• 소성∙가공
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• 제19권6호
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• pp.357-362
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• 2010

Dry sliding wear behavior of pure Fe and Cu which have BCC and FCC crystal structure, respectively, was investigated. The wear characteristics of the pure metals with different crystal structure were compared. Dry sliding wear tests were carried out using a pin-on-disk wear tester at various loads under the constant sliding speed condition of 0.15 m/s against a silica ball at room temperature. Sliding distance was fixed as 600 m for all wear tests. Wear rate of a specimen was calculated by dividing the weight loss of the specimen after the test by the specific gravity and sliding distance. Worn surfaces and wear debris were analyzed by SEM. The wear of both pure Fe and Cu proceeded with surface deformation, resulting in similar wear rates despite of their structure difference under the current test conditions. Wear rates of both metals were low if the surface deformation due to wear forms thick surface-deformation layer that is strain hardened beneath the wearing surface. The pure Cu specimens showed a lot of oxides on the worn surface when tested at low loads less than 5 N, which resulted in very low wear rate.

• 한국결정성장학회지
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• 제9권1호
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• pp.132-136
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• 1999

볼밀을 사용하여 $Fe_{30}Cr_{70}$ 혼합분말을 질소가스 분위기 중 기계적 합금화(MA) 처리하였다. 그 결과 비정질상이 생성되었으며 불활성 아르곤 가스 분위기중 MA 처리를 행한 경우에는 bcc 고용체가 얻어졌다. 기계적 합금화 처리한$(Fe_{30}Cr_{70})_{0.85}N_{0.15)$분말시료의 열분석 결과 약 $550^{\circ}C$에 비정질상의 결정화에 의한 발열 peak가 관찰되었다. bcc 결정질에서 비정질상으로의 구조변화 과정을 Xtjs 회절 및 중성자 회절법에 의해 관찰되었다. 그 결과, 이 합금계에서의 비정질화는 모든 결정구조에서 전형적으로 존재하는 8면체 unit가 우선적으로 붕괴되어 4면체 unit로 변환되어 가는 과정임을 알 수 있었다. 또한, 중성자 회절에 의한 결정구조해석 결과 질소원자는 금속원자로 이루어진 4면체의 중심에 위치하고 있음을 알 수 있었다.

• 한국자기학회지
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• 제15권4호
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• pp.241-245
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• 2005

CoFeNi 합금은 HDD, MEMS 분야에서 head core 재료로 쓰이는 permalloy(FeNi)합금보다 뛰어난 우수한 자기적 특성을 가진 재료로써 최근 많이 연구되어지고 있다. CoFeNi 합금의 조성과 전기도금 시 전류조건에 따른 미세구조와 결정학적 특성이 자기 특성에 미치는 영향을 조사하였으며, 높은 포화자화와 낮은 보자력을 갖는 CoFeNi 삼원계 합금을 전기도금 방식으로 제조하는데 성공하였다. 포화자화 1.9 T, 보자력 0.16 A/m를 갖는 대표적인 CoFeNi film의 조성은 $Co_{30}\;Fe_{34}\;Ni_{36}(at\%)$이며, 미세결정립과 ffc-bcc 상의 혼재가 낮은 보자력을 갖는 요인임을 XRD, TEM의 결과로부터 확인 하였다.

• 한국자기학회지
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• 제16권5호
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• pp.249-254
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• 2006

CoFeNi 합금은 HDD, MEMS 분야에서 head core 재료로 쓰이는 permalloy(FeNi)합금보다 뛰어난 우수한 자기적 특성을 가진 재료로써 최근 많이 연구되어지고 있다. 전기도금된 CoFeNi합금 박막의 열처리에 따른 미세구조 변화와 결정학적 특성이 자기특성에 미치는 영향을 조사하였다. 삼원계 합금을 열처리하면 전기도금 시 결정의 크기와 결정구조의 변화가 자기특성에 영향을 미친다. 이를 조사하여 열처리를 통하여 얻어지는 CoFeNi계 박막의 자기 특성을 향상시키고자 하였고, $300{\sim}400^{\circ}C$까지 열처리를 함으로써 보자력을 최소화하고 포화자화 값을 증가시켰다. 포화자화 값의 증가는 bcc상의 생성으로 야기되는 것으로 판단된다.

• Journal of Magnetics
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• 제3권1호
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• pp.31-35
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• 1998

Metal/cobalt ferrite composite thin films with the saturation magnetization (M_s$)of~580 emu/cm3 and the coercivity(Hc) of 1700 Oe were prepared by the reactive sputtering. With increasing substrate temperature, Ms of the thin films increased, while Hc of the thin films decrease. This sttributed to the precipitation of $Co_xFe_{1-x}(x {\appro}x0.62)$ metal phase in the thin films. The metal phase showed the BCC structure ($a_0$=2.89 $\AA$) and Im3m space group. Also, the cobalt ferrite phase was identified as$ CoFe_2O_4$ with a cubic structure ($a_0=8.39 $\AA$$) and a space group of Fd3m. For the higher cobalt content than the stoichiometric composition,$ Co_{37.8}Fe_{62.2}$, the thin films with high Ms and Hc could be obtained in the wide substrate temperature range (200-40$0^{\circ}C$).

• 한국수소및신에너지학회논문집
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• 제16권2호
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• pp.122-129
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• 2005

The characteristics of hydrogen storage have been investigated in the Ti-Cr-Mo and Ti-Cr-V ternary alloys with bcc structure. The alloys were melted by arc furnace and remelted 4-5 times for homogeneity. The lattice parameters, microstructures and phases of the alloys were examined by SEM, EDX and XRD, and the Pressure-Composition isotherms of the alloys were measured. From these data the relationship of the maximum and effective hydrogen storage capacities vs. chemical composition, lattice parameter and the radius of tetrahedral site were analyzed and discussed. The results showed that all of these alloy, in the range of the this study, had mainly bcc solid solutions with small amount of Ti segregation due to a lower melting point of Ti compared with other elements. Lattice parameters of the alloys were very near to the atomic average values of lattice parameters of the constituent elements. It was also found that maximum hydrogen storage capacities of the Ti-Cr-Mo alloys increased with increasing Ti content and the radius of tetrahedral site but the effective hydrogen storage capacities decreased after showing the maximum. The hydrogen storage capacities of the Ti-Cr-V alloys were almost same even though the V contens were quite different from alloy to alloy and this could be attributed to the almost same Ti/Cr ratio of the alloys. The maximum effective hydrogen storage capacity of the Ti-Cr-Mo alloys was revealed at Ti content of about 40${\sim}$50 at% and radius of tetrahedral site of 0.43${\sim}$0.45 nm. The Ti-Cr-V alloys showed the hydrogen storage capacities of 3.0 wt% and effective hydrogen storage capacities of 1.5 wt%.

• Journal of Welding and Joining
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• 제32권3호
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• pp.89-94
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• 2014

AISI 304 austenitic stainless steel is widely used for LNG pipes for LNG transmission thanks to its good metallurgical and mechanical properties. In the present research, impact toughness of a gas tungsten arc welded AISI 304 stainless steel pipe was evaluated between room and liquid nitrogen ($-196^{\circ}C$) test temperatures. In addition, a comparative study was made of the fracture behavior of FCC crystal structured stainless steel weldments and BCC crystal structured mild steels(A-grade and SS400). The results showed a slight decrease in the impact energy of the AISI 304 base metal, heat affected zone(HAZ), and welded zone with decreasing test temperature. In addition, the welded metal has the highest absorbed impact energy, followed by HAZ and the base metal.

• 한국진공학회지
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• 제4권S2호
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• pp.148-155
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• 1995

(1) The metastable crystalline(MX) phases formed by ion mixing are classified into 5 types, i.e. the super-saturated solid solutions and the enlarged HCP-I phases reported earlier, and the newly observed FCC-I phases in hcp-based alloys, The FCC-ll and HCP-ll phases in bcc-based alloys. The growth kinetics of the MX phases is discussed. (2) The interfacial free energy in the multilayered films was found to play an important role in ion beam mixing(IM) induced amorphization. By adding sufficient interfaces, amorphous alloys were obtained even in the systems with rather positive heat of formation. (3) Gibbs free energy diagrams of some representative systems were constructed, by calculating the free energy curves of all the competing phases. Steady-state thermal annealing was conducted and the results confirmed the relevance of the constructed diagrams, which were inturn employed to interpret the MX phase formation as well as the glass forming ability upon IM in the binary metal systems.

• 한국수소및신에너지학회논문집
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• 제9권1호
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• pp.31-37
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• 1998

Ti-Cr-V의 3원계 합금에 대하여 결정구조 격자상수 및 $30^{\circ}C$에서의 수소저장 특성을 조사하였다. 실험영역에서 Ti-Cr-V의 3원계 합금은 거의 모두 bcc구조를 갖는 단일상으로 구성되어 있고, 수소저장용량 및 유효수소저장용량은 합금 조성의 Ti/Cr비에 크게 의존하였으며, Ti/Cr비 약 0.75에서 그 최대치를 보였다. 합금들의 격자상수는 Ti/Cr비가 증가함에 따라 직선적으로 증가하였다. Ti/Cr비와 격자상수, 수소저장용량 및 유효수소 저장용량의 관계를 각 원소의 수소와의 친화력 및 순금속에서의 격자상수의 차이로써 설명하였다.

• 한국분말재료학회지
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• 제13권5호
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• pp.340-350
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• 2006

Nanostructured materials exhibit attractive mechanical properties that are often superior to the performance of their coarse-grained counterparts. However, one major drawback is their low ductility, which limits their potential applications. In this paper, different strategies to obtain both high strength and enhanced ductility in nanostructured materials are reported for Ti-base and Zr-base alloys. The first approach consists of designing an in-situ composite microstructure containing ductile bcc or hop dendrites that are homogeneously dispersed in a nanostructured matrix. The second approach is related to refining the eutectic structure of a Ti-Fe-Sn alloy. For all these materials, the microstructure, mechanical properties, deformation and fracture mechanisms will be discussed.