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The strain controlled low-cycle fatigue properties of recently developed weldable Al-Zn-Mg-Mn alloy and commercial Al 7039 alloy were studied in air, distilled water and 3.5wt.% NaCl solution. While the tensile strength of the Al-Zn-Mg-Mn is greater than that of 7039 alloy, the fatigue life of the Al-Zn-Mg-Mn alloy is found comparable to those of the Al 7039 alloy at the condition of the same total strain range in all the environments tested. However, the fatigue life of the Al-Zn-Mg-Mn alloy is appears longer than that of the Al 7039 in terms of the dissipated energy per cycle in the specimen. These results are considered to be caused by the difference in cyclic deformation behavior between the weldable Al-Zn-Mg-Mn alloy and Al 7039 alloy.

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Ni-Al₂O₃ composite powders were prepared by reduction of Ni^(++) from ammoniacal nickel sulfate solution on alumina core by hydrogen gas at elevated temperature and pressure. The reduction rate and the porperties of nickel layer were investigated by SEM, X-ray, size and chemical analysis. The reduction of Ni^(++) showed the maximum value when the molar ratio of NH₃/Ni^(++) was 2. In order to prevent the agglomeration of Ni powder and act as catalysis for reduction, Fe^(++) should be required and the anthraquinone was slightly influenced as catalysis. The concurrent addition of Fe^(++) and anthraquinone catalytically increased nickel deposition reaction. Optimum condition obtained in this study was reduction temperature 130℃, stirring speed 700rpm, hydrogen partial pressure 350psi and reduction time 45mins. Then the prepared composite powder obtained uniform and continuous nickel coating layer of nodule shape on alumina particles.

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Shape Memory Characteristics associated with the B2⇔B19 transformation in a Ti-35Ni-15Cu(at%) alloy have been investigated by means of thermal cycling test under constant load and optical microscopy. The B2→B19 transformation start temperature under load, M´_s(ℓ) increased linearly with increasing applied stress up to about 100MPa, above which a deviation from the linearity occured. Considerably large residual elongation started to occur at about 100MPa and thus, the maximum recoverable transformation elongation associated with the B2→B19 transformation was found to be 2.9%. Preferentially oriented martensite variants in relation to the applied stress was more stable on heating than the variants which formed a triangular shape.

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A complex tungsten carbide alloy with Ni as binding metal and TiC and SiC as additives was developed. The chemical composition and processing technique were designed such that SiC coated the WC particles prior to sintering. The additives were found to improve density and limited the rate of grain coarsening during sintering. As a result, a fine grain size in the range of 1 to 2 ㎛ and a Vickers microhardness of greater than 1600 were obtained. The role of SiC was viewed as hindering the mobility of WC particle boundary. Apparently, TiC reduced the grain size by decreasing the extent of solution and re-precipitation of WC in Ni. The increased hardness due to the addition of TiC was attributed to the solid solution hardening of both WC matrix and the interface. An evidence to support this hypothesis was presented by analyzing the distribution characteristics of the participating elements in microscopic scals.

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The redution rates of synthetic chromites consisting of FeO and Cr₂O₃ using graphite powder as a reductant have been measured by means of thermo-balance under Ar atmosphere at the temperature range of 1050˚∼1250℃. The synthetic chromites mixed with graphite of 20 w/o and bentonite of 3 w/o were shaped into briquette(10㎜ in dia. and 10㎜ in height) under 3 ton/㎠ pressure. From the comparison between the results of the experiment and the calculated values from Fick`s diffusion rate equation on the isothermal reduction of synthetic chromite, it can be concluded that the reaction rates of iron and chromium ion are controlled by diffusion process up to 70% reduction degree. Diffusion coefficients of iron or chromium ions For the sample CF1, CF2, and CF3(FeO/Cr₂O₃ mole ratio =1/1, 2/1, and 1/2, respectively) was 10^(-10)㎠/sec and the apparant diffusion coefficients could be expressed as 0.0674 exp(-55,447/RT) for sample CFl, 0.075exp(-51,955/RT) for CF2, and 1.971×10⁴exp(-89,176/RT) for CF3 using Arrhenius typ plotting, respectively.

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The effect of P addition on the formation of recrystallization texture in intersititial free (IF) extra low carbon steel sheet has been investigated. IF steel sheet exhibited high r-value texture (more specifically, {554}$lt;225$gt; type texture) independent of heating rate at the final annealing after cold rolling. Ti-P and Nb-P steels, however, enhanced near {100} grain provided that slow heating cycle, i.e., box annealing cycle was applied, and therefore r-value (deep drawability) is deteriorated for these steels. On the other hand, when rapid heating cycle, i.e., continous annealing cycle was applied for these steels, the growth of uncleated {100} grain was inhibited by large amount of recrystallized {111} grains, developing strong {111}({554}$lt;225$gt;) recrystallization texture. Futhermore, the {111} components increased with low finishing temperature at 800℃ in the hot rolling stage, was attributed to coarse precipitates of Fe(Nb, Ti)P in the matrix. It is considered that lowering the hot rolling temperature and adding the Ti and Nb can effectively reduce the grain boundary segregation of phosphorus, in the Fe-Ti(Nb)-P alloy, cause a decrease coarse precipitates on the grain boundary.

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The powder formation mechanisms in the centrifugal emulsification process which has recently been developed as a new powder making process were studied. The increment of total suface energy of metallic liquids due to shape change from a bulk to droplets was assumed as resulting from the drag force by the filter. The calculated mean size of powders agrees relatively well with that of the experiments. In order to build a exact theoretical model, effects of liquid convection on powder making process as well as the surface energy changes due to the powder shape change were considered.

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MoSi₂ powders were prepared by the SHS (Self-Propagating High-Temperature Synthesis) Method. The measured reaction temperatures varied from 1600K to 1900K, while the reaction rate varied from 1 to 4 ㎜/sec. More than 50% of major metallic impurities were removed through evaporation during the high-temperature synthesis. The reaction temperature and rate were the highest when the precursor Mo and Si powders were mixed at the stoichiometric ratio(Si/Mo=2). At this composition, the measured temperature at the reaction front was 1853K, slightly lower than the theoretical adiabatic temperature, 1900K. The small discrepancy indicates that the reaction is close to adiabatic but not perfectly so. When the precursor powders contained either Mo or Si in excess, both the reaction temperature and rate were found to decrease, with the decreasing rate steeper in Si-rich composition than in Mo-rich one. the difference was explained in terms of the amounts of MoSi₂ at each composition. The reaction rate increased with the apparent bulk density and decreased with the particle size. The apparent activation energy for the reaction was found to be 40±3 ㎉/㏖. This value corresponds to the activation energy of 43 ㎉/㏖ calculated from the growth of Mo_5Si₃ in Mo_5Si₂-Mo diffusion couple. The interdiffusion of Mo and Si through MoSi₂ controls the synthesis reaction.

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A study has been performed on rapidly solidified Al-Mg-Cr alloy as a candidate for engineering applications requiring high strength and weldability. The objective of this work was to investigate the development of microstructure during extrusion snd tensile properties. This work has been achieved by employing a combination of X-ray diffraction, transmission electron microscopy, differential scanning calorimeter, and instron universal testing machine. The P/M Al-Mg-Cr alloy has a much finer grain and precipitates size than does I/M 5083. Through a combination of DSC and X-ray analysis obtained from Al-Mg-Cr powder and X-ray analysis from Al-Mg-Cr extrudate, the precipitate phase of being contributed to tensile strength of the extrudate is Cr₂Mg₃Al_(18).

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The sensitization phenomena to intergranular attack of Type 409L stainless steel containing 0.014% C and 0.0063% N has been determined by chemical etching test after subjecting the alloy to various heat treatments. Type 409L stainless steel is highly resistant to intergranular attack when 1.5㎜ thick specimens are water quenched from above 1100℃ temperature. Air cooling from temperatures between 950℃ and 1100℃, and between 500℃ and 600℃ causes to increase in intergranular corrosion comparing to the annealed base materials. Precipitates in the grain boundaries of sensitized specimens were identified as titanium nitride by STEM and EDX analysis. It is strongly suggested that the presence of such precipitates induce to develop intergranular corrosion in this alloy.

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