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Changes in transformation behaviour and transformation temperatures of Ti-49Ni-1Cu and Ti-46Ni-4Cu shape memory alloys due to thermal cycling under constant load have been investigated by means of electrical resistivity measurements and thermal cycling tests under constant load. Transformation behaviour of thermomechanically treated Ti-49Ni-1Cu alloy was B2-B19` under the applied stress of 110 MPa and not changed with increasing thermal cycling number. On the other hand, under the applied stress of 50 MPa, it was B2-R-B19` and changed into B2-B19` with increasing thermal cycling number. In solution treated Ti-Ni-Cu alloys, the B2-B19` transformation start temperature decreased under the applied stress of 50 MPa, while was almost unchanged under the applied stress of 110 MPa with increasing thermal cycling number. In thermo-mechanically treated Ti-Ni-Cu alloys, however, it rised with increasing cycling number, irrespective of the amount of applied stress.

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An attempt to improve ductility of the NiAl-base shape memory alloys has been made by the addition of Fe. Also, the effect of the annealing treatment on the microstructure and the transformation temperature of the NiAl-base shape memory alloy has been studied. It has been found that a small amount of γ phase (fcc) formed by the addition of Fe has a drastic effect on the hot workability. The transformation temperature increases with increasing the annealing temperature and the annealing time causing the variation of the composition and the volume fraction of matrix, which is composed of β phase. The variation of shape recovery with increasing of the annealing temperature is due to the change of the volume fraction of martensite caused by the variation of composition, the fraction of β phase, the morphology of γ phase and the grain growth of β phase. The transformation temperature and the shape memory effect are controlled by annealing at the appropriate temperature in the coexisting region of β and γ phase.

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The practical application of the Cu-Al-Ni shape memory alloys has been restricted because of their brittleness and degradation of shape memory ability, that are mainly caused by their high elastic anisotropy(A=13) and large grain size. In order to clarify the way of the improvement of the aforementioned properties, the effects of grain refining on the ductility and thermocycling properties of the alloys has been studied by adding small quantity of B, Ti, Zr. The addition of such elements to Cu-Al-Ni alloys caused significant decrease of grain size and the increase of elongation from 5% to 7-10%, in comparison to those of Cu-Al-Ni base alloys. After 30 cycles under 200g load, recovery displacement was decreased to 55% in the Cu-Al-Ni alloys with large grain size but decreased to 81% in Cu-Al-Ni-Zr alloys with fine grain size. The change of transformation, temperature were found smaller in the grain refined Cu-Al-Ni-Zr alloys. It is thus concluded that the grain refining by adding small amount of Zr to the Cu-Al-Ni allay improved the ductility and the stabilization of thermocycling properties.

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Growth kinetics of Nb(CN) precipitates have been studied in the 0.03wt.% Nb bearing HSLA steel which was compressively rolled at high temperature(850℃∼1000℃) up to 0.3 strain and isothermally held. Interrupted compression test was also carried out to observe the recrystallization phenomena associated with the precipitation at high temperature. The precipitates were analyzed by the TEM. Observed precipitates revealed that they were nucleated heterogeneously at dislocations and spherical shape. The mean particle size of the precipitates were found to increase with increasing time and temperature. The slope obtained from log plot of precipitate diameter versus time was about 0.5, indicating that the growth behavior followed the Zener`s diffusion controlled growth theory. The slope was about 0.3 for the Ostwald ripening region at longer holding time. The nucleation of precipitates was found to retard softening phenomena owing to pinning effect. In ripenening region of precipiates, restart of softening was followed with eliminating of precipitate pinning effect. This result clearly indicate that the growth kinetics of Nb(CN) precipitates affect both the softening and the recrystallization behavior.

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The mechanical properties and thermal stability of amorphous Al_(88)Ni_9(Fe,Zr)₃and Al_(88)Ni_(10)(Y,Ce)₂ alloys produced by single roller melt-spinning method were investigated. Amorphous alloys containing nanoscale Al particles which are obtained by aging treatment in the temperature range above the crystallization temperature(T_x) exhibited σ₁ and H_v higher than those of amorphous single phase alloys with the same composition. T_x in the mixed phase alloys increased significantly with rising aging temperature. This indicates that the precipitation of the Al nanoparticles thermally stabilizes the remained amorphous matrix. The H_v for the mixed alloys increased monotonically with increasing the precipitation amount(V_f) of the Al phase. The σ₁and ε₁ showed a maximum value in an optimum V₁ value. This is probably thought because the Al nanoparticles which have higher mechanical strength compared with the amorphous matrix with the same composition act as an effective resistance to shear deformation of the amorphous matrix. The amorphous Al_(88)Ni_9Fe₃ exhibited combined effect of the dispersion strengthening and a large elongation resulted from the precipitation of the Al nanoparticles at elevated temperature.

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The objective of this work was to obtain a slurry with thixotropic behavior by semi-liquid method for the application of magnesium as a light material in automobile industry. This work has been studied as a basic step for establishing a new forming process-semi-liquid forming. Magnesium alloys were prepared by a grain refining method-controlled solidification, and then heated to obtain a desired microstructure. Processing variables included the initial grain size, temperature, and holding time. Variations in intergranular and grain boundary liquid fraction were measured as functions of material temperature and holding time. With increasing the holding time, intergranular liquid fraction decreased, whereas grain boundary liquid fraction increased. The process towards spheroidisation of the solid phase was observed and the morphological changes of the slurry were expected to be calculated by LSW (Lifshitz, Slyosov, Wagner)theory.

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The kkwaenggwari, one of Korean percussion instruments, is being made by hammering sheets of tin bronze containing 22% tin. This study is to investigate the possibility if deep drawing can be applied to make the instrument. The mechanical properties of the alloy obtained from the cold and hot tensile tests were used to simulate deep drawing of the alloy sheet using the elasto-plastic FEM. The calculated results indicated that deep drawing at room temperature was not applicable, whereas the process could be applicable when the sheet preheated at about 650℃ was under partial contact between the die and the blank.

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A numerical model has been developed to analyze the heat transfer, fluid flow and deformation behavior of solidifying shell in continuously cast round billet. The temperature distribution of the billet and the mold and the fluid flow pattern of molten steel were determined using finite difference method. The thermo-elasto-plastic stress fields in the billet and the formation of air gap along the mold wall were analyzed using finite element method. The heat transfer coefficient between the solidifying shell and the mold wall was calculated by coupling above two procedures. This model shows good agreements with the reported experimental results. The effects of fluid flow on stress fields have been simulated with the variation of casting and carbon contents. The effects of casting variables on the temperature distribution and the shell thickness were also predicted.

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Rapidly solidified powders were fabricated by using gas atomizer in Al_(100-(x+y))Mm_xNi_y(x+y≤16 at%) alloys. The Microstructures of rapidly solidified powders are dependent upon alloy composition and powder size. It was found that Ni addition is very effective for amorphous formability in gas atomized Al-Misch metal-Ni alloy powders. In the powder diameter less than 20 ㎛, as the amount of Ni are increased, microstructures are changed from equilibrium phase consisting of fcc-Al and various metallic compounds(Al₄Ce, Al_(11)La₃,……) to amorphous or mixed phase consisting of super saturated fcc-Al, compound and amorphous. Thermal stability of non-equilibrium amorphous phase in Al_(84),_Mm_8Ni_8 powder was significantly higher than that of Al_(88)Mm₄Ni_8 powder. For example, crystallization temperature of gas-atomized powder is about 578 K for Al_(84)Mm_8Ni_8 and 444 K for Al_(88)Mm_8Ni_8 alloy. Al_(84)Mm_8Ni_8 powder has a obvious glass transition temperature(T_g). As powder size is increased, amorphous formability of powders is decreased slightly in the same composition. This phenomena is presumed to result from difference in the degree of supercooling on the various size of powder.

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Wear-resistant pipes with ceramic inner layer were manufactured by a centrifugal-thermit process of Fe₃O₄ and Al powders and characteristics of the ceramic layer was investigated. The ceramic layer was found to be composed of Al₂O₃, FeAl₂O₄ and Fe phases. A solidification model of the reaction products was proposed, which explained cavity distribution inside the ceramic layer. As the centrifugal-force increases, separation of the reaction products, Fe and ceramic compounds, became more distinct and better bonding between the steel-pipe substrate and the reaction products was achieved. With heat-treated tool steel as a counter material, the wear of the ceramic layer was negligible within the tested sliding distance under the stress of 25g/㎟. Erosion resistance of the ceramic layer was also superior to the bare pipe.

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