• 열처리공학회지
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• 제22권1호
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• pp.8-15
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• 2009

Structural studies have been performed on precipitation hardening found in $Ni_{3}Al$ based ordered alloys using transmission electron microscopy (TEM). Tilt experiments by the weak-beam method were made to obtain some information concerning the cross slip mechanism of the superlattice dislocation. The strength of ${\gamma}'-Ni_3$(Al,Ti) increases over the temperature range of experiment by the precipitation of fine $\gamma$ particles. The peak temperature where a maximum strength was obtained shifted to higher temperature. Over the whole temperature range, the interaction between dislocation and $\gamma$ precipitates is attractive. On the temperature range of 773 K to 973 K, the dislocations in ${\gamma}'$ matrix move on (111) primary slip plane. When the applied stress is removed, the dislocations make cross slip into (010) plane, while those in $\gamma$ precipitates remain on the (111) primary slip plane. The increase of high temperature strength in ${\gamma}'-Ni_3$(Al,Ti) containing $\gamma$ precipitates is due to the restraint of cross slip of dislocations from (111) to (010) by the dispersion of disordered $\gamma$ particles.

• 대한치과기공학회지
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• 제20권1호
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• pp.37-49
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• 1998

실용치과재료로 사용되고 있는 Ag-Pd-Cu 3 원계 합금의 시효석출과정을 Pd 및 Cu의 용질 농도의 조성비가 약 1.7인 합금과 이 합금에서 2wt%Au의 첨가합금에 미치는 영향을 조사 분석하여 아래와 같은 결론을 얻었다. Ag-25Pd-15Cu 3원 합금은 ${\alpha}$의 단일상에서 ${\alpha}_1$ (Cu-rich), ${\alpha}_2$(Ag-rich) 및 PdCu 규칙상에 의해서 경화반응이 진행되며 연속승온시효에 의하면 $100{\sim}300^{\circ}C$의 저항증가와 $300{\sim}500^{\circ}C$의 저항감소라고 하는 2단계 변화에 의해서 경화곡선이 얻어졌다. 또한 본 합금의 시효과정은 ${\alpha}{\to}{\alpha}+{\alpha}_2+PdCu{\to}{\alpha}_1+{\alpha}_2+PdCu$이고 2상분리 반응에 경화되며 최고경화는 ${\alpha}_1,\;{\alpha}_2$ 및 PdCu 규칙상의 혼합영역에서 나타났다. 이들 석출반응은 입계반응이고 반응의 진행과 함께 경도값은 상승하고 경화촉진에 기여하였다. 또한 Nodule은 미세한 lamella조직을 나타내고 이들 ${\alpha}_2$와 PdCu상과의 미세한 혼합상의형성이 시효경화에 기여하는 주된 원인이 되었다. 과시효는 lamella의 조대화와 PdCu상의 ${\alpha}2$상으로의 용해에 따른 정량적 감소에 대응하였다. 석출상은 thin lamella구조의 잘 방위된 미세한 판상석출물로서 이들 미세 판상석출물은 AuCu($L1_0$)type의 face-centered tetragonal(fct)의 초격자구조였다. 규칙화된 미세한 판상석출물은 stair-step mode로서 twinning에 의해 형성되며 이것은 시효에 의해 $L1_0$ type의 PdCu 규칙상과 같은 초격자 형성시 정방비틀림 때문이라고 생각된다. 이들 twinning lamella는 귀금속원소에 의해 형성된 $L1_0$ type의 PdCu 규칙상과 같기 때문에 이들 합금의 부식저항에도 기여하였다. Ag-25Pd-15Cu합금은 전반적으로 양호한 내식성을 나타내며 Pd.Cu=1인 합금에서보다도 Pd함량이 높은 Pd/Cu=1.7에서 내식성이 보다 우수한 것은 Pd 함량이 내식성에 기여하였고 2%Au의 첨가에 의해서 부식성을 개선할 수 있었다.

• 열처리공학회지
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• 제19권1호
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• pp.10-19
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• 2006

Microstructure and morphology of precipitates in $Ni_3Al$- and TiAl-based intermetallics containing carbon have been investigated in terms of transmission electron microscopy(TEM). In an $L1_2$-ordered $Ni_3Al$ alloy with 4 mol.% of chromium and 0.2~3.0 mol.% of carbon, fine octahedral precipitates of $M_{23}C_6$ type carbide were formed in the matrix by aging at temperatures around 973 K after solution annealing at 1423 K. TEM examination revealed that the $M_{23}C_6$ phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the $M_{23}C_6$ precipitates then adopt a rod-like morphology elongated parallel to the <100> directions. In the $L1_0$-ordered TiAl containing 0.1~2.0 mol.% carbon, TEM observations revealed that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the $L1_0$ matrix, appear in the matrix and preferentially at dislocations. Selected area electron diffraction(SAED) patterns analyses have shown that the needle-shaped precipitate is $Ti_3AlC$ of perovskite type. The orientation relationship between the $Ti_3AlC$ and the $L1_0$ matrix is found to be $(001)_{Ti3AlC}//(001)_{L10\;matrix}$ and $[010]_{Ti3AlC}//[010]_{L10\;matrix}$. By aging at higher temperatures or for longer period at 1073 K, plate-like precipitates of $Ti_2AlC$ with a hexagonal structure are formed on the {111} planes of the $L1_0$ matrix. The orientation relationship between the $Ti_2AlC$ and the $L1_0$ matrix is $(0001)_{Ti2AlC}//(111)_{L10\;matrix}$ and $_{Ti2AlC}//_{L10\;matrix}$.

• 한국재료학회지
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• 제17권8호
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• pp.420-424
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• 2007

Precipitation behavior has been studied in NiTi-based ordered alloy using transmission electron microscopy. The hardness after solution treatment is high in NiTi alloy suggesting the large contribution of solid solution strengthening in this alloy system. However, the amount of age hardening is not large as compared to the large microstructural variations during aging. At the beginning of aging, the $L2_1-type$ $Ni_2AlTi$ precipitates keep a lattice coherency with the NiTi matrix. By longer periods of aging $Ni_2AlTi$ precipitates lose their coherency and change their morphology to the globular ones surrounded by misfit dislocations. Misfit dislocations, which are observed on {100} planes of H-precipitates have the Burgers vector of a <100> with a pure edge type. The lattice misfits of $NiTi-Ni_2AlTi$ system is estimated from the spacings of misfit dislocations to be 1.3% at 1273 K. The lattice misfits decrease with increasing aging temperature in this system.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.220-221
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• 2003

Equiatomic FePt and CoPt alloy thin films have received considerable attention as possible magnetic and magneto-optic recording because of their high magnetic anisotropy energy and high coercivity. The high coercivity in these thin films is due to the presence of finely dispersed ordered FePt phase mixed with disordered FePt phase. However, a high temperature treatment, either substrate heating during deposition or post annealing, is needed to obtain the ordered L1$\_$0/ phase with high value of magneto crystalline anisotropy. Recent microstructural studies on these films suggest that the average grain size ranges from 10-50 nm and the grains are magnetically coupled between each other. On the other hand, the ultrahigh-density magnetic recording media with low media noise imposes the need of a material, which consists of magnetically isolated grains with size below 10 nm. The magnetic grain isolation can be controlled by the amount of additional non-magnetic element in the system which determines the interparticle separation and therefore the interparticle interactions. Recently, much research work has been done on various non-magnetic matrices. Preliminary studies showed that the samples prepared in B$_2$O$_3$ and Carbon matrices have shown strong perpendicular anisotropy and fine grain size down to 4nm, which suggest these nanocomposite films are very promising and may lead to the realization of a magnetic medium capable of recording densities beyond 1 Tb/in$^2$. So, in this work, the effect of Carbon doping on the magnetic properties of FePt nanoparticles were investigated.

• 한국분말재료학회지
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• 제11권3호
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• pp.242-246
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• 2004

FePt nanoparticles for high-density magnetic recording media were synthesized by the simultaneous chemical reduction of Fe(acac) $_2$ and Pt(acac) $_2$ with 1,2-hexadecanediol as the reducing reagent. TEM images showed that the shape of as-synthesized FePt nanoparticle was spherical and average particle size was 3 nm. Also, SAD pattern showed that crystal structure was disordered FCC (face centered cubic). These FCC structured nanoparticles were transformed FCT (face centered tetragonal) structure by annealing at 55$0^{\circ}C$ for 30 min in Ar atmosphere. XRD analysis revealed that as-synthesized FePt nanoparticles were transformed from disordered FCC to ordered FCT. Finally, the coercivity of 2 kOe for FePt nanoparticles with FCT structure was obtained by VSM measurement.

• 열처리공학회지
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• 제22권6호
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• pp.345-353
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• 2009

The precipitates of $L2_1$-type $Ni_2AlHf$ phase in B2-ordered NiAl system has been observed by using transmission electron microscope (TEM). The hardness of as-quenched NiAl-Hf alloys is high due to the larger strengthening. However, age hardening of this alloy is not main effect to increase hardness compared to the large microstructural variations during aging. At the beginning of aging, the $L2_1$-type $Ni_2AlHf$ precipitates keep a lattice coherency with the NiAl matrix. The orientation relationship between the $Ni_2 AlHf$ precipitate and the NiAl matrix is <100>$_{Ni2AlHf}$//<100>$_{NiAl}$, {001}$_{Ni2AlHf}$//{001}$_{NiAl}$. By aging treatment for long time $Ni_2AlHf$ precipitates lost their coherency and change their morphology to the spherical ones surrounded by misfit dislocations. The orientation relationship between the NiAl matrix and the $Ni_2AlHf$ precipitates, however, has been kept even after longer aging time. The lattice misfit between the $Ni_2AlHf$ precipitate and the NiAl matrix has been calculated by the selected electron diffraction patterns, and the spacings of misfit dislocations is about 4.5% at 1173 K.

• 대한치과기공학회지
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• 제19권1호
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• pp.21-35
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• 1997

Au 함량이 20% 미만인 Au-Ag-Pd합금의 기초합금인 Ag-Pd-Cu 3원계 합금의 시효경화 특성을 규명할 목적으로 20wt% Pd 및 20wt% Cu의 용질농도구성비가 1이 되는 3원 합금과 여기에 2wt% Au의 첨가합금에 미치는 석출상의 영향을 분석, 조사하여 아래와 같은 결론을 얻었다. Ag-20wt% Pd-20wt% Cu 3원 함금은 ${\alpha}$의 단일상에서 Ag-rich의 ${\alpha}2$상 및 PdCu규칙상에 의하여 경화반응이 진행되며 연속승온과정에서 $100{\sim}300^{\circ}C$의 경도증가와 $300{\sim}500^{\circ}C$의 경도감소의 2단계 경화특성이 얻어졌다. 연속승온시효과정은 Au첨가에 관계없이 2단계의 석출반응이 저온영역에서는 stage I, stage II로 나타나고 stage I은 고온에서의 소입에 의해 도입된 과잉공공의 이동 및 소멸에 의한 반응이고 stage II는 평형농도의 공공확산에 의한 반응에 대응하였다. 또한 본 합금의 시효석출과정은 ${\alpha}\to{\alpha}+{\alpha}2+PdCu\to{\alpha}_1+{\alpha}_2+PdCu$이고 최대 경화는 ${\alpha}_1,\;{\alpha}_2$, PdCu의 3상공존구역에서 나타났다. 이들 석출반응은 입계반응이고 반응의 진행과 함께 경도값은 상승하며 경화능에 직접적으로 기여하였다. 또한 석출상은 미세한 lamella조직의 nodule을 나타내고 이들 ${\alpha}_1,\;{\alpha}_2$ 및 PdCu상과의 미세한 혼합상의 형성이 시효경화능에 기여하는 주된 원인이 되었다. 과시효는 lamella의 조대화와 PdCu상의 ${\alpha}_2$상으로의 용해에 따른 정량적 감소에 대응하였다. 본 합금의 시효열처리 온도는 $450^{\circ}C$가 적절하며 $1{\sim}120min$ 시효시간에 걸쳐서 소정의 경화특성을 얻을 수 있었다.

• 한국재료학회지
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• 제16권4호
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• pp.241-247
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• 2006

Structural studies have been performed on precipitation hardening discovered in $L1_2-ordered\;Ni_3(Al,Cr)$ containing 0.2 to 3.0 mol% of carbon using transmission electron microscopy (TEM). Fine octahedral precipitates of $M_{23}C_6$ appeared in the matrix by aging at temperatures around 973 K after solution treatment at 1423 K. TEM examination revealed that the $M_{23}C_6$ phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the $M_{23}C_6$ precipitates then adopt a rod-like morphology elongated parallel to the <100> directions. Deformation at temperature below 973 K, typical Orowan loops were observed surrounding the $M_{23}C_6$ particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface between matrix and particles.

• 한국토양비료학회지
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• 제44권6호
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• pp.1063-1070
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• 2011

본 연구는 수용액 내 존재하는 Cd, Pb을 다양한 화학적 안정화제를 이용하여 안정화 효율성을 평가하였다. 연구에 사용한 안정화제는 중금속 이온과의 반응특성 별로 석회물질, 광물질 등으로 구분하여 문헌조사를 바탕으로 5종을 선정하여 사용했다. 안정화 효율성 평가방법은 용액 내 중금속 함량을 단계적으로 제조하여 안정화 효율성, 반감기 및 반응속도 산정 및 반응 후 안정화제의 반응생성물 확인의 순으로 진행했다. 안정화 효율성 평가결과 석회물질 ($CaCO_3$)을 다량 함유하여 기본적으로 pH를 8이상으로 교정하는 안정화제의 경우 처리량에 상관없이 대부분 불용화되는 것으로 나타났으며, 낮은 산도교정 물질은 50% 수준의 효율성을 갖는 것으로 나타났다. 또한, 효율성이 크게 나타난 물질을 대상으로 반응속도상수 (K)를 산출한 결과 Cd의 경우 처리량에 따라 증가하였지만, Pb의 경우 초기에 반응속도가 빠르게 일어나 처리량에 따른 평가는 불가능 하였다. 다량의 중금속 이온과 반응시킨 안정화제의 표면관찰을 통한 생성물 검정 결과 SEM 사진으로 반응 전 후의 생성물 확인을 간접적으로 확인하였다. 또한, SEM-EDS 분석결과 반응 후 물질 표면에서 Cd과 Pb의 성분 검출을 확인하였다. 그리고 XRD 분석을 통해 효율성이 좋았던 물질에서 Cd과 Pb 성분의 검출이 확인되어 수용액 상에 이온형태로 존재하는 중금속의 복원에 안정화제를 이용한 저감은 효율적일 것으로 판단된다.