In-X(X=Pb, Sn) 합금의 마르텐사이트변태거동 특성에 관한 연구

한창석 ( Chang Suk Han ),한승오 ( Seung Oh Han ) 한국열처리공학회 2010 熱處理工學會誌 Vol.23 No.5

The phase transformations and the shape memory effect in In-rich Pb alloys and In rich-Sn alloys have been studied by means of X-ray diffractometry supplemented by metallographic observations. The alloys containing 12~15 at.%Pb transform from the α2 (fct) phase to the α1 (fct) phase by way of an intermediate phase (m phase) on cooling. The results of X-ray diffraction show that the metastable intermediate phase is observed both on cooling and heating, and has a face-centered orthorhombic (fco) structure. It is concluded that the α1 →/← α2 transformation is expressed by the α1 →/← m →/← α2 transformation both on usual cooling and heating with the rate more than 8 × 10(-3) K/s. The m →/← a2 transformation takes place with a mechanism involving macroscopic shear and are of diffusionless (martensitic) type. The temperature hysteresis in the two transformations is 10~13 K between the heating and cooling transformations. The alloys containing 0~11 at.%Sn are -phase solid solutions with a face centered tetragonal structure (c/a> 1) at room temperature, the axial ratio increasing continuously with tin content. The In-(11~15) at.%Sn alloys are mixtures of α and β phases, the β phase having a f. c. tetragonal structure (c/a < 1). The alloys containing more than 15 at.%Sn are β-phase solid solutions. The In-(12.9~15.0) at.%Sn alloys show a shape memory effect only when quenched to the temperature of liquid nitrogen, although their effect becomes weak and finally disappears after keeping at room temperature for a long time. The β → α` phase transformation is of the diffusionless (martensitic) type, and takes place between 330 K at 12.9 at.%Sn and 150 K at 14.5 at.%Sn. The hysteresis of transformation temperatures on heating and cooling is considerably large (29~40 K), depending on the composition. Both In-Pb and In-Sn alloys showed distinct the shape memory effects.

페리하이드라이트의 산화음이온 흡착 특성과 광물상 변화

김규례(Gyure Kim),김영규(Yeongkyoo Kim) 대한자원환경지질학회 2023 자원환경지질 Vol.56 No.3

페리하이드라이트는 산상광산배수를 포함한 자연 환경에서 쉽게 관찰되는 산화철 광물로 결정도가 낮고 높은 비표면적을 갖고 있어 다른 이온과의 반응성이 매우 우수하여 환경유해물질과의 반응을 통하여 이의 제거가 가능하다. 그러나 페리하이드라이트는 준안정성 광물이기 때문에 표면적이 작고 결정도가 높은 다른 광물로의 상변화로 흡착된 이온들의 방출 가능성도 존재한다. 본 연구에서는 비산염, 크롬산염, 셀레늄산염의 페리하이드라이트에 대한 흡착 특성과 광물상 변화까지 고려한 페리하이드라이트의 산화음이온 제거 효능을 연구하였다. 실험 시 pH 4와 8에서 연구에 사용된 산화음이온들의 흡착은 pH 8에서 셀레늄산염을 제외하고 Langmuir와 Freundlich 두 흡착 모델과 잘 일치하였다. 각 산화음이온의 흡착량은 pH에 따른 표면 전하의 차이로 인하여 pH 4의 경우 pH 8보다 더 높았다. 흡착 량은 비산염, 크롬산염, 그리고 세레늄산염의 순서를 보여주었다. 이러한 흡착모델과 흡착량은 각 산화음이온의 흡착 시 페리하이드라이트 표면에서 일어나는 서로 다른 흡착 기작을 잘 대변한다. 이러한 흡착 특성은 광물상의 변화와도 밀접한 연관성이 있었다. pH 4에서는 침철석 혹은 적철석으로의 상변화를 보여주었으나, pH 8에서는 적철석으로의 상변화만이 관찰되었다. 산화음이온 종 중 비산염은 가장 높은 흡착력을 보여주며, 흡착 후 페리하이드라이트의 실험 기간 내 거의 상변화를 일으키지 않았다. 이와 달리 크롬산염과 셀레늄산염은 비산염에 비하여 광물상 변화가 더 빨랐으며 세 산화음이온 중 셀레늄산염의 지연 효과가 가장 낮았다. 페리하이드라이트는 비산염에 대하여 높은 흡착 능력과 낮은 상변화로 인하여 효과적인 제거가 가능하지만 다른 두 산화음이온 종은 낮은 흡착량과 추가적인 광물상 변화로 비산염에 비하여 제거 효과가 떨어지고 크롬산염의 경우 낮은 pH 환경에서 낮은 농도의 경우에에만 효율적인 제거가 가능할 것으로 판단된다. Ferrihydrite is an iron oxide mineral that is easily found in the natural environment, including acid mine drainage, and has a low crystallinity and high specific surface area, resulting in high reactivity with other ions, and can remove environmentally hazardous substances. However, because ferrihydrite is a metastable mineral, there is a possibility of releasing adsorbed ions by phase transformation to other minerals having low surface area and high crystallinity. In this study, the adsorption characteristics of arsenate, chromate, and selenate on ferrihydrite and the oxyanion removal efficiency of ferrihydrite were studied considering mineral phase transformation. At both pH 4 and 8, the adsorption of oxyanions used in the study were in good agreement with both Langmuir and Freundlich adsorption models except for selenate at pH 8. Due to the difference in surface charge according to pH, at pH 4 a higher amount of ions were adsorbed than at pH 8. The adsorption amount were in the order of arsenate, chromate, and selenate. These different adsorption models and adsorption amounts were due to different adsorption mechanisms for each oxyanions on the surface of ferrihydrite. These adsorption characteristics were closely related to changes in the mineral phase. At pH 4, a phase transformation to goethite or hematite was observed, but only a phase transformation to hematite was observed at pH 8. Among the oxyanion species on ferrihydrite, arsenate showed the highest adsorption capacity and hardly caused phase transformation during the experimental period after adsorption. Contrary to this, chromate and selenate showed faster mineral phase transformation than arsenate, and selenate had the lowest retardation effect among the three oxyanions. Ferrihydrite can effectively remove arsenate due to its high adsorption capacity and low phase transformation rate. However, the removal efficiency for other two oxyanions were low by the low adsorption amount and additional mineral phase transformation. For chromate, the efficient removal is expected only at low concentrations in low pH environments.

Ti-Ni-Fe 합금의 R상 변태온도에 미치는 Fe 조성과 열처리 온도의 영향

김원석,금나영,김진용,김재일 대한금속·재료학회 2024 대한금속·재료학회지 Vol.62 No.4

R-phase transformations in TiNi shape memory alloys (Nitinol) have various applicationsbecause of their small thermal hysteresis and low fatigue resistance. Adding a third element such as Feor Al is one of the useful ways to induce R-phase transformation. Controlling the R-phase transformationtemperature is crucial for industrial and bio-field applications. However, the effects of adding Fe haverarely been reported. In this study, the effects of Fe addition and heat treatment temperature on the Rphasetransformation temperature of TiNiFe shape memory alloys were systematically investigated. Results showed that increasing Fe composition decreases the R-phase and martensitic transformationtemperatures of 19K/1at%Fe and 51 K/1at%Fe, respectively. Additionally, in the Ti–49Ni–1Fe alloy,rather than a martensite transformation, the R phase transformation temperature was constantirrespective of heat treatment temperature and increasing number of thermal cycles. This means thatthe R-phase transformation temperature is not affected by dislocation density resulting from the heatcycling or cold working processes. This allows practical applications of R-phase transformation to beeasily realized. Furthermore, this means that the R-phase transformation temperature is only affectedby the Ni content of the matrix.

Phase Transformation Comparison of TiO2 Nanorods and TiO2 Thin Film After Annealing

Yi Chen,Sang Yeol Yang,김재환 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.3

This paper reports the degree of phase transformation of titanium dioxide (TiO2) thin film and TiO2 nanorods before and after annealing. TiO2 nanorods were synthesized with titanium isoproxide (TIP) in Oleic acid,having approximately 5 nm diameter and 30 nm length. TiO2 thin film was fabricated by sol-gel method using TIP, ethanol and hydrochloric acid. The characteristics of TiO2 nanorods and thin film were investigated with transmission electron microscope, atomic force microscope and x-ray diffraction patterns. Although the TiO2 thin film shows no crystallite peak, as-synthesized TiO2 nanorods show broad anatase phase diffraction peaks. After annealing the TiO2 nanorods at 850°C for 3 h, only approximately 3.1% of crystallite phase was transformed from anatase phase to rutile phase. This slow phase transformation might be due to the small diameter of the nanorods, which is thermodynamically more stable than the anatase crystallite phase. However, although the film has small grains on the surface, approximately 59.5% of phase was transformed from anatase to rutile crystallite structure after the thin film annealing. This large amount of phase transformation might be due to the two dimensional structure of the thin film.

Phase Transformations of 24Cr-14Ni-0.7Si Stainless Steel under Different Aging Conditions

Chih-Chun Hsieh,Dong-Yih Lin 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.2

This study discusses the development of a phase transformation in 24Cr-14Ni-0.7Si stainless steel after aging under various aging temperatures, times, and N2/Air ratios. The observation of OM indicated that the initial state of δ-ferrite in the test material appeared as complete dendrite structures at short aging times and then exhibited lacy and dispersed structures when the aging time increased. This led to a gradual austenitization transformation as the nitrogen/air ratio increased, accelerating the δ/σ phase transformation and retarding the δ/γ phase transformation at the same time. The δ/σ phase transformation was dominant when the aging temperature was 800 °C. A line scanning analysis of the EPMA showed that the X-ray spectrum of Cr at the δ/γ interphase boundary was raised. In addition, Si showed lower X-ray spectrum energy after the δ/γ phase transformation. Clearly, Si had a stabilizing effect on the δ-ferrite and σ-phase. Furthermore, it had the fastest precipitation ratio for the δ/σ phase transformation at 800°C among all aging temperatures.

기계적 합금화로 제조된 Fe_0.92Mn_0.08Si₂의 상변화 및 열전 특성

김영섭,조경원,김일호,어순철,이영근,Kim, Young-Seob,Cho, Kyung-Won,Kim, Il-Ho,Ur, Soon-Chul,Lee, Young-Geun 한국재료학회 2003 한국재료학회지 Vol.13 No.5

In an attempt to enhance phase transformation and homogenization of Mn-doped $FeSi_2$, mechanical alloying of elemental powders was applied. Cold pressing and sintering in vacuum were carried out to produce a dense microstructure, and then isothermal annealing was employed to induce a phase transformation to the $\beta$-$FeSi_2$semiconductor. Phase transitions in this alloy system during the process were investigated by using XRD, EDS and SEM. As-milled powders after 100 h of milling were shown to be metastable state. As-sintered iron silicides consisted of untransformed mixture of $\alpha$-$Fe_2$$Si_{5}$and $\varepsilon$-FeSi phases. $\beta$-$FeSi_2$phase transformation was induced by subsequent isothermal annealing at $830^{\circ}C$, and near single phase of $\beta$-$FeSi_2$was obtained after 24 h of annealing. Thermoelectric properties in terms of Seebeck coefficient, and electrical conductivity were evaluated and correlated with phase transformation. Seebeck coefficient electrical resistivity and hardness increased with increasing annealing time due to $\beta$ phase transformation.

성장모델과 유한요소법의 연계해석을 통한 변태소성 전산모사

조이길(Y.-G. Cho),김진유(J.-Y. Kim),차필령(P.-R. Cha),이재곤(J.K. Lee),한흥남(H.N. Han) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5

Transformation plasticity is that when a phase transformation of ferrous or non-ferrous alloys progresses even under an extremely small applied stress compared with a yield stress of the material, a permanent deformation occurs. One of widely accepted description for the transformation was proposed by Greenwood and Johnson [1]. Their description is based on an assumption that a weaker phase of an ideal plastic material could deform plastically to accommodate the externally applied stress and the internal stress caused by the volumetric change accompanying the phase transformation. In this study, an implicit finite element model was developed to simulate the deformation behavior of a low carbon steel during phase transformation. The finite element model was coupled with a phase field model, which could simulate the kinetics for ferrite to austenite transformation of the steel. The thermo-elasto-plastic constitutive equation for each phase was adopted to confirm the weaker phase yielding, which was proposed by Greenwood and Johnson [1]. Form the simulation, the origin of the transformation plasticity was quantitatively discussed comparing with the other descriptions of it.

Phase Transformation Modeling for Hypo Peritectic Steel in Continuous Cooling

Jun‑hyun Jo,Kyung‑woo Yi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

Phase change of steel during cooling affects the slab qualities in continuous casting. Especially, crack susceptibility of hypoperitectic steel is high because large volume shrinkage occurs by peritectic phase transformation during solidification andcooling. In continuous cooling, phase change is different from the behaviors under the equilibrium condition, such as undercoolingand extend of peritectic reaction, etc. Therefore, we develop a new phase change model considering thermodynamics,empirical equations, and carbon diffusion in each phase to predict phase change behavior during continuous cooling. Inthis model, phase change of hypo peritectic steel comprises 5 stages until all phases become the γ phase. The velocities ofthe δ/γ interface and phase fractions during cooling are calculated according to cooling rate, undercooling of the γ phase,and carbon contents. The results show that if solidification ends by the δ phase during dTp,the γ phase is formed by massivetransformation. On the contrary, if peritectic reaction starts with liquid, the γ phase is formed and grows by diffusionaltransformation. In latter case, massive transformation of remaining δ phase can occur with high undercooling or very fastcooling rates. This analysis shows that there are several different paths depending on carbon contents of hypo peritectic steels.

Diffusion-accompanied Phase Transformation of $TiSi_2$ Film Confined in Sub-micron Area

Kim, Yeong-Cheol The Korean Ceramic Society 2001 The Korean journal of ceramics Vol.7 No.2

Phase transformation of TiSi$_2$ confined in sub-micron area of which the size is around or smaller than the grain size of C49 TiSi$_2$ phase is studied. It has been known that the C49 to C54 phase change is massive transformation that occurs abruptly starting from C54 nuclei located at triple point grain boundaries of C49 phase. When the C49 phase is confined in sub-micron area, however, the massive phase transformation is observed to be hindered due to the lack of the triple point grain boundaries of C49 phase. Heat treatment at higher temperatures starts to decompose the C49 phase, and the resulting decomposed Ti atoms diffuse to, and react with, the underneath Si material to form C54 phase that exhibits spherical interface with silicon. The newly formed C54 grains can also trigger the massive phase transformation to convert the remaining undecomposed C49 grains to C54 grains by serving as nuclei like conventional C54 nuclei located at triple point grain boundaries.

Phase transformation of guanosine 5′‐monophosphate in drowning‐out crystallization: Comparison of experimental results with mathematical modeling

Nguyen, Anh‐,Tuan,Kang, Jeong‐,Ki,Choi, Guang Jin,Kim, Woo‐,Sik WILEY‐VCH Verlag 2011 Crystal research and technology Vol.46 No.1

<P><B>Abstract</B></P><P>The phase transformation of Guanosine 5′‐Monophousphate (GMP) in drowning‐out crystallization using a batch system was experimentally monitored and mathematically modeled. The solid (amorphous and crystalline GMP hydrate) and liquid phases of the GMP products were simultaneously monitored using a video microscope, FT‐IR, and UV/Vis spectroscopy during the phase transformation. For the modeling, the phase transformation was assumed to occur via the simultaneous dissolution of amorphous GMP and growth of crystalline GMP hydrate in the solution. Based on a comparison of the experimental results and model predictions, both the dissolution and growth of the GMP solids were found to contribute competitively to the phase transformation. When varying the crystallization conditions, in this case the agitation speed and feed concentration, the phase transformation was significantly promoted when increasing the agitation speed, yet independent of the feed concentration. The simple mathematical model used for the GMP phase transformation was quite successful in describing the experimental results. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)</P>