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Dependence of the effective permeability on annealing and the annealing-induced structural change for amorphous Fe_(73.5)Cu₁M₃Si_(13.5)B_9(M=V, Nb, Mo, Ta or W)and Fe_(73.5)Cu₁Nb₃(Si_xB_(1-x))_(22.5)(x=0∼0.8) alloys were investigated. Crystalline Fe_(73.5)Cu₁M₃Si_(13.5)B_9(M=V, Nb, Mo, W)alloys with α-Fe phase which was obtained by annealing at above T_x showed higher effective permeability than with amorphous phase, and the increase in permeability upon crystallization was large in the order of V$lt;W$lt;Mo$lt;Nb. For amorphous Fe_(73.5)Cu₁Nb₃(Si_xB_(1-x))_(22.5) alloys in the composition range from x=0.5 to 0.8, soft magnetic property was improved by crystallization. Moreover, in that composition range, the effective permeability increased with the Si content(x). Superior soft magnetic property of the high-Si alloys was attributed to both the small magnetocrystalline anisotropy and the low magnetostriction. The effective permeabilities measured at 1㎑ and 5 m0e for crystalline Fe-Cu-Mo-Si-B and Fe-Cu-Nb-Si-B(0.5≤x≤0.8) alloys were about 1∼2 × 10⁴, and it was comparable to that of the zero-magnetostriction Co-based amorphous alloys.

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Magnetic measurements on the annealed and rapidly solidified FeAl_(1-x)Cr_x series (x= 0.05∼0.40) have been made at temperatures from 77K up to 500K. Annealed specimens showed paramagnetism when x$lt;0.30, superparamagnetism when x=0.30, 0.35 and seemed to be ferromagnetic with Curie temperature below 77K when x=0.40. Rapidly solidified specimens appeared superparamagnetic when x◎0.35 and seemed to be ferromagnetic with Curie temperature below 77K when x=0.40. The magnetic properties were analyzed on the point of view of the local environmental effect.

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YBa₂Cu₃O_(7-x) Preform was melted and solidified into ribbon shape via melt spinning process. The as-spun ribbon contains melt-decomposed phases of rod shaped 211 phase aligned to spinning direction and Ba, Cu-rich matrix. Superconducting 123 phase is formed by a heat treatment through reaction between the 211 phase and the matrix. The grain morphology of the 123 phase is very much dependent of the presence of liquid phase during the heat treatment. The highly aligned large grain structure with strong (00ℓ) peak obtained through peritectic transformation indicates that the 123 phase is predominantly grown from the rod shaped 211 phase through reaction at the interface with the matrix. Heat treatment below peritectic transformation temperature yielded equiaxed type grain structure, indicating the random nucleation and growth of 123 phase. In case of a bulk specimen prepared by conventional powder consolidation technique, sintering above peritectic transformation temperature produced large grain structures but with random orientations. This strongly indicates that the presence of liquid phase can improve grain structure by promoting grain growth but is not effective for aligning the grains during the 123 phase formation.

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A computer program for calculation of the solidification process of steel with the fluid flow in 2-D cylindrical system was developed. TEACH-2E source program of Patankar et al. was modified to simulate the solid-liquid two phase phenomenon. In this study it was treated as one phase. The energy equation was solved by modifed heat capacity method and the momentum equation by giving effectively large viscosity to solid phase. From this method the fluid flow and temperature profile could be obtained. It was found from this study that fluid flow patterns during filling of motten metal were hardly changed by Gr number and the transition from forced to natural convection was completed within 5∼13 minutes after pouring. When convection effect was domimnt, the planar solidlfication started to occur from the bottom of the mold and It was found that the greater the Gr number, the faster the solidification process.

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YBa₂Cu₃O_(7-x) oxide superconductors was fabricated by sintering process and upsetforging method, respectively, and microstructures and conduction properties were compared. There was no difference in crystal structure between the as-sintered and the upset-forged specimens. The upset-forging enhanced the (001) x-ray reflection presumably due to preferred crystal orientation of the YBa₂Cu₃O_(7-x) superconductor. Furthermore, the grain size of the 123-phase increased as the reduction ratio became larger during the upset-forging. The critical temperature for zero resistivity of both samples was almost the same, i.e., about 90K These results have demonstrated the potential of producing YBa₂Cu₃O_(7-x) superconducting wire or tape effectively using a upset-forging method. The critical current density of the upset-forged sample, however, was lower than that of the sintered one, which fact might be ascribed to microcrack formation during fast upset-forging.

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Morphology, size distribution, microstructure and hardness of Al-5wt % Pb and Al-10wt %Pb alloy powder were studied, which were processed by centrifugal atomization. To investigate the dispersion characteristics of lead, the temperature of atomization has been varied from 30℃ to 60℃ of the two-liquid phase line. Also, the solidified structure and cooling rate of the powder have been examined. The shape of particles are tear-drop-like, ligament, irregular and the particle size varies from 20 ㎛ to 600 ㎛. For the S. E. M. observation, Back-Scattered Image technique was applied. Within the experimental conditions, it was found that the lead particles were thoroughly dispersed in the matrix. In the case of powders which were smaller than 150 ㎛ (-100+325mesh), Pb particles existed as fine and uniform dispersoids (1㎛ - 3㎛) throughout the Al matrix. However, providing the atomized temperature of melt was 60℃ below the two-liquid phase line, segregation of Pb became significant. The degree of segregation of Al-10wt % Pb was more than that of Al-5wt % Pb. At 30℃ below the two-liquid phase line, the size of dispersed Pb particle became irregular in the powder size above 200 ㎛. The cooling rate of the powder was calculated to be l0²-10⁴K/s.

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To obtain fundamental informations for fine hexagonal boron nitride powders, the preparation of fine hexagonal boron nitride powders by vapor phase reaction procedures of BCl₃with NH₃has been carried out in the temperature range of 700-1400℃. The effects of reaction conditions on particle size and morphology of hexagonal boron nitride powders have been investigated by utilizing X-ray diffraction, SEM and IR spectroscopy techniques. The synthesis temperature of the h-BN crystal is higher than 1100℃. The h-BN crystal was obtained by heating at 1100℃ or higher in NH₃ambient again the reaction products which was obtained in the temperature range of 700-1100℃. The size of the reaction products obtained at 1400℃ is about 0.1 ㎛ and the shape of h-BN is spherical. Crystallite size and lattice parameter are found to have little influence in the molar ratio of BCl₃and NH₃. Temperature dependence of the crystasllite size is weak and the lattice parameters a and c decreases gradually with increasing reaction temperature.

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The hexagonal boron nitride which was obtained as a reaction product by the vapor phase reaction of BCl₃and NH₃was decomposed again thermally in the temperature range of 1100-1450℃ to synthesize boron nitride whiskers and powders. The effects of reaction conditions on the particle size and morphology of the hexagonal boron nitride were investigated by utilizing X-ray diffraction and SEM. The boron nitride whisker was obtained by thermal decomposition of the reaction product which was obtained at 300℃. The procedures of the BN formation are as follows: Amorphous--(BN)4H--BN. The reaction products obtained at 500℃ were decomposed thermally for 9 hours at 1200℃, the particle size and shape were 230㎚ and sphere-shaped, respectively.

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This paper identified the main metallurgical factor leading to the embrittlement of an RSP/PM AI-Fe-V-Si alloy after high temperature exposure above 480℃. Although the RSP/PM AI-Fe-V-Si alloy shows excellent high temperature stability compared with an IM 2219 Al alloy, the RSP/PM alloy exhibits the very uncommon behavior that the ductility and fracture toughness of the alloy decrease along with the yield strength after high temperature exposure. Detailed microstructural analyses suggest that the formation of coarse θ-Al₃Fe phase in the form of band structure causes the embrittlement of the alloy exposed to temperatures above 480℃. Also, it is found that the non-uniform distribution of the silicide dispersoids due to the cooling rate difference between the wheel side and the air side of melt spun ribbons is responsible for the formation of θ-Al₃Fe phases. Therfore, it is concluded that the achievement of the uniform microstructure by the control of RSP condition is essential for the safe application of RSP/PM Al alloys at higher temperatures.

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This study is concerned with a correlation between the microstructure and the micromechanism of fracture processes in an RSP/PM Al-8.5Fe-1.3V-1.7Si alloy. The specimens were exposed to the temperatures ranging from 150℃ to 480℃ for 100 hours, followed by room temperature tensile tests, fracture toughness tests and void initiation tests. This RSP/PM Al alloy did not show any significant change in room temperature tensile strength, tensile elongation and fracture toughness even after exposure up to 425℃ for 100 hours. However, tensile elongation and fracture toughness decreased significantly after exposed to 480℃ for 100 hours. Detailed microstructructural analyses showed that the alloy ahs a band structure due to non-uniform distribution of the silicide dispersoids. After exposure to 480℃, the formation of θ-Al₃Fe phases occurs at band structure boundaries by the dissolution of coarse silicide dispersoids, resulting in a loss of ductility and fracture toughness. The micromechanical processes involved in void and microcrack formation were identified and quantified. The results are interpreted using a simplified ductile fracture initiation model based on the basic assumption that crack extention starts to occur at a certain critical strain over a microsturcturally significant critical distance. This model enables us to correlate fracture toughness and microstructure, confirming that the formation of θ-Al₃Fe phases is the main metallurgical factor which contributes to the embrittlement phenomenon after exposure to 480℃ for 100 hours.

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