• Proceedings of the KWS Conference
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• 2006.10a
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• pp.109-111
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• 2006

In this study, microstructure and mechanical properties for the friction stir welded 2519Al-T87 alloy of the thickness of 38.8mm were studied using DSC, OM, SEM and micro hardness tester. DSC analysis show that GP Zone, ${\theta}'$ and $\theta$ phases in upper part and ${\theta}'$ and $\theta$ phase in lower part of the FSW zone. Recrystallized large grains are observed in HAZ, and elongated small and large grain in the TMAZ. In SZ, very small grains forms by high plastic deformation and heat from friction by tool and specimen.

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.85-92
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• 1993

Oxynitride glasses in Na-Ca-Si-O-N system were prepared by melting at 135$0^{\circ}C$ for 2 hours in N2 gas. The effects of Si/Na mole ratio and the various Si3N4 contents were investigated. Stable oxynitride glasses can be obtained up to 9wt.% Si3N4 content in case the Si/Na mole ratio was 2.12 and 1.62, but $\beta$-Si3N4 was precipitated at 9wt.% Si3N4 content in case the Si/Na mole rtio was 1.12. Density (p), chemical durability, hardness (Hv), and fracture toughness (KIC) increased with increasing Si3N4 content. In cae the Si/Na mole ratio was 1.12, the increment of properties was remarkable but hardness and fracture toughness did not increase no longer owing to precipitation of $\beta$-Si3N4.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.39-43
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• 1994

The effects of ageing treatment on the mechanical properties of two Cu-bearing HSLA(High Strength Low Alloy) steels, HSLA-A and HSLA-B ,were studied by means of SEM, TEM, tensile, charpy impact and hardness tests. These steels showed excellent combination in strength and toughness at an ageing of $650^{\circ}C$ by the precipitation of $\varepsilon$-Cu and low carbon alloying. The peak strength was achieved at an ageing of 50$0^{\circ}C$ in both steels, while the impact energy was very low in this peak strength. With ageing temperature above this temperature, strength was decreased whereas impact energy increased. A marked increase in hardness above 675$^{\circ}C$ was associated with the formation of “M-A constituents” which forms during cooling from austenite-ferrite two phase region. The impact transition temperature of HSLA-A and HSLA-B steels were -l$25^{\circ}C$ and -145$^{\circ}C$, respectively.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.3-9
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• 2006

The phase changes, nitride precipitation and hardness variations of 14%Cr-6.7Ni-0.65Mo-0.26Nb-0.05V-0.03C super martensitic stainless steel were investigated after nitrogen permeation heat treatment at a temperature range between $1050^{\circ}C$ and $1150^{\circ}C$. The nitrogen-permeated surface layer was transformed into austenite. The rectangular type NbN, NbCrN precipitates and fine round type precipitate were coexisted in the surface austenite layer, while the interior region that was free from nitrogen permeation kept the martensitic phase. The hardness of surface austenite showed 280 Hv, while the interior region of martensite phase represented 340 Hv. When tempering the nitrogen-permeated steel at $450^{\circ}C$, a maximum hardness of 433 Hv was appeared, probably this is attributed to the secondary hardening effect of the precipitates. The nitrogen concentration decreased gradually with increasing depth below the surface after showing a maximum of 0.3% at the outmost surface. The strong affinity between nitrogen and Cr enabled the substitutional element Cr to move from interiors to the surface when nitrogen diffuse form surface to the interior. Corrosion resistance of nitrogen permeated steel was superior to that of solution-anneaed steel in the solution of 1N $H_2SO_4$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.6
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• pp.561-565
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• 2007

Because of a good wear resistance and a stable contact resistance, Ag-CdO is widely used as electrical contact material. But, the Cd-oxide mainly exists as a coarse particle and adversely affected to environment. As a reason, $Ag-SnO_2$ alloy has been developed. The Sn-oxide maintains stable and fine particle even at high temperature. In order to investigate the effect of Misch metal (Mm) additional that affects the formation of the oxide and the formation of fine matrix Ag, we studied the microstructures and properties of Ag-Sn-In(-Mm) material fabricated by rapid solidification process. The experimental procedure were melting using high frequency induction, melt spinning, and internal oxidation. The Mm addition makes Ag matrix more fine than no Mm addition. The reason is that the addition of Misch metal decreased a latent heat of fusion of alloy, as a result the rapid solidification effect of alloy is increased. The maximum hardness shows at 0.3 wt%Mm. after that the hardness is decreased until 0.4 wt% Mm, but still larger than no Mm addition alloy. At 0.5 wt% Mm alloy, the precipitation of Misch metal causes a decrease of hardness than no Mm addition alloy.

• Journal of the Semiconductor & Display Technology
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• v.12 no.4
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• pp.55-59
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• 2013

Mold die sticking arises from silica filler abrasion to the cavity surface. Ni-P electroplating was examined to substitute conventional hard Cr plating. More than 4% of Phosphorus in the electroplated film produces nano crystal structure and annealing makes $Ni_3P$ precipitated to get hardness values equivalent to hard Cr.

• Membrane Journal
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• v.17 no.3
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• pp.191-196
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• 2007

In the study, excess of lime-soda ash(L-S) was added to groundwater for chemical precipitation of hardness ions. After formation of the coagulated flocs, sedimentation step was replaced with crossflow ultrafiltration(UF) process using tubular ceramic membrane. As results, our treated water was below total hardness(TH) 10 mg/L as $CaCO_3$ from groundwater using washing water in a soymilk factory. Then, we investigated the change of permeat flux(J) and dimensionless permeate flux($J/J_0$) during experiments for variations of TMP(Trans-membrane pressure) or flow rate, to see effect of TMP or flow rate on membrane fouling by the coagulated Inorganic flocs. In the result, membrane fouling and rejection rate of total hardness were not affected by TMP and flow rate variations in the range of our experiments.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.105-110
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• 2001

It has recently been raised main issue how solve the problem of insufficient energy. One of the solution is to increase the thermal efficiency of power generation system. For the purpose of high efficiency, it is necessary to increase the steam temperature and pressure. So, the use of modified $9{\sim}12%Cr$ steel having superior creep rupture strength and oxidation resistance is required to endure such severe environment. The evaluation of creep properties of those heat resistance material is very important to secure the reliability of high temperature and pressure structural components. Since creep properties are determined by microstructural change such as carbide precipitation and coarsening, It is certain that there are some relationship between creep properties and hardness affected by microstructure. In this study, SP-Creep ruptured test for newly developed 9Cr steel being used as boiler valve material was performed, and creep properties of the material were evaluated. Also, hardness test were performed and hardness results were related to the creep properties such as LMP and creep strength to verify the availability of SP-Creep test as creep test method.

• Journal of Powder Materials
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• v.13 no.3 s.56
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• pp.178-186
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• 2006

The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.237-245
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• 1997

A study was conducted to examine the effects of In addition on the precipitation behaviors of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry, transmission electron microscopy and micro-hardness tester. DSC analysis was measured over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $2{\sim}20^{\circ}C$/min. The heat evolution peaks due to the formation of GP zone and ${\delta}$'phase shift to higher temperature and the peaks to $T_1$ and ${\theta}$'phases shift to lower temperature by In addition. From this result, it was proved that the formation of GP zone and ${\delta}$'phase is suppresed whereas that of $T_1$ and ${\theta}$'phases are accelerated by the In addition of 0.15wt%. The age hardening curve aged at $190^{\circ}C$ showed that the In bearing alloy(alloy B) has more faster age hardening response and a higher peak hardness than In-free alloy(alloy A), attributed to the fine and homogeneous distribution of $T_1$ and ${\theta}$'phases. The activation energies for the formation of ${\delta}$'phase in In-free and In-bearing alloys are 22.3kcal/mol and 18.6kcal/mol, respectively. Those for $T_1(+{\theta}^{\prime})$ phase of In-free and In-bearing alloys are 24.3 and 37.5kcal/mol, respectively. Quenched-in excess vacancies play an important role to the formation of precipitates.