5M H₂SO₄ and SO₄^= addition to 0.5M KSCN, E_b decreased. With increasing sensitization, IT and E_b decreased in electrolytes containing Cl^-, SO₄^= and SCN^-. In addition, IT increased in the case of SO₄^= addition to 0.5M HCl solution. The morphology of pits produced by Cl^- addition showed irregular shape and smooth shape by SO₄^= addition. The SCN^- resulted in small pits and intergranular corrosion.

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Seven kinds of sinters having different basicities were reduced at 900℃ with either 90%CO10%CO₂ gas mixture or Hz gas. The data were analyzed by the one-irrtertace unreacted-core model and the reduction rate changes by with CO and H: were compared. The results are summarized as follows;(1) The average reduction rates in H₂, were calculated from reduction curves between the reduction degree of 40% and 60% were 5∼7 times than that in CO except for one kind of sinter. (2) The ratio of the chemical reaction rate constant (Kc) between CO reduction and Hz reduction showed little difference except for one kind of sinter. The rate constants of Hz reduction were 2∼3 times higher than those of CO reduction. (3) the ratio of the effective diffusivity in the product layer (De) between CO reduction and H₂ Reduction was different among various sinters. The values of the effective diffusivity of H₂ reduction were 4∼14 times higher than Chose of CO reduction.

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The liquid phase sintering behaviors of WC-Co compacts with milled and unmilled WC powders and large Co powder had been observed and compared to those observed previously in W-Ni and Fe-Cu alloys which show spherical grains. The compacts with milled WC powder show steady densification even during heating to the liquid phase sintering temperature. The compacts with unmilled WC powders show pronounced local densification during the liquid phase sintering, producing large pores. This observation is attributed to the rearrangement of the polyhedral grains under asymmetric capillary forces. In the compacts with large Co powder, large pores are initially produced when the Co particles melt and flow into the surrounding fine capillaries, but during the subsequent sintering treatment, the pores are filled by the Co-rich liquid as has been observed in W-Ni and Fe-Cu powder compacts. The mechanism of the pore filling process in WC-Co is expected to be quite complex because of the polyhedral grain shape.

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The purpose of this study is to obtain basic information on the density, the coefficient of thermal expansion and the thermal conductivity of compocasted Al-xSi-2 Cu-1 Mg/y Al₂O₃,(x=6, 12, 18, y=0∼10wt.%) composites. With the content of Al₂O₃ particaes, the density, the thermal expansion coefficient and the themal conductivity decrease. The coefficient of thermal expension between 20 and 300℃ is 22×10^(-6)∼19.7×10^(-6)/℃ for the alloy with 0wt.% Al₂O₃ and 17.8×10^(-6)∼15.4×10^(-6)/℃ for the composite with 10wt% Al₂O₃. The thermal conductivity at 300℃ is 121∼169 w·m^(-1)·k^(-1) for the alloy(y=0) and 99∼120 w·m^(-1)·k^(-1) for the composite(y=10)

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The effect of dopants, rolling amount, annealing temperature and texture on the production of molybdenum single crystals by secondary recrystallization was investigated systematically. Secondary recrystallization of every doped specimen occurred at a temperature higher than 2100℃ In the case of the specimen doped with Ca(OH)₂, single crystals were made at the lowest temperature of 2100℃ In the specimens doped with Mg(OH)₂ and MgO rolled to 95%, however, single crystals were not made when annealed at 2100℃ and 2200℃ , respectively. The orientation of textures of rolling and primary recrystallization was {100}(hkl). The orientation of the single crystal deviated from {100}$lt;hkl$gt; by 1020°.

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Ta₂O₃, thin films on p-type (100) Si substrate were prerared by thermal oxidation at 450∼650℃ of DC magnetron sputtered tantalum films. Capacitance and relative dielectric constant of the Ta₂O_5 film were found to be 1.71 fF/μ㎡ and 31.7, respectively, at 500℃, 2h. Leakage current had a minimum value of 5×10^(-6)A/㎠ for 1MV/㎝ at 600℃, 1h. It was found that the 650℃ 1h oxidation treatment induced formation of crystalline δ-Ta₂O_5 of hexagonal structure The dc conduction characteristics of Ta₂O_5 films can be interpreted by assuming Poole-Frenkel conduction. the dielectric properties of the tantalum oxide films were improved by proper oxidation treatments.

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PLZT powders, one of ferroelectric ceramics, were prepared from the following raw materials of Pb(NO₃)₂, La(NO₃)₃·6H₂O, ZrOCl₂·8H₂O, and TiCl₄. Each one of the 1st three components were dissolved in deionized water and the last one was dissolved in ethyl alcohol. In order to avoid the fromation of PbCl₂, a two-stage coprecipitation method was used : coprecipitating the complex hydroxide of lanthanum, zirconium, and titanium with ammonia solution; adding lead nitrate solution to the dispersed LZT solution and coprecipitating PLZT hydroxide again with ammonia solution. The precipitates were washed and dried by the three different methods, and then calcined at temperatures ranging from 300℃ to 1100℃. Tests for the X-ray diffraction and the particle size distribution were carried out and the morphologies were observed by scanning electron microscopy. Perovskite crystal structure were found on the samples calcined for 2hours at temperatures higher than 650℃. The most fine-grained size distribution was. observed in the powders of freeze-dried precipitate. The sizes of the primary particles, which mutually agglomerate to form distinct secondary particles, were between 0.1-0.6μ and the morphologies were nearly spherical.

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The effect of Ti/C+N ratio of type 409 stainless steel on the microstructure of the steel after annealing was investigated. The annealing experiments were carried out using batch annealing and continuous annealing process. The optimum Ti/C+N ratio of the steel was 10 minimum in order t.o obtain fully ferritic structure after continuous annealing. In the case of the lower Ti/C+N ratio(below 10), the hot rolled stainless steel should be applied to batch annealing process to avoid the formation of martensite after continuous annealing process. The optimum condition of continuous annealing was about 3 min at 950℃.

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