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The isothermal oxidation behavior of W-Mo-(29~48wt%)Cr alloys were investigated at 1000, 1100 and 1200℃ in air. The oxidized layers and their morphologies were analyzed by scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The oxidation resistance was improved as the Cr content increased. The oxidation rates of W-Mo-Cr alloys containing 41~48wt % Cr followed a parabolic rate law and the measured rate constant(kp) of oxidation was approximately 1.92 × 10(-2)~9.55 × 10(-11)(g/cm2)2sec(-l) between 1000℃ and 1200℃. At the surface of this alloys, a Cr2O3 protective layer was continuously formed, and below the protective layer, CrZO3 internal oxide formed. The depth of internal oxidation zone was found to decrease with increasing Cr content. The oxidation resistance of W-Mo-(29~35wt%)Cr alloys was good at 1000℃, however, decreased rapidly as the temperature increased. The observed optimum Cr content for oxidation resistance was more than 35% at 1100℃ and 41% at 1200℃. The oxidation mechanism of W-Mo-Cr alloys was proposed.

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For the purpose of ameliorating of toughness by boundary control, Be was added to Al-Li multiphase alloys. Interface behaviors during ageing were investigated by means of the measurements of hardness and tensile strength, and also the observation of optical and transmission electron micrographs. In order to evaluate the fracture toughness, instrumented Charpy impact test was carried out and fracture surface was observed with a scanning electron micrograph. Grain size was refined by α-Be particles that acted on dragging force at grain boundary in Al-Li-Cu-Be alloy. And PFZ half width in Al-Li-Cu-Be alloy was decreased by early precipitation of T₁ phases compared with Be-free alloy. Double eak phenomenon which was observed at the hardness and tensile tests in Al-Li-Cu-Zr-Be alloy may be estmated by the precipitation of secondary T₁ phases due to the change of δ′, T₁ and θ′ phases stability. And considering toughness and elongation, it is possible to think that the secon peak condition may be the most optimum condition of heat treatment because of the remarkable improvement of elongation in Al-Li-Cu-Zr-Be alloy. In case of Al-Li-Cu-Zr alloy containing minor Be, higher impact absorbed energy than that of Be-free alloy was observed. This remarkable improvement of fracture toughness was attributed to the change of fracture mechanism from brittle to ductile mode. the high energy fracture mode of minor Be added alloy was associated with homogeneous deformation due to various interface controls.

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In view of the importance of Pb-Sn eutectic alloy in soldered interconnection, the creep phenomena in eutectic bulk solders with microstructures similar to the solder joints have been investigated. A variety of loading paths (tensile, fatigue, load relaxation, and creep) along with microstructural examination were employed to characterize constitutieve behavior and identify potential creep mechanisms(e.g. grain boundary sliding) that might have an impact on fatigue. The experimental work was directed as a clearer description of what some of these phenomena might actually be and how they might be related to the underlying creep mechanisms. The mechanisms of grain boundary sliding and creep strengthening in a wavy eutectic alloy were proposed and the creep strength can be explained based on the stabilized subgrain boundaries caused by the two-phase microstructure.

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A flat plate can be manufactured by a new spray deposition method with a reciprocating spray nozzle and moving substrate. The shape and the temperature of the depostit. The shape and the temperature of the depostit produced by this process is analyzed by numerical method. An integral model for this spray deposition process has been developed and some necessary data of the spray deposition apparatus are measured experimentally. Governing equation of the temperature change of deposit is one dimensional heat conduction equation and solved by Fully Implicit FDM and TDMA. The unique feature of this process is the variation of deposition rate with time due to the variation of the position of the spray nozzle. As deposition rate is varying, the mesh size of the finite difference method also varies. The thickness of the deposit is governed by substrate speed and the waviness is governed by the reciprocating speed of the nozzle. Since the cooling rate of the deposit is gevened mainly by the deposit thickness, the substrate speed is its main controlling factor. Two parameters, Semi-Liquid Film Formation Thickness(SLFFT) and Maximum Liquid Fraction(MLF) are proposed for the prediction of deposit microstructure.

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In order to examine the reduction behaviour of fine iron ores in gas conveyed systems, rise rate of particles temperature are examined and effect of temperature, grain size and feeding rate of iron ore on reduction rate were studied. Results can be summarrized as follows ; 1. After supply of fine ores in gas conveyed systems, their velocity became almost instantaneously equal to the gas velocity. Accordingly the reduction time is nearly equal to the length of reactor tube divided by gas velocity. 2. Calculation of rise rate of particles temperature with assumption of lumped -heat-capacity systems showed that particles temperature became equal to the surrounding temperature in 0.1∼0.3 sec for the grain size below 100㎛. Temperature rise was slow for the paticles with grain size above 100㎛. 3. The reduction rate increased with the increasing temperature and with the decreasing ratio of fine iron ore to gas volume. 4. The fine ores which can be difficultly treated in the fludized bed could be reduced in the gas conveyed systems.

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The objective of this paper is to investigate study the variation in microstructures at high temperature of TiC films deposited on the SKH9 tool steels by PECVD. We performed vacuum annealing of SKH9/TiC samples in the temperature range of 700∼1000℃, and studied on the microsturctures of TiC films by using the XRD, SEM, TEM and AES. TiC films as coated had (220) preferred orientation and it changed into (200) at 800℃ and (220) at 1000℃, respectively. The lattice parameter of TiC films decreased with vacuum annealing. At 900℃, it increased by the diffusion of carbon from the substrate into the films. At 1000℃, TiC films changed into zone 2 structure with dense columnar grains. Above 900℃, Fe and Cr diffused into TiC films and formed complex carbides of (Fe, Cr, Ti)_xC type. TiC films as coated had fine micrograins with 10∼100㎚ size. At 800℃, the growth of micrograins occurred and the size of micrograins increased to 50∼300㎚. Also at 1000℃, TiC films had very fine grain size(10∼70㎚). This is thought due to the Ac₁ transformation of substrates.

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This paper is intended as an investigation of high temperature behavior of TiC films deposited on the SKH9 tool steels by PECVD. Vacuum annealing of SKH9/TiC samples was performed in the temperature range of 700∼1000℃, and the variation in chemical composition and state was studied by AES, RGA and XPS analysis, and also micro hardness and scratch test was conducted. By vacuum annealing, Ti/C ratio of TiC films became about 1, and chlorine and oxygen contents in the films decreased. The chemical state of chlorine in the TiC lattice was Ti-Cl or Ti-C-H-Cl banding and evaporated to form Cl₂ or HCl with vacuum annealing. Oxygen formed TiO₂, TiO_xCl, H₂O and Ti-C-H-O compound. With the increase of the annealing temperature, the amount of TiO₂ bonding increased, but total oxygen content in the films decreased because of evaporation of H₂O or decomposition of TiO_xCl and Ti-C-H-O bond. Judging from the above results, it is obvious that hydrogen exists in the TiC films. Also, The micro hardness and critical load of TiC films decreased with the vacuum annealing.

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Pure iron powders are nitrified at room temperature by ball milling in NH₃ gas atmosphere. Super-saturated bcc iron-nitrides are obtained for the N concentration below 14.9 at.%N and the high temperature ε-phase with the hcp structure for more than 19.4 at.%N. The atomic volume of Fe in the metastable bcc phases is found to be smaller than that in the bct iron-nitrides reported in the literature. Saturation magnetization at room temperature gradually decreases with the nitrogen content, which is in sharp contrast to the enhancement in magnetization due to nitrification reported for the N-martensite. We have shown that mechanical alloying in the NH₃atmosphere can nitrify pure iron powders even at room temperature and gives rise to the super-saturated bcc iron-nitrides up to 14.9 at.% N. The high temperature ε-phase with the hcp structure is obtained for the iron-nitrides containing more than 19.4 at.%N. In the composition range between 14.9 at.%N and 19.4 at.%N, a mixture of the bcc and hcp phases is produced. The stomic volume of Fe in the bcc phase is found to be smaller than that in the N-martensite. We also reveal that the magnetization at room temperature gradually decreases with the N concentration. Here a lack of the tetragonal distortion has been proposed to be the tetragonal distortion has been proposed to be the likely cause for the low value of saturation magnetization compared to bct iron-nitrides.

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Meta-stable austenitic Cr-Ni steels were cold rolled and reversion treated under various conditions to develop ultra-fine grain structure, and the tensile properties of these steels were analyzed. The steels demonstrated the yield point behavior which is often observed in law carbon ferritic steels. The difference between upper and lower yield points was decreased and the amount of yield paint elongaton was reduced, as the grain size was coarsened. This behavior was closely related with the austenite stability. Steels reversion treated at high heating rates underwent diffusionless transformation. The yield stregnths of these steels were lower than those treated at slow heating rates which underwent diffusional transformation. The Hall-Petch relation appeared to hold in the present steels, but the linearity between the inverse square root of grain size and the yield strength was gradually diminished as the grain size was ultra-refined. It was suggested that approriate combinations of the alloy chemistry and the thermomechanical processing condition enabled development of ultra-fine grain high strength austenitic steels with yield strength as high as 1200MPa.

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Ternary Al-Ti-X(X=B, V, Ce, Zr) alloy powders were produced by mechanical alloying and compacted in Cu can, then extruded into a rod at 550℃, STEM micrographs and EDS analyses of the as-extruded bar revealed the 3rd element such as V, Zr, Ce only in the precipitates of Al₃Ti substituting the Ti. The precipitate size of Al₃(Ti+X) was smaller than Al₃Ti. The third elements may decrease the lattice mistatch of Al-Al₃Ti particles by altering the dimension of the intermetallic`s unit cell and produced the smaller precipitate. The results of STEM and hardness test of as-extruded specimens exposed for 500hr. at 300℃ and 400℃ show Al₃(Ti+X) was thermally stable. Room temperature and high temperature tensile strengths at 300, 400, 500℃ of mechanically alloyed Al-Ti-X alloy were superior to those of Al-8wt.%Ti alloy, and the rate of decrease of strength with temperature was less in Al-Ti-X alloy. This improvement of tensile strength was due to the dispersion of fine Al₃(Ti+X) procipitates.

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