• 한국재료학회지
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• 제10권9호
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• pp.636-641
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• 2000

Zr-0.86Sn 합금이 $\beta{\rightarrow}\alpha$상변태 특성에 미치는 Fe와 V의 영향을 광학현미경과 투과전자현미경으로 연구하였다. 공냉의 경우에는 V의 첨가량이 증가함에 다라 $\beta{\rightarrow}\alpha+\beta$변태온도가 감소하여 미세한 $\alpha$-lath들의 폭을 더욱 감소시켰으나, Fe의 경우에는 첨가량이 증가함에 다라 오히려 $\alpha$-lath의 폭이 약간 증가하였다. 수냉의 경우에는 모든 합금에서 martensite 미세구조를 보였다. 수냉한 Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V 그리고 Zr-0.8Sn-0.2V 합금에서는 주로 slipped martensite 미세구조가 형성된 반면에 수냉한 Zr-0.8Sn-0.4V 합금에서는 twinned martensite 미세구조가 관찰하였다. 수냉한 Zr-0.8Sn 합금에서 V의 첨가향이 증가함에 따라 slipped martensite에서 twinned martensite 미세구조로의 천이는 M(sub)s 온도의 감소에 기인한 것으로 생각된다.

• 한국재료학회지
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• 제12권4호
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• pp.317-323
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• 2002

Effect of V and Sb content on characteristics of ${\beta}\;to\;{\alpha}$ phase transformation in Zr-0.84Sn alloy has been studied using optical microscopy and transmission electron microscopy. As V content increased, the ${\beta}{\to}{\beta}+{\alpha}$ transformation temperature was lowered, thus allowing the width of $\alpha$-lath in air-cooled Zr-0.86Sn-0.40V alloy to be fine. The width of ${\alpha}$-lath in air-cooled Zr-0.84Sn-xSb, however, was rarely changed with Sb content. The ${\beta}\;to\;{\alpha}$ transformed microstructures of water-quenched Zr-0.84Sn, Zr-0.84Sn-0.10V and Zr-0.84Sn-0.19V alloys were mainly slipped martensite. On the other hand, those of wafter-quenched Zr-0.86Sn-0.40V and Zr-0.85Sn-0.05Sb alloys were predominantly twinned martensite. In case of water-quenched Zr-0.85Sn-0.12Sb and Zr-0.84Sn-0.17Sb alloys, basketweave structure was observed. The transition of slipped martensite to twinned martensite in Zr-0.84Sn-xV alloys and the transition of twinned martensite to basketweave structure in Zr-0.84Sn-xSb alloys were due to the decrease of $M_s$ temperature.

• 열처리공학회지
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• 제13권3호
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• pp.158-162
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• 2000

The high temperature oxidation behavior and the surface defect in Fe-25Mn-1.5A1-0.5C steel was investigated by XRD (X-ray Diffractin) and electron microscopy. The intra- and inter-granular oxides were formed by the selective oxidation of manganese and aluminum, which were identified to MnAl2O4 phase. Aluminum nitride (AlN) was formed in front of these oxides. The ${\gamma}$-matrix was transformed to ${\alpha}$- and ${\varepsilon}$- phases by the selective oxidation of manganese. The surface defect, micro-scab was induced by the difference of the high temperature ductility between the matrix and the inter-granular oxide.

• Bulletin of the Korean Chemical Society
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• 제26권12호
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• pp.2027-2032
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• 2005

This paper demonstrates details of thermal behavior of Langmuir-Blodgett (LB) film of poly(tert-butyl methacrylate) (PtBMA) by using the principal component analysis based two-dimensional correlation spectroscopy (PCA2D) through eigenvalue manipulating transformation (EMT). By uniformly lowering the power of a set of eigenvalues associated with the original data, the smaller eigenvalues becomes more prominent and the subtle contribution from minor components is now highlighted much more strongly than the original data. Thus, the subtle difference of thermal behavior of LB film of PtBMA from minor components, which is not readily detectable in the conventional 2D correlation analysis, is much more noticeable than the original data. PCA2D correlation spectra with EMT operation for the temperature-dependent IR spectra of LB film of PtBMA reveal the hidden property of phase transition processes during heating.

• 대한기계학회논문집A
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• 제24권11호
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• pp.2749-2761
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing. Finite element results by using the proposed model also well predicted experimental data in the literature for densification behavior of nanocrystalline zirconia powder during pressureless sintering and sinter forging.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.363-368
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing.

• 동력기계공학회지
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• 제3권3호
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• pp.76-82
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• 1999

This study presents a methodology to predict the hardenability of quenched carbon steels. The equation of transient heat conduction is analyzed to formulate a cooling curve by a finite element method which incorperates coupled effects of temperature on physical properties, the metallic structures and also the latent heat by phase transformation. The volume traction of martensite and pearlite are the structural analysis for hardenability analysis. In order to demonstrate the feasibility of adopting a full quench model respectively. This procedure could be used as the database for optimal condition of heat treatment processes.

• 한국결정성장학회지
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• 제3권1호
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• pp.37-44
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• 1993

수열반응법으로 합성한 칼시아 안정화 지르코니아 분말을 $1200^{\circ}C~1400^{\circ}C$의 온도에서 소결시켜 Ca-TZP 세라믹스를 제조한 후 소결체의 물성과 $250^{\circ}C$에서의 등온 상전이 거동을 고찰하였다. 그 결과 소결밀도가 약 97%이고 평균 입자크기가 $0.1~0.25{\mu}m$인 미세한 구조의 정방정상 지르코니아 다결정체(Ca-TZP) 세라믹스를 제조할 수 있었다. 이러한 Ca-TZP 세라믹스는 종래의 Y-TZP 세라믹스에 비햐여 열안정성이 매우 우수하였다.

• Journal of Welding and Joining
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• 제17권2호
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• pp.84-90
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• 1999

The shape of weld nuggest in arc spot welding of 304 stainless steel was found by searching thermal history of a weld joint through a three-dimensional finite element model. The problem consists of one in which the finite element mesh is growing continuously in time in order to accomodate metal transfer in arc spot welding using element rebirth technique. The analysis was performed on the basis of experimental results. The finite element program MARC, along with a few user subroutines, was employed to obtain the numerical results. Temperature-dependent thermal properties, stir effect in weld pool, effect of phase transformation, and the convective and radiative boundary conditions are included in the model. Numerically predicted shape of weld nuggest is compared with the experimentally observed shape.

• 한국재료학회지
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• 제9권3호
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• pp.322-326
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• 1999

본 연구는 냉간가공과 열처리를 통해 Cu-26.65Zn-4.05Al-0.31Ti(wt%) 형상기억합금의 결정립을 미세화하기 위한 목적으로 수행하였다. 냉간가공을 위하여는 α-상이 가능한 많이 존재하는 (α+β)-조직을 가져야 하는데, 이는 550℃에서 열처리함으로써 얻었고, 최종두께 1mm로 냉간압연하였다. 총 압연율은 70%와 90%이었다. 냉간압연한 판재를 800℃에서 가열 후 급랭함으로써 형상기억특성을 갖는 상으로 변태시켰으며, 이 대 결정립크기를 측정한 결과, 열간압연한 경우보다 냉간압연과 열처리를 한 경우의 결정립이 월등히 작아졌음을 보여주었다. 냉간압연과 열처리를 한 경우에는 냉간압연 변형율이 큰 경우가 결정립이 더 작아지는 경향을 보였다. 또한 결정립크기가 작아짐에 따라 변태온도가 저하되었으며 오스테나이트상이 더 안정하게 되었음을 확인할 수 있었다. In this study, cold-rolling and appropriate annealing was adopted for the grain refining of Cu-26.65Zn-4. 05Al-0.31Ti(wt%) shape memory alloy. For the cold deformation of this alloy the ducti1e α-phase must be contained. After heat treatment at 550℃ the (α+β)-dual phase with 40vol.% α-phase was obtained which could be rolled at room temperature. This alloy was cold rolled into a final thickness of 1.0mm with total reduction degrees of 70% and 90%. The rolled sheets were betanized at 800℃ for various times, then quenched into ice water. The grain size of co]d rolled samples were 60∼80 ㎛ which is much smaller comparing with the hot-rolled samples. And the 90% rolled sample showed smaller grain size than the case of the 70% rolled one. The small grain size had influence on the phase transformation temperatures and stabilization of the austenitic phases.