• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.60-63
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• 2003

Semi-solid forming is the process of stirring alloy during solidification, making the mixture of liquid and solid, solidifying it, reheating it to the solid-liquid coexistent temperature, and then injecting this semi solid slurry into dies. In the semi-solid die casting process, it is very important to find out the correlation of injection condition, microstructure and mechanical properties. Especially, an improper injection condition is the main cause of liquid segregation and non-homogeneous mechanical properties due to the difference of solid fraction according to the position of the products. To ensure the database requisite to the semi-solid die casting product, it is essential to acquire the mechanical properties considering liquid segregation to the injection condition. In this study, the effect of injection condition on liquid segregation, formability, microstructure and mechanical properties in a thin product was investigated.

• Journal of Powder Materials
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• v.9 no.3
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• pp.182-188
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• 2002

Conventional Fe-Co alloys are important soft magnetic materials that have been widely used in industry. Compared to its polycrystalline counterpart, the nanostructured materials have showed superior magnetic properties, such as higher permeability and lower coercivity due to the single domain configuration. However, magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as grain size, internal strain and crystal structure. Thus, studies on synthesis of nanostructured materials with controlled microstructure are necessary for a significant improvement in magnetic properties. In the present work, starting with two powder mixtures of Fe and Co produced by mechanical alloying (MA) and hydrogen reduction process (HRP), differences in the preparation process and in the resulting microstructural characteristics will be described for the nano-sized Fe-Co alloy particles. Moreover, we discuss the effect of the microstructure such as crystal structure and grain size of Fe-Co alloys on the magnetic properties.

• Transactions on Electrical and Electronic Materials
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• v.6 no.4
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• pp.144-148
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• 2005

The microstructure and electrical properties of varistor ceramics, which are composed of Zn-Pr­Co-Cr-Dy-oxide system, were investigated at various dysprosia $(Dy_2O_3)$ addition contents. The $DY_2O_3$ microstructurally played the role of inhibition for the densification and grain growth. As the $DY_2O_3$ content increased, the density decreased in the range of $5.51-4.90 g/cm^3$, reaching maximum at $0.5 mol\%$ and the average ZnO grain size decreased in the range of $17.7-6.0{\mu}m$. The incorporation of $DY_2O_3$ significantly improved the nonlinear properties of varistors, above 30 in nonlinear exponent, compared with that without $DY_2O_3$. The varistors with the best performance of nonlinear properties was obtained $DY_2O_3$ content of $1.0 mol\%$, 49 in nonlinear exponent and $0.5{\mu}A$ in leakage current.

• Journal of Welding and Joining
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• v.8 no.2
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• pp.27-39
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• 1990

The effect of silicon and manganese, in the ranges of 0.3% to 1.0wt% Si and 0.7 to 2.6wt%Mn, on the microstructure and mechanical properties of flux cored arc welded deposits have been investigated for the purpose of improving mechanical properties. Microstructure of weld metals was mainly influenced by manganese content, and manganese increased the volum fraction of acicular ferrite and refined the microstructure. Also, tensile properties were governed by manganese content, ultimate tensile strength and yield strength were increased by approximately 82MPa and 58MPa per 1% Mn addition to the deposit. Toughness was improved by increasing Mn content and lowering Si content. Optimal impact properties were obtained at above 1.8wt% Mn and below 0.5wt% Si. Acicular ferrite was predominant factor in improving mechanical properties. Formation of acicular ferrite was promoted by manganese and no direct relationship between AF(acicular ferrite) proportion and oxygen in weld metal was found.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.1
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• pp.9-16
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• 2008

It is important not only to reduce the casting defects of piston but also to improvement in the mechanical properties(hardness) of piston for the air compressor. The blow hole is typical casting defects in the conventional cast of aluminium alloy(AC8A-T6) piston. Because of the heat treatment method, mechanical properties of the aluminium alloy for piston was decided on the heat treatment method and cycle. Therefore, we tested on the development of mechanical properties and on the casting defects of piston for the air compressor in accordance with the heat treatment and casting condition. After the heat treatment and casting was carried out as several times, and was compared with the imported piston. As a result of several investigations; microstructure, hardness and casting defects of piston was changed under the influence of the heat treatment and casting method. When the cooling rate was controlled and the uni-cast method used, it bas the same mechanical properties and microstructure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.8
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• pp.496-500
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• 2017

$Pb(Mn_{1/3}Nb_{2/3})_{0.07}(Ni_{1/3}Nb_{2/3})_{0.10}(Zr_{0.5}Ti_{0.5})_{0.83}O_3$ composition ceramics with high piezoelectric properties were fabricated by the columbite precursor method for ultrasonic generators, and the effects of sintering temperature on microstructure and piezoelectric properties were systematically investigated. It was found that the tetragonality of the ceramics decreased with increase in sintering temperature. Moreover, excellent physical properties such as $d_{33}=447pC/N$, ${\varepsilon}_r=1,843$, $k_p=0.641$, and $Q_m=1,207$ were obtained for an ultrasonic generator when the second calcination temperature and sintering temperature were $720^{\circ}C$ and $920^{\circ}C$, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.83-92
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• 1998

In this paper, an experimental study has been carried out to develop an aluminum forged piston which has good mechanical properties. Through the experiment, the cavity filling, microstructure and mechanical properties of the final product are investigated with respect to chosen process parameters, which are die shape, heat-treatment condition and preform shape. The mechanical properties of the forged piston are compared with these of the cast piston. As the results, an appropriate die-shape is obtained to produce a perfect piston. The suitable heat-treatment condition and preform-shape are found to good hardness and minute microstructure in the forged piston. And we could obtain the mechanical properties(tensile strength, elongation and hardness) of the forged piston are superior to these of the cast piston.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.323-331
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• 2015

Zirconium alloys are widely used in nuclear reactors as structural materials. During the operation, they are exposed to fast neutrons. Ion irradiation is used to simulate the damage introduced by neutron irradiation. In this article, we briefly review the neutron irradiation damage of zirconium alloys, then summarize the effect of ion irradiation on microstructural evolution, mechanical and corrosion properties, and their relationships. The microstructure components consist of dislocation loops, second phase precipitates, and gas bubbles. The microstructure parameters are also included such as domain size and microstrain determined by X-ray diffraction and the S-parameter determined by positron annihilation. Understanding the relationships of microstructure and properties is necessary for developing new advanced materials with higher irradiation tolerance.

• Transactions of Materials Processing
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• v.31 no.3
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• pp.151-159
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• 2022

Ti alloys are used in a wide range of applications, especially for aviation and medical purposes, because of their high specific strength and excellent corrosion properties. When subjected to various manufacturing processes, one of the most popular Ti alloys, Ti-6Al-4V, exhibits a variety of microstructural and mechanical properties that makes it an attractive lightweight metal. The purpose of this study was to analyze the microstructure and mechanical properties of Ti alloy wires. Subsequently, the microstructure and electrochemical behavior of Ti alloy bolts produced from these wires were analyzed. The Ti alloy wires are manufactured with different diameters (6.22, 7.81 mm alloys), and their microstructures are measured using electron backscatter diffraction. Recrystallization was observed to occur significantly in the 7.81 alloy than in the 6.81 alloy, and the strain distribution of 7.81 alloy is seen to be likely more uniform than 6.22 alloy. Ti alloy bolt was then forged under moderate temperature by using the 7.81 alloy. Results of the electrochemical analysis indicate that the Ti alloy bolt has excellent corrosion resistance.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.11b
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• pp.15-31
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• 1999

The Pusan Clay is analyzed hereafter from a point of view of mineralogy and microstructure. Results indicate that the Pusan Clay is basically illitic in nature and that the soil microstructure reveals some characteristics which could be responsible for its brittle behavior as observed from sample disturbance. The overall analysis would tend to consider that the Pusan Clay profile analyzed here shows mechanical properties similar to well structured soils or so-called cemented soils.