Key Engineering Materials Vols. 353-358

Abstract: The current in-service inspection (ISI) strategy for the nuclear piping in many countries consists of both the code requirements such as ASME B & PV Code Sec. XI and the country-specific regulatory requirements, so called as the enhanced ISI. The enhanced ISI reflects the operating experience of piping failure, while the ASME Code Sec. XI requirement is based on random sampling for the inspection points. In this study, a new strategy for ISI of nuclear piping was proposed based on piping failure frequency. This strategy basically reflects the operating experience because the piping failure frequency is based on the piping failure database. The new concept of minimum inspection rate was also introduced in this new ISI strategy. As pilot study, the new ISI strategy was applied to the Class 1 piping system such as reactor coolant system and safety injection system of Ulchin Unit 5 which is the 1,000 MWe Korean Standard PWR. The results from the proposed new strategy were compared to those from the ASME Code Sec. XI. The results show that the new ISI strategy reasonably reflects the operating experience. The results also show that the concept of the minimum inspection rate can compensate the unbalance in the number of inspection points between the very large differences in the piping failure frequency.

Abstract: In order to contribute to the development of the joining technique of Cf/SiC, joining of SiC ceramic to high strength graphite was investigated. This joining has been successfully realized by reaction joining process using a preceramic polymer, polysiloxane, mixed with the active additive Al-Si powder as joining material. The weld strength is strongly affected by the technological parameters and the ingredient ratio (polysiloxane:Al-Si powder). The optimized factors have been obtained by orthogonal experiments, under which the achieved three-point bending strength of the joints is 96.8% of the strength of the welding base material graphite. The microstructure and composition of the weld zone were analyzed by SEM, EDX and XRD. The results show that the joining material has transformed into a densified interlayer with the thickness of about 15μm. Also, diffusion takes place in the interfacial area, which contributes to a sound interfacial bonding. The interlayer is composed of SiC, Al2O3 and Si.

Abstract: The welding temperature patterns of gas tungsten arc welding for copper thick plates during Ar, He or N2 shielded arc welding were simulated, and the size of weld pools and heat-affected zones have been compared. It was predicted that the heat-affected zone in the welded joints during Ar arc welding is the widest and that during N2 arc welding is the narrowest, while the size of weld pools using Ar (preheating at 400°C), He and N2 (without preheating) shielding arc welding is very similar. Among the three kinds of gases shielded arc welding, the temperature gradient of welded joints during Ar arc welding is the least and that during N2 arc welding is the greatest. The temperature rise velocity at the arc center during N2 arc welding is the highest, and those at the zone close to the weld pool of welded joints during He arc and N2 arc welding are a few higher than that during Ar arc welding.

Abstract: Vessels are rarely subjected to accidental loads such as the collision, grounding and stranding. But these accidental loads cause a lot of damages to hull structure including a large deformation, fracture, tearing and so on. In case of carrying dangerous goods such as crude oil, these accidents can induce a serious environmental pollution. All ocean-going vessels were made by welding. The welding residual stress is a significant shortcoming of welding remains at the hull structure, even though welding technology in shipbuilding field has provided a variety of advantages, e.g. remarkable shortening of the shipbuilding time. The aim of this paper is to investigate the effects of the residual stress in a grounding accident. When a ship runs aground against a sea-obstacle like a rock, this accident can be classified as a grounding. Among parameters of grounding accident scenarios such as the ship speed, the initial striking point, and loading conditions of the ship, only ship speed varies from 10 to 15 knots under ballast condition with/without consideration of residual stress(this sentence is not clear to the read). The initial striking point is at the bow of the center line of ship. A series of nonlinear numerical simulations with large deformation and fracture were carried out using LS-DYNA. As a result, two cases with residual stress have longer damage length. The difference seems to be relatively small, but not negligible.

Abstract: Molybdenum sulfide nanoparticles were prepared via quick homogeneous precipitation method (QHPM) by the reaction between Na2MoO4 and CH3CSNH2 in the presence of sulfuric acid at 80 oC. The as-synthesized molybdenum sulfide particles were studied by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results showed that the as-synthesized molybdenum sulfide was amorphous MoS3 nanoparticles with an average size of 40 nm. The resultant amorphous MoS3 nanoparticles were then calcined under hydrogen gas flow at a selected temperature for 50 minutes. The results of XRD, TEM, and HRTEM confirmed that the MoS2 nanoparticles with about 40 nm were prepared from the amorphous MoS3 nanoparticles at 780 oC.

Abstract: Cr2O3 nano-powders were successfully fabricated with using chromium nitrate and aqueous ammonia as starting material and urea as dispersant agent by sol-gel method. The formation of crystalline phase during heat treatment of dry gel was characterized by differential thermogravimetry (DTG) and X-ray diffraction (XRD) techniques and the temperature of calcination was determined as 400°C. Scanning electron microscopy (SEM) was utilized to observe the morphology of the as-fabricated Cr2O3 particles. The results showed that Cr2O3 particles are spherical or square with little agglomeration and a diameter of about 30 nm. The specific surface area of Cr2O3 particles was measured as 44.23 m2/g by Brunauer-Emmett-Teller (BET).

Abstract: Over the last 100 years innovative techniques in the fabrication of ceramics have led to their use as high-tech materials. Inert bioceramics, such as ZrO2, have inherently low level of reactivity compared with other materials such as polymers and metals as well as surface reactive or resorbable ceramics. The aim of this study was to validate the effect of incision using a zirconia inert bioceramic scalpel to incise animal body and to prove incision property of tissues before clinic. The experiments of incisions concrescence using a sterilized Zirconia inert bioceramic scalpel were investigated in this paper. We used 4-month-old inbred line SD rats as experiment animals. They were divided into three groups to undergo incision on the back skin and subcutaneous tissue. The subcutaneous tissue and musculature samples were obtained and analyzed by optical microscopy at 3, 7 and 14 days for histopathological evaluation respectively. The experimental results showed that no wound dehiscence was observed after suture removal at 14 days after the operation. The experiments proved that an inert bioceramic scapel was nontoxic, nonallergenic, and noncarcinogenic for incisions that obtained normal concrescence criteria two weeks after operation.

Abstract: Hydroxyapatite is a kind of ideal biomaterials for bone and teeth replacement, but its low strength and brittleness need to improve. As bone replacing materials, hydroxyapatite (HAP) and zirconia both have advantage and disadvantage. Nano-sized HAP-ZrO2 powders and HAP-TZP (3Y) (3mol% yttria - stabilized cubic zirconia) bioceramic for artificial joint have been fabricated in this paper. The nano-sized HAP-ZrO2 powders with homogeneous distribution could be synthesized by two-step precipitation method. The HAP-TZP bioceramic with small grain size could be obtained by using hot-press sintering technology, and the sintering parameters are: sintering temperatures T=1300°C, sintering pressure p=30MPa and sintering time t=30min. The mechanical properties, microstructures and fracture pattern that were analyzed by SEM and optical microscopy of the HAP-TZP bioceramic were investigated systematically. The results show that no reaction between HAP and ZrO2 powders, which could be attributed to the very short sintering time of hot press sintering.

Abstract: We studied the effects of the Ca and Sr additions on the microstructure and the cracking process of magnesium alloys with in-situ scanning electron microscope (SEM) images. We found that the Ca addition is not only able to refine the Mg17Al12 phase but also form a new Al2Ca phase, which lead to improved ductile of cast magnesium alloys at elevated temperature. The MgAlCaSr phase can be improved the hot resistance. However, the number of cracks per unit area increases with increasing Ca addition.

Abstract: Titanium oxides films were deposited on tensile sample and vascular stents made of 316L stainless steel by unbalanced magnetron sputtering. The effects of structures, deposition temperature, Ti interlayer and thickness on the adhesion of titanium oxide films were investigated by tensile tests. The results revealed that the structure of the Ti-O films affect their adhesion dramatically. TiO film is brittle and fragile, lacking ability of deformation. Therefore its adhesion was worse than that of TiO2 film. The higher substrate temperature was helpful to improve adhesion of film, the adhesion of the TiO film deposited at 673K was better than those of the TiO films deposited at 323K and 473K. The adhesion of the TiO film with Ti interlayer was better than the one without interlayer. The introduction of Ti interlayer was beneficial to adhesion of film. The adhesion of thinner TiO2 film was better than that of thicker one. TiO2 film deposited on stents had good adhesion. After expansion, the film didn’t crack and peel off. TiO2 film has potential application on the vascular stents for improving its blood compatibility.