• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.38.1-38.1
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• 2011

Yellow gold는 아름다운 광택과 손쉬운 가공성의 장점 때문에 장신구를 비롯한 다양한 분야에서 그 활용 가치가 매우 높다. 본 연구에서는 yellow gold의 hardness 강화 및 품질향상을 위하여 다양한 열처리 조건 별 기계적 특성 변화를 비교 관찰 하였다. 열처리 전 yellow gold alloy의 구성성분을 조사하기 위하여 EPMA와 ICP-MS를 사용하여 정성분석 및 정량분석 결과를 수치화 하였다. 총 44개의 14K yellow gold를 사용하여 $750^{\circ}C$, 30 min 의 조건에서 solid solution treatment 후 $200{\sim}350^{\circ}C$ 온도 범위에서 $50^{\circ}C$ 간격으로 age-hardening을 실시하였다. 또한 열처리 전과 후 grain 들의 배열 및 size 변화를 관찰하기 위해 식각을 실시하였다. 식각된 시료는 optical microscope (OM)을 통해 각 열처리 조건에 따라 전 후 변화를 관찰 하였다. 열처리 전 14K yellow gold의 hardness의 평균값은 120.6 Hv를 나타내었다. Solid solution treatment 후 hardness는 95.7 Hv로 평균값이 감소하였고, age-hardening 후에는 14K yellow gold는 $260^{\circ}C$에서 159.8 Hv, $270^{\circ}C$에서 170.2 Hv로 열처리 전에 비해 약 41% 증가된 결과를 나타내었다. 하지만 $270^{\circ}C$ 부터는 over-aging 현상을 나타내었다. OM 분석 결과 열처리 전 불균일했던 grain들의 배열이 solid solution treatment 및 quenching 후 다소 균일해 짐을 확인할 수 있었고, grain size 또한 열처리 전에 비해 증가함을 알 수 있었다. Solid solution treatment 후 모든 시료의 hardness 값이 전반적으로 감소하였다가 age-hardening을 통해 grain들의 배열이 점차 안정화 되면서 hardness가 증가 하였고, over-aging 구간에서는 급격히 감소하는 경향을 나타내었다. 이 결과로 우리는 14K yellow gold에 대한 age-hardening 최적조건을 도출 하였고, 각 열처리 조건 별 grain 배열 상태의 변화를 관찰 할 수 있었다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.107.1-107.1
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• 2012

Because of beautiful glossy and color, the value of gold leverage is very high in Europe. For improve the quality of white gold, we performed heat treatment on 14K white gold alloys at various age-hardening conditions. Age-hardening behavior and the related phase transformation changes were studied to elucidate the hardening mechanism of 14K white gold alloys. For solid solution treatment [ST], casted 14K white gold alloy specimens were treated at high temperature ($750^{\circ}C$) during 30 minute, and the specimens dropped to water for quenching immediately. For Age-hardening treatment [AT], the specimens were treated at various temperatures ($250^{\circ}C{\sim}300^{\circ}C$). After the heat treatment, we observed increased hardness from 144 Hv to 214 Hv by Vicker's hardness tester. Variation of the grain size measured by optical microscopy (OM) and scanning electron microscopy (SEM) images. By electron probe micro-analysis (EPMA) mapping analysis, we investigated that irregular particles were changed uniformly. After heat treatment, 14K white gold alloys showed improved hardness and became uniformity of grain size by age-hardening treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.283-283
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• 2013

Because of beautiful glossy and color, the value of gold leverage is very high in Europe. To improve the quality of gold alloys, we performed heat treatment on 14 K white gold alloys by variously changing age-hardening conditions. Age-hardening behavior and the related phase transformation changes were studied to elucidate the hardening mechanism of 14 K white gold alloy. For solid solution treatment [ST], casted gold alloy specimens were treated at high temperature ($750^{\circ}C$) for 30 minutes, and the specimens dropped to water to quench them. For Age-hardening treatment [AT], the specimens were treated at various temperatures ($250{\sim}300^{\circ}C$). After the heat treatment, we observed the phenomenon to increase hardness from 126 Hv to 166 Hv by Vicker's hardness tester. Through electron probe micro-analysis (EPMA) mapping analysis, we investigated that irregular particles were changed uniformly. In the SEM and OM images, two phases of matrix and particle-likestructures were observed, and the precipitation of these elements from the matrix progressed during age-hardening. By transmission electron microscope and X-ray diffraction observation, it was revealed that the formation of the Au3Cu superstructure contributed to the age-hardening at $270^{\circ}C$ in the gold alloy. After the heat treatment, this analysis shows that casted gold alloys were to improve hardness and to moderate surface defects at specific temperatures and duration.

• Journal of Technologic Dentistry
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• v.27 no.1
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• pp.65-71
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• 2005

Experimental Ti-13%Zr and Ti-13%Zr-5%Cu alloys were made in an argon-arc melting furnace. The grade 2 CP Ti was used to control. The alloys were cast into phosphate bonded $SiO_2$ investment molds using an argon-arc casting machine, and The hardness and microstructures of the castings were investigated in order to reveal their possible use for new dental casting materials and to collect useful data for alloy design. The hardness of the Ti-13%Zr-5%Cu alloy(379Hv) became higher than that of Ti-13%Zr(317Hv) alloy, and the hardness of this alloys became higher than that of CP Ti(247Hv). Increasing in the hardness of the Ti-13%Zr-5%Cu alloy was considered to be solid solution hardening as the Ti-Zr system shows a completely solid solution for both high temperature $\beta$phase and low temperature $\alpha$ phase and also the inclusion of the eutectoid structure($\alpha Ti+Ti_{2}Cu$). No martensitic structures are observed in the specimen made of CP Ti, but Ti-13%Zr and Ti-13%Zr-5%Cu alloys show a kind of martensitic structure. Ti-13%Zr-5%Cu shows the finest microstructure. From these results, it was concluded that new alloys for dental casting materials should be designed as Ti-Zr-Cu based alloys.

• Journal of Power System Engineering
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• v.7 no.4
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• pp.44-48
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• 2003

Alumium alloys casting are gaining increased acceptance in the automotive and electronic industeries and squeeze casting is the most efficient method of manufacturing such mass produced parts. This study has been investigated the microstructures and mechanical properties of Al-7.0Si-0.4Mg(AC4C)alloy fabricated by squeeze casting process for development of Engine Mountain Bracket. The microstructure of squeeze casted specimen were composed of eutectic structure Alumimim solid solution and $Mg_2Si$ precipitates. The tensile strength of as-solid solution treatment Al-7.0Si-0.4Mg alloy revealed 2985MPa. It was found that Al-7.0Si-0.4Mg alloy have good aging hardening effect results are presented to show the validity of the control method.

• Journal of Korea Foundry Society
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• v.33 no.3
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• pp.122-126
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• 2013

Recently, heat-resistant aluminum alloy has been re-focused as a downsizing materials for the internal combustion engines. Heat-resistant Al alloy development and many researches are still ongoing for the purpose of improving thermal stability, high-temperature mechanical strength and fatigue properties. The conventional principle of heat-resistant Al alloy is the precipitation of intermetallic compounds by adding a variety of elements is generally used to improve the mechanical properties of Al alloys. Heat resistant aluminum alloys have been produced by CrW homogeneous solid solution to overcome the limit of conventional heat resistant aluminum alloy. From EPMA, it is found that CrW homogeneous soild solution phases with the size of $50-100{\mu}m$ have been dispersed uniformly, and there is no reaction between aluminum and CrW alloy. In addition, after maintaining at high temperature of 573 K, there is no growth of hardening phase, nor desolved, but CrW still exists as a homogeneous solid solution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.2
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• pp.122-130
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• 1981

Equation of equilibrium is derived and solved for an infinite isotropic solid under applied hydrostatic stress which is uniform at large distance, and disturbed by a spherical precipitate which has isotropoc elastic constants dirrerent form those of the matrix. A linear strain hardening behavior of the matrix is assumed, and an elasto-plastic sloution is obtained. The difference of the total strain energy stored inthe infinite solid with and without a precipitate is computed, and compared with that for purely elastic case. Finally the effect of the ratio of the bulk modulus of the precipitate to that of the matrix and the effct of linear strain hardening rate on the plastic zone size and the energy difference are discussed.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.281-288
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• 1996

This study has been investigated the influence of solid solution treatment on the microstructure of Mg-6Al-xZn(x=0,1,2) alloys fabricated by squeeze casting process. The products having clean surface and fine microstructure are fabricated by adopting the liquid metal forging method. The microstructures of as-fabricated state show ${\beta}(Mg_{17}Al_{12})$ precipitates between the dendrite boundaries. It is found that the hardness of the alloys is increased with increasing amount of zinc due to the solid solution hardening effect of zinc. In the changes of microstructure upon solid solution treatment time at $405^{\circ}C$, ${\beta}$ phases are dissolved in ${\alpha}$ matrix up to 1hr and the microstructure are coarsened rapidly after 2hrs. The microhardness are decreased rapidly until 1hr of solution treatment time and then stabilized. From the above results, it is concluded that the optimum solid solution treatment condition for Mg-6Al-xZn alloys is at $405^{\circ}C$ for 1hr. The solution treatment time is greatly reduced comparing to conventional casting(at $385{\sim}418^{\circ}C$ for 10~14hrs) due to the formation of the super-saturated solid solution by liquid metal forging.

• Journal of Powder Materials
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• v.19 no.4
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• pp.317-321
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• 2012

In this study, Cu-5Ni-10Sn(wt%) spinodal alloy was manufactured by gas atomization spray forming, and the microstructural features and mechanical properties of Cu-5Ni-10Sn alloy have been investigated during homogenization, cold working and age-hardening. The spray formed Cu-5Ni-10Sn alloy consisted of an equiaxed microstructure with a mixture of solid solution ${\alpha}$-(CuNiSn) grains and lamellar-structure grains. Homogenization at $800^{\circ}C$ and subsequent rapid quenching formed a uniform solid solution ${\alpha}$-(CuNiSn) phase. Direct aging at $350^{\circ}C$ from the homogenized Cu-5Ni-10Sn alloy promoted the precipitation of finely distributed ${\gamma}$' or ${\gamma}-(Cu,Ni)_3Sn$ phase throughout the matrix, resulting in a significant increase in microhardness and tensile strength. Cold working prior to aging was effective in strengthening Cu-5Ni-10Sn alloy, which gave rise to a maximum tensile strength of 1165 MPa. Subsequent aging treatment slightly reduced the tensile strength to 1000-1100 MPa due to annealing effects.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.92-98
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• 1999

(Mo.W)Si$_2$ composites were fabricated by vacuum hot-pressing elemental Mo, W and Si powders at various temperatures. Elemental Mo, W and Si powders were alloyed in the proper proportions to form solid solutions. The microstructure and properties of these materials was characterized by using x-ray diffraction, optical microscopy, energy dispersive x-ray spectroscopy and Vicker's technique. It was found that tungsten was mainly substituted for Mo atoms, and made a completed solid solution of (Mo.W)Si$_2$ over 1$600^{\circ}C$. The lattice parameters and Vickers hardness increased largely with increasing reaction temperature by the most soluble elements, due to the solid-solution hardening.