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IN 939 W 합금의 소결 승온 속도에 따른 물리적 특성과 미세조직 분석
전준협,이준호,서남혁,손승배,정재길,이석재,Jeon, Junhyub,Lee, Junho,Seo, Namhyuk,Son, Seung Bae,Jung, Jae-Gil,Lee, Seok-Jae 한국분말재료학회 (*구 분말야금학회) 2022 한국분말재료학회지 (KPMI) Vol.29 No.5
Changes in the mechanical properties and microstructure of an IN 939 W alloy according to the sintering heating rate were evaluated. IN 939 W alloy samples were fabricated by spark plasma sintering. The phase fraction, number density, and mean radius of the IN 939 W alloy were calculated using a thermodynamic calculation. A universal testing machine and micro-Vickers hardness tester were employed to confirm the mechanical properties of the IN 939 W alloy. X-ray diffraction, optical microscopy, field-emission scanning electron microscopy, Cs-corrected-field emission transmission electron microscopy, and energy dispersive X-ray spectrometry were used to evaluate the microstructure of the alloy. The rapid sintering heating rate resulted in a slightly dispersed γ' phase and chromium oxide. It also suppressed the precipitation of the η phase. These helped to reinforce the mechanical properties.
오승진,전준협,손인진,이석재,Oh, Seung-Jin,Jeon, Junhyub,Shon, In-Jin,Lee, Seok-Jae 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.5
In the present study, we have investigated the effect of sintering process conditions on the stability of the austenite phase in the nanocrystalline Fe-5wt.%Mn-0.2wt.%C alloy. The stability and volume fraction of the austenite phase are the key factors that determine the mechanical properties of FeMnC alloys, because strain-induced austenite-martensite transformation occurs under the application of an external stress at room temperature. Nanocrystalline Fe-5wt.%Mn-0.2wt.%C samples are fabricated using the spark plasma sintering method. The stability of the austenite phase in the sintered samples is evaluated by X-ray diffraction analysis and hardness test. The volume fraction of austenite at room temperature increases as the sample is held for 10 min at the sintering temperature, because of carbon diffusion in austenite. Moreover, water quenching effectively prevents the formation of cementite during cooling, resulting in a higher volume fraction of austenite. Furthermore, it is found that the hardness is influenced by both the austenite carbon content and volume fraction.
방전플라즈마소결로 제조된 나노결정 FeNiCrMoMnSiC 합금의 오스테나이트 안정성과 기계적 특성
박정빈,전준협,서남혁,김광훈,손승배,이석재,Park, Jungbin,Jeon, Junhyub,Seo, Namhyuk,Kim, Gwanghun,Son, Seung Bae,Lee, Seok-Jae 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.4
In this study, a nanocrystalline FeNiCrMoMnSiC alloy was fabricated, and its austenite stability, microstructure, and mechanical properties were investigated. A sintered FeNiCrMoMnSiC alloy sample with nanosized crystal was obtained by high-energy ball milling and spark plasma sintering. The sintering behavior was investigated by measuring the displacement according to the temperature of the sintered body. Through microstructural analysis, it was confirmed that a compact sintered body with few pores was produced, and cementite was formed. The stability of the austenite phase in the sintered samples was evaluated by X-ray diffraction analysis and electron backscatter diffraction. Results revealed a measured value of 51.6% and that the alloy had seven times more austenite stability than AISI 4340 wrought steel. The hardness of the sintered alloy was 60.4 HRC, which was up to 2.4 times higher than that of wrought steel.
밀링 조건이 고엔트로피 합금의 미세조직 및 기계적 특성에 미치는 영향
서남혁,전준협,김광훈,박정빈,손승배,이석재,Seo, Namhyuk,Jeon, Junhyub,Kim, Gwanghoon,Park, Jungbin,Son, Seung Bae,Lee, Seok-Jae 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.2
High-entropy alloys have excellent mechanical properties under extreme environments, rendering them promising candidates for next-generation structural materials. It is desirable to develop non-equiatomic high-entropy alloys that do not require many expensive or heavy elements, contrary to the requirements of typical high-entropy alloys. In this study, a non-equiatomic high-entropy alloy powder Fe<sub>49.5</sub>Mn<sub>30</sub>Co<sub>10</sub>Cr<sub>10</sub>C<sub>0.5</sub> (at.%) is prepared by high energy ball milling and fabricated by spark plasma sintering. By combining different ball milling times and ball-to-powder ratios, we attempt to find a proper mechanical alloying condition to achieve improved mechanical properties. The milled powder and sintered specimens are examined using X-ray diffraction to investigate the progress of mechanical alloying and microstructural changes. A miniature tensile specimen after sintering is used to investigate the mechanical properties. Furthermore, quantitative analysis of the microstructure is performed using electron backscatter diffraction.
철계 비동일분율 고엔트로피 합금의 인장 강도에 미치는 소결 조건 영향
서남혁,전준협,김광훈,박정빈,손승배,이석재,Seo, Namhyuk,Jeon, Junhyub,Kim, Gwanghun,Park, Jungbin,Son, Seung Bae,Lee, Seok-Jae 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.3
We fabricate the non-equiatomic high-entropy alloy (NE-HEA) Fe<sub>49.5</sub>Mn<sub>30</sub>Co<sub>10</sub>Cr<sub>10</sub>C<sub>0.5</sub> (at.%) using spark plasma sintering under various sintering conditions. Each elemental pure powder is milled by high-energy ball milling to prepare NE-HEA powder. The microstructure and mechanical properties of the sintered samples are investigated using various methods. We use the X-ray diffraction (XRD) method to investigate the microstructural characteristics. Quantitative phase analysis is performed by direct comparison of the XRD results. A tensile test is used to compare the mechanical properties of small samples. Next, electron backscatter diffraction analysis is performed to analyze the phase fraction, and the results are compared to those of XRD analysis. By combining different sintering durations and temperature conditions, we attempt to identify suitable spark plasma sintering conditions that yield mechanical properties comparable with previously reported values. The samples sintered at 900 and 1000℃ with no holding time have a tensile strength of over 1000 MPa.
소성유기마르텐사이트 변태에 의한 나노결정 FeCrC 소결합금의 기계적 강도 향상
김광훈,전준협,서남혁,박정빈,손승배,이석재,Kim, Gwanghun,Jeon, Junhyub,Seo, Namhyuk,Park, Jungbin,Son, Seung Bae,Lee, Seok-Jae 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.3
The effect of sintering conditions on the austenite stability and strain-induced martensitic transformation of nanocrystalline FeCrC alloy is investigated. Nanocrystalline FeCrC alloys are successfully fabricated by spark plasma sintering with an extremely short densification time to obtain the theoretical density value and prevent grain growth. The nanocrystallite size in the sintered alloys contributes to increased austenite stability. The phase fraction of the FeCrC sintered alloy before and after deformation according to the sintering holding time is measured using X-ray diffraction and electron backscatter diffraction analysis. During compressive deformation, the volume fraction of strain-induced martensite resulting from austenite decomposition is increased. The transformation kinetics of the strain-induced martensite is evaluated using an empirical equation considering the austenite stability factor. The hardness of the S0W and S10W samples increase to 62.4-67.5 and 58.9-63.4 HRC before and after deformation. The hardness results confirmed that the mechanical properties are improved owing to the effects of grain refinement and strain-induced martensitic transformation in the nanocrystalline FeCrC alloy.
다른 크기의 분말 적층을 통해 얻은 Fe-6%Mn합금의 경사 미세조직과 기계적 특성
서남혁,이준호,신우철,전준협,박정빈,손승배,정재길,이석재,Seo, Namhyuk,Lee, Junho,Shin, Woocheol,Jeon, Junhyub,Park, Jungbin,Son, Seung Bae,Jung, Jae-Gil,Lee, Seok-Jae 한국분말재료학회 (*구 분말야금학회) 2022 한국분말재료학회지 (KPMI) Vol.29 No.5
A typical trade-off relationship exists between strength and elongation in face-centered cubic metals. Studies have recently been conducted to enhance strength without ductility reduction through surface-treatment-based ultrasonic nanocrystalline surface modification (UNSM), which creates a gradient microstructure in which grains become smaller from the inside to the surface. The transformation-induced plasticity effect in Fe-Mn alloys results in excellent strength and ductility due to their high work-hardening rate. This rate is achieved through strain-induced martensitic transformation when an alloy is plastically deformed. In this study, Fe-6%Mn powders with different sizes were prepared by high-energy ball milling and sintered through spark plasma sintering to produce Fe-6%Mn samples. A gradient microstructure was obtained by stacking the different-sized powders to achieve similar effects as those derived from UNSM. A compressive test was performed to investigate the mechanical properties, including the yielding behavior. The deformed microstructure was observed through electron backscatter diffraction to determine the effects of gradient plastic deformation.
다이캐스팅으로 제조된 Silafont-36 합금의 기계적 특성에 미치는 T6 열처리 영향
서남혁 ( Namhyuk Seo ),최승규 ( Seunggyu Choi ),전준협 ( Junhyub Jeon ),윤상일 ( Sang-il Yoon ),김동현 ( Dong-hyeon Kim ),김태영 ( Taeyoung Kim ),손승배 ( Seung Bae Son ),이석재 ( Seok-jae Lee ) 조선대학교 공학기술연구원 2020 공학기술논문지 Vol.13 No.4
Silafont-36 alloy is an Al-Si-Mg based alloy widely used in automotive applications. Its mechanical properties can be changed through T5 or T6 heat treatment. In this study, we investigated the influence of T6 heat treatment on the mechanical properties of Silafont-36 alloy prepared by die casting. The standard T6 heat treatment condition is as follows: (1) solution heat treatment for 2 hours in vacuum atmosphere at 510°C and water quenching, and (2) artificial aging treatment for 4 hours at 180°C in vacuum atmosphere and air cooling. Heat treatments were applied based on the above treatment conditions with changes in the solution treatment and artificial aging treatment conditions. Tensile test, hardness test, and microstructure analysis were performed on the heat-treated specimens. As the solution treatment temperature increased, the tensile strength increased. On the other hand, tensile strength decreased with increasing aging temperature and holding time. From a microstructure analysis, it was confirmed that the tensile strength increased with decreasing secondary dendrite arm spacing.
아공정 Al-Si-Cu-Mg 합금의 액상선 온도 곡선 예측
김근학 ( Keunhak Kim ),박동성 ( Dongsung Park ),오승진 ( Seung-jin Oh ),전준협 ( Junhyub Jeon ),윤상일 ( Sang-il Yoon ),김기선 ( Ki-sun Kim ),김태영 ( Tae-young Kim ),이석재 ( Seok-jae Lee ) 한국열처리공학회 2018 熱處理工學會誌 Vol.31 No.6
In the present study we proposed new equations to predict the liquidus temperature curve for hypoeutectic Al-Si-Cu-Mg alloy. A thermodynamic simulation was carried out to calculate the liquidus temperature, eutectic temperature and eutectic Si concentration with different Si, Cu, and Mg contents in hypoeutectic Al-Si alloys. Regressed equations were derived using the thermodynamic simulation results by multiple regression analysis. The proposed equations were compared with the equations reported previously by other researchers and agreed better with the experimental data. The addition of Cu and Mg lowered the eutectic temperature. The eutectic Si concentration was decreased by adding Cu whereas that was increased by adding Mg. Al-Si binary phase diagram was successfully predicted with a consideration of the effect of Cu and Mg addition by using the proposed equations. (Received October 2, 2018; Revised October 15, 2018; Accepted November 6, 2018)