발간논문

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In this study, the influence of additional amounts of Ni and Sn on mechanical, electrical properties, and microstructure of Cu-base alloys was studied and then was investigated on the fitness of these alloys to a lead frame material in electronics. The grain of Cu-Ni-Sn alloys was finer than that of Cu-Sn alloy, which resulted in improvement of the strength and hardness. The effect of Ni addition on the strength was clear below lwt% but insensible above it. Compared with Cu-4wt%Sn alloy, the strength level of alloys added 0.5-lwt%Ni and 1-1.5wt%Sn showed similar to that of Cu-4wt%Sn alloy, but electrical conductivity showed about twice as high as that of Cu-4wt%Sn alloy. Meanwhile, Cu-base alloys containing 0.5-lwt%Ni and 1-1.5wt%Sn showed the good work hardenability with a high value above Hv 150 by 50% cold working and the good thermal resistivity with the tensile strength of 35㎏/㎟, even when they were annealed for 30min. at 600℃. From the above results, it seemed that Cu-0.5∼1wt%Ni-1∼1.5wt%Sn alloys could be applicable to a lead frame material.

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The investigation has been carried out for the clarifing of the microstructure variation, stress-strain behavior, high temperature stability and fracture behavior at elevated temperature in unidirectionally solidified Al-FeNiAl_9 eutectic composite alloy by means of detailed measurements of stress-strain and scanning electron micrography. The thermal stability under unloded state of FeNiAl_9 eutectic phase at elevated temperature is more prominent than that of FeAl₃eutectic phase. The fracture strain decrease with increasing the solidification rate and the maximum fracture stress increase with increasing the strain rate at elevated temperature. The fracture mode in deforming at elevated temperature is divided into two types, one is the brittle fracture mode which occured in the region of low temperature-high strain rate, and the other is the ductile fracture mode which occured in the region of high temperature-low strain rate. The brittle fracture is occured by the growth of microcracks originated on fiber defects. And the ductile fracture is occured by the formation of shearing deformation band produced by structural release in matrix-fiber interface.

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The effect of distribution of martensite particles on tensile properties in dual phase steels heat treated by the intercritical annealing and the repeated treatment before intercritical annealing with the initial structures of both ferrite plus pearlite and martensite were investigated. For this investigation Fe/1.4%Mn/0.08%C and Fe/1.4%Mn/0.12%C alloys were prepared throughout the experiment. The results obtained from this study are summarized as follows. The relationships between tensile strength and uniform elongation were improved by decreasing the ferrite grain size. With increasing the volume fraction of martensite, the uniform elongation of 0.12%C-1.4Mn steel appeared nearly to remain unchanged due to the fact that the ferrite matrix became clean by decreasing carbide precipitation with increasing intercritical annealing temperatures for the same period of annealing time. Repeated heat treatment before intercritical annealing was found to increase the number of martensite (austenite) particles per unit area on polish surface after intercritical annealing. After intercritical annealing, the specimen of the initial martensite structure showed greater number of martensite particles per unit area than the specimen containing ferrite plus pearite initial structure. For the specimen of the initial martensite structure, repeated heat treatment before intercritical annealing was found to decrease the tensile strength and to increase the uniform elongation after intercritical annealing, whereas for the specimen of ferrite plus pearlite initial structure, repeated heat treatment before intercritical annealing was found to increase the uniform elongation without the decrease in tensile strength after intercritical annealing.

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In the multiphase diffusion couple, the moving boundary problem is of importance such as the growth and kinetics of interphase and/or phase transformation. The geometry of interface in the multiphase diffusion couple can be identified as planar, nonplanar or complexities. From the solution of the Fick`s 2nd law, one can extend the solution to the ternary as well as binary diffusion. Based on the assumption of the constant D on each phase in ternary system, the concentration profile may he obtained theoretically with interdiffusion coefficients and interface concentration without diffusion experiments. In this study, the multiphase diffusion couples in the Cu-Ni-Zn alloys were employed for the application of the extended solution to ternary system. The agreement of calculation of the concentrations, C^αand C^β, on each phase in a two-phase β₂/α₁couple was good to the result of the experiment. As simple nonplanar interphase in the diffusion couple, circlar cylinder, sphere, ellipsoid and elliptical paraboloid were assumed for the concentration and growth of the interface with a two-phase β₂/α₄Cu-Ni-Zn diffusion couple. Based on calculation the growth of the nonplanar interface of β₂/α₄couple corresponded with the circular cylinder model. Hence, the moving boundary of nonplanar interface of β/α Cu-Ni-Zn alloy diffusion couple at 775℃ may be grown forming the circular cylinder.

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In order to investigate the effect of mercury-alloy ratio, particle size, particle shape and adding elements on triturations, photographic observation of trituration process and microstructual observation of amalgam at low temperature have been observed, and also wettability and temperature measurement of the capsule during trituration carried out. The results obtained from this study were as follows. 1. Trituration of prealloy and mercury in amalgametor was mainly influenced by wettability of prealloy particle. 2. The time required for trituration of prealloy particles decreased with increasing mercury-alloy ratio and particle size. 3. According to microstructural observation at low temperature, Ag-Hg and Sn-Hg phase appeared in early stages of amalgam.

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Microstructural Analysis was carried out by using a Scanning Electron Microscope and X-ray Diffractometer in Rapidly Solidified Sn-Pb alloy. Nucleation of Pb phase occurred at higher temperature than Sn, due to large supercooling of liquid in R.S.P., thus Sn dendrite was not detected at hypoeutectic composition but Pb dendrite was at higher Pb content than 34% Pb. It was supposed that G/R criterion obtained from directional solidification could not be applicable in R.S.P. because Pb phase was able to nucleate in front of S/L interface owing to large supercooling of liquid. Pb was supersaturated in Sn phase but Sn was not largely in Pb phase, and directionality of micro-structure was observed as Pb content increases.

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In this experiment, titanium nitride films were deposited by Activated Reactive Evaporation at low substrate temperature, and these were characterized by (1) phase identification, lattice parameter determination, and preferred orientation from X-ray diffraction, (2) observation of microstructures of the surface and the fractured cross section of the deposits, and (3) microhardness testing. From the results of the characterization, conditions for the formation of titanium nitrides and overall physical properties were discussed. Kinds of the phases present in the deposits could be predicted by the relative ratio of deposition rate to gas pressure, and the lattice parameter of TiN increased as the nitrogen gas pressure increased, and the deposits were under residual compressive stress condition. TiN in the deposits showed a strong (111) preferred orientation and the microhardness of the deposits increased as more Ti₂N phase were present in the deposits. Deposits belonged to zone 1 of Movchan-Demchishin model, judged from the microstructure of the surface and the fractured cross section, as were observed the longitudinal porosities several hundres A wide between tapered crystallites. Size of the domes in the surface increased as the deposition rate increased and differences in fracture mode were observed between TiN deposits and TiN＋Ti₂N deposits.

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