• 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.

• Journal of Biomedical Engineering Research
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• v.17 no.2
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• pp.247-254
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• 1996

The relationship between the isothermal age-hardening behavior and the phase transformation in the commercial dental Au-Ag-Cu-Pd alloy was investigated Age-hardening was mostly attributed to the lattice distortions of the supersaturated w phase resulting from the transformation to the metastable phasel which were more distinct at lower aging temperature. The lattice distortions resulting from the transformation of the metastable phases to the equilibrium phases also made a contribution to the age-hardening.

• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.322-322
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• 2011

White gold는 아름다운 광택과 손쉬운 가공성의 장점 때문에 장신구를 비롯한 다양한 분야에서 그 활용 가치가 매우 높다. 본 연구에서 우리는 열처리를 통한 white gold의 hardness강화 및 품질향상을 위하여 다양한 열처리 조건별 기계적 특성변화를 비교 관찰 하였다. 열처리 전 white gold alloy의 구성성분을 조사하기 위하여 EPMA와 ICP-MS를 사용하여 분석 후 그 값을 수치화 하였다. 14K, 18K White gold alloy 총 32개의 시료를 사용하여 $750^{\circ}C$, 30 min의 조건에서 solid treatment 및 quenching 후 $200^{\circ}C{\sim}350^{\circ}C$ 온도 범위에서 $50^{\circ}C$ 간격으로 age-hardening을 실시하였다. 열처리 전과 후 각 조건별 hardness 변화는 Vicker's hardness tester를 사용하여 측정하였다. 또한 age-hardening 후 모든 시료는 optical microscope (OM)을 사용하여 각 열처리 조건 별 grain 들의 배열 및 size의 변화를 관찰하였다. 열처리 전 14K, 18K white gold alloy의 hardness의 평균값은 각각 162 Hv와 196 Hv를 나타내었다. solid treatment 후 그 수치가 146 Hv, 172 Hv로 감소하였고, age-hardening 후에는 hardness 값이 점차 증가하여 14K는 $260^{\circ}C$에서 226 Hv, 18K는 $270^{\circ}C$에서 268 Hv의 가장 높은 수치를 나타내었다. 또한 14K 및 18K는 각각 $260^{\circ}C$, $270^{\circ}C$ 이상에서는 over-aging 현상을 나타내었다. OM 분석 결과 열처리 전 불균일했던 grain들의 배열이 solid treatment 및 quenching 후 다소 균일해짐을 확인할 수 있었고, grain size 또한 열처리 전에 비해 증가함을 알 수 있었다. Solid treatment 후 모든 시료의 hardness값이 전반적으로 감소하였다가 age-hardening을 통해 grain들의 배열이 점차 안정화 되면서 hardness가 증가 하였고, over-aging 구간에서는 급격히 감소하는 경향을 나타내었다. 이 결과들로부터 우리는 14K, 18K white gold alloy 에 대한 age-hardening 최적조건을 도출하였고, 각 열처리 조건별 grain 배열 상태의 변화를 관찰 할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.5
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• pp.29-35
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• 1994

The microstructual refinement process of Al-5Cr-2Zr alloys mechanical alloying 30h can be divided in five stages ; initial stage, welding predomminance stage, spherical partical formation stage, convolution welding predominance stage, and steady state. The rate of structural of aluminium splats was roughly logarithmic with processing time ; ${\in}$=k/0.78 ln(1+0.0028t). The age hardening in rapidly solidified Al-5Cr-2Zr alloys is ascribed to the coherency and dispersion hardening. Coherency hardening is occurred by matastable cubic Al3Zr precipitates in Al-Cr-Zr alloys. Dispersion hardening after mechanical alloying is attributed to the finely-dispersed $Al_2O_3$ and $Al_4C_3$ in Al-5Cr-2Zr alloys.

• Journal of Powder Materials
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• v.12 no.4 s.51
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• pp.303-308
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• 2005

Various kinds of Mg-Zn-Ca base alloys were rapidly quenched via melt spinning process. The meltspun ternary and quaternary alloy ribbons were heat-treated, and then the effects of additional elements on age hardening behavior and phase change of precipitates were investigated using Vickers hardness tester, XRD, and TEM equipped with EDS system. In ternary alloys, age hardening was mostly due to the distribution of $Mg_6Ca_2Zn_3$ and $Mg_2Ca$. The stable phases of precipitates were varied according to the aging temperature and the alloy composition. With the increase of Ca content, $Mg_2Ca$ precipitates were detected more than $Mg_6Ca_2Zn_3$ precipitates. In quaternary alloys, the precipitates taken from Mg-Zn-Ca-Co were identified as new quaternary phase, whereas those taken from Mg-Zn-Ca-Zr as MgZnCa containing Zr. In general, the ternary alloy showed higher peak hardness and thermal stability than the quaternary considering the total amounts of the solutes. It implies that the structure of precipitate should be controlled to have the coherent interface with the Mg matrix.

• 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.84-92
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• 2014

The purpose of study is to analyze mechanism with early high portland cement and hardening accelerator. As the result, it was concluded that hardening accelerator makes accelerates appearance of $Ca(OH)_2$ through experiment using TG-DTA when it hydrates with cement. On the result of compressive strength, as increasing the amount of hardening accelerator used, early compressive strength was improved. Also, as a result of hydration heat, hardening accelerator accelerates hydration of $C_3S$ that is cement's component. On the result of XRD's analyzation, hydration product for each age could be check and it was shown that as increasing the amount of hardening accelerator used, peak point of hydration product was recorded high. As the result of SEM, appearance of C-S-H was shown as the amount of $Ca(OH)_2$'s appearance and each age according to additive contents of hardening accelerator. Therefore hardening accelerator used on this study is effective on getting early compressive strength.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.5
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• pp.243-249
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• 2007

The age hardening behavior and mechanical properties of an extruded Al-Zn-Mg-(Cu)-0.1 wt.%Sc alloy were investigated with the Sc addition and ageing temperature. The results showed that the $Al_3Sc$ compounds were formed by Sc addition and distributed preferentially along the extrusion direction. The age hardening of Al-Zn-Mg-Cu-0.1 wt.%Sc alloy which was treated by T6 process was more significant than that of Al-Zn-Mg-0.1 wt.%Sc alloy. The tensile property of Al-Zn-Mg-Cu+0.1 wt.%Sc alloy was also higher than that of Al-Zn-Mg-0.1 wt.%Sc alloy, which is 691 MPa and 584 MPa in strength and 9% and 11% in elongation, respectively.

• Journal of Biomedical Engineering Research
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• v.15 no.4
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• pp.389-394
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• 1994

The age-hardening behavior and the structural changes in a commercial dental Au-Ag-Cu-Pd alloy were investigated by means of hardness test, optical and scanning electron microscopic observation, energy dispersive spectroscopy and X-ray diffraction study. The drastic reduction in hardness by prolonged aging occurred after a rapid increase in hardness at the initial stage by the isothermal aging at $350^{\circ}C$. This softening was due to the broad precipitates formation of the lamellar structure which was composed of the f.c.t. AuCu I ordered f.c.t. phase containing Pd and the f.c.c. Ag-rich $\alpha$1 solid solution f.c.c.phase containing Au.