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Ferritic stainless steel has been applied frequently owing to its advantages such as good thermal conductivity, low coefficient of linear expansion, good stress corrosion resistance, and no Ni. However, the welding process will cause the grain size of the weld zone and the heat-affected zone to grow seriously, resulting in a decrease in the toughness of the welded joint. The paper discusses in detail the traditional and improved welding methods of ferritic stainless steel. These improved methods can effectively reduce the grain size or increase the penetration. The process of introducing electric and magnetic pulses can compress the arc, increase the weld penetration, stir the molten pool, refine the grains, and improve the strength and toughness of the weld. The future development direction of ferritic stainless steel welding is discussed at the end of the article.

Since carbon dots (CDs) exhibit excellent biocompatibility, low cytotoxicity, near-infrared (NIR) absorbance, and superior photostability, many types of CDs are considered as powerful candidates for photothermal therapy (PTT) applications. However, the development of a desirable CD is still difficult due to insufficient photothermal conversion, thus resulting in the use of high laser power densities at a high dose of CDs for the PTT effect. Herein, bioinspired sulfur-doped CDs (S-CDs) with strong NIR absorbance were prepared from Camellia japonica flowers via a facile hydrothermal method for enhancing the photothermal conversion efficiency. The as-prepared S-CDs exhibited various advantages including cost-effective preparation, good water-solubility, high biocompatibility, intense NIR absorption, and excellent photothermal effect with robust photostability. Most importantly, the optimal low dose of S-CDs (45 μg mL−1) successfully led to efficient PTT performance with a high photothermal conversion efficiency (55.4%) under moderate laser power (808 nm, 1.1 W cm−2) for safe and effective cancer therapy.

The effect of high-frequency axial magnetic field (HFAMF) on the shape of the welding arc and welding formation of tungsten inert gas (TIG) welding is analyzed theoretically and experimentally. The 316L stainless steel plate was welded with HFAMF produced by the excitation coil installed on the welding torch. The influence of the HFAMF on the welding process is studied by changing the magnetic frequency from 0 to 2000 Hz. The experimental results show that when the magnetic field frequency reaches 1500 Hz, the arc rotation radius is decreased to the minimum; the arc shape changes from cone to compressed cylinder; and the arc temperature, the arc pressure, and the depth-width ratio of the weld beam reached the maximum. Otherwise, the effect of applied HFAMF on the stress of arc and weld pool is discussed, and the mechanism of arc contraction is analyzed.

This study provides a comprehensive evaluation of general characteristics of sized silk fabrics for the painting purpose. Two particular types of silk fabrics used for painting background were compared: a recreation of historical material and a mass produced material of present day. The sizing process made the surface characteristics of the silk fabrics more suitable for painting. The dyeing properties of the fabrics were related to the surface area of the fabrics, and had no significant effect on their mechanical properties. The antibacterial activity of the tannin-based natural dyestuffs were maintained after the sizing. The performance assessment by the KES-FB system showed that the fabrics are more prone to deteriorate after the sizing because the glue layer receives the most of the physical stresses.

Epoxy resins with acidic compounds feature adhesion, robustness, and deoxidizing ability. In this study, hybrid adhesive films with deoxidizing and curing capabilities for semiconductor packaging were fabricated. The compatibilizing effects and mechanical properties were chiefly investigated by using various additive binders (thermoplastic amorphous polymers) and compatibilizing agents. The curing, deoxidizing, thermal, and rheological properties were systematically investigated. For uniform film formation and maximizing deoxidizing curable abilities, a thermoplastic--thermoset mixture containing a phenyl and carboxylic acid-based additive (benzoic acid), and a polycarbonate was chosen as the model adhesive film. Without either a phenyl or an acidic group in the compatibilizing agent, deoxidizing and compatibilizing effects were not achieved. The manufactured hybrid adhesive film can be effectively used, especially for electronic devices that require deoxidization and adhesion.

Stress corrosion cracking is one of the aging phenomena for the major structure components in nuclear power plant. During the operation of a power plant, stress corrosion cracks are initiated and g...

This article reviews the multiscale nature of stress corrosion cracking (SCC) observed by high-resolution characterizations in austenite stainless steels and Ni-base superalloys in light water reactors (including boiling water reactors, pressurized water reactors, and supercritical water reactors) with related opinions. A new statistical summary and comparison of observed degradation phenomena at different length scales is included. The intrinsic causes of this multiscale nature of SCC are discussed based on existing evidence and related opinions, ranging from materials theory to practical processing technologies. Questions of interest are then discussed to improve bottom-up understanding of the intrinsic causes. Last, a multiscale modeling and simulation methodology is proposed as a promising interdisciplinary solution to understand the intrinsic causes of the multiscale nature of SCC in light water reactors, based on a review of related supporting application evidence.

The technology of curable adhesive films capable of deoxidization is still in its infancy. Herein, an eco-friendly solution lies in utilizing an epoxy binder, a diacid, and a thermoplastic matrix with low transition temperature, namely, poly(ethylene glycol) (PEG). We fabricated a specially designed hybrid adhesive film with curable and deoxidizing capabilities by harnessing and controlling acidic moieties. The deoxidizing capability of the films and the crystallinity of PEG in the cured films were further controlled by the combination of acidic concentrations and reaction times. Acidic concentrations higher than the stoichiometric ratio (1:1) between the epoxy binder and pimelic acid considerably hindered the PEG crystallinity in the cured films. This suppressed crystallinity was observed based on DSC, POM, XRD, and FTIR results. The rheological and mechanical properties were systematically examined. The fabricated hybrid adhesive films with curable deoxidizing capabilities can be useful in a myriad of applications, such as electronics and semiconductor packaging that require soldering.

The new Si epitaxial (epi) defects not seen in scanning electron microscope (SEM) measurements were investigated. Morphologies of these defects were measured by atomic force microscope (AFM) but source of defect was not found in transmission electron microscope (TEM) measurements. In order to find the origin of the invisible defect, we observed the morphological changes of the various substrate defects after epi growth process. Most of the defects were removed during hydrogen (H 2 ) baking and hydrogen chloride (HCl) etching steps, but some particles survived. Among the survived defects, it was confirmed that the non-metallic particles having 200 nm or more were the origin of the invisible epi defects.

This study compared the arc shapes and microstructures obtained from gas tungsten arc welding of AZ91 magnesium alloy for different parameters of an external alternating cusp-shaped magnetic field which was applied during the welding process; the parameters included excitation currents of 1 A to 3 A and excitation frequencies of 0 Hz–100 Hz. The experimental results showed that the tungsten inert gas (TIG) arc did not rotate under the external alternating cusp-shaped magnetic field, but its cross section was continuously elongated or flattened with the change in frequency. As the excitation current and frequency changed, the arc expanded or compressed, the weld shape and the microstructure changed. When the excitation current was 2 A and the excitation frequency 80 Hz, the arc was obviously compressed, the weld appeared smooth, the depth-to-width ratio was the largest, and the microstructure was fine-grained.

Targeting atomistic initiation of stress corrosion cracking (SCC) of Alloy 690, reactive molecular dynamics simulations of SCC of polycrystalline Ni60Cr30Fe10 alloys under water with dissolved oxygen at 900 K were performed employing newly developed reactive force field (ReaxFF) of Ni-Cr-Fe-H-O system. Observed atomistic mechanochemical mechanism involve dissolution-precipitation and diffusion-oxidation behaviors for corrosion, and cleavage-slipping-twinning behaviors for cracking initiation with its driving forces including loacl shear stress/strain and oxidation-enhanced atomistic stress. Roles of cold work, tensile strain and grain boundary (GB) structures in impacting these mechanochemical behaviors were explored based on calculated surface and GB energy, GB diffusivity and atomistic stress/strain.

A novel haze technique for analyzing point-defect distribution in Czochralski Si (CZ-Si) wafers without intentional contamination by transition metals was proposed. Based on the background haze in high-temperature oxidation, a three-step oxidation process including two-step low-temperature precipitation and a single-step high-temperature wet oxidation process was designed. After the newly designed heat processing and preferential etching, surface haze was formed selectively on the interstitial-dominant region of the wafer. Through electron microscopy analysis, surface defects decorated with Ni were observed, which suggested that the surface accumulation of non-gettered Ni adsorbed from the furnace causes surface haze on the interstitial-dominated region. The widths of the hazes could be optimized by adjusting the processing times of the first two steps, which affected the Ni gettering ability in the vacancy-dominated regions of the wafers. Additionally, the second stage at 1000 °C was associated with precipitate growth, as well as with haze formation.

Herein, the effect of pre-annealing on oxygen precipitation in a silicon P/P-epitaxial wafer was investigated using an experimental approach. Czochralski-grown silicon wafers were annealed at 800–900 °C to enhance their bulk micro defects (BMDs), before the epitaxial growth process. The effect of the pre-annealing temperature on oxygen precipitation was greater than that of the pre-annealing time, and the effect of pre-annealing temperature varied between polished and epitaxial wafers. Regarding pre-annealed epitaxial wafers that were annealed at low temperatures, the pre-annealing time also had as large an effect on BMD formation as the pre-annealing temperature. These experimental results were used to determine the optimal pre-annealing temperature for enhancing oxygen precipitation in epitaxial wafers. The experimental results regarding the optimal conditions were consistent with prior hypotheses. Crystal originated particles (COPs) and COP-free crystals exhibited their highest BMD density values at similar pre-annealing temperatures.

The dpa (displacement per atom) damage for 14-MeV neutron in a pfc materials was simulated using MCNPX/SPECTER code. The dpa values in the main components of the structural material SS316L, Fe, Cr and Ni, were calculated to analyze the effect of nuclear damage. According to the neutron wall load for ITER design base, a neutron flux of 3.5 × 1013 neutrons/cm2·sec was applied. The simulated dpa values were found to be as 3.0 dpa/fpy for Fe, 2.9 dpa/fpy for Cr and 3.1 dpa/fpy for Ni. For practical experiments, the simulated dpa values due to the irradiation damage of 17-MeV protons were found to be as 0.67 dpa at the peak and 0.05 at the surface for SS316L using by SRIM code at the same fluence. For the 17-MeV proton irradiation, the Bragg peak appears at a 0.64-mm depth. Also, SS316L specimens irradiated by a 17-MeV proton beam with a fluence of 1016 protons/cm2 were analyzed by using transmission electron microscopy.

Acoustic emission (AE) is one of the promising methods for detecting the formation of stress corrosion cracks (SCCs) in laboratory tests. This method has the advantage of online inspection. Some studies have been conducted to investigate the characteristics of AE parameters during SCC propagation. However, it is difficult to classify the distinct features of SCC behavior. Because the previous studies were performed on slow strain rate test or compact tension specimens, it is difficult to make certain correlations between AE signals and actual SCC behavior in real tube-type specimens. In this study, the specimen was a AISI 304 stainless steel tube widely applied in the nuclear industry, and an accelerated test was conducted at high temperature and pressure with a corrosive environmental condition. The study result indicated that intense AE signals were mainly detected in the elastic deformation region, and a good correlation was observed between AE activity and crack growth. By contrast, the behavior of accumulated counts was divided into four regions. According to the waveform analysis, a specific waveform pattern was observed during SCC development. It is suggested that AE can be used to detect and monitor SCC initiation and propagation in actual tubes.

An experimental study was conducted to investigate the effect of carbon nanotubes on the zinc corrosion resistance of sealing layer formed on the Tungsten Carbide spray coating. Using the nanotubes, a sealing agent in the form of solid-liquid suspensions was made and applied to the surface of spray coating. A series ofexperiments, consisted of three stages such as preparation of test piece, molten-pot immersion test, and evaluation of micro structure, were undertaken to demonstrate complicated interaction existing between zinc ions and sealing layer containing the nanotubes. Experimental results showed newly developed sealing layer were less susceptible to corrosion and thus coated layer was well protected even in the case of 10 days exposure. Comparison of the micro structure after molten pot test also indicated that carbon nanotubes still remained in the matrix and organized more reliable frame work constituted with boron nitride and chromium compound. It was revealed that carbon nanotubes in the sealing layer played positive role to enhance zinc corrosion resistance in the perspective of both fibrous structure and inherent chemical stability.Key Words : Carbon nanotube, Thermal spray, Sink roll, Corrosion resistanceISSN 1225-6153Online ISSN 2287-8955

The welding of zirconium alloy components is one of the most critical processes in the fabrication of nuclear fuel rods used in pressurized water reactors. For this, various welding processes, such as gas tungsten arc welding, electron beam welding, laser beam welding, and resistance pressure welding (RPW), are used around the world. In Korea, the RPW process is being used to fabricate nuclear fuel assembly fuel rods. This study investigated changes in the weldment shape owing to welding conditions such as welding current, welding force, and overlapping. The welding soundness of the weldment was evaluated by hydraulic burst test. The welding temperature of the weld zone was measured using a thermal infrared method. Discontinuous black spots in the weld line, regarded as a non-bonding defect, were confirmed as spots caused by the carbide precipitation of zirconium during welding.

In gas metal arc welding, electromagnetic force, plasma stream force, gravity, and surface tension are the most important factors that affect metal transfer and spatter generation rate. In this paper, different kinds of external electromagnetic fields were introduced to gas metal arc welding (GMAW). The photos of arc plasma and droplet and electric signals covering welding current and arc voltage were acquired synchronously by an analysis and evaluation system based on LabView for GMAW. It was confirmed that the metal transfer frequency was improved, and spatter generation rate was diminished under controls of external electromagnetic fields. The influencing rules of external electromagnetic fields on electromagnetic force, the gravity, the plasma stream force, and surface tension were studied by three physical models, and the mechanism of external electromagnetic fields was revealed. This paper is for the purpose of discussing these factors and will make a profit for the application of electromagnetic coupling control to short-circuit GMAW.

The interactions of 14.1-MeV neutrons from nuclear fusion reactions with a pfc (plasma facing component) are analyzed using the MCNPX/SPECTER code system. The dpa (displacement per atom) values in the three-layered pfc of graphite, Cu, and SS316L based on the KSTAR (Korea Superconductor Tokamak Advanced Reactor) device are calculated by the SPECTER code. The production rates of hydrogen and helium gas are calculated for an analysis of the nuclear damage effect. The serious irradiation condition of the ITER (International Thermonuclear Experimental Reactor), a neutron flux of 3.5 × 1013 neutrons/cm2·sec, was applied. The dpa values during oneyear operation were estimated as 0.6 dpa for graphite, 4.6 dpa for Cu and 2.2 dpa for SS316L. And the production rates of H and He atom for SS316L were estimated to be 40 appm/dpa and 11 appm/dpa, respectively.

The finite element analysis on temperature field and stress field during submerged-arc welding (SAW) was carried out by means of assembly language of FORTRAN on the base of ABAQUS. A finite element model was established to study the effects on weld bead formation by using longitudinal magnetic field of low-frequency and different process parameters loaded with moving heat source. A practical SAW experiment was conducted to verify the results of the numerical simulation. It was shown that a molten pool with a wider weld face and a lower penetration could be obtained by the control of longitudinal magnetic field of low-frequency. In addition, the fusion line after this treatment was smoother than with conventional SAW. The results of practical SAW experiment were consistent with those of the numerical simulation. It was confirmed that the longitudinal magnetic field of low-frequency could contribute in diminishing the dilution rate and improving the performance of surfacing layers.

This study aims to detecting and analyzing the defects of damaged carbon fiber reinforced compositesafter impacts, particularly focusing on barely visible impact damages. The impact test was progressed by a drop-weightmachine and applied to introduce simulated damages on laminated composites used in aircrafts. Various non-destructive testing (NDT) techniques were applied to identify the defects on the specimens with different levels ofimpact energies. Based on the measurements data, the levels of the barely visible impacts, and the applicability andeffectiveness of the detection methods were discussed. Generally, the results demonstrated that their inner damagescontained bigger footprints than those on the surfaces. However, when the damage energy was low, it was found thatthe inner damage size could be smaller than those appeared on the surfaces.초록 : 본 연구에서는 탄소섬유강화플라스틱(CFRP, carbon fiber reinforced plastics)에 충격을 가하여 발생하는 결함에 대한 분석을, 특히 눈으로 식별이 어려운 손상(Barely Visible Impact Damage: BVID)을 중심으로 진행하였다. 낙하형 충격시험기를 통하여 충격 시험을 진행하였고, 추의 자유 낙하를 통하여 실제 항공기에 적용된 복합재료에충격에 의한 손상을 모사한 후, 표면과 내부에 다양한 비파괴 검사를 적용하여 충격에너지에 따른 시편의 결함 거동을 확인하고 살펴보았다. 이를 위해 여러 가지 비파괴 검사법을 사용하여 결함을 비교, 분석, 검토하였다. 그 결과 눈으로 식별이 어려운 손상과 이를 측정하기 위해 사용된 각각의 측정법에 따른 특성이 논의되었다. 일반적으로 육안으로 보이는 표면결함보다 큰 결함이 내부에 발생하였으나, 충격에너지가 작아지면 내부결함이 표면결함보다 작을 수 있다는 사실이 관찰되었다.

In this study, a new heat plate with a groove for butt-welding was developed to investigate the misalignment effects on the joining strengths of polyethylene double walled pipes. Thermal analyses of the material determined the temperature profile of the welding. After the welding, the joining characteristics of the pipes were compared with those welded by the conventional heat plate. The results of the stiffness and flattening tests showed that there were no big differences between the joints made from these two plates. In the leakage test, however, the pipes welded with the conventional heat plate leaked below the required test conditions, while the pipes welded with the grooved heat plate did not show any leakage, even in a range higher than the required conditions. The tensile and bending strength were also improved. The results demonstrated that the grooved heat plate accomplished more complete fusion at the pipe joints and induced high quality joints.

1990년대 자동차 산업에 있어 최대 관심사는 엔진 개발을 통한 최대의 연료 효율을 확보하고 자동차의 무게를 증가시켜 안전성과 편안함을 개선하고 차량 사용에 있어 기능적인 부분을 부가하는 것이었다. 하지만, 최근 전 세계적인 에너지 및 환경규제 등의 문제가 대두되기 시작하면서 일본, 유럽 등지에서 법제화를 통해 자동차 중량을 감소시키는 것이 큰 이슈로 대두되고 있다. 자동차에 있어 무게를 줄이게 되면 차량의 연비를 줄일 수 있으며, 배기가스 배출을 감소시키게 되어 화석연료의 소비 감소 및 환경오염 방지에 큰 역할을 할 수가 있다. 반면 자동차의 안전성, 편의성 등을 바라는 다양한 소비자의 욕구를 충족시키기 위해 많은 장치들을 자동차에 추가 장착함으로써 자동차의 중량은 증가하게 되었다. 따라서 이러한 상반되는 문제를 해결하기 위해 철강 소재에서 마그네슘 합금, 알루미늄 합금, 플라스틱 등의 가벼운 비철합금 소재의 사용이 제안되고 있으나 가격, 안전성, 내구성 등의 문제로 그 사용은 제한되고 있는 실정이다. 이에 따라 자동차구조용 소재는 안전성 및 내구성을 위해 높은 강도와 연성을 동시에 확보하고 있는 고장력강재의 사용이 증가하고 있다. DP 강, TRIP 강, CP 강, Hot-stamping 강 등 600MPa부터 1,500MPa까지 다양한 강도의 강재들이 차체 제작에 있어 사용되고 있다

Infrared thermography uses infrared energy radiated from any objects above absolute zero temperature, and the range of its application has been constantly broadened. As one of the active test techniques detecting radiant energy generated when energy is applied to an object, ultrasound infrared thermography is a method of detecting defects through hot spots occurring at a defect area when 15~100 kHz of ultrasound is excited to an object. This technique is effective in detecting a wide range affected by ultrasound and vibration in real time. Especially, it is really effective when a defect area is minute. Therefore, this study conducted thermography through lock-in signal processing when an actual defect exists inside the austenite STS304 seamless pipe, which simulates thermal fatigue cracks in a nuclear power plant pipe. With ultrasound excited, this study could detect defects on the rear of a pipe by using an aluminium reflector. Besides, by regulating the angle of the aluminium reflector, this study could detect both front and rear defects as a single infrared thermography image.

일반적으로 용접 구조물의 피로강도는 용접부와 같은 기하학적 불연속부에 있어서의 응력집중에 의해 결정된다. 이때 응력집중은 구조적 형상에 의한 전체적인 요인 및 용접부 비드 등의 국부적인 요인의 의해 영향을 받는 것으로 알려져 있으며, 기계 및 구조물의 80% 이상이 피로에 의해서 여러 가지 형태의 원인으로 파손되고 있다고 알려져 있다. 좀 더 구체적으로 구분하면, 용접부의 피로 수명을 저하시키는 원인으로는 앞서 설명한 바와 같이 구조적 불연속 및 용접변형에 의한 부정합(misalignment), 국부적 응력 집중의 영향, 언더컷, 블로우 홀, 개재물 등에 의한 용접결함 그리고 용접 인장 잔류응력의 영향 등 크게 네 가지로 구분될 수 있다. 피로파괴는 때때로 매우 위험한 결과를 초래하기 때문에 이를 방지하고 높은 수명시간을 확보하기 위해서는 설계-시공-후처리 각각의 단계에서 다음과 같은 사항들이 고려되어야 한다. 첫째로 용접연결부의 설계 단계에서는 진동 및 공명(resonance)이 발생하는 위치를 되도록 피하여 피로하중이 최소화될 수 있게 이뤄져야 하며, 부식 환경의 노출 최소화 및 응력집중계수를 낮게 설계하여야 한다. 둘째로 시공단계에서는 모재와 용가재, 용접공정의 올바른 선택, 시공 전 그루브 형상 및 표면 준비 등의 철저한 준수 및 작업자의 숙련도 검증 등의 사항이 요구된다. 마지막으로 시공이 끝나면 적절한 후처리(post weld improvement)를 거쳐 최종적으로 피로강도를 향상시킬 수 있는데, 본회에서는 앞서 기고한 용접 연결부의 설계 방안에 이어 그 두 번째로 용접후처리 단계에서 실시할 수 있는 용접부 피로수명 연장기법에 대해 IIW Recommendation

Welding is an essential process in the automotive industry. Most welding processes that are used for auto body are spot welding and CO 2 welding are used in a small part. In production field, CO 2 welding process is decreased and spot welding process is increased due to welding quality is poor and defects are occurred in CO 2 welding process frequently. But CO 2 welding process should be used at robot interference parts and closed parts where spot welding couldn’t. Because of the 0.65mm ~ 2.0mm thickness steel sheet were used in the automotive industry, poor quality of welding area such as burn through and under fill were happened frequently in CO 2 process. In this paper, we will study about the penetration depth which gives a huge impact on burn through changing a degree of base metal, welding position and torch angle. Voltage, current and welding speed were fixed but degree of base metal, welding position and torch angle were changed. And Cold- Rolled(CR) steel sheet was used. Penetration depth was analysed by multiple regression analysis to derive approximate calculations. And reliability of approximate calculations were confirmed through additional experiments. As the results of this research, we confirmed the effect of torch and plate angle to bead shape. And we present a possibility that can simulate more accurate to weld geometry, as deduced the verification equations that has tolerance of less than 21.69%.Key Words : Welding position, Angle of plate, Torch angle, Penetration depth, Multiple regression analysis

This study detected SCC defects of dissimilar metal welded(STS304 and SA106 Gr. b) pipes using the ultrasonic infrared thermography method and the lock-in image treatment method among infrared thermography method. The infrared excitement equipment has 250 Watt of output and 20 kHz of frequency. By using the ultrasound infrared thermography method, the internal defects of dissimilar metal weld joints of pipes used at nuclear power plants could get detected. By an actual PT test, it was observed that the cracks inside the pipe existed not as a single crack but rather as a multiple cracks within a certain area and generated a hot spot image of a broad area on the thermography image. In addition, UT technology could not easily defects detected by the width of fine hair cracks. but, ultrasound infrared thermography technique was defect detected.

The interactions of fusion reaction products such as 2.45-MeV and 14.06-MeV neutrons and 3.05-MeV protons with the KSTAR PFC (plasma facing component) are analyzed using Monte Carlo codes. The dpa (displacement per atom) values in the three-layered PFC of graphite, Cu, and SS316L are calculated, and the depth profile was analyzed for different-type secondary particles. The PHITS code was used for this study. The deposited energy was also calculated for analysis of the nuclear heating effect. The serious irradiation condition of the International Thermonuclear Experimental Reactor (ITER) parameter, a neutron flux of 3.5 × 1013 neutrons/cm2·sec, was applied. The dpa values during one year operation were estimated as 0.75 dpa for graphite, 4.57 dpa for Cu, and 2.69 dpa for SS316L.

In this study, mechanical analyses of a butt welding technology for joining Polyethylene pipe are presented. The pipe had unique structure with double wall, and its section topology was not flat. For an effective repair of leakage and replacements of the pipe, the butt welding technology was developed and tested. For the material characterizations, thermodynamic analyses such as thermal gravimetric analysis and differential scanning calorimetry were performed. Based on the test results, the process temperature and time were determined to ensure safe joining of the pipes using a hot plate apparatus. The welding process was carefully monitored by measuring the temperature. Then, the joined pipes were tested by various methods to evaluate the quality. The analyses results showed the detail process mechanism during the joining process, and the test results demonstrated the successful application of the technology to the sewage pipe repairs.

The new metrology, Advanced Poly-silicon Ultra-Trace Profiling (APUTP), was developed for measuring bulk Cu and Ni in heavily boron-doped silicon wafers. A Ni recovery yield of 98.8% and a Cu recovery yield of 96.0% were achieved by optimizing the vapor phase etching and the wafer surface scanning conditions, following capture of Cu and Ni by the poly-silicon layer. A lower limit of detection (LOD) than previous techniques could be achieved using the mixture vapor etching method. This method can be used to indicate the amount of Cu and Ni resulting from bulk contamination in heavily boron-doped silicon wafers during wafer manufacturing. It was found that a higher degree of bulk Ni contamination arose during alkaline etching of heavily boron-doped silicon wafers compared with lightly boron-doped silicon wafers. In addition, it was proven that bulk Cu contamination was easily introduced in the heavily boron-doped silicon wafer by polishing the wafer with a slurry containing Cu in the presence of amine additives.

The effects of material properties modeling on the solder failure analyses by numerical simulations are studied. The packaging structure of plastic ball grid array on printed circuit board was modeled. Two different types of molding compounds and two different types of substrates were employed and combined for the plastic ball grid array package modeling. The material properties were assumed as temperature dependent elastic and viscoelastic, and finite element method was used to calculate and analyze the strain energy densities of the solder balls. The chip warpage was also studied, and related with the solder ball reliability analyses by discussing the viscoelastic characteristics of the materials and their influences on the deformations. The results showed that the warpage developments of the packaging structure showed very different behaviors, and the mechanism of the strain energy density accumulations in the solder balls were also different depending on the material properties modeling and their combinations. This study demonstrates that appropriate modeling of the material properties is critical for the interpretation and understanding the microelectronics reliability mechanisms.

김재성 * ·이영기 ** ·안주선 * ·이보영 ***,† * 한국항공대학교 항공우주 및 기계공학과 ** 한국타이어 RE 개발팀/연구생산기술본부 *** 한국항공대학교 항공우주 및 기계공학부 Abstract The weight reduction of the transportations has become an important technical subject Al and Al alloys, especially Al 5052 alloys have been being applied as door materials for automobile. One of the most widely known car weight-reduction methods is to use light and corrosion-resistant aluminum alloys. However, because of high electrical and thermal conductivity and a low melting point, it is difficult to obtain good weld quality when working with the aluminum alloys. Also, Pulse MIG welding is the typical aluminum welding process, but it is difficult to apply to the thin plate, because of melt-through and humping-bead. In order to enhance weld quality, welding parameters should be considered in optimizing the welding process. In this experiment, Al 5052 sheets were used as specimens, and these materials were welded by adopting new Cold Metal Transfer (CMT) pulse process. The proper welding conditions such as welding current, welding speed, torch angle 50° and gap 0~1mm are determined by tensile test and bead shape. Through this study, range of welding current are confirmed from 100A to 120A. And, the range of welding speed is confirmed from 1.2m/min to 1.5m/min.

Waste water is disposed to sewage disposal plant by underground PE double wall pipes. Various processes have been introduced to join PE pipes, but most of these methods have many disadvantages such as costs, lack of reliability and difficulties in joining, etc. Recently butt welding has been paid much attention to joint PE pipes as this process has many advantages such as cost, safety and reliability. In this study, newly developed heat plate, a patent-pending heat plate with a groove, was used to butt-weld PE double wall pipes with different misalignment gaps to simulate real underground conditions, and the butt welding temperature of PE pipe was determined by thermal analysis (Thermal Gravimetric Analysis, Differential Scanning Calorimetry and Dynamic Mechanical Analysis). The resulting joining characteristics of double wall pipes were compared with those from a conventional heat plate, in terms of stiffness, flattening and leakage tests. The results from the stiffness and flattening test showed that there were no big differences between the butt-welded joints made from these two plates. From the leakage test, although PE pipes welded with a conventional heat plate did leak below the required test conditions (10 min. at 0.75kgf/cm2), the pipes welded with a patent-pending grooved heat plate did not show any leakage even at a pressure 1.5 times higher than the required conditions. It was noted that by utilizing a grooved heat plate more complete fusion at the pipe joints could be obtained, which in turn induced a high quality joints.

SCC (Stress Corrosion Crack) is a key issue in the nuclear industry of piping section. When weldingthe pipe, heat input occurs to the trend of thermal stress. And heat input affected residual stress to the pipe.In this study, the effect of residual stress for the SCC in the piping was determined.Experimental method is four kinds of specimens(1 pass, 5 pass, 10pass, 15pass) are produced toSCC. ANSYS codeanalyze the temperature gradient forthe specimen. Using the temperature gradient analyzedtothe residual stress in the pipe. According to this result, ascertain the effect of residual stress to SCC

Steel structures such as ships, ocean structures, automobile, aircraft and bridges should be designed and manufactured to be able to endure under various environmental conditions such as static load, impact, fatigue and torsion etc. Especially, many researches about improvement of fatigue strength have been performed in relation towelding to be used for connection of steel structures. In case that welded structures were applied cyclic fatigue load, the factors such as profile of weld bead, direction and size ofapplied load, welding residual stress and undercut have affected fatigue life. Generally, if curvature radius of welding(r) toe and welding aangle(θ) are larger the fatigue strength is better than smaller ones. However, in case that the one side in lapjoint area was welded, shape(such as gap size, lap length) of lap joint ismore affect than welding toe and angle on the stress value. In this study, fatigue strength for the ferritic stainless steel was evaluated through stress analysis using finite element method and fatigue test according to the lap length and gap size. In addition, to remove notch effect or stress concentration effect in the lap joint area, fatigue strength was evaluated by welding as the full penetration condition.

In this study, the effect of various seed layers (95Ni–5Cr, 80Ni–20Cr and Cr) on the adhesion strength of flexible copper clad laminate (FCCL), which was manufactured by the roll-to-roll process, was evaluated after heat treatment. The changes in the morphology, chemical bonding, and adhesion properties were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and a 90° peel test. The results showed that both the peel strength and thermal resistance of the FCCL increased as the Cr ratio of the seed layer increased. The roughness of the fracture surface decreased as the heat treatment temperature and holding time increased. The heat treatment of the FCCL increased the proportion of C–N bonds and reduced that of the C–O and carbonyl (C=O) bonds in the polyimide. The chemical function and roughness of the fracture surface were affected by the composition and ratio of the seed layer. Therefore, the adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.

Depressive failure at the connecting locations between the phenol reactor shell and the stripper tray is one of the primary failure modes in a phenol stripper reactor. The occurrence of cracking failure of an AISI 304 tray in the phenol stripper reactor resulted in an emergency shutdown of the petrochemical plant. Possible causes for the stripper tray cracking were analyzed using a FEM analysis with an ANSYS program and solutions to prevent further cracking failures of the stripper trays are suggested. Variables such as operation pressure and stripper tray thickness were evaluated in terms of safe operation of the phenol production reactor. The simulation results from the ANSYS analysis showed that the stress concentration at the fractured area of the stripper tray could be reduced by a factor of 2 by doubling the thickness of the existing stripper tray. Therefore, for safe and efficient operation of the phenol production line, the design of the stripper should be modified by increasing the thickness of the existing stripper tray. A detailed simulation analysis of the process is discussed.

This paper has studied failure of an oil storage tank. During operation, several cracks were observed at the fillet weldment between reactor shell and annular plates in the bottom of oil storage tank. Extreme stresses in the structure during its operation were determined taking into account shape and geometry imperfections as well as corrosion influence. Both reactor shell and annular plates are made of carbon steel (SM53C). In this study, in order to identify the causes for the fillet weldment cracking, failure analysis such as fractography, tensile test, hardness test, corrosion test(SSRT), chemical analysis was performed. The failure of oil storage tank is the result of the combined and synergistic interaction of mechanical stress and corrosion reactions. Although cracks were initiated by corrosion, failure was generated by propagation of crack caused by stresses concentration. It was recommended that (1) the local stresses be reduced by improved weld toe geometry, and (2) the reinforcement be used in order to avoid failure by stresses concentration.

Recently, a demand of ferritic STS is increasing rapidly in automobile exhaust system. Exhaust manifolds are the part nearest to the engine so that the material is exposed to high temperature exhaust gas. Excellent heat resistant properties, especially high temperature strength, thermal fatigue resistance and high corrosion resistance are necessary for these parts. STS429L contains 15 weight percent of Cr and low Mo, so has good price competitive. And it has excellent high temperature strength and corrosion resistance, so receives attentions as material that applying to exhaust manifold. In tensile test of lap joint welded STS 429L, most of specimens are failed in base metal, but occurs brittle fracture in weld metals at some specimens in the face of good welding conditions. In the process of tensile test, lap joint welded STS429L specimens are transformed locally. The brittle fracture occurs that local transforming area exists in weld metals. But, butt welding specimens made by same materials showed ductile fracture in tensile test and bending test. In this study, suppose the reason of brittle fracture is in the combined local transform and tensile stress, through analysis of bead geometry, evaluate geometrical factor of brittle fracture in lap joint welded STS429L.

In this work, three kinds of Cr-based nitride coatings such as monolithic CrN, CrSiN coatings, and multilayered CrSiN∕AlN coating with bilayer period of 3.0nm were deposited on both Si (100) wafer and AISI H13 steel substrates by unbalanced magnetron sputtering. Thermal stability of these coatings was evaluated by annealing the coatings at temperatures between 600 and 1000°C for 30min in air. In addition, the corrosion behaviors of these coatings were investigated by potentiodynamic polarization tests in a deaerated 3.5wt.% NaCl solution at 40°C. Results from annealing test show the monolithic CrN and CrSiN coatings were completely oxidized after annealed at 800 and 900°C, and their cross sectional images and atomic force microscopy showed a loose and very porous morphology due to the oxidation. Also, the hardness values of the monolithic CrN and CrSiN coatings were decreased significantly from 22 and 27GPa to 8 and 14GPa, respectively. However, the multilayered CrSiN∕AlN coating still exhibited a dense microstructure without visible change after annealed at 1000°C, and moreover, the relatively high hardness of 25GPa was maintained. The superior thermal stability of the CrSiN∕AlN multilayer coating could be attributed to the formation of the dense and stable oxidation barrier consisted of the Al2O3, Cr2O3, and amorphous SiO2 phases near the surface region, which retard the diffusion of oxygen into the coating. In the potentiodynamic polarization test results, it was found that the significantly improved corrosion resistance of the multilayered CrSiN∕AlN coating was observed in comparison with those from the monolithic CrN and CrSiN coatings, and its corrosion current density (icorr) and protective efficiency were measured to be approximately 4.21μA∕cm2 and 95%, respectively.In this work, three kinds of Cr-based nitride coatings such as monolithic CrN, CrSiN coatings, and multilayered CrSiN∕AlN coating with bilayer period of 3.0nm were deposited on both Si (100) wafer and AISI H13 steel substrates by unbalanced magnetron sputtering. Thermal stability of these coatings was evaluated by annealing the coatings at temperatures between 600 and 1000°C for 30min in air. In addition, the corrosion behaviors of these coatings were investigated by potentiodynamic polarization tests in a deaerated 3.5wt.% NaCl solution at 40°C. Results from annealing test show the monolithic CrN and CrSiN coatings were completely oxidized after annealed at 800 and 900°C, and their cross sectional images and atomic force microscopy showed a loose and very porous morphology due to the oxidation. Also, the hardness values of the monolithic CrN and CrSiN coatings were decreased significantly from 22 and 27GPa to 8 and 14GPa, respectively. However, the multilayered CrSiN∕AlN coating still exhibited a dense m...

Ferritic stainless steels have a good heat resistance and economic advantage. They are used for applications such as automotive exhaust systems where resistance to general corrosion is superior to carbon steels. However, there are not enough research for ferritic stainless steels on weldability mainly used as automotive exhaust manifolds. In this study, mechanical and microstructure properties of as-welded STS 429L and STS 444 ferrite stainless steels were confirmed by tensile, bending, hardness test, optical microscopy and scanning electron microscopy. Tensile strength of the STS 444 is higher than the STS 429L when it is a raw material. In contrast to this fact, STS 429L indicated higher tensile strength after butt welded. In addition, the hardness have a increasing tendency as getting down on the bead.

Ferritic stainless steels of the 400 series have been available for automotive exhaust system, heat exchanger, radiater etc. in various industrial because heat resistance, corrosion resistance and strength are excellent. Especially, automotive exhaust system is required good heat resistance because typical temperature of exhaust system exposed during operation of engine is reach up to . However, research for effect of high temperature in ferritic stainless steels is not enough. In this study, high temperature tensile properties of lap weld of ferritic stainless steels(STS 429) were investigated. In accordance with heat input, lap welds had been produced and were evaluated at high temperature() to compare high temperature tensile properties. In addition, room temperature tensile tests were carried out for non-aging and aging specimens. As a result of R.T tensile test, non-aging specimens were fractured in base metal except for low heat input specimen and aging specimens were fractured in weld metal. Also high temperature tensile test were carried out by aging specimen. After high temperature tensile test, fracture of aged specimen was occurred in base metal except for low heat input specimen. Fracture surface of low heat input specimen in weld metal was confirmed as brittle fracture with observation using scanning electron microscope(SEM). Significant decrease in ultimate tensile strength (between 82 and 85%) was observed for aged ferritic stainless steels(STS 429) when tested at high temperature.