• Journal of Korea Foundry Society
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• v.36 no.5
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• pp.167-173
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• 2016

The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to 'standard heat-treatment'_(SHT), 'HIP (Hot Isostatic Pressing) heat-treatment'_(HHT), and 'HIP-simulated heat-treatment'_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the 'SHT' specimen, and needle shaped ${\delta}$ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and ${\delta}$ phases in the 'SHT' specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after 'HHT' and 'HS' treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of ${\gamma}^{{\prime}{\prime}}$ precipitation that occurs. Due to the higher fraction of coarse ${\gamma}^{{\prime}{\prime}}$ phases, the 'HHT' treated Alloy 718 showed excellent tensile strength.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.348-349
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• 2006

The plastic deformation behavior of cemented carbides is related to the WC grain boundary strength. Ab initio calculations predict that Co and Mn segregate to WC/WC grain boundaries. To experimentally study the effect of Mn, a WC-Co-Mn material was manufactured and compared to a WC-Co material. The microstructure was studied using scanning electron microscopy (SEM), including electron backscatter diffraction (EBSD). Special attention was paid to the WC grain size and the frequency of special low-energy grain boundaries. Mn was found to have negligible effect on both the WC grain growth and the fraction of $\sum2$ WC/WC boundaries in the as-sintered material.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.72-73
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• 2021

For the development of high-fluidity concrete using low-binder, The effect of the use of the developed acrylic viscosity agent on the physical properties of concrete evaluated. The amount acrylic viscosity agent used was 1.5%, 1.7%, and 2.0% based on the binder amount of 400kg/m3, and slump flow test, slump flow 500mm arrival time measurement, air volume measurement, and U-Box passing test were conducted to determine the effect of the physical properties of concrete. it was judged that 1.5% of the acrylic viscosity agent used in high-fluidity concrete using low-binder was most suitable.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.129-130
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• 2021

For the development of high-fluidity concrete using low-binder, The effect of the use of the developed acrylic viscosity agent on the physical properties of concrete evaluated. The amount acrylic viscosity agent used was 0.28%, 0.29% and 0.30% based on the binder amount of 350kg/m³, and slump flow test, air volume measurement, U-Box passing test and strength compressive were conducted to determine the effect of the physical properties of concrete. it was judged that 0.29% of the cellulose type viscosity agent used in high-fluidity concrete using low-binder was most suitable.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.22-25
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• 1995

This study is aimed for analyzing the effect on replacing change of fly ash and silica fume of high performance concrete. From the results, the flowability is good when the replacing rate of fly ash increases. The placeability is best in the ratio of 15 to 5 ; F.A:S.F and the segregation-resistibility is appeared good when the replacing ratio of silica fume increases.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.392-398
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• 1990

To improve free-cutting property, fine Pb, Bi particles is necessary to be distributed evenly in Al-Cu alloy. The control of added element size and distribution are very difficult because of the physical properties of Pb, Bi. The effect of master alloy compositions on microstructure and particle distribution was investigated. The ribbon shape of Pb-50wt% Bi master alloy showed the best results. And Ti addition improved even distribution of Pb, Bi particles. Particles grown from $L_2$ phase were considered to be the Pb, Bi compound.

• Journal of Korea Foundry Society
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• v.28 no.1
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• pp.25-30
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• 2008

To develop a functionally graded microstructure of cylindrical liner, effect of centrifugal casting parameters such as pouring temperature of hyper-eutectic Al-Si alloy melt, mold pre-heating temperature, and rotational frequency of mold on distribution of primary Si particles across wall thickness were investigated. Segregation tendency of Si particles toward inner side of cylindrical liner increased as the increase of rotational frequency of mold, pouring temperature of melt and mold pre-heating temperature. Especially, distribution density of primary Si particles within 1.5 mm from inner surface of cylindrical liner was above 35% under the centrifugal casting condition of $750^{\circ}C$ melt pouring temperature, $300^{\circ}C$ mold pre-heating temperature, and 2500 rpm mold rotational frequency.

• Journal of Powder Materials
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• v.6 no.2
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• pp.152-162
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• 1999

The present study is concerned with the effect of PM process variables on the microstructure by using atomized superalloy powders. It is suggested that the inhomogeneity of composition is strongly dependent on the process variables. The contents of segregation elements of plasma rotating electrode process (PREP) powders are larger than those of Ar atomization (AA) powders. As HIP treatment temperature in-increases, the secondary phases on the prior particle boundaries (PPB) have continuous,uniform distribution and high density, but the amount of PPB decreases suddenly at 1150$^{\circ}$C. Segregated phases on the PPB are identified to be MC type carbide. Brittle MC type carbides on the PPB provide fracture initiation sites and preferred fracture path, thereby leading to intergranular type brittle fracture.

• Journal of the Korean institute of surface engineering
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• v.27 no.1
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• pp.29-35
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• 1994

The effects of coating of 3$\mu\textrm{m}$ thickness on the mechanical property of alumina after heat treatment at 100$0^{\circ}C$ for 30minutes under $10^{-6}$torr vacuum was quantified in terms of modulus of rupture(MOR) using Weibull plot. While the copper coating did not change MOR of alumina due to the nonwetting behavior of Cu on $Al_2O_3$, the reactive titanium metal coating caused a noticeable 29% reduction in averaged MOr strength. This was related with the combined effects of microcracks in coating formed during heat treatment and good bonding character between Ti and $Al_2O_3$. The effect of cosputtering of Ti and Cu, bilayer coatings of Cu/Ti and Ti/Cu were also investigated. It was found that Ti, cosputtered, Cu/ti and Ti/Cu coatings reduced MOR strength of alumina in the order listed. This was correlated with the amount of Ti at coating/alumina inter-face associated with a coated layer or segregation of Ti during heat treatment.

• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.1-11
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• 1999

The effect of aliovalent dopents, $Nb_3O_5$ and MnO, on the grain growth kinetics of 12 mol% ceria stabilized tetragonal zirconia polycrystals (Ce-TZP) was studied. All specimens were sintered at $1550^{\circ}C$ for 20 minutes prior to annealing at different temperatures to study grain growth kinetics. Grain growth kinetics of Ce-TZP and 1 mol% $Nb_2O_5$ doped Ce-TZP (Ce-TZP/$Nb_3O_5$) during annealing at 1475, 1550, and $1600^{\circ}C$ adequately matched with square law $(D^2-D_\;o^2=k_at)$. However, grain growth in 1 mol% MnO suppressed grain growth in Ce-TZP by drag force exerted by $Mn^{+2}$ ions which segregated strongly to the positively-charged grain boundaries of Ce-TZP, $Nb_2O_5$ enhanced grain growth by increasing the concentration of vacancies of $Zr^{+4}$ ion and $Ce^{+4}$ ions. Surface analysis with X-ray photoelectron spectroscopy (XPS) showed the segregation of Mn+2 ions to grain boundaries. The kinetics of grain growth obtained in the base Ce-TZP and the Ce-TZPs with the aliovalent dopants were examined in the context of impurity drag effect and space charge effect.