The aim of this review is to communicate some essential knowledge of the underlying mechanism of the corrosion of structural containment alloys during molten salt reactor operation in the context of prospective online monitoring in future MSR installations. The formation of metal halide species and the progression of their concentration in the molten salt do reflect containment corrosion, tracing the depletion of alloying metals at the alloy salt interface will assure safe conditions during reactor operation. Even though the progress of alloying metal halides concentrations in the molten salt do strongly understate actual corrosion rates, their prospective 1st order kinetics followed by near-linearly increase is attributed to homogeneous matrix corrosion. The service life of the structural containment alloy is derived from homogeneous matrix corrosion and near-surface void formation but less so from intergranular cracking (IGC) and pitting corrosion. Online monitoring of corrosion species is of particular interest for molten chloride systems since besides the expected formation of chromium chloride species CrCl2 and CrCl3, other metal chloride species such as FeCl2, FeCl3, MoCl2, MnCl2 and NiCl2 will form, depending on the selected structural alloy. The metal chloride concentrations should follow, after an incubation period of about 10,000 hours, a linear projection with a positive slope and a steady increase of < 1 ppm per day. During the incubation period, metal concentration show 1st order kinetics and increasing linearly with time1/2. Ideally, a linear increase reflects homogeneous matrix corrosion, while a sharp increase in the metal chloride concentration could set a warning flag for potential material failure within the projected service life, e.g. as result of intergranular cracking or pitting corrosion. Continuous monitoring of metal chloride concentrations can therefore provide direct information about the mechanism of the ongoing corrosion scenario and offer valuable information for a timely warning of prospective material failure.

To improve the shortcomings and expand the advantages of the single-roll melt drag method, which is a type of continuous strip casting method, the melt drag method with a molding belt is applied to AZ31 magnesium alloy. By attaching the forming belt to the melt drag method, the cooling condition of the thin plate is improved, making it possible to manufacture thin plates even at high roll speed of 100 m/min or more. In addition, it is very effective for continuous production of thin plates to suppress oxidation of the molten metal on the roll contact surface by selecting the protective gas. As a result of investigating the relationship between the contact time between the molten metal and the roll and the thickness of the sheet, it is possible to estimate the thickness of the sheet from the experimental conditions. The relationship between the thin plate thickness and the grain size is one in which the thinner the thin plate is, the faster the cooling rate of the thin plate is, resulting in finer grain size. The contact state between the molten metal and the roll greatly affects the grain size, and the minimum average grain size is 72 μm. The thin plate produced using this experimental equipment can be rolled, and the rolled sample has no large cracks. The tensile test results show a tensile strength of 303 MPa.

High-strength low-alloy (HSLA) steels show excellent toughness when trace amounts of transition elements are added. In steels, prior austenite grain size (PAGS), which is often determined by the number of added elements, is a critical factor in determining the mechanical properties of the material. In this study, we used two etching methods to measure and compare the PAGS of specimens with bainitic HSLA steels having different Nb contents These two methods were nital etching and picric acid etching. Both methods confirmed that the sample with high Nb content exhibited smaller PAGS than its low Nb counterpart because of Nb’s ability to hinder austenite recrystallization at high temperatures. Although both etching approaches are beneficial to PAGS estimation, the picric acid etching method has the advantage of enabling observation of the interface containing Nb precipitate. By contrast, the nital etching method has the advantage of a very short etching time (5 s) in determining the PAGS, with the picric acid etching method being considerably longer (5 h).

We investigate the effect of phosphorous content on the microstructure and magnetic properties of Fe83.2Si5.33-0.33xB10.67-0.67xPxCu0.8 (x = 1–4 at.%) nanocrystalline soft magnetic alloys. The simultaneous addition of Cu and P to nanocrystalline alloys reportedly decreases the nanocrystalline size significantly, to 10–20 nm. In the P-containing nanocrystalline alloy, P atoms are distributed in an amorphous residual matrix, which suppresses grain growth, increases permeability, and decreases coercivity. In this study, nanocrystalline ribbons with a composition of Fe83.2Si5.33-0.33xB10.67- 0.67xPxCu0.8 (x = 1–4 at.%) are fabricated by rapid quenching melt-spinning and thermal annealing. It is demonstrated that the addition of a small amount of P to the alloy improves the glass-forming ability and increases the resistance to undesirable Fex(B,P) crystallization. Among the alloys investigated in this work, an Fe83.2Si5B10P1Cu0.8 nanocrystalline ribbon annealed at 460oC exhibits excellent soft-magnetic properties including low coercivity, low core loss, and high saturation magnetization. The uniform nanocrystallization of the Fe83.2Si5B10P1Cu0.8 alloy is confirmed by high-resolution transmission electron microscopy analysis.

In this study, AlSi10Mg powders with average diameters of 44 μm are additively manufactured into bulk samples using a selective laser melting (SLM) process. Post-heat treatment to reduce residual stress in the as-synthesized sample is performed at different temperatures. From the results of a tensile test, as the heat-treatment temperature increases from 270 to 320oC, strength decreases while elongation significantly increases up to 13% at 320oC. The microstructures and tensile properties of the two heat-treated samples at 290 and 320oC, respectively, are characterized and compared to those of the as-synthesized samples. Interestingly, the Si-rich phases that network in the as-synthesized state are discontinuously separated, and the size of the particle-shaped Si phases becomes large and spherical as the heat-treatment temperature increases. Due to these morphological changes of Si-rich phases, the reduction in tensile strengths and increase in elongations, respectively, can be obtained by the post-heat treatment process. These results provide fundamental information for the practical applications of AlSi10Mg parts fabricated by SLM.

Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/ Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 oC, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

Ti-based alloys are widely used in biomaterials owing to their excellent biocompatibility. In this study, Ti- Mn-Cu alloys are prepared by high-energy ball milling, magnetic pulsed compaction, and pressureless sintering. The microstructure and microhardness of the Ti-Mn-Cu alloys with variation of the Cu addition and compaction pressure are analyzed. The correlation between the composition, compaction pressure, and density is investigated by measuring the green density and sintered density for samples with different compositions, subjected to various compaction pressures. For all compositions, it is confirmed that the green density increases proportionally as the compaction pressure increases, but the sintered density decreases owing to gas formation from the pyrolysis of TiH2 powders and reduction of oxides on the surface of the starting powders during the sintering process. In addition, an increase in the amount of Cu addition changes the volume fractions of the α-Ti and β-Ti phases, and the microstructure of the alloys with different compositions also changes. It is demonstrated that these changes in the phase volume fraction and microstructure are closely related to the mechanical properties of the Ti-Mn-Cu alloys.

Iron and copper are practically immiscible in the equilibrium state, even though their atomic radii are similar. As non-equilibrium solid solutions, the metastable Fe-Cu alloys can be synthesized using special methods, such as rapid quenching, vapor deposition, sputtering, ion-beam mixing, and mechanical alloying. The complexity of these methods (multiple steps, low productivity, high cost, and non-eco-friendliness) is a hinderance for their industrial applications. Electrical explosion of wire (EEW) is a well-known and effective method for the synthesis of metallic and alloy nanoparticles, and fabrication using the EEW is a simple and economic process. Therefore, it can be potentially employed to circumvent this problem. In this work, we propose the synthesis of Fe-Cu nanoparticles using EEW in a suitable solution. The powder shape, size distribution, and alloying state are analyzed and discussed according to the conditions of the EEW.

The electronic structure and magnetic properties of chalcopyrite (CH) AlGaAs2 with dopant Mn at 3.125 and 6.25 % concentrations are investigated using first-principles calculations. The CH AlGaAs2 alloy is a p-type semiconductor with a small band-gap. The AlGaAs2:Mn shows that the ferromagnetic (FM) state is the most energetically favorable one. The Mn-doped AlGaAs2 exhibits FM and strong half-metallic ground states.The spin polarized Al(Ga,Mn)As2 state (Al-rich system) is more stable than the (Al,Mn)GaAs2 state (Ga-rich system), which has a magnetic moment of 3.82mB/Mn. The interaction between Mn-3d and As-4p states at the Fermi level dominates the other states.The states at the Fermi level are mainlyAs-4p electrons, which mediate strong interaction between the Mn-3d and As-4p states. It is noticeable that the FM ordering of dopant Mn with high magnetic moment originates from the As(4p)-Mn(3d)-As(4p) hybridization, which is attributed to the partially unfilled As-4pbands. The high FM moment of Mn is due to the double-exchange mechanism mediated by valence-band holes.

Predicting the quality of materials after they are subjected to plasma sintering is a challenging task because of the non-linear relationships between the process variables and mechanical properties. Furthermore, the variables governing the sintering process affect the microstructure and the mechanical properties of the final product. Therefore, an artificial neural network modeling was carried out to correlate the parameters of the spark plasma sintering process with the densification and hardness values of Ti-6Al-4V alloys dispersed with nano-sized TiN particles. The relative density (%), effective density (g/cm3), and hardness (HV) were estimated as functions of sintering temperature (oC), time (min), and composition (change in % TiN). A total of 20 datasets were collected from the open literature to develop the model. The high-level accuracy in model predictions (>80%) discloses the complex relationships among the sintering process variables, product quality, and mechanical performance. Further, the effect of sintering temperature, time, and TiN percentage on the density and hardness values were quantitatively estimated with the help of the developed model.

본 논문에서는 해양플랜트에 주로 사용되는 알루미늄 사다리의 독자 모델을 개발하기 위하여, 개량형 알루미늄 합금(6082-T6) 을 적용하고 국제 기준에 부합한 구조강도 설계를 하였다. 국제기준은 ISO, NORSOK, Austria Standard를 참고하였으며, 모든 조건이 만족할 수 있도록 하중 조합을 하였다. 설계된 모델은 유한요소법 [Finite elements method]을 근간으로 하는 해양플랜트 전용 해석프로그램인 SACS를 사용하여 구조 안전성을 검증하여 응력 및 처짐이 모두 허용기준 이내에 만족함을 확인하였다. 개발모델은 모든 허용기준을 만족하면서도 가볍고, 생산성이 향상되어 향후 많은 분야에서 사용이 될 것으로 기대해본다.

The purpose of this study is to investigate the densification behavior and the corresponding microstructural evolution of tantalum and tantalum-tungsten alloy powders for explosively formed liners. The inherent inhomogeneous microstructures of tantalum manufactured by an ingot metallurgy might degrade the capability of the warhead. Therefore, to overcome such drawbacks, powder metallurgy was incorporated into the near-net shape process in this study. Spark plasma-sintered tantalum and its alloys with finer particle sizes exhibited higher densities and lower grain sizes. However, they were contaminated from the graphite mold during sintering. Higher compaction pressures in die and isostatic compaction techniques also enhanced the sinterability of the tantalum powders; however, a full densification could not be achieved. On the other hand, the powders exhibited full densification after being subjected to hot isostatic pressing over two times. Consequently, it was found that the hot isostatic-pressed tantalum might exhibit a lower grain size and a higher density as compared to those obtained in previous studies.

We propose a novel stripping solution containing acids (HCl and HNO3), an oxidant [(NH4)2S2O8], and complexing agents (NaCl and citric acid) to remove surface passivation layers from 14K gold alloys fabricated using an investment casting process. The optimized solution employing only HCl acid is determined by varying molar fractions of HCl and HNO3 on 14K yellow gold samples. Stripping properties are also identified for red and white gold alloy samples under the optimized stripping conditions. The removal of passivation layers, weight loss, and microstructure evolution are characterized using Raman spectroscopy, a precision scale, and optical microscopy. The proposed stripping solution effectively removes passivation layers more rapidly than conventional cyanide stripping. Weight loss increases linearly for up to 5 min for all 14K gold alloys. Red gold exhibits the greatest weight loss, followed by yellow gold and white gold. The results of microstructural analysis reveal that the conformal stripping occurs according to time. These results imply that the proposed oxidative chloride stripping might replace conventional cyanide stripping.

This study has related to lightweight automobiles due to global warming with the reduction of fossil fuel reserves are rapidly progressing around the automobile industry. This study has revealed the relationship for the mechanical properties via the analyzed microstructure, precipitated phase variation of the wheel hub of a commercial vehicle manufactured using molten forging technology using A356 and A357 alloys, which are high-strength Al-Si-Mg base cast aluminum alloys. Differential scanning calorimetry has performed to analyze the precipitation amount of each alloy that influences the mechanical properties of aluminum alloy. The XRD analysis has measured for the microstructure's crystal phase on A356 and A357 alloys. In this paper has evaluated to compare the properties of the A356 alloy and the A357 alloy for the mechanical properties. The A356 alloy has confirmed that a microstructure is finer than A357 alloy, and a quantity of precipitated material is more than A357 alloy. Therefore, this study confirmed that the A356 alloy has better mechanical properties than the A357 alloy.

The composition of martensite transformation in NiAl alloy is determined using pure nickel and aluminum powder by vacuum hot press powder metallurgy, which is a composition of martensitic transformation, and the characteristics of martensitic transformation and microstructure of sintered NiAl alloys are investigated. The produced sintered alloys are presintered and hot pressed in vacuum; after homogenizing heat treatment at 1,273 K for 86.4 ks, they are water-cooled to produce NiAl sintered alloys having relative density of 99 % or more. As a result of observations of the microstructure of the sintered NiAl alloy specimens quenched in ice water after homogenization treatment at 1,273 K, it is found that specimens of all compositions consisted of two phases and voids. In addition, it is found that martensite transformation did not occur because surface fluctuation shapes did not appear inside the crystal grains with quenching at 1,273 K. As a result of examining the relationship between the density and composition after martensitic transformation of the sintered alloys, the density after transformation is found to have increased by about 1 % compared to before the transformation. As a result of examining the relationship between the hardness (Hv) at room temperature and the composition of the matrix phase and the martensite phase, the hardness of the martensite phase is found to be smaller than that of the matrix phase. As a result of examining the relationship between the temperature at which the shape recovery is completed by heating and the composition, the shape recovery temperature is found to decrease almost linearly as the Al concentration increases, and the gradient is about -160 K/ at% Al. After quenching the sintered NiAl alloys of the 37 at%Al into martensite, specimens fractured by three-point bending at room temperature are observed by SEM and, as a result, some grain boundary fractures are observed on the fracture surface, and mainly intergranular cleavage fractures.

Aluminum (Al) - based powders have attracted attention as key materials for 3D printing because of their excellent specific mechanical strength, formability, and durability. Although many studies on the fabrication of 3Dprinted Al-based alloys have been reported, the influence of the size of raw powder materials on the bulk samples processed by selective laser melting (SLM) has not been fully investigated. In this study, AlSi10Mg powders of 65 μm in average particle size, prepared by a gas atomizing process, are additively manufactured by using an SLM process. AlSi10Mg powders of 45 μm average size are also fabricated into bulk samples in order to compare their properties. The processing parameters of laser power and scan speed are optimized to achieve densified AlSi10Mg alloys. The Vickers hardness value of the bulk sample prepared from 45 μm-sized powders is somewhat higher than that of the 65 μm-sized powder. Such differences in hardness are analyzed because the reduction in melt pool size stems from the rapid melting and solidification of small powders, compared to those of coarse powders, during the SLM process. These results show that the size of the powder should be considered in order to achieve optimization of the SLM process.

우리나라는 지진에 대해 비교적 안전한 지역으로 인식되고 있었으나, 최근 경주지진과 포항지진이 발생하면서 시설물에 상당한 피해가 발생되면서 지진피해 저감장치를 적용한 내진설계 및 보강에 대한 연구와 개발이 수행되고 있다. 이미 건축된 구조물의 유지⋅보수에 대한 관심이 높아짐에 따라, 구조물의 감쇠, 강성 등을 국부적으로 변화시켜 지진 하중에 의한 에너지를 흡수하고 소산시키는 내진설계 방식인 제진기술이 활용되고 있다. 그러나 강한 지진이 발생할 때 제진 장치의 손상으로 인하여 사용성이 매우 떨어지게 되는 문제점이 발생되고 있다. 최근에는 이러한 문제를 해결하기 위해, 구조물의 가새 부재에 별도의 열처리를 하지 않고 응력 제거만으로 원형복원이 가능한 초탄성 형상기억합금을 적용하는 연구가 진행되고 있다. 따라서 본 연구에서는 비좌굴 가새 부재에 초탄성 형상기억합금을 사용하여 자동복원이 가능한 프레임 구조물을 구성하여 비선형 정적해석을 수행하여 구조물의 내진성능을 평가하고, 초탄성 형상기억합금의 재료적 특성의 우수성을 검증하고자 한다.

High-entropy alloys (HEAs) are generally defined as solid solutions containing at least 5 constituent elements with concentrations between 5 and 35 atomic percent without the formation of intermetallic compounds. Currently, HEAs receive great attention as promising candidate materials for extreme environments due to their potentially desirable properties that result from their unique structural properties. In this review paper, we aim to introduce HEAs and explain their properties and related research by classifying them into three main categories, namely, mechanical properties, thermal properties, and electrochemical properties. Due to the high demand for structural materials in extreme environments, the mechanical properties of HEAs including strength, hardness, ductility, fatigue, and wear resistance are mainly described. Thermal and electrochemical properties, essential for the application of these alloys as structural materials, are also described.

In order to analyze the effect of hot asymmetric rolling on the microstructure and texture of aluminum alloy and to investigate the effect of the texture on the formability and plastic anisotropy of aluminum alloy, aluminum 6061 alloy is asymmetrically rolled at room temperature, 200 ℃, 350 ℃, and 500 ℃, and the results are compared with symmetrically rolled results. In the case of asymmetric rolling, the equivalent strain (εeq) is greatest in the upper roll part where the rotational speed of the roll is high and increases with increasing rolling temperature. The increase rate of the mean misorientation angle with increasing temperature is larger than that during symmetrical rolling, and dynamic recrystallization occurs the most when asymmetrical rolling is performed at 500 ℃. In the case of hot symmetric rolling, the {001}<110> rotated cube orientation mainly develops, but in the case of hot asymmetric rolling, the {111}<110> orientation develops along with the {001}<100> cube orientation. The hot asymmetric rolling improves the formability (r) of the aluminum 6061 alloy to 0.9 and reduces the plastic anisotropy (Δr) to near zero due to the {111}<110> shear orientation that develops by asymmetric rolling.