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In this study, Al-2.5Li-1.3Cu-0.7Mg-(0.12Zr, 0.05Ti-O.O1B) alloy was produced, and the effect of heat treatment on the mechanical properties and microstructures was investigated. The ingot structure of Ti-B added alloys is regular and the average grain size is smaller than that of Zr added alloy. After homogenization treatment, the grain size of Ti-B added alloy become even finer than that of Zr refiner. The hardness and ultimate tensile strength of super-saturated solid solution heat-treated at 520℃ for 30min was, 90Hv and 275㎫ at only Zr additional alloy, respectively, 110Hv and 340㎫ at only Ti-B, and 114Hv and 360㎫ at Zr and Ti-B. The strength of the alloy containing Ti-B was much higher than that of the alloy containing Zr, but recrystallization during heat treatment caused the hardness and tensile strength of three alloys similar. The maximum hardness and U.T.S. of three alloys at 190℃ heat treament were, respectively, 140∼144Hv and 438∼456㎫ at 8 hour. And after the time, hardness and U.T.S. were down, but the slope of the alloy containing Zr was gentler than that of not. This was the reason that precipitated Al₃Zr phase retrained growth of δ`(Al₃Li) phase. Elongation graph reversed in comparison with strength, and showed 4.5∼5% at 8 hour. The results of TEM observation showed principal hardening phase δ`, and Al₃Zr phase, the complex phase were observed. In conclusion, the ingot structure of Ti-B additional alloys was regular and fine, and Zr addition was effective to restrain abrupt decrease of mechanical properties during heat treatment.

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The investigation has been carried out for the microstructural variation, phase transition, stress-strain behavior and fracture at elevated temperature in unidirectionally solidified AI-Fe-X(X=Ni, Zr) alloys by means of detailed stress-strain analysis and scanning electron microscopy. The X-ray diffraction and EDS analysis show the presence of Al₃Fe, Al₃Zr, and Al_6Fe compounds in Al-Fe-Zr alloy but show the presence NiFeAl_9 compound in Al-Fe-Ni alloy. The morphology of the composite structure has changed depending on the alloy, i.e., from the plate type to the rod type in Al-Fe-Zr alloy, and the ribbon type to the rod type in Al-Fe-Ni alloy. The mechanical properties of unidirectionally solidified Al-Fe-Ni alloy is better than those of the unidirectionally solidifed Al-Fe-Zr alloy. The fracture mode is divided into two type; one is the brittle fracture mode occurred in Al-Fe-Ni alloy, the other is the ductile fracture mode in Al-Fe-Zr alloy.

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Annealing behavior of phosphorus ion-implanted p-type (100) Si with and without silicon oxide (dose : 1×10^(15) ion/㎠, energy : 160 keV) was investigated by means of double crystal X-ray diffratometry(DXRD) and secondary ion mass spectroscopy(SIMS). Rocking curves and concentration profiles of the samples annealed at 700-900℃ reveal two strained layers, one layer in which a lattice constant is larger than the intrinsic value, d_0, the other layer smaller than d_0. The former is related to the Si surface layer of 50nm into which recoil-implanted oxygen penetrated, and the latter to the deep layer within the recrystallized region. As annealing temperature increases, lattice strain of the layers decreases. The strained layers measured by rocking curves are recovered after 1050℃ annealing. Annealing behavior of the recoil-implanted oxygen in the d$gt;d_0strained layer is analyzed with SIMS concentration profiles. The results show that the annealing behavior is consistent with the DXRD rocking curve measurements.

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High temperature dynamic softening characteristics related to microstructures have been examined for Al-(0.6, 1.3)wt%Fe alloys deformed in torsion at temperatures between 300℃ and 500℃, and at strain rates of 2.65×10^(-2)/sec to 1.2/sec. The flow stress as a function of strain rose to a maximum value then gradually decreased towards a steady state deformation. The effect of temperature on the flow stress was more pronounce than that of strain rate in this experimental range. The high temperature restoration mechanism was found to be dynamic recrystallization(DRX). From the relations between flow stresses and microstructures including intermetallic compounds at specific points on a flow curve, it can be assumed that the intermetallic compounds promoted dynamic recrystallization and prohibited grains from growing during the high temperature deformation. The relation between Zenner-Hollomon parameter, Z, and the microstructure was also studied and the equiaxied DRX grains were shown at low value of Z range.

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The precipitation/recrystallization interaction in HSLA steels were investigated using computer modelling based on the classical nucleation and growth theory. Using the computer model developed, the RPTT(recrystallization-precipitation-temperature-time) diagram was constructed to analyze the interaction between precipitation and recrystallization in hot rolled Nb steels. The three region interaction behavior was confirmed in the RPTT diagram, which was in agreement with the reported interaction of precipitation and recrystallization. It was found that the kinetics of precipitation after recrystallization was faster than that of strain-free precipitation. it has been generally known that the nose of the precipitation curve was shifted to a shorter time and a higher temperature with increasing strain, diffusivity, C and Nb contents and decreasing interfacial energy. However, with regard to the strain effect, the nose temperature was shifted to a longer time and a lower temperature with increasing strain greater than a critical value. It was found that the average size of precipitate before completing precipitation were less than 5OA. Comparison of the reported data with the predicted behavior appeared to be satisfactory, which indicates that the present precipitation model can be used to describe the interaction of precipitation and recrystallization in Nb microalloyed steels.

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The effect of phosphorus and boron addition on the development of {111} recrystallization texture and the strength in Ti-stabilized extra low carbon steel sheet has been investigated. A proper combination of alloying elements and heat treatments in steel sheet for deep drawing gave a strong {111} recrystallitation texture and high strength through a simulated continuous annealig cycle. The additions of phosphorus had a minor influence on the development of {111} recrystallization texture and {111} components increased with low finishing temperature at 850℃ in the hot rolling stage. Increasing the phosphorus content increases the large amount of precipitates which are composed of FeTiP compounds. Also, the Ti content of the compounds has been increased. The additions of phosphorus and boron were usful to enhance the strength and the tensile stenghth of Fe-Ti-1.0%P-0.004%B steel in the annealed condition was 80㎏f/㎟.1992)

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The mechanism far the amorphization induced by mechanical alloying(MA) has been studied in the immiscible Cu-Ta system. A mixture of copper and tantalum powders at a composition ratio Ta : Cu=7 : 3 was used. The first 30h of milling essentially results in the reduction in Ta and Cu grain size down to about 100Å without measurable formation of an amorphous phase. The thermally assisted amorphization(TAA) becomes noticeable after 60h of milling. The higher the ambient temperature, the faster the amorphization proceeds. The TAA effect is also observed by annealing a partially amorphous MA powders. The microstructure after 30h of milling is such that fine Cu crystallites are embedded in the finely-grained Ta matrix. Here an interfacial energy contribution is large enough to raise the free energy to that of an amorphous phase. Now high temperature milling or annealing allows an energetically down-hill process to occur. This is most likely responsible for the observed TAA effect in the Cu-Ta system characterized by a positive heat of mixing. (Received August 10, 1992)

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The effect of coating SiC on WC powder surface was investigated in an effort to replace Co with Ni as the binder metal for cemented carbides based on WC-Co system. The density, microstructure and pore distribution of materials conventionally sintered at 1450℃ were examined as a function of the amount of SiC. The SiC-coating retarded coarsening of WC grains compared to conventional WC-Ni so that it resulted in a relatively uniform distribution of the grain size. Other improved characteristics of SiC-coated material include suppression of formation of the pores and θ phase (W₃Ni₃C), which are trouble some in WC-Ni system because of their deleterious effect on transverse rupture strength, and enhancement of hardness as compared to similar materials based on WC-Co and WC-Ni.

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Experiments were performed to investigate the effect of the thermomechanical treatment on the reverse transformation from martensite (α`) to austenite(γ). The mechanism of austenite reversion was changed from the diffusional transformation to the shear transformation with increase of the heating rate in Fe-14.5% Cr-8.7% Ni alloy. The reversion temperature was decreased with decrease of the heating rate and with increase of the amount of cold reduction in the diffusionally reverted steels. However, temperatures were not affected by these parameters in the shear transformed steels. Fine grained austenite was obtained by the reversion treatment of Fe-14.5%Cr-8.7% Ni alloy which had about 25% athermal martensite in the as-hot rolled condition. This was attributed to the fact that the Ms temperature was lowered by refining the reverted austenite grain size.

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This paper is concerned with a study of the microstructural development of the adiabatic shear band formed by dynamic torsional experiments using thin-walled tubular specimens of a tempered martensitic HY-100 steel. The strain rates imposed were about 10³/sec and local temperature increases of about 600℃ within the shear bands were measured. The shear band microstructure was examined by optical and transmission electron microscopy, revealing following two distinct microstructures, i.e., highly elongated narrow subgrains extended in the shear direction and fine equiaxed cells. Although the proportions of the two microstructures varied for different specimens, the microstructural observations were interpreted by a process of dynamic recovery accompanying large deformation and high temperature rise within the shear band. There was no evidence to support phase transformation to austenite followed by martensite formation or dynamic recrystallization.

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