Haynes 282 초내열합금의 다른 열처리 인자 적용 및 장기 열간 노출에 따른 미세조직과 기계적 특성 고찰

김진혁 창원대학교 2020 국내석사

In this study, we investigated the microstructure evolution and the mechanical properties of Haynes 282 superalloy in tension at 750 ˚C. Especially, The well-known strengthening phase in superalloy which is called γ′ precipitate was observed differently as various heat treatment conditions. Also, the thermal stability is very important factor which should be considered for application in thermal power plant. Therefore, long-tern thermal exposure was conducted at 750 ℃ up to 5000hr for all the heat treatment conditions. We conducted the standard 2step aging heat treatment (1010 ˚C/2h + 788 ˚C/8h) and newly suggested 1step aging heat treatment (800 ˚C/4h) which have advantages in time reduction and economics. Moreover, three different cooling rates (WQ, AC, FC) were conducted to study mass effect which can occur in large scale products. The γ′precipitates were observed and calculated average size and distribution after heat treatment. The average γ′precipitate size for standard 2step aging heat treatment was 17.3 nm. In case of 1step aging heat treatment, the average γ′precipitate size was increased along the decrement of cooling rate as 12.1 nm (WQ), 15.4 nm (AC) and 39.2 nm (FC). And, the γ′precipitate exhibit spherical shape. The tensile properties were measured at 750 ℃. The yield strength exhibit similar values (over 600 MPa) and for all conditions. Only a slight decrease of strength is observed, as expected, when precipitates were larger. However, the plastic behaviors were significantly different in stress-strain curve. Different strain hardening was observed. It implies that the different deformation mode was occurred. The deformation mechanism was investigated by TEM analysis. In all the cases, we observed a mixed mode of deformation such as climbing, shearing and bypassing. However, only 1step aging after FC condition showed shearing mechanism as a dominant mechanism which can be evidence of stress-strain curve. To approach theoretically, the strength increment associated to each mechanism was measured by using precipitation strengthening model. And, the results were well agreed with the observed TEM micrographs. For all the conditions calculated the existence of mixed mode of deformation mechanism. However, only 1step aging after FC condition calculated as showing shearing mechanism as a dominant mechanism. To idenfiy the thermal stability, the thermal exposure at 750 ℃ for up to 5000hr was conducted. The formation of deleterious phase was not detect even for the 5000hr exposure. The mechanical properties were very satisfying despite long-term exposure in all the cases. The yield strength was higher than 600MPa for all heat treatment conditions. This suggests that the newly suggested 1step aging heat treatment can replac with standard 2step aging heat treatment. There was significant coarsening of γ′precipitates during thermal exposure. However, they still remained sherical shape and the size was 79.6 nm for standard 2step aging heat treatment and 73.5 nm (WQ), 73.5 nm (AC), 83.1 nm (FC) for 1step aging heat treatment. The shape of γ′precipitates is important factor to evaluate the degradation. Therefore, the spherical shape implies that the γ′precipitates is maintaining the coherent interface with γ matrix suggesting high stability of the microstructure of Haynes 282 superalloy at 750 ℃. The coherency was analyzed after 5000hr at 750 ℃ for the 1step aging after FC condition. The perfect coherency along the interface between the γ materix and γ′precipitates. This coherency is believed to significantly contribute to the high resistance to thermal degradation of Haynes 282.

열처리 공정에 대한 유한요소해석과 강인강의 조직미세화에 관한 연구

이광오 부산대학교 2007 국내박사

Heat treatment is widely used in various manufacturing processes to improve the mechanical properties of a product such as surface hardness, wear resistance and service life by intentionally manipulating chemical and metallurgical structures. However, unwanted results such as improper hardness, hardening depth and dimensional change or distortion are concurrently occurred after heat treatment. Traditionally, process parameters of heat treatment for specific metallic product have been determined by many experiments. These trial and errors needed high cost but couldn't offer information on the thermal, mechanical and microstructural change during heat treatment. In recent years, along with fast improvement in simulation technologies, analysis for the change of metallic structures, temperature, and stress/strain incorporating phase transformation in heat treatment process has become realistic. However, these heat treatment simulations have not used practically in real fields since thermal-mechanical-metallic coupled analysis must be performed and a large number of properties about three fields need to conduct simulations. Therefore, several data for simulating heat treatment such as transformation kinetic equation constants, diffusion coefficient, thermal conductivity, heat capacity, latent heat, young's modulus, coefficient of thermal expansion, strain/stress curves) as well as boundary conditions like surface reaction rate were obtained for two industrially common materials(AISI 4118H and AISI 52100) in this study. And a lab-based finite element code, MPL-HTC, was developed for calculating surface heat transfer coefficients(HTC) which have a great influence upon the microstructure and residual stress. Using these data, finite element analysis for quenching and carburization were performed and results of simulations were verified by comparing predicted values and experimental ones. Meanwhile, current applications require bearings to sustain high speed, high temperature and high torque in a heavily contaminated environment as a result of the demand for high efficiency, high power, compactness in modern vehicles as well as the stringent durability requirements and extended warranty standard. Greater bearing life is demanded under these extreme environments. So, bearing makers are improving the quality of bearings through research on bearing design and the development of new materials and heat treatments. It's well known that bearing steels with fine grain size are superior in fatigue properties to conventional bearing steels. Thus, a model for predicting prior austenite grain size of high strength bearing steels in reheating process was proposed to develop heat treatment cycles first and then double quenching heat treatment processes were developed to improve the durability of high strength steel through grain refinement. Microstructure with a prior austenite grain size of approximately 5 µm in diameter could be obtained using proposed heat treatment, accordingly the durability of bearing steels could be substantially enhanced. 열처리는 화학적 야금학적 구조를 인위적으로 조작함으로써 표면강도, 내마모성 및 제품수명과 같은 기계적 성질을 향상시키기 위하여 많은 제조공정들에 폭넓게 이용되고 있다. 그러나 부적절한 경도, 경화 깊이 및 치수변형과 같은 원치 않는 결과들이 열처리 후에 발생하게 된다. 전통적으로 특정 금속제품의 열처리 공정변수들은 주로 많은 실험들을 통해 결정되어 왔다. 이러한 시행착오법들은 많은 시간과 비용을 요구하지만 열처리 과정중의 열적, 기계적 및 미세 조직적 변화에 관한 정보들을 제공해 주지는 못하였다. 최근 시뮬레이션 기술의 급속한 발전과 더불어 열처리 공정중의 상변태를 고려한 금속구조, 온도 및 응력/변형율의 변화에 대한 유한요소해석이 가능하게 되었다. 그러나 이러한 열처리 공정에 대한 시뮬레이션들은 실제공정으로 적용되지 못하고 있는 데 열처리 공정의 시뮬레이션에는 열적-기계적-금속적 연성효과가 고려되어야 하며, 따라서 이러한 3가지 분야에 대한 수많은 물성치들이 요구되기 때문이다. 그러므로 본 논문에서는 열처리 공정을 시뮬레이션하기 위한 상변태 운동역학 방정식과 그 상수들, 확산계수, 열전도도, 열용량, 잠열, 탄성계수, 열팽창계수, 응력 변형율과 같은 수많은 재료 물성 데이터들과 경계조건으로서 표면반응속도가 산업계에서 흔히 사용되는 강인강(AISI 4118H steel, AISI 52100 steel)에 대해 획득되었다. 그리고 열처리 후의 미세조직과 잔류응력에 영향을 큰 미치는 열전달 계수를 계산하기 위한 유한요소프로그램인 MPL-HTC를 개발하였다. 이러한 데이터들을 이용하여 ?칭 열처리 공정과 침탄 열처리 공정에 대한 유한요소해석이 수행되었으며, 해석결과와 실험결과의 비교를 통해 해석결과의 타당성을 검증하였다. 한편, 최근 자동차 업계에서는 고효율, 고출력 및 경량화에 따른 소형화에 대한 결과로서 오염된 환경하에서 고속, 고온 및 큰 토크를 전달할 수 있을 뿐 아니라 보증기한의 연장과 내구성에 대한 엄격한 요구조건을 만족시킬 수 있는 고성능의 베어링이 요구되고 있다. 이러한 가혹한 환경하에서는 고수명의 베어링을 만들어내기 위해서 베어링 메이커들은 베어링의 형상 설계, 새로운 재료 개발 및 열처리 방법의 개발 등을 통해 베어링의 품질을 향상시키려 하고 있다. 미세 입자를 가진 베어링강의 경우, 일반적인 베어링강에 비해 피로성능이 대단히 뛰어나다는 것이 알려져 있다. 입자 미세화를 통해 베어링의 내구성을 향상시키기 위하여 먼저 베어링강의 재가열 공정 중 구 오스테나이트 입자크기를 예측하기 위한 모델을 개발하였고, 이를 이용하여 이중 ?칭 열처리 공정을 개발하였다. 제안된 열처리 사이클을 통해 약 5㎛직경 정도의 구 오스테나이트 입자크기의 미세조직이 얻어졌으며, 따라서 베어링강의 내구성이 상당히 향상될 수 있었다.

코일 전류 및 중탄소강 상변태를 고려한 고주파 열처리

최진규 경상국립대학교 대학원 2023 국내박사

The quality of high-frequency heat treatment is determined by various parameters such as input power, heating and cooling time, the shape of coil, and the material of the object to be heated and hardened. Since the 1970s, studies have been conducted using finite element analysis to reduce the loss caused by these parameters. Previous researchers studied high-frequency induction heating and heat treatment for design parameters such as frequency change, shape, radius, and thickness of heated and hardened objects, but did not consider input current during high-frequency heat treatment. This paper proposes a high-frequency heat treatment simulation method using resonance RLC(resistor–inductor-capacitor) circuit and electromagnetic-heat transfer-metal phase transformation. When the specimen was heated at 51.9 kHz and 242 A for 60 seconds, the maximum heating temperature was 364.3℃, and the maximum heating temperature of the high-frequency induction heating simulation applying electrical and heat transfer material properties was 377.5℃. The error rate of the experiment and simulation is 3.6%. The reliability of the high-frequency induction heating simulation was confirmed by comparing and analyzing the high-frequency induction heating measurement temperature and simulation temperature results. A high-frequency heat treatment method was established using electromagnetic-heat transfer-metal phase transformation. High-frequency heat treatment was performed on the AISI 1045 specimen using a 6 kW induction heating power supply. The current value of the coil using a resonant RLC circuit, electromagnetic & heat transfer material properties, and phase transformation functions dependent on temperature are applied to the simulation. In the high-frequency heat treatment experiment, the heating temperature was 797.9℃ and the hardening depth was 0.8 mm, and the reliability was verified by comparing the simulation heating temperature of 813℃ and the predicted hardening depth of 0.8 mm. The error rate of the heating temperature results was 1.9% and the hardening depth results are the same. High-frequency heat treatment experiments and simulation of the park gear of the automobile transmission were performed. During high-frequency heat treatment, the heating temperature and hardening depth were measured. In addition, by applying the resonance RCL circuit, the current value of the coil during high-frequency heat treatment, the electromagnetic and heat transfer material properties dependent on the temperature, and the phase transformation function were applied to the simulation. In the high-frequency heat treatment experiment, the heating temperature was 977.4℃ and the 1st direction hardening depth was 1.5 mm, 2nd direction hardening depth was 3 mm, 3rd direction hardening depth was 2.5 mm, and the reliability was verified by comparing the simulation heating temperature of 1,097℃ and the 1st direction predicted hardening depth of 1.6 mm, 2nd direction predicted hardening depth of 2.8 mm, 3rd direction predicted hardening depth of 2.7 mm. The error rate of the heating temperature results was 12.2% and the hardening depth results are 7.1%. The high-frequency induction heating simulation error rate of the AISI 4140 specimen is 3.6%, the high-frequency heat treatment simulation error rate of the AISI 1045 specimen is 1.6%, and the high-frequency heat treatment simulation error rate of the park gear is 7.1%. Through this, it can be seen that a high-frequency heat treatment simulation method using resonance RLC circuits and electromagnetic-heat transfer-metal phase transformation can be applied to various products.

Conversion Characteristics of Doraji (Platycodon grandiflorum) Saponins by Heat, Pressure, and Organic Acid Treatments

송명섭 충북대학교 2019 국내석사

The objective of this study was to compare conversion characteristics of Doraji saponin through heat treatment, pressure treatment and organic acid treatment. Physiochemical properties were compared between Normal and Etteum Doraji, and saponin conversion characteristics were confirmed according to the treatment method. Carbohydrate contents were higher (87.04%) for Etteum Doraji than Normal Doraji (84.97%). And crude protein, curde fat, crude ash contents of Etteum Doraji were higher than that of Noraml Doraji. Free sugar and organic acid content were not different significantly between Normal and Etteum Doraji. The crude saponin contents of Normal and Etteum Doraji presented 10.63 and 18.74 mg/g respectively, and Etteum Doraji was approximately two time higher than Normal Doraji. β-Glucosidase activities of crude enzyme extracted by Normal and Etteum Doraji were measured at 36.40 and 33.43 unit/mL, respectively, and enzyme-inactivated Doraji were measured at 1.17 and 0.54 unit/mL, respectively. Saponin content of the heat treated Doraji increased up to 60 ℃, and then decreased by increasing temperature. β-Glucosidase activities of crude enzyme extracted by Normal and Etteum Doraji also showed the range of 36.40 ~ 5.85 and 33.43 ~ 4.86 unit/mL according to heat treatment. Platycoside E and platycodin D3 tended to decrease, while platycodin D tended to increase by rising temperature, and total saponin content was decreased rapidly after 100℃. The pressure treated Doraji saponin content increased significantly at 150MPa for 3hr, and the total saponin content tended to increase steadily with increasing treatment time. But platycoside E and platycodin D content was decreased, while platycodin D content was increased with increasing treatment time (3 ~ 24h). The β-glucosidase activity of crude enzyme extracted by Normal and Etteum Doraji also showed the range of 36.40 ~ 83.39 and from 33.43 ~ 81.68 unit/mL according to pressure treatment. Enzyme inactivation so affected the change of saponin with pressure and heat treatment that did not increase in platycodin D. The saponin content of organic acid treated Doraji increased from 7.04 to 7.47 mg/g with citric acid (0.5M), respectively. The content of saponin was decreased tendency with increasing organic acid treatment concentration (0.5 ~ 2 M). The content of saponin was rapidly decreased with increasing organic acid concentration and temperature. Therefore, the cause enhanced saponin contetns of Doraji treated by pressure and heat treatment are postulated that biological factor and enzyme activation play a major factor. This study provides important information on the application of pressure treatment for improving the utilization of Doraji saponin such as platycodin D. 도라지는 사포닌을 비롯하여 약리효능이 우수한 사포닌 뿐만 아니라 진해, 거담 등 기관지 염증에 우수하여 아시아지역에서 주로 섭취한다. 신품종 으뜸도라지는 일반도라지에 비해 사포닌이 2 ~ 3배가량 많고 40% 생산력이 우수하여 1년재배가 가능하다. 따라서 본 연구에서는 열처리, 고압처리, 유기산처리 하여 일반도라지와 으뜸도라지의 이화학적 특성들을 비교하고, 사포닌의 전환특성을 비교하여 기능성 식품 소재로의 적용가능성에 대하여 연구하고자 하였다. 탄수화물 함량은 일반도라지가 높은 함량을 보였다 (87.04%). 조단백질, 조지방, 조회분, 함량은 일반도라지와 으뜸도라지 사이의 차이가 크게 나타나지 않았다. 유리당은 fructose와 sucrose가 검출되었으며, 일반도라지와 으뜸도라지 사이의 차이가 크게 나타나지 않았다. 유기산은 citric acid와 DL-malic acid가 검출되었으며, 일반도라지와 으뜸도라지가 유사하게 나타났다. 조사포닌 함량은 10.63 및 18.74 mg/g으로 나타났으며 일반도라지에 비해 으뜸도라지가 2배가량 높게 측정되었다. β-Glucosidase 활성은 각각 36.40 및 33.43 unit/mL로 측정되었으며, 효소 불활성화된 도라지는 각각 1.17 및 0.54 unit/mL로 측정되었다. 열처리 도라지의 구성사포닌 함량변화는 40℃ 에서 전체 사포닌의 함량이 증가하였으며, 60℃까지 증가하는 경향을 보였으며, 그 이후의 온도에서는 감소하는 경향을 보였다. platycoside E, platycodin D3의 함량이 감소하면서 platycodin D의 함량이 증가하였다. 효소 활성 측정 결과 열처리 온도에 따라 36.40 ~ 5.85 및 33.43 ~ 4.86 unit/mL의 범위로 나타났으며 60℃ 이후에는 감소하는 경향을 나타내어 사포닌 변화와 같은 경향을 보였다. 고압처리 도라지는 3시간에서 전체 사포닌의 함량이 증가하였으며, 그 이후에 총 사포닌 함량은 증가하지만, platycoside E, platycodin D3의 함량이 감소하면서 platycodin D의 함량이 증가하였다. 고압처리에 따른 도라지의 효소활성은 36.40 ~ 83.39 및 33.43 ~ 81.68 unit/mL의 범위로 나타났으며 12시간까지 증가하다가 그 이후에는 활성이 유지되어 고압처리 도라지의 사포닌 변화와 같은 경향을 보였다. 효소 불활성화 도라지는 온도의 증가와 관계없이 일정하다가 100℃ 이상에서 사포닌 함량이 급격히 감소하였다. 유기산처리 도라지의 구성사포닌 함량은 유기산 농도가 증가함에 따라 0.5 M 유기산 처리구 에서 7.04 및 7.47 mg/g으로 증가하였다가 감소하는 경향을 보였다. 열처리와 유기산처리 복합처리한 도라지의 구성사포닌 함량은 유기산 농도와 열처리 온도가 증가함에 따라 감소하는 경향을 보였다. 결과적으로, 열처리와 압력처리 한 도라지의 사포닌이 크게 증가한 이유는 생물학적 요인과 효소 활성이 주요 요인으로 작용한다고 판단된다. 따라서, 열처리와 고압처리시 platycodin D와 같은 도라지 사포닌이 증가하여 가공식품 및 기능성 식품의 소재로도 활용 가능성이 높을 것으로 판단된다.

Enhancing the mechanical properties of Al-Si-Mg and Fe-Cr-Mn-C alloys using L-PBF additive manufacturing

주효문 Graduate School, Yonsei University 2024 국내박사

열처리에 따른 무전해 Ni-P-Al2O3 복합도금층의 특성 연구

마승환 충북대학교 2018 국내박사

Many basic subjects of electroless Ni-P plating, such as the improvement of bath solutions, new alloy deposition, the mechanisms, especially the theory of electroless plating, composite plating and so forth have been studied. Considerable advances in such issues have been made in recent years, especially since the beginning of the new century. Electroless deposition uses the chemical reaction between a reducing agent and a metal salt in a liquid solution so that the metal ion can be reduced to a metal atom on a substrate. Compared with electroplating, electroless plating can be plated uniformly over all surfaces, regardless of size, shape and electrical conductivity. Understanding and enhancement of the unique material properties of electroless Ni–P deposits have become significant, and have broadened the deposits application and role in varied industries, in particular for the use as protective and functional coatings. There is improvement in material properties, such as solderability, wear and corrosion resistances, and magnetic response through plating and heat treatment processing. It is evident that the crystallization and phase transformation behaviour is determined by the alloy compositions and thermal processing conditions, such as phosphorus content, heating rate and processing end temperature. In this study, the heat treatment after electroless Ni-P alloy plating was studied, and physical properties of Ni-P-Al2O3 complexation and heat treatment effect through alumina were confirmed. As a result, the correlation between crystallization and phase transformation behaviour of electroless Ni–P deposits, and those influencing factors, is of importance to the optimised design of specific material properties for targeted applications. However, despite being the subject matter of many previous investigations, there appear to be conflicting results regarding the microstructural and material properties, and crystallization and phase transformation behaviour of electroless Ni–P deposits, under those mentioned influencing factors. These variations are likely caused by many other related factors, such as heat treatment condition and testing and measuring techniques. The surface morphology of the electroless Ni-P alloy plating before heat treatment was nodular, and it was confirmed that the nodular structure gradually became coarse when annealed at 200 to 600 ℃. In addition, there was no variation in the plating thickness up to 600 ℃ during the heat treatment, but the plating thickness decreased sharply at 800 ℃. For this reason, it was confirmed that internal stress and peeling occurred due to high temperature during heat treatment. XRD and TEM were used to examine the effects of different heat treatment condition on the crystallization behavior of Ni-P plating. A single heat treatment of the Ni-P at 600 ℃/hr yielded Ni, Ni3P and more complex crystalline Ni-P compounds in the formation. It was confirmed that the electroless Ni-P alloy plating was excellent in the corrosion resistance as an amorphous structure and it was confirmed that the precipitation of Ni3P upon heat treatment affects not only the hardness but also the corrosion resistance improvement. Plating with nickel alloyed with other materials such as phosphorus and aluminum oxide results in improvement of wear resistance, which is proved through many experiments. By comparing with nickel only plating and analyzing improvement of abrasion resistance, we can check compatibility of Ni-P-Al2O3 composite plating to more various industries. Ni-P-Al2O3 composite showed a higher hardness than the existing Ni-P plated film. Especially, the rapid increase of hardness after heat treatment is due to the amorphous Ni-P plated layer showing a mixed crystal mixed with Al2O3 after heat treatment at 600 ℃. That is, alumina composite plating can increase the hardness and abrasion resistance significantly, but it is confirmed that the corrosion resistance is lowered. 금속 표면처리 기술은 제품의 소재표면에 화학적·전기 화학적인 방법으로 처리하여 대상제품에 대하여 내구성 및 기능성을 향상시키거나 새로운 특성을 부여하는 기술로 제조 산업에 있어 하나의 독립적인 분야로 자동차, 전기·전자부품, 환경·에너지 산업에 전반적으로 중요한 역할을 하고 있다.[1] 무전해 도금은 도금액에 존재하는 금속이온을 전기적인 방법이 아닌 환원 방식으로 피도금인 소재에 환원 석출시켜 소재에 도금피막을 형성시키는 화학도금으로써 A. Brenner와 G. E. Riddell가 특허를 출원하였으며, 현재 공업적 도금방법으로써 그 적용범위도 확대되어, 널리 적용되고 있는 표면처리 기술 중 하나이다.[2] 일반적인 전기도금은 피도금물의 외형 및 양극과의 거리에 따라 피막두께가 차이가 있으며, 이러한 두께편차는 피막특성에 악영향을 줄 수 있어 균일한 전착두께 및 기계적인 특성인 경도와 내마모성 등의 향상을 목적으로 무전해 도금이 적용되어지고 있다.[3] 무전해 도금은 용매 속에 금속염과 환원제가 같이 포함되어 있는 형태로 낮은 설비비용, 단순한 공정으로 도금액에 침지하는 것으로 복잡한 형상의 피도금물을 균일한 두께의 피막을 얻을 수 있을 뿐만 아니라 피도금물의 전도성, 비전도성 등을 불문하고 도금할 수 있는 이점이 있어 그 적용 영역이 산업 분야에 널리 적용되고 있다.[4] 그 밖에 도금액의 종류 및 도금조건에 따라 원하는 도금피막의 특성을 얻을 수 있기 때문에 여러 가지 기능성 도금피막이 가능하다.[5] 특히 무전해 도금 중 가장 많이 적용되고 있는 Ni-P 합금도금은 1844년 Wart에 의해서 발견되어 복잡한 형상의 피도금물의 홈이나 관 내부까지도 균일한 두께를 얻을 수 있다. 또한 Phosphorus(P)의 함량에 따라 비정질 구조를 나타내는데 Ni-P 합금도금 후 400 ℃에서 열처리 시 도금피막이 결정화되어 기계적인 특성인 내식성, 내마모성, 평활성 및 납땜성 등이 우수한 피막을 얻을 수 있다.[4] 최근에는 기계적인 특성인 내식성, 내마모성 및 내열성 등의 산업분야 요구로 인하여 무전해 Ni-P에 비해 더 향상된 물성을 가지는 복합도금에 대한 연구가 진행되고 있다.[5-8] 무전해 복합도금은 무전해 도금액에 10 ㎛ 이하의 분산입자인 SiC, Al2O3, Diamond, WC, TiN, PTFE, C 등을 분산시켜 Ni이 도금 될 때 부유하는 미립자가 도금 층에 분산되어 복합 도금층을 이루게 된다. 즉, 석출금속에 따라 입자가 매립되어 생성되는 것으로 공석된 입자는 금속 매트릭스(matrix)에 불규칙적으로 분포된 분산상의 복합도금(composite plating)이 형성되어 도금피막의 내마모성 윤활성, 내열성 및 내식성 등의 향상을 목적으로 한다.[6] 탄화규소, 인, 산화알루미늄 주석과 같은 다른 재료와의 합금을 통한 니켈 도금은 경도 및 내마모성 향상을 일으키며 이는 여러 실험을 통해 밝혀졌다. 니켈합금도금의 경도 및 내마모성 향상을 분석하고 이를 토대로 더 다양한 산업에의 적합성을 확인할 수 있을 것이다.[9] Ni-P 합금도금 및 Ni-P-additive의 복합도금은 다양한 기능적 특성이 있음에도 불구하고 무전해 Ni-P 합금도금에 대한 결정화 메커니즘과 무전해 복합도금의 강화 메커니즘에 대한 연구는 미비한 실정이며 명확한 규명이 되지 않고 있어, 지속적인 연구가 요구되는 실정이다.[7-8] 따라서 본 연구는 황산니켈염과 차아인산나트륨을 환원제로 하는 조성에 착화제 및 완충제 역할을 하는 아세트산나트륨을 첨가하여 무전해 Ni-P 합금 도금 수행 후 열처리를 통해 Ni-P 도금층 결정화, 경도 및 내식성, 내마모성 등의 물리적 특성을 평가하고자 하였다. 이후 최적의 열처리 조건을 토대로 도금액과의 반응성이 낮은 Alumina(Al2O3)를 이용하여 Ni-P-Al2O3 복합도금을 제조한 후 Al2O3 첨가량에 따른 표면형상 및 물리적 특성인 경도, 내식성 및 내마모성을 평가하고자 한다.

구리 및 구리합금의 내식성에 미치는 어닐링 열처리의 영향

이진규 한국해양대학교 대학원 2006 국내박사

Copper is a well known alloying element that is used to improve the resistance to general corrosion of stainless steel as well as copper alloy. And Cu cation have the anti-fouling effect to inhibit adhesion of marine algae and shellfish to the surface of heat exchanger cooling pipe or outside wall of the ship. Therefore there are some anti-fouling methods using the copper such as anti-fouling paint mixed with copper oxide or MGPS(Marine Growth Preventing System) by using Cu cation dissolved to the sea water solution. However, although a copper have the anti-fouling effect, it cannot be avoided that copper and copper alloy materials were inevitably corroded in sea water solution with dissolved oxygen or chloride ion when a heat exchanger was constructed with copper and copper alloy for anti-fouling. Therefore in order to get the synergic effect of the anti-fouling as well as corrosion resistance it is necessary to improve corrosion resistance of copper and copper alloy by some optimum methods. In this study, the annealing heat treatment to promote the corrosion resistance in sea water solution was investigated with a electrochemical point of view. Annealing heat treatment was carried out with parameters of heating temperature such as 100℃, 200℃, 700℃, 800℃, 900℃ and 1000℃ for 1 hr. The corrosion resistance was evaluated with electrochemical methods such as variation of corrosion potential, anodic and cathodic polarization curves, cyclic voltammogram, AC impedance, SEM photograph and vickers hardness measurement etc. Chapter 3.1 shows the effect of annealing heat treatment to the corrosion resistance of pure copper. The grain size of the surface at 700℃ annealing temperature was the smallest than that of other annealing temperatures, and the corrosion potential showed more positive potential than that of other annealing temperatures. The galvanic current between Ti and Cu with annealing temperature at 700℃ was the largest value in case of non-flow condition, however in case of flow condition its value was the smallest than that of the other temperatures. Therefore in order to increase anti-fouling effect by Cu cation, in non-flow condition of sea water, the optimum annealing temperature was 700℃ for one hour, however in case of flow condition non heat treatment might be desirable. In chapter 3.2, the corrosion resistance with annealing heat treatment was investigated about Cu-10%Ni alloy. Vickers hardness value was decreased with increasing of heating temperature. However corrosion resistance showed the increasing tendency with increasing of heating temperature. Especially it was shown that corrosion resistance was clearly promoted by annealing temperature at 1000℃ more than other temperatures. Annealing temperature at 200℃, vickers hardness increased than other temperatures and corrosion resistance was slightly improved compared to the no heat treatment. So in case of considering the mechanical property as well as corrosion resistance, it is considered that the desirable heating temperature may be 200℃ . Chapter 3.3 was examined about Cu-30%Ni alloy in sea water solution with a electrochemical point of view. Vickers hardness was decreased with increasing heating temperature the same as Cu-10%Ni alloy. However in annealing temperature at 200℃, vickers hardness contrary increased than both no heat treatment and other heating temperature. The improvement of corrosion resistance was also observed with annealing heat treatment the same as Cu-10%Ni alloy. Especially in case of Cu-30%Ni alloy, corrosion resistance was apparently improved in annealing heat treatment at 1000℃. Thus to improve the corrosion resistances in sea water as well as anti-fouling effect, the annealing heat treatment may be important for Cu-30%Ni alloy . Eventually, it is necessary to perform the annealing heat treatment for corrosion resistance improvement of Cu-Ni alloy material which is being used as a heat exchanger having the anti-fouling effect.

Effect of time on nutraceuticals and antioxidant properties in high temperature and high pressure treated Lonicera japonica Thunb

이준구 경희대학교 대학원 2018 국내석사

The major objectives of the present study were to evaluate the effect of time on nutraceuticals (total phenolic, total flavonoid, chlorogenic acid, caffeic acid, 4,5-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid, rutin, quercetin, and luteolin) and antioxidant properties (DPPH radical scavenging activity, ABTS radical scavenging activity, FRAP value, and reducing power) in high temperature and high pressure treated Lonicera japonica Thunb. (LJ). In the first part of this study, heat treatments were applied to LJ at 100°C for different heating time (30, 60, 90, 120, and 150 min). Based on the results of total phenolic and total flavonoid content, LJ heated for 60 min had the highest contents of total phenolic (2594.18 ug GAE/100 mg) and total flavonoid (5644.10 ug RE/100 mg). The anaylsis of LJ by RP-HPLC revealed that chlorogenic acid, belonged to phenolic acids, was the major compound. The chlogenic acid content in the control was 1006.51 ug/100 mg, and increased about 35.9% after heat treatment for 60 min. The other phenolic acids (caffeic acid, 4,5-dicaffeoylquinic acid, and 3,5-dicaffeoylquinic acid), and flavonoids (rutin, quercetin, and luteolin) also significantly increased after heat treatments, but optimal heating time was different for respective compounds. In the anaylsis of individual organic acids, quinic acid and shikimic acid contents were significantly elevated with increasing heating time from 30 to 150 min. For antioxidant properties, DPPH radical scavenging activity, ABTS radical scavenging activity, FRAP value, and reducing power of LJ were assesed, and all of these results showed that 60 min of heating time was enough to improve antioxidant properties of LJ. According to Pearson correlation, total phenolic, total flavonoid, chlorogenic acid, caffeic acid, and quercetin contents were positively correlated with antioxidant properties of LJ. In the second part of the present study, high pressure treatments were subjected to LJ at 400 MPa for different pressure time (1, 5, 10, 20, and 40 min). Chlorophyll a, b, and total chlorophyll contents in LJ (4.52, 2.36, and 6.85 ug/g, respectively) were significantly increased after high pressure treatment, and maximum contents of those compounds (6.87, 3.63, and 10.34 ug/g) were observed after 1 min of pressure time. In the analysis of color values, the net color difference (△E) of LJ samples treated for 1-40 min were under 1.82, indicating that high pressure treatment did not affect the original color of LJ. Total phenolic (2142.56-2203.94 ug GAE/100 mg) and total flavonoid contents (4692.71-5206.60 ug RE/100 mg) in all of the pressure-treated LJ samples were significantly higher than those of the control (2013.08 ug GAE/100 mg and 4494.79 ug RE/100 mg, respectively). In the RP-HPLC analysis, after high pressure treatments for 1-40 min, the chlorogenic acid contents in LJ were in the range of 1145.11-1244.60 ug/100 mg, and were significantly higher than those of the control (1006.51 ug/100 mg). The other individual phenolic acids (caffeic acid, 4,5-dicaffeoylquinic acid, and 3,5-dicaffeoylquinic acid) and flavonoids (rutin, quercetin and luteolin) in LJ also significantly increased after high pressure treatments. In particular, the maximum contents of individual phenolic acids and flavonoids were observed in LJ treatead for 5 min, except for quercetin. The analysis of antioxidant properties (DPPH radical scavenging activity, ABTS radical scavenging activity, FRAP value, and reducing power) of LJ revealed that they can be significantly increased by high pressure treatment regardless of pressure time. In conclusion, based on the results obtained from the present study, heat treatment and high pressure treatment can be used in the food industry to improve the contents of nutraceuticals and antioxidant properties of LJ. In particular, high pressure treatment is highly efficient technology because it can elevate antioxdant properties of LJ in short time.

T5 열처리에 따른 차압주조된 A356 합금의 미세조직과 기계적 성질

김상원 전북대학교 일반대학원 2019 국내석사

Recently, the consumption of aluminum alloys for weight reduction of automobile has been increased in order to improve fuel efficiency and to meet environmental regulations. Specifically, A356 alloy, one of the Al-Si-Mg casting alloys, has been widely used for automobile parts due to high strength and corrosion resistance, and excellent deformability. Mass productions of A356 automobile parts are based on various casting processes such as gravity die casting, low pressure die casting, and counter pressure die casting. Especially, counter pressure die casting process pressurizes both the lower chamber containing molten aluminum and the upper chamber with metal molds so as to fill the mold under higher pressure than atmospheric pressure, resulting refinement of solidified microstructure, prevention of shrinkage defects, enhancement of mechanical properties. Meanwhile, A356 alloy castings are generally followed by heat treatment process in order to improve mechanical properties. Most widely used heat treatment process for A356 alloy is so-called T6 heat treatment process which consists of solution heat treatment and subsequent artificial aging treatment. The optimal conditions for T6 heat treatment of A356 alloy have been extensively investigated experimentally but the results are limited to the gravity or low pressure die cast. If the aluminum cast has finer microstructure than those conventional casting methods (such as counter pressure casts), the optimal heat treatment condition for those cast should be determined either by experimental verification of the reported one from literatures or by new investigation with a series of heat treatment experiments. When it comes to the optimization issue of heat treatment condition, it is the typical method to conduct a number of heat treatment experiments at different time and temperature conditions, followed by microstructure observation and mechanical test. This experimental approach, however, is time-consuming and expensive routines. Therefore, it is efficient to utilize numerical simulation techniques including yield strength modeling based on precipitation kinetics, and statistical approaches based on machine learning for optimization of heat treatment process. In the present study, experimental investigations on microstructure and mechanical property of conter pressure cast A356 aluminum alloy under T5 (artificial aging only after casting) were conducted with a number of heat treatments under the temperature range of 160 to 200°C for 6 to 9 hours. Also, a yield strength model was developed based on the precipitation kinetics of which is experimentally confirmed in the present study and the optimal T5 heat condition was determined from the model calculations.

열처리를 통한 Ti-6Al-4V 주조재 합금의 기계적 성질 개선

오성탁 전북대학교 일반대학원 2016 국내석사

Titanium alloys have been used in a number of parts as not only aerospace components but also marine and biomedical applications due to lightweight, high specific strength, and corrosion resistance. Particularly, Ti-6wt%Al-4wt%V alloy which is one of α+β titanium alloys has been utilized in the various applications due to its excellent combination of strength and ductility. In addition, Ti-6Al-4V alloy is heat-treatable to develop a variety of microstructure and mechanical property combinations. Thus, in wrought Ti-6Al-4V alloy, the improvement of their mechanical properties by a heat treatment has been studied for a long time. However, in cast Ti-6Al-4V alloy, it is still required to study on heat treatment process and strengthening mechanism to derive the increased strength and ductility of cast Ti-6Al-4V alloy. From the above viewpoint, in this study, the microstructure refinement which is one of the strengthening mechanisms is applied to improve the mechanical properties by the heat treatment on cast Ti-6Al-4V alloy. Additionally, the effect of the heat-treatment condition and stabilizer partitioning (Al,V) on the microstructure control and phase transformation of the β phase was investigated. Moreover, the further strengthening mechanism was investigated to obtain the improvement of the strength and ductility. The precipitation strengthening by α2 (Ti3Al) precipitates is well known in Ti-6Al-4V alloy to improve the further mechanical properties. However, it needs a long time to precipitate the α2 phase. To overcome this disadvantage, the short-time aging treatment was performed after the solution treatment in present study. With the relatively short aging time, the further strengthening mechanism of the retained β phase on microstructure and mechanical properties was investigated. From the results in present study, the microstructure of cast Ti-6Al-4V alloy was greatly refined through the solution and subsequent aging treatments due to α and β phases decomposed from α' martensite. As well as, the microstructure control was determined by the prior solution treatment. The solution heat-treated microstructure and phase transformation of the β phase was strongly dependent on the concentration of vanadium in the β phase in cast Ti-6Al-4V alloy. Furthermore, although the short-aging treatment for 5 minutes was conducted, its combination of tensile strength and elongation was further improved, relatively compared to that of aged specimen for 1440 minutes. Its effects and reasons were discussed in present study.