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Effects of Mn addition on lattice relation and microstructure in monolithic CuAl_2 and Al-50 wt%CuAl_2 alloys were investigated. The AlCuMn compound was produced with increasing the contents of Mn above 2 wt% in both CuAl_2 intermetallic compound and Al-50 wt%CuAl_2 alloys. Not only the lattice parameter of monolithic CuAl_2 intermetallic compound and but also that of matrix and second phase in Al-50 wt%CuAl_2 alloy were also decreased with increasing Mn content. For the analysis of the lattice relation of matrix and precipitated particles in Al-Cu alloys, simple lattice matching model in Al-Cu alloy was established. According to lattice matching model, the degree of lattice mismatch between Al matrix and CuAl_2 second phase were decreased remarkably with addition of 0.5 wt%Mn.

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The dislocation density and the composition of the β-Zr phase in Zr-2.5Nb pressure tubes were determined using a X-ray diffractometer and TEM. Through Fourier analysis of diffraction line profiles of {11-20}, {10-10} and {0001} planes, the coherent block size and the lattice strain energy were evaluated. Using those values, then, the a-and c-type dislocation densities were determined for an unirradiated Zr-2.5Nb pressure tube, which were consistent with the independently measured values for the same specimen using the AECL`s own method. TEM analysis showed that the a- and c-type dislocation densities in the Zr-2.5Nb tube are 4.0×10 exp (14) m^-2 and 0.97×10 exp (14) m^-2, respectively, which could not be compared directly with the dislocation densities determined by an X-ray analysis. The Nb content of the β-Zr phase was determined using an X-ray from a change in the interplanar spacing of the {100} planes, which agrees well with that determined by TEM using the carbon replica method.

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A study has been on the microstructure and mechanical properties of strip cast Al6061 alloy with and without 0.5Mn addition. The microstructure of the as-cast alloys is characterized by the presence of Si particles along cell boundaries. It also shows that there is a development of well-defined subgrains caused by hot rolling effect during strip casting. Si particles present along the cell boundaries transform into fine α-AlFeSi particles during solution treatment in the base alloy. There is also a presence of α-AlFeSi particles in the Al matrix. The addition of Mn results in an increase in the volume fraction of α-AlFe(Mn)Si particles in the Al matrix. Due to the increased volume fraction of α-AlFe(Mn)Si particles in the Mn containing alloy, the Mn containing alloy has less amount of Mg_2Si precipitates in the Al matrix than the base alloy. Accordingly, the Mn containing alloy shows lower yield strength but higher ultimate tensile strength due to higher work hardening rate than the base alloy. The present study shows that the strip casting is a viable process for the fabrication of structural Al alloys.

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TRIP is the transformation of the retained austenite into martensite during the deformation. Therefore, it is very important to measure the initial volume fraction of the retained austenite in TRIP steels. The conventional XRD single peak comparison lacked in the reliability and accuracy in quantitative analysis of retained austenite due to carbide, absorption and especially texture. In the present study, the initial volume fraction of the retained austenite has been measured in the C-Si-Mn TRIP steels after various heat treatments. Among various techniques, Mossbouer spectroscopy, neutron diffraction (Rietveld refinement), and image analysis could measure quantitatively the volume fraction of retained austenite.

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In order to understand more clearly the hot deformation mechanism of Alloy 718 and consequently to determine the "safe" process design window, a number of compression tests were carried out in the range of temperature, 927℃-1066℃ and strain rate, 5×10^-4/s-5/s up to the true strain of 0.7. Based on dynamic materials model, the optimal process design windows, where the deformation is stable, were proposed through the analysis of the constitutive relationships among true stress, true strain, strain rate and temperature. The instability of deformation was confirmed by observing the microstructure of the compression tested samples. Some characteristic microstructures of the localized deformation, such as twinning and shear band, were observed in the samples deformed under the unstable deformation conditions.

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Tempering of 0.2% C alloyed steel was tried to carry out employing induction heating method in this study. Mechanical properties of the steel tempered by induction heating and salt bath heating were compared to check the possibility of induction heating for industrial application. Results show that yield and tensile strength decreased and reduction of area and total elongation increased with increasing tempering temperature. It was found that one needs just increased tempering temperature with the induction heating method to obtain desired properties of tempered steel for proper formability, This evident fact was revealed from the unique relationship of reduction of area and total elongation as a function of tensile strength. The increased impact strength could be obtained with induction heating tempering. Prior austenite grain size affected to yield strength and impact strength but not tensile strength, reduction of area and elongation. It was concluded that induction heating method would be one of the competitive heat treating processes for steels in industrial fields.

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Equal Channel Angular Pressing(ECAP) was carried out on the 6061 aluminum alloy at room temperature, 373K, 423K, and 473K. The microstructures and mechanical properties of specimens pressed at different temperatures and cycles were investigated. All specimens pressed at different temperatures show ultra fine-grained microstructures with the average grain size less than 0.5 ㎛ and dislocation cell structure. When the pressing temperature increased higher than 423K, the tensile strength of the specimens decreased and the total elongation increased. In case of specimens pressed for 4 cycles at 473K, the fraction of grains having high angle grain boundaries is higher than that pressed at room temperature. The specimen pressed for 4 cycles at room temperature shows higher increase of the 0.2% yield strength, ultimate tensile strength and hardness, and much higher decrease of work hardening index.

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The rapid cooling in continuous casting process produces large thermal stress in the slabs, due to steep thermal gradient between the interior and the exterior of the slabs and a mechanically induced stress caused by friction in the mold, roll pressure, etc. There is also an occurrence of tensile stress at the upper region and compressive stress at the lower region of the slabs at the straightening zone at around 700℃-900℃ in the case of vertical continuous casters. In the case of steels with poor hot ductility, the combination of the stresses mentioned above quite often results in the formation of cracks. Among various types of steels, it is known that steels containing strong carbide formers such as Nb are particularly susceptible to cracking during continuous casting. The present study is concerned with microstructural analyses of the Nb containing steel (A steel) and Nb+B containing steels (B steel) to reduce the transverse corner crack at the straightening zone, with emphasis on elucidating the mechanism of hot ductility. There are differences in the microstructures between the A steel and the B steel. The B steel has a smaller amount of ferrite films along the prior austenite grain boundaries than the A steel. Also, the B steel contains proeutectoid ferrite within the prior austenite grains and 5-㎛-sized coarse Fe_23(B, C)_6 along the prior austenite grain boundaries as well as within the prior austenite grains. The ductility trough is virtually non-existent in the B steel, although variation of values of reduction of area (RA) with temperature shows that the A steel has a trough of RA between 700℃ to 850℃. It is believed that the presence of intraganular ferrite improves the homogeneity of deformation and accordingly the hot ductility of the B steel.

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The effects of HIPping on high-cycle fatigue properties of investment cast A356 Al alloys were investigated in this study. Tensile and high-cycle fatigue tests were conducted for cast alloys, two of which were HIPped, and then the test data were analyzed in relation with microstructures, tensile and fracture properties, and fatigue fracture mode. Eutectic Si particles were homogeneously dispersed in the matrix of the cast A356 Al alloys, but there were many large pores formed as cast defects. The high-cycle fatigue results indicated that fatigue strength of the HIPped alloys was higher than that of the non-HIPped alloys because of the significant reduction in volume fraction of pores by HiPping. In the non-HIPped specimens, fatigue cracks initiated at large pores adjacent to the specimen surface and then propagated down to several hundreds micrometers depth while coalescing with other large pores. On the other hand, the HIPped specimens, where pores did not affect the fatigue substantially, fatigue cracks propagated along eutectic Si particles formed at solidification cell boundaries, thereby showing improved fatigue strength by 40∼50% over the non-HIPped specimens.

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The effects of the viscosity, gate speed, and gate geometry on the flow behaviors of the molten and the semi-liquid A356 Al alloys were studied. Two different fluids, i.e. thixotropic fluid(semi-liquid A356 Al alloy) and Newtonian fluid(molten ADC12 Al alloy), were chosen as the model fluids for monitoring the difference in flow patterns during die filling. High speed photography was employed to elucidate the real time flow patterns of the molten and the semi-liquid alloys during die filling sequence. The effects of the gate speed of the incoming fluid and the gate geometry on the die filling characteristics were investigated. In the case of the fluid flow exhibited by the semi-liquid A356 Al alloy, die filling was observed to proceed in a laminar manner while maintaining its free surface. In the case of the molten Al alloy, however, the leading edge of the fluid was completely shattered even at a relatively low injection speed, resulting in die filling accompanied by turbulence.

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