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The objective of this study is to investigate fracture characteristics of aluminum alloys deformed by ballistic impact. The testing materials used in this study were 2090 Al-Li, Weldalite, and 7039 Al alloys. After the ballistic impact testing, metallurgical observations were conducted using optical microscope and SEM. Adiabatic shear bands were observed in the impacted regions of all alloys, but the amount and the morphology of the shear bands were quite different in each alloy. Ballistic performance of the aluminum alloys against ballistic impact loading was also discussed by comparing the shear banding behavior with ballistic properties.

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Multistage torsion tests in the range of 1200∼750℃, 3.78×10^(-1)∼5.00/sec were performed to study rolling simulation of a V-microalloyed steel with declining temperature T, constant and varying strain rate ε, and constant pass strain ε₁. The dependence of the flow stress on temperature, strain rate, and holding time was examined. On each pass of multistage simulation, the flow stress could be calculated from the relation with 1n ε vs. 1n σ. The dependence of the strain rate on flow stress and temperature in this multistage deformation followed a power-law, ε=A σⁿ exp(-Q/RT), which is similar to cantinuous deformation. The microstructure was observed with optical microscopy and STEM after testing, exhibited grain refinement with progressing the process and reducing finish-rolling temperature. As the finish-rolling temperatures decrease, the vanadium carbide precipitates play an important role in the strength of a V-microalloyed steel.

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In this study, the vacuum refining trials of nickel base superalloy Rene 80 were done using 2kg laboratory vacuum induction melting apparatus. It was possible to lower the oxygen and nitrogen contents of superalloy Rene´ 80 to 4 ppm and 1 ppm, respectively, by low temperature vacuum refining after melt down (1500-1550℃) 1-3 mtorr), strong stirring of melt by induction, addition of alloying element with sequence of Ti after Al, low temperature vacuum refining after addition of alloying elements (1500-1550℃, 1-3 mtorr) and use of calcia lined crucible.

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Diamondlike carbon thin films were prepared on Si (001) wafer by plasma enhanced chemical vapor deposition and we observed the variation of the optical band gap of DLC thin films with respect to deposition condition. The change of the optical band gap of the DLC thin films was investigated as a function of DC self bias which was the most important variable in PECVD and the secondary gas. When DC self bias was applied, the optical band gap decreased monotonously and when DC self bias was not applied, the degree of the change of the optical band gap decreased greatly. The change of the optical band gap had a close relation with the concentration of C-H bond in DLC thin films and the content of hydrogen decreased with the increase of DC self bias and we could verify these results by using FT-IR spectroscopy. And, It was seen that nitrogen and hydrogen gas used for secondary gas had a role of increasing the decreasing rate of the optical band gap by the breakage of C-H bond of DLC thin films during the deposition.

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Nd_(16)Fe_(77.5)B_(5)Cu_(1.5) alloys were prepared by the hot-pressing method. The stress distribution during compression was calculated with a finite element method program(SPID). The calculated stresses were effective stress(σ_(eff), compressive direction stress(σz), and shear stress(τ_(rz). The computer simulation showed that σ_z was very high at the center-part of the specimen, and decreased toward the peripery-part of a specimen. It was expected from the computer simulation results that the magnetic properties would be better at the center-part of a specimen than any other parts, However, it turned out that the mid-part in between the center-and peripery-part showed the best magnetic properties. Casting before hot press was thought to be responsible for this discrepancy.

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The purpose of present study is to establish a new inelastic deformation theory based on dislocation mechanisms and grain boundary sliding applicable at high temperature. The basic concept of this theory is that the grain boundary sliding accomodated by grain matrix deformation plays a major role in the large superplastic deformation. Expanding the unified internal variable theory of inelastic deformation, new constitutive parameters and mechanical equation of state for grain boundary sliding are proposed from the consideration of dislocation kinetics. A series of load relaxation tests were then conducted to verify for the existence of mechanical equations of state for 7475 Al alloy. The stress-strain rate curves obtained from the load relaxation tests of 7475 Al alloy were found to fit well to the proposed state equations. The combined effect of temperature and grain size on the behavior of grain boundary sliding is also shown to be well characterized by the two structural parameters ∑_g and σ in the proposed state equations. A modification of the Hall-Petch equation is also suggested to replace the flow stress σ by σ. Finally, the conventional strain rate sensitivity parameter should also be replaced by new parameters defined by the internal state variables.

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Thickness and frequency dependence of core loss in the non-oriented electrical steel containing 3.1wt% Si was investigated in the range of 0.20-0.70㎜ in thickness and 50-400㎐ in frequency. As the specimen becomes thinner, the eddy current loss decreases whereas the hysteresis loss increases. Due to this phenomenon, there exists a thickness where the minimum core losss can be otained at a given frequency. The portion of eddy current loss in the core loss increases with frequency, and this tendency becomes more prominent in thicker specimen. The respective portions of eddy current and hysteresis loss are found to be dependent on specimen thickness and test frequency.

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In order to investigate the mechanism of embrittlement and to improve hot ductility in boron steel, effect of cooling rate and strain rate on the hot ductility were investigated at temperature range from 650℃ to 850℃. Hot ductility was improved with the slow cooling rate, which is due to the low occupation ratio of precipitates on the grain boundary. And hot ductility was improved with the increased strain rate. This is because hot deformation has been transfered from grain boundary sliding to grain deformation, and precipitates on the grain boundary do not contributed to the initiation of void.

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When N₂was used as a shielding gas during the TiN surface-alloying treatment by irradiation of CO₂laser beam on TiN-coated steel, TiN did not decompose completely into Ti and nitrogen regardless of C-content in steel. When scanning speed of laser beam was fast, energy density was not enough to melt down TiN and this was dispersed in surface-alloyed region. Even though Ti content was more than 1.2% in surface-alloyed layer, it was believed that part of Ti content was inactive to shrink austenite region due to the formation of TiC and also C was austenite former in steel, thus martensitic structure was formed by rapid cooling of that layer, Therefore the increase in hardness of the surface-alloyed layer was attributed to refinement of grain size and dispersion of TiN in low carbon steel, while it was due to the formation of martensitic structure in addition to dispersion of TiN in high carbon steel.

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The kinetics of reduction of hematite pellets with gas mixture H2- H2O was investigated in the range 600℃ to 1000℃. From the analysis of data obtained, it was observed that the diffusion of gas through the reduced iron layer became the controlling factor. A simplified Langmuir-Hinshelwood rate equation of the form, k=k_s·P_(H2)/(1＋b_(H20)·P_(H2O), was found to represent satisfactorily the measured rate data ; where k(g atom 0/min.) is the rate constant derived from diffusion controlled model, k_5 is the rate constant(g atom 0/min·atm) averaged over the pellet, b_(H2O)(atm^(-1)) is the adsorption equilibrium constant for gas mixture. The value of b_(H2O), which is a measure of the `poisoning effect` of the H₂O decreases from 30.31atm^(-1) at 600℃ to 0.75atm^(-1) at 1000℃ for acid pellets and decreases from 9.90atm^(-1) at 600℃ to 2.60atm^(-1) at 1000℃ for basic pellets.

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