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In order to investigate the microstructure and mechanical properties of stainless steel(SS) with various Ti content. The SS specimens containing Ti up to 1.0wt% were fabricated at vacuum furnace and solutionized for 1hr at 1050℃ . and subsequently sensitized for 5hr at 650℃ under argon atmosphere. The microstructures were examined by using optical microscopy, TFM. XRD, SEM and EDX. The δ-ferrite phase in γ grain boundaries and TiC precipitates in grain increased with increasing Ti content. M_(23)C_6 precipitates were observed, especially, at γ/δ interfaces for the sensitized SS. The hardness of both the solutionized and the sensitized SS increased with Ti content. The tensile strength of the solutioniaed SS decreased with increasing Ti content and that of the sensitized SS containing 0.42wt% Ti appeared to be the best due to of TiC formation.

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Effects of Cd addition on the aging characteristics of Al-Cu-Mn-Ti-Zr alloy were investigated usimg scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The air-melted Al-Cu-Mn-Ti-Zr alloy ingots with and without Cd were solution treated at 543℃ for 13 hours, followed by water quenching. Aging treatments were carried out at 170℃ up to 24 hours. In case of Cd-containing allays, the accelerated age-hardening makes the peak hardness higher than that of Cd-free alloys. It is due to the fact that Cd atoms stimulate θ′(CuAl₂) precipitates and increase the density of θ′ precipitates by forming Cd-clusters, which are known to act as heterogeneous nucleation sites of θ′ precipitation With increasing Cd contents up to 0.2%, peak hardness and tensile strength were increased. But beyond 0.2% Cd contents, peak hardness and tensile strength were deteriorated because of localized segregation of Cd atoms. The elongation was, maintained up to 0.15% Cd contepts, but decreased rapidly beyond 0.15% Cd contents. Therefore, it can be inferred that the optimum contents of Cd in Al-Cu-Mn-Ti-Zr alloy is about 0.15.

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Induction melting method under pressurized nitrogen gas was used to produce austenitic stainless steels dissolved with high content of nitrogen. Fe-Mn-Cr-Ni allay system was melted using Cr-nitride ferrous allay(6wt.% N) as a main additive element. The concentration and dissolution behaviors of nitrogen in as-casted alloys were investigated to clarify the effectiveness of induction melting method under pressurized nitrogen gas and Cr-nitride ferrous alloy in producing high nitrogen austenitic stainless steels having excellent mechanical, corrosion-resistance and non-magnetic properties. Nitrogen concentration in molten alloys was increased with increasing nitrogen pressure up to 1.5 atm. This result can be explained by Sievert`s law. The nitrogen concentration of about 6.900 ppm was obtained in a molten alloy when melted at the nitrogen pressure of 1.5 atm. XRD and XPS measurements were carried out to investigate the dissolution behavior of nitrogen in a molten alloy. Although it was failed to detect some nitrides by XRD, XPS measurement revealed the existence of nitride such as Cr₂N. Therefore it can be concluded that the dissolved nitrogen in a molten alloy exists as two states, one is as a solid solution state, the other is as a nitride state. It seems reasonable to conclude the most of nitrogen were dissloved as a solid solution state, and some nitrogen are apt to be formed into a nitride.

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The effect of annealing temperature on the evolution of the annealing texture in high purity aluminium foils was studied by X-ray texture measurements and microstructure observations. Upon annealing at a lower temperature, the preferred orientations in the annealing texture were quite similar to those found in the cold rolling texture, although the foils were completely recrystallized in the microstructure. Annealing at a higher temperature led to the formation of the strong cube texture. The lowest annealing temperature at which the cube texture begins to develop was dependent on the purity of aluminium foils. The orientation density of the cube orientation increased with the purity of the fails: Since the development of the cube orientation seemed to be related with the size of annealed gains, it was concluded that the grain growth played an important role in the evolution of the cube texture.

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To improve the property of Al-Mg alloy, increase of Mg concentration has been carefully studied even though serious problems associated with the precipitation of β(Al₃Mg₂), as like low thermal-stability in mechanical properties and low corrosion resistance. are generated with higher Mg concentration. In the present works, changes of β precipitate behavior, and mechanical properties by La and misch metal(Mm) addition in high Mg content Al-Mg alloy have been investigated and showed that precipitation of β phase is retarded and thermal stability of mechanical properties have improved by La, misch metal(Mm) additions.

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The purposes of this study are to clarify effects of Fe. Mn alloying on microstructure and ductility of the NiAl base shape memory alloys. It has been found that the γ phase formed by the alloying Fe or Fe+Mn has a drastic effect not only on the hot workability but also on the tensile ductility at room temperature. The enhancement in ductility is mainly due to presence of the γ phase with a high ductility and grain refinement of the β phase by the adjacent γ phase for annealing. The specimens quenched from 1300℃ consisted of the β′(L1_0) and r(disorded fcc). The β′ martenste have a {111} $lt;112$gt; internal twins. The c/a value of the β′ phase is 0.86-0.87, almost equal to that of the binary Ni-Al β′ phase. And the lattice parameter of the γ phase is 0.358-0.359㎚.

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Wear characteristics of 7075 Al/SiC_p composites fabricated by spray forming and extrusion process are studied. This study shows a wear transition from mild to severe wear as a function of applied load, sliding velocity and friction temperature with wear mapping approach. 7075 Al/SiC_p composites exhibit the transition from mild to severe wear when a load, sliding velocity or temperature reaches a critical value respectively. In mild wear regime; wear rate increases with increasing applied load. But wear rate decreases with increasing sliding velocity. At constant load and velocity in mild wear conditions, wear rate decreases with increasing friction temperature. The reasons are that the worn surface of disk was covered with much more iron oxides at elevated temperatures than at room temperature which played a role as solid lubricant. But in severe wean regime, this oxide layer is not stable and fractured, leading to increase wear rate and friction coefficient. Wear transition map of 7075 Al/SiC_p composites is constructed on applied load and sliding velocity axes with elevated temperatures. Severe wear regime is enlarged with increasing temperature on the wear transition map and wear transition conditions move to lower load and velocity at elevated temperatures than at room temperature. Therefore safe operating range of aluminum metal matrix composite parts is reduced at elevated temperatures.

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The purpose of this paper is to provide a deeper understanding of the wear behaviour of 7075 Al/SiC_p composites through a detailed examination of the subsurface regions beneath the worn surface and the wear debris. Such an examination indicates that the subsurface layer beneath the worn surfaces of the composite pins is composed of the mechanically mixed layer(MML) except the samples tested on 10N and 0.2㎧. In the result of phase analysis of MML, it consists of intermetallic compounds such as FeAl₂ or Al_(13)Fe₄ as well as the fine mixture of Al, SiC, α-Fe and Fe oxides in the previously reported literatures. The hardness of MML is about HK 700-800 and the presence of the very hard MML indicates more wear resistance than without MML. On the basis of the above experimental observations; the dominant wear mechanisms in mild and severe wear regime are examined.

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Fe-Al intermetallic compounds were manufactured by using the field-activated combustion synthesis process. Effects of chemical composition(Fe:Al=1:2, 1:1, 21), compaction pressure(150. 250, 350㎫) and electrical resistance on the reaction were investigated. As the molar ratio of Al, compaction pressure and electric field increased, the combustion temperature and velocity increased. The structure and composition of reaction products were characterized with X-ray, SEM and EDXS to determinethe. As a results, final product was influenced with the composition of reactants, but was not influenced with compression presure.

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The phases in the surface layer irradiated by high-energy electron beam were quantitatively analyzed by M ssbauer spectroscopy. A plain carbon steel, a gray cast iron, and a TiB₂/steel surface-alloyed material were irradiated by using an electron accelerator (1.4 MeV), and then their microstructures were examined by using m ssbauer spectroscopy as well as optical microscopy. Upon irradiation, the unirradiated microstructures containing ferrite-pearlite, flake graphites and the pearlite matrix, or TiB₂ powders on the steel surface were changed to martensite-bainite, martensite-ledeburite-austenite, or ferrite-bainite-pearlite, respectively, depending on the material composition and the irradiation condition. These M ssbauer analysis data matched well with the microstructures of the irradiated surface layer. Thus the M ssbauer ,spectroscopy in conjunction with microstructural observations was very useful in quantifying the phases in the complex microstructure formed by electron beam irradiation.

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