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As-cast structure refinement of Ti-46Al alloy by hafnium and boron additions  [PDF]
Zhang Li,Su Yanqing,Yang Huimin
China Foundry , 2009,
Abstract: The infl uence of Hf and B on the solidifi cation structure of cast Ti-46Al alloys was investigated. The results show that the coupling effect of Hf and B changes the solidifi cation structure morphology and strongly refi nes the grain size. When the Hf+B contents were increased from 0 + 0.0 to 3 + 0.2, 5 + 0.6 and 7 + 1.0 (in at. %), the solidification structure morphology changed from coarse columnar dendrite to fine columnar dendrite, then to equiaxed dendrite, and further to fi ne near granular grain whilst the average grain size decreased to 20 μm. It is concluded that the columnar dendrite refinement is due to the effect of Hf and B on the decrease of Al diffusion coeffi cient in the melt. The fi ne near granular grain formation is attributed to the combined constitutional supercooling formed by Al and B segregation that is strengthened by Hf and B additions at the solid/liquid interface during solidifi cation, and the TiB2 precipitates acting as heterogeneous nuclei
Effect of strontium and solidifi cation rate on eutectic grain structure in an Al-13 wt% Si alloy  [PDF]
Liao Hengcheng,Bi Juanjuan,Zhang Min
China Foundry , 2009,
Abstract: The influence of strontium addition and solidification rate on eutectic grain structure in a near-eutectic Al-Si alloy was investigated. The characteristic temperature of eutectic nucleation (TN), minimum temperature prior to recalescence (TM), and the growth temperature (TG) during cooling were determined by quantitative thermal analysis. All characteristic temperatures were found to decrease continuously with increasing Sr content and solidifi cation rate. Microstructural analysis also revealed that the eutectic grain size decreases with increasing Sr content and solidifi cation rate. Such eutectic grain refi nement is attributed to the increased actual under-cooling ahead of the liquid/solid interface during solidifi cation.
Phase field modeling of multiple dendrite growth of Al-Si binary alloy under isothermal solidifi cation  [PDF]
Sun Qiang,Zhang Yutuo,Cui Haixia
China Foundry , 2008,
Abstract: Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in metallic systems. In this study, the growth process of multiple dendrites in Al-2-mole-%-Si binary alloy under isothermal solidifi cation was simulated using phase fi eld model. The simulation results showed the impingement of arbitrarily oriented crystals and the competitive growth among the grains during solidifi cation. With the increase of growing time, the grains begin to coalesce and impinge the adjacent grains. When the dendrites start to impinge, the dendrite growth is obviously inhibited.
Solute redistribution and Rayleigh number in the mushy zone during directional solidifi cation of Inconel 718
Wang Ling,Dong Jianxin,Liu Lin
China Foundry , 2009,
Abstract: The interdendritic segregation along the mushy zone of directionally solidifi ed superalloy Inconel 718 has been measured by scanning electron microscope (SEM) and energy dispersion analysis spectrometry (EDAX)techniques and the corresponding liquid composition profile was presented. The liquid density and Rayleigh number (Ra) profi les along the mushy zone were calculated as well. It was found that the liquid density difference increased from top to bottom in the mushy zone and there was no density inversion due to the segregation of Nb and Mo. However carbide formation in the freezing range and the preferred angle of the orientated dendrite array could prompt the fl uid fl ow in the mushy zone although there was no liquid density inversion. The largest relative Rayleigh number appeared at 1,326 篊 for Inconel 718 where the fl uid fl ow most easily occurred.
Microstructure evolution of directionally solidifi ed Sn-16%Sb hyperperitectic alloy  [PDF]
Hu Xiaowu,Li Shuangming,Liu Lin
China Foundry , 2008,
Abstract: The directionally solidifi ed microstructure of Sn-16%Sb hyperperitectic alloy has been investigated at various solidifi cation rates using a high-thermal gradient directional solidifi cation apparatus. The results indicate that the solidifi cation microstructure consists of hard primary intermetallic SnSb phase embedded in a matrix of soft peritectic β-Sn phase. The primary SnSb phase exhibits faceted growth with tetragonal or trigonal shapes. At the same time, the primary SnSb phase is refi ned with an increase in the solidifi cation rate and dispersed more uniformly in the matrix of β-Sn phase. The volume fraction of the SnSb phase fi rstly decreases and then increases when the solidifi cation rate increases in directional solidifi cation of Sn-16%Sb hyperperitectic alloy.
Thermal analysis control of in-mould and ladle inoculated grey cast irons  [PDF]
Mihai Chisamera,Iulian Riposan,Stelian Stan
China Foundry , 2009,
Abstract: The effect of addition of 0.05wt.% to 0.25 wt.% Ca, Zr, Al-FeSi alloy on in-ladle and in-mould inoculation of grey cast irons was investigated. In the present paper, the conclusions drawn are based on thermal analysis. For the solidification pattern, some specific cooling curves characteristics, such as the degree of undercooling at the beginning of eutectic solidifi cation and at the end of solidifi cation, as well as the recalescence level, are identifi ed to be more infl uenced by the inoculation technique. The degree of eutectic undercooling of the electrically melted base iron having 0.025% S, 0.003% Al and 3.5% Ce is excessively high (39–40℃), generating a relatively high need for inoculation. Under these conditions, the in-mould inoculation has a more signifi cant effect compared to ladle inoculation, especially at lower inoculant usage (less than 0.20 wt.%). Generally, the efficiency of 0.05wt.%–0.15wt.% of alloy for in-mould inoculation is comparable to, or better than, that of 0.15wt.%–0.25wt.% addition in ladle inoculation procedures. In order to secure stable and controlled processes, representative thermal analysis parameters could be used, especially in thin wall grey iron castings production.
Effect of Metallic, Nonmetallic, Water Cooled and Cryogenic Chills on Pearlite Content (PC), Eutectic Cell Count (ECC) and Grain Size (GS) of Hypo Eutectic Nickel Alloyed Cast Iron  [PDF]
Joel Hemanth
Modeling and Numerical Simulation of Material Science (MNSMS) , 2017, DOI: 10.4236/mnsms.2017.71001
Abstract: This paper presents the results obtained, deductions made from solidification behaviour and a series of micro structural studies such as pearlite content, eu-tectic cell count and grain size of hypoeutectic gray cast iron which was sand cast (CO2 moulding) using metallic, nonmetallic, water cooled and subzero (cryogenic) end chills. Hypo-eutectic cast irons containing C 3.42, Si 2.4 and Ni 1.5 with impurity contents (S, P, Mn etc.) were solidified unidirectionally in an American Foundrymen Society (AFS) standard mould, the end of which was provided with different end chills to study the effect of chilling during solidifi-cation. The melts were inoculated with 0.3% Fe-Si to promote graphitization. It was observed that the transition from one structure to another is more gradual than normally obtained in the structure of cast irons solidified mul-ti-directionally in a sand mould at room temperature. Austenite dendrite interactions were shown to be a major factor in determining the microstructure, in which the higher dendrite reaction leads to changes in DAS, ECC and GS. It is observed that, the number of eutectic cells is an index of graphite nucleation and the effect of these on structure, since the eutectic cells are developed on the graphite nuclei during solidification.
Microstructure variation and growth mechanism of hypoeutectic Al-Si alloy solidifi ed under high pressure  [PDF]
Zhang Guozhi,Yu Xifeng,Liu Xinggang
China Foundry , 2009,
Abstract: The microstructure of hypoeutectic Al-9.21wt.%Si alloy solidified under 5.5 GPa was studied. The results show that the solidifi cation microstructure is refi ned. The primary α phase is the extended solid solution. The solid solubility of Si in α phase is up to 8.26wt.%. The growth mode of the α phase is cellular, and this cellular growth mechanism is interpreted in terms of the decrease of the diffusivity and the extended solid solution under high pressure. By calculation, it can be known that the the diffusivity of solute in the liquid under normal pressure is as high as two hundred times that under high pressure. The microhardness of the hypoeutectic Al-Si alloy solidified under high pressure is higher than that of solidifi ed under normal pressure. After annealing, Si precipitates from the solid solution, the microhardness of the alloy decrease, but, still higher than that of solidifi ed under normal pressure.
The Effect of Copper Addition on the Mechanical and Wear Properties of Grey Cast Iron  [PDF]
J. O. Agunsoye, S. A. Bello, S. B. Hassan, R. G. Adeyemo, J. M. Odii
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2014, DOI: 10.4236/jmmce.2014.25048
Abstract: An alloy of cast iron and copper (Fe-Cu) has been developed using a stir cast process. The compo-sitional, microstructural characterization and wear property of the developed Fe-Cu alloy were carried out with the aids of X-ray diffractometer, scanning electron microscope (SEM) and pin on Disc machine. The mechanical properties such as hardness and impact energy were investigated. Wear linear equations were generated with the aids of MATLAB linear fitting. The results revealed that the presence of copper (99% pure) in the melt of grey cast iron inhibited the formation of cementite. However, the impact energy of the grey cast iron increased with %weight (wt) of copper addition. Hence, the hardness and wear resistance of the developed Fe-Cu alloy were sacrificed. Hence, the developed Fe-Cu alloy is an excellent material which can be used in the vibration damping application especially in the shock absorber.
Effects of addition of iron (Fe) filings to green moulding sand on the microstructure of grey cast iron
Adedayo, Adeleke Victor;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2010, DOI: 10.1590/S1678-58782010000200011
Abstract: cast irons are important engineering materials, which possess a wide range of attractive properties. their properties are significantly dependent on the microstructure of the cast, cast iron components. a way of controlling the microstructure of cast iron is through the control of cooling rates during solidification. to control cooling rate mould properties are important. this paper presents the report of a study of the effects of additions of iron filings to green moulding sand on the microstructure of grey cast iron. five sand samples were prepared with different fe content ranging from 1 wt% to 5 wt%. a control sand sample, which had no iron content, was also prepared. the properties of the sand samples were tested and used to cast some grey cast iron samples whose microstructure were observed by optical microscopy. the results show that addition of fe filing does not have any adverse effects on the properties of green moulding sand; however, the microstructures show a dependence on heat storage capacity of the mould.
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