• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.138.2-138.2
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• 2005

• 한국분말재료학회지
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• 제13권6호
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• pp.387-395
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• 2006

본고에서는 고유한 원자구조에 기인한 우수한 특성으로 인해 구조재료 및 기능재료로서 그 활용이 기대되고 있는 벌크 아몰퍼스 소재에 있어 온간압출, 온간압연, 방전 플라즈마 소결(Spark Plasma Sintering)등 과냉각액체온도구간에서의 점성유동을 이용한 고화성형 공정의 최근 기술동향에 대해 간략히 소개했다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 춘계학술대회 논문요약집
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• pp.59-59
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• 2004

최근의 전자통신 및 정밀의료 부품들은 제품의 경량화 및 집적화로 인해 크기는 작으면서도 많은 기능이 요구되어지는 다기능ㆍ소형화 추세에 있다. 따라서, 부품들은 복잡한 형상에 초고기능과 초정밀도가 요구되어 고강도의 재료와 MEMS 및 Nano-technology로 성형ㆍ가공된다. 이러한 방법은 고비용을 요하며 실용화에 많은 문제점을 내포하고 있다. 반면에 이러한 부품들을 생산단가가 저렴한 전통적인 소성가공기술로 생산할 경우에는 부품의 강도 및 정밀도에 한계를 갖게 된다.(중략)

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.101-106
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• 2003

In order to investigate the mechanical behavior of newly developed materials, the evaluation of mechanical properties using small-size specimen is essential. For those purposes, an instrumented impact testing apparatus, which provides the load-displacement curve under impact loading without oscillations, was devised. To develop the test procedure with the setup, the impact behaviors of various kinds of structural materials such as S45C, SCM4, Ti alloys (Ti-6V-4Al) and Zr-based bulk amorphous metal, were investigated through the instrumented Charpy V-notch impact tests. The calibrations of the dynamic load and displacement that was calculated based on the Newton' second law were carried out through the quasi-static load test and the comparison of a directly measured value using a laser displacement meter. Satisfactory results could be obtained. The crack initiation and propagation processes during impact fracture could be well divided on the curve, depending on the intrinsic characteristic of specimen tested; ductile or brittle. The absorbed impact energy in Zr-basd BAM was largely used for crack initiation not for crack propagation process. The fracture surfaces under impact loading showed different feature when compared with the static cases.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1246-1251
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• 2003

The fracture behaviors of Zr-based bulk amorphous metals(BAMs) having compositions of $Zr_{55}Al_{10}Ni_{5}Cu_{30}$, were investigated under impact loading and quasi-static conditions. For experiments, a newly devised instrumented impact testing apparatus and the subsize Charpy specimens were used. The influences of loading rate and the notch shape on the fracture behavior of the Zr-based BAM were examined. The Zr-based BAMs showed an elastic deformation behavior without any plastic deformation on it before fracture. Most fracture energies were absorbed in the process of the crack initiation. The maximum load and fracture absorbed energy under quasi-static condition were larger than those under impact condition. However, there existed relatively insignificant notch shape effect. Fracture surfaces under impact loading were smoother than those under quasi-static loading. The absorbed fracture energy appeared differently depending on the extent of the vein-like pattern region due to the shear bands developed at the notch tip. It can be found that the fracture energy of the Zr-Al-Ni-Cu alloy is closely related with the development of shear bands during fracture.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1804-1809
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• 2003

The purpose of this study is to clarify the bulk/sheet forming characteristics of bulk amorphous alloys in the supercooled liquid state. The temperature dependences of Newtonian viscosities of amorphous materials are obtained based on the previous experimental works. Finite element analyses for compression forming and sheet deep drawing of amorphous materials are performed. Effects of friction coefficients and temperature are examined and formability of amorphous material is explained in detail.

• 대한기계학회논문집A
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• 제27권10호
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• pp.1630-1635
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• 2003

The deformation and fracture behaviors of a bulk amorphous metal, Zr-based one (Zr$\_$41.2/Ti$\_$13.8/Cu$\_$12.5/Ni$\_$10/Be$\_$22.5/: Vitreloy), were investigated over a strain rate range (7x10$\^$-4/～4 s$\^$-1/). The uniaxial compression test and the indentation test using 3mm-diameter WC balls were carried out under quasi-static loading conditions. As a result, at the uniaxial compressive state, the fracture stress of the material was very high (～1,700MPa) and the elastic strain limit was about 2%. The fracture strength showed a strain rate independent behavior up to 4 s$\^$-1/. Using indentation tests, the plastic deformation behavior of the Zr-based BAM up to a large strain value of 15% could be achieved, even though it was the deformation under locally constrained condition. The Meyer hardness of the Zr-based BAM measured by static indentation tests was about 5 GPa and it revealed negligible strain hardening behavior. At indented sites, the plastic indentation occurred forming a crater and well-developed multiple shear bands were generated around it along the direction of 45 degree when the indentation load exceeded 7kN. With increasing indentation load, shear bands became dense. The fracture surface of the specimen after uniaxial compressive tests showed vein-like pattern, typical morphology of many BAMs.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.139-142
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• 2005

Cu-Ni-Zr-Ti bulk amorphous thin strips were produced by multi-pass warm rolling of the amorphous powder at temperatures in the supercooled liquid region. Process variables for rolling of the bulk amorphous strips were properly controlled to prevent onset of crystallization and failure during rolling up to three passes. During rolling of the amorphous powder, both the deformation and densification took place and the newly developed surface on the deformed amorphous particles enhances the consolidation leading to an increase in the strength. The strain state during rolling was analyzed by FEM.

• 소성∙가공
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• 제13권8호
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• pp.696-703
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• 2004

The purpose of this study is to examine the bulk/sheet forming characteristics of bulk amorphous alloys in the super cooled liquid state. Recently it is reported that amorphous alloys exhibit stress overshoot/undershoot and non-Newtonian behaviors even in the super cooled liquid state. The stress-strain curves with the temperature-dependences as well as strain-rate dependence of Newtonian/non-Newtonian viscosities of amorphous alloys are obtained based on the previous experimental works. Then, those curves are directly used in the thermo-mechanical finite element analyses. Upsetting and deep drawing of amorphous alloys are simulated to examine the effects of process parameters such as friction coefficient, forming speed and temperature. It could be concluded that the superior formability of an amorphous alloy can be obtained by taking the proper forming conditions.

• 한국자기학회지
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• 제12권4호
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• pp.154-159
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• 2002

벌크 비정질 형성능과 큰 포화자속밀도를 가지는 FeBSiNb계 아몰퍼스 합금 리본을 22~102$\mu\textrm{m}$의 두께 범위에서 단롤형 액체 급냉법으로 제조하였다. 이 합금은 두께 증가에 따라 보자력이 감소하고 최대투자율 및 교류투자율이 증가하였으며, 자기이력곡선의 각형비가 감소하였다. 한편 전기 비저항은 두께와 상관없이 거의 일정한 값을 나타내었다. 또 지구 관찰 결과, 두께가 증가하면 내부 자기 이방성의 변화에 따라 자구가 미세화 되고 보다 복잡한 자구 구조를 갖는 것으로 나타났다. 두께 81$\mu\textrm{m}$인 합금의 경우, 24 mOe의 작은 보자력과 1KHz에서 12,000이상의 높은 실효투자율을 나타내어 일반적인 고 연자성 비정질 합금(두께 약 20$\mu\textrm{m}$)의 특성을 능가하였다. 이와 같은 두꺼운 FeBSiNb 비정질 합금의 우수한 연자성은 자벽이동에 대한 표면 고착 효과의 감소 및 수직자기이방성 성분의 출현과 미세화 된 자구 구조에 그 원인이 있는 것으로 평가되었다.