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Metastable liquid phase separation(MLPS) in Cu-Fe binary system was investigated using an electromagnetic levitation technique. The temperature of the MLPS(Tsep) was measured directly from the time-temperature profile during cooling in the levitated state. The metastable liquid miscibility boundary of Cu-Fe binary system was illustrated using these measured Tsep. In Fe-rich alloys, phase separation generally appeared as dispersed L2(Cu-rich) droplets in a L1(Fe-rich) matrix, whereas for alloys containing Fe less than 53 wt%, L1 droplets formed in a L2 matrix. Secondary MLPS was occured in the primary separated L1 droplets by increasing the cooling rate during phase separation.

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In previous researeh, martensitic transformation start temperature of 35Ti-50Ni-15Hf alloy was highest among (50-X)Ti-Ni-XHf(X = 0∼20 at.%) alloys. In this research, shape memory characteristics of (85-X) Ti-XNi-15Hf(X = 48∼51 at.%) alloys were investigated by means of X-ray diffractometry, differential scanning calorimetry and thermal cycling test under constant load. Stress dependence of tranaformation temperature was increased with increasing Ni content. The maximum recoverable elongation was decreased with increasing Ni content. Residual elongation did not occur under applied stress of 120 MPa in broth 36Ti-49Ni-l5Hf and 35Ti-5ONi-15Hf alloys. Aging temperature dependence of transformation temperature in 37Ti-48Ni-15Hf, 36Ti-49Ni-15Hf, 35Ti-50Ni-15Hf and 40Ti-50Ni-10Zr alloys was lower than that of a Ti-Ni binary alloy. Thermal cycling dependence of transformation temperature in a 37Ti-48Ni-15Hf alloy was lower than that of a 40Ti-50Ni-10Zr alloy.

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Decomposition precess of α phage in Cu-(9-X)Ni-XMn-6Sn alloy has been investigated by means of side band observation around (200)_α X-ray diffraction peak, hardness, and microstructural observations. When the specimens are aged below 400℃ after solution treatment, the supersaturated solid solution α` is decomposed by three stages. When the specimens are aged above about 500℃, however, the equilibrium cellular structure consisting of α phase and DO_3 type superlattice forms from the initial stage of transformation without any reactions such as spinodal decomposition and transition of metastable phase. In Cu-8Ni-1Mn-6Sn and Cu-7Ni-2Mn-6Sn alloys, the first stage and the second stage in the decomposition of supersaturated solid solution are occurred at the same time. And all stages are occurred earlier than Cu-9Ni-6Sn alloy.

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Structural changes during mechanical alloying and post-heat treatment of Al_(65)Cu_(20)Fe_(15) alloy powder were studied by using X-ray diffractometry, transmission electron microscopy and thermal analysis. Al_(65)Cu_(20)Fe_(15) alloy sample precessed for 10 hrs showed a layered structure consisted of Al, Cu and Fe containing layers. DSC of the specimens showed two broad exothermic peaks: one is weak in the temperature range of 300∼390℃ and the other strong 390∼480℃. The first exothermic peak seems to correspond to the formation of Al₂Cu and Al_7Cu₂Fe phases and the second peak to the formation of mixture of quasicrystalline approximant and ordered Al(Fe, Cu) β phases from the previously formed Al₂Cu, Al_7Cu₂Fe and unreacted Fe phases. Al_(65)Cu_(20)Fe_(15) alloy sample processed for 120 hrs showed a homogeneous distribution of nano scaled Al(Fe, Cu) β particle in an amorphous matrix. During heat treatment of the sample, the microstructure transformed into a mixture of ordered Al(Fe, Cu) β phase and Al_13Fe₄. Direct formation of quasicrystalline phase was not observed in as-mechanically alloyed Al_(65)Cu_(20)Fe_(15) alloy powder.

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The microstructure of twin related silicon crystal in a cast Al-Si-Mg(A 356) alloy was investigated by electron microscopy. Two kinds of eutectic silicon crystals with different size are observed in the alloy quenched from 535℃. Stacking faults and micro-single twins are observed in the eutectic silicon crystals larger than 2㎛ in diameter. The multiple twins grown by the twin-plane re-entrant edge(TPRE) mechanism based on {111} twinning with <211> growth direction are observed in fine eutectic silicon crystals. The {111} planes meet at the twin plane to form three re-entrant angles of 141°, each with a matching ridge on the opposite side. Specially, the five-fold twinned eutectic silicon crystal containg five twin planes with a common <110> axis is observed. The silicon crystals, which are different from eutectic silicon crystal, are precipitated with the definite crystallographic relationship of <001>_(Al) ∥ <110>_(si) in the alloy aged at 175℃. The special crystallographic relationship and interfaces are interpreted by matching silicon and aluminum lattice spacing.

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Tensile behavior of mechanically alloyed(MA) Al-5 wt.%Nb alloy extrusion was examined at various temperatures and strain rates. The tensile ductility of MA Al-5wt.%Nb alloy extrusion was greatly reduced with increasing temperature and/or decreasing strain rate. The SEM observations of side and fracture surfaces of tensile fractured specimens demonstrated that the overall void density formed during deformation was considerably reduced, along with the sign of decreased plasticity around the dimples on the fracture surface. To understand the effect of grain size on the deformation behavior of submicron grain sized alloys, Al-5 vol. %Al₃Nb composite extrusions with different grain sizes were fabricated and tensile tested at different temperatures. The present study confirms that the reduction in tensile ductility of submicron grain sized alloys at elevated temperatures are undoubtedly related to the grain size. Fast dynamic recovery rates, due to the lack of dislocation substructures, in submicron grain sized alloys appears to be responsible for the elevated temperature reduction in tensile ductility.

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The purpose of this study is to develop an Al-0.8%Mg-1.0%Si alloy that combined bake hardenability and formability. A differential scanning calorimeter, transmission electron microscope, tensile test and Erichsen test were employed to investigate bake hardenability and formability of Al-Mg-Si alloys. A new Cr and Be addition Al-Mg-Si alloy which combined bake hardenability and formability has been developed. The bake hardenability and formability of Al-0.8%Mg-1.0%Si was improved by the two step aging treatment(120℃/4hrs→180℃/0.5hrs), and by the complex addition of the 0.1%Cr and 0.057%Be elements. Erichsen value of Al-Mg-Si-Cr-Be alloy is similar to that of Al-Mg-Si alloys, but the strength of Al-Mg-Si-Cr-Be alloy is higher than that of Al-Mg-Si alloys in two step aging treatment(120℃/4hrs→180℃/0.5hrs).

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High speed steel KIMM-23 was manufactured by powder metallurgy processing with Hot Isostatic Pressing (HIP) and hot working followed by gas quenching and tempering at various heat treatment conditions. In this study, it was found that secondary carbide forming elements of Mo, W (the main forming elements of the M_6C carbide) and V (the main forming element of the MC carbide) were gradually increased in matrix because more carbides were dissolved as austenitizing temperature increased. Hardness and bend strength were evaluated and microstructures (the type and volume fraction of carbides) were analyzed by SEM/EDX after heat treatment. The peak hardness at 1175℃×540℃ and the peak bend strength was obtained at 1150℃×540℃ respectively.

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Temperature and strain rate dependence of elongation and flow stress in Zircaloy-4 CANDU nuclear fuel claddings were studied. The elongation minimum and strain rate sensitivity minimum ocurred at each strain rate and the minima were shifted to higher temperature with increaging strain rate. The loss of ductility associated with dynamic strain aging was observed between 250∼400℃. SEM observation revealed that the fracture surface of Zircaloy-4 nuclear fuel claddings was ductile irrespective of strain rate and temperature. The predicted strain rate sensitivity and elongation are in reasonably good agreement with experimental data in the temperature region of the dynamic strain aging. In the temperature region of the flow stress plateau, the decreases in the strain rate sensitivity due to dynamic strain aging result in a low ductility. Above the temperature range of the flow stress plateau, the high strain rate sensitivity due to dynamic strain aging causes high ductility.

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Microstructure and mechanical properties of HT9 and HT9M steels for liquid metal reactor(LMR) core materials have been investigated. The tempering temperature at which cell structure was formed by rearrangement of dislocations was same in two steels. More carbides were precipitated in HT9 steel due to high carbon content and precipitation of carbides was delayed in HT9M steel. Thus the decrease of hardness with tempering temperature in HT9M steel was lower than that of HT9 steel. The yield strength was decreased, the fine prior austenite grain was formed, and the formation of δ-ferrite was restricted in HT9M steel by decreasing the Cr and carbon content and increasing the Nb content. Thus the impact property of HT9M steel was improved.

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