Papers by Keyword: Microstructure

Abstract: Microstructure of post-homogenization is significant to prevent particle stimulated nucleation of recrystallization. This paper investigated microstructure evolution in alloy 7050 during cooling from homogenization. Two intermetallic phases, Al₇Cu₂Fe and Mg₂Si were insoluble during homogenization. Cooling to 460 °C and 400 °C follow by quenching, precipitates nucleated discontinuously on the grain boundaries, no precipitates was found within the grains. The precipitates were found near the grain boundaries when quenching from 350 °C, and precipitated uniformly within the center of the grains when quenching from 250 °C. The sizes of the precipitates increased with the decreased of the quenching temperature. Controlling of the post-homogenization microstructure is beneficial to prevent particle stimulated nucleation of recrystallization.

Abstract: The effect of tempering temperature on the microstructures and mechanical properties of a microalloy low carbon bainitic steel was investigated by microscopic analysis and testing of mechanical properties. The results show that the microstructures of the tested steel primarily consists of lath bainite, granular bainite, quasipolygonal ferrite and little acicular ferrite at different tempering temperatures. With the tempering temperature increasing, the proportion of lath bainitie decreases, while the volume of granular bainite and quasipolygonal ferrite increases. At the tempering temperatures of 550-650°C and tempering time of 1 hour, the steel was mostly composed of granular bainite, quasipolygonal ferrite and a little lath bainite, which a good combination of strength and toughness can be obtained.

Abstract: The solar selective absorbing coating is the key component of solar energy collector which determines the heat conversion efficiency. The coating materials mentioned in this paper were prepared by Al as substrate, Al₂O₃-Pt as absorbing layer and metal Ag as infrared reflector. We got three kinds of coatings by adjusting the magnetron sputtering process. Respectively testing and analyzing the performance and microstructure showed that element content of Al, N, O in the coating are of important influence on its performance, meanwhile, the better the crystallization of coatings surface, the more helpful to improve the performance of its corrosion resistance and its moisture and heat resistance.

Abstract: Mechanical properties of Al-12Zn-2.4Mg-1.2Cu alloy extruded sheet were investigated by tensile tests. Microstructures were investigated by optical microscopy (OM) and scanning electron microscope (SEM). The result shows that no matter in the L direction or in the T direction, the tensile strength and yield strength decrease with the increasing of the extrusion temperature in different states. The tensile strength and yield strength in the L direction are higher than in the T direction at different extrusion temperatures and different treatment states. When temperature is 340°C, the highest tensile strength is 780 MPa and the highest yield strength is 753 MPa in the two-stage solution and two-stage aging state. The reason for the higher mechanical properties are in the L direction in different states is mainly depend on the distribution direction of the grains.

Abstract: Although friction stir welded joints of similar or dissimilar metals exhibit good mechanical properties, the nugget zone in the weld region usually shows a deviation in the properties from the rest of the region due to grain coarsening. The effect of grain coarsening at the nugget zone is further aggravated when the friction stir welded joints are subjected to annealing treatment resulting to a wide variation in the properties. In order to overcome the above problem, in the present study an attempt has been made to retard grain coarsening at the nugget zone by the addition of suitable ceramic particles in the nugget zone during welding. SiC particles of 12 microns size is added at the nugget zone in the weld region during friction stir welding of Al 6351 aluminium alloy. The test results reveal that the addition of reinforcement particles resulted in the improvement of uniformity of properties across the weld region both in the as-weld and in the annealed condition.

Abstract: This study was focused on the effect of VC addition on the microstructure and mechanical properties of the prepared ultrafine grained cemented carbides. VC was added to the rawoxide materials which were synthesized to the WC-Co composite powder by the in-situ reduction and carbonization process. The ultrafine grained WC-Co alloys were fabricated by the spark plasma sintering technique using the prepared WC-Co composite powder. The phase constitution, microstructure characteristics and mechanical properties of the sintered ultrafine grained cemented carbides were analyzed quantitatively. The study proposed that VC plays a significant role in decreaseing the grain size of the prepared WC-Co alloy. The ultrafine grained WC-Co alloy with high comprehensive properties can be obtained as an appropriate addition of VC in the developed process.

Abstract: Differentiation in microstructural characteristics of Punica granatum fruit in response to different dynamic temperatures (2 oC, 4 oC, 6 oC, and 8 oC) during cold storage inside the fibre insulation materials was investigated. The results from Fourier Transform Infrared Spectroscopy (FTIR) measurements showed that the polyester fibre exhibited an advantage and the radiation heat transfer was analyzed in the area of far-infrared. By evidence, the examination by scanning electron microscope (SEM) revealed that effect of dynamic temperature on Punica granatum fruits was structurally different. The fruits stored at higher temperature (6 oC and 8 oC) were associated with fractured cell walls and collapse of cells.

Abstract: Microstructure of Ti-6Al-4V laser weld joint heat affected zone was observed. The results suggested that the heat affected zone microstructure first transformed to lamellar structure, then the grain growth and transformed to equiaxial grains. At the same temperature, the grain growth rate was faster at lower deformation rate, and the microstructure was more uniform.

Abstract: The effect of different salt additions on the granular microstructure of samples of the high temperature superconductor YBa₂Cu₃O_7δ (YBCO) synthesized by a biomimetic method has been investigated. Attempting biotemplating using salts with the rock-salt structure, most such salts were found to be chemically compatible with the YBCO biosynthesis, but only NaCl and KCl were observed to result in the desirable strongly anisotropic platelet growth to form clusters with localized orientational alignment. Broadening the range of additions to other chloride salts of varying structures resulted in an increase in the CuO impurity content of the samples, but with all the YBCO formed exhibiting platelet growth. Chloride salts are therefore considered to be good candidates for addition to the biomimetic YBCO synthesis in order to achieve anisotropic platelet growth.

Abstract: Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these parts is very important to prolong their lifetime in a economical point of view. In this study, 0.5Mo filler metal was welded with SMAW method in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal zone, heat affected zone and base metal zone were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H₂SO₄ solution. The heat affected and base metal zones exhibited the highest and lowest values of hardness respectively. And, the corrosion current density of the heat affected zone indicated the lowest value, having the highest value of hardness. It appeared that the corrosive products with red color was wholly covered on the surface of the base metal zone, while its products was not observed in the heat affected zone. The microstructure of the pearlite with black color was more or less observed in the base metal zone with patterns such as crystal and needle, in particular, the crystal pattern of ferrite microstructure with white color was considerably included in the base metal and heat affected zone, and the ferrite microstructure was significantly observed in the weld metal zone. In particular, the polarization characteristics such as impedance, polarization curve associated with corrosion resistance property were well in good agreement with each other. Keywords: Forged steel, Microstructure, 0.5Mo filler metal, SMAW, Weld metal zone, Electrochemical method, Corrosion current density, Hardness.