• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_2
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• pp.669-674
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• 2020

Liquid-phase-sintered (LPS) SiC materials were briefly examined with their microstructure and mechanical property. Especially, effect of high-temperature exposure on the tendency of fracture toughness of LPS-SiC were introduced. The LPS-SiC was fabricated in hot-press by sintering powder mixture of sub-micron SiC and sintering additives of Al₂O₃-Y₂O₃. LPS-SiC represented dense morphology and SiC grain-growth with some amount of micro-pores and clustered additives as pore-filling. The strength of LPS-SiC might affected by distribution of micro-pores. LPS-SiC tended to decrease fracture toughness depending on increasing exposure temperature and time.

• Journal of Surface Science and Engineering
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• v.26 no.4
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• pp.192-202
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• 1993

The characteristics of the high-performance ceramic coatings fabricated on the optimum processings con-ditions for the atmospheric plasma spraying are evaluated by various material tests and analyses. The opti-mum processing parameters for the plasma spraying are determined by using the two-level orthogonal arrays of fractional factorial testing method as a statistical approach. Material tests for the coating specimens are carried out to evaluate microstructure, hardness, adhesion strength, and deposition efficiency. The properties of Al2O3-13%TiO2 coating are discussed with regard to the effective processings parameters. The decarburization effects of WC-12%Co coating is examined by XRD analysis in terms of the arc power and the secondary gas species. The hardness of Al2O2-13%TiO2 coating is increased with the arc power and shows the maximum value at around 40 lpm of Ar gas flowrate, which appears to be the most critical parame-ter on the deposition efficiency. For reducing the decarburization of WC-12%Co coating, the injection of inert He gas instead of reactive H2 gas as a secondary gas is more effective than the dropping of arc power to lessen the plasma enthalpy.

• Journal of Surface Science and Engineering
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• v.27 no.5
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• pp.292-302
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• 1994

Alloy deposits of 80Sn-20Pb, electroplated on Cu-based leadframe alloy from an organic sulfonate bath were aged at $150^{\circ}C$ to form intermetallic phases between substrate and deposit, and effects of the deposit morphology, influenced by deposition conditions, on the fracture resistance of the 80Sn-20Pb deposit aged at $150^{\circ}C$ were examined. The growth rate of intermetallic compound layer on aging depended on the microstructure of deposit ; it was fastest in deposit formed using pulse current in bath without grain refining additive, but slowest in deposit formed using dc current in bath containing grain refining additive in spite of similar structure with equivalent grain size. The grain refining additive incorporated in electrodeposit appears to inhibit diffusion of atoms on aging, resulting in slow growth of intermetallic layer in the thickness direction but substantial growth in the lateral one. Density of surface cracks that were occurring when samples were subjected to the $90^{\circ}$-bending test increased with increasing the thickness of intermatallic layer on aging. For the same aged samples, the surface crack density of the sample electrodeposited from a bath containing the grain refining additive was the least due to the inhibiting effect of the additive incorporated into the deposit during electrolysis on atomic diffusion.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.263-270
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• 2012

This study investigates the effect of heat treatment on the mechanical properties of a forged Ni-based superalloy called Nimonic 80A. Nimonic 80A ingot samples were fabricated by vacuum spray casting to achieve a fine and homogenized microstructure. The ingot samples were subsequently hot-forged with the diameter of 220 mm at 1373 K. From the center to the surface of the forged Nimonic 80A, its average grain size decreased and its micro-Vickers hardness increased slightly. Solution treatment was carried out at 1353 K with 8 hours of air cooling followed by aging treatment, which was carried out in the range of 873-1073 K with various times from 0.5 to 256 hours. To set the optimum aging conditions, micro-Vickers hardness tests were performed. The maximum hardness value of 388.0 Hv was obtained by aging at 973 K for 32 hours. Also, tensile tests were performed for optimum aging conditions at room temperature and 873 K. The results can be used effectively to perform reasonable heat treatment of Nimonic 80A superalloy.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.531-538
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• 2012

In this study, we evaluated the fluidity of the Al-Zn based alloys which exhibit excellent mechanical properties. We conducted computer simulations of fluid flow using the results of DSC, DTA analysis and Java-based Materials Properties software (J. Mat. Pro). Such computer simulations were then compared with the results obtained from experimental observations. The computer simulation results and the experimental results were very similar in fluidity length. It was found that the fluidity length of Al-Zn alloys is improved by increasing the Zn content while decreasing the solidus temperature of an alloy. In addition, we elucidate the effect of Zn addition on variations in different mechanical properties and the microstructure characteristics of (Al-xZn3Cu0.4Si0.3Fe) x=20, 30, 40, and 45 wt% alloys fabricated by gravity casting.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1078-1083
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• 2010

In this study, high temperature oxidation behavior of Alloy 617 was investigated to evaluate the effect of grain size for Alloy 617. The grain size of grain-refined Alloy 617 (GR617) was reduced to $5{\mu}m$ from $71{\mu}m$ for as-received Alloy 617 (AR617) by recrystallization after cold rolling. After high temperature aging, the oxide layers of AR617 and GR617 consisted of $Cr_2O_3$ external oxide scale and $Al_2O_3$ internal oxide. The external oxide scale resulted in a Cr-depleted zone and a carbide free zone below the scale. The depth of the carbide free zone was deeply formed in GR617. On the other hand, the depth of the internal oxide layer in GR617 was shorter than that in AR617. After a 3-point bending test, crack propagation of GR617 was more restricted than that of AR617 because of the different microstructure of the internal oxide.

• Korean Journal of Metals and Materials
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• v.48 no.10
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• pp.936-941
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• 2010

Al-Zn based alloys are the most common types of wrought Al alloys. Although Al-Zn alloys have high strength, they cannot be applied to a conventional casting process. In this study, Al-Zn-based alloys applicable to a die casting process were developed successfully. The developed Al-45 wt% Zn-based alloys showed a fine equiaxed grain structure and high strength. A fine equiaxed grain having an average size of $25{\mu}m$ was obtained by the die casting process. The UTS and elongation of the new alloy are 475 MPa and ~3.5%, respectively. In addition, we elucidate the effect of a Zn addition on variations in different mechanical properties and the microstructure characteristics of (Al96.3-xZnxCu3Si0.4Fe0.3) x=20, 30, 40, and 45 wt% alloys fabricated by a die casting process.

• Korean Journal of Metals and Materials
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• v.50 no.5
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• pp.383-387
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• 2012

The activation of Mg-10 wt%$Fe_2O_3$ was completed after one hydriding-dehydriding cycle. Activated Mg-10 wt%$Fe_2O_3$ absorbed 5.54 wt% H for 60 min at 593 K under 12 bar $H_2$, and desorbed 1.04 wt% H for 60 min at 593 K under 1.0 bar $H_2$. The effect of the reactive grinding on the hydriding and dehydriding rates of Mg was weak. The reactive grinding of Mg with $Fe_2O_3$ is believed to increase the $H_2$-sorption rates by facilitating nucleation (by creating defects on the surface of the Mg particles and by the additive), by making cracks on the surface of Mg particles and reducing the particle size of Mg and thus by shortening the diffusion distances of hydrogen atoms. The added $Fe_2O_3$ and the $Fe_2O_3$ pulverized during mechanical grinding are considered to help the particles of magnesium become finer. Hydriding-dehydriding cycling is also considered to increase the $H_2$-sorption rates of Mg by creating defects and cracks and by reducing the particle size of Mg.

• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.796-804
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• 2018

The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.627-633
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• 2008

The austenitic Fe-Mn alloys have received considerable attention as a possible candidate for the automotive structural materials due to their high strength and high formability with high elongation. This research investigates the effect of alloying elements on the phase transformation, deformation behavior and mechanical properties in high Mn steels for the development of a high strength high ductility steel. The mechanical stability of austenitic phases is very important for high ductility and it depends largely on the composition of carbon, manganese and aluminum. The dominant deformation mode shifts from TRIP to TWIP mode as the amount of C, Mn and Al is increased. Especially, even a small amount of Al addition facilitates significantly TWIP deformation due to the increase of stacking fault energy in Fe-Mn alloys, this leads to increase the ductility and also decrease the crack sensitivity.