• Journal of Welding and Joining
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• v.21 no.3
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• pp.78-84
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• 2003

The changes of microstructure and hardness of TLP bonds of directionally solidified Ni base superalloy, GTD-111, with variation of homogenizing and aging treatment were investigated. The specimens were bonded at 1403K for 7.2ks using different insert metals such as MBF-50, MBF-80 and MBF-90 and they were homogenized at 1393K with various holding time. At center of bonded interlayer homogenized for hold time 30h, the contents of aluminum and titanium were approximately 90% and 95% of base metal, respectively. In this study, aging was performed at three different kinds : one step aging ; 1113K $\times$ 16h, two step aging ; 1113K $\times$ 10h ⇒ 1103K $\times$ 10h, three step aging ; 1113K $\times$ 10h ⇒ 1103K $\times$ 8h ⇒ 922K $\times$ 24h. ${\gamma}$' volume fraction and hardness of joints were high in the sequence of one step, two step and three step aging, whereas ${\gamma}$' volume fraction and hardness of joints obtained by three step aging treatment were higher than those of raw material. Tensile properties of joints bonded with MBF-80 and MBF-90, homogenized at 1393K for 30h and then three step aged became excellent than those of raw material, however, joint bonded with MBF-50 was poor.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.2
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• pp.57-60
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• 2019

The impact of two-step treatment on the mechanical properties of the 6061 Al alloy was investigated by testing the hardness and electrical conductance values. After two-step aging treatment, the hardness and electrical conductivity of the alloy was increased, and if the first aging treatment temperature was lower than the secondary aging treatment temperature, both the hardness and the electrical conductivity were not increased. The higher the temperature of the first aging treatment, the higher the hardness. The temperature of the first aging treatment is $175^{\circ}C$, $150^{\circ}C$, $120^{\circ}C$, and the second is $175^{\circ}C$ and $120^{\circ}C$.

• Food Science and Preservation
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• v.23 no.3
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• pp.301-309
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• 2016

The objective of this study was to investigate physicochemical and antioxidant characteristics of immature flat persimmon during 7 heat treatment aging steps. The pH decreased, and hence, acidity increased with aging. Hunter L value decreased with aging. The a value rapidly increased until step 3, whereas the b value decreased. Fructose content decreased while glucose contents slightly increased during aging. Hardness, chewiness and gumminess rapidly decreased, indicating softening in texture, but it was negligible after aging step 3. Phenolic compounds including gallic acid and homogentisic acid were detected at step 3 and then gradually increased with aging. However, contents of flavonoid and tannin were much higher in step 1 sample than others. The antioxidant activities observed by DPPH, ABTS, and FRAP assay were the highest at step 1 possibly due to the higher levels of flavonoids and tannin acid in the step 1 sample.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.263-268
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• 2011

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at $90^{\circ}C$ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at $60^{\circ}C$ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

• Journal of Korean Association for Spatial Structures
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• v.13 no.4
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• pp.67-74
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• 2013

The Age-adjusted effective Modulus Method(AEMM) is one of the methods adopted for the construction stage analysis of concrete structures. The AEMM uses the aging factor to consider the effects of the varying concrete stress. In the aspects of computation time and the accuracy of the results, the AEMM is considered as one of most appropriate methods for construction stage analysis of tall building structures. Previous researches proposed appropriate values of the aging factor in the forms of graphs or using very simple equations. In this paper, an equation for estimating the aging factor as a function of rebar ratio in the section, compressive strength of concrete, notional member dimension, and age of concrete at the load application. The validity of aging factor proposed in this paper were examined by the comparison with the results of step-by step method.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.101-107
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• 2020

In this paper, step-curing, which includes the change of curing temperature on the curing process, was applied to reduce curing day of HTPB/AP based propellant. This study targets the improvement of productivity of HTPB/AP based solid rocket motor. Comparison of mechanical properties of propellant resulted in the change of normal curing condition (60℃, 5 days) to step-curing condition (60℃, 1 day / 65℃, 3 days). Post-cure test was conducted to determine the impact on the shelf life of the solid rocket motor. The aging characteristics of propellants were analyzed by measuring mechanical properties and thermal expansion factor. To step-cured propellant, accelerated aging test was performed for 12 weeks, followed by tensile test. Sm(bar) and Em(%) were higher than 8 bar and 40% each, showing excellent mechanical properties.

• Korean Journal of Materials Research
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• v.10 no.7
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• pp.493-498
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• 2000

The effects of RRA treatment on the microstructures and mechanical properties of 7050 Al alloy were investigated by differential scanning calolimetry, transmission electron microscopy, microhardness measurement and electrical conductivity. The hardness of 2nd-step aged specimen at $175^{\circ}C$ was decreased to mimimum value and increased to a peak hardness, and then re-decreased with retrogression treatment. It was found that the hardness of 2nd-step aged specimen was further increased by 3rd step aging treatment($120^{\circ}C$x24h). The initial decrease in hardness during 2nd-step aging was due to the partial dissolution of pre-existing GP zone, the major precipitation hardening phase at T6 condition. It was confirmed that the major precipitation hardening phase at 3rd-step aging was GP zone and η' phase. The electrical conductivity increased continually through 2nd-step and 3rd-step aging treatment. It was conclude that the optium 2nd-step aging condition was at $175^{\circ}C$ for 50min by considering the hardness and electrical conductivity.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.9-16
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• 2011

To develop a 6061 aluminum alloy with low residual stress and high tensile strength, a cryogenic treatment process was investigated. Compared to the conventional heat treatment process for precipitation hardening with artificial aging, the cryogenic treatment process has two additional steps. The first step is cryogenic quenching of the sample into liquid nitrogen, the second step is up-hill quenching of the sample into boiling water. The residual stress for the sample was measured by the $sin^2{\psi}$ method with X-ray diffraction. The 6061 aluminum alloy sample showed 67% relief in stress at the cryogenic treatment process with artificial aging at $175^{\circ}C$. From this study, it was found that the optimum cryogenic treatment process for a sample with low residual stress and high tensile strength is relatively low cooling speed in the cryogenic quenching step and a very high heating speed in the up-hill quenching step.

• Journal of the Korean Ceramic Society
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• v.40 no.2
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• pp.132-138
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• 2003

The effect of synthesis condition, type of starting materials, mole ratio, mixing. aging, and crystallization temperature and time, on the size of FAU-type zeolite has been studied. Different mixing route may lead to the different phase of zeolite even with the same starting materials. In general, the size of particles is smaller after aging, especially at lower aging temperature. Two step mixture gel preparation method resulted to not only the reduction of crystallization time but also that of particle size, but without the aging of two mixture gels before the preparation of the overall gel in the second step, only the crystallization time was reduced, not the particle size. The FAU-type zeolite with average particle size 0.4$\mu$m and BET surface area 838 $m^2$/g was obtained from starting materials of liquid sodium silicate, sodium aluminate, and sodium hydroxide with two step preparation of mixture gel, aging of the mixture gels in two steps, which effectively reduced the crystallization time and particle size.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.695-700
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• 1999

Effects of two-step aging treatment on the stress corrosion cracking(SCC) resistance of 7050 Al alloy were investigated by transmission electron microscopy, electrical conductivity measurement and stress corrosion facter(SCF) evaluation. It was found that η', principal hardening phase, transformed to η during over aging above maximum hardness, and SCC resistance was improved by increasing of the size and interspacing of η particles in matrix and grain boundary. The electrical conductivity increased with aging time, but SCF decreased due to the decrease of yield strength. This results mean increase of SCC resistance The optimum two-step aging condition in forged 7050 Al alloy was to be first aged at $120^{\circ}C$ for 6h and then finally aged at $175^{\circ}C$ for 12h.