• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.1
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• pp.12-19
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• 2022

The propellants used in the gas generator of the ducted rocket are fuel-rich propellants, which contain an excessive amount of metal fuel and a small amount of oxidizing agent compared to general solid rocket propellants. In this paper, boron powder and MgAl(Magnesium-Aluminium alloy) were applied to produce fuel-rich propellants. The optimum formulation was determined by characterizing these metal fuel-rich propellants. Analysis of combustion products in the gas generators confirmed that the fuel-rich propellants containing fine boron powder itself instead of boron-bead could be useful in gas generators.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.2
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• pp.66-72
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• 2024

To investigate the effect of deformation condition on microstructure and texture formation behaviors of AZ91 magnesium alloy with three kinds of initial texure during high-temperature deformation, plane strain compression tests were carried out at high-temperature deformation conditions - temperature of 673 K~723 K, strain rate of 5 × 10^-3s^-1, up to a strain of -1.0. To clarify the texture formation behavior and crystal orientaion distribution, X-ray diffraction and EBSD measurement were conducted on mid-plane section of the specimens after electroltytic polishing. As a result of this study, it is found that the main component and the accumulation of pole density vary depending on initial texture and deformation caondition, and the formation and development basal texture components ({0001} <$10\bar{1}0$>) were observed regardless of the initial texure in all case of specimens.

• Korean Journal of Materials Research
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• v.4 no.8
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• pp.906-914
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• 1994

Plastic behavior of two-phase intermetallic compounds based on $LI_{2}$-type $(Al, Cr)_3$ Ti was investigated using compression test at R.T. and 77K. $LI_{2}$ single phase alloys and two-phase alloys consisting of mainly $LI_{2}$ phase and a few or 20% second phases were selected from AI-Ti-Cr phase diagram. In general, compared with Llz single phase, two-phase alloys consisting of 20% second phase showed relatively high yield strength and poor ductility. Among the alloys, however, AI-21Ti-23Cr alloy consisting of 20% $Cr_{2}Al$ phase showed available ductility as well as high yield strength. Plastic behavior of $LI_{2}$ single phase alloys and two-phase alloys consisting of a few% $Cr_{2}Al$ was also investigated. Homogenization of arc melted ingots substantially reduced the amount of second phases but introduced extensive pore. When Cr content increased in $Ll_{2}$ single phase alloys after the homogenization, the volume fraction of pore in the alloys decreased, and no residual pore was observed in two-phase alloys consisting of a few% $Cr_{2}Al$ phase. Environmental effect on the ductility of the alloys was investigated using compression test at different strain rates($1.2 \times 10^{-4}/s$ and $1.2 \times 10^{-2}/s$). Environmental embrittlement was least significant in A1-25Ti-10Cr alloy consisting of LIZ single phase among the alloys tested in this study. However, based on the combined estimation of the pore formation, environmental embrittlement and ingot cast structure, AI-21Ti-23Cr alloy consisting of 20% $Cr_{2}Al$ as the second phase is expected to show the best tensile elongation behavior.

• Journal of Conservation Science
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• v.25 no.2
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• pp.207-217
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• 2009

After replicating 10 bronze types such as Gyemija, Gyeongjaja, Eulhaeja, etc. before the Imjin war, we studied the change of microstructure from each casting process, method, and alloy ratio by Gyechukja replicated from "Donggukyeojiseungnam". We selected the average of compositions of Eulhaeja in the National Museum of Korea as the standard(Cu 86.7%, Sn: 9.7%, Pb: 2.3%) of bronze types, so we decided on the alloy's composition of Cu 87%, Sn 15%, Pb 8% added to 5% Sn and Pb contents because of evaporating the Sn and the Pb. Before replicating major metal types, we made master-alloy first, melting it again, and then replicated metal types. The composition of the 1'st replicated Gyechukja showed the range of Cu 85.81~87.63%, Sn 9.27~10.51%, Pb 3.05~3.19%. The 2'nd replicated Gyechukja made using the branch metal left after casting the 1st replica. The 2nd replicated Gyechukja showed the composition range of Cu 87.21~88.09%, Sn 9.06~9.36%, Pb 2.80~3.05%. This result decreases a little contents of Sn and Pb as compared with metal types of the 1st replica. However, it's almost the same as the Eulhaeja's average composition ratio in the National Museum of Korea. As a result of observing the microstructure of restored Gyechukja, it showed the dendrite structure of the typical casting structure and the segregation of Pb. There is no big difference of microstructure between the 1st and the 2nd restored metal types, even though the 2nd restored types partially decreases the eutectoid region in comparison with the 1st types. The systematic and scientific restoration experiment of metal types using Joseon period will be showed the casting method and alloy ratio, and this will be of great help to the study of restoration metal types in the future.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.43-43
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• 2009

단련용 다결정 Ni기 초내열합금은 우수한 가공성, 내산화성, 고온특성 등으로 가스터빈 연소기, 디스크, 증기발생기 전열관 등 발전용 고온부품 소재에 널리 적용되고 있다. 최근 발전설비의 고효율화를 꾀하기 위해 작동 온도를 현격히 증가시키는 기술방향으로 발전하고 있고, 소재측면에서는 기존의 초내열합금 대비 고기능성을 확보할 수 있는 차세대 Ni기 초내열합금 개발이 유럽, 미국, 일본, 중국 등을 중심으로 활발히 이루어지고 있다. 이러한 소재의 고온강도 (온도수용성)를 향상시키기 위해서는 통상 규칙격자 금속간화합물인 $Ni_3(Al,Ti)-{\gamma}'$상의 분율을 증가시킬 수 있지만, ${\gamma}'$상분율이 증가할 경우 용접 및 후열처리 동안 용접열영향부 (HAZ)에서 액화균열이 발생할 가능성이 높아진다. 결정립계를 따라 발생하는 HAZ 액화균열은 입계특성에 의해 크게 영향을 받을 것으로 판단된다. 한편, 본 연구자들은 최근 입계 serration 현상을 단련용 합금에 도입시키는 특별한 열처리를 이론적 접근법을 통해 개발하였다. 형성된 파형입계는 결정학적인 관점에서 조밀 {111} 입계면을 갖도록 분해 (dissociation)되어 낮은 계면에너지를 갖게 됨을 확인하였으며, 입계형상 변화뿐만 아니라 탄화물 특성변화까지 유도하여 크리프 수명을 기존대비 약 40% 정도 향상시킴을 확인하였다. 이러한 직선형 입계 대비 'special boundary'로 간주되는 파형입계가 도입될 경우, HAZ 결정립크기 변화 및 액화거동에 미치는 영향을 고찰하고, 아울러 입계특성 제어가 용접성/용접부 품질 향상에 기여할 수 있는 가능성도 토의하고자 하였다. 본 연구에서는 재현 HAZ 열사이클 시험을 통해 미세구조를 정량적으로 비교하였다. 상대적으로 입계구조가 안정된 파형입계의 이동속도가 高계면 에너지를 갖는 직선형 입계보다 느려 HAZ 결정립 성장이 효과적으로 억제됨을 확인할 수 있었다. 입계 액화거동을 살펴보면, 두 시편 모두 $M_{23}C_6$, MC 등 입계탄화물 계면이 빠른 승온중 액화반응 (constitutional liquation)에 의해 입계가 액화되었으며, 이후 급냉에 의해 입계에 액상막이 존재한 흔적이 발견되었다. 최고온도별로 입계액화 폭/비율을 정량적으로 비교한 결과, 파형입계가 직선입계 대비 대체로 낮음을 확인할 수 있었으며, 때때로 액화되지 않고 잔존하는 입계 탄화물이 관찰되었다. 재현 HAZ 미세조직을 통해 Hot ductility 시험 결과를 유추하자면, 파형입계가 직선입계 보다 좁은 취성온도영역 (Brittle Temperature Range)을 나타낼 것으로 예상되어, 입계특성제어에 의해 Ni기 초내열합금의 용접성을 향상 가능성을 확인하였다.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.175-183
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• 2022

With the expansion of the automobile market, the demand for Nd as an essential rare earth material for automobile motors is rapidly increasing. Research on the calcio-thermic reduction process between Nd₂O₃ and calcium-based alloys has been extensively studied in order to manufacture Nd. In this study, Ca-Cu, as a reducing for Nd₂O₃, was prepared by electrolysis in CaCl₂ molten salt. Cu wire and graphite were employed as a working electrode and a counter electrode for electrolysis reaction, respectively. The reference electrode was manufactured by putting Ag wire in a mixture of AgCl and CaCl₂ at a ratio of 1:99 mol%. The cyclic voltammetry results showed that the deposition of Ca²⁺ on the surface of working electrode was observed from a potential of -1.8 V, and the reduction potential of Ca²⁺ decreased as the reaction temperature increased. The diffusion coefficient of Ca²⁺ calculated by the chronoamperometry experiment was found to be 5.4(±6.8)×10^-6 cm²/s. In addition, Ca-Cu liquid alloy was prepared by applying a constant potential to Cu electrodes. The element ratio of Ca-Cu alloy formed by applying a potential of -2.0 V was found to Ca:Cu=1:4.

• Korean Journal of Heritage: History & Science
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• v.52 no.1
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• pp.4-21
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• 2019

In this paper, 23 Silla gold earrings from the sixth and seventhand centuries, excavated from the Yeongnam region, were analyzed. Based on the silver content of the gold plate, they were classified into three types. The classifications included type I(20-50wt%), type II(10-20wt%) and type III (less than 10wt%). In the analysis process, the composition and morphological differences were identified on the surface of the gold plate. In the case of type I and II earrings, it was observed that the fine holes were concentrated in a relatively higher part of the gold content. The causes of the difference in the surface composition of the gold plate were divided into four categories: 1) surface treatment, 2) thermal diffusivity in the manufacturing process, 3) differences in composition of alluvial gold, and 4) the refining method of gold. It is possible that depletion gilding was attempted to increase the gold content while intentionally removing the other metals from the surface of the gold alloy in the portion where the gold deposit is relatively concentrated on the surface of the gold plating. The highest copper content was detected in the earring with the highest gold content of the analyzed earrings, and it was assumed that thermal diffusion had occurred between the gold plate and the metal rod during the manufacturing process rather than intentional addition. Copper was detected only in the thin ring earring type, and copper was not detected in the thick ring earring type or pendant type. It also proves that this earring has a high degree of tightness at higher temperatures, as there was an invisible edge finish on other earrings and horizontal wrinkles on the gold plate surface. In terms of the material of the gold plate, we examined whether the silver content of the gold plate was natural gold or added by alloy through analyzing the alluvial gold collected in the region. As a result of the analysis, it was found that on average about 13wt% of silver is included. This suggests that type II is natural gold, type III is refined gold, and type I seems to have been alloyed with natural gold. Here, we investigated the refining method introduced in the ancient literature, both at home and abroad, about the possibility of alloying silver after the refining process of type III earrings and then making pure gold. It was found that from ancient refining methods, silver which had been present in the natural gold was removed by reacting and combining with silver chloride or silver sulfide, and long-term efforts and techniques were required to obtain pure gold through this method. Therefore, it was concluded that the possibility of adding a small amount of silver in order to increase strength after making pure gold through a refining process is low.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.2
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• pp.95-101
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• 2019

Purpose: The aim of this study is to evaluate the effects of various primers on the microtensile bond strength (${\mu}TBS$) of resin cements to cobalt-chromium (Co-Cr) dental casting alloy. Materials and methods: Four adhesive primers (Universal primer, Metal primer II, Alloy primer, and Metal/Zirconia primer) and two resin cements (Panavia F2.0, G-CEM LinkAce) were tested. One hundred fifty Co-Cr beams were prepared from Co-Cr ingots via casting ($6mm\;ength{\times}1mm\;width{\times}1mm\;thick$). The metal beams were randomly divided into ten groups according to the adhesive primers and resin cements used; the no-primer groups served as the control (n = 15). After sandblasting with aluminum oxide ($125{\mu}m$ grain), the metal and resin cements were bonded together using a silicone mold. Prior to testing, all metal-resin beams were examined under stereomicroscope, and subjected to the ${\mu}TBS$ test. The mean value of each group was analyzed via one-way ANOVA with Tukey's test as post hoc (${\alpha}=.05$) using SPSS software. Results: The mean ${\mu}TBS$ of all groups was ranged from 20 to 28 MPa. There is no statistically significant difference between groups (P > .05). Mixed failure, which is the combination of adhesive and cohesive failures, is the most prevalent failure mode in both the Panavia F2.0 and G-Cem LinkAce groups. Conclusion: The ${\mu}TBS$ of all tested groups are relatively high; however, the primers used in this study result in no favorable effect in the ${\mu}TBS$ of Panavia F2.0 and G-Cem LinkAce resin cement to Co-Cr alloy.

• Korean Journal of Materials Research
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• v.3 no.1
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• pp.33-42
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• 1993

Abstract The increasing application of $Al_2$,$O_3$ and related ceramics as engineering materials is because of their attractive properties of fine ceramics. One solution to the wide variety of ceramic to metal combination lies in the effective joining. Active metal brazing of $Al_2$,$O_3$, to STS304 was investigated using Cu -Ti alloys. Titanium additive is chosen since it is good oxide former~. Brazing is performed under vacuum($10^{-3}$-$10^{-4}$ torr), a temperature between 1100 and 120$0^{\circ}C$ and time of 0.5-1.5hr. The microstructure of the brazed joints of $Al_2$,$O_3$ to STS304 with Cu-Ti insert metals were examined by using optical microscope and SEM and reaction products were analyzed by using EDX, WDX and XRD. Also interfacial reactions occuring during the brazing of $Al_2$,$O_3$/Cu-Ti/STS304 system are discussed. Experimental results showed formation of Titanium oxide T$i_2$$O_3$ which is attributable to the joining $Al_2$,$O_3$ to STS304 with Cu-Ti insert metal.

• Korean Journal of Materials Research
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• v.5 no.8
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• pp.913-920
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• 1995

RFe$_2$(R=rare earth) Laves Phase intermetallic compounds are one of the promising materials for magnetostrictive applications, due to large magnetostriction coefficients in the order of 10$^{-3}$ . However, because RFe$_2$intermetallic compounds have large magnetostriction constants as well as large magnetocrystalline anisotropy constants, a large external magnetic field is necessary to reach saturation magnetostriction. Hence researches on giant magnetostriction have been concentrated on producing materials exhibiting a high value of magnetostriction in a low magentic field. The main research trend of the giant magnetostriction to obtain the large value in the low magnetic filed, fortunately as the signs of magnetocrystalline anisotropy constans in RFe$_2$intermetallic compounds alternate with the rare earth metals, has been to substitute the rare earth metal for others and hence to reduce the magnetocrystalline anisotropy energy. In addition, amorphous RFe$_2$alloys have been researched. In this research, both of the methods which are substitution of the rare earth metal and amorphization in RFe$_2$ intermetallic compounds are simultaneously conducted to obtain the large magnetostriction coefficient in the low external magnetic field. Among them, SmFe$_2$and PrFe$_2$are selected, and amorphized in substrate-free bulk state. Magnetism in amorphous bulk (Sm$_{1-x}$ Pr$_{x}$) Fe$_2$alloys is investigated in the low magnetic field.ld.