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Effect of carbon on the carbide microstructure of spray-formed high speed steels, Fe-xC-4.3Cr-6.5Mo-5.5W-5V-8.5Co, was investigated by calculating the phase equilibria via Thermo-Calc program and by analyzing their carbide micronstructure via transmission electron microscopy in particular. The calculation showed that the volume fraction of fine secondary carbides increases with carbon concentration and that fine secondary MC carbides become more prominent over M_6C carbides at larger carbon concentration. The result further showed that the driving force for the secondary MC carbides is distinctively larger than that for the secondary M_6C carbides. These results were in good agreement with the microstructural analysis using particularly TEM showing that the fine secondary carbides are mostly the MC carbides and that their volume fraction increases with carbon concentration. Tempering treatment results in a large increase of the hardness and bend strength of these steels. This is primarily because of the precipitation of fine secondary MC carbides during tempering treatment. This tempering effect was more pronounced at larger carbon content because of the larger amount of precipitation of fine secondary MC carbides. The bend deflection in as-rolled condition decreased with increasing carbon content. This appeared to be closely related to the variation of the amount of coarse primary carbides with carbon content.

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To investigate the effects of graphite contents on the mechanical and vibration damping properties, through manufacturing Al/Gr. composites by compacting and extruding Al and graphite powders, rolling its specimen up to 80%, and testing the specimen for its hardness, tensile strength, vibration damping, etc. The followings are the results as; microstructure observation showed that the Al/Gr. composites are uniformed distribution, which means its adequacy for composites. When Al/Gr. composites was rolled, the graphite shape was modified to plate shape at the parallel side to the rolling direction. According to the result of hardness tests on graphite, the more the graphite content and the smaller the rolling ratio, the less the hardness. The result of tensile strength tests show that the tensile strength increase as the graphite content deceases or the rolling ratio increases. The more the graphite content or the smaller the rolling ratio, the bigger the vibration damping coefficient. When Al contains graphite up to 15%, the tensile strength decreases by 27%, whereas, the vibration damping coefficient increases by 80%, which means inverse proportional relationship between the two.

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The effects of final annealing process on the mechanical properties of Zirconium alloys (Zr-0.4Nb-0.8Sn-xFeCrMn, Zr-0.2Nb-1.1Sn-xFeCrMn, Zr-1Nb-xFeCr), which were developed for nuclear fuel cladding applications. The mechanical properties were evaluated by tensile and creep tests. The creep test was performed at 400℃ under an applied stress of 150㎫ as a function of time. The tensile strength decreased rapidly with increasing the annealing temperature. Given an alloy, the yield strength of TD(transverse direction) was higher than that of RD(rolling direction). However, the tensile strength and elongation of TD were lower than those of RD. The creep strength with the annealing temperature showed to be much similiar trend to the tensile strength. The creep resistance of Alloy 1 (Zr-0.4Nb-0.8Sn-xFeCrMn) and Alloy 2 (Zr-0.2Nb-1.1Sn-xFeCrMn) appeared to be higher than those of Alloy 3 (Zr-1Nb-xFeCr) mainly due to the effect of solid solution hardening by Sn in Alloy 1 and Alloy 2.

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The mechanical and corrosion properties of thixoformed A357 alloys were examined with different reheating temperatures, and the results were compared with those of permanent mold cast A357 alloys. It was found that the thixoforming process significantly improved the mechanical properties (i.e., tensile elongation, impact energy and resistance to fatigue crack propagation) and the corrosion resistance of A357 alloys. A 380% increase in tensile elongation and a 120% increase in impact energy were, for example, observed with thixoforming process of A357 alloy in the as-fabricated condition, as compared to the PMC counterparts. The impact energy was extremely sensitive to reheating temperature due to the coarsening of eutectic Si particles. The resistance to fatigue crack propagation for the thixoformed alloy was also much higher than that of permanent mold cast counterpart in the as-fabricated condition. The resistance to both general corrosion and stress corrosion cracking was also greatly improved with thixoforming process. The present observations strongly suggest that the enhancement with thixoforming A357 alloy is largely associated with the size and shape of eutectic Si particles.

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The microstructure and texture evolution of Fe-16%Cr ferritic stainless steel has been studied with the variation of annealing process. Interrelation between ridging phenomenon and microtexture was investigated. The annealing process was conducted in 4 different types, such as B-C, B-B, C-C and C-B. (B: batch annealing, C: continuous annealing) in both hot band and cold rolled steels. The rolling and recrystallization textures at each process were examined by orientation distribution function(ODF). In order to investigate the orientation of each grain and the existence of grain colonies, microtexture measurements were performed with electron back-scatter diffraction(EBSD) on the TD section. The ridging behavior was surveyed after 15% tensile elongation. It was found that the ridging property was improved remarkably in C-B annealing process due to the disintegration of coarse colonies after full recrystallization. It was clearly found that the ridging phenomenon was closely related with the existence of grain clusters or grain colonies having the {001}$lt;110$gt; orientation.

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This articles is concerned with the mean-field micromechanics model that has been developed by several investigators as a powerful modification of Eshelby`s theory for the study of the macromechanical behavior of composite materials. The energy approach that has been proposed is generalized and its applications to specific problem are presented and discussed. First, a general framework of the model is reformulated with emphasis on clarification of the key approximation involved. The model is then applied to the prediction of overall elastic properties of Al-SiC composites. For the system with randomly oriented spheroidal particles in particular, the overall Young`s, bulk and shear moduli, computed as functions of the particle aspect ratio. The remainder of this article is devoted to the analysis of elastic-plastic responses of composite materials.

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Codeposition behaviors of silicon carbide particles and nickel onto a steel in nickel Watts baths have been investigated using a rotating disc electrode. The zeta potential measurement and adsorption behavior of nickel ions onto the silicon carbide(SiC) particles suggests that SiC particles were attracted to the cathode after an adsorption of positive nickel ions in the bath. The polarization studies indicated that the addition of SiC particles enhanced the mass transfer of nickel ions onto the cathode surface and thus increased the current density. The SiC content in nickel-silicon carbide (Ni-SiC) deposits increased with increasing rotation speed and applied voltage.

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The microstructure and the mechanical properties of squeeze cast SiC whisker-reinforced aluminum composites based on either A356 Al or A390 Al matrices has been studied. One advantage of compositing procedure using SiC whisker preform is the possibility of selectively reinforcing near net-shape components, thus reducing the cost of fabricating a high performance component. Microstructural examination shows that roughly 17 vol. pct. whiskers were randomly oriented and inter-penetrated. Although, SiC preform was applied in squeeze casting procedure in order to get a uniform distribution of SiC whiskers, two types of reinforcement-free regions were identified; (i) continuous `veins` of the matrix alloy which are believed to be caused by cracks formed within the whisker preform during squeeze casting, and (ii) discontinuous `unreinforced areas` also of the matrix alloy, which are a result of small non-uniform distributions of SiC whiskers during preform fabrication. It is observed that there are severe differences of micro-hardness values and chemical compositions in such areas. The differences are caused by the variation of $quot;Mg gettering effect$quot; and the variation is believed to be closely related with the morphology of whiskers. In addition, tension and compression tests shows the addition of 17 vol. pct. of whiskers increased the elastic modulus by about 30-35% and showed discrepancy between tensile yield strength and compressive yield strength. The discrepancy between tensile and compressive strength indicates the presence of thermal residual stress in composite specimen.

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The high cycle fatigue behavior of squeeze cast SiC whisker-reinforced aluminum composites based on either A356 Al or A390 Al matrices has been studied. Squeeze cast Al/SiCw specimens, which contain roughtly 17 vol. pct. whiskers from two different sources, have been examined for their high cycle fatigue strength under fully reversed test conditions using a staircase method to determine the mean fatigue strength at 10^7 cycles. The results show 30 to 40% increases in the fatigue strength of the A356 Al-based composites when compared to the unreinforced matrix alloy, but much less fatigue strengthening in the A390Al-based composites. A fractographic analysis indicates that about 80% of the composite specimens fail as a result of crack initiation within regions which are characterized by low volume fractions of the SiC whiskers. These reinforcement-free regions assume two forms: continuous $quot;veins,$quot; which are the more deleterious to fatigue, and discontinuous $quot;unreinforced areas,$quot; which are deleterious only in certain shapes and sizes. Both finite element analysis and Eshelby-based analysis indicate that the localized stresses within the unreinforced regions appear to be high enough to initiate fatigue cracks, especially if unreinforced ares are elongated and their major axis is aligned to the stress axis. The fractographic analysis also identifies the importance of primary Si particles in limiting the fatigue strength of the A390Al-based composites. In addition, low level of Mg in the ureinforced region, which is caused by a $quot;Mg ettering$quot; effect, results in the low hardness and significantly decreases the fatigue strength.

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In continuous electroplating of steel strip using sulfate bath, the bath can be easily contaminated by ferrous ions dissolved from steel strip due to it low pH. When the phosphate conversion coating was applied subsequently on the electro-galvanized coating layer, which was plated from the contaminated bath, the surface defect called black mark could be formed on the phosphate surface. The formation of black mark on the phosphate surface seemed to be arisen from the uneven co-deposition of iron into the electro-galvanized layer, which would render non-uniform coating weight distribution of the phosphate layer. Because only the uppermost layer of the electro-galvanized coating affects the coating weight of the phosphate layer, it could be possible to prevent the formation of black mark if the ordinary high current density plating is followed by the final low current density plating, which would give uniform and low iron content in the electro-galvanized coating layer.

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