Papers by Keyword: Microstructural Characteristic

Abstract: The structural requirements for power plants service environment characteristically demand for welded joints of multi-materials and hybrid structures. The excellent corrosion resistance of AISI 316 and API 5L X56; the negligible response of AISI 316 to magnetic field and the economic viability of API 5L X56 makes these alloy considerable as hybrid structure in power plants application. Also, the appropriate filler metals that will support the intended properties for the proposed service condition is critical for a quality Dissimilar metal welded joint (DMWJ). This study investigates the effect of filler metals on the microstructural and mechanical properties of DMWJ produced from carbon steel API 5L X56 and stainless steel 316L using Gas Tungsten Arc (GTA) welding techniques. The DMWJs were produced using duplex ER2209, austenitic ER308 and austenitic ER316 grade filler. Microstructural evaluation of the joints revealed macro segregation occurrence and formation of type II boundaries at the interface of API 5L X56 steel. In tension tests, the ER2209 filler metal joints showed the maximum ultimate tensile strength values compared to the welds of other filler metals. The average yield strengths of the three welded joints were higher than those of AISI 316L base metal (BM), which indicates that the yield strength of all the welded joints can satisfy the minimum requirements of engineering application for the API 5L X56/AISI 316L DMWJs. The highest hardness value of about 237.5Hv was obtained in the ER2209 filler metal weld. Keywords: AISI 316; API 5L X56; Dissimilar metal welds; GTAW; Mechanical properties; Microstructural characteristics.

Abstract: This research objective is to study the microstructural modification by Al additions in cast nickel base superalloy, GTD-111 by means of vacuum arc melting process. The Al additions to the alloy were 1, 2 and 3% by weight. After that, all casted specimens were performed with different reheat treatment conditions, which consist of solutioning temperatures of 1125°C, 1145°C, 1165°C, 1185°C and 1205°C, respectively, for 6 hours following with precipitation aging at 845°C for 24 hours. After all reheat treatments, the microstructures were investigated and analyzed by SEM. From all obtained results, it was founded that the specimens with Al additions for 1-2%wt. following with reheat treatment show the decrease in size of γ’ precipitated particles when increasing solutioning temperatures. 3%wt. of Al addition was too high content resulting in already improper microstructural characteristics. However all obtained data of area fractions of precipitate phase were almost the same. Effect of Al addition and solutioning temperature did not provide any significant effect in this case. The mechanical property behavior: hardness was investigated by using Vickers hardness tester. It was found that the hardness all was very similar and increased with higher solutioning temperatures.

Abstract: The microstructure characteristics of complex binders under two curing conditions were studied by observing the micro-morphology, analyzing the pore character and means of spectrum test. The results showed that high temperature curing improved the pore structure formed in the early hydration period and reduced the porosity and the coarse pores in pastes. More hydration products were generated on the surface of fly ash particles that made the microstructure of pastes more denser than cured in room temperature. However, high temperature curing had insignificant influence on the CaO/SiO₂ ratio of C-S-H gel in pastes and contributed little to the improvement of the later hydration degree and microstrcture of fly ash-cement pastes.

Abstract: By using the electron microscope scanner, we have done some research and analysis about the internal microcosmic structure of sea sand concrete. And combined with micro-XRD analysis as well integrative thermal analysis, we made observations of the internal composition of sea sand concrete., studying the effect on which sea sand makes during concrete hydration and the effect which fly ash made on the micro-structural characteristics of sea sand concrete.

Abstract: The well-aligned growth structures which derive from directional solidification of ceramic eutectics are of great interests due to their potential use in electronic devices and as structural materials at high temperatures. Because of the complexity of the component system and very high melting points, the solidification behavior on the oxide ceramic eutectic is still unclear up to date. In the presented paper, the Al₂O₃-Y₂O₃-ZrO₂ ternary eutectic ceramic is remelted by a DTA apparatus. The maximal heating temperature is 1950 °C. The melting and solidification behavior are investigated by the DTA analysis. The solidification microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The results show that solidus temperature and the liquidus temperature are 1738.4 °C and 1750.1 °C, respectively. The formation path of eutectic phase is discussed. The microstructure of as-solidified eutectic ceramic shows a divorced ternary eutectic structure consisting of Al₂O₃, YAG and ZrO₂ phases with a random distribution. Furthermore, the microstructural comparison with directionally solidified ternary eutectic ceramic is presented and discussed.

Abstract: This paper presents the rehydration performance of binary binders made with dehydrated cement paste (DCP) and phosphogypsum (GP). DCP was obtained by thermal treatment of hardened cement pastes in which the initial water to cement ratio was 0.5. DCP we mixed with phosphogypsum (PG) to prepare the binary binders . The effect of PG on the physical and mechanical properties of the binary binders was investigated. Scanning electron microscope (SEM) was used to indentify the structural characteristics of the rehydration products. The results showed that the setting time was prolonged and the compressive strength increased slightly by mixing DCP with PG. Microstructural observations indicated that an remarkable amount of ettringite intergrows with the hydrated calcium silicate to form a network structure. Thus, the addition of phosphogypsum can not only utilize the industrial by-product, but enhances the hydraulic properties of the DCP.

Abstract: The presence of twins in ZnO varistors raises interesting questions concerning the potential role of those electrically distinctive twin boundaries in the characteristics of ZnO varistors. The paper uses Voronoi networks to simulate the microstructures of ZnO varistors. The relation between the relative standard deviation of grain size and the ratio of twin number to grain number is obtained. It indicates that the relative standard deviation decreases with the increasing of the twin ratio. On the other hand, ZnO varistor samples with different content of Al2O3 additive were prepared to gain different twin ratios. The simulation has the same conclusion as that obtained from experiments. The probable mechanism of ZnO grain growth inhibition by twins is that the twins increase the mobility viscosity of ZnO grains and grain boundaries, and drag ZnO grains and liquid grain boundaries during the sintering course, then the grain growth is inhibited, and the microstructure becomes more uniform.