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Effects of V and Zr additions on the microstructures and the mechanical properties of two-phase intermetallic compounds consisting of LI2 matrix and 20vol.% Cr2Al were investigated. Among the V-added two-phase intermetallic compounds, Al-2lTi-20Cr-3V showed the best ductility as well as relatively high yield strength. V was found to substitute for Cr and improve the ductility of Cr2Al phase, In the case of Zr-added two-phase alloys, the particle size of Cr2Al was refined, and Zr was found to be soluble only in Li matrix As Zr content increased in the Zr-added two-phase alloys, the yield strength increased, but the ductility decreased. It was found in Zr-added two-phase alloys that the loss of ductility in Li matrix due to Zr additions was more significant than the ductilizing effect due to second phase refinement. Zr-added two-phase alloys, however, shoed higher yield strength than V-added two-phase alloys over the entire temperature range tested. Based on the results obtained, plastic deformation behavior of two-phase intermetallic compounds alloyed with V and Zr were examined. Al-19Ti-21Cr-2V-2Zr showed the best mechanical properties among the alloys tested, which is suggested to be the alloy composition to optimize the effects of V and Zr additions simultaneously.

keyword : Intermetallic compounds, Ll2 (Al, Cr)3Ti, Plastic deformation behavior, V additions, Zr additions

Strand deformation is induced by bulging, roll misalignment and strand passline condition(roll gap profile during casting) and has a major role in formation of various defects such as crack and segregation. In order to prevent excessive slab deformation during casting, it is essential to predict how strand is deformed through on-line measuring of displacement. In the present paper, bulging measuring system has been developed to diagnose strand deformation during casting and its effects on slab qualities has been discussed, Excessive pressing by pinch roll, which was concluded to be a main reason of band shape centerline-segregation, was successfully predicted by on-line displacement measuring. And band segregation could be removed by reducing pinch roll pressure. Diagnosing of strand stoppage reveals that large bulging is induced with time by high temperature creep and causes large fluctuation of displacement after casting restart. In-cast roll gap profile in the casting direction can also be predicted by measuring roll displacement in the straightener and horizontal zones. In addition, the frequency of transversal corner crack has been reduced by improvement of in-cast roll gap profile.

keyword : Slab bulging, Strand deformation, Roll misalignment, Roll gap profile during casting, Measurement of bulging, Band shape center-segregation, Transversal corner crack, High temperature creep, Roll displacement

MnBi Bi eutectic alloy was directionally solidified under enhanced gravity conditions, for a destabilizing thermal gradient, Growth rates were either 1.0cm/h or 1.2cm/h. The thermal gradient applied externally was fixed with 20K/cm under rotational conditions. The experiment shows that the formation of striations can be avoided at certain conditions of net accelerations. This result was discussed in view of the change of critical Rayleigh number, Rac2. To do this, we measured temperature fluctuations in the Bi-melt under similar conditions to growth experiments.

keyword : MnBi/Bi eutectic, Directional solidification, Critical Rayleigh number, Striation, Centrifuge, Enhanced gravity

In this study, the influence of impurity element P on modification of eutectic Si with Sr addition was examined by the observation of microstructures, DSC thermal analysis, tension test and fractographs observation. When the content of P was 1.3ppm, the eutectic morphology was the fine neeldle phase. In case of P 17.5ppm, eutectic Si appeared coarse flake phase. The increase of P in the melt deteriorated modification of eutectic Si and ascended eutectic temperature. UTS and elongation decreased with the increase of P content.

keyword : Al-7wt% Si-0.3wt% Mg, Eutectic Si, Sr Modification, P. UTS

The present study is concerned with nucleation and growth of α phase during heat treatment in TiAl-Mo-Mn intermetallic alloy processed by hot extrusion of elemental powders. TEM and X-ray diffraction analysis show that the microstructure of as-hot extruded alloy consists of γ, α2 and B2 phases. The volume fraction of α2 and B2 phases are 16% and 20%, respectively. It shows that the B2 phase which contain significant amount of Mo have orientation relationship with γplates inside them. Microstructural evolution during heat treatment reveals that the α2 phase nucleates and grows in lamellar form by edgewise and sidewise mechanism. Edgewise growth of α2 phase is more rapid than the sidewise growth due to the coherent interface between α2 and γ phases along the sidewise direction, Sidewise growth of α2 phase occurs by ledge mechanism. It has been shown that the α phase nucleates in γ plates located at thy lamellar boundaries and grows along the direction which can make incoherent interface. γphase present in the B2 phase affects the growth of α phase by providing the preferential site for a growth.

keyword : Powder Metallurgy, Hot extrusion, TiAl, B2, Incoherent growth

Effects of heating rate on the temperature profile of the combustion synthesis and on the homogeneity of the reaction product are investigated. Analysis of the temperature profile using a simple mathematical model indicated that a significant fraction of reactants is consumed during the precombustion duration, forming intermetallic compounds at the reactant interface, which was confirmed experimentally. The relationship between the parameters measured from the temperature profile and the degree of conversion of reactants to products are discussed.

keyword : Intermetallics, Heating rate, Combustion, Synthesis

The effects of heating rate on the precombustion reaction, ignition temperature and phase formed during combustion reaction have been investigated for TiAl, NiAl, NiTi and FeTi intermetallics. The experimental results indicated that two different types of the combustion reaction were found: self-sustaining and non-self-sustaining reaction. The combustion reaction of Ti-Al and Ni-Al system was included a self-sustaining reaction and Ni-Ti and Fe-Ti reaction system a non-self-sustaining one. The system with non-self-sustaining characteristics changed to a self-sustaining one as the sample is heated to elevated temperature by external heat sources such as furnace. The non-self-sustaining system in general took longer precombustion duration prior to the ignition of the combustion reaction.

keyword : Intermetallics, Heating rate, Combustion synthesis, Self-sustaining reaction, Mon-self-sustaining reaction

The structure and texture of copper electrodeposits have been studied in a macro/microscopic viewpoint. The copper specimens composed by three different kinds of fibre texture, namely, near random, (110) and (111) have been obtained at various deposition conditions. The macro/microtexture have been investigated by X-ray and EBSD in SEM, respectively. The crystallographic orientation of each grain of copper electrodeposits could be roughly estimated using crystallographic etch pit method and it was compared with the results measured from EBSD. The through thickness orientation variation was also investigated using EBSD technique in SEM. The twin distribution and its density could be well characterized through this method.

keyword : EBSD, Cu electrodeposit, Texture, twin

Under deposition conditions limited by gas transport, the chemical vapor deposition of silicon on molybdenum substrate was investigated in the temperature range of 1173K and 1473K using hot-wall horizontal reactor and SiCl4-H2 gas mixtures. The deposition amount of silicon increased proportionally to the square root of total flow rate of reactants in which the outer layer of molybdenum substrate was pure silicon at 1173K, but to the quarter of that in which that was MoSi2 at 1473K. The deposition rate of silicon obeyed linear law at pure silicon but parabolic law at MoSi2. This suggested that the deposition rate of silicon was dependent on the concentration of silicon on substrate surface because the gaseous diffusion flux of reactants through a boundary layer was a function of that. This phenomenon was confirmed by the results obtained at 1298K that the deposition rate of silicon obeyed parabolic law below 4.3 hrs and changed linear law over 4.3 hrs.

keyword : Molybdenum, Silicon, CVD, Molybdenum disilicide

Bus makers have applied Zn-Fe coated steel sheet to bus outer bodies because of its high corrosion resistance. But it was difficult for the makers to phosphate the bus bodies by themselves because the size of bus body was too big to immerse it in phosphating bath. Therefore. the bus makers have required steel makers to provide Zn-Fe coated steel sheet that was phosphated directly in EGL(Electro-Galvanizing Line). But it was also found to be difficult that Zn-Fe electroplated steel sheet was phosphated in the high speed continuous EGL. because the phosphating time in the process was too short to complete the phosphating reaction. It was observed on this process that the Zn-Fe coated steel sheet could be phosphated perfectly even in as short reaction time-about 3~7 seconds-as EGL by precipitating copper on it before phosphating. Precipitating copper on Zn-Fe coated steel sheet was carried out by dipping the steel sheet for 3~7 seconds in copper solution of about 0.5~1.0g/l concentration. This method. reducing phosphating time by precipitating copper on Zn-Fe coated steel sheet before phosphating was named as Cu-Dash treatment.

keyword : Zn-Fe alloy electroplated, Phosphatability, Cu-flash, EGL, Immersion plating