• 동력기계공학회지
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• 제14권3호
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• pp.58-63
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• 2010

A laser beam welding and an electric arc welding were combined, and the positive points of each welding method are drawn such as high speed, low thermal load, deep penetration, and high productivity. The fiber laser-MIG conjugated welding. namely the hybrid welding has been studied mainly for the automation industry of a pipeline welding. In this study, the MIG welding was combined with a fiber laser welding to make up the hybrid welding. The weld shapes, microstructures and mechanical properties for weld zones after the hybrid welding or only fiber laser welding were investigated on the 700 MPa grade Ultra Fine Grained(UFG) high strength steel. The amount of acicular ferrite in weld metals and HAZ(heat affected zone) was observed larger after hybrid welding compared with after only laser welding. The Vickers hardness of the top area of the fusion zone after fiber laser welding was higher compared with after hybrid welding.

• 한국표면공학회지
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• 제35권4호
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• pp.232-240
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• 2002

The composition and the microstructure of the Zn-Cr alloys electroplated in chloride bath with EDTA were studied according to electrolysis conditions. The cathode current efficiency decreased with increasing both Cr/(Cr+Zn) ratio and current density. The Cr content of the alloy deposits increased with Cr/(Cr+Zn) ratio and current density The phase structure of Zn-Cr alloy deposits changed from η-Zn through η-Zn+${\gamma}$'-ZnCr to ${\gamma}$'-ZnCr with increasing Cr content of alloys. The surface morphology of Zn-Cr alloy deposits changed from fine needle shaped crystallites through the mixed structure of needle-shaped and granular one to the colony structure with fine granular crystallites according to the change of phase structure

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1045-1047
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• 2006

Fabrication of $Mg_{95.75}Zn_1Y_3Yb_{0.25}$ bulk alloy has been performed through the consolidation of rapidly solidified ribbons. The $Mg_{95.75}Zn_1Y_3Yb_{0.25}$ bulk alloy exhibited excellent mechanical properties, high tensile yield strength of 530 MPa, and large elongation of 3 %. Microstructure of the alloy was characterized by equiaxed fine grains that consist of -Mg, long period ordered (LPO) structure phase, and $Mg_5RE$-type cubic compound. The strengthening of the alloys may be due to fine grains with LPO structure phase and $Mg_5RE$-type compound.

• 한국세라믹학회지
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• 제43권9호
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• pp.515-518
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• 2006

The microstructure of $ZrO_2$ toughened $Al_2O_3$ ceramics was carefully controlled so as to obtain dense and fine-grained ceramics, thereby improving the properties and reliability of the ceramics for capillary applications in semiconductor bonding technology. $Al_2O_3-ZrO_2(Y_2O_3)$ composite was produced via Ceramic Injection Molding (CIM) technology, followed by Sinter-HIP process. Room temperature strength, hardness, Young's modulus, thermal expansion coefficient and toughness were determined, as well as surface strengthening induced by the fine grained homogenous microstructure and the thermal treatment. The changes in alumina/zirconia grain size, sintering condition and HIP treatment were found to be correlated.

• 소성∙가공
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• 제18권7호
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• pp.544-549
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• 2009

This study aimed to elucidate the deformation mechanism during low-temperature superplasticity of fine-grained Ti-6Al-2Sn-4Zr-2Mo-0.1Si alloy in the context of constitutive equation. For this purpose, initial coarse equiaxed microstructure was refined to $2.2{\mu}m$ via dynamic globularization. Globularized microstructure exhibited large superplastic elongations(434-826%) at temperatures of $650-750^{\circ}C$ and strain rate of $10^{-4}s^{-1}$. It was found that the main deformation mechanism of fine-grained material was grain boundary sliding accommodated by dislocation motion with both stress exponent (n) and grain size exponent (p) values of 2. When the alpha grain size, not sub-grain size, was considered to be an effective grain size, the apparent activation energy for low-temperature superplasticity of the present alloy(169kJ/mol) was closed to that of Ti-6Al-4V alloy(160kJ/mol).

• 한국재료학회지
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• 제26권5호
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• pp.287-291
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• 2016

The effect of heat treatment on the microstructure and mechanical properties of cast Ti-6%Al-4%V alloy was investigated. Heat treatment of cast Ti-6Al-4V alloy was conducted by solution treatment at $950^{\circ}C$ for 30 min; this was followed by water quenching and then aging at $550^{\circ}C$ for 1 to 1440 min. The highest hardness of the heat-treated specimens was obtained by solution treatment and subsequent aging for 5 min due to precipitates of fine ${\alpha}$ that formed from retained ${\beta}$ phase. The tensile strength of this alloy increased without dramatic decrease of the ductility due to microstructural refinement resulting from the decomposition of ${\alpha}^{\prime}$ martensite into fine ${\alpha}$ and ${\beta}$ phases, and also due to the fine ${\alpha}$ phase formed from the retained ${\beta}$ phase by aging treatment for 5 min. In addition, this strengthening might be caused by the transformation induced plasticity (TRIP) effect, which is a strain-induced martensite transformation from the retained ${\beta}$ phase during deformation, and which occurs even after aging treatment at $550^{\circ}C$ for 5 min.

• 한국분말재료학회지
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• 제3권4호
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• pp.271-278
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• 1996

In this study, the effect of the transition elements on the microstructure and mechanical properties of rapidly solidified Al-Mg-X alloys was investigated. As a result of the rapid solidification processing, fine equiaxed grains with a mean diameter of 2 $\mu$m were observed in these alloys. Many fine particles were found to be distributed rather homogeneously throughout the matrix with relatively large particles occasionally at grain boundaries. The ultimate tensile strengths of Al-Mg-X alloys were found to decrease rather remarkably at 150 $^{\circ}C$ without the gain of the ductility at 150 $^{\circ}C$, which may result from segregation of $\beta$ ($Al_{3}Mg_{2}$) precipitates. Fine dimples were observed on the fracture surfaces for all alloy systems and the variation of the size and shape of dimples was not observed upon alloy systems. The ductility at 530 $^{\circ}C$ was found to be ~100%, suggesting that grain boundary sliding did not contribute to ductiliy despite he grain size stabilization. The absence of superplastic behavior may be associated with low boundary misorientation in rapidly solidified Al-Mg-X alloys.

• 한국자기학회지
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• 제5권5호
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• pp.543-547
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• 1995

A set of $Fe_{1-x}Ni_{x}$ (x=0.10, 0.25, 0.30, 0.35, 0.50, 0.60, 0.75, 0.85) fine particles prepared by the gas evaporation technique was studied by $M\"{o}ssbauer$, XRD and other techniques. The XRD and $M\"{o}ssbauer$ patterns of the sample with x=0.10 ($Fe_{90}Ni_{10}$) were found to be exceptionally different, showing an austenite phase stability when the particles are quenched. This phase stability is quite different from that of the corresponding bulk alloy. Using binomial distrbution fits of the $M\"{o}ssbauer$ spectra of the particles in terms of nearest and next nearest neighbour configurations around the Fe atoms, an analysis of this phase stability is given. The changes in the relative intensities of the resulting magnetic sextets are used to determine the increase in martensite following the austenite-martensite transformation process. The stable austenite can, therefore, be determined. This stability may be related to the oxide surface layer and the small number of atoms of these fine particles.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 SMICS 2004 International Symposium on Maritime and Communication Sciences
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• pp.96-99
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• 2004

The combination of mechano-chemical activation and Self-propagating High-temperature Synthesis (SHS) has widened the possibilities for both methods. For YBCO systems the investigation showed that a short-term mechano-chemical activation of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors of YBCO composition with a grain size d ＜1 ${\mu}{\textrm}{m}$ is developed. The specific feature of the technique is formation of the YBa$_2$Cu$_3$O$_{7-{\delta}}$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors (HTS) are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples.fine samples.

• 콘크리트학회논문집
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• 제25권1호
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• pp.3-9
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• 2013

초고강도 콘크리트에서 잔골재로 세척사 대신에 전기로 산화 슬래그를 사용했을 경우, 재령 91일 압축강도가 약 15 MPa 정도 향상되었다. 압축강도가 향상된 원인을 규명하기 위해 잔골재의 Ca 성분 용출 특성을 고찰하였고, 잔골재와 페이스트 계면에서의 미세조직, 기공율, 미소경도 및 Ca/Si 몰비를 검토하였다. 그리고 잔골재 형상에 의한 강도 증진 효과를 알아보기 위해 잔골재의 표면 거칠기를 AFM으로 측정하였다. 실험 결과, 초고강도 콘크리트에서 전기로 산화 슬래그 잔골재 사용에 의한 강도 증진 기구는 화학적 기구와 물리적 기구로 구분할 수 있다. 화학적 기구로는, 전기로 산화 슬래그에서 함유되어 있는 가용성 Ca 성분이 용출되어 잔골재와 페이스트 사이에 반응생성물을 형성시켜 조직을 치밀화 시킴으로 잔골재-페이스트간의 부착력을 증진 시키는 것으로 나타났다. 그리고 물리적 기구로는, 전기로 산화 슬래그 잔골재는 세척사에 비해 표면의 굴곡도가 2배 정도 커서, 잔골재와 페이스트 간의 interlocking strength를 증가시킴으로서 압축강도 발현에 기여하는 것으로 판단했다.