• Korean Journal of Materials Research
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• v.3 no.3
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• pp.282-291
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• 1993

Joining ${Al}_{2}{O}_{3}$ and STS 304 stainless steel by active metal brazing method with using CuI Owt % Ti and Cu -7 .5wt % Zr insert metal, their interfaces were analyzed and strength of the joint brazed with Cu-7.5wt % Zr insert metal also investigated with shear strength testing method. In brazing with Cu-lOwt% Ti insert metal, the single reaction layer was formed by the reaction with Ti and ${Al}_{2}{O}_{3}$ at the interface between ${Al}_{2}{O}_{3}$ and insert metal, but the double reaction layer was found in brazing with Cu-7.5wt % Zr insert metal because of the difference of their wettability on the surface of ${Al}_{2}{O}_{3}$. Fracture shear strength about 86MPa was obtained from ${Al}_{2}{O}_{3}$/Cu-7.5wt% Zr/STS 304 stainless steel joint and reasonable strength of the joints is attributed to the formation of double reaction layer at the interface.

• Journal of Powder Materials
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• v.9 no.3
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• pp.189-198
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• 2002

In this work, transient liquid phase (TLP) bonding of Ni-Cr heat resisted cast alloy (HP) was investigated. And also the behaviors of the solid particles distributed in the interlayer during TLP bonding were investigated. The MBF-60 and solid particles (Ni, Fe, and $Al_2O_3$ powders respectively) added MBF-60 which will be a liquid phase coexisting with solid particles at the bonding temperature were used as insert metal. The effective and sound bonding was possible by spark plasma sinter-bonding due to the differences of electric resistance between base metal and liquid insert layer which creates high temperature region. During the isothermal solidification, $Al_2O_3$ particles and solid particles of liquid phase sintered insert metal have shown no growth, while Ni and Fe particles grow rapidly. In this TLP bonding using the MBF-60 and distributed Fe, Ni particles as insert materials, the whole isothermal solidification process was dominated by the growth rate of the solid particles distributed in the interlayer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.9
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• pp.679-687
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• 2003

Shock wave reduction in electrorheological(ER) smart structures is studied. ER insert is a composite structure comprising two elastic outer layers between which is sandwiched layer of ER fluid. When a voltage is applied across the outer layers. the shear modulus and the loss factor of the ER fluid are enabled, and thus the dynamic properties of the composite structure is altered. For the shock wave reduction in a hull mount of a submerged structure, ER inserts are made on the hull mount structure. To investigate the ER insert shape. many types of ER insert pattern are considered. Modal test of ER insert structures is performed to obtain the mode shapes, natural frequencies and the acceleration transmissibility. The acceleration transmissibility is reduced at such a frequency region when an electric field is applied. It is observed that the natural frequencies and mode shapes can be tunable by applying electric field. The ER-inserted hull mount is installed in an integrated system and the overall performance of shock wave reduction is tested. The possibility of shock wave reduction in the hull mount is demonstrated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.2
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• pp.139-146
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• 2021

In hybrid rocket combustion, the oxidizer swirl injection is frequently used to stabilize the combustion as the rotational velocity component affects the boundary layer flow. However, as the swirl strength increases, a problem arises where the combustion performance changes too much. Thus, this study attempts to control the low frequency instability while minimizing the change in combustion performance by adapting attenuated swirl injection with fuel insert used in reference [7]. To this end, a series of experimental tests were performed by varying swirl intensity and the location of the fuel insert. In the tests, the occurrence of combustion instability and combustion performance were closely monitored. The results confirmed that combustion instability was successfully suppressed at the condition of the swirl angle 6 degree and the location of fuel insert 310 mm. And, the changes in combustion pressure, O/F ratio, and fuel regression rate were found as minimal compared to the baseline case. Also the results reconfirmed that the formation of positive coupling between two high frequency oscillations in 500 Hz band, combustion pressure(p') and heat release oscillation(q'), is the necessary and sufficient condition of the occurrence of low frequency instability.

• Journal of Welding and Joining
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• v.13 no.4
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• pp.147-154
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• 1995

In order to study the bonding mechanism of Ni/B/Ni transient liquid phase bonding system, width of liquid layers were calculated, where in this system melting point of insert material(B) is higher than bonding temperature and melting point of base metal(Ni). Caclulated values were compared with experimental ones which were measured by bonding Ni/B/Ni system at 1433-1474K under vacuum atmosphere. As results, the width of initial liquid layer of Ni/B/Ni system was calculated as $W_{IL}$ = $W_{o}$[1 + {2.100..rho.$_{S/}$ ( $X_{3}$ + $X_{4}$)..rho.$_{Ni}$ }-.rho.$_{S/}$.rho. Ni/], and it was nearly same with experimental values. Maximum width of liquid layer, width of liquid layer during isothermal solidification and isothermal solidification time were calculated also.o.o.o.

• Journal of Welding and Joining
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• v.21 no.2
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• pp.64-69
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• 2003

The bonding phenomena and mechanical property of duplex stainless steel during brazing have been investigated. The UNS32550 was used for base metal, and the MBF50 was used for insert metal. Brazing was carried out under the various conditions (brazing temperature : 1473K, 1498K, holding time : 0∼1.8ks). There were various microconstituents in the bonded interlayer because of reaction between liquid insert metal and base metal. In the early stage of brazing, BN is formed in the bonded interlayer and base metal near the bonded layer. Cr made is formed in the bonded interlayer. The amount of BN and Cr nitrides decrease with the increase of bonding temperature and holding time. Superior shear strength of 550MPa is obtained by restraining the formation of nitrides. (Received January 17, 2003)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.65-70
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• 2002

The brazing of duplex stainless steels which is an essential process for rocket engine manufacturing has been investigated on bonding phenomena and shear strength. The UNS32550 was used for base metal, and the MBF-50 was used for insert metal. Brazing was carried out under the various conditions (brazing temperature : 1473K, 1498K, holding time : 0, 0.3, 0.9, 1.8 ks). There were various phases in the joint because of reaction between liquid insert metal and base metal, In the early stage, BN is formed in the bonded interlayer and base metal near the bonded layer. Cr nitride is formed in the bonded interlayer. The amount of BN and Cr nitride decrease with the increase of holding time. Superior shear strength of 550MPa is obtained by restraining the formation of nitride.

• Journal of Welding and Joining
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• v.18 no.4
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• pp.96-103
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• 2000

This study investigated the effects of bonding temperature and bonding atmosphere on high temperature mechanical properties of transient liquid phase(TLP) bonded joints of heat resistant alloy using MBF-50 insert metal. Specimens were bonded at 1,423~1,468K for 600s. Microconstituents of {TEX}$Cr_{7}(C,B)_{3}${/TEX}were formed in the bonded region when the bonding temperature was low. The amount of microcostituents in the bonded layer decreased with increasing the bonding temperature, and the microconstituents in the bonded layer disappeared at the bonding temperature above 1,468K. The tensile strength of the joints at elevated temperatures increased with the increase the bonding temperature and was the same level as one of the base metal in the bonding temperature over 1,453K. Microstructure and alloying element distributions of the bonded region bonded in Ar and $N_2$atmosphere were similar to those of the bonded in vacuum. The creep rupture strength and rupture lives of joints were almost identical to those of base metal.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.2
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• pp.64-77
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• 1989

In this study, the experiments were carried out for the purpose of establishment of aluminium cementation to steel surface by diffusible heat treatment after making the coated film onto the substrate by arc spray method. Also, the microstructure and mechanical properties of the cementation layer produced by this study were inspected for various heat treatment and spraying conditions. Main results obtained are as follow ; 1. The coating film characteristics which have excellent errosion-resistance, high temperature oxidation-resistance are obtained by aluminium penetration heat treatment after making the sprayed aluminum coating film onto the steel substrate. 2. Aluminium diffusion penetration takes place at higher temperature than 660.deg.C, and the more heat treatment time and the higher heat treatment temperature adopted, the deeper diffusion layer obtained. 3. Insert gas arc spraying using argon gas as the carrier gas higher improvement of mechanical property than that of compressed air environment. 4. The coating film characteristics appeared to be improvement of adhesive property, porosity plugging effect by heat treatment in air environment.

• Transactions on Electrical and Electronic Materials
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• v.17 no.4
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• pp.201-203
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• 2016

Transparent conductive multilayers have been fabricated using transparent amorphous Si doped indium oxide (ISO) semiconductors and metallic Ag of ISO/Ag/ISO. The resistivity of a multilayer is dependent on the middle layer thickness of silver. The thickness of the Ag layer is fixed at 11 nm and takes into account cost and optical transmittance. As-deposited ISO/Ag (11 nm)/ISO multilayer shows a measured resistivity of 7.585×10⁻⁵ Ω cm. After a post annealing treatment of 400℃, the resistivity is reduced to 4.332×10⁻⁵ Ω cm. The reduction of resistivity should be explained that the mobility of the multilayer increased due to the optimized crystalline, meanwhile, the Hall concentration of the multilayer showed an obscure change because the carriers mainly come from the insert of the Ag layer.